Online Submission
Manuscript Tracking
Peer Review
Editor Work2019 Vol. 27, No. 4
Previous Issue
2019, 27(4): 699-705.
Abstract
3637KB
This paper focuses on the detailed acoustic emission characteristics of the two different types of the brittle rocks. They are granite and sandstone. Through the uniaxial compression test, the acoustic emission signals during the failure process of the granite and sandstone specimens are recorded. The data analyses cover the mechanical responses and acoustic emission characteristics. The following acoustic emission parameters are used:accumulative AE count, accumulative AE energy, AF, RA, and b values. The research outcomes are as follows. (1) The deformation and strength parameters of the rock specimens are obtained and the parameter variabilities are analyzed. (2) The accumulative AE count and accumulative AE energy are influenced by the bond strength of the grains and uniformity of the rock specimens. (3) It needs to be further investigated that whether the AF and RA values can be used to differentiate the tensile and shear cracks in rocks and the threshold of AF and RA values of rocks if they can be used. (4) Micro-crack activities are still dominant when the sandstone specimen is approaching the peak stress. This paper obtains some important features of the brittle rock specimens under uniaxial conditions, which provides a good start for the future research work.
This paper focuses on the detailed acoustic emission characteristics of the two different types of the brittle rocks. They are granite and sandstone. Through the uniaxial compression test, the acoustic emission signals during the failure process of the granite and sandstone specimens are recorded. The data analyses cover the mechanical responses and acoustic emission characteristics. The following acoustic emission parameters are used:accumulative AE count, accumulative AE energy, AF, RA, and b values. The research outcomes are as follows. (1) The deformation and strength parameters of the rock specimens are obtained and the parameter variabilities are analyzed. (2) The accumulative AE count and accumulative AE energy are influenced by the bond strength of the grains and uniformity of the rock specimens. (3) It needs to be further investigated that whether the AF and RA values can be used to differentiate the tensile and shear cracks in rocks and the threshold of AF and RA values of rocks if they can be used. (4) Micro-crack activities are still dominant when the sandstone specimen is approaching the peak stress. This paper obtains some important features of the brittle rock specimens under uniaxial conditions, which provides a good start for the future research work.
2019, 27(4): 706-716.
As aggregates of mineral particles, the macroscopic mechanical behaviors of rock are obviously affected by mineral particle size and size heterogeneity. The effect of size heterogeneity on rock macroscopic mechanical behaviors(elasticity modulus, peak strength and poisson's ratio) is studied using the software of particle flow code PFC2D. Different kinds of particle sizes are included in a model and size ratio are used to reflect particle size heterogeneity. Six size heterogeneous scenarios are designed and conducted in the numerical uniaxial compression tests. The type numbers of particle sizes included in a model are respectively continuous distribution, ten kinds, eight kinds, five kinds, three kinds and two kinds. Each scenario includes five mean grain sizes and four size ratios. The results show that particle size and size heterogeneity play an important role in the macro-mechanical properties of these numerical tests. Elasticity modulus and peak strength of samples decrease with the increase of average particle size. With the increase of the size heterogeneity, elasticity modulus and peak strength also show a decreasing trend overall, but during some local change stages show an increasing trend affected by the number and content of fine particles. The effect of particle size and size heterogeneity on Poisson's ratio is smaller. The effect mechanism of particle size on elastic modulus is mainly achieved by influencing the porosity of the model. The achieved results disclose that the change of rock macroscopic properties is the combined action of particle size effect and size heterogeneity effect, and supply references for studying the influence of particle size parameters on strength and deformation feature of rock materials.
As aggregates of mineral particles, the macroscopic mechanical behaviors of rock are obviously affected by mineral particle size and size heterogeneity. The effect of size heterogeneity on rock macroscopic mechanical behaviors(elasticity modulus, peak strength and poisson's ratio) is studied using the software of particle flow code PFC2D. Different kinds of particle sizes are included in a model and size ratio are used to reflect particle size heterogeneity. Six size heterogeneous scenarios are designed and conducted in the numerical uniaxial compression tests. The type numbers of particle sizes included in a model are respectively continuous distribution, ten kinds, eight kinds, five kinds, three kinds and two kinds. Each scenario includes five mean grain sizes and four size ratios. The results show that particle size and size heterogeneity play an important role in the macro-mechanical properties of these numerical tests. Elasticity modulus and peak strength of samples decrease with the increase of average particle size. With the increase of the size heterogeneity, elasticity modulus and peak strength also show a decreasing trend overall, but during some local change stages show an increasing trend affected by the number and content of fine particles. The effect of particle size and size heterogeneity on Poisson's ratio is smaller. The effect mechanism of particle size on elastic modulus is mainly achieved by influencing the porosity of the model. The achieved results disclose that the change of rock macroscopic properties is the combined action of particle size effect and size heterogeneity effect, and supply references for studying the influence of particle size parameters on strength and deformation feature of rock materials.
2019, 27(4): 717-722.
The physical and mechanical property of mud stone largely depend on the microscopic pore structure and the varying pattern in the soil mass. They can adversely affect its engineering characteristic. This paper aims to study the effect of compaction on the micro-porosity of micro-expansion mud stone for high-speed railway. It prepared six kinds of remodeled mud stone samples with different dry densities. It employs freezer dryer to conduct desiccation on saturated samples, and then conducts analytical investigation on micro-pore shape, pore volume, and pore area under different compaction status through mercury intrusion porosimetry. The results indicate that apart from the cylindrical pores exists in the remodeled mud stone, it also contains a large number of bottle neck pores. It proceeds classification on pores with different apertures referring to the pore partition method proposed by shear. It discovers that the pores inside remodeled mud stone are mostly found between particles and aggregates. The compaction performance on microscopic is the transformation from macro-void to small pores caused by the compression of macro-void. The total area of mud stone pores with different degree of compaction is closely identical. The pore area mainly exists in particle. The larger the compaction effect, the smaller the pore area in aggregate. It conducts reasonable analysis and description for the phenomenon. The actual porosity measured with the mercury intrusion method is smaller than that of theoretical calculating result. Linear regression analysis is used to analyze the relationship between measured porosity and calculated porosity, which ensures the correctness and rationality of the measured mud stone micro pore structure through the mercury intrusion method. The research achievement can provide reference frame for expansion mud stone in territorial high-speed railway construction, possess reference significance for similar engineering construction.
The physical and mechanical property of mud stone largely depend on the microscopic pore structure and the varying pattern in the soil mass. They can adversely affect its engineering characteristic. This paper aims to study the effect of compaction on the micro-porosity of micro-expansion mud stone for high-speed railway. It prepared six kinds of remodeled mud stone samples with different dry densities. It employs freezer dryer to conduct desiccation on saturated samples, and then conducts analytical investigation on micro-pore shape, pore volume, and pore area under different compaction status through mercury intrusion porosimetry. The results indicate that apart from the cylindrical pores exists in the remodeled mud stone, it also contains a large number of bottle neck pores. It proceeds classification on pores with different apertures referring to the pore partition method proposed by shear. It discovers that the pores inside remodeled mud stone are mostly found between particles and aggregates. The compaction performance on microscopic is the transformation from macro-void to small pores caused by the compression of macro-void. The total area of mud stone pores with different degree of compaction is closely identical. The pore area mainly exists in particle. The larger the compaction effect, the smaller the pore area in aggregate. It conducts reasonable analysis and description for the phenomenon. The actual porosity measured with the mercury intrusion method is smaller than that of theoretical calculating result. Linear regression analysis is used to analyze the relationship between measured porosity and calculated porosity, which ensures the correctness and rationality of the measured mud stone micro pore structure through the mercury intrusion method. The research achievement can provide reference frame for expansion mud stone in territorial high-speed railway construction, possess reference significance for similar engineering construction.
2019, 27(4): 723-728.
The long-term stability of slope in red clay region directly depends on the creep behavior of red clay. A specially designed tri-axial creep testing setup based on leverage loading method is adopted to investigate the creep behavior for red clay. Time history of axial displacement of specimen under drained condition is monitored subjected to stepwise axial load and constant confining stress. The Chen's method is used to transform the axial displacement time history equivalently into a cluster of creep curves for different loaded axial stresses. Furthermore, a threshold value of axial stress corresponding to the creep failure of red clay specimen is determined by using isochronal curve method. A novel element creep model incorporating soil consolidation theory and Kelvin rheological model is established to characterize the coupled consolidation-creep behavior of red clay. The model parameters of this element creep model are correlated reasonably with loaded axial stress by fitting on tested creep curves under part of adopted axial loads. The above correlations are furtherly incorporated into the creep model to predict the creep response of axial displacement of specimens under remaining axial stresses. The predicted axial displacement creep curves are compared with the measured data in tests. The good agreement found in comparison validates the effectiveness and accuracy of the presented element creep model.
The long-term stability of slope in red clay region directly depends on the creep behavior of red clay. A specially designed tri-axial creep testing setup based on leverage loading method is adopted to investigate the creep behavior for red clay. Time history of axial displacement of specimen under drained condition is monitored subjected to stepwise axial load and constant confining stress. The Chen's method is used to transform the axial displacement time history equivalently into a cluster of creep curves for different loaded axial stresses. Furthermore, a threshold value of axial stress corresponding to the creep failure of red clay specimen is determined by using isochronal curve method. A novel element creep model incorporating soil consolidation theory and Kelvin rheological model is established to characterize the coupled consolidation-creep behavior of red clay. The model parameters of this element creep model are correlated reasonably with loaded axial stress by fitting on tested creep curves under part of adopted axial loads. The above correlations are furtherly incorporated into the creep model to predict the creep response of axial displacement of specimens under remaining axial stresses. The predicted axial displacement creep curves are compared with the measured data in tests. The good agreement found in comparison validates the effectiveness and accuracy of the presented element creep model.
2019, 27(4): 729-736.
Two industry by-products, soda residue(SR) and ground granulated blastfurnace slag(GGBS), and sodium silicate(SS)were utilized to stabilize dredged silt at high water content. The unconfined compressive tests and X-ray diffraction were conducted to analyze the strength characteristics and the mechanism. The results indicate that the increase in dosage of SS, SR and GGBS can increase the unconfined compressive strength for the samples with the initial water content of 110%. The order of factors for strength of 3 days curing is SS > SR > GGBS. The order changes to SS > SR > GGBS for samples cured for 7 and 28 days. SS has a significant impact on the strength of 28 days curing. When the dosage of SS is fixed and the total dosage of SR and GGBS is the same, the effect of SR is stronger than that of GGBS. The hydration reaction among SS, SR, GGBS and soil minerals produces hydration products including ettringite, calcium chloro-aluminate hydrates, gismondine, and calcium silicate hydrates. They play the filling-in and cementation effects. The solidification scheme to meet the requirement of fill construction was determined. The results can provide a theoretical basis and data support for the resource utilization of SR and GGBS as stabilizer for dredged silt at high water content.
Two industry by-products, soda residue(SR) and ground granulated blastfurnace slag(GGBS), and sodium silicate(SS)were utilized to stabilize dredged silt at high water content. The unconfined compressive tests and X-ray diffraction were conducted to analyze the strength characteristics and the mechanism. The results indicate that the increase in dosage of SS, SR and GGBS can increase the unconfined compressive strength for the samples with the initial water content of 110%. The order of factors for strength of 3 days curing is SS > SR > GGBS. The order changes to SS > SR > GGBS for samples cured for 7 and 28 days. SS has a significant impact on the strength of 28 days curing. When the dosage of SS is fixed and the total dosage of SR and GGBS is the same, the effect of SR is stronger than that of GGBS. The hydration reaction among SS, SR, GGBS and soil minerals produces hydration products including ettringite, calcium chloro-aluminate hydrates, gismondine, and calcium silicate hydrates. They play the filling-in and cementation effects. The solidification scheme to meet the requirement of fill construction was determined. The results can provide a theoretical basis and data support for the resource utilization of SR and GGBS as stabilizer for dredged silt at high water content.
2019, 27(4): 737-744.
Dynamic triaxial test was carried out on the expansive soil from Yanzhou-Shijiusuo railway roadbed. It is to study the effects of water content, vibration frequency and dynamic stress on its cumulative plastic strain, dynamic strength and critical dynamic stress. The experimental results show that when the axial cumulative strain reaches 5%as the failure standard, the relationship between the number of cycles and the cumulative plastic strain curve shows three states:stable type, critical type and destructive type. Both the dynamic strength and the critical dynamic stress decrease significantly with the increase of water content. The critical dynamic stress in saturated state is only 40kPa, which is lower than the actual dynamic load of the train. We find that critical state line exists between the critical dynamic stress and saturation and can be used to judge whether the specimen is stable, critical or failure. The vibration frequency has the following effects on the dynamic characteristics of expansive soil. When frequency equals to 0.5~2Hz, the dynamic strength increases with the increase of frequency. When the frequency continues to increase to 5Hz, the dynamic strength of expansive soil increases significantly. When frequency equals to 0.5~5Hz, the critical dynamic stress increases with the increase of frequency, which is approximately linear. The related research results are of great significance to reveal the mechanical properties of expansive soil under dynamic loading and to ensure the safe operation of railway lines in expansive soil area.
Dynamic triaxial test was carried out on the expansive soil from Yanzhou-Shijiusuo railway roadbed. It is to study the effects of water content, vibration frequency and dynamic stress on its cumulative plastic strain, dynamic strength and critical dynamic stress. The experimental results show that when the axial cumulative strain reaches 5%as the failure standard, the relationship between the number of cycles and the cumulative plastic strain curve shows three states:stable type, critical type and destructive type. Both the dynamic strength and the critical dynamic stress decrease significantly with the increase of water content. The critical dynamic stress in saturated state is only 40kPa, which is lower than the actual dynamic load of the train. We find that critical state line exists between the critical dynamic stress and saturation and can be used to judge whether the specimen is stable, critical or failure. The vibration frequency has the following effects on the dynamic characteristics of expansive soil. When frequency equals to 0.5~2Hz, the dynamic strength increases with the increase of frequency. When the frequency continues to increase to 5Hz, the dynamic strength of expansive soil increases significantly. When frequency equals to 0.5~5Hz, the critical dynamic stress increases with the increase of frequency, which is approximately linear. The related research results are of great significance to reveal the mechanical properties of expansive soil under dynamic loading and to ensure the safe operation of railway lines in expansive soil area.
2019, 27(4): 745-752.
The eolian deposit fine sand in desert area has slight to severe collapsibility. Eliminating the collapsibility for the foundation soil of eolian deposit fine sand is a problem to be solved urgently in engineering. Combined with the engineering example, the dynamic compaction method is used to reinforce the foundation soil of eolian deposit fine sand. The effect and law of the dynamic compaction method to eliminate the collapsibility of the eolian deposit fine sand are evaluated with shallow plate loading test and laboratory soil test. The results show that the collapsibility of the eolian deposit fine sand is mainly affected by the moisture content and the density. The water content is especially prominent for the collapsible deformation. Before the dynamic compaction, the water content of the soil should be sufficient to make the soil moisture content reach the optimal water content. In the dynamic consolidation and reinforcement, the optimum hammer number in the filled site is 10 strike, and the optimum hammer number in the excavated site is 8 strike. The dynamic design of information construction(ie., the observational method) has to be used. After dynamic compaction, the bearing capacity of the eolian deposit fine sand is two times more than that before the dynamic compaction. In the collapsible test, the deformation increment of the eolian deposit fine sand is less with the time. The dynamic compaction method improves the collapsibility of the aeolian fine sand, among which the water is the main factor of controlling the collapsibility, and the dynamic compaction is the secondary factor. The research results help to provide reference for the design and construction of the foundation soil of eolian deposit fine sand by dynamic compaction, and provide reference for similar foundation treatment.
The eolian deposit fine sand in desert area has slight to severe collapsibility. Eliminating the collapsibility for the foundation soil of eolian deposit fine sand is a problem to be solved urgently in engineering. Combined with the engineering example, the dynamic compaction method is used to reinforce the foundation soil of eolian deposit fine sand. The effect and law of the dynamic compaction method to eliminate the collapsibility of the eolian deposit fine sand are evaluated with shallow plate loading test and laboratory soil test. The results show that the collapsibility of the eolian deposit fine sand is mainly affected by the moisture content and the density. The water content is especially prominent for the collapsible deformation. Before the dynamic compaction, the water content of the soil should be sufficient to make the soil moisture content reach the optimal water content. In the dynamic consolidation and reinforcement, the optimum hammer number in the filled site is 10 strike, and the optimum hammer number in the excavated site is 8 strike. The dynamic design of information construction(ie., the observational method) has to be used. After dynamic compaction, the bearing capacity of the eolian deposit fine sand is two times more than that before the dynamic compaction. In the collapsible test, the deformation increment of the eolian deposit fine sand is less with the time. The dynamic compaction method improves the collapsibility of the aeolian fine sand, among which the water is the main factor of controlling the collapsibility, and the dynamic compaction is the secondary factor. The research results help to provide reference for the design and construction of the foundation soil of eolian deposit fine sand by dynamic compaction, and provide reference for similar foundation treatment.
2019, 27(4): 753-759.
This paper studies effects of sludge solidified with paper sludge ash(PS ash) and cement. The main factors are about the contents of PS ash and cement which influence solidified sludge mechanical properties and permeability. Multiple methods are used to conduct permeability tests and hydrostatic leaching tests by adding PS ash and cement. Final, the paper analyzes the change rule of hydraulic characteristics of solidified body with influencing factors. Test results show that:the unconfined compressive strength of the solidified sludge has a "staircase" distribution with the contents of PS ash and cement. The permeability of solidified sludge reaches the minimum as 0.48×10-5cm·s-1, when the contents of cement and PS ash are 20% and 17.5%, respectively. When the content of PS ash is certain, the content of metal ions decreases as the increasing of cement content. PS increases the ash content for curing Cd and Cu ion effect when the cement content is between 8%~12%. The curing effect of other metal ions is shown the best when the cement content is above 12%, and decreased as the increasing of the content of PS ash.
This paper studies effects of sludge solidified with paper sludge ash(PS ash) and cement. The main factors are about the contents of PS ash and cement which influence solidified sludge mechanical properties and permeability. Multiple methods are used to conduct permeability tests and hydrostatic leaching tests by adding PS ash and cement. Final, the paper analyzes the change rule of hydraulic characteristics of solidified body with influencing factors. Test results show that:the unconfined compressive strength of the solidified sludge has a "staircase" distribution with the contents of PS ash and cement. The permeability of solidified sludge reaches the minimum as 0.48×10-5cm·s-1, when the contents of cement and PS ash are 20% and 17.5%, respectively. When the content of PS ash is certain, the content of metal ions decreases as the increasing of cement content. PS increases the ash content for curing Cd and Cu ion effect when the cement content is between 8%~12%. The curing effect of other metal ions is shown the best when the cement content is above 12%, and decreased as the increasing of the content of PS ash.
2019, 27(4): 760-765.
This paper presents a united expression of the compression lines of normal compressed clay, overconsolidated clay and sand by introducing a special vertical stress in single logarithmic coordinates. And then, based on the new expression and the concept of compression modulus, we obtain a calculation method for the compressive modulus of soil. Evolutionary laws of compressive modulus are presented and analyzed with the special vertical stress and compression index changing, respectively. Finally, comparisons with the test results and foundation settlement in engineering case indicate the rationality of this calculation method.
This paper presents a united expression of the compression lines of normal compressed clay, overconsolidated clay and sand by introducing a special vertical stress in single logarithmic coordinates. And then, based on the new expression and the concept of compression modulus, we obtain a calculation method for the compressive modulus of soil. Evolutionary laws of compressive modulus are presented and analyzed with the special vertical stress and compression index changing, respectively. Finally, comparisons with the test results and foundation settlement in engineering case indicate the rationality of this calculation method.
2019, 27(4): 766-774.
This paper aims to research the variation law of temperature field and its influencing factors of shallow unsaturated loess in the northwestern of China. A one-dimensional soil column model is built and placed under outdoor natural conditions. It is used to test the outdoor evaporation model under atmospheric temperature cycle. The experimental results show that the soil temperature decreases with the increase of depth in the depth range of 0~10cm, and the temperature is the lowest at 5~10cm in the surface layer of the soil sample. Under the same external conditions, the initial volume content of the soil is higher and the degree of compaction is higher. The larger the thermal conductivity and the greater the temperature change. As the depth increases and the evaporation time increases, the difference in thermal conductivity caused by compaction and water content is superimposed. So the temperature difference between soils with different compaction degrees and different water contents at the same depth increases. Both of the initial volume content of the soil and the compaction degree of soil have an effect on the temperature migration. Compared with the change of compaction degree, the change of soil volume content has a more significant effect on soil temperature migration. With the increase of evaporation time, the temperature gradually increases from the surface to the inside. The temperature in the depth direction decreases firstly and then increases. The soil temperature growth curve at different depths is roughly a "S" type increasing curve, which can be divided into three stages of evaporation.
This paper aims to research the variation law of temperature field and its influencing factors of shallow unsaturated loess in the northwestern of China. A one-dimensional soil column model is built and placed under outdoor natural conditions. It is used to test the outdoor evaporation model under atmospheric temperature cycle. The experimental results show that the soil temperature decreases with the increase of depth in the depth range of 0~10cm, and the temperature is the lowest at 5~10cm in the surface layer of the soil sample. Under the same external conditions, the initial volume content of the soil is higher and the degree of compaction is higher. The larger the thermal conductivity and the greater the temperature change. As the depth increases and the evaporation time increases, the difference in thermal conductivity caused by compaction and water content is superimposed. So the temperature difference between soils with different compaction degrees and different water contents at the same depth increases. Both of the initial volume content of the soil and the compaction degree of soil have an effect on the temperature migration. Compared with the change of compaction degree, the change of soil volume content has a more significant effect on soil temperature migration. With the increase of evaporation time, the temperature gradually increases from the surface to the inside. The temperature in the depth direction decreases firstly and then increases. The soil temperature growth curve at different depths is roughly a "S" type increasing curve, which can be divided into three stages of evaporation.
2019, 27(4): 775-793.
Variation of moisture is an inevitable process in natural soil, which influences engineering properties significantly. Mastering the evolution characteristics of soil structure in wetting/drying process systematically is meaningful for understanding the macro mechanical properties. Based on a large number of literatures, the evolution rules during drying, wetting and wetting/drying cycling processes are summarized and some insights are as follows. (1)Water content is the key factor to microstructure. The soils on the wet side of optimum water content have a matrix type of structure with a single pore size distribution, whereas the soils on the dry side of optimum water content display an aggregate structure with a bimodal pore size distribution. (2)On the drying path before shrinkage limit, the decrease of total volume is mainly caused by the shrink of macro-voids. Different sizes of voids are influenced in different suction domain. (3)On the wetting path, inter-aggregate voids and intra-aggregate voids both increase and the latter are dominant. The evolution characteristic is relative to confining condition closely. (4)The change of soil structure in wetting/drying cycling isn't reversible completely, and the accumulated expansion/shrink derives from the deformation of macro-voids. With the development of wetting/drying cycling, the volumetric strain will reach an equilibrium, which can be described by the elastic void ratio. Additionally, the wide spread applied techniques to soil structure research are summarized and include SEM, ESEM, MIP, and CT. Finally, based on the current situation, writers proposed the researching emphasis and direction in the future, ranging from new sample preparation methods, further research on the wetting process, combining between micro-structural parameters and macro mechanical models etc.
Variation of moisture is an inevitable process in natural soil, which influences engineering properties significantly. Mastering the evolution characteristics of soil structure in wetting/drying process systematically is meaningful for understanding the macro mechanical properties. Based on a large number of literatures, the evolution rules during drying, wetting and wetting/drying cycling processes are summarized and some insights are as follows. (1)Water content is the key factor to microstructure. The soils on the wet side of optimum water content have a matrix type of structure with a single pore size distribution, whereas the soils on the dry side of optimum water content display an aggregate structure with a bimodal pore size distribution. (2)On the drying path before shrinkage limit, the decrease of total volume is mainly caused by the shrink of macro-voids. Different sizes of voids are influenced in different suction domain. (3)On the wetting path, inter-aggregate voids and intra-aggregate voids both increase and the latter are dominant. The evolution characteristic is relative to confining condition closely. (4)The change of soil structure in wetting/drying cycling isn't reversible completely, and the accumulated expansion/shrink derives from the deformation of macro-voids. With the development of wetting/drying cycling, the volumetric strain will reach an equilibrium, which can be described by the elastic void ratio. Additionally, the wide spread applied techniques to soil structure research are summarized and include SEM, ESEM, MIP, and CT. Finally, based on the current situation, writers proposed the researching emphasis and direction in the future, ranging from new sample preparation methods, further research on the wetting process, combining between micro-structural parameters and macro mechanical models etc.
2019, 27(4): 794-802.
Ordinary kriging interpolation methods can be used in predicting submarine stratum thickness and obtaining its spatial distribution characteristics, using profile data as source data and borehole data as validation data. In this paper, three variogram models and different sampling interval are chosen to estimating submarine stratums thickness. The results show that ordinary kriging is an effective method of predicting submarine stratum thickness. The variogram model with the best structural analysis is not the model with minimal error. The choice of variogram model should be figured out through comprehensive analysis of interpolation output. The most suitable model for estimation of submarine stratums thickness in this well field is spherical model. Gauss model comes the second. For spherical model, the influence to regression effect in undulating stratum is greater than gentle stratum. An analysis of the variation ratio of the SE prediction show that reducing the sampling interval can greatly reduce the interpolation error for undulating stratum, and has little effect on improving the interpolation accuracy for gentle stratum.
Ordinary kriging interpolation methods can be used in predicting submarine stratum thickness and obtaining its spatial distribution characteristics, using profile data as source data and borehole data as validation data. In this paper, three variogram models and different sampling interval are chosen to estimating submarine stratums thickness. The results show that ordinary kriging is an effective method of predicting submarine stratum thickness. The variogram model with the best structural analysis is not the model with minimal error. The choice of variogram model should be figured out through comprehensive analysis of interpolation output. The most suitable model for estimation of submarine stratums thickness in this well field is spherical model. Gauss model comes the second. For spherical model, the influence to regression effect in undulating stratum is greater than gentle stratum. An analysis of the variation ratio of the SE prediction show that reducing the sampling interval can greatly reduce the interpolation error for undulating stratum, and has little effect on improving the interpolation accuracy for gentle stratum.
2019, 27(4): 803-810.
This paper aims to examine the collapsible loess in Xining area. The burial depth and humidifying water content are analyzed with the confined compression tests for the change regularity in the collapsible deformation and compressive deformation of loess under humidifying conditions. Qualitative analysis is carried out on the microstructure of different humidification loess samples by means of scanning electron microscopy. Macro-microscopic analysis is further carried out for the relationship between the microstructure of the loess sample and the collapse deformation. The results show the follows. (1)With the increase of water content, the amount of collapse deformation and compression under the same pressure gradually become smaller. The soil will be compressed, the strength will be increased, the compressibility will be weakened, and the collapsibility will be weakened or there will be no collapsibility when the water content increases to a certain extent. (2)Due to the influence of loess stress history on its structure and collapsibility, with the increase of burial depth and water content, the 5m loess exhibits less humidification and deformation and compressive deformation than the 3m loess. (3)With the increase of water content before and after immersion, the arrangement of pores tends to be stable, the particle distribution is gradually concentrated. The degree of agglomeration becomes higher, the proportion of pore area gradually decreases, the pore morphology gradually becomes narrow and the macroscopic humidifying deformation of loess before and after water immersion consistent performance.
This paper aims to examine the collapsible loess in Xining area. The burial depth and humidifying water content are analyzed with the confined compression tests for the change regularity in the collapsible deformation and compressive deformation of loess under humidifying conditions. Qualitative analysis is carried out on the microstructure of different humidification loess samples by means of scanning electron microscopy. Macro-microscopic analysis is further carried out for the relationship between the microstructure of the loess sample and the collapse deformation. The results show the follows. (1)With the increase of water content, the amount of collapse deformation and compression under the same pressure gradually become smaller. The soil will be compressed, the strength will be increased, the compressibility will be weakened, and the collapsibility will be weakened or there will be no collapsibility when the water content increases to a certain extent. (2)Due to the influence of loess stress history on its structure and collapsibility, with the increase of burial depth and water content, the 5m loess exhibits less humidification and deformation and compressive deformation than the 3m loess. (3)With the increase of water content before and after immersion, the arrangement of pores tends to be stable, the particle distribution is gradually concentrated. The degree of agglomeration becomes higher, the proportion of pore area gradually decreases, the pore morphology gradually becomes narrow and the macroscopic humidifying deformation of loess before and after water immersion consistent performance.
2019, 27(4): 811-818.
The simulation of soil constitutive properties of methane hydrate-bearing sediments is very important for the safe exploitation of methane hydrates. First, the influence mechanism of hydrate on the mechanical properties of sediments such as strength, dilatancy and softening is analyzed. The higher hydrate saturation has a significant effect on mechanical properties of methane hydrate bearing sediments. Based on the modified Cam-clay model, we have introduced the hydrate saturation and unified hardening parameter to modify the yield function, in order to reflect the impact of methane hydrate on shear strength and dilatancy and softening characteristics. And then, an elastoplastic constitutive model considering the formation and degradation of cementation of the methane hydrate is proposed and the corresponding elastoplastic matrix is derived. Finally, the comparison between the simulation results and the existing triaxial test data shows that the model can predict the strength, dilatancy and softening of the methane hydrate bearing sediments well, and the rationality and validity of the model are verified.
The simulation of soil constitutive properties of methane hydrate-bearing sediments is very important for the safe exploitation of methane hydrates. First, the influence mechanism of hydrate on the mechanical properties of sediments such as strength, dilatancy and softening is analyzed. The higher hydrate saturation has a significant effect on mechanical properties of methane hydrate bearing sediments. Based on the modified Cam-clay model, we have introduced the hydrate saturation and unified hardening parameter to modify the yield function, in order to reflect the impact of methane hydrate on shear strength and dilatancy and softening characteristics. And then, an elastoplastic constitutive model considering the formation and degradation of cementation of the methane hydrate is proposed and the corresponding elastoplastic matrix is derived. Finally, the comparison between the simulation results and the existing triaxial test data shows that the model can predict the strength, dilatancy and softening of the methane hydrate bearing sediments well, and the rationality and validity of the model are verified.
2019, 27(4): 819-824.
The disintegration and collapsibility of weathered red sandstone soil after wetting process can put a great threat on the stability of embankment. This paper investigates the wetting deformation and strength behavior of the red sandstone weathered soil. We performed a series of triaxial tests in this research using single lines method. The paper evaluates the effects of density, confining pressure and stress level on wetting axial strain. It observes that, wetting axial strain increases with the increase of both the confining pressure and the stress level, while decreases with the increase of density. The test results reveal that the wetting axial strain exhibits a linear relationship with the stress level, and an empirical expression is proposed based on the test results. In addition, the peak strength of the specimen after wetting decreases slightly with the increase of stress level, and is lower than the peak strength under saturated states.
The disintegration and collapsibility of weathered red sandstone soil after wetting process can put a great threat on the stability of embankment. This paper investigates the wetting deformation and strength behavior of the red sandstone weathered soil. We performed a series of triaxial tests in this research using single lines method. The paper evaluates the effects of density, confining pressure and stress level on wetting axial strain. It observes that, wetting axial strain increases with the increase of both the confining pressure and the stress level, while decreases with the increase of density. The test results reveal that the wetting axial strain exhibits a linear relationship with the stress level, and an empirical expression is proposed based on the test results. In addition, the peak strength of the specimen after wetting decreases slightly with the increase of stress level, and is lower than the peak strength under saturated states.
2019, 27(4): 825-831.
Weathered granite in Xiamen is a kind of regional special soil. Its mechanical index is usually investigated with in-situ test because of disturbance. The in-situ mechanical properties of the weathered soils are evaluated by seismic dilatometer test of typical weathering granite layer at three sites of Xiamen Metro Line 1. The results show that the weathered soil derived from granite in Xiamen is classified as silty-sandy soil with quasi-overconsolidation characteristics. Its OCR values are generally larger than 1. It belongs to a part drainage type. Mechanical behavior of the weathered soil particularly is sensitive to the degree of weathering. As burial depth increases, the degree of weathering is gradually weakened. This will cause the horizontal stress of soil decreases, while the strength, rigidity and the shear wave velocity of soil increase. Furthermore, the soil classification is transformed from silt to sandy soil, the quasi-overconsolidation characteristics are weakened and the drainage characteristics is translated from the non-drainage type to the drainage type. Therefore, the seismic dilatometer test is especially suitable for weathered granite stratum with the good reliability and wide applicability. The study has direct guidance for the optimization design of the weathered soil foundation in Xiamen.
Weathered granite in Xiamen is a kind of regional special soil. Its mechanical index is usually investigated with in-situ test because of disturbance. The in-situ mechanical properties of the weathered soils are evaluated by seismic dilatometer test of typical weathering granite layer at three sites of Xiamen Metro Line 1. The results show that the weathered soil derived from granite in Xiamen is classified as silty-sandy soil with quasi-overconsolidation characteristics. Its OCR values are generally larger than 1. It belongs to a part drainage type. Mechanical behavior of the weathered soil particularly is sensitive to the degree of weathering. As burial depth increases, the degree of weathering is gradually weakened. This will cause the horizontal stress of soil decreases, while the strength, rigidity and the shear wave velocity of soil increase. Furthermore, the soil classification is transformed from silt to sandy soil, the quasi-overconsolidation characteristics are weakened and the drainage characteristics is translated from the non-drainage type to the drainage type. Therefore, the seismic dilatometer test is especially suitable for weathered granite stratum with the good reliability and wide applicability. The study has direct guidance for the optimization design of the weathered soil foundation in Xiamen.
2019, 27(4): 832-841.
The Yarlung Zangbo River in Tibet is the core area of the eastern tectonic knot. This paper aims to study the current uplifting status of the Big Bend Region at Yarlung Zangbo River. It uses the ArcGIS platform. The research teams calculate the ASTER-DEM30m area-elevation integral value of the Big Bend Region at the lower Yarlung Zangbo River. The Hypsometry Index is a method based on the digital elevation model to obtain the characteristics of river evolution and the corresponding response index of tectonic activity. It examines the uplift difference in the study area in combination with the basic data of structure, lithology, climate, Quaternary depositsand rivers. The results show that the uplift area with HI>0.43 is mainly located outside the Big Bend suture zone and its distribution is well coupled with the Ⅲ-grade planation plane in each block. While the distribution range of Lhasa fault uplift area with HI>0.60 is the largest, and the distribution area of the Gyalha Bair fault uplift area is the smallest, which is only distributed in a small range of the Big Bend Region. The eroded cutting area with HI < 0.43 is located at the Ⅰ and Ⅱ grade valley shoulders of the river and the mature area of rivers. The Linzhi-Paizhen section with HI < 0.35 mainly manifests as erosion and down cut. It is concluded that the tectonic compressive action still exists in the study area, and the influence of climate, rivers and fault zone density are generated under the tectonic setting. The above factors would gradually inhibit the tectonic uplift with the passage of time, and the promotion effect of erosion is different in different regions. When the tectonic effect plays a major role, fault block is dominated by uplift with HI>0.43. The influence of climatic action led to the uplift stagnation for Gyalha Bair and Namjagbarwa Mountains, with HI < 0.43. The Linzhi block with HI < 0.35 indicates that the intensity of erosion will increase under the influence of climate, rivers and fault zone density. So the area mainly manifests as erosion and down cut, with no sign of uplift. Therefore, under the combined influence of tectonics, climate, river development and fault zone density, the uplift function is gradually weakened from the outside to the inside of the lower reaches of the Yarlung Zangbo River Basin, and the differences in the local area are determined by the difference in the role of the influencing factors.
The Yarlung Zangbo River in Tibet is the core area of the eastern tectonic knot. This paper aims to study the current uplifting status of the Big Bend Region at Yarlung Zangbo River. It uses the ArcGIS platform. The research teams calculate the ASTER-DEM30m area-elevation integral value of the Big Bend Region at the lower Yarlung Zangbo River. The Hypsometry Index is a method based on the digital elevation model to obtain the characteristics of river evolution and the corresponding response index of tectonic activity. It examines the uplift difference in the study area in combination with the basic data of structure, lithology, climate, Quaternary depositsand rivers. The results show that the uplift area with HI>0.43 is mainly located outside the Big Bend suture zone and its distribution is well coupled with the Ⅲ-grade planation plane in each block. While the distribution range of Lhasa fault uplift area with HI>0.60 is the largest, and the distribution area of the Gyalha Bair fault uplift area is the smallest, which is only distributed in a small range of the Big Bend Region. The eroded cutting area with HI < 0.43 is located at the Ⅰ and Ⅱ grade valley shoulders of the river and the mature area of rivers. The Linzhi-Paizhen section with HI < 0.35 mainly manifests as erosion and down cut. It is concluded that the tectonic compressive action still exists in the study area, and the influence of climate, rivers and fault zone density are generated under the tectonic setting. The above factors would gradually inhibit the tectonic uplift with the passage of time, and the promotion effect of erosion is different in different regions. When the tectonic effect plays a major role, fault block is dominated by uplift with HI>0.43. The influence of climatic action led to the uplift stagnation for Gyalha Bair and Namjagbarwa Mountains, with HI < 0.43. The Linzhi block with HI < 0.35 indicates that the intensity of erosion will increase under the influence of climate, rivers and fault zone density. So the area mainly manifests as erosion and down cut, with no sign of uplift. Therefore, under the combined influence of tectonics, climate, river development and fault zone density, the uplift function is gradually weakened from the outside to the inside of the lower reaches of the Yarlung Zangbo River Basin, and the differences in the local area are determined by the difference in the role of the influencing factors.
2019, 27(4): 842-852.
Rock avalanches is generally rapid downslope flowage of rock fragments composed of solid particles and some pore fluid. During rock avalanche slide, particle grading occurs, and certain sedimentation characteristics are exhibited in the deposit. For the study of kinematic sieving process in particle mass movement, the chute experiments have been conducted, and the sequence of particles with different size in vertical section and slide direction section are mainly studied. Then, based on the description of the vertical sorting and horizontal sorting, the grain-size distribution of the deposit zones is analyzed with sieve analysis, which presents larger grains prevail in the upper part of the deposit. The content of large particle exhibits double peak morphology of distribution in the slide direction section. The two distribution characteristics are also founded in Xinmocun rockavalanche and Pusacun rockavalanche, which are macroscopic reflection of the interaction of rock fragment during the particle flows and are important geological evidence for the study of rock avalanche kinematics. Finally, according to lots of chute experiments and case studies, the conclusion is proposed that:the dispersive pressure and kinematic sieving during the movement are main reasons for the formation of the vertical inverse grading and the longitudinal double peak morphology in the rock avalanche deposit. The kinematic sieving process energized by undulated sliding surface, and the momentum between particles.
Rock avalanches is generally rapid downslope flowage of rock fragments composed of solid particles and some pore fluid. During rock avalanche slide, particle grading occurs, and certain sedimentation characteristics are exhibited in the deposit. For the study of kinematic sieving process in particle mass movement, the chute experiments have been conducted, and the sequence of particles with different size in vertical section and slide direction section are mainly studied. Then, based on the description of the vertical sorting and horizontal sorting, the grain-size distribution of the deposit zones is analyzed with sieve analysis, which presents larger grains prevail in the upper part of the deposit. The content of large particle exhibits double peak morphology of distribution in the slide direction section. The two distribution characteristics are also founded in Xinmocun rockavalanche and Pusacun rockavalanche, which are macroscopic reflection of the interaction of rock fragment during the particle flows and are important geological evidence for the study of rock avalanche kinematics. Finally, according to lots of chute experiments and case studies, the conclusion is proposed that:the dispersive pressure and kinematic sieving during the movement are main reasons for the formation of the vertical inverse grading and the longitudinal double peak morphology in the rock avalanche deposit. The kinematic sieving process energized by undulated sliding surface, and the momentum between particles.
2019, 27(4): 853-861.
There are two main factors that influence the accuracy of landslide displacement prediction. One is the reliability of the prediction model and the other is the quality of field monitoring data. Currently, conventional landslide monitoring technology and evaluation methods have many limitations and shortcomings. In this paper, we propose a new evaluation methodology of the combination of fiber-optic monitoring technology, monitoring data and PSO-SVM prediction model. We use it to predict the deep displacement of Majiagou No. 1 landslide in the Three Gorges Reservoir. Firstly, by analyzing 320 fiber-optics monitoring data of landslide deep displacement, we decompose accumulative displacement into trend and fluctuant components based on the time series method. Then, the trend displacement is predicted with the fitting method. The fluctuant displacement is predicted with the PSO-SVM model. Lastly, the prediction of cumulative displacement is computed with the predicted periodic and fluctuant displacement values. Research results show that the root mean square error is 0.51mm and an average absolute percentage error is 0.37mm, which demonstrate this model has a preferable prediction effect. The predicted total displacement show great consistency with the measured total displacement, with the RSME of 0.54mm and the correlation coefficient of 0.98, respectively. This method can be used to make short-term predictions of landslide deep displacement.
There are two main factors that influence the accuracy of landslide displacement prediction. One is the reliability of the prediction model and the other is the quality of field monitoring data. Currently, conventional landslide monitoring technology and evaluation methods have many limitations and shortcomings. In this paper, we propose a new evaluation methodology of the combination of fiber-optic monitoring technology, monitoring data and PSO-SVM prediction model. We use it to predict the deep displacement of Majiagou No. 1 landslide in the Three Gorges Reservoir. Firstly, by analyzing 320 fiber-optics monitoring data of landslide deep displacement, we decompose accumulative displacement into trend and fluctuant components based on the time series method. Then, the trend displacement is predicted with the fitting method. The fluctuant displacement is predicted with the PSO-SVM model. Lastly, the prediction of cumulative displacement is computed with the predicted periodic and fluctuant displacement values. Research results show that the root mean square error is 0.51mm and an average absolute percentage error is 0.37mm, which demonstrate this model has a preferable prediction effect. The predicted total displacement show great consistency with the measured total displacement, with the RSME of 0.54mm and the correlation coefficient of 0.98, respectively. This method can be used to make short-term predictions of landslide deep displacement.
2019, 27(4): 862-872.
Prediction model in landslide displacement is the key part for building landslide early warning system. The reliability and accuracy of prediction model mainly depend on the main controlling factors and the basic theoretical model. Researchers have already made a great achievement on the displacement prediction models according to practical cases. However, insufficient understanding due to multi-factors influence on landslide movement still exist, because of the strong individual feature and complex tendency forecasting in landslide movement. Kualiangzi landslide, a typical type of translational landslides in Southwest of China, is selected in this paper to make a deep research based on previous data collection. Grey relational analysis and correlation coefficient analysis are used to ensure the main controlling factors influencing landslide movement. A model combining GM(1, 1) grey model and the wavelet neural network optimization(WNN)model optimized by the improved adaptive genetic algorithm(IAGA) is presented. Through mining and analyzing the monitoring data of Kualiangzi landslide for five years, the results show that landslide movement is influenced by the accumulative rainfall, osmotic pressure, groundwater table and soil moisture content. The predicted results are in good agreement with the real-time monitoring data. After comparative analysis, the results show that in terms of the stability and accuracy, this model are better than the models of traditional BP neural network, wavelet neural network and GA-WNN. The new model has a good application prospects in the field of landslide early warning and forecasting.
Prediction model in landslide displacement is the key part for building landslide early warning system. The reliability and accuracy of prediction model mainly depend on the main controlling factors and the basic theoretical model. Researchers have already made a great achievement on the displacement prediction models according to practical cases. However, insufficient understanding due to multi-factors influence on landslide movement still exist, because of the strong individual feature and complex tendency forecasting in landslide movement. Kualiangzi landslide, a typical type of translational landslides in Southwest of China, is selected in this paper to make a deep research based on previous data collection. Grey relational analysis and correlation coefficient analysis are used to ensure the main controlling factors influencing landslide movement. A model combining GM(1, 1) grey model and the wavelet neural network optimization(WNN)model optimized by the improved adaptive genetic algorithm(IAGA) is presented. Through mining and analyzing the monitoring data of Kualiangzi landslide for five years, the results show that landslide movement is influenced by the accumulative rainfall, osmotic pressure, groundwater table and soil moisture content. The predicted results are in good agreement with the real-time monitoring data. After comparative analysis, the results show that in terms of the stability and accuracy, this model are better than the models of traditional BP neural network, wavelet neural network and GA-WNN. The new model has a good application prospects in the field of landslide early warning and forecasting.
2019, 27(4): 873-879.
The structure and distribution simulation of strata is an urgent demand in geological informatization as well as engineering. Current study methods are mostly based on borehole data,drawing stratigraphic section or building three-dimensional geological model through interpolation. Interpolation is an important factor in accuracy. However,the determination of interpolation method is subjective,lacking of scientific consideration and therefore difficult to apply to other distinct. Therefore,this study proposes a stratigraphic sequence simulation method based on machine learning. The method considers the borehole data as type and thickness sequence,and presents the stratigraphic sequence simulation model based on recurrent neural network and sequence to sequence learning. Comparing the simulation sequence to the actual borehole data,the result indicates that the machine learning-based model are capable of describing the stratigraphic sequence above bedrock using coordinate information. This study provides a new method for stratigraphy study.
The structure and distribution simulation of strata is an urgent demand in geological informatization as well as engineering. Current study methods are mostly based on borehole data,drawing stratigraphic section or building three-dimensional geological model through interpolation. Interpolation is an important factor in accuracy. However,the determination of interpolation method is subjective,lacking of scientific consideration and therefore difficult to apply to other distinct. Therefore,this study proposes a stratigraphic sequence simulation method based on machine learning. The method considers the borehole data as type and thickness sequence,and presents the stratigraphic sequence simulation model based on recurrent neural network and sequence to sequence learning. Comparing the simulation sequence to the actual borehole data,the result indicates that the machine learning-based model are capable of describing the stratigraphic sequence above bedrock using coordinate information. This study provides a new method for stratigraphy study.
2019, 27(4): 880-889.
A method of landslide displacement prediction based on time series analysis model is proposed. It combines artificial bee colony algorithm(ABC)with support vector regression machine(SVR). The existing problems of landslide displacement prediction methods are summarized. We select Baishuihe landslide in The Gorges Reservoir area as the research object. We study the influence of landslide displacement, rainfall, reservoir water level and other factors on the change of landslide displacement with time. Firstly, the landslide displacement is decomposed into a trend term and a periodic term by time series addition model and moving average method. We use the polynomial least square method to fit and predict the trend term of landslide displacement. Then we use artificial bee colony support vector machine model to train and predict the periodic term of landslide displacement. In this paper, seven factors affecting the displacement of periodic terms are selected for the analysis. We use the grey system correlation analysis method to calculate the correlation degree between each factor and the displacement of the same period term. The total displacement prediction value of landslide is the sum of trend and periodic displacement prediction values. Compared with BP neural network and PSO-SVR model, this method has higher accuracy in landslide displacement prediction, and has better application prospects in disaster prevention and mitigation.
A method of landslide displacement prediction based on time series analysis model is proposed. It combines artificial bee colony algorithm(ABC)with support vector regression machine(SVR). The existing problems of landslide displacement prediction methods are summarized. We select Baishuihe landslide in The Gorges Reservoir area as the research object. We study the influence of landslide displacement, rainfall, reservoir water level and other factors on the change of landslide displacement with time. Firstly, the landslide displacement is decomposed into a trend term and a periodic term by time series addition model and moving average method. We use the polynomial least square method to fit and predict the trend term of landslide displacement. Then we use artificial bee colony support vector machine model to train and predict the periodic term of landslide displacement. In this paper, seven factors affecting the displacement of periodic terms are selected for the analysis. We use the grey system correlation analysis method to calculate the correlation degree between each factor and the displacement of the same period term. The total displacement prediction value of landslide is the sum of trend and periodic displacement prediction values. Compared with BP neural network and PSO-SVR model, this method has higher accuracy in landslide displacement prediction, and has better application prospects in disaster prevention and mitigation.
2019, 27(4): 890-902.
Groundwater inflow is one of the widespread disasters in underground tunneling, which directly affects the construction progress, the stability of the cave and resident safety. A large number of studies in predicting the groundwater inflow have proposed various methods associated with different application conditions. However, in order to accurately predict the groundwater inflow into tunnels, it is crucial to select a reasonable method for the specific condition. In this study, the previous methods are classified into four different types including empirical formula, analytical formula, numerical and physical simulation methods. The empirical formula method originates from the compilation of numerous engineering cases, focusing on similar geological conditions. The analytical formula method based on the strict theoretical derivations provides a fast and simple way for the assessment of groundwater inflow into tunnels. The numerical simulation method can analyze the complicated hydrogeological conditions. The physical simulation method intuitively characterizes the inflow laws by experiments. The theoretical principles, merits and drawbacks of these methods are summarized in detail. Furthermore, some potential research topics are prospected for further improvement.
Groundwater inflow is one of the widespread disasters in underground tunneling, which directly affects the construction progress, the stability of the cave and resident safety. A large number of studies in predicting the groundwater inflow have proposed various methods associated with different application conditions. However, in order to accurately predict the groundwater inflow into tunnels, it is crucial to select a reasonable method for the specific condition. In this study, the previous methods are classified into four different types including empirical formula, analytical formula, numerical and physical simulation methods. The empirical formula method originates from the compilation of numerous engineering cases, focusing on similar geological conditions. The analytical formula method based on the strict theoretical derivations provides a fast and simple way for the assessment of groundwater inflow into tunnels. The numerical simulation method can analyze the complicated hydrogeological conditions. The physical simulation method intuitively characterizes the inflow laws by experiments. The theoretical principles, merits and drawbacks of these methods are summarized in detail. Furthermore, some potential research topics are prospected for further improvement.
2019, 27(4): 903-913.
Topography is the primary determinant factor of geological route selection. This paper takes Jinsha River Basin of Sichuan-Tibet Railway as the research object. The hypsometric integral, average elevation, relief, average slope and terrain curvature of each sub-catchment are compared and analyzed using geographic information system technology. The entropy weight method is used to evaluate the adaptability of each sub-catchment to geological route selection. So the macro-trend of the line and select the ideal channel can be determined. The results show that the evaluation has a good consistency with field investigations. The channel selection model based on terrain and geomorphological parameters can be applied to similar railway constructions in mountainous areas and have certain theoretical significance and engineering value.
Topography is the primary determinant factor of geological route selection. This paper takes Jinsha River Basin of Sichuan-Tibet Railway as the research object. The hypsometric integral, average elevation, relief, average slope and terrain curvature of each sub-catchment are compared and analyzed using geographic information system technology. The entropy weight method is used to evaluate the adaptability of each sub-catchment to geological route selection. So the macro-trend of the line and select the ideal channel can be determined. The results show that the evaluation has a good consistency with field investigations. The channel selection model based on terrain and geomorphological parameters can be applied to similar railway constructions in mountainous areas and have certain theoretical significance and engineering value.
2019, 27(4): 914-922.
This paper attempts to accurately evaluate the stability of debris slopes located in the eastern Tibet section of the G318 highway. It can provide a reference for the highway public sector to carry out maintenance, with a view to thoroughly solve the serious damage of debris slopes to this section. We investigated all the debris slopes along the section of the district 1277km in the past 3 years. According to the composition of the debris, the size of the particles and the characteristics of the movement, the basic characteristics and failure mode of all kinds of debris slopes are described. The correlation between the main factors and the slope stability is analyzed with the information entropy and FLAC numerical simulation. The stability evaluation model of the debris slope based on support vector machine is established using the analysis results of the influence factors. The results show that:(1)Debris slopes can be subdivided into 3 types of sliding sand slopes, rolling rock slopes and gravel slopes. The characteristics of the 3 types of debris slopes are as follows:The sand slipping is of small cale, but happens suddenly and often in groups; The rolling stone slope is mainly composed of spalling or partially slipping of alluvial and diluvial deposits, with a large number and great harm. The gravel slopes are sudden burst with large energy, high speed, a certain scale and great harm. (2)Information entropy theory is used to analyze the correlation degree of 10 factors on the stability of the debris slope. The effective factors in turn are rainfall snow melting, average slope, debris, average slope height, vegetation coverage, engineering construction, earthquake, weathering degree, ground shaking and river erosion. (3)Numerical simulation shows the main influencing factors. The slope safety coefficients are compared after normalization with its curve slope relationship:rainfall snow melting(0.8) > average slope(0.66) > average slope height(0.52) > vegetation coverage(0.46) > construction(0.43). The greater the gradient of the curve, the greater the correlation between the factor and the stability of the debris slope. The conclusion is consistent with the field investigation and analysis. (4)Combining the information entropy and the results of numerical simulation using FLAC analysis, six of the main factors are selected for the stability evaluation model of the debris slope. The model accuracy rate is 89.29% and 93.75%respectively through the model training, back estimation and test, which can be used for the stability evaluation of debris slope to give some advises and reference for maintenance.
This paper attempts to accurately evaluate the stability of debris slopes located in the eastern Tibet section of the G318 highway. It can provide a reference for the highway public sector to carry out maintenance, with a view to thoroughly solve the serious damage of debris slopes to this section. We investigated all the debris slopes along the section of the district 1277km in the past 3 years. According to the composition of the debris, the size of the particles and the characteristics of the movement, the basic characteristics and failure mode of all kinds of debris slopes are described. The correlation between the main factors and the slope stability is analyzed with the information entropy and FLAC numerical simulation. The stability evaluation model of the debris slope based on support vector machine is established using the analysis results of the influence factors. The results show that:(1)Debris slopes can be subdivided into 3 types of sliding sand slopes, rolling rock slopes and gravel slopes. The characteristics of the 3 types of debris slopes are as follows:The sand slipping is of small cale, but happens suddenly and often in groups; The rolling stone slope is mainly composed of spalling or partially slipping of alluvial and diluvial deposits, with a large number and great harm. The gravel slopes are sudden burst with large energy, high speed, a certain scale and great harm. (2)Information entropy theory is used to analyze the correlation degree of 10 factors on the stability of the debris slope. The effective factors in turn are rainfall snow melting, average slope, debris, average slope height, vegetation coverage, engineering construction, earthquake, weathering degree, ground shaking and river erosion. (3)Numerical simulation shows the main influencing factors. The slope safety coefficients are compared after normalization with its curve slope relationship:rainfall snow melting(0.8) > average slope(0.66) > average slope height(0.52) > vegetation coverage(0.46) > construction(0.43). The greater the gradient of the curve, the greater the correlation between the factor and the stability of the debris slope. The conclusion is consistent with the field investigation and analysis. (4)Combining the information entropy and the results of numerical simulation using FLAC analysis, six of the main factors are selected for the stability evaluation model of the debris slope. The model accuracy rate is 89.29% and 93.75%respectively through the model training, back estimation and test, which can be used for the stability evaluation of debris slope to give some advises and reference for maintenance.
2019, 27(4): 923-932.
This paper aims to calculate ultimate bearing capacity of bridge double-piles foundation in karst areas and combines the theorem of the limit analysis with finite element method. The computation procedure is provided on the basis of MATLAB. The modified Hoek-Brown criterion is employed to describe the characteristic of rock mass. The method of hyperbolic approximation is used in the process of optimization computation to solve the problem that singular point can not be differentiated. Based on the numerical results, the effects of different parameters on the bearing capacity factor Nσ are evaluated. The results reveal the follows. (1)The value of Nσ increases with increasing the subcharge over rock mass, with an increase in the rock socketed depth, and the rate of increase in Nσ is insensitive. (2)The value of Nσ decreases with increasing the radius of the cave, and first decreases, then increases with increasing the horizontal distance between piles and caves. (3)The value of Nσ increases non-linear with increasing the value of GSI, and the relationships between Nσ and mi, and the vertical distance are approximately linear. (4)The rock unit weight has a neglible effect on Nσ, when the larger distance between piles and caves exist. (5)Three types failure pattern are provided, including general shear failue, punching failure controlled by the left pile, punching failure with bearing failure. At last, the method proposed in this paper is verified by comparing the results reported by the previous investigations.
This paper aims to calculate ultimate bearing capacity of bridge double-piles foundation in karst areas and combines the theorem of the limit analysis with finite element method. The computation procedure is provided on the basis of MATLAB. The modified Hoek-Brown criterion is employed to describe the characteristic of rock mass. The method of hyperbolic approximation is used in the process of optimization computation to solve the problem that singular point can not be differentiated. Based on the numerical results, the effects of different parameters on the bearing capacity factor Nσ are evaluated. The results reveal the follows. (1)The value of Nσ increases with increasing the subcharge over rock mass, with an increase in the rock socketed depth, and the rate of increase in Nσ is insensitive. (2)The value of Nσ decreases with increasing the radius of the cave, and first decreases, then increases with increasing the horizontal distance between piles and caves. (3)The value of Nσ increases non-linear with increasing the value of GSI, and the relationships between Nσ and mi, and the vertical distance are approximately linear. (4)The rock unit weight has a neglible effect on Nσ, when the larger distance between piles and caves exist. (5)Three types failure pattern are provided, including general shear failue, punching failure controlled by the left pile, punching failure with bearing failure. At last, the method proposed in this paper is verified by comparing the results reported by the previous investigations.
微信 | 公众平台 
