Online Submission
Manuscript Tracking
Peer Review
Editor Work2021 Vol. 29, No. S1
Previous Issue
2021, 29(S1): 1-7.
Abstract
4522KB
In this paper, the pile-soil load transfer characteristics under different water level of reservoir area were studied, and the evolution law of the negative friction resistance of the pile shaft was discussed to provide certain engineering guidance for the pile foundation design in the reservoir area. Numerical results show that the rise and fall of water level has a significant impact on the development of the pile-head settlement and the negative friction resistance. The drop in the water level promotes the negative friction of the pile body, which increases the axial force in the pile body and the pile-head settlement. In addition, the distribution of negative friction resistance and the settlement of pile top are affected by the number of water level cycles and pile head load. With the increase of the number of cycles and the load, both the settlement and negative friction resistance increase, and the first cycle of water level fluctuation has the greatest impact on it.
In this paper, the pile-soil load transfer characteristics under different water level of reservoir area were studied, and the evolution law of the negative friction resistance of the pile shaft was discussed to provide certain engineering guidance for the pile foundation design in the reservoir area. Numerical results show that the rise and fall of water level has a significant impact on the development of the pile-head settlement and the negative friction resistance. The drop in the water level promotes the negative friction of the pile body, which increases the axial force in the pile body and the pile-head settlement. In addition, the distribution of negative friction resistance and the settlement of pile top are affected by the number of water level cycles and pile head load. With the increase of the number of cycles and the load, both the settlement and negative friction resistance increase, and the first cycle of water level fluctuation has the greatest impact on it.
2021, 29(S1): 8-17.
The permeability, compressibility and consolidation characteristics of soil after freeze-thaw process are important factors that affect the deformation rate and amount of deformation after the artificial ground freezing construction. This paper aims to systematically reveal the effect of cooling temperature on deformation characteristics of coastal soft clayey soil, and carries out a series of tests include moisture content test, density test, penetration test and consolidation test on the undisturbed and frozen-thawed Shanghai Quaternary marine mucky clay at cooling temperatures of -5 to -25℃; combined with the changes in moisture content and density after freeze-thaw process at different cooling temperatures, it discusses the influence mechanism of vertical permeability coefficient and compression coefficient of soft clay. The results show that after undergoing single freeze-thaw cycle in a closed system, the moisture content and density of frozen-thawed soil decrease, while the freeze-thaw process enhances the permeability and compressibility of soil. As the cooling temperature decreases, the effect of freezing-thawing on the moisture content is weakened, while the effect on density is strengthened. The redistribution and phase conversion of water inside the samples caused by freezing-thawing are the fundamental reasons for the change of soil microstructure, which in turn leads to the differences in permeability and compressibility before freezing and after thawing. The compression coefficient and the initial void ratio of frozen-thawed soil are in an exponential relationship, suggesting that it is possible to provide the value of compression coefficient for deformation prediction by combining the laboratory test with the fitting formula. The vertical consolidation coefficient of frozen-thawed soil decreases linearly with the decrease of cooling temperature, hence the soil subjected to freezing-thawing should be temperature-zoned when calculating the amount of deformation. These findings help to promote the quantitative study of cooling temperature on the deformation characteristics of soft clayey soil, and provide some guidance for the application of artificial ground freezing method in coastal areas.
The permeability, compressibility and consolidation characteristics of soil after freeze-thaw process are important factors that affect the deformation rate and amount of deformation after the artificial ground freezing construction. This paper aims to systematically reveal the effect of cooling temperature on deformation characteristics of coastal soft clayey soil, and carries out a series of tests include moisture content test, density test, penetration test and consolidation test on the undisturbed and frozen-thawed Shanghai Quaternary marine mucky clay at cooling temperatures of -5 to -25℃; combined with the changes in moisture content and density after freeze-thaw process at different cooling temperatures, it discusses the influence mechanism of vertical permeability coefficient and compression coefficient of soft clay. The results show that after undergoing single freeze-thaw cycle in a closed system, the moisture content and density of frozen-thawed soil decrease, while the freeze-thaw process enhances the permeability and compressibility of soil. As the cooling temperature decreases, the effect of freezing-thawing on the moisture content is weakened, while the effect on density is strengthened. The redistribution and phase conversion of water inside the samples caused by freezing-thawing are the fundamental reasons for the change of soil microstructure, which in turn leads to the differences in permeability and compressibility before freezing and after thawing. The compression coefficient and the initial void ratio of frozen-thawed soil are in an exponential relationship, suggesting that it is possible to provide the value of compression coefficient for deformation prediction by combining the laboratory test with the fitting formula. The vertical consolidation coefficient of frozen-thawed soil decreases linearly with the decrease of cooling temperature, hence the soil subjected to freezing-thawing should be temperature-zoned when calculating the amount of deformation. These findings help to promote the quantitative study of cooling temperature on the deformation characteristics of soft clayey soil, and provide some guidance for the application of artificial ground freezing method in coastal areas.
2021, 29(S1): 18-27.
The hydropower station in southwest China usually has large-scale underground powerhouse. Subjected to high in situ stress and complex geological condition, the construction of these powerhouses often encounters deformation and failure of surrounding rock mass. This paper takes the Baihetan right bank underground powerhouse as a case study, which is large-scale and under high in situ stress. Via site monitoring and field investigation, we analyzed the response characteristics of deformation and failure of surrounding rock mass in the underground powerhouse. With the factors including in situ stress and rock mass property, we discussed the mechanism of deformation and failure of surrounding rock mass. The results show that the second principal stress with a direction approximately perpendicular to the powerhouse axis plays a dominant role in the stress adjustment of the main powerhouse. When the main powerhouse was excavated, stress concentration zones formed at the upstream spandrel and the foot of downstream sidewall. In these two areas, stress-dominated failures occurred, such as spalling, surrounding rock mass fracture and shotcrete cracking. The underground excavation under high in situ stress causes strong unloading of surrounding rock mass, which leads to the large deformation with time effect. In the parts of arch and sidewalls, the surrounding rock mass deformation increased continuously as the stratified excavation progressed.
The hydropower station in southwest China usually has large-scale underground powerhouse. Subjected to high in situ stress and complex geological condition, the construction of these powerhouses often encounters deformation and failure of surrounding rock mass. This paper takes the Baihetan right bank underground powerhouse as a case study, which is large-scale and under high in situ stress. Via site monitoring and field investigation, we analyzed the response characteristics of deformation and failure of surrounding rock mass in the underground powerhouse. With the factors including in situ stress and rock mass property, we discussed the mechanism of deformation and failure of surrounding rock mass. The results show that the second principal stress with a direction approximately perpendicular to the powerhouse axis plays a dominant role in the stress adjustment of the main powerhouse. When the main powerhouse was excavated, stress concentration zones formed at the upstream spandrel and the foot of downstream sidewall. In these two areas, stress-dominated failures occurred, such as spalling, surrounding rock mass fracture and shotcrete cracking. The underground excavation under high in situ stress causes strong unloading of surrounding rock mass, which leads to the large deformation with time effect. In the parts of arch and sidewalls, the surrounding rock mass deformation increased continuously as the stratified excavation progressed.
2021, 29(S1): 28-37.
With the background of the comprehensive pipe corridor project in Changhe West Road, Tongzhou District, Beijing, the simulation model of the back wall system of the pipe jacking initiation shaft was established by ABAQUS software in order to study the effect of jacking reaction force on the back wall system of rectangular pipe corridor with large section. This report analyses force and deformation of the back wall system and the surrounding soil layer in different jacking stages, by combining the jacking force monitoring data during the whole process of pipe corridor jacking. The numerical simulation results show five main results. The horizontal displacement of the back-back soil in the loading area increases and then decreases with the increase of depth under the action of the reaction force, while the horizontal displacement of the front wall soil gradually decreases with the increase of depth. The horizontal displacement of the surface soil around the wall gradually decreases with the increase of distance from the well perimeter; and the soil displacement decreases significantly within the reinforcement area, while the vertical displacement does not change significantly. The overall soil pressure is smaller than the passive soil pressure when back soil pressure in the loading area increases; and the overall soil pressure is smaller than the static soil pressure when the overall soil pressure at the front wall decreases. The soil reaction force and displacement at the loading centre show a linear trend with the increase of the top force. The concrete support at different locations of the starting well is significantly affected by the reaction force.
With the background of the comprehensive pipe corridor project in Changhe West Road, Tongzhou District, Beijing, the simulation model of the back wall system of the pipe jacking initiation shaft was established by ABAQUS software in order to study the effect of jacking reaction force on the back wall system of rectangular pipe corridor with large section. This report analyses force and deformation of the back wall system and the surrounding soil layer in different jacking stages, by combining the jacking force monitoring data during the whole process of pipe corridor jacking. The numerical simulation results show five main results. The horizontal displacement of the back-back soil in the loading area increases and then decreases with the increase of depth under the action of the reaction force, while the horizontal displacement of the front wall soil gradually decreases with the increase of depth. The horizontal displacement of the surface soil around the wall gradually decreases with the increase of distance from the well perimeter; and the soil displacement decreases significantly within the reinforcement area, while the vertical displacement does not change significantly. The overall soil pressure is smaller than the passive soil pressure when back soil pressure in the loading area increases; and the overall soil pressure is smaller than the static soil pressure when the overall soil pressure at the front wall decreases. The soil reaction force and displacement at the loading centre show a linear trend with the increase of the top force. The concrete support at different locations of the starting well is significantly affected by the reaction force.
2021, 29(S1): 38-44.
As the preferred buffer/backfill material of deep geological disposal for high-level radioactive waste, the long-term stability of Gaomiaozi bentonite's barrier function needs further study. In this paper, the rheometer was used to measure the shear strength of Gaomiaozi bentonite with different standing ages(hereinafter referred to as the setting strength), to explore its characteristics and mechanism of changes. Basing on the dynamic balance study of the bond breakage and reconstruction of bentonite particles, a tensile index model was improved to reflect the evolution of bentonite strength over time. With the prolonging of standing time, the microstructure of bentonite gradually tends to be uniform. The bentonite particles with extremely low electrolyte content tend to be overlapped, and the setting strength will be significantly improved; while the bentonite particles with higher electrolyte content are always parallel lapped, and the setting strength basically unchanged. This paper provides practical experience for the design, construction and long-term safety evaluation of the geological repository for high-level radioactive waste, which can also be helpful for the study of thixotropic hardening of ordinary clay.
As the preferred buffer/backfill material of deep geological disposal for high-level radioactive waste, the long-term stability of Gaomiaozi bentonite's barrier function needs further study. In this paper, the rheometer was used to measure the shear strength of Gaomiaozi bentonite with different standing ages(hereinafter referred to as the setting strength), to explore its characteristics and mechanism of changes. Basing on the dynamic balance study of the bond breakage and reconstruction of bentonite particles, a tensile index model was improved to reflect the evolution of bentonite strength over time. With the prolonging of standing time, the microstructure of bentonite gradually tends to be uniform. The bentonite particles with extremely low electrolyte content tend to be overlapped, and the setting strength will be significantly improved; while the bentonite particles with higher electrolyte content are always parallel lapped, and the setting strength basically unchanged. This paper provides practical experience for the design, construction and long-term safety evaluation of the geological repository for high-level radioactive waste, which can also be helpful for the study of thixotropic hardening of ordinary clay.
2021, 29(S1): 45-52.
Based on the traditional solidifying materials, a new polymer material was introduced in this paper. As for the insufficient early strength of solidified high water content silty soil and practical engineering applicability problems, a series of soil tests were carried out under two working conditions of in-site filling and off-site filling. The influence of environmental factors, dosage of curing agent and initial water content on the early strength of solidified silty soil were studied, and the optimal dosage of curing agent was determined. The damage property of solidified silty soil was analyzed by one-dimensional compressive stress-strain curve. The microstructure of solidified soil was analyzed by SEM, and the solidification mechanism of curing agent was explored. The test results show that the new polymer curing agent has a good curing effect on high water content silt. The optimal dosage of curing agent is 5%, and the unconfined compressive strength of cured silt soil can reach 2.4MPa for 7 days. The off-site filling conditions were more conducive to the strength development of solidified soil, which increased by about 30% compared with in-situ filling. Brittle failure occurs when solidified soil reaches ultimate strength, which should be avoided in engineering use. By analyzing the microstructure of solidified silty soil, it shows that the strength of solidified silt mainly comes from the agglomeration of soil particles with polar ions and the cementation of soil particles by the chain network structure formed by the hydration of high polymer.
Based on the traditional solidifying materials, a new polymer material was introduced in this paper. As for the insufficient early strength of solidified high water content silty soil and practical engineering applicability problems, a series of soil tests were carried out under two working conditions of in-site filling and off-site filling. The influence of environmental factors, dosage of curing agent and initial water content on the early strength of solidified silty soil were studied, and the optimal dosage of curing agent was determined. The damage property of solidified silty soil was analyzed by one-dimensional compressive stress-strain curve. The microstructure of solidified soil was analyzed by SEM, and the solidification mechanism of curing agent was explored. The test results show that the new polymer curing agent has a good curing effect on high water content silt. The optimal dosage of curing agent is 5%, and the unconfined compressive strength of cured silt soil can reach 2.4MPa for 7 days. The off-site filling conditions were more conducive to the strength development of solidified soil, which increased by about 30% compared with in-situ filling. Brittle failure occurs when solidified soil reaches ultimate strength, which should be avoided in engineering use. By analyzing the microstructure of solidified silty soil, it shows that the strength of solidified silt mainly comes from the agglomeration of soil particles with polar ions and the cementation of soil particles by the chain network structure formed by the hydration of high polymer.
2021, 29(S1): 53-60.
In the study of the stability of the underground cavern chamber surrounding rock, the reasonableness of the selection of rock mechanical parameters is directly related to the correctness of the whole analysis and calculation. In this paper, the inverse analysis of the mechanical parameters of the surrounding rock during the construction period of the right bank underground plant cavern group of Baihetan Hydropower Station is carried out using the orthogonal design-BP neural network displacement inverse analysis method and based on the field monitoring data. The inverse parameters were used to study the stress and deformation evolution characteristics of the surrounding rocks of the cavern group during the construction period of the underground plant. The study shows that:the consistency between the finite element calculated displacement values and the field monitoring values is high, which verifies the reasonableness of the inversion method; the overall deformation of the surrounding rocks in the plant area is "phased", and the deformation growth is mainly caused by excavation and unloading, while the deformation produced by creep is relatively small; due to the influence of faults and fault zones, the overall stress in the surrounding rocks near the small pile number area of the plant is higher than that in the larger pile. The overall stress is greater in the area of small pile number, and the upstream displacement deformation is greater while the downstream side of the surrounding rock is more obvious stress concentration, so the monitoring of the deformation of the surrounding rock in this vicinity should be strengthened.
In the study of the stability of the underground cavern chamber surrounding rock, the reasonableness of the selection of rock mechanical parameters is directly related to the correctness of the whole analysis and calculation. In this paper, the inverse analysis of the mechanical parameters of the surrounding rock during the construction period of the right bank underground plant cavern group of Baihetan Hydropower Station is carried out using the orthogonal design-BP neural network displacement inverse analysis method and based on the field monitoring data. The inverse parameters were used to study the stress and deformation evolution characteristics of the surrounding rocks of the cavern group during the construction period of the underground plant. The study shows that:the consistency between the finite element calculated displacement values and the field monitoring values is high, which verifies the reasonableness of the inversion method; the overall deformation of the surrounding rocks in the plant area is "phased", and the deformation growth is mainly caused by excavation and unloading, while the deformation produced by creep is relatively small; due to the influence of faults and fault zones, the overall stress in the surrounding rocks near the small pile number area of the plant is higher than that in the larger pile. The overall stress is greater in the area of small pile number, and the upstream displacement deformation is greater while the downstream side of the surrounding rock is more obvious stress concentration, so the monitoring of the deformation of the surrounding rock in this vicinity should be strengthened.
2021, 29(S1): 61-66.
Internal erosion of soil by piping has been considered as one of the most common reasons for the failures of hydraulic structures as well as natural slopes. Recent explorations on dissolution test by using the erodible material to simulate the detachment of soil particles have provided valuable insights into the quantitative evaluation of mechanical consequence of internal erosion. In this research, piping effect was successfully achieved by dissolving a preplaced glucose column inside the sandy specimen. Variations on the small strain properties including the Young's modulus and Poisson's ratio were investigated through a series of cyclic loadings with the help of local displacement transducers. Shear strength at the post-erosion state was also obtained. According to the test results, non-uniform local strains occurred along the erosion path. The void ratio of eroded specimen became larger after the dissolution of glucose. Obvious reduction in Young's modulus and increase in Poisson's ratio were observed. Due to the compression and clogging of the eroded voids, no significant degradation in the peak shear strength was found in the eroded specimen compared with the clean sand specimen.
Internal erosion of soil by piping has been considered as one of the most common reasons for the failures of hydraulic structures as well as natural slopes. Recent explorations on dissolution test by using the erodible material to simulate the detachment of soil particles have provided valuable insights into the quantitative evaluation of mechanical consequence of internal erosion. In this research, piping effect was successfully achieved by dissolving a preplaced glucose column inside the sandy specimen. Variations on the small strain properties including the Young's modulus and Poisson's ratio were investigated through a series of cyclic loadings with the help of local displacement transducers. Shear strength at the post-erosion state was also obtained. According to the test results, non-uniform local strains occurred along the erosion path. The void ratio of eroded specimen became larger after the dissolution of glucose. Obvious reduction in Young's modulus and increase in Poisson's ratio were observed. Due to the compression and clogging of the eroded voids, no significant degradation in the peak shear strength was found in the eroded specimen compared with the clean sand specimen.
2021, 29(S1): 67-73.
Internal erosion is one of the major causes of underground disasters such as sinkhole, underground cavity, loose sand body and water-rich body, which can be initiated by four erosion models. In this study, an erosion-controlled experimental method was adopted to dissolve two types of preplaced salt granules in gap-graded sand, with the aim of simulating the process of suffusion and concentrated leak erosion. Small strain shear wave velocity was measured with bender elements. Shear strength, angle of shearing resistance and dilation rate of eroded soil under different confining pressures were measured by triaxial tests. Experimental data showed that shear wave velocity decreased gradually with the dissolution of salt granules and the peak shear strength decreased significantly after internal erosion. The reduction of shear wave velocity and the shear strength increased with the level of confining pressures. Given the same mass of the erodible material, the mechanical degradation of shear wave velocity, shear strength and dilatancy during concentrated leak erosion was observed to be significantly higher compared with suffusion. The stress-strain behavior of dense sand with the relative density of 80% was strain hardening under suffusion, while the behavior of concentrated leak erosion tended to be strain softening. The volumetric strain at post erosion state was still dilatancy but with a lower trend.
Internal erosion is one of the major causes of underground disasters such as sinkhole, underground cavity, loose sand body and water-rich body, which can be initiated by four erosion models. In this study, an erosion-controlled experimental method was adopted to dissolve two types of preplaced salt granules in gap-graded sand, with the aim of simulating the process of suffusion and concentrated leak erosion. Small strain shear wave velocity was measured with bender elements. Shear strength, angle of shearing resistance and dilation rate of eroded soil under different confining pressures were measured by triaxial tests. Experimental data showed that shear wave velocity decreased gradually with the dissolution of salt granules and the peak shear strength decreased significantly after internal erosion. The reduction of shear wave velocity and the shear strength increased with the level of confining pressures. Given the same mass of the erodible material, the mechanical degradation of shear wave velocity, shear strength and dilatancy during concentrated leak erosion was observed to be significantly higher compared with suffusion. The stress-strain behavior of dense sand with the relative density of 80% was strain hardening under suffusion, while the behavior of concentrated leak erosion tended to be strain softening. The volumetric strain at post erosion state was still dilatancy but with a lower trend.
2021, 29(S1): 74-81.
In this paper, the shear strength characteristics of rubber-reinforced unsaturated expansive soil are studied, the effects of the size and content of rubber on the deviatoric stress, failure strain, shear strength parameters, internal friction angle and cohesion of unsaturated expansive soil were studied by unconsolidated undrained(UU) triaxial test. The test results show that the mixing effect of 80 mesh rubber is better than that of 60 mesh rubber, and 5% 80 mesh rubber can increase the peak strength of the expansive soil. The peak strength of ESR decreased with the increase of rubber content, and the decrease of peak strength depends on the decrease of cohesion. It should be noted that the failure strain of ESR increases with the increase of rubber content, i.e. the increase of plasticity and the decrease of stiffness of expansive soil are mainly caused by the addition of rubber. The different appearance of ESR depends on different test methods, different soil types and different rubber reinforcement forms. Under the test conditions of this paper, adding 5% 80 mesh rubber powder is the best choice for improving the plasticity and strength related properties of expansive soil.
In this paper, the shear strength characteristics of rubber-reinforced unsaturated expansive soil are studied, the effects of the size and content of rubber on the deviatoric stress, failure strain, shear strength parameters, internal friction angle and cohesion of unsaturated expansive soil were studied by unconsolidated undrained(UU) triaxial test. The test results show that the mixing effect of 80 mesh rubber is better than that of 60 mesh rubber, and 5% 80 mesh rubber can increase the peak strength of the expansive soil. The peak strength of ESR decreased with the increase of rubber content, and the decrease of peak strength depends on the decrease of cohesion. It should be noted that the failure strain of ESR increases with the increase of rubber content, i.e. the increase of plasticity and the decrease of stiffness of expansive soil are mainly caused by the addition of rubber. The different appearance of ESR depends on different test methods, different soil types and different rubber reinforcement forms. Under the test conditions of this paper, adding 5% 80 mesh rubber powder is the best choice for improving the plasticity and strength related properties of expansive soil.
2021, 29(S1): 82-87.
We analysed the change trend and failure mechanism of the strength of concrete-cement soil interface considering the age effect by large-scale shear test. Combined with the results of cement shear test and unconfined compression test, the relationship between the strength of concrete cement soil interface, the shear strength of cement soil and the results of unconfined compression test was analysed qualitatively. The results show that the failure process of the concrete cement soil interface can be divided into three parts:(1) The formation of cracks in the concrete-cement soil interface; (2) The interface between cement soil and concrete begins to peel off; (3) The interface between cement soil and concrete is completely separated, and the two are in friction contact. The shear strength of concrete cement soil interface increases slowly in the early stage of curing, and increases rapidly in the middle and late stage. The unconfined compressive strength and shear strength of cement soil increase logarithmically with age, and have a positive correlation with the strength of concrete cement soil interface.
We analysed the change trend and failure mechanism of the strength of concrete-cement soil interface considering the age effect by large-scale shear test. Combined with the results of cement shear test and unconfined compression test, the relationship between the strength of concrete cement soil interface, the shear strength of cement soil and the results of unconfined compression test was analysed qualitatively. The results show that the failure process of the concrete cement soil interface can be divided into three parts:(1) The formation of cracks in the concrete-cement soil interface; (2) The interface between cement soil and concrete begins to peel off; (3) The interface between cement soil and concrete is completely separated, and the two are in friction contact. The shear strength of concrete cement soil interface increases slowly in the early stage of curing, and increases rapidly in the middle and late stage. The unconfined compressive strength and shear strength of cement soil increase logarithmically with age, and have a positive correlation with the strength of concrete cement soil interface.
2021, 29(S1): 88-95.
Tidal channels are widely distributed in the Zhoushan islands, and submarine slope instability events are widely developed. Frequent submarine landslides pose a great threat to offshore facilities such as submarine optical cables, sea reclamation projects, ports and wharfs. The investigation and research on its occurrence mechanism has attracted more and more attention. Based on the self-developed seabed deformation observation system, combined with the pore water pressure observation system and hydrodynamic observation system, this paper has carried out 75 day deformation observation on the typical seabed slope in the southwest of Zhujiajian island in Zhoushan since August 29, 2019. The results show that the sediment deformation in the observation range is divided into three parts. The cumulative deformation of the sediment on the potential sliding surface at the bottom of the seabed slope(12~13.5m under the seabed) is about 0.75mm. The lateral deformation process presents the characteristics of step change, and the deformation direction is consistent with the slope tendency, and the top deformation is consistent with the tidal direction. It is found that the change of tide level will change the change of sediment excess pore water pressure, and the change of excess pore pressure difference between deep and shallow sediments is the main trigger factor for the lateral deformation of potential sliding surface of submarine slope in the observation area. There are many tidal channels in the sea area of Zhoushan islands, and the instability of submarine slopes is widely developed.
Tidal channels are widely distributed in the Zhoushan islands, and submarine slope instability events are widely developed. Frequent submarine landslides pose a great threat to offshore facilities such as submarine optical cables, sea reclamation projects, ports and wharfs. The investigation and research on its occurrence mechanism has attracted more and more attention. Based on the self-developed seabed deformation observation system, combined with the pore water pressure observation system and hydrodynamic observation system, this paper has carried out 75 day deformation observation on the typical seabed slope in the southwest of Zhujiajian island in Zhoushan since August 29, 2019. The results show that the sediment deformation in the observation range is divided into three parts. The cumulative deformation of the sediment on the potential sliding surface at the bottom of the seabed slope(12~13.5m under the seabed) is about 0.75mm. The lateral deformation process presents the characteristics of step change, and the deformation direction is consistent with the slope tendency, and the top deformation is consistent with the tidal direction. It is found that the change of tide level will change the change of sediment excess pore water pressure, and the change of excess pore pressure difference between deep and shallow sediments is the main trigger factor for the lateral deformation of potential sliding surface of submarine slope in the observation area. There are many tidal channels in the sea area of Zhoushan islands, and the instability of submarine slopes is widely developed.
2021, 29(S1): 96-105.
Displacement is a significant apparent feature of the slope stability. The Log-fit method is a common method to predict the time of the slope failure based on the observed displacement data. In practice, the influence of measurement error, environmental noise and model assumptions may make it difficult to predict the slope failure time. In this paper, the uncertainties in slope failure time prediction were divided into observational uncertainty and model uncertainty. We suggested a method to calibrate the observational uncertainty based on the residual Bootstrap method. We collected the cases of rainfall induced landslides, and then calibrated the model uncertainty of the Log-fit method when adopted to predict the failure time of rainfall induced landslides. On this basis, we proposed a probabilistic method to predict the slope failure time considering both uncertainties. The suggested method can provide both the most likely failure time of the slope and the failure probability associated with different predicted failure time. It is demonstrated through the illustrative examples that the result from the probabilistic method accords better with the observed failure time of the slope, which can provide useful information for the early warning of landslide disasters.
Displacement is a significant apparent feature of the slope stability. The Log-fit method is a common method to predict the time of the slope failure based on the observed displacement data. In practice, the influence of measurement error, environmental noise and model assumptions may make it difficult to predict the slope failure time. In this paper, the uncertainties in slope failure time prediction were divided into observational uncertainty and model uncertainty. We suggested a method to calibrate the observational uncertainty based on the residual Bootstrap method. We collected the cases of rainfall induced landslides, and then calibrated the model uncertainty of the Log-fit method when adopted to predict the failure time of rainfall induced landslides. On this basis, we proposed a probabilistic method to predict the slope failure time considering both uncertainties. The suggested method can provide both the most likely failure time of the slope and the failure probability associated with different predicted failure time. It is demonstrated through the illustrative examples that the result from the probabilistic method accords better with the observed failure time of the slope, which can provide useful information for the early warning of landslide disasters.
2021, 29(S1): 106-116.
PS-InSAR and SBAS-InSAR technologies are widely used in land subsidence monitoring. Due to the different technical principles, the monitoring accuracy of the two technologies is affected by the scattering characteristics of ground objects. In order to study the difference of the monitoring accuracy of the two technologies in the area of complex ground object scattering characteristics, this paper used PS-InSAR and SBAS-InSAR technologies to monitor the ground subsidence in the surrounding area of 20×20km2 centered on 110 wells in the west water source of Suzhou. We used the measured data of the fiber optic monitoring hole SK01 in downtown Suzhou to correct the results of time-series InSAR monitoring. To compare the settlement results obtained by the two technologies, we selected the vicinity of No. 15, No. 48, and No. 98 wells and characteristic points in the suburbs and central areas of the city for time series analysis and perform accuracy analysis in the densely built area. The results show that the monitoring results of the two technologies in the study area are consistent and correlated, and the linear correlation coefficient R of the settlement rate of the high-coherence point with the same coordinates reaches more than 0.96. However, in the rapid settlement area, the SBAS-InSAR technology is more robust in solving, and the settlement rate of the central area of the settlement funnel on the west side of the water source is monitored to be between -43.2 and -30.0mm ·a-1. In areas with weak ground scattering in the suburbs, the numerical deviations of the monitoring results of the two technologies are relatively large, and the deviation of the annual average settlement rate reaches 5.7mm ·a-1, which is about 2 to 3 times that of other areas. In areas with strong ground scattering in the central areas, PS-InSAR can reflect the settlement difference between the building structure and the surrounding environment from a smaller scale.
PS-InSAR and SBAS-InSAR technologies are widely used in land subsidence monitoring. Due to the different technical principles, the monitoring accuracy of the two technologies is affected by the scattering characteristics of ground objects. In order to study the difference of the monitoring accuracy of the two technologies in the area of complex ground object scattering characteristics, this paper used PS-InSAR and SBAS-InSAR technologies to monitor the ground subsidence in the surrounding area of 20×20km2 centered on 110 wells in the west water source of Suzhou. We used the measured data of the fiber optic monitoring hole SK01 in downtown Suzhou to correct the results of time-series InSAR monitoring. To compare the settlement results obtained by the two technologies, we selected the vicinity of No. 15, No. 48, and No. 98 wells and characteristic points in the suburbs and central areas of the city for time series analysis and perform accuracy analysis in the densely built area. The results show that the monitoring results of the two technologies in the study area are consistent and correlated, and the linear correlation coefficient R of the settlement rate of the high-coherence point with the same coordinates reaches more than 0.96. However, in the rapid settlement area, the SBAS-InSAR technology is more robust in solving, and the settlement rate of the central area of the settlement funnel on the west side of the water source is monitored to be between -43.2 and -30.0mm ·a-1. In areas with weak ground scattering in the suburbs, the numerical deviations of the monitoring results of the two technologies are relatively large, and the deviation of the annual average settlement rate reaches 5.7mm ·a-1, which is about 2 to 3 times that of other areas. In areas with strong ground scattering in the central areas, PS-InSAR can reflect the settlement difference between the building structure and the surrounding environment from a smaller scale.
2021, 29(S1): 117-126.
The water-sediment separation function of retaining dams makes it an important engineering measure for the prevention of debris flow disaster. The loose material accumulated downstream of the retaining dam has gradually become the main material source of the next debris flow. Therefore, it is necessary to analyze the erosion process and the variation characteristics of water content and pore pressure under the influence of retaining dam. and it is of great guiding value to the prevention and forecast of gully debris flow. Taking the debris flow deposition downstream of the second retaining dam of Cutou Gully in Wenchuan County as the research object, using the laboratory physical model test and combined with rainfall data, digital terrain data, and in-situ deposition parameters, this study simulated the erosion process of deposition under the different intensity of rainfall and over-dam flow conditions. The sensors were used to deeply explore water content variation and pore water pressure in the erosion process. Four groups of experiments were carried out in this study, and the experimental factors included four rainfall intensities and four corresponding runoff. It turns out that:(1) Under the influence of retaining dam, the regularity of erosion process is more obvious:splash erosion → surface erosion → headward erosion → lateral cutting erosion → collapse; (2) The infiltration of rainwater in the accumulation body is from shallow to deep, and reaches saturation when the water content reaches about 23%; (3) Under the action of runoff erosion, the pore water pressure increases rapidly before the debris flows starts; (4) The over-dam flow is an important reason for the damage of the deposition. The action mechanism is mainly to change the soil particle skeleton, increase the pore water pressure, reduce the effective stress of the soil, and accelerate the water infiltration. Under the comprehensive action, the failure of the deposition starts from the toe of the slope and then to the upstream and deep. The research results are of great significance for improving the soil erosion characteristics of the deposition and revealing the erosion mechanism under complex hydrodynamic conditions.
The water-sediment separation function of retaining dams makes it an important engineering measure for the prevention of debris flow disaster. The loose material accumulated downstream of the retaining dam has gradually become the main material source of the next debris flow. Therefore, it is necessary to analyze the erosion process and the variation characteristics of water content and pore pressure under the influence of retaining dam. and it is of great guiding value to the prevention and forecast of gully debris flow. Taking the debris flow deposition downstream of the second retaining dam of Cutou Gully in Wenchuan County as the research object, using the laboratory physical model test and combined with rainfall data, digital terrain data, and in-situ deposition parameters, this study simulated the erosion process of deposition under the different intensity of rainfall and over-dam flow conditions. The sensors were used to deeply explore water content variation and pore water pressure in the erosion process. Four groups of experiments were carried out in this study, and the experimental factors included four rainfall intensities and four corresponding runoff. It turns out that:(1) Under the influence of retaining dam, the regularity of erosion process is more obvious:splash erosion → surface erosion → headward erosion → lateral cutting erosion → collapse; (2) The infiltration of rainwater in the accumulation body is from shallow to deep, and reaches saturation when the water content reaches about 23%; (3) Under the action of runoff erosion, the pore water pressure increases rapidly before the debris flows starts; (4) The over-dam flow is an important reason for the damage of the deposition. The action mechanism is mainly to change the soil particle skeleton, increase the pore water pressure, reduce the effective stress of the soil, and accelerate the water infiltration. Under the comprehensive action, the failure of the deposition starts from the toe of the slope and then to the upstream and deep. The research results are of great significance for improving the soil erosion characteristics of the deposition and revealing the erosion mechanism under complex hydrodynamic conditions.
2021, 29(S1): 127-134.
The landslide in Huangbu village of the Yuanjiang River occurred on June 24, 2017. The resulting surge damaged many houses. It also injured many people. At the same time, there are about 230000 cubic meters of rock and soil around the landslide. They may cause greater disasters. In this paper, we used the water wave dynamic model to repeat the surge disaster caused by Huangbu village landslide. Then we predicted what will happen if the rock and soil around slides. The results show that Naixin model is suitable for surge simulation. Affected by heavy rainfall, the landslide in Huangbu village, Yuanjiang River occurred on June 24, 2017, with a landslide volume of 161000m3. The surge caused damage to houses across the river and injured many people. At the same time, there are 230000 cubic meters of hidden dangers on both sides of the landslide, which may cause greater disasters. Therefore, based on the repetition of previous landslide surge, this paper verifies the rationality of the model, then predicts the surge disasters that may be caused by landslide hidden dangers on both sides, and divides the potential risk range, so as to provide a basis for disaster prevention and reduction.
The landslide in Huangbu village of the Yuanjiang River occurred on June 24, 2017. The resulting surge damaged many houses. It also injured many people. At the same time, there are about 230000 cubic meters of rock and soil around the landslide. They may cause greater disasters. In this paper, we used the water wave dynamic model to repeat the surge disaster caused by Huangbu village landslide. Then we predicted what will happen if the rock and soil around slides. The results show that Naixin model is suitable for surge simulation. Affected by heavy rainfall, the landslide in Huangbu village, Yuanjiang River occurred on June 24, 2017, with a landslide volume of 161000m3. The surge caused damage to houses across the river and injured many people. At the same time, there are 230000 cubic meters of hidden dangers on both sides of the landslide, which may cause greater disasters. Therefore, based on the repetition of previous landslide surge, this paper verifies the rationality of the model, then predicts the surge disasters that may be caused by landslide hidden dangers on both sides, and divides the potential risk range, so as to provide a basis for disaster prevention and reduction.
2021, 29(S1): 135-143.
The stability analysis of landslide dam is the focus of current research. It is very important for emergency rescue to evaluate the landslide dam stability accurately and quickly. The typical rapid stability models of landslide dam at home and abroad are summarized and compared. Then, based on the established database of landslide blocking river, the influence of landslide dam length on its stability is fully considered. A rapid evaluation model of landslide dam stability, including the parameters of dam length, dam width and reservoir capacity of the barrier lake, is proposed by using logistic regression method. Taking the case of Baige landslide-induced river blocking, the case study is carried out based on the established rapid evaluation model. The research results indicate that the comprehensive correct rate of the proposed model is 86.7%, and the false positive rate is 5.1%, which indicates that the model is safe in engineering. The predicted stability of the Baige landslide dam is consistent with the actual situation. The reservoir capacity of Baige barrier lake obtained by reverse calculation is 1.4×108m3, smaller than the actual reservoir capacity, which can provide the response time for the emergency rescue of the barrier lake disaster. The research results can provide useful reference for hazard assessment of landslide dam and emergency management of barrier lake disaster.
The stability analysis of landslide dam is the focus of current research. It is very important for emergency rescue to evaluate the landslide dam stability accurately and quickly. The typical rapid stability models of landslide dam at home and abroad are summarized and compared. Then, based on the established database of landslide blocking river, the influence of landslide dam length on its stability is fully considered. A rapid evaluation model of landslide dam stability, including the parameters of dam length, dam width and reservoir capacity of the barrier lake, is proposed by using logistic regression method. Taking the case of Baige landslide-induced river blocking, the case study is carried out based on the established rapid evaluation model. The research results indicate that the comprehensive correct rate of the proposed model is 86.7%, and the false positive rate is 5.1%, which indicates that the model is safe in engineering. The predicted stability of the Baige landslide dam is consistent with the actual situation. The reservoir capacity of Baige barrier lake obtained by reverse calculation is 1.4×108m3, smaller than the actual reservoir capacity, which can provide the response time for the emergency rescue of the barrier lake disaster. The research results can provide useful reference for hazard assessment of landslide dam and emergency management of barrier lake disaster.
2021, 29(S1): 144-151.
Since the planning of a road expansion at the front edge of the Xiaohelong landslide, it is necessary to conduct an analysis of its genesis mechanism and evaluate the stability of the landslide with a view to preventing it from posing a risk to the safety of the proposed road and pedestrians. This paper carried out a detailed geotechnical investigation to clarify the engineering geological conditions within the survey area of the Xiaohelong landslide, and analysed the factors affecting the formation of the landslide as well as the deformation process. After that, this research employed FLAC3D software to make an analysis of the stability of the landslide under either natural or rainfall conditions on the basis of strength reduction theory. The research indicates that:1) The influencing factors of the Xiaohelong landslide consist of internal factors such as topography and geomorphology, stratigraphic lithology, together with external inducing factors such as meteorological conditions and human engineering activities. 2) The research area is originally a natural side slope of forest land. However, due to the manual excavation, the right side of the slope collapses and gradually destabilizes over time, resulting in a landslide. Simultaneously, the rear edge of the slope on the left side produces scarps and cracks, which, together with the the excavation of the front edge, causes the rear part to lose support, forming a traction landslide. 3) By evaluating the stability of the landslide, this research obtains the landslide stability form, the slope strain distribution law and the slope deformation law. According to the calculation, the safety coefficient under natural conditions is 1.1 while that under rainfall conditions is 1.08, both of which are ranging from 1.05 to 1.15 with metastable state. The results of this paper can provide reference for the analysis of the genesis mechanism and stability evaluation of analogous landslides.
Since the planning of a road expansion at the front edge of the Xiaohelong landslide, it is necessary to conduct an analysis of its genesis mechanism and evaluate the stability of the landslide with a view to preventing it from posing a risk to the safety of the proposed road and pedestrians. This paper carried out a detailed geotechnical investigation to clarify the engineering geological conditions within the survey area of the Xiaohelong landslide, and analysed the factors affecting the formation of the landslide as well as the deformation process. After that, this research employed FLAC3D software to make an analysis of the stability of the landslide under either natural or rainfall conditions on the basis of strength reduction theory. The research indicates that:1) The influencing factors of the Xiaohelong landslide consist of internal factors such as topography and geomorphology, stratigraphic lithology, together with external inducing factors such as meteorological conditions and human engineering activities. 2) The research area is originally a natural side slope of forest land. However, due to the manual excavation, the right side of the slope collapses and gradually destabilizes over time, resulting in a landslide. Simultaneously, the rear edge of the slope on the left side produces scarps and cracks, which, together with the the excavation of the front edge, causes the rear part to lose support, forming a traction landslide. 3) By evaluating the stability of the landslide, this research obtains the landslide stability form, the slope strain distribution law and the slope deformation law. According to the calculation, the safety coefficient under natural conditions is 1.1 while that under rainfall conditions is 1.08, both of which are ranging from 1.05 to 1.15 with metastable state. The results of this paper can provide reference for the analysis of the genesis mechanism and stability evaluation of analogous landslides.
2021, 29(S1): 152-159.
Many low-angle dip bedding slopes distribute alongside Jinsha River, some of which have evolved into gently, stable macro-paleo-landslides. The existing city are just located in these gently paleo-landslides, which may also be planned to be extension areas. Therefore, it is important to study the evolution process and mechanism of landslide renewed, to prevent the paleo-landslides from renewing and being unstable. The article has analyzed the evolution process and mechanism of landslide renewed, taking the landslide in east side of Yongshan County as example. The evolution renewing processes have been divided into 4 phases:(1) superstratum cracked and dislocated due to interlayer squeezing and plastic flow of soft interlayer, (2) superstratum sliding fast, collapsing and partly disassembling to block the Jindi River, (3) landslide accumulation collapsing, densifying, creeping deformation, then intending to be stable, (4) part of sliding blocks renewing. Surface water seepage from atmospheric precipitation, daily used water is the main inducement for the landslide renewing; secondly, this landslide area meets seismic active period recently. This study provides a theoretical basis for the late comprehensive prevention and control of landslides in eastern side of Yongshan County, and provides experience and reference for the investigation and comprehensive prevention and control of similar renewing paleo-landslides. In the meantime, this study is valuable for the prevention and control of these similar paleo-landslides and urban planning alongside Jinsha River.
Many low-angle dip bedding slopes distribute alongside Jinsha River, some of which have evolved into gently, stable macro-paleo-landslides. The existing city are just located in these gently paleo-landslides, which may also be planned to be extension areas. Therefore, it is important to study the evolution process and mechanism of landslide renewed, to prevent the paleo-landslides from renewing and being unstable. The article has analyzed the evolution process and mechanism of landslide renewed, taking the landslide in east side of Yongshan County as example. The evolution renewing processes have been divided into 4 phases:(1) superstratum cracked and dislocated due to interlayer squeezing and plastic flow of soft interlayer, (2) superstratum sliding fast, collapsing and partly disassembling to block the Jindi River, (3) landslide accumulation collapsing, densifying, creeping deformation, then intending to be stable, (4) part of sliding blocks renewing. Surface water seepage from atmospheric precipitation, daily used water is the main inducement for the landslide renewing; secondly, this landslide area meets seismic active period recently. This study provides a theoretical basis for the late comprehensive prevention and control of landslides in eastern side of Yongshan County, and provides experience and reference for the investigation and comprehensive prevention and control of similar renewing paleo-landslides. In the meantime, this study is valuable for the prevention and control of these similar paleo-landslides and urban planning alongside Jinsha River.
2021, 29(S1): 160-166.
The primary condition of rock slope stability analysis is the determination of the most dangerous sliding surface. In this paper, Dijkstra algorithm was utilized to search for the most dangerous sliding surface of the high rock slope of the urban flood control project in Yongji County, Jilin Province. The fracture system was identified and interpreted by the digital close-range photogrammetry method. Considering the complexity of the fracture system in the high rock slope, it is extremely difficult to search for the most dangerous sliding surface on the three-dimensional scale. Therefore, the representative slope of the study area was selected and the Dijkstra algorithm was used to search the most dangerous sliding surface in the two-dimensional section plane of high rock slope. The research results show that the connectivity rate of the potentially dangerous sliding surface of the main sliding surface ranges from 59.87% to 70.45%. The potentially dangerous sliding surface with the maximum connectivity rate of 70.45% is regarded as the potentially most dangerous sliding surface.
The primary condition of rock slope stability analysis is the determination of the most dangerous sliding surface. In this paper, Dijkstra algorithm was utilized to search for the most dangerous sliding surface of the high rock slope of the urban flood control project in Yongji County, Jilin Province. The fracture system was identified and interpreted by the digital close-range photogrammetry method. Considering the complexity of the fracture system in the high rock slope, it is extremely difficult to search for the most dangerous sliding surface on the three-dimensional scale. Therefore, the representative slope of the study area was selected and the Dijkstra algorithm was used to search the most dangerous sliding surface in the two-dimensional section plane of high rock slope. The research results show that the connectivity rate of the potentially dangerous sliding surface of the main sliding surface ranges from 59.87% to 70.45%. The potentially dangerous sliding surface with the maximum connectivity rate of 70.45% is regarded as the potentially most dangerous sliding surface.
2021, 29(S1): 167-175.
The occurrence of sliding on rocky slopes is not only related to their slope structure and tectonic development, but also to external dynamic factors. The MS6.5 earthquake in Ludian, Yunnan Province in 2014 caused many large landslides and extra-large landslides. But, the Yunnan Jinggu MS6.6 earthquake that occurred in the same year only caused only small and medium-sized landslides. In order to identify the main causes of extra-large caused by the Ludian earthquake, this paper takes the Red Rock extra-large landslide induced by the Ludian earthquake as an example. The particle flow PFC2D discrete element software was used to analyzing it, solves the problem of distortion of the tension-compression ratio by used two parallel cohesive models, soft and hard, and its cause and failure mode under the influence of various factors such as laminae, stress-release cracks, potential sliding surface, weathering cracks in the slope body, and earthquake are discussed. Based on the results of orthogonal tests and the development of slope cracks, the failure modes of seismically induced Red Rock landslides and the main factors affecting the scale of Red Rock landslides are discussed. The results show that the reason for the occurrence of an extra-scale landslides in Red Rock under the action of earthquake is the formation of deep sliding surface. The formation of deep sliding surface mainly comes from the influence of its own top-down ‘hard-soft-hard’ structure. The failure mode of the Red Rock landslide can be summarized as:Central soft rock and slope superficial damage-Hard rock overhang-Formation of shear bands-Large-scale landslide-Accumulation. The research in this paper has certain theoretical and engineering guidance significance for the prevention, assessment and management of seismically induced landslide hazards containing softly interbedded reverse-slip rock masses.
The occurrence of sliding on rocky slopes is not only related to their slope structure and tectonic development, but also to external dynamic factors. The MS6.5 earthquake in Ludian, Yunnan Province in 2014 caused many large landslides and extra-large landslides. But, the Yunnan Jinggu MS6.6 earthquake that occurred in the same year only caused only small and medium-sized landslides. In order to identify the main causes of extra-large caused by the Ludian earthquake, this paper takes the Red Rock extra-large landslide induced by the Ludian earthquake as an example. The particle flow PFC2D discrete element software was used to analyzing it, solves the problem of distortion of the tension-compression ratio by used two parallel cohesive models, soft and hard, and its cause and failure mode under the influence of various factors such as laminae, stress-release cracks, potential sliding surface, weathering cracks in the slope body, and earthquake are discussed. Based on the results of orthogonal tests and the development of slope cracks, the failure modes of seismically induced Red Rock landslides and the main factors affecting the scale of Red Rock landslides are discussed. The results show that the reason for the occurrence of an extra-scale landslides in Red Rock under the action of earthquake is the formation of deep sliding surface. The formation of deep sliding surface mainly comes from the influence of its own top-down ‘hard-soft-hard’ structure. The failure mode of the Red Rock landslide can be summarized as:Central soft rock and slope superficial damage-Hard rock overhang-Formation of shear bands-Large-scale landslide-Accumulation. The research in this paper has certain theoretical and engineering guidance significance for the prevention, assessment and management of seismically induced landslide hazards containing softly interbedded reverse-slip rock masses.
2021, 29(S1): 176-183.
The elevation of coastal cities is a precious resource. Under the conditions of climate change and sea level rise, land subsidence leads to the loss of elevation of coastal cities, which seriously threatens the safety of cities. It is of great significance to analyze the influence of multi-layer aquifer on land subsidence, study the mechanism of land subsidence and ensure the safe elevation of the city. In this paper, the research site is the mining and irrigation deep wells in Shanghai. We extract water level contour of each aquifer and surface subsidence curve, combined with the superposition of MAPGIS software, and digitize the isopotential line. Then we obtained the data of multi-layer groundwater level and land subsidence from 2011 to 2019 by taking the deep wells of mining and irrigation in Shanghai as sampling points. The correlation between multi-layer groundwater level and land subsidence is established by using multiple regression method. The ground subsidence of regions with relatively high determination coefficient R2 is greatly affected by deep groundwater exploitation, recharge and engineering precipitation, while the ground subsidence of regions with relatively low determination coefficient R2 is greatly affected by excavation and unloading of engineering construction, long-term load of high-rise buildings and dense building groups, and subway vibration. Our research provides prediction equations for the development trend of land subsidence under the pattern of mining and irrigation in the future, and can provide a reference basis for the control of land subsidence in Shanghai.
The elevation of coastal cities is a precious resource. Under the conditions of climate change and sea level rise, land subsidence leads to the loss of elevation of coastal cities, which seriously threatens the safety of cities. It is of great significance to analyze the influence of multi-layer aquifer on land subsidence, study the mechanism of land subsidence and ensure the safe elevation of the city. In this paper, the research site is the mining and irrigation deep wells in Shanghai. We extract water level contour of each aquifer and surface subsidence curve, combined with the superposition of MAPGIS software, and digitize the isopotential line. Then we obtained the data of multi-layer groundwater level and land subsidence from 2011 to 2019 by taking the deep wells of mining and irrigation in Shanghai as sampling points. The correlation between multi-layer groundwater level and land subsidence is established by using multiple regression method. The ground subsidence of regions with relatively high determination coefficient R2 is greatly affected by deep groundwater exploitation, recharge and engineering precipitation, while the ground subsidence of regions with relatively low determination coefficient R2 is greatly affected by excavation and unloading of engineering construction, long-term load of high-rise buildings and dense building groups, and subway vibration. Our research provides prediction equations for the development trend of land subsidence under the pattern of mining and irrigation in the future, and can provide a reference basis for the control of land subsidence in Shanghai.
2021, 29(S1): 184-190.
A large number of transportation infrastructures along the river are built on liquefiable valley sites. Earthquake-induced site liquefaction is one important cause of severe earthquake damage to riverside buildings. Valleys show a significant topography effect which means valleys of different sizes present different seismic response. It is of great significance to conduct systematic investigation on the correlation between topography effect and site liquefaction. In this paper, we employed OpenSees to analyze 5 liquefiable site models with different valley depths to explore the influence of valley depth changes on pore water pressure. It is found that during shaking, there is a significant correlation between the valley depth parameter and the pore water pressure of saturated sand within a certain depth range from the valley bottom. As the valley becomes deeper and free water body emerges, the shear shrinkage on the shallow area of the valley bottom gradually weakens, the dilatancy gradually strengthens, and the instantaneous liquefaction zone gradually migrates from the shallow surface area of the slope to deeper. In addition, compared with the saturated sand near the midpoint of the valley bottom, the correlation between pore water pressure of saturated sand near the slope toe and valley depth is more significant. The numerical modeling technology presented in this paper as well as the insights obtained in this investigation can provide some reference for the site selection of new riverside constructions and the design of site anti-liquefaction.
A large number of transportation infrastructures along the river are built on liquefiable valley sites. Earthquake-induced site liquefaction is one important cause of severe earthquake damage to riverside buildings. Valleys show a significant topography effect which means valleys of different sizes present different seismic response. It is of great significance to conduct systematic investigation on the correlation between topography effect and site liquefaction. In this paper, we employed OpenSees to analyze 5 liquefiable site models with different valley depths to explore the influence of valley depth changes on pore water pressure. It is found that during shaking, there is a significant correlation between the valley depth parameter and the pore water pressure of saturated sand within a certain depth range from the valley bottom. As the valley becomes deeper and free water body emerges, the shear shrinkage on the shallow area of the valley bottom gradually weakens, the dilatancy gradually strengthens, and the instantaneous liquefaction zone gradually migrates from the shallow surface area of the slope to deeper. In addition, compared with the saturated sand near the midpoint of the valley bottom, the correlation between pore water pressure of saturated sand near the slope toe and valley depth is more significant. The numerical modeling technology presented in this paper as well as the insights obtained in this investigation can provide some reference for the site selection of new riverside constructions and the design of site anti-liquefaction.
2021, 29(S1): 191-202.
As an important part of offshore wind turbine foundation design, the marine soil parameter evaluation would directly affect the safety of wind turbine and project cost. At present, piezocone penetration test(CPTU) is one of the most widely used in-situ testing methods in offshore geotechnical engineering. The disadvantage of CPTU is that soil parameters cannot be directly measured, which could only be interpreted by raw data. How to select appropriate CPTU interpretation parameter of clay strength is a difficult problem to be solved at present. In this paper, based on an offshore wind project in Guangdong offshore area, in-situ CPTU and hand torvane shear, pocket penetrometer, miniature laboratory vane shear, triaxial UU, consolidated quick shear and triaxial CU tests were carried out, the strength profiles were obtained by linear regression of the laboratory test results, where the clay samples under 60m were found to be severely disturbed, consolidated quick shear and triaxial CU test could reduce the effect of disturbance. Based on the hand torvane shear, pocket penetrometer, miniature laboratory vane shear, triaxial UU, consolidated quick shear and triaxial CU tests results, the average values of CPTU interpretation parameters Nkt for clay strength are obtained as 21.68, 19.52, 17.83, 18.63, 15.73 and 13.63, respectively. We suggest using Nkt of 21.68 as the interpretation parameter for the lower bound limit, Nkt of 15.75 to 17.83 as the best estimate, and Nkt of 13.63 as the upper bound limit. By using the calibrated Nkt parameters for clay strength interpretation, it is found that the interpretation results are in good agreement with the linear correlated strength profile. By normalised by the vertical effective stress, the normalised undrained shear strength su/σ'v0 is obtained as 0.298 for normally consolidated clay in Guangdong offshore area. After interpretation of overconsolidation ratio by CPTU data, the clay strength obtained by SHANSEP method is also in good agreement with laboratory test results, which can be applied in offshore wind power projects in the future.
As an important part of offshore wind turbine foundation design, the marine soil parameter evaluation would directly affect the safety of wind turbine and project cost. At present, piezocone penetration test(CPTU) is one of the most widely used in-situ testing methods in offshore geotechnical engineering. The disadvantage of CPTU is that soil parameters cannot be directly measured, which could only be interpreted by raw data. How to select appropriate CPTU interpretation parameter of clay strength is a difficult problem to be solved at present. In this paper, based on an offshore wind project in Guangdong offshore area, in-situ CPTU and hand torvane shear, pocket penetrometer, miniature laboratory vane shear, triaxial UU, consolidated quick shear and triaxial CU tests were carried out, the strength profiles were obtained by linear regression of the laboratory test results, where the clay samples under 60m were found to be severely disturbed, consolidated quick shear and triaxial CU test could reduce the effect of disturbance. Based on the hand torvane shear, pocket penetrometer, miniature laboratory vane shear, triaxial UU, consolidated quick shear and triaxial CU tests results, the average values of CPTU interpretation parameters Nkt for clay strength are obtained as 21.68, 19.52, 17.83, 18.63, 15.73 and 13.63, respectively. We suggest using Nkt of 21.68 as the interpretation parameter for the lower bound limit, Nkt of 15.75 to 17.83 as the best estimate, and Nkt of 13.63 as the upper bound limit. By using the calibrated Nkt parameters for clay strength interpretation, it is found that the interpretation results are in good agreement with the linear correlated strength profile. By normalised by the vertical effective stress, the normalised undrained shear strength su/σ'v0 is obtained as 0.298 for normally consolidated clay in Guangdong offshore area. After interpretation of overconsolidation ratio by CPTU data, the clay strength obtained by SHANSEP method is also in good agreement with laboratory test results, which can be applied in offshore wind power projects in the future.
2021, 29(S1): 203-212.
Offshore wind power industry in China has been developing rapidly in recent years, and particularly with the new proposal of "carbon peak and carbon neutralization", it is entering a new period of steady development. According to the characteristics of offshore wind power engineering, this paper summarizes a large number of engineering investigation practice and research results and wraps up the major engineering geological problems as well as corresponding countermeasures in offshore wind farm construction. This paper mainly introduces four major engineering geological problems, including sea area earthquake and active fault, deep soft soil, special rock and soil and marine geological disaster, with an emphasis on their impacts on the stability of the site, foundation, cable and other structures. Considering the characteristics of these four types of engineering geological problems, marine geophysical exploration, offshore drilling, in-situ test, advanced geotechnical test, physical model test as well as numerical analysis should be incorporated and widely applied to the investigation of different engineering geological problems. The presented investigation and evaluation methods for various engineering geological problems are of great significance on construction and safe operation of offshore wind power in the future.
Offshore wind power industry in China has been developing rapidly in recent years, and particularly with the new proposal of "carbon peak and carbon neutralization", it is entering a new period of steady development. According to the characteristics of offshore wind power engineering, this paper summarizes a large number of engineering investigation practice and research results and wraps up the major engineering geological problems as well as corresponding countermeasures in offshore wind farm construction. This paper mainly introduces four major engineering geological problems, including sea area earthquake and active fault, deep soft soil, special rock and soil and marine geological disaster, with an emphasis on their impacts on the stability of the site, foundation, cable and other structures. Considering the characteristics of these four types of engineering geological problems, marine geophysical exploration, offshore drilling, in-situ test, advanced geotechnical test, physical model test as well as numerical analysis should be incorporated and widely applied to the investigation of different engineering geological problems. The presented investigation and evaluation methods for various engineering geological problems are of great significance on construction and safe operation of offshore wind power in the future.
2021, 29(S1): 213-222.
The Tongluo Mountain tunnel of the Chengdu-Dazhou-Wanzhou Railway will pass through some areas with complex structures, and be going to suffer damage from coal seam gas and natural gas at the same time. For the simplicity, we call this kind of tunnel as the coal-and-gas tunnel. The methods which researchers often used to calculate the absolute gas emission rate, can no longer effectively evaluate the gas level of the coal-and-gas tunnel. We first used the experimental data of coal samples and the gas concentration data detected in the forecasting holes to calculate the absolute gas emission rate, and evaluated the gas level of the Tongluo Mountain tunnel by the conventional methods. Following that, we summarized the geological information and engineering data such as structure, lithology, and groundwater exposure of the tunnel site, etc., and used the fuzzy comprehensive evaluation method to evaluate the gas level of the tunnel again. By comparing with some of the existing similar tunnels in the area, we verified the effectiveness of the fuzzy comprehensive evaluation method. The results show that it is inadequate to evaluate the gas level of the coal-and-gas tunnel by calculating the absolute gas emission rate. The evaluation result of fuzzy comprehensive evaluation method is more reliable, because it can take the influence of a variety of comprehensive factors into consideration and evaluate the gas level of each section of the tunnel. The Tongluo Mountain tunnel is rated as a high-gas tunnel. Among the 9 sections of work area with gas, there are 3 high-gas sections and 2 low-gas sections. The research provides a new method to evaluate the gas level of coal-and-gas tunnels under the influence of multiple factors.
The Tongluo Mountain tunnel of the Chengdu-Dazhou-Wanzhou Railway will pass through some areas with complex structures, and be going to suffer damage from coal seam gas and natural gas at the same time. For the simplicity, we call this kind of tunnel as the coal-and-gas tunnel. The methods which researchers often used to calculate the absolute gas emission rate, can no longer effectively evaluate the gas level of the coal-and-gas tunnel. We first used the experimental data of coal samples and the gas concentration data detected in the forecasting holes to calculate the absolute gas emission rate, and evaluated the gas level of the Tongluo Mountain tunnel by the conventional methods. Following that, we summarized the geological information and engineering data such as structure, lithology, and groundwater exposure of the tunnel site, etc., and used the fuzzy comprehensive evaluation method to evaluate the gas level of the tunnel again. By comparing with some of the existing similar tunnels in the area, we verified the effectiveness of the fuzzy comprehensive evaluation method. The results show that it is inadequate to evaluate the gas level of the coal-and-gas tunnel by calculating the absolute gas emission rate. The evaluation result of fuzzy comprehensive evaluation method is more reliable, because it can take the influence of a variety of comprehensive factors into consideration and evaluate the gas level of each section of the tunnel. The Tongluo Mountain tunnel is rated as a high-gas tunnel. Among the 9 sections of work area with gas, there are 3 high-gas sections and 2 low-gas sections. The research provides a new method to evaluate the gas level of coal-and-gas tunnels under the influence of multiple factors.
2021, 29(S1): 223-232.
The Qiaojia Basin locates at the lower reaches of the Jinsha River and adjoins to the"Y-shape" converging point of Zemuhe, Daliangshan and Xiaojiang faults. It extends 13km with a width of 3~5km in surface, and the thickness of Qiaojia Basin is at least 733.6m, which is the deepest known intramountain basin in Southwestern China. The scale, sedimentary construction, and evolution mechanism of the Qiaojia Basin have been confusing for long time because of lack of field evidence. This paper reports 20 boreholes(the maximal depth is 748m) and a wide-area electromagnetic resistivity sounding profile across the Qiaojia Basin, and acquiring the following conclusions:(1) The maxim depth of the Qiaojia Basin is deeper than 733.6m according to borehole records and may be deeper than 900m inferred by geophysical profile result. (2) The Qiaojia Basin consists of six groups of alluvial sediments, groups ①, ② are modern in-laid terraces, while groups ③-⑥ are vertical accretion sediments in the buried Qiaojia Basin. (3) the Qiaojia Basin is a pull-apart basin between Zemuhe Fault and Xiaojiang Fault, and was born in 1.1Ma(Early Pleistocene). Qiaojia Basin stopped growth at about 34ka because of the final connectivity of these two faults. The sediment construction of Qiaojia Basin were dominated by alluvial deposits, intercalated with lacustrine and fluvial, and intersperse with flood fans. (4) No great quantity of landslide deposits was found in the Qiaojia Basin. Thus, the Qiaojia Gigantic paleo-landslide may be not existent.
The Qiaojia Basin locates at the lower reaches of the Jinsha River and adjoins to the"Y-shape" converging point of Zemuhe, Daliangshan and Xiaojiang faults. It extends 13km with a width of 3~5km in surface, and the thickness of Qiaojia Basin is at least 733.6m, which is the deepest known intramountain basin in Southwestern China. The scale, sedimentary construction, and evolution mechanism of the Qiaojia Basin have been confusing for long time because of lack of field evidence. This paper reports 20 boreholes(the maximal depth is 748m) and a wide-area electromagnetic resistivity sounding profile across the Qiaojia Basin, and acquiring the following conclusions:(1) The maxim depth of the Qiaojia Basin is deeper than 733.6m according to borehole records and may be deeper than 900m inferred by geophysical profile result. (2) The Qiaojia Basin consists of six groups of alluvial sediments, groups ①, ② are modern in-laid terraces, while groups ③-⑥ are vertical accretion sediments in the buried Qiaojia Basin. (3) the Qiaojia Basin is a pull-apart basin between Zemuhe Fault and Xiaojiang Fault, and was born in 1.1Ma(Early Pleistocene). Qiaojia Basin stopped growth at about 34ka because of the final connectivity of these two faults. The sediment construction of Qiaojia Basin were dominated by alluvial deposits, intercalated with lacustrine and fluvial, and intersperse with flood fans. (4) No great quantity of landslide deposits was found in the Qiaojia Basin. Thus, the Qiaojia Gigantic paleo-landslide may be not existent.
2021, 29(S1): 233-243.
As a commonly used type of compressed air storage, deep-buried tunnels may face different types of in-situ stress fields. When the tunnel is inflated and pressurized, its stability will be more complicated. We use ABAQUS finite element software to establish three-dimensional models of deep-buried compressed gas energy storage tunnels. By changing the angle between the tunnel axis direction and the maximum horizontal principal stress, the characteristics of displacement, stress and plastic zone are studied and we determine the best axis layout. The results show that under different types of in-situ stress field conditions, the convergent displacement of the tunnel is suppressed after the compressed air energy storage tunnel is inflated and pressurized, the uniformity of the compressive stress of the surrounding rock at each part is improved, and the stability of the tunnel is enhanced; after inflation and pressurization, displacement, stress and plastic zone change to a certain extent with different included angles, and their performance in different stress fields is different; after inflation and pressurization, the plastic zone range of surrounding rock under different stress field conditions is all obviously reduced, only locally distributed at the top of the arch; comprehensive analysis of the changes in the displacement, stress and plastic zone can determine the optimal layout of the axis:in the σH and σHV type stress field, the angle between the tunnel axis direction and the maximum horizontal principal stress should be less than 45° as much as possible, while in the σV type stress field, the angle between the tunnel axis direction and the maximum horizontal principal stress should be slightly greater than 45°. The results have certain reference value for the geological site selection and axis layout of the compressed gas energy storage tunnel.
As a commonly used type of compressed air storage, deep-buried tunnels may face different types of in-situ stress fields. When the tunnel is inflated and pressurized, its stability will be more complicated. We use ABAQUS finite element software to establish three-dimensional models of deep-buried compressed gas energy storage tunnels. By changing the angle between the tunnel axis direction and the maximum horizontal principal stress, the characteristics of displacement, stress and plastic zone are studied and we determine the best axis layout. The results show that under different types of in-situ stress field conditions, the convergent displacement of the tunnel is suppressed after the compressed air energy storage tunnel is inflated and pressurized, the uniformity of the compressive stress of the surrounding rock at each part is improved, and the stability of the tunnel is enhanced; after inflation and pressurization, displacement, stress and plastic zone change to a certain extent with different included angles, and their performance in different stress fields is different; after inflation and pressurization, the plastic zone range of surrounding rock under different stress field conditions is all obviously reduced, only locally distributed at the top of the arch; comprehensive analysis of the changes in the displacement, stress and plastic zone can determine the optimal layout of the axis:in the σH and σHV type stress field, the angle between the tunnel axis direction and the maximum horizontal principal stress should be less than 45° as much as possible, while in the σV type stress field, the angle between the tunnel axis direction and the maximum horizontal principal stress should be slightly greater than 45°. The results have certain reference value for the geological site selection and axis layout of the compressed gas energy storage tunnel.
2021, 29(S1): 244-250.
Deep foundation pit dewatering not only wastes groundwater resources, but also causes urban land subsidence. The statistical data of foundation pit drainage in the region is of great significance to the study of regional land subsidence. However, in the past, there was no monitoring drainage data during the dewatering construction of deep foundation pit, and only data such as foundation pit area, excavation depth and rough location information can be obtained. We need to use the existing data to estimate the drainage of deep foundation pit. In this paper, we determine the dewatering target aquifer by determining the geological zoning of deep foundation pit engineering, estimate the safe drawdown of foundation pit aquifer system through the three-dimensional geological information of the zoning, and estimate the drainage of foundation pit by analytical method and numerical method. Taking Shanghai as an example in 2020, it is estimated that the overall drainage of foundation pit reached 9.71 million cubic meters, the minimum drainage of single foundation pit was 28.8 cubic meters, and the maximum drainage reached 778000 cubic meters. The estimation method proposed by us can provide a reference basis for the historical analysis of urban groundwater resources and the correlation analysis of land subsidence.
Deep foundation pit dewatering not only wastes groundwater resources, but also causes urban land subsidence. The statistical data of foundation pit drainage in the region is of great significance to the study of regional land subsidence. However, in the past, there was no monitoring drainage data during the dewatering construction of deep foundation pit, and only data such as foundation pit area, excavation depth and rough location information can be obtained. We need to use the existing data to estimate the drainage of deep foundation pit. In this paper, we determine the dewatering target aquifer by determining the geological zoning of deep foundation pit engineering, estimate the safe drawdown of foundation pit aquifer system through the three-dimensional geological information of the zoning, and estimate the drainage of foundation pit by analytical method and numerical method. Taking Shanghai as an example in 2020, it is estimated that the overall drainage of foundation pit reached 9.71 million cubic meters, the minimum drainage of single foundation pit was 28.8 cubic meters, and the maximum drainage reached 778000 cubic meters. The estimation method proposed by us can provide a reference basis for the historical analysis of urban groundwater resources and the correlation analysis of land subsidence.
2021, 29(S1): 251-258.
The risk factors of tunnel construction are not only the objective factors such as complex geological conditions, but also the subjective factors such as construction level. Therefore, this paper attempts to integrate subjective influencing factors into the evaluation index system. Six factors such as surrounding rock conditions, geological prediction ability and construction team quality are selected as the risk evaluation indexes of tunnel construction according to relevant codes and engineering examples. It takes shenzhen east transit expressway connecting line tunnel construction as an example and uses analytic hierarchy process to determine index weight. According to the unascertained measure method, we evaluated the construction risk level of the tunnel and analyzed the possible risk points, and put forward targeted improvement measures and construction suggestions. On the basis of on-site rectification, the model was used to re-evaluate until the risk is acceptable. Engineering practices showed that this method achieves ideal risk control effect.
The risk factors of tunnel construction are not only the objective factors such as complex geological conditions, but also the subjective factors such as construction level. Therefore, this paper attempts to integrate subjective influencing factors into the evaluation index system. Six factors such as surrounding rock conditions, geological prediction ability and construction team quality are selected as the risk evaluation indexes of tunnel construction according to relevant codes and engineering examples. It takes shenzhen east transit expressway connecting line tunnel construction as an example and uses analytic hierarchy process to determine index weight. According to the unascertained measure method, we evaluated the construction risk level of the tunnel and analyzed the possible risk points, and put forward targeted improvement measures and construction suggestions. On the basis of on-site rectification, the model was used to re-evaluate until the risk is acceptable. Engineering practices showed that this method achieves ideal risk control effect.
2021, 29(S1): 259-267.
In the process of tunnel construction, underground karst is one of the main causes of ground collapse. In view of the situation that there are hidden karst caves in the soil layer around the shield tunnel, to explore the influence of karst caves on the law of surface settlement, this paper carries out research from the aspects of karst cave shape, different positions and different horizontal lengths by using GTS/NX finite element software. The results show that the lateral ellipse cave is the most unfavorable shape. In the horizontal position, the karst cave is located on one side of the tunnel, especially in the direction of 40°~50°, and the surface settlement increases significantly. There is a "critical clear distance" in the vertical position, which minimizes the surface settlement. When the horizontal length of the cave exceeds a certain value, the surface settlement increases sharply. The surface settlement law obtained by the research provides the basis for the deformation of the stratum where the karst cave is located, the prediction of the accident and the formulation of the treatment scheme.
In the process of tunnel construction, underground karst is one of the main causes of ground collapse. In view of the situation that there are hidden karst caves in the soil layer around the shield tunnel, to explore the influence of karst caves on the law of surface settlement, this paper carries out research from the aspects of karst cave shape, different positions and different horizontal lengths by using GTS/NX finite element software. The results show that the lateral ellipse cave is the most unfavorable shape. In the horizontal position, the karst cave is located on one side of the tunnel, especially in the direction of 40°~50°, and the surface settlement increases significantly. There is a "critical clear distance" in the vertical position, which minimizes the surface settlement. When the horizontal length of the cave exceeds a certain value, the surface settlement increases sharply. The surface settlement law obtained by the research provides the basis for the deformation of the stratum where the karst cave is located, the prediction of the accident and the formulation of the treatment scheme.
2021, 29(S1): 268-276.
The geological, climate, and environmental conditions of the Sichuan-Tibet Railway crossing area are complex, and there will be a large number of unresolved scientific and technological problems during its construction and operation. Aiming at the long-term freeze-thaw cycle of the rock mass in the alpine mountainous area, coupled with the long-term dynamic train load, the damage evolution law of the rock mass, and its influence on the stress state and deformation trend of the cutting slope, it will be the Sichuan-Tibet Railway disaster reduction and prevention, which is one of the key issues that needs to be solved urgently. Based on this, this article analyzes the measured data to obtain the law of traffic vibration propagation, that is, the farther the track is, the smaller the peak speed, and the vertical speed is greater than the horizontal direction. Based on this, the Z-direction equivalent load model is established; through indoor rock freezing and thawing cyclic test found that as the number of freeze-thaw cycles increases, the peak strength and elastic modulus of the rock are significantly weakened. For example, the peak strength and elastic model decrease, and the compaction section becomes longer. Compared with the PFC2D numerical simulation analysis, it can be seen that in the early freeze-thaw stage, the slope deformation is mainly vertical displacement. With the increase in the number of freeze-thaw cycles, the increase in the horizontal displacement of the slope is greater than the vertical; freeze-thaw and dynamic load coupling conditions Under this condition, the horizontal deformation of the slope will be accelerated, and slope failure and instability will easily occur. The research results can provide a certain scientific basis and theoretical support for slope risk prevention and control during the operation period of the Sichuan-Tibet Railway and similar projects.
The geological, climate, and environmental conditions of the Sichuan-Tibet Railway crossing area are complex, and there will be a large number of unresolved scientific and technological problems during its construction and operation. Aiming at the long-term freeze-thaw cycle of the rock mass in the alpine mountainous area, coupled with the long-term dynamic train load, the damage evolution law of the rock mass, and its influence on the stress state and deformation trend of the cutting slope, it will be the Sichuan-Tibet Railway disaster reduction and prevention, which is one of the key issues that needs to be solved urgently. Based on this, this article analyzes the measured data to obtain the law of traffic vibration propagation, that is, the farther the track is, the smaller the peak speed, and the vertical speed is greater than the horizontal direction. Based on this, the Z-direction equivalent load model is established; through indoor rock freezing and thawing cyclic test found that as the number of freeze-thaw cycles increases, the peak strength and elastic modulus of the rock are significantly weakened. For example, the peak strength and elastic model decrease, and the compaction section becomes longer. Compared with the PFC2D numerical simulation analysis, it can be seen that in the early freeze-thaw stage, the slope deformation is mainly vertical displacement. With the increase in the number of freeze-thaw cycles, the increase in the horizontal displacement of the slope is greater than the vertical; freeze-thaw and dynamic load coupling conditions Under this condition, the horizontal deformation of the slope will be accelerated, and slope failure and instability will easily occur. The research results can provide a certain scientific basis and theoretical support for slope risk prevention and control during the operation period of the Sichuan-Tibet Railway and similar projects.
2021, 29(S1): 277-284.
The response characteristics of pore water pressure in argillaceous seabed under typhoon are unclear. A typical muddy seabed in Zhujiajian, Zhoushan was selected as the research object, and the pore water pressure dynamic response of seabed in the observation area was studied at different depths by using the self-developed seabed pore water pressure probe rod combined with the hydrodynamic observation platform. The observation results show that the pore water pressure response type of muddy seabed in the observation area during typhoon Lichema is mainly transient response. The influence depth of waves on pore water pressure of seabed sediments increases with the increase of effective wave height, and the maximum influence depth can reach 3 meters. The amplitude attenuation rate of seabed pore water pressure in the observation area decreases with the increase of wave period, and the attenuation is obvious in the depth direction. At the same time, shallow gas in sediments will also lead to the amplitude attenuation of pore water pressure. The strong wave action caused by Typhoon Lichema can significantly reduce the effective stress in the shallow sediments of the seabed. The results reveal the response characteristics of pore water pressure of muddy seabed under typhoon, which is of great reference significance to judge whether typhoon will cause the instability of seabed surface.
The response characteristics of pore water pressure in argillaceous seabed under typhoon are unclear. A typical muddy seabed in Zhujiajian, Zhoushan was selected as the research object, and the pore water pressure dynamic response of seabed in the observation area was studied at different depths by using the self-developed seabed pore water pressure probe rod combined with the hydrodynamic observation platform. The observation results show that the pore water pressure response type of muddy seabed in the observation area during typhoon Lichema is mainly transient response. The influence depth of waves on pore water pressure of seabed sediments increases with the increase of effective wave height, and the maximum influence depth can reach 3 meters. The amplitude attenuation rate of seabed pore water pressure in the observation area decreases with the increase of wave period, and the attenuation is obvious in the depth direction. At the same time, shallow gas in sediments will also lead to the amplitude attenuation of pore water pressure. The strong wave action caused by Typhoon Lichema can significantly reduce the effective stress in the shallow sediments of the seabed. The results reveal the response characteristics of pore water pressure of muddy seabed under typhoon, which is of great reference significance to judge whether typhoon will cause the instability of seabed surface.
2021, 29(S1): 285-292.
Based on the existing survey data and the MapGIS platform, this paper took the core area of Helinger New Area in Inner Mongolia as the research object. We selected 9 factors from 4 aspects(hydrogeology, engineering geology, bad geology and landform) to form an underground space suitability evaluation index system, and used Analytic Hierarchy Process to evaluate the suitability of the underground space in the study area. The evaluation results showed that the more suitable shallow underground space and the more suitable middle underground space in the study area accounted for 99.71% and 95.03% of the total area; the more suitable deep underground space was in the southeast of the study area, accounting for 26.95% of the total area. The sub-suitable areas were widely distributed in the central and western regions of the study area, accounting for 72.27% of the total area. This research demonstrate that the comprehensive suitability of underground space resources in the study area is mainly more suitable area and sub-suitable area, and the suitability of underground space resources in different vertical levels and different locations is different in the study area. Overall, the spatial distribution of resource conditions is "the best in the shallow layer, the second in the middle layer and the worse in the deep layer".
Based on the existing survey data and the MapGIS platform, this paper took the core area of Helinger New Area in Inner Mongolia as the research object. We selected 9 factors from 4 aspects(hydrogeology, engineering geology, bad geology and landform) to form an underground space suitability evaluation index system, and used Analytic Hierarchy Process to evaluate the suitability of the underground space in the study area. The evaluation results showed that the more suitable shallow underground space and the more suitable middle underground space in the study area accounted for 99.71% and 95.03% of the total area; the more suitable deep underground space was in the southeast of the study area, accounting for 26.95% of the total area. The sub-suitable areas were widely distributed in the central and western regions of the study area, accounting for 72.27% of the total area. This research demonstrate that the comprehensive suitability of underground space resources in the study area is mainly more suitable area and sub-suitable area, and the suitability of underground space resources in different vertical levels and different locations is different in the study area. Overall, the spatial distribution of resource conditions is "the best in the shallow layer, the second in the middle layer and the worse in the deep layer".
2021, 29(S1): 293-301.
Taking the tailings pond slope landfills near a substation engineering area as the research object, the representative profiles of the tailings pond slope landfills are selected and divided into four areas based on the topographic, geomorphological and geophysical data of the field survey, and the computational profile model of the tailings pond slope landfills and their basement is established. The extended finite element method is used to simulate the deformation characteristics of the tailings pond slope landfills under no rainfall and different rainfall intensities. The strength reduction method is used to get the safety factor of the landfills, and the stability of the tailings pond landfills and its risk to the substation engineering site are analyzed and evaluated. The results show that the strength reduction method can effectively obtain the potential slip surface of the slope, and it is feasible to use the displacement abrupt point at a specific position on the slope as the criterion of slope instability. The maximum safety factor of the tailings pond slope landfills under normal working conditions(no rainfall) is 1.35, which meets the basic requirements of the safety factor of slope engineering in the code. Under different rainfall intensities, the safety factor of the slope is between 1~1.22, and under the condition of 80mm·h-1 heavy rainfall, the tailings pond slope landfills can still remain stable.
Taking the tailings pond slope landfills near a substation engineering area as the research object, the representative profiles of the tailings pond slope landfills are selected and divided into four areas based on the topographic, geomorphological and geophysical data of the field survey, and the computational profile model of the tailings pond slope landfills and their basement is established. The extended finite element method is used to simulate the deformation characteristics of the tailings pond slope landfills under no rainfall and different rainfall intensities. The strength reduction method is used to get the safety factor of the landfills, and the stability of the tailings pond landfills and its risk to the substation engineering site are analyzed and evaluated. The results show that the strength reduction method can effectively obtain the potential slip surface of the slope, and it is feasible to use the displacement abrupt point at a specific position on the slope as the criterion of slope instability. The maximum safety factor of the tailings pond slope landfills under normal working conditions(no rainfall) is 1.35, which meets the basic requirements of the safety factor of slope engineering in the code. Under different rainfall intensities, the safety factor of the slope is between 1~1.22, and under the condition of 80mm·h-1 heavy rainfall, the tailings pond slope landfills can still remain stable.
2021, 29(S1): 302-309.
Baihetan Hydropower Station is located on the borders of Sichuan and Yunnan provinces, China. It is the world's largest hydropower station under construction with the largest single-unit capacity. After completion, it will be the world's second largest hydropower station after the Three Gorges project in China. This paper systematically summarizes the main engineering geological problems in the dam site during the survey and design process, including:regional structural stability problem, asymmetric strong unloading problem, interbedded and intra-bedded dislocation zones problem, and columnar joint basalt problem. And we proposed corresponding engineering countermeasures and treatment measures, in view of the above major engineering geological problems, such as:by rationally adjusting the layout of the project and strengthening the support measures of the slope and caverns. We solved the influence of strong unloading, interbedded and intra-bedded dislocation zones on the stability of the dam foundation, slope and powerhouse complex. By adaptability design of arch dam structural combined with comprehensive control measures of excavation deformation, we solved the problems of columnar jointed basalt as the dam foundation rock mass. Baihetan hydropower station, as a typical high dam and large reservoir hydropower project, whose related research results can provide useful reference for the investigation and design of major projects in future.
Baihetan Hydropower Station is located on the borders of Sichuan and Yunnan provinces, China. It is the world's largest hydropower station under construction with the largest single-unit capacity. After completion, it will be the world's second largest hydropower station after the Three Gorges project in China. This paper systematically summarizes the main engineering geological problems in the dam site during the survey and design process, including:regional structural stability problem, asymmetric strong unloading problem, interbedded and intra-bedded dislocation zones problem, and columnar joint basalt problem. And we proposed corresponding engineering countermeasures and treatment measures, in view of the above major engineering geological problems, such as:by rationally adjusting the layout of the project and strengthening the support measures of the slope and caverns. We solved the influence of strong unloading, interbedded and intra-bedded dislocation zones on the stability of the dam foundation, slope and powerhouse complex. By adaptability design of arch dam structural combined with comprehensive control measures of excavation deformation, we solved the problems of columnar jointed basalt as the dam foundation rock mass. Baihetan hydropower station, as a typical high dam and large reservoir hydropower project, whose related research results can provide useful reference for the investigation and design of major projects in future.
2021, 29(S1): 310-315.
The distribution of plant roots is an important factor affecting slope stability under rainfall conditions by more and more studies. In order to study the influence of different types of roots on slope stability indoor simulated rainfall experiments were accomplished, to analyze the influence modes of different types of plant roots and explore the influence mechanism of root characteristic size and distribution. Results show that in the process of soil deformation the small discontinuous pores in the slope is easy to close and block automatically and not easy to form new local failure. Furthermore, woody plants with coarse roots have adverse effects on slope stability and the local failure is likely to occur at the location of plant roots contacting with soil, but roots of herbaceous plants have a significant strengthening effect on soil and its effects are confined to a certain range. It reveals that there is geometric scale and spatial distribution features for the effects of plant roots on slope, while the root system has the most significant effect on preventing slope instability when it is distributed near the initial point of potential sliding surface. The research results provide a reference for the influence mechanism of plant roots under rainfall conditions.
The distribution of plant roots is an important factor affecting slope stability under rainfall conditions by more and more studies. In order to study the influence of different types of roots on slope stability indoor simulated rainfall experiments were accomplished, to analyze the influence modes of different types of plant roots and explore the influence mechanism of root characteristic size and distribution. Results show that in the process of soil deformation the small discontinuous pores in the slope is easy to close and block automatically and not easy to form new local failure. Furthermore, woody plants with coarse roots have adverse effects on slope stability and the local failure is likely to occur at the location of plant roots contacting with soil, but roots of herbaceous plants have a significant strengthening effect on soil and its effects are confined to a certain range. It reveals that there is geometric scale and spatial distribution features for the effects of plant roots on slope, while the root system has the most significant effect on preventing slope instability when it is distributed near the initial point of potential sliding surface. The research results provide a reference for the influence mechanism of plant roots under rainfall conditions.
2021, 29(S1): 316-322.
The micro deformation of reservoir basin and bank slope induced by impoundment of high dam in canyon area mostly refers to the non-unstable deformation caused by the adjustment of mountain stress, which is generally several centimeters to tens of centimeters. In other researches, it is also called valley deformation(horizontal direction), reservoir basin deformation(vertical direction), etc. At present, monitoring and analysis have only been carried out in a few super high dam projects in China, such as Jinping I, Xiaowan, Xiluodu, etc. The proposed mechanisms and quantitative analyses are incomplete and unsystematically. The deformation law obtained from different engineering monitoring data is different, so it is difficult to explain the deformation mechanism by single theory. In particular, due to the lack of engineering experience and the lack of corresponding technical standards in the design, the long-term impact of bank slope micro deformation caused by high dam impoundment on dam is unknown. Therefore, this paper summarized the relevant research, discussed the possible mechanism of micro deformation of reservoir basin and bank slope, and finally prospected the research in future.
The micro deformation of reservoir basin and bank slope induced by impoundment of high dam in canyon area mostly refers to the non-unstable deformation caused by the adjustment of mountain stress, which is generally several centimeters to tens of centimeters. In other researches, it is also called valley deformation(horizontal direction), reservoir basin deformation(vertical direction), etc. At present, monitoring and analysis have only been carried out in a few super high dam projects in China, such as Jinping I, Xiaowan, Xiluodu, etc. The proposed mechanisms and quantitative analyses are incomplete and unsystematically. The deformation law obtained from different engineering monitoring data is different, so it is difficult to explain the deformation mechanism by single theory. In particular, due to the lack of engineering experience and the lack of corresponding technical standards in the design, the long-term impact of bank slope micro deformation caused by high dam impoundment on dam is unknown. Therefore, this paper summarized the relevant research, discussed the possible mechanism of micro deformation of reservoir basin and bank slope, and finally prospected the research in future.
2021, 29(S1): 334-343.
In order to master the dynamic height and developing law of the Water Conducting Fractured Zone(WCFZ) caused by the coal mining in large depth and thickness, the Brillouin optical time domain reflector(B OTDR) is applied to the field predicting. Taking the 150313 working face of Yinying Coal Mine as the background, with the detailed introduction of BOTDR and the theoretical analysis of the specific geological and productive conditions of the working face, the studies were carried out about the layout of the optical fiber(OF), the occurrence optimization of layout boreholes, the temporary safety measures and the characteristics of strain distribution. The test results showed that the optical fiber strain(1) appears strain peak distribution in the stratum with Lower strength and plateau distribution in the stratum with higher strength, (2) presents three stages:the initial platform stage, fast stretching stage and the final slow lifting stable stage in a single stratum, (3) characterize the height of WCFZ increases gradually with non-uniformity and non-linearity, and tends to be stable at last. The field test results are consistent with the theoretical calculation values and the previous similar model simulation test results, which shows that the BOTDR strain test method proposed in this paper is effective and feasible, and has certain practical and universal significance for popularizing the BOTDR monitoring of the WCFZ in coal mines and other similar underground structures.
In order to master the dynamic height and developing law of the Water Conducting Fractured Zone(WCFZ) caused by the coal mining in large depth and thickness, the Brillouin optical time domain reflector(B OTDR) is applied to the field predicting. Taking the 150313 working face of Yinying Coal Mine as the background, with the detailed introduction of BOTDR and the theoretical analysis of the specific geological and productive conditions of the working face, the studies were carried out about the layout of the optical fiber(OF), the occurrence optimization of layout boreholes, the temporary safety measures and the characteristics of strain distribution. The test results showed that the optical fiber strain(1) appears strain peak distribution in the stratum with Lower strength and plateau distribution in the stratum with higher strength, (2) presents three stages:the initial platform stage, fast stretching stage and the final slow lifting stable stage in a single stratum, (3) characterize the height of WCFZ increases gradually with non-uniformity and non-linearity, and tends to be stable at last. The field test results are consistent with the theoretical calculation values and the previous similar model simulation test results, which shows that the BOTDR strain test method proposed in this paper is effective and feasible, and has certain practical and universal significance for popularizing the BOTDR monitoring of the WCFZ in coal mines and other similar underground structures.
2021, 29(S1): 344-351.
The abandoned quarrying mines in Lishu County, Jilin Province have caused a large area of land damage and vegetation damage, and the high and steep slopes formed in the historical mining process have produced hidden dangers to the safety of local people. In view of this situation, in order to effectively restore the ecological environment of the mine, eliminate the hidden danger of geological disasters and develop characteristic tourism projects, this paper puts forward the remolding scheme of the abandoned mine slope. According to the overall planning requirements, the existing mine slope is remade to eliminate potential geological disasters, and at the same time, trees are planted in the pit and the platform to restore the slope ecology. Finally, the finite difference method is used to calculate and analyze the stability of the mine slope under the current conditions and after remolding. The results show that:1) Under the current condition, the high and steep slope is affected by unloading and weathering, and the rock mass cracks gradually increase, especially the unloading effect of the top rock mass gradually strengthens, and the local joint cutting of the current slope is easy to appear the phenomenon of block loss; 2) The remolding enhances the stability of the mine slope and meets the specification requirements. The research results provide a reference for the remolding design of the abandoned mine slope.
The abandoned quarrying mines in Lishu County, Jilin Province have caused a large area of land damage and vegetation damage, and the high and steep slopes formed in the historical mining process have produced hidden dangers to the safety of local people. In view of this situation, in order to effectively restore the ecological environment of the mine, eliminate the hidden danger of geological disasters and develop characteristic tourism projects, this paper puts forward the remolding scheme of the abandoned mine slope. According to the overall planning requirements, the existing mine slope is remade to eliminate potential geological disasters, and at the same time, trees are planted in the pit and the platform to restore the slope ecology. Finally, the finite difference method is used to calculate and analyze the stability of the mine slope under the current conditions and after remolding. The results show that:1) Under the current condition, the high and steep slope is affected by unloading and weathering, and the rock mass cracks gradually increase, especially the unloading effect of the top rock mass gradually strengthens, and the local joint cutting of the current slope is easy to appear the phenomenon of block loss; 2) The remolding enhances the stability of the mine slope and meets the specification requirements. The research results provide a reference for the remolding design of the abandoned mine slope.
2021, 29(S1): 352-359.
Pipejacking construction has many advantages, such as needing less equipment, simple working procedure, shorter construction period and low cost, etc. Pipejacking construction has been widely used in urban culvert pipes, alure and other projects. Thixotropic mud is an important lubricant in pipejacking and it's very essential for a long-distance and large-section pipejacking project. This paper used bentonite thixotropic mud as base mud, which mass ratio is bentonite:CMC:anhydrous sodium carbonate water=80:2:3:920. Nano-ZnO, nano-SiO2 and nano-Al2O3 were selected as additive. Through measuring the mud density, pH, six-speed viscosity, filter loss, mud cake adhesion coefficient and drainage rate, the optimum of nanomaterial and its concentration were determined. The conclusion is as follows:the drag reduction property of the thixotropic mud with the concentration of 2% nano-SiO2 is the best, which is about 14% higher than that of base mud. The conclusion can provide some reference for improving the drag reduction perperty of thixotropic mud in long-distance and large-section pipejacking construction, and provide some reference for the application of nanomaterials in thixotropic mud.
Pipejacking construction has many advantages, such as needing less equipment, simple working procedure, shorter construction period and low cost, etc. Pipejacking construction has been widely used in urban culvert pipes, alure and other projects. Thixotropic mud is an important lubricant in pipejacking and it's very essential for a long-distance and large-section pipejacking project. This paper used bentonite thixotropic mud as base mud, which mass ratio is bentonite:CMC:anhydrous sodium carbonate water=80:2:3:920. Nano-ZnO, nano-SiO2 and nano-Al2O3 were selected as additive. Through measuring the mud density, pH, six-speed viscosity, filter loss, mud cake adhesion coefficient and drainage rate, the optimum of nanomaterial and its concentration were determined. The conclusion is as follows:the drag reduction property of the thixotropic mud with the concentration of 2% nano-SiO2 is the best, which is about 14% higher than that of base mud. The conclusion can provide some reference for improving the drag reduction perperty of thixotropic mud in long-distance and large-section pipejacking construction, and provide some reference for the application of nanomaterials in thixotropic mud.
2021, 29(S1): 360-367.
Artificial ground freezing(AGF) is a construction method widely used in coastal tunnel engineering reinforcement. With more underground construction in coastal areas, clay-sand composite strata bring more challenges to AGF. Based on the actual engineering case of AGF, we designed a model tests to simulate the influence of soft clay-sand composite strata seepage on freezing process. We analyzed the frost heave displacement, temperature field distribution and water content change of upper clay layer under different seepage conditions of the underlying sand layer. We find that the existence of seepage in soft clay-sand composite strata not only influence the development of frozen wall, but also promotes the water migration of upper clay layer. Meantime paralleled fissures are well-developed surrounding frozen wall observed by image during freezing and subsequent image processing. All above increases thaw settlement and shorten the duration sharply. The research results above can provide important theoretical basis and significant reference for the application of AGF in soft clay-sand composite strata.
Artificial ground freezing(AGF) is a construction method widely used in coastal tunnel engineering reinforcement. With more underground construction in coastal areas, clay-sand composite strata bring more challenges to AGF. Based on the actual engineering case of AGF, we designed a model tests to simulate the influence of soft clay-sand composite strata seepage on freezing process. We analyzed the frost heave displacement, temperature field distribution and water content change of upper clay layer under different seepage conditions of the underlying sand layer. We find that the existence of seepage in soft clay-sand composite strata not only influence the development of frozen wall, but also promotes the water migration of upper clay layer. Meantime paralleled fissures are well-developed surrounding frozen wall observed by image during freezing and subsequent image processing. All above increases thaw settlement and shorten the duration sharply. The research results above can provide important theoretical basis and significant reference for the application of AGF in soft clay-sand composite strata.
2021, 29(S1): 368-376.
Through filling and static load tests, four steel corrugated arch culvert sections are selected, including trough section in the middle of the culvert axis, peak section in the middle of the culvert axis, trough section at the culvert opening, and wave crest section at the culvert opening, and set up strain gauges, earth pressure boxes and deformation measuring instruments, the mechanical characteristics of corrugated steel arch culverts such as stress, strain and displacement are studied, and the mechanical deformation characteristics and deformation laws of corrugated steel arch culverts under static load are obtained. The research results show that:1) Under the load of the same fill height, the vertical stress of the corrugated steel arch culvert is smaller than the vertical stress of the soil without culvert. The earth pressure is greater than the stress in the soil at the same height; 2) Due to the difference in the direction of the surrounding earth pressure on the culvert in the various stages of filling construction, the phenomenon of tension and compression changes at multiple locations during the filling process of the culvert, culvert culvert, culvert waist. The strain at the location is often larger, so this point is a weak point relative to other measuring points.
Through filling and static load tests, four steel corrugated arch culvert sections are selected, including trough section in the middle of the culvert axis, peak section in the middle of the culvert axis, trough section at the culvert opening, and wave crest section at the culvert opening, and set up strain gauges, earth pressure boxes and deformation measuring instruments, the mechanical characteristics of corrugated steel arch culverts such as stress, strain and displacement are studied, and the mechanical deformation characteristics and deformation laws of corrugated steel arch culverts under static load are obtained. The research results show that:1) Under the load of the same fill height, the vertical stress of the corrugated steel arch culvert is smaller than the vertical stress of the soil without culvert. The earth pressure is greater than the stress in the soil at the same height; 2) Due to the difference in the direction of the surrounding earth pressure on the culvert in the various stages of filling construction, the phenomenon of tension and compression changes at multiple locations during the filling process of the culvert, culvert culvert, culvert waist. The strain at the location is often larger, so this point is a weak point relative to other measuring points.
2021, 29(S1): 377-383.
Ground-borne vibration induced by high-speed train loads on composite foundation with piles results in vibration of adjacent buildings. This paper built a track-embankment-composite foundation with piles-building three-dimension finite element model to analyze the vibration response of a six-story building, which was at a distance of 30m from the track centerline. Performance of thickness and embedment depth of the raft foundation on vibration reduction was also considered. The results show that the vertical vibration response is predominant and the top floor has higher response than the first floor under the high-speed train load. The vertical dominant frequency on each floor is about 3.5Hz and the horizontal one is about 6.7Hz. The peak value and vibration level of vertical acceleration both decrease with the increase of thickness and embedment depth of the raft foundation, but the decrement lessens. It is useful to increase the thickness and embedment depth of the raft foundation to reduce the vibration of buildings near rails induced by high-speed train loads.
Ground-borne vibration induced by high-speed train loads on composite foundation with piles results in vibration of adjacent buildings. This paper built a track-embankment-composite foundation with piles-building three-dimension finite element model to analyze the vibration response of a six-story building, which was at a distance of 30m from the track centerline. Performance of thickness and embedment depth of the raft foundation on vibration reduction was also considered. The results show that the vertical vibration response is predominant and the top floor has higher response than the first floor under the high-speed train load. The vertical dominant frequency on each floor is about 3.5Hz and the horizontal one is about 6.7Hz. The peak value and vibration level of vertical acceleration both decrease with the increase of thickness and embedment depth of the raft foundation, but the decrement lessens. It is useful to increase the thickness and embedment depth of the raft foundation to reduce the vibration of buildings near rails induced by high-speed train loads.
2021, 29(S1): 384-392.
Based on a complex karst tunnel of an expressway, numerical simulation and field test methods are used to analyze V level surrounding rock deformation, supporting structure and plastic zone stress characteristics under the action of the stress field, seepage field and stress field coupling field in this paper. It also discusses the distribution law of seepage pressure and support deformation of tunnels with different grouting rings. The numerical results show that the displacement of surrounding rock and initial support under the coupling of seepage field and stress field is greater than that under the condition of considering only stress field. In order to ensure the safety of tunnel supporting structure, we simulated the grouting effect under different grouting ring thickness, and obtained that the grouting ring thickness under the effect of stress field is at least 8m, whereas the thickness of grouting ring should be at least 10m when the two fields are coupled. Finally, through the deformation monitoring data, it is verified that the calculation of grouting circle thickness is reasonable, which provides a reference for similar complex karst tunnel engineering in southwest area.
Based on a complex karst tunnel of an expressway, numerical simulation and field test methods are used to analyze V level surrounding rock deformation, supporting structure and plastic zone stress characteristics under the action of the stress field, seepage field and stress field coupling field in this paper. It also discusses the distribution law of seepage pressure and support deformation of tunnels with different grouting rings. The numerical results show that the displacement of surrounding rock and initial support under the coupling of seepage field and stress field is greater than that under the condition of considering only stress field. In order to ensure the safety of tunnel supporting structure, we simulated the grouting effect under different grouting ring thickness, and obtained that the grouting ring thickness under the effect of stress field is at least 8m, whereas the thickness of grouting ring should be at least 10m when the two fields are coupled. Finally, through the deformation monitoring data, it is verified that the calculation of grouting circle thickness is reasonable, which provides a reference for similar complex karst tunnel engineering in southwest area.
2021, 29(S1): 393-400.
Rock-socketed piles are widely used in geotechnical engineering to bear lateral load. However, it is still difficult for us to accurately analyze its lateral bearing capacity. We established a numerical simulation model of rock-socketed piles under the lateral load by using FLAC3D, and compared the simulated results with the measured results. Due to the high coincidence degree between the two results, we further analyzed the influence of rock mass parameters(elasticity modulus E, cohesion c, angle of internal friction φ), pile diameter, outcrop height, socketed depth and pile concrete strength on the lateral bearing capacity of rock-socketed pile. The results show that the increase of rock mass(E, c, φ) can increase the lateral bearing capacity of pile. E affects its lateral bearing capacity at the beginning of the force, and c, φ has an impact after the rock mass enters the plastic stage. Pile diameter has a significant influence on the lateral bearing capacity of pile. There is a critical value for the impact of socketed depth. When the socketed depth exceeds 3 times of pile diameter in this simulation, the lateral bearing capacity of pile increases slowly. The increase of pile concrete strength can enhance its lateral bearing capacity, but the effect is not obvious. The increase of outcrop height reduces the lateral bearing capacity of pile. Based on rock mass and pile body, this paper overcomes the lack of comprehensive selection of influencing factors in the past, and the results can provide reference for the design of rock-socketed piles in future projects.
Rock-socketed piles are widely used in geotechnical engineering to bear lateral load. However, it is still difficult for us to accurately analyze its lateral bearing capacity. We established a numerical simulation model of rock-socketed piles under the lateral load by using FLAC3D, and compared the simulated results with the measured results. Due to the high coincidence degree between the two results, we further analyzed the influence of rock mass parameters(elasticity modulus E, cohesion c, angle of internal friction φ), pile diameter, outcrop height, socketed depth and pile concrete strength on the lateral bearing capacity of rock-socketed pile. The results show that the increase of rock mass(E, c, φ) can increase the lateral bearing capacity of pile. E affects its lateral bearing capacity at the beginning of the force, and c, φ has an impact after the rock mass enters the plastic stage. Pile diameter has a significant influence on the lateral bearing capacity of pile. There is a critical value for the impact of socketed depth. When the socketed depth exceeds 3 times of pile diameter in this simulation, the lateral bearing capacity of pile increases slowly. The increase of pile concrete strength can enhance its lateral bearing capacity, but the effect is not obvious. The increase of outcrop height reduces the lateral bearing capacity of pile. Based on rock mass and pile body, this paper overcomes the lack of comprehensive selection of influencing factors in the past, and the results can provide reference for the design of rock-socketed piles in future projects.
微信 | 公众平台 
