Online Submission
Manuscript Tracking
Peer Review
Editor Work2020 Vol. 28, No. S1
Previous Issue
2020, 28(S1): 1-8.
Abstract
4294KB
This paper is based on the finite element platform Opensees. It established a one-dimensional shear beam soil column model with variable permeability coefficient and the accuracy of the model was verified by a centrifuge test results. The target is to explore the effect of seismic load type and relative density of sand on liquefaction deformation of saturated sand. Therefore, We selected the El-Centro seismic wave and Northridge seismic wave as inputting load. The simulated vertical displacement and excess pore pressure ratio of soil column under impact and vibration seismic wave were compared and analyzed when the relative density of sand was different. The results show that the vertical displacement under the vibration seismic wave is obviously larger than impact type; The increase of relative density can effectively reduce the vertical settlement of soil, and the effect is more obvious under the action of vibration seismic wave than that of impact seismic wave; The maximum pore pressure ratio of shock type seismic wave is larger than that of vibration type seismic wave, but the duration of high pore pressure is shorter and the dissipation process of pore pressure is faster; Loose sand is easier to achieve liquefaction conditions.
This paper is based on the finite element platform Opensees. It established a one-dimensional shear beam soil column model with variable permeability coefficient and the accuracy of the model was verified by a centrifuge test results. The target is to explore the effect of seismic load type and relative density of sand on liquefaction deformation of saturated sand. Therefore, We selected the El-Centro seismic wave and Northridge seismic wave as inputting load. The simulated vertical displacement and excess pore pressure ratio of soil column under impact and vibration seismic wave were compared and analyzed when the relative density of sand was different. The results show that the vertical displacement under the vibration seismic wave is obviously larger than impact type; The increase of relative density can effectively reduce the vertical settlement of soil, and the effect is more obvious under the action of vibration seismic wave than that of impact seismic wave; The maximum pore pressure ratio of shock type seismic wave is larger than that of vibration type seismic wave, but the duration of high pore pressure is shorter and the dissipation process of pore pressure is faster; Loose sand is easier to achieve liquefaction conditions.
2020, 28(S1): 9-18.
The compressibility of the crack is the key factor to control permeability. Crack opening is changed by the compression, with the opening becomes smaller and the permeability is lower. Due to the long period of shale gas production, the creep characteristics of the reservoir under in-situ stress must be considered. Permeability of the cracks is related to its deformation. Based on the single-fracture cubic law and the Bandis curve of fracture deformation under normal effective stress, the fluid-solid coupling model of single fracture is derived. The paper takes the function of normal stiffness as the research core, considers the interaction of the complex environment in deep formation. Nonlinear viscoelastic-plastic model is developed to describe the shale fractures creep. It demonstrates the permeability equation with time-dependent. The assumptions are that the rock matrix is impermeable and linear elastic, and that fluid flows only in fractures. According to the flow conservation at the nodes of the fractures network, a method to calculate the permeability of the complex network is established. As an example, the stress-time related permeability model of the branch hydraulic fractured rocks is deduced. Numerical simulation method for analyzing the seepage process of the branch-shaped hydraulic fracture network is put forward. The results show that the fractures are closed unevenly under creep condition and normal closures of fractures are time-dependent. The permeability of the fractures decreases with the increasing of time, and the velocity decreases sharply in the initial stage. With the increasing of the aperture and the trace length, the permeability increases.
The compressibility of the crack is the key factor to control permeability. Crack opening is changed by the compression, with the opening becomes smaller and the permeability is lower. Due to the long period of shale gas production, the creep characteristics of the reservoir under in-situ stress must be considered. Permeability of the cracks is related to its deformation. Based on the single-fracture cubic law and the Bandis curve of fracture deformation under normal effective stress, the fluid-solid coupling model of single fracture is derived. The paper takes the function of normal stiffness as the research core, considers the interaction of the complex environment in deep formation. Nonlinear viscoelastic-plastic model is developed to describe the shale fractures creep. It demonstrates the permeability equation with time-dependent. The assumptions are that the rock matrix is impermeable and linear elastic, and that fluid flows only in fractures. According to the flow conservation at the nodes of the fractures network, a method to calculate the permeability of the complex network is established. As an example, the stress-time related permeability model of the branch hydraulic fractured rocks is deduced. Numerical simulation method for analyzing the seepage process of the branch-shaped hydraulic fracture network is put forward. The results show that the fractures are closed unevenly under creep condition and normal closures of fractures are time-dependent. The permeability of the fractures decreases with the increasing of time, and the velocity decreases sharply in the initial stage. With the increasing of the aperture and the trace length, the permeability increases.
2020, 28(S1): 19-24.
The influence factors of liquefaction resistance of special sand(silt sand, clayey sand and silt sand) in Anqing area were studied by dynamic triaxial test and SEM. The effects of particle size and gradation, particle content and microstructure on sand liquefaction were studied. Research shows:the larger the skeleton particles, the stronger the resistance to liquefaction; the more uniform the particles in the sand, that is,the better the gradation of the soil, the stronger the sand's resistance to liquefaction; with the increase of fine particle mass content, the anti-liquefaction capacity of sand decreases first and then increases, and the corresponding fine particle content content of different types of sands is the weakest. This is mainly due to the different content of fine particles. When the content of fine particles is small, it mainly plays the role of lubrication, which is unfavorable to the liquefaction resistance of sand.
The influence factors of liquefaction resistance of special sand(silt sand, clayey sand and silt sand) in Anqing area were studied by dynamic triaxial test and SEM. The effects of particle size and gradation, particle content and microstructure on sand liquefaction were studied. Research shows:the larger the skeleton particles, the stronger the resistance to liquefaction; the more uniform the particles in the sand, that is,the better the gradation of the soil, the stronger the sand's resistance to liquefaction; with the increase of fine particle mass content, the anti-liquefaction capacity of sand decreases first and then increases, and the corresponding fine particle content content of different types of sands is the weakest. This is mainly due to the different content of fine particles. When the content of fine particles is small, it mainly plays the role of lubrication, which is unfavorable to the liquefaction resistance of sand.
2020, 28(S1): 25-32.
The distribution of groundwater has a significant impact on the stability and treatment of slopes(landslides), and there are many influencing factors. At present, there are no analytical formula for the steady state phreatic surfaces of homogeneous soil overlying irregular impervious geological interface, especially knowing that the slope(landslide) body has a known water level, accurately determining the infiltration line of the slope body between the known water levels plays an important role in evaluating the stability of the slope(landslide).Therefore, It is necessary to study the steady state phreatic surfaces of homogeneous soil overlying irregular impervious geological interface. Based on the simplification of free surface flow, this paper deduces the expression of groundwater single-width aquifer flow of homogeneous soil on the bed with a certain slope(impermeable). According to the bed inclination angle, the expression of homogeneous aquifer flow(Boussinesq equation) is divided into two kinds of expressions(downstream slope and reverse slope). According to two Boussinesq equations and the principle of fluid continuity, the steady seepage analytical formula of phreatic surfaces and the flow of homogeneous soil overlying irregular impervious geological interface are obtained. By comparing with the results of numerical simulation(Autobank finite element program),it can be seen that the analytical solution in this paper is basically consistent with the phreatic surfaces and the flow rate of finite element numerical simulation(Autobank finite element program). Due to the use of the Dupuit approximation, there is a certain error between the analytical solution and the numerical solution. The error along the slope is greater than that of the reverse slope, and the larger error of the slope is larger than that of the smaller slope. Fortunately, the error caused by the approximation is very small. Generally speaking, the analytical method of the steady-state phreatic surfaces is reliable, stable and logical.
The distribution of groundwater has a significant impact on the stability and treatment of slopes(landslides), and there are many influencing factors. At present, there are no analytical formula for the steady state phreatic surfaces of homogeneous soil overlying irregular impervious geological interface, especially knowing that the slope(landslide) body has a known water level, accurately determining the infiltration line of the slope body between the known water levels plays an important role in evaluating the stability of the slope(landslide).Therefore, It is necessary to study the steady state phreatic surfaces of homogeneous soil overlying irregular impervious geological interface. Based on the simplification of free surface flow, this paper deduces the expression of groundwater single-width aquifer flow of homogeneous soil on the bed with a certain slope(impermeable). According to the bed inclination angle, the expression of homogeneous aquifer flow(Boussinesq equation) is divided into two kinds of expressions(downstream slope and reverse slope). According to two Boussinesq equations and the principle of fluid continuity, the steady seepage analytical formula of phreatic surfaces and the flow of homogeneous soil overlying irregular impervious geological interface are obtained. By comparing with the results of numerical simulation(Autobank finite element program),it can be seen that the analytical solution in this paper is basically consistent with the phreatic surfaces and the flow rate of finite element numerical simulation(Autobank finite element program). Due to the use of the Dupuit approximation, there is a certain error between the analytical solution and the numerical solution. The error along the slope is greater than that of the reverse slope, and the larger error of the slope is larger than that of the smaller slope. Fortunately, the error caused by the approximation is very small. Generally speaking, the analytical method of the steady-state phreatic surfaces is reliable, stable and logical.
2020, 28(S1): 33-38.
In order to effectively solve the problem of resource utilization of environmental dredging sediment, we took the environmental dredging sediment of a lake in Wuhan as the research object. The main physical and chemical properties of the dredging sediment were analyzed by field sampling test. Three kinds of amendments for planting soil were prepared as improvement materials, using desulfurized gypsum and organic fertilizer. The influence of leaching amount on physical and chemical properties of improved sediment was analyzed by leaching test. The results of leaching test showed that the physical and chemical indexes of the dredging sediment with suitable modifier were significantly improved, and the contents of organic matter, available phosphorus, available potassium and other nutrient elements were significantly increased, which met the relevant technical requirements of green planting soil. The effects of different amendments on the growth of tested plants were studied by pot test. The results of pot test showed that the tested plants grew well in the improved sediment, and the improved material with the highest content of organic matter had the best improvement effect, which verified the feasibility of improvement of environmental dredging sediment for planting soil.
In order to effectively solve the problem of resource utilization of environmental dredging sediment, we took the environmental dredging sediment of a lake in Wuhan as the research object. The main physical and chemical properties of the dredging sediment were analyzed by field sampling test. Three kinds of amendments for planting soil were prepared as improvement materials, using desulfurized gypsum and organic fertilizer. The influence of leaching amount on physical and chemical properties of improved sediment was analyzed by leaching test. The results of leaching test showed that the physical and chemical indexes of the dredging sediment with suitable modifier were significantly improved, and the contents of organic matter, available phosphorus, available potassium and other nutrient elements were significantly increased, which met the relevant technical requirements of green planting soil. The effects of different amendments on the growth of tested plants were studied by pot test. The results of pot test showed that the tested plants grew well in the improved sediment, and the improved material with the highest content of organic matter had the best improvement effect, which verified the feasibility of improvement of environmental dredging sediment for planting soil.
2020, 28(S1): 39-44.
The preliminary accelerated mortar-bar test showed that the aggregate has potential alkali activity hazards in intake complex of CCS hydropower station in Ecuador. Used volcanic ash and volcanic ash+silica fume as admixture to inhibit the alkali activity of aggregate. The results show that adding volcanic ash or volcanic ash+silica fume has a significant inhibition effect on the alkali reaction, and with the amount increasing, the expansion rate of the mortar-bar specimen has a significant decrease trend; while the sample expansion ratio of volcanic ash+silica fume is smaller than volcanic ash, so using volcanic ash+silica fume as admixture has better inhibition effect on alkali activity. This research enabled the project to use local materials as concrete aggregates in the construction process, saved engineering investment and shortened construction period; at the same time, it provided valuable experience for overseas engineering survey design and construction.
The preliminary accelerated mortar-bar test showed that the aggregate has potential alkali activity hazards in intake complex of CCS hydropower station in Ecuador. Used volcanic ash and volcanic ash+silica fume as admixture to inhibit the alkali activity of aggregate. The results show that adding volcanic ash or volcanic ash+silica fume has a significant inhibition effect on the alkali reaction, and with the amount increasing, the expansion rate of the mortar-bar specimen has a significant decrease trend; while the sample expansion ratio of volcanic ash+silica fume is smaller than volcanic ash, so using volcanic ash+silica fume as admixture has better inhibition effect on alkali activity. This research enabled the project to use local materials as concrete aggregates in the construction process, saved engineering investment and shortened construction period; at the same time, it provided valuable experience for overseas engineering survey design and construction.
2020, 28(S1): 45-50.
According to the summary of the special properties belonging to Xigeda strata in Panzhihua area and the problem about its mechanical parameter values, this paper put forward the reasonable range of different mechanical parameter values of this strata, with the influence of mechanical parameter values on projects. Taking a deep foundation pit in Panzhihua as an example, we conducted the in-situ shear test and the basic mechanical test of Xigeda strata, and found out that the parameters varied greatly. The reasonable parameter values can significantly reduce the limit time and the cost. Additionally, we calculated the change of reinforcement caused by the change of shear strength parameters by LIZHENG deep foundation pit software, and conducted the sensitivity analysis on the change of safety factor caused by change of mechanical parameters. Based on that, we concluded the influence of the change of cohesion and internal friction angle on projects, then confirmed the geotechnical parameter values of Xigeda strata taken in previous projects was too conservative, and put forward the reasonable scope of parameter values of Xigeda strata, in order to save the cost and the limit time of projects, so as to provide a certain reference for similar projects.
According to the summary of the special properties belonging to Xigeda strata in Panzhihua area and the problem about its mechanical parameter values, this paper put forward the reasonable range of different mechanical parameter values of this strata, with the influence of mechanical parameter values on projects. Taking a deep foundation pit in Panzhihua as an example, we conducted the in-situ shear test and the basic mechanical test of Xigeda strata, and found out that the parameters varied greatly. The reasonable parameter values can significantly reduce the limit time and the cost. Additionally, we calculated the change of reinforcement caused by the change of shear strength parameters by LIZHENG deep foundation pit software, and conducted the sensitivity analysis on the change of safety factor caused by change of mechanical parameters. Based on that, we concluded the influence of the change of cohesion and internal friction angle on projects, then confirmed the geotechnical parameter values of Xigeda strata taken in previous projects was too conservative, and put forward the reasonable scope of parameter values of Xigeda strata, in order to save the cost and the limit time of projects, so as to provide a certain reference for similar projects.
2020, 28(S1): 51-55.
Traditional soil stabilization method causes serious pollution problem which hinder the development of environment-friendly society in China. This research uses environment-friendly material biopolymer as an additive to explore its effect on soil unconfined compressive strength and shear strength after different curing time. Results indicate:with the increase of curing time, the unconfined compressive strength and shear strength of sand treated with xanthan gum biopolymer improved significantly; the addition of xanthan gum increased the soil cohesion to increase soil strength; it can be found by scanning electron microscope observation images that xanthan gum biopolymer aggregated around sand particles, connecting individual soil particles together, and forming larger aggregates from discrete particles, which plays a role in changing soil structure. The environment-friendly green organic material xanthan gum biopolymer can significantly improve the strength of soil, showing its potential in geotechnical engineering applications.
Traditional soil stabilization method causes serious pollution problem which hinder the development of environment-friendly society in China. This research uses environment-friendly material biopolymer as an additive to explore its effect on soil unconfined compressive strength and shear strength after different curing time. Results indicate:with the increase of curing time, the unconfined compressive strength and shear strength of sand treated with xanthan gum biopolymer improved significantly; the addition of xanthan gum increased the soil cohesion to increase soil strength; it can be found by scanning electron microscope observation images that xanthan gum biopolymer aggregated around sand particles, connecting individual soil particles together, and forming larger aggregates from discrete particles, which plays a role in changing soil structure. The environment-friendly green organic material xanthan gum biopolymer can significantly improve the strength of soil, showing its potential in geotechnical engineering applications.
2020, 28(S1): 56-63.
Granular materials are widely used in both industrial and engineering fields, where the quality of products and projects are highly dependent on the packing density and homogeneity of the granular materials. In this paper, previous studies conducted by domestic and overseas scholars on the packing density and homogeneity of granular materials are carefully reviewed and summarized. Results in the literature indicate that the packing density are related to the particle properties(particle size, shape and surface roughness, etc.),container properties(container size, shape and surface roughness, etc.),packing techniques(drop height, vibration condition, filling intensity and sequence, etc.),particle size ratio and distribution. The packing inhomogeneity(degree of segregation) increases with the increase of particle size difference, density difference and vibration acceleration, but decreases with the increase of size range, size class amount and vibration frequency, with indistinct susceptibility to particle shape. As for bentonite pellets used in high-level radioactive waste repository, it is worth devoting to improve the scientific and efficient in-situ packing techniques.
Granular materials are widely used in both industrial and engineering fields, where the quality of products and projects are highly dependent on the packing density and homogeneity of the granular materials. In this paper, previous studies conducted by domestic and overseas scholars on the packing density and homogeneity of granular materials are carefully reviewed and summarized. Results in the literature indicate that the packing density are related to the particle properties(particle size, shape and surface roughness, etc.),container properties(container size, shape and surface roughness, etc.),packing techniques(drop height, vibration condition, filling intensity and sequence, etc.),particle size ratio and distribution. The packing inhomogeneity(degree of segregation) increases with the increase of particle size difference, density difference and vibration acceleration, but decreases with the increase of size range, size class amount and vibration frequency, with indistinct susceptibility to particle shape. As for bentonite pellets used in high-level radioactive waste repository, it is worth devoting to improve the scientific and efficient in-situ packing techniques.
2020, 28(S1): 64-69.
With the large-scale development of water conservancy projects in my country, marine silt has a certain impact on the offshore environment and the construction and maintenance of engineering facilities, and affects ports and waterway transportation. Therefore, a large amount of marine silt is urgently awaiting treatment and utilization. This paper explores the relationship between soil pH,soil salinity and leaching amount through leaching tests, and using admixtures composed of straw, sand, biochar, organic fertilizer, desulfurized gypsum and other materials to modify marine sludge test. The results of the study showed that the soil pH value and soil salt content of the sample soil fell within the standard value after the intermittent 1000 mL leaching volume; the soil alkalinity did not decrease but slightly increased at the beginning of leaching; the salt content decreases with the increase of the number of leaching. During the intermediate stage(4 to 8 times) of leaching, due to the formation of seepage channels in the soil column, the efficiency of reducing the soil salt content decreases. The marine sludge was first leached and "washed with salt", and admixtures were added to modify the marine sludge. After modification, it was suitable for plant growth, which verified the feasibility of modified marine sludge for planting soil.
With the large-scale development of water conservancy projects in my country, marine silt has a certain impact on the offshore environment and the construction and maintenance of engineering facilities, and affects ports and waterway transportation. Therefore, a large amount of marine silt is urgently awaiting treatment and utilization. This paper explores the relationship between soil pH,soil salinity and leaching amount through leaching tests, and using admixtures composed of straw, sand, biochar, organic fertilizer, desulfurized gypsum and other materials to modify marine sludge test. The results of the study showed that the soil pH value and soil salt content of the sample soil fell within the standard value after the intermittent 1000 mL leaching volume; the soil alkalinity did not decrease but slightly increased at the beginning of leaching; the salt content decreases with the increase of the number of leaching. During the intermediate stage(4 to 8 times) of leaching, due to the formation of seepage channels in the soil column, the efficiency of reducing the soil salt content decreases. The marine sludge was first leached and "washed with salt", and admixtures were added to modify the marine sludge. After modification, it was suitable for plant growth, which verified the feasibility of modified marine sludge for planting soil.
2020, 28(S1): 70-76.
With the practice of island and reef reclamation projects in the Nansha waters, the research on the physical and mechanical properties of reef limestone has gradually become a research focus in the field of engineering geology. A reef limestone core was obtained from a borehole with a depth of 300 meters on an island and reef in Nansha, and passed the vertical and horizontal wave tests, uniaxial and triaxial compression tests, and reef limestone rheological tests. The following conclusions are obtained:the relationship between the shear wave velocity and the longitudinal wave velocity of the deep reef limestone rock sample is Vs=0.4447Vp+409.94; the reef limestone still has a large bearing capacity after being destroyed, and the reef limestone fractures in a broken strip shape, Breaks along the growth weak surface, the strength of the reef limestone is also very random due to the strength randomness of the cave and the weak surface; the stress threshold for the accelerated creep of the reef limestone is about 5-6 MPa, when the loading level reaches 5-6 MPa the process of accelerated creep occur. The test conclusions provide a basis for the construction of the South China Sea Reef Project, and also provide reference materials for the in-depth study of the engineering geomechanical properties of coral reefs.
With the practice of island and reef reclamation projects in the Nansha waters, the research on the physical and mechanical properties of reef limestone has gradually become a research focus in the field of engineering geology. A reef limestone core was obtained from a borehole with a depth of 300 meters on an island and reef in Nansha, and passed the vertical and horizontal wave tests, uniaxial and triaxial compression tests, and reef limestone rheological tests. The following conclusions are obtained:the relationship between the shear wave velocity and the longitudinal wave velocity of the deep reef limestone rock sample is Vs=0.4447Vp+409.94; the reef limestone still has a large bearing capacity after being destroyed, and the reef limestone fractures in a broken strip shape, Breaks along the growth weak surface, the strength of the reef limestone is also very random due to the strength randomness of the cave and the weak surface; the stress threshold for the accelerated creep of the reef limestone is about 5-6 MPa, when the loading level reaches 5-6 MPa the process of accelerated creep occur. The test conclusions provide a basis for the construction of the South China Sea Reef Project, and also provide reference materials for the in-depth study of the engineering geomechanical properties of coral reefs.
2020, 28(S1): 77-85.
Debris flow which has rapid character and strong destruction is a common natural disaster in the mountainous areas of China. The terrain of our country is high in the west and low in the east, and the terrain is complex and changeable. Chinese alpine and high-altitude mountainous areas are widely distributed. In addition, various types of debris flow disasters occurred frequently, especially in summer. Based on the analysis of a large number of alpine mountain debris flow researches, we summarize some key issues of these special research problems:the formation conditions and development rules of the debris flow in the alpine natural environment, the disaster chain effect, and the alpine mountain debris flow research methods and prevention measures. Among them, the problem of debris flow caused by glacier-lake breakout and debris flow blocking rivers has attracted wide attention. In addition, the Qinghai-Tibet Plateau has also become an important focus of the study of debris flow in the alpine mountain areas. The paper also combines the main research problems and environmental change trends in recent years, and puts forward development suggestions for the study of debris flow in the alpine mountain area in the future.
Debris flow which has rapid character and strong destruction is a common natural disaster in the mountainous areas of China. The terrain of our country is high in the west and low in the east, and the terrain is complex and changeable. Chinese alpine and high-altitude mountainous areas are widely distributed. In addition, various types of debris flow disasters occurred frequently, especially in summer. Based on the analysis of a large number of alpine mountain debris flow researches, we summarize some key issues of these special research problems:the formation conditions and development rules of the debris flow in the alpine natural environment, the disaster chain effect, and the alpine mountain debris flow research methods and prevention measures. Among them, the problem of debris flow caused by glacier-lake breakout and debris flow blocking rivers has attracted wide attention. In addition, the Qinghai-Tibet Plateau has also become an important focus of the study of debris flow in the alpine mountain areas. The paper also combines the main research problems and environmental change trends in recent years, and puts forward development suggestions for the study of debris flow in the alpine mountain area in the future.
2020, 28(S1): 86-95.
In the Changning shale gas development blocks in Sichuan, casing deformation occurred in more than 30% of horizontal wells during hydraulic fracturing, which in turn seriously restricted the efficient development of shale gas. Based on the principle of geomechanics, this paper analyzed the mechanical conditions of casing deformation caused by fracture zone sliding induced by fracturing in Changning shale gas area. Firstly, we used the logging and testing data of well Ning 201 to establish the in-situ stress model in Changning area. We used density logging to determine vertical stress, pressure build-up test to determine pore pressure, rock mechanics test to determine rock mechanical parameters, stress quadrilateral to determine the range of the horizontal minimum stress and the horizontal maximum stress, and used in-situ stress profile and focal mechanism solution to determine stress state. Secondly, based on the seismic and microseismic data, we identify the fracture zones of H19 platform, and counted the strike and dip characteristics of the fracture zones. Thirdly, based on the mechanical model of fault activation, we analyzed the activation of fracture zones of H19 platform. According to the location of fracture zones on Mohr circle and the order of activation, we divided the fracture zones into six groups. We analyzed the influence of pore pressure and stress mode on the activation of fracture zones, and pointed out the internal and external causes of fault slip induced by hydraulic fracturing in Changning block. Finally, we compared the characteristics of in-situ stress, fracture zone development and fracture zone activity in Changning and Fuling blocks. The results showed that:(1)The vertical stress in Changning area is 2.6 SG,the pore pressure is 2.0 SG,the horizontal minimum stress is 2.4~2.7 SG, and the horizontal maximum stress is 3.4G~3.7 SG, and Changning area is a strike-slip/reverse stress state. (2)The dips of fracture zones of H19 platform are in the range of 71°~90°. (3)The bottom-hole pressure required for the activation of all fracture zones of H19 platform is 3.0 SG. During hydraulic fracturing, the average value of bottom hole pressure is 2.8 SG, and the maximum value of bottom hole pressure is 3.1 SG,almost all fracture zones are activated. The difference between the shear stress and sliding resistance of fracture zone gets the minimum value in the strike-slip/reverse stress state, which is the internal cause that the fracture zones are relatively easy to be activated in Changning area. Hydraulic fracturing reduces the sliding resistance greatly, which is the external cause of fault slip induced by fracturing in Changning area. (4)The magnitude of three-dimensional stress in Fuling block is similar to that in Changning block, which is also a strike-slip/reverse stress state. But the fracture zone is not developed, or develop only some fractures with low dip angle. When hydraulic fracturing, the construction pressure is smaller. This is the main reason why the casing deformation in Fuling block is not as frequent as that in Changning block. This result states the geomechanical reasons of casing deformation in Changning area, which provides theoretical significance to solve the problem of casing deformation in Changning area.
In the Changning shale gas development blocks in Sichuan, casing deformation occurred in more than 30% of horizontal wells during hydraulic fracturing, which in turn seriously restricted the efficient development of shale gas. Based on the principle of geomechanics, this paper analyzed the mechanical conditions of casing deformation caused by fracture zone sliding induced by fracturing in Changning shale gas area. Firstly, we used the logging and testing data of well Ning 201 to establish the in-situ stress model in Changning area. We used density logging to determine vertical stress, pressure build-up test to determine pore pressure, rock mechanics test to determine rock mechanical parameters, stress quadrilateral to determine the range of the horizontal minimum stress and the horizontal maximum stress, and used in-situ stress profile and focal mechanism solution to determine stress state. Secondly, based on the seismic and microseismic data, we identify the fracture zones of H19 platform, and counted the strike and dip characteristics of the fracture zones. Thirdly, based on the mechanical model of fault activation, we analyzed the activation of fracture zones of H19 platform. According to the location of fracture zones on Mohr circle and the order of activation, we divided the fracture zones into six groups. We analyzed the influence of pore pressure and stress mode on the activation of fracture zones, and pointed out the internal and external causes of fault slip induced by hydraulic fracturing in Changning block. Finally, we compared the characteristics of in-situ stress, fracture zone development and fracture zone activity in Changning and Fuling blocks. The results showed that:(1)The vertical stress in Changning area is 2.6 SG,the pore pressure is 2.0 SG,the horizontal minimum stress is 2.4~2.7 SG, and the horizontal maximum stress is 3.4G~3.7 SG, and Changning area is a strike-slip/reverse stress state. (2)The dips of fracture zones of H19 platform are in the range of 71°~90°. (3)The bottom-hole pressure required for the activation of all fracture zones of H19 platform is 3.0 SG. During hydraulic fracturing, the average value of bottom hole pressure is 2.8 SG, and the maximum value of bottom hole pressure is 3.1 SG,almost all fracture zones are activated. The difference between the shear stress and sliding resistance of fracture zone gets the minimum value in the strike-slip/reverse stress state, which is the internal cause that the fracture zones are relatively easy to be activated in Changning area. Hydraulic fracturing reduces the sliding resistance greatly, which is the external cause of fault slip induced by fracturing in Changning area. (4)The magnitude of three-dimensional stress in Fuling block is similar to that in Changning block, which is also a strike-slip/reverse stress state. But the fracture zone is not developed, or develop only some fractures with low dip angle. When hydraulic fracturing, the construction pressure is smaller. This is the main reason why the casing deformation in Fuling block is not as frequent as that in Changning block. This result states the geomechanical reasons of casing deformation in Changning area, which provides theoretical significance to solve the problem of casing deformation in Changning area.
2020, 28(S1): 96-101.
For the bedrock-talus landslides, we used the Flac3D software to discuss the influence of the factors such as the embedded depth, sectional dimension and elastic modulus of the rear-piles on the thrust of the landslide behind the double-row piles, and finally give some practical suggestions for the design of the double-row piles. The analysis showed that the above three factors do not change the thrust distribution pattern on the fore and rear piles. The thrust behind the rear-piles decrease linearly with the increase of the embedded depth of the pile top while the thrust behind the fore-piles increase slightly. The sectional dimension of the rear-piles have great influence on the thrust of themselves but little influence on the thrust of the fore-piles. The elastic modulus of the rear-piles have little influence on the thrust of themselves and the fore-piles.
For the bedrock-talus landslides, we used the Flac3D software to discuss the influence of the factors such as the embedded depth, sectional dimension and elastic modulus of the rear-piles on the thrust of the landslide behind the double-row piles, and finally give some practical suggestions for the design of the double-row piles. The analysis showed that the above three factors do not change the thrust distribution pattern on the fore and rear piles. The thrust behind the rear-piles decrease linearly with the increase of the embedded depth of the pile top while the thrust behind the fore-piles increase slightly. The sectional dimension of the rear-piles have great influence on the thrust of themselves but little influence on the thrust of the fore-piles. The elastic modulus of the rear-piles have little influence on the thrust of themselves and the fore-piles.
MONITORING THE GROUND SUBSIDENCE OVER YAN'AN HIGH-FILLED REGION BY USING TIME SERIES INSAR TECHNIQUE
2020, 28(S1): 102-107.
In August 2018,the land creation project over Yan'an loess hilly-gully region has completed its geotechnical engineering. A total of 21.3 km2 of new land is created for urban construction. In order to monitor the ground subsidence due to land creation, 191 sentinel-1A images spanning from October 2014 to July 2019 are processed by small baseline subset InSAR(SBAS-InSAR)technique. The results showed that the subsidence area is mainly concentrated in the land filling area, where the maximum deformation rate reaches 10 cm·y-1. Based on the analysis and field investigation, the severe subsidence over the study area is caused by the consolidation of filling soil, and the filling thickness is the main factor controlling the subsidence rate. Our result demonstrates the reliability of SBAS-InSAR technique in ground subsidence monitoring over soil-filling region, and the obtained deformation results can provide sound management for local government.
In August 2018,the land creation project over Yan'an loess hilly-gully region has completed its geotechnical engineering. A total of 21.3 km2 of new land is created for urban construction. In order to monitor the ground subsidence due to land creation, 191 sentinel-1A images spanning from October 2014 to July 2019 are processed by small baseline subset InSAR(SBAS-InSAR)technique. The results showed that the subsidence area is mainly concentrated in the land filling area, where the maximum deformation rate reaches 10 cm·y-1. Based on the analysis and field investigation, the severe subsidence over the study area is caused by the consolidation of filling soil, and the filling thickness is the main factor controlling the subsidence rate. Our result demonstrates the reliability of SBAS-InSAR technique in ground subsidence monitoring over soil-filling region, and the obtained deformation results can provide sound management for local government.
2020, 28(S1): 108-115.
The engineering properties of carbonaceous mudstone may be significantly reduced when water is introduced, which can easily cause engineering problems. A landslide project was used in this paper to study the role of carbonaceous mudstone stratum in the formation of landslide. Data collection, on-site investigation and laboratory test were used to investigate the occurrence environment and basic characteristics of the landslide area. According to the causes of landslide development, we analyzed the formation mechanism, and concluded that the main factor for the formation of the landslide is poor hydrologic characteristics of carbonaceous mudstone stratum, and the main inducing factor is the continuous rainfall. On this basis, we analyzed the slope stability qualitatively and quantitatively, and concluded that the slope will continue to slide under the rainfall conditions and should be treated as soon as possible. According to the characteristics of the landslide, we introduced a comprehensive treatment scheme to contral this landslide, including anti-slide pile, crack fillup, intercepting ditch, retaining wall and displacement monitoring.
The engineering properties of carbonaceous mudstone may be significantly reduced when water is introduced, which can easily cause engineering problems. A landslide project was used in this paper to study the role of carbonaceous mudstone stratum in the formation of landslide. Data collection, on-site investigation and laboratory test were used to investigate the occurrence environment and basic characteristics of the landslide area. According to the causes of landslide development, we analyzed the formation mechanism, and concluded that the main factor for the formation of the landslide is poor hydrologic characteristics of carbonaceous mudstone stratum, and the main inducing factor is the continuous rainfall. On this basis, we analyzed the slope stability qualitatively and quantitatively, and concluded that the slope will continue to slide under the rainfall conditions and should be treated as soon as possible. According to the characteristics of the landslide, we introduced a comprehensive treatment scheme to contral this landslide, including anti-slide pile, crack fillup, intercepting ditch, retaining wall and displacement monitoring.
2020, 28(S1): 116-124.
Taking Yanzi River Basin as an example, this paper studied the effect of influencing factor classification results on landslide susceptibility mapping. According to the historical landslides data and geological environment characteristics, this paper used elevation, slope, aspect, plane curvature, profile curvature, stratigraphic lithology, distance to faults, distance to roads, normalized difference vegetation index, topographic wetness index and standardized precipitation index as the influencing factors. With different classification data, the classification results are different, which will produce different susceptibility maps. Therefore, for continuous factor classifica￣tion, this paper used the landslide points and all points in the study area as the classification data, respectively. The optimal classification number of continuous impact factors was determined by the inflection point method, and the corresponding classification interval was determined by Fisher-Jenks algorithm. Discrete impact factors were classified according to the actual situation. After influencing factor classification, support vector machine method was used to construct susceptibility mapping models, and the receiver operating characteristic(ROC)curve was used to evaluate the model performance. The results show the inflection point method and Fisher-Jenks algorithm can be well applied to the classification of continuous influencing factors. Compared with using all points in the entire study area to determine the factor classification criteria, the classification effect of using landslide points is better and the susceptibility map performs better. The areas under ROC curve corresponding to the two methods are 0.82(using all points in the study area as classification data) and 0.87(using all landslides points as classification data),respectively. The susceptibility maps of the Yanzi River Basin drawn in this paper can be used as a reference for disaster prevention and reduction.
Taking Yanzi River Basin as an example, this paper studied the effect of influencing factor classification results on landslide susceptibility mapping. According to the historical landslides data and geological environment characteristics, this paper used elevation, slope, aspect, plane curvature, profile curvature, stratigraphic lithology, distance to faults, distance to roads, normalized difference vegetation index, topographic wetness index and standardized precipitation index as the influencing factors. With different classification data, the classification results are different, which will produce different susceptibility maps. Therefore, for continuous factor classifica￣tion, this paper used the landslide points and all points in the study area as the classification data, respectively. The optimal classification number of continuous impact factors was determined by the inflection point method, and the corresponding classification interval was determined by Fisher-Jenks algorithm. Discrete impact factors were classified according to the actual situation. After influencing factor classification, support vector machine method was used to construct susceptibility mapping models, and the receiver operating characteristic(ROC)curve was used to evaluate the model performance. The results show the inflection point method and Fisher-Jenks algorithm can be well applied to the classification of continuous influencing factors. Compared with using all points in the entire study area to determine the factor classification criteria, the classification effect of using landslide points is better and the susceptibility map performs better. The areas under ROC curve corresponding to the two methods are 0.82(using all points in the study area as classification data) and 0.87(using all landslides points as classification data),respectively. The susceptibility maps of the Yanzi River Basin drawn in this paper can be used as a reference for disaster prevention and reduction.
2020, 28(S1): 125-132.
As a complex geology, there is no systematic research on the toppling classification until now. Based on the development characteristics investigation of typical topplings in western hydropower projects, the topplings are classified across two dimensions:single factor and multiple factors. Rock formation tendency, genesis, deformation position and deformation stage are used as single-factor classification basis. Lithology combination and rock mass structure, slope structure, deformation failure mode are taken as multi-factor classification basis. This paper also carries out a primary research on the deformation aging classification for a toppling. The analytical approach above provides a new orientation for the toppling field identification and systematic classification. Take the classification result on the basis of deformation failure mode as the base name for a toppling to define, while others as the additional modification for comprehensive name. This new naming method can reflect the feature information of a toppling more comprehensively.
As a complex geology, there is no systematic research on the toppling classification until now. Based on the development characteristics investigation of typical topplings in western hydropower projects, the topplings are classified across two dimensions:single factor and multiple factors. Rock formation tendency, genesis, deformation position and deformation stage are used as single-factor classification basis. Lithology combination and rock mass structure, slope structure, deformation failure mode are taken as multi-factor classification basis. This paper also carries out a primary research on the deformation aging classification for a toppling. The analytical approach above provides a new orientation for the toppling field identification and systematic classification. Take the classification result on the basis of deformation failure mode as the base name for a toppling to define, while others as the additional modification for comprehensive name. This new naming method can reflect the feature information of a toppling more comprehensively.
2020, 28(S1): 133-141.
Some geophysical prediction methods has different suitability when using in the double shield TBM(tunnel boring machine) affected by the double shield TBM equipment, construction technology. We analyze the suitability of different geophysical methods in double shield TBM advance geological prediction. Taking a double shield TBM tunnel with large embedded depth in southeast Tibet for example, we studied the application effect of EH4(high frequency magnetotelluric method),ISP(integrated seismic prediction),HSP(horizontal sound probing) and improved TRT(tunnel reflection tomography) in advance forecast of the tunnel. Used as a macro forecasting tool, EH4 can find large-scale unfavorable geological body. ISP and HSP are used as active and passive sources methods, could provides a more accurate prediction for the geological conditions. The two methods have good consistency. Improved TRT method solves the problem of seismic source hammer excitation and detector installation, has good precision for advance geological prediction. TRT also providing reflection interface and wave velocity curve, these data are beneficial to the analysis and judgment of geological engineers. Research shows that using EH4 as the macro forecasting method, ISP,HSP and TRT as the comprehensive prediction methods, has a good geological forecasting effect in southeast Tibet double shield TBM tunnel, prediction results provide a basis for engineering construction and technical treatment.
Some geophysical prediction methods has different suitability when using in the double shield TBM(tunnel boring machine) affected by the double shield TBM equipment, construction technology. We analyze the suitability of different geophysical methods in double shield TBM advance geological prediction. Taking a double shield TBM tunnel with large embedded depth in southeast Tibet for example, we studied the application effect of EH4(high frequency magnetotelluric method),ISP(integrated seismic prediction),HSP(horizontal sound probing) and improved TRT(tunnel reflection tomography) in advance forecast of the tunnel. Used as a macro forecasting tool, EH4 can find large-scale unfavorable geological body. ISP and HSP are used as active and passive sources methods, could provides a more accurate prediction for the geological conditions. The two methods have good consistency. Improved TRT method solves the problem of seismic source hammer excitation and detector installation, has good precision for advance geological prediction. TRT also providing reflection interface and wave velocity curve, these data are beneficial to the analysis and judgment of geological engineers. Research shows that using EH4 as the macro forecasting method, ISP,HSP and TRT as the comprehensive prediction methods, has a good geological forecasting effect in southeast Tibet double shield TBM tunnel, prediction results provide a basis for engineering construction and technical treatment.
2020, 28(S1): 142-148.
The control of the seepage field of the water-sealed cavern is important for the construction and operation of the cavern. Grouting treatment of the surrounding rock to derecrease the overall permeability coefficient of the rock around the cave is the most direct and effective engineering treatment. To deal with the excessive discharge water in some sections of the cavern of water-sealed oil cavern during the construction, a method for estimating the overall water inflow of the three-dimensional cavern using numerical calculation results of two-dimensional seepage analysis is proposed. Then, the method is adopted to analyze the amount of water in the cavern under different grouting treatment schemes under the conditions of artificial water curtain. Finally, the optimization measures of grouting at the bottom of the oil cavern are proposed. The results show that the scheme of 5 m-grouting to the whole floor is the best method from the perspective of the effect of reducing discharge water. The target permeability coefficient of the grouting can be adjusted according to the demand of the project for the control of seepage quantity. From the perspective of economy, the scheme of curtain grouting more than 12 m-depth on both sides of the bottom of the cavern can achieve good results. Considering the engineering cost and the effect of reducing the water inflow, the optimization scheme 3 can be selected, that is,the sections of the cavern with a permeability coefficient of 10 Lu have the treatment of the 5 m whole grouting, and the sections with the permeability coefficient of 1 Lu have only curtain grouting on both sides of the bottom, with the depth greater than 12 m. The conclusions of this study can provide a reference for similar projects.
The control of the seepage field of the water-sealed cavern is important for the construction and operation of the cavern. Grouting treatment of the surrounding rock to derecrease the overall permeability coefficient of the rock around the cave is the most direct and effective engineering treatment. To deal with the excessive discharge water in some sections of the cavern of water-sealed oil cavern during the construction, a method for estimating the overall water inflow of the three-dimensional cavern using numerical calculation results of two-dimensional seepage analysis is proposed. Then, the method is adopted to analyze the amount of water in the cavern under different grouting treatment schemes under the conditions of artificial water curtain. Finally, the optimization measures of grouting at the bottom of the oil cavern are proposed. The results show that the scheme of 5 m-grouting to the whole floor is the best method from the perspective of the effect of reducing discharge water. The target permeability coefficient of the grouting can be adjusted according to the demand of the project for the control of seepage quantity. From the perspective of economy, the scheme of curtain grouting more than 12 m-depth on both sides of the bottom of the cavern can achieve good results. Considering the engineering cost and the effect of reducing the water inflow, the optimization scheme 3 can be selected, that is,the sections of the cavern with a permeability coefficient of 10 Lu have the treatment of the 5 m whole grouting, and the sections with the permeability coefficient of 1 Lu have only curtain grouting on both sides of the bottom, with the depth greater than 12 m. The conclusions of this study can provide a reference for similar projects.
2020, 28(S1): 149-156.
BIM technology plays an important role in the tunnel engineering, and needs to be developed urgently. To explore the application, we established the BIM geological model of the Pingfengling Tunnel. This model based on Revit software and the secondary development plug-in. We compared the model section and the geological section, and studied the model degree of coincidence. We analyzed the design and construction process of the tunnel through the BIM model. The conclusions are as follows:(1)We use plug-in for stratigraphic modeling and civil3d for fault modeling, to facilitate and efficiently build the BIM geological models; (2)When drilling data is lacking, the geological survey data, like geologic sections, can be utilized to add "virtual drilling" to improve the accuracy and reliability of the model; (3)Most areas of the model have a higher degree of coincidence, and areas with large terrain undulations have a lower degree of coincidence; (4)According to analysis, we should excavate the open tunnels on the both sides of the tunnel and use composite lining in the middle section. The fault on the east side intersects the tunnel at a large angle, which needs to be reinforced and seepage-proof to prevent collapse and water gushing.
BIM technology plays an important role in the tunnel engineering, and needs to be developed urgently. To explore the application, we established the BIM geological model of the Pingfengling Tunnel. This model based on Revit software and the secondary development plug-in. We compared the model section and the geological section, and studied the model degree of coincidence. We analyzed the design and construction process of the tunnel through the BIM model. The conclusions are as follows:(1)We use plug-in for stratigraphic modeling and civil3d for fault modeling, to facilitate and efficiently build the BIM geological models; (2)When drilling data is lacking, the geological survey data, like geologic sections, can be utilized to add "virtual drilling" to improve the accuracy and reliability of the model; (3)Most areas of the model have a higher degree of coincidence, and areas with large terrain undulations have a lower degree of coincidence; (4)According to analysis, we should excavate the open tunnels on the both sides of the tunnel and use composite lining in the middle section. The fault on the east side intersects the tunnel at a large angle, which needs to be reinforced and seepage-proof to prevent collapse and water gushing.
2020, 28(S1): 157-168.
It is inevitably that the process of EPB shield tunneling disturbs the rock and soil around tunnel, which has intensively caused ground deformation and threatened the safety of surrounding structures/buildings. To study the law and control measures of ground deformation during the EPB shield tunneling process, this paper, based on the Longzhen Exit and Entry lines of Guangzhou Rail Transit Line 18,analyzed the shield construction parameters and ground deformation data caused by the construction of this small-spacing double-track tunnels. The conclusions are as follows:the ground deformation experiences five development stages with four deformation trends during the EPB shield tunneling process in small-spacing double-track tunnels; the ground deformation effect of the pre-built line on the later-built line is generally consistent with the effect of the pre-built line on itself, while the significant influenced area is between the two tunnel axes; the influence factors of ground deformation include shield construction parameters, engineering geological conditions and shield downtime, so optimizing the shield construction parameters, reinforcing the stratums and reducing shield downtime can effectively control the ground deformation. The research results have provided theoretical basis in area of shield construction control of Guangzhou Rail Transit Line 18 and other relevant small-spacing double-track tunneling projects.
It is inevitably that the process of EPB shield tunneling disturbs the rock and soil around tunnel, which has intensively caused ground deformation and threatened the safety of surrounding structures/buildings. To study the law and control measures of ground deformation during the EPB shield tunneling process, this paper, based on the Longzhen Exit and Entry lines of Guangzhou Rail Transit Line 18,analyzed the shield construction parameters and ground deformation data caused by the construction of this small-spacing double-track tunnels. The conclusions are as follows:the ground deformation experiences five development stages with four deformation trends during the EPB shield tunneling process in small-spacing double-track tunnels; the ground deformation effect of the pre-built line on the later-built line is generally consistent with the effect of the pre-built line on itself, while the significant influenced area is between the two tunnel axes; the influence factors of ground deformation include shield construction parameters, engineering geological conditions and shield downtime, so optimizing the shield construction parameters, reinforcing the stratums and reducing shield downtime can effectively control the ground deformation. The research results have provided theoretical basis in area of shield construction control of Guangzhou Rail Transit Line 18 and other relevant small-spacing double-track tunneling projects.
2020, 28(S1): 169-173.
In the work of geotechnical investigation in Astana, Kazakhstan, we found that the equipment specifications and test data recording methods of KDZ-001 heavy cone dynamic penetration detector adopted by the Almaty Geological Exploration Center are different from the requirements of relevant Chinese codes. The test results take the dynamic penetration resistance qd as the only index, so it is impossible to carry out engineering geological evaluation according to the Chinese standard heavy dynamic penetration hammer number N'63.5. In this paper, by comparing and analyzing the specifications and test process of KDZ-001 heavy cone dynamic penetration probe, we propose a novel method to convert the revised heavy dynamic penetration hammer number N'63.5 into dynamic penetration resistance qd for engineering geological evaluation, and establish a reference table for evaluating the compactness of gravel soil with qd as the index. In the investigation practice, we applied the method to evaluate the compactness of gravel soil in Astana area, then we carried out the physical mechanical stratification. Finally, we carried out the engineering geological evaluation on the bearing capacity of sand and gravel soil in Astana area, by combining with the geotechnical test report and other in-situ test reports, and achieved good effects.
In the work of geotechnical investigation in Astana, Kazakhstan, we found that the equipment specifications and test data recording methods of KDZ-001 heavy cone dynamic penetration detector adopted by the Almaty Geological Exploration Center are different from the requirements of relevant Chinese codes. The test results take the dynamic penetration resistance qd as the only index, so it is impossible to carry out engineering geological evaluation according to the Chinese standard heavy dynamic penetration hammer number N'63.5. In this paper, by comparing and analyzing the specifications and test process of KDZ-001 heavy cone dynamic penetration probe, we propose a novel method to convert the revised heavy dynamic penetration hammer number N'63.5 into dynamic penetration resistance qd for engineering geological evaluation, and establish a reference table for evaluating the compactness of gravel soil with qd as the index. In the investigation practice, we applied the method to evaluate the compactness of gravel soil in Astana area, then we carried out the physical mechanical stratification. Finally, we carried out the engineering geological evaluation on the bearing capacity of sand and gravel soil in Astana area, by combining with the geotechnical test report and other in-situ test reports, and achieved good effects.
2020, 28(S1): 174-180.
In order to study the influence of vehicle load on the stability of highway retaining wall, introduce an improved equivalent soil thickness method which based on the Coulomb earth pressure theory and iterative calculation of fracture angle convergence value to get a new converted soil thickness. Combined with the example of a retaining wall of Ankang Highway, the results show that the improved method is more accurate in evaluating the stability of the retaining wall. Using the numerical method to analyze the mechanical response of the retaining wall under vehicle load, and it is considered that the affected part of the retaining wall under the vehicle load is mainly the upper middle part. The smaller the distance between the car and wall is,the more significant the vibration response of the soil behind the wall is, and the greater the additional dynamic earth pressure is,but the horizontal displacement of the retaining wall is not greatly affected by it.
In order to study the influence of vehicle load on the stability of highway retaining wall, introduce an improved equivalent soil thickness method which based on the Coulomb earth pressure theory and iterative calculation of fracture angle convergence value to get a new converted soil thickness. Combined with the example of a retaining wall of Ankang Highway, the results show that the improved method is more accurate in evaluating the stability of the retaining wall. Using the numerical method to analyze the mechanical response of the retaining wall under vehicle load, and it is considered that the affected part of the retaining wall under the vehicle load is mainly the upper middle part. The smaller the distance between the car and wall is,the more significant the vibration response of the soil behind the wall is, and the greater the additional dynamic earth pressure is,but the horizontal displacement of the retaining wall is not greatly affected by it.
2020, 28(S1): 181-189.
Danjiangkou reservoir is the source of the Middle Route of the South-to-North Water Diversion Project, the geological environment survey of the water source area is very important. During the survey process, the amount of geological environmental data is huge and the degree of comprehensive utilization is low. In order to make more effective use of these data, and meet the needs of multi-source, heterogeneous data management and real-time dynamic update, the paper carried out secondary development on the MapGIS geographic information system platform and the MapGIS IGserver platform, and established the Danjiangkou water source area environmental geological survey data cloud platform based on WebGIS. The establishment of the cloud platform has realized the management and sharing of the geological environment survey results data and field survey data of the water source area. On the basis of studying the characteristics of the geological environment of the water source area, we established a combinable geological environmental quality evaluation system, and realized the cloud evaluation of geological environmental quality. The platform provides geological support for in-depth geological research and analysis and national land planning in the water source area of Danjiangkou reservoir.
Danjiangkou reservoir is the source of the Middle Route of the South-to-North Water Diversion Project, the geological environment survey of the water source area is very important. During the survey process, the amount of geological environmental data is huge and the degree of comprehensive utilization is low. In order to make more effective use of these data, and meet the needs of multi-source, heterogeneous data management and real-time dynamic update, the paper carried out secondary development on the MapGIS geographic information system platform and the MapGIS IGserver platform, and established the Danjiangkou water source area environmental geological survey data cloud platform based on WebGIS. The establishment of the cloud platform has realized the management and sharing of the geological environment survey results data and field survey data of the water source area. On the basis of studying the characteristics of the geological environment of the water source area, we established a combinable geological environmental quality evaluation system, and realized the cloud evaluation of geological environmental quality. The platform provides geological support for in-depth geological research and analysis and national land planning in the water source area of Danjiangkou reservoir.
2020, 28(S1): 190-198.
The calcareous soil of coast reef is limited in distribution, and is seldom used in engineering and lacks engineering geological research. In order to find out the spatial distribution and physical and mechanical characteristics of the calcareous soil on the coast reef, and service design, we referred to the results of previous studies on calcareous soils and collected the existing geological data in Timor-leste, and carried out field geological survey, drilling, standard penetration test and laboratory physical and mechanical test. We have studied the landform, spatial distribution, mineral chemical composition, grain size distribution, specific gravity, permeability coefficient and shear strength of calcareous soil in Timor-leste coast reef. We have summarized the physical and mechanical characteristics of calcareous soil in coast reef under the landform of sand dam and lagoon. Our study results are as following:(1)The landform of Timor-leste coast reef has its own characteristics. The land is low hill landform, the coast area is bay landform. The bay has developed sand bar, sand beach and lagoon. (2)The study area has developed six unit layers from top to bottom in the stratigraphic space:Unit 1 modern calcareous gravelly sand on the surface of sand bar, Unit 2 very soft to soft clay/silt at the lagoon surface, Unit 3 thick layers of calcareous gravelly sand in the upper part, Unit 4 silty/clayey gravelly sand/grave at the middle part, Unit 5 sitly/clay gravelly sand/grave at the lower part and Unit 6 highly to moderately weathered phyllite at the bottom. (3)The calcareous soil in Timor-leste is composed of pebbled sand lithologically and gravel locally, containing about 19% fine-grained soil. The mineral composition is mainly aragonite and calcite, followed by mica and quartz. The sediment is mainly derived from marine coral clasts and partly from terrestrial sediments. Calcareous soils, similar to atolls and barrier reefs, are also characterized by the presence of land-based sediments. (4)The special gravity of calcareous soil on coast reef is 2.70,which is larger than quartz sand, reflecting the unique special gravity formed by different mineral composition. (5)Coast-reef calcareous soil is mainly medium sand, coarse sand and gravel, but the permeability coefficient is lower than the conventional value due to the presence of more fine grains. Attention should be paid when filling. (6)The cohesion of calcareous gravelly sand of coast reef is 0, and the internal friction Angle is 33 degrees in loose state, 36 degrees in dense state, and 41 degrees in dense state, which is similar to the mature empirical evaluation of quartz gravelly sand. Our studies show that the calcareous soil in Timor-leste coast reef contains some feldspar, quartz. The mechanical strength of rock and soil is similar to that of conventional quartz sand. The empirical relationship of rock and soil parameters evaluated by the quartz sand in situ test can be applied to the calcareous soil of east Timor shore reef with reliable results. The determination of the physical and mechanical properties of calcareous soil in timor-leste coast reef provides a reference for similar types of calcareous soil geotechnical engineering applications.
The calcareous soil of coast reef is limited in distribution, and is seldom used in engineering and lacks engineering geological research. In order to find out the spatial distribution and physical and mechanical characteristics of the calcareous soil on the coast reef, and service design, we referred to the results of previous studies on calcareous soils and collected the existing geological data in Timor-leste, and carried out field geological survey, drilling, standard penetration test and laboratory physical and mechanical test. We have studied the landform, spatial distribution, mineral chemical composition, grain size distribution, specific gravity, permeability coefficient and shear strength of calcareous soil in Timor-leste coast reef. We have summarized the physical and mechanical characteristics of calcareous soil in coast reef under the landform of sand dam and lagoon. Our study results are as following:(1)The landform of Timor-leste coast reef has its own characteristics. The land is low hill landform, the coast area is bay landform. The bay has developed sand bar, sand beach and lagoon. (2)The study area has developed six unit layers from top to bottom in the stratigraphic space:Unit 1 modern calcareous gravelly sand on the surface of sand bar, Unit 2 very soft to soft clay/silt at the lagoon surface, Unit 3 thick layers of calcareous gravelly sand in the upper part, Unit 4 silty/clayey gravelly sand/grave at the middle part, Unit 5 sitly/clay gravelly sand/grave at the lower part and Unit 6 highly to moderately weathered phyllite at the bottom. (3)The calcareous soil in Timor-leste is composed of pebbled sand lithologically and gravel locally, containing about 19% fine-grained soil. The mineral composition is mainly aragonite and calcite, followed by mica and quartz. The sediment is mainly derived from marine coral clasts and partly from terrestrial sediments. Calcareous soils, similar to atolls and barrier reefs, are also characterized by the presence of land-based sediments. (4)The special gravity of calcareous soil on coast reef is 2.70,which is larger than quartz sand, reflecting the unique special gravity formed by different mineral composition. (5)Coast-reef calcareous soil is mainly medium sand, coarse sand and gravel, but the permeability coefficient is lower than the conventional value due to the presence of more fine grains. Attention should be paid when filling. (6)The cohesion of calcareous gravelly sand of coast reef is 0, and the internal friction Angle is 33 degrees in loose state, 36 degrees in dense state, and 41 degrees in dense state, which is similar to the mature empirical evaluation of quartz gravelly sand. Our studies show that the calcareous soil in Timor-leste coast reef contains some feldspar, quartz. The mechanical strength of rock and soil is similar to that of conventional quartz sand. The empirical relationship of rock and soil parameters evaluated by the quartz sand in situ test can be applied to the calcareous soil of east Timor shore reef with reliable results. The determination of the physical and mechanical properties of calcareous soil in timor-leste coast reef provides a reference for similar types of calcareous soil geotechnical engineering applications.
2020, 28(S1): 199-205.
The continuous development of offshore engineering construction has put forward higher requirements for offshore geotechnical engineering investigation. Due to the fact that conventional marine in-situ test is difficult to meet the economic, fast and convenient requirements of projects such as offshore wind power development, port dredging and pipeline and cable surveys, free fall penetration test has attracted attention. The development of free fall penetration test is reviewed and a kind of free fall penetration technology is introduced for marine soft soil. The methods of undrained shear strength of soft soil and classification of sediment based on FFP are summarized. The authors designed a new free fall piezocone penetrometer for evaluating the characteristics of offshore geotechnical engineering and proposed the FFP engineering characteristic evaluation framework. The analysis shows that free fall penetration test has a broad application prospect in offshore geotechnical engineering testing.
The continuous development of offshore engineering construction has put forward higher requirements for offshore geotechnical engineering investigation. Due to the fact that conventional marine in-situ test is difficult to meet the economic, fast and convenient requirements of projects such as offshore wind power development, port dredging and pipeline and cable surveys, free fall penetration test has attracted attention. The development of free fall penetration test is reviewed and a kind of free fall penetration technology is introduced for marine soft soil. The methods of undrained shear strength of soft soil and classification of sediment based on FFP are summarized. The authors designed a new free fall piezocone penetrometer for evaluating the characteristics of offshore geotechnical engineering and proposed the FFP engineering characteristic evaluation framework. The analysis shows that free fall penetration test has a broad application prospect in offshore geotechnical engineering testing.
2020, 28(S1): 206-212.
In recent years, the drop waterproof curtain(such as bottom-stopping diaphragm wall) has been widely used in deep foundation pit engineering in Wuhan. In many subway station foundation pit dewatering projects, the idea of the drop waterproof curtain stopping water+pipe well dewatering is adopted. However, in the construction of some transfer stations, the dewatering design of the new subway station does not consider thedrop waterproof curtain of the existing station, and the influence of the existing curtain on the new foundation pit may not be ignored. In this paper, Visual Modflow seepage numerical simulation software is used to study 8 working conditions established on the basis of typical first-grade terrace hydrogeological model of the Yangtze river, and the influence of existing curtain on the dewatering of new foundation pit is discussed. The results show that the maximum and minimum depth reduction in the new foundation pit tend to increase first and then decrease with the increase of the distance between the existing curtain and the new foundation pit.
In recent years, the drop waterproof curtain(such as bottom-stopping diaphragm wall) has been widely used in deep foundation pit engineering in Wuhan. In many subway station foundation pit dewatering projects, the idea of the drop waterproof curtain stopping water+pipe well dewatering is adopted. However, in the construction of some transfer stations, the dewatering design of the new subway station does not consider thedrop waterproof curtain of the existing station, and the influence of the existing curtain on the new foundation pit may not be ignored. In this paper, Visual Modflow seepage numerical simulation software is used to study 8 working conditions established on the basis of typical first-grade terrace hydrogeological model of the Yangtze river, and the influence of existing curtain on the dewatering of new foundation pit is discussed. The results show that the maximum and minimum depth reduction in the new foundation pit tend to increase first and then decrease with the increase of the distance between the existing curtain and the new foundation pit.
2020, 28(S1): 213-218.
Dredging sludge has the characteristics of huge volume, high moisture content and low structural strength. Development of compound curing agent of sludge could efficiently solve its problem of space occupation and environmental pollution, promoting resource utilization of sludge. We selected cement as major curing agent, and carried out experiment on sludge solidified as subgrade filling. By experiment of single factor, this study implements the screen of main addition agents. We carried out further experiment to analyze the effect of addition proportion of curing agent to moisture content, unconfined compressive strength and CBR value of subgrade fillig. The results show that cement, flyash and offscum could improve the sludge strength efficiently, but flyash has a limited effect on reducing mosture content. In addition, heavy use of flyash would cause lamellar structure of solidified sludge. Systematically considering CBR value, puddlability and price, the compound curing agent is consist of 5% cement, 6% flyash, 50% offscum and 0.5% accelerator. The compound curing agent could improve the original sludge by forming skeleton structure and establishing hydrophobic channel.
Dredging sludge has the characteristics of huge volume, high moisture content and low structural strength. Development of compound curing agent of sludge could efficiently solve its problem of space occupation and environmental pollution, promoting resource utilization of sludge. We selected cement as major curing agent, and carried out experiment on sludge solidified as subgrade filling. By experiment of single factor, this study implements the screen of main addition agents. We carried out further experiment to analyze the effect of addition proportion of curing agent to moisture content, unconfined compressive strength and CBR value of subgrade fillig. The results show that cement, flyash and offscum could improve the sludge strength efficiently, but flyash has a limited effect on reducing mosture content. In addition, heavy use of flyash would cause lamellar structure of solidified sludge. Systematically considering CBR value, puddlability and price, the compound curing agent is consist of 5% cement, 6% flyash, 50% offscum and 0.5% accelerator. The compound curing agent could improve the original sludge by forming skeleton structure and establishing hydrophobic channel.
2020, 28(S1): 219-224.
Excavation and landfills in construction have caused a lot of slope problems in the site, which has a huge impact on the production and life of the people. The practical and feasible solutions are put forward to ensure the safety and economic benefits of the project. In this paper, the research object is the slope engineering of section B8B9 of Chongqing Coal Chemical Electrification Park. Through sufficient investigation, clearly defined the engineering geological conditions. Then used FLAC3D strength reduction method to analyze the slope stability under natural and rainstorm conditions in detail. The results show that:The slope is in an unstable state under natural conditions. Under the influence of rainstorm, the stability will continue to decline, and finally shear failure will occur along the bottom sliding surface of silty clay layer. Considering the factors of safety and economy, designed the anchor protection scheme, which can make the slope stability meet the specification requirements. The research results can provide reference for the stability analysis and protection design of similar slopes.
Excavation and landfills in construction have caused a lot of slope problems in the site, which has a huge impact on the production and life of the people. The practical and feasible solutions are put forward to ensure the safety and economic benefits of the project. In this paper, the research object is the slope engineering of section B8B9 of Chongqing Coal Chemical Electrification Park. Through sufficient investigation, clearly defined the engineering geological conditions. Then used FLAC3D strength reduction method to analyze the slope stability under natural and rainstorm conditions in detail. The results show that:The slope is in an unstable state under natural conditions. Under the influence of rainstorm, the stability will continue to decline, and finally shear failure will occur along the bottom sliding surface of silty clay layer. Considering the factors of safety and economy, designed the anchor protection scheme, which can make the slope stability meet the specification requirements. The research results can provide reference for the stability analysis and protection design of similar slopes.
2020, 28(S1): 225-229.
The mountain is high and steep in the western mountain canyon area. Even a very steep excavation slope ratio will produce a very high slope during slope excavation, resulting in difficult treatment and long construction period. Therefore, it is necessary to excavate as little as possible, carry out strong support in time, and achieve "high cleaning up, strong support, low opening and early entry" for the entrance of the spillway tunnel. In this way, the slope height of excavation can be greatly reduced, the construction difficulty can be reduced, the construction period can be reduced, and the investment can be saved. After the intake slope of the tunnel spillway was optimized, the tower foundation moved outward and was close to the slope surface. Attention should be paid to the unloading of rock mass and the adverse effects of unfavorable combination of structural planes on the slope below the tower foundation, stability analysis and calculation should be carried out, and support treatments should be taken when necessary. This paper summarized the successful treatment experience of flood discharge tunnel intake slope optimization and tower foundation slope in Changheba hydropower project on Dadu river, which can provide experience for other similar projects.
The mountain is high and steep in the western mountain canyon area. Even a very steep excavation slope ratio will produce a very high slope during slope excavation, resulting in difficult treatment and long construction period. Therefore, it is necessary to excavate as little as possible, carry out strong support in time, and achieve "high cleaning up, strong support, low opening and early entry" for the entrance of the spillway tunnel. In this way, the slope height of excavation can be greatly reduced, the construction difficulty can be reduced, the construction period can be reduced, and the investment can be saved. After the intake slope of the tunnel spillway was optimized, the tower foundation moved outward and was close to the slope surface. Attention should be paid to the unloading of rock mass and the adverse effects of unfavorable combination of structural planes on the slope below the tower foundation, stability analysis and calculation should be carried out, and support treatments should be taken when necessary. This paper summarized the successful treatment experience of flood discharge tunnel intake slope optimization and tower foundation slope in Changheba hydropower project on Dadu river, which can provide experience for other similar projects.
INTELLIGENT RECOGNITION OF LAYERED GEOLOGICAL BODY BASED ON MACHINE LEARNING AND SEISMIC EXPLORATION
2020, 28(S1): 230-236.
Seismic exploration is a non-destructive detection technology widely applied in oil and gas exploration or geological structure exploration. The seismic signals are quite difficult to be interpreted due to the complexity of underground structures and the inhomogeneous media. Limitations of current methods used in seismic signals interpretation and needs for expert knowledge considerably reduce the efficiency of interpretation. We established a nonlinear model using neural network to predict geological information. Firstly, we generated thousands of random layered geological models of media in rock, water and air. Then we got one signal data each model by using finite difference method to simulate the propagation of seismic waves. At last, 80% signals and geological models data are used as training data sets and 20% as test data sets. As the tests show, this neural network accurately predicts signals the depths of underground media interface and velocity of the media between. We didn't use any filtering or feature extraction method in the work above. This method improves the seismic exploration economically and efficiently. The method of machine learning nicely fits in the simplified geological situation in karst area. This research is a preliminary discussion on the feasibility of applying machine learning method into seismic exploration.
Seismic exploration is a non-destructive detection technology widely applied in oil and gas exploration or geological structure exploration. The seismic signals are quite difficult to be interpreted due to the complexity of underground structures and the inhomogeneous media. Limitations of current methods used in seismic signals interpretation and needs for expert knowledge considerably reduce the efficiency of interpretation. We established a nonlinear model using neural network to predict geological information. Firstly, we generated thousands of random layered geological models of media in rock, water and air. Then we got one signal data each model by using finite difference method to simulate the propagation of seismic waves. At last, 80% signals and geological models data are used as training data sets and 20% as test data sets. As the tests show, this neural network accurately predicts signals the depths of underground media interface and velocity of the media between. We didn't use any filtering or feature extraction method in the work above. This method improves the seismic exploration economically and efficiently. The method of machine learning nicely fits in the simplified geological situation in karst area. This research is a preliminary discussion on the feasibility of applying machine learning method into seismic exploration.
2020, 28(S1): 237-243.
Yichang is in a critical period of building a modern mega-city, and it is also a period when resource and environmental constraints are tightening and the contradiction between ecological environment protection and economic development is intensifying. The development and utilization of underground space can expand the urban resource environmental bear capacity without increasing the land use and destroying the surface landscape pattern, which is of great significance to the urban construction of ecological civilization demonstration area. Based on the comprehensive geological survey project carried out in Yichang, under the dual constraints of geological environment and urban development characteristics, the environmental factors influencing the development of underground space resources in the study area are analyzed. Then, the explosibility, suitability and potential value of the underground space resources are evaluated, hoping to provide decision support for the related development planning.
Yichang is in a critical period of building a modern mega-city, and it is also a period when resource and environmental constraints are tightening and the contradiction between ecological environment protection and economic development is intensifying. The development and utilization of underground space can expand the urban resource environmental bear capacity without increasing the land use and destroying the surface landscape pattern, which is of great significance to the urban construction of ecological civilization demonstration area. Based on the comprehensive geological survey project carried out in Yichang, under the dual constraints of geological environment and urban development characteristics, the environmental factors influencing the development of underground space resources in the study area are analyzed. Then, the explosibility, suitability and potential value of the underground space resources are evaluated, hoping to provide decision support for the related development planning.
2020, 28(S1): 244-251.
To investigate the accuracy and information of GM(1. 1)model bases on interval series in predicting groundwater level in this paper, three interval methods of boundary point modeling, transformation modeling and parameter modeling are selected for comparison and analysis. The GM(1. 1)model of interval sequence has some delay effect and disorder effect. When the fluctuation range of actual water level is small, the prediction accuracy of the model is higher. The prediction accuracy of parameter modeling is better than that of boundary point modeling and transformation modeling. Compared with the point prediction, the interval series GM(1. 1)model is more beneficial to groundwater resource management and development.
To investigate the accuracy and information of GM(1. 1)model bases on interval series in predicting groundwater level in this paper, three interval methods of boundary point modeling, transformation modeling and parameter modeling are selected for comparison and analysis. The GM(1. 1)model of interval sequence has some delay effect and disorder effect. When the fluctuation range of actual water level is small, the prediction accuracy of the model is higher. The prediction accuracy of parameter modeling is better than that of boundary point modeling and transformation modeling. Compared with the point prediction, the interval series GM(1. 1)model is more beneficial to groundwater resource management and development.
2020, 28(S1): 252-258.
Based on the characteristics of regional geological conditions in Guangzhou and the theoretical knowledge of risk zoning, the evaluation index system of geological risk zoning for planning and construction in Guangzhou is constructed. The first level indexes are 7 factors and 11 secondary factors. Through the GIS,the geological risk zoning map of Guangzhou planning and construction is drawn, which is divided into seven areas。The excellent area, medium thick soft soil area, thick layer soft soil area and the weak karst development area are drawn high-intensity and medium-intensity development areas, accounting for 46.7% of the total area of Guangzhou. Strong karst development area and mined-out area are drawn moderately developed areas, accounting for 3.7% of the total area of Guangzhou. The Mountain area are drawn restricted development area, accounting for 49.6% of the total area of Guangzhou. At the same time, the geological risks are given in the process of urban construction by different areas. It can be used for reference for other cities with similar geological conditions.
Based on the characteristics of regional geological conditions in Guangzhou and the theoretical knowledge of risk zoning, the evaluation index system of geological risk zoning for planning and construction in Guangzhou is constructed. The first level indexes are 7 factors and 11 secondary factors. Through the GIS,the geological risk zoning map of Guangzhou planning and construction is drawn, which is divided into seven areas。The excellent area, medium thick soft soil area, thick layer soft soil area and the weak karst development area are drawn high-intensity and medium-intensity development areas, accounting for 46.7% of the total area of Guangzhou. Strong karst development area and mined-out area are drawn moderately developed areas, accounting for 3.7% of the total area of Guangzhou. The Mountain area are drawn restricted development area, accounting for 49.6% of the total area of Guangzhou. At the same time, the geological risks are given in the process of urban construction by different areas. It can be used for reference for other cities with similar geological conditions.
微信 | 公众平台 
