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2022 Vol. 30, No. 4
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A laboratory rainfall test model is designed according to the characteristics of the overburden slope. The test results shows that the initial water content distribution is inversely proportional along the elevation. It is futher assumed that rainfall infiltration is controlled by the total rainfall when the slope surface is unsaturated. An analytical calculation method for rainfall infiltration in the overburden slope under undrained condition is then established. A slope stability calculation method for unsaturated overburden slope is also established considering the rainfall infiltration theory and the shear strength variation of unsaturated soils. The influence of overburden thickness,initial water content distribution parameters and slope angle on slope stability are analyzed. Research results are as follows:(1)The initial water content distribution in the overburden slope is approximated with an inverse proportional distribution. Based on the total rainfall control assumption,an analytical calculation method is obtained for the rainfall infiltration of the overburden slope considering the initial water content distribution. (2)With the assumption of a semi-infinite space volume,a method is given for calculating the factor of safety of the sliding surface at different positions of the overburden slope under rainfall infiltration. (3)The initial stability of the slope decreases with the increase of the thickness of the overburden soil under the same rainfall conditions. The influence of rainfall infiltration on the stability of overburden slope decreases with the increase of overburden thickness. (4)The stability of the slope decreases with the increase of the initial water content distribution parameter of the overburden soil when the rainfall is the same. The longer the rainfall time,the more obvious the influence of initial water content distribution on slope stability. (5)The stability of the overburden slope at different angles gradually decreases with the increase of rainfall. In the initial state,the minimum stability coefficient caused by the increase of the slope angle decreases the most. As the rainfall increases,the slope stability is gradually reduced by the angle. A laboratory rainfall test model is designed according to the characteristics of the overburden slope. The test results shows that the initial water content distribution is inversely proportional along the elevation. It is futher assumed that rainfall infiltration is controlled by the total rainfall when the slope surface is unsaturated. An analytical calculation method for rainfall infiltration in the overburden slope under undrained condition is then established. A slope stability calculation method for unsaturated overburden slope is also established considering the rainfall infiltration theory and the shear strength variation of unsaturated soils. The influence of overburden thickness,initial water content distribution parameters and slope angle on slope stability are analyzed. Research results are as follows:(1)The initial water content distribution in the overburden slope is approximated with an inverse proportional distribution. Based on the total rainfall control assumption,an analytical calculation method is obtained for the rainfall infiltration of the overburden slope considering the initial water content distribution. (2)With the assumption of a semi-infinite space volume,a method is given for calculating the factor of safety of the sliding surface at different positions of the overburden slope under rainfall infiltration. (3)The initial stability of the slope decreases with the increase of the thickness of the overburden soil under the same rainfall conditions. The influence of rainfall infiltration on the stability of overburden slope decreases with the increase of overburden thickness. (4)The stability of the slope decreases with the increase of the initial water content distribution parameter of the overburden soil when the rainfall is the same. The longer the rainfall time,the more obvious the influence of initial water content distribution on slope stability. (5)The stability of the overburden slope at different angles gradually decreases with the increase of rainfall. In the initial state,the minimum stability coefficient caused by the increase of the slope angle decreases the most. As the rainfall increases,the slope stability is gradually reduced by the angle.
On basis of the Dakshanamurthy and Fredlund's 2D plane strain consolidation theory of unsaturated soils,the Fourier sinusoidal series expansion and Laplace transformation are adopted to give the semi-analytical solution of excess pore-air pressure,excess pore-water pressure and settlement considering the piece-wise cyclic loading,and the degenerate method is applied to verify the correctness of the semi-analytical solution obtained in this paper. Then,combined with three specific piece-wise cyclic loads,the influence on the consolidation of unsaturated soils are analyzed with the change of permeability coefficient ratio(ka/kwkx/kz) and load characteristic parameters(a). The results investigated in this paper show that the settlement will be accelerated by amplifying the value of ka/kw or kx/kz. The loading parameter can speed up the consolidation and result in a smaller settlement. The 2D plane strain consolidation of unsaturated soils is obviously affected by the piece-wise cyclic loading,therefore the consolidation process of unsaturated soils can be effectively controlled by changing the construction speed and setting the radial drainage device in the actual construction process,that is,the research results in this paper can provide important theoretical basis for the design and construction of unsaturated soils foundation. On basis of the Dakshanamurthy and Fredlund's 2D plane strain consolidation theory of unsaturated soils,the Fourier sinusoidal series expansion and Laplace transformation are adopted to give the semi-analytical solution of excess pore-air pressure,excess pore-water pressure and settlement considering the piece-wise cyclic loading,and the degenerate method is applied to verify the correctness of the semi-analytical solution obtained in this paper. Then,combined with three specific piece-wise cyclic loads,the influence on the consolidation of unsaturated soils are analyzed with the change of permeability coefficient ratio(ka/kwkx/kz) and load characteristic parameters(a). The results investigated in this paper show that the settlement will be accelerated by amplifying the value of ka/kw or kx/kz. The loading parameter can speed up the consolidation and result in a smaller settlement. The 2D plane strain consolidation of unsaturated soils is obviously affected by the piece-wise cyclic loading,therefore the consolidation process of unsaturated soils can be effectively controlled by changing the construction speed and setting the radial drainage device in the actual construction process,that is,the research results in this paper can provide important theoretical basis for the design and construction of unsaturated soils foundation.
This paper studies the strength decay law of the glauberite salt rock of Guankou formation of Cretaceous in Southwest China under actions of water and temperature. It simulates the immersion test of glauberite salt rock sample in distilled water at a temperature of 30~70℃ by a home-made test device. During the 40-day immersion,we test the uniaxial compressive strength,elastic modulus,P-wave velocity,and failure mode of the glauberite salt rock. We summary the changes of the rock parameters with time and temperature before and after water immersion through the curves of the parameters versus the time or the temperature. We analyze the characteristics of rock microstructure changes before and after soaking by polarizing microscope. We examine the influence of composition,structure,time,temperature and other factors on the strength attenuation of the glauberite salt rock. We put forward some valuable conclusions. They are a new supplementary research results of the influence of water and temperature on the strength of glauberite salt rock. The rock strength decays sharply with increasing soaking time. After 7 days of immersion,the rock strength decays 50% to 72% of the initial strength. After 16 days of immersion,the rock strength decays 21%to 47% of the initial strength. After soaking for 30 to 40 days,the rock strength decays to 10% of the initial strength. The test data proves the same attenuation law of strength parameters such as uniaxial compressive strength,elastic modulus,and P-wave velocity of glauberite salt rock over immersion time. The dissolution and corrosion of the soluble components in glauberite salt rock are the fundamental factors affecting the strength decay of salt rock. The solubility of minerals such as glauberite,anhydrite,and gypsum in glauberite salt rock is slightly affected by temperature in the test temperature range of 30~70℃. Under the same immersion time,the strength difference between each immersion temperature is less than 10% of the initial strength. The immersion time can attenuate the strength of glauberite salt rock by more than 90%. Therefore,we consider that the more important external factor that affects the strength attenuation of glauberite salt rock is the soaking time. The research results have deepened the understanding of the water-rock interaction of saline rock,especially glauberite salt rock,and also provide a data reference for the problems of saline rock and soil engineering. This paper studies the strength decay law of the glauberite salt rock of Guankou formation of Cretaceous in Southwest China under actions of water and temperature. It simulates the immersion test of glauberite salt rock sample in distilled water at a temperature of 30~70℃ by a home-made test device. During the 40-day immersion,we test the uniaxial compressive strength,elastic modulus,P-wave velocity,and failure mode of the glauberite salt rock. We summary the changes of the rock parameters with time and temperature before and after water immersion through the curves of the parameters versus the time or the temperature. We analyze the characteristics of rock microstructure changes before and after soaking by polarizing microscope. We examine the influence of composition,structure,time,temperature and other factors on the strength attenuation of the glauberite salt rock. We put forward some valuable conclusions. They are a new supplementary research results of the influence of water and temperature on the strength of glauberite salt rock. The rock strength decays sharply with increasing soaking time. After 7 days of immersion,the rock strength decays 50% to 72% of the initial strength. After 16 days of immersion,the rock strength decays 21%to 47% of the initial strength. After soaking for 30 to 40 days,the rock strength decays to 10% of the initial strength. The test data proves the same attenuation law of strength parameters such as uniaxial compressive strength,elastic modulus,and P-wave velocity of glauberite salt rock over immersion time. The dissolution and corrosion of the soluble components in glauberite salt rock are the fundamental factors affecting the strength decay of salt rock. The solubility of minerals such as glauberite,anhydrite,and gypsum in glauberite salt rock is slightly affected by temperature in the test temperature range of 30~70℃. Under the same immersion time,the strength difference between each immersion temperature is less than 10% of the initial strength. The immersion time can attenuate the strength of glauberite salt rock by more than 90%. Therefore,we consider that the more important external factor that affects the strength attenuation of glauberite salt rock is the soaking time. The research results have deepened the understanding of the water-rock interaction of saline rock,especially glauberite salt rock,and also provide a data reference for the problems of saline rock and soil engineering.
Loess deposits are loose,collapsible,and easy eroded,which resulting in frequent geohazards such as landslides mudslides and water-soil loss in the Loess Plateau. To alleviate soil erosion and reduce the occurrence rate of geological disasters at present,this article uses sodium polyacrylate as the soil stabilizer to improve Dong Zhiyuan's remodeled loess in Gansu Province. Laboratory disintegration test,penetrant test,water erosion test,and triaxial compression test are adopted to analyze the property differences of solidified loess with different proportions. The results show that after solidification with the sodium polyacrylate mixture,the shear failure resistance and water stability performance of the soil are improved with the increase of the mixture proportion. Specially,with 3.5% of sodium polyacrylate mixture,the disintegration and erosion resistance is greatly improved. The disintegration rate is only 1.15%after seven dry and wet cycles. Compared with unreinforced soil,the principal stress difference at shear failure increases 25.29%,28.23% and 22.48%under 100kPa,200kPa and 300kPa,respectively. The penetration rate is reduced by 217.41 times. We explain the phenomenon and mechanism from the microstructure of the loess combined with the triaxial test date,size grading and field emission scanning electron microscope. The sodium polyacrylate mixture wraps and connects soil particles,which changes soil grain composition and grading,increases the cohesive force and internal friction angle between soil particles,and improves the soil shear resistance and water stability. The sodium polyacrylate mixture has a good solidification improvement effect on the loess. Our research results provide a new method for alleviating soil erosion and reducing disasters in the Loess Plateau. Loess deposits are loose,collapsible,and easy eroded,which resulting in frequent geohazards such as landslides mudslides and water-soil loss in the Loess Plateau. To alleviate soil erosion and reduce the occurrence rate of geological disasters at present,this article uses sodium polyacrylate as the soil stabilizer to improve Dong Zhiyuan's remodeled loess in Gansu Province. Laboratory disintegration test,penetrant test,water erosion test,and triaxial compression test are adopted to analyze the property differences of solidified loess with different proportions. The results show that after solidification with the sodium polyacrylate mixture,the shear failure resistance and water stability performance of the soil are improved with the increase of the mixture proportion. Specially,with 3.5% of sodium polyacrylate mixture,the disintegration and erosion resistance is greatly improved. The disintegration rate is only 1.15%after seven dry and wet cycles. Compared with unreinforced soil,the principal stress difference at shear failure increases 25.29%,28.23% and 22.48%under 100kPa,200kPa and 300kPa,respectively. The penetration rate is reduced by 217.41 times. We explain the phenomenon and mechanism from the microstructure of the loess combined with the triaxial test date,size grading and field emission scanning electron microscope. The sodium polyacrylate mixture wraps and connects soil particles,which changes soil grain composition and grading,increases the cohesive force and internal friction angle between soil particles,and improves the soil shear resistance and water stability. The sodium polyacrylate mixture has a good solidification improvement effect on the loess. Our research results provide a new method for alleviating soil erosion and reducing disasters in the Loess Plateau.
The static lateral pressure coefficient,K0,describes the in-situ stress state of soils and is an important parameter in engineering calculations. In this paper,K0 consolidation test at constant strain rate is conducted on the Malan loess at different water contents to investigate the variation of K0. Both intact and remoulded specimens are employed and tested. It is found that:(1)K0 of Malan loess is not a constant value. According to the structural evolution during the test,the consolidation process can be divided into pre-collapse and post-collapse stages. K0 of the pre-collapse stage(K0i)increases linearly with increase in water content,while that of the post-collapse stage(K0s)follows a hyperbolic growth pattern with increase in water content. In addition,K0s is always greater than K0i. (2)The K0i from the intact specimens is less than that of the remoulded ones. The intact Malan loess has a strong vertical structure,which weakens the development of horizontal stress. The remoulded Malan loess is homogeneous and isotropic,resulting in a higher K0i. (3)In the post-collapse stage,the original structure of the intact specimens is destroyed,resulting in a structure similar to that of the remoulded specimens. This makes comparable K0s values for both intact and remoulded Malan loess. (4)Compared with other soils,K0s of Malan loess always show a lower value(K0s of saturated intact Malan loess is about 0.45,while that of other soils can be as high as 0.8). Numerical simulation of slopes under different K0 values shows that soil with low K0 is more susceptible to the formation of deep vertical tensile cracks. This to some extent explains the formation of typical macroscopic landform,such as loess wall and loess column. The static lateral pressure coefficient,K0,describes the in-situ stress state of soils and is an important parameter in engineering calculations. In this paper,K0 consolidation test at constant strain rate is conducted on the Malan loess at different water contents to investigate the variation of K0. Both intact and remoulded specimens are employed and tested. It is found that:(1)K0 of Malan loess is not a constant value. According to the structural evolution during the test,the consolidation process can be divided into pre-collapse and post-collapse stages. K0 of the pre-collapse stage(K0i)increases linearly with increase in water content,while that of the post-collapse stage(K0s)follows a hyperbolic growth pattern with increase in water content. In addition,K0s is always greater than K0i. (2)The K0i from the intact specimens is less than that of the remoulded ones. The intact Malan loess has a strong vertical structure,which weakens the development of horizontal stress. The remoulded Malan loess is homogeneous and isotropic,resulting in a higher K0i. (3)In the post-collapse stage,the original structure of the intact specimens is destroyed,resulting in a structure similar to that of the remoulded specimens. This makes comparable K0s values for both intact and remoulded Malan loess. (4)Compared with other soils,K0s of Malan loess always show a lower value(K0s of saturated intact Malan loess is about 0.45,while that of other soils can be as high as 0.8). Numerical simulation of slopes under different K0 values shows that soil with low K0 is more susceptible to the formation of deep vertical tensile cracks. This to some extent explains the formation of typical macroscopic landform,such as loess wall and loess column.
Sludge has the characteristics of high water content,poor mechanics and high pollutant content. Municipal sludge can be converted into sludge solidified soil by sludge solidification technology for safe treatment and rational utilization of municipal sludge. This paper aims to rationally and effectively utilize the mechanical properties of municipal sludge solidified soil. It studies the dynamic long-term mechanical indexes of municipal sludge solidified soil after different freezing temperatures and different freezing-thawing cycles. The cyclic dynamic load of municipal sludge solidified soil in natural environment is simulated using dynamic triaxial tester of different freezing temperatures and different freezing-thawing cycles. The experimental results show that the failure mode of sludge solidified soil presents brittle failure characteristics and has obvious shear surface. Under the coupling action of freezing at low temperature and multiple freeze-thaw cycles,with the decrease of freezing temperature and the increase of freeze-thaw cycles,the axial strain growth rate and final value of sludge solidified soil would also increase. By analyzing the dynamic stress-strain curves at different times,the relationship between the dynamic strength and the number of freeze-thaw cycles is obtained under different freeze-thaw temperature cycles,which provides a theoretical basis for the calculation of the dynamic strength of the sludge solidified soil. The change rule of static and dynamic long-term strength of sludge solidified soil is basically consistent with the increase of the number of freeze-thaw cycles. Under the same conditions,the static long-term strength of the sludge solidified soil is obviously greater than its dynamic long-term strength. Sludge has the characteristics of high water content,poor mechanics and high pollutant content. Municipal sludge can be converted into sludge solidified soil by sludge solidification technology for safe treatment and rational utilization of municipal sludge. This paper aims to rationally and effectively utilize the mechanical properties of municipal sludge solidified soil. It studies the dynamic long-term mechanical indexes of municipal sludge solidified soil after different freezing temperatures and different freezing-thawing cycles. The cyclic dynamic load of municipal sludge solidified soil in natural environment is simulated using dynamic triaxial tester of different freezing temperatures and different freezing-thawing cycles. The experimental results show that the failure mode of sludge solidified soil presents brittle failure characteristics and has obvious shear surface. Under the coupling action of freezing at low temperature and multiple freeze-thaw cycles,with the decrease of freezing temperature and the increase of freeze-thaw cycles,the axial strain growth rate and final value of sludge solidified soil would also increase. By analyzing the dynamic stress-strain curves at different times,the relationship between the dynamic strength and the number of freeze-thaw cycles is obtained under different freeze-thaw temperature cycles,which provides a theoretical basis for the calculation of the dynamic strength of the sludge solidified soil. The change rule of static and dynamic long-term strength of sludge solidified soil is basically consistent with the increase of the number of freeze-thaw cycles. Under the same conditions,the static long-term strength of the sludge solidified soil is obviously greater than its dynamic long-term strength.
The unreasonable storage capacity design can lead to a low utilization rate of site storage capacity. The simple dumping measures adopted at present would also cause potential safety hazards such as collapse and landslide. This paper aims to explore reasonable landfill method,increase landfill capacity and prevent safety accidents. This paper studies the capacity utilization of Lijia'ao landfill site in Longwei District of Wuzhou City for 4 years. The mechanical properties of engineering muck are studied by in-situ test and laboratory test. The process of filling is simulated by 3D geological modeling and LANDFILL. The site is calculated by LANDFILL and Sowers consolidation model. The settlement and capacity change are compared and analyzed. The results show that:(1)the composition of engineering muck is uneven due to the large disturbance,and are mainly composed of sandy fine grain soil(CLS) and low liquid limit clay(CL)in the half-saturated and-saturated states; (2)the engineering muck are mostly in fluid-plastic state and soft-plastic state,with low compacting degree and low average foundation bearing capacity; (3)the simulation results show that the expansion rate can be increased from 8.9%to 25.1%after the drainage measures and the landfill technology are improved. The capacity can be effectively improved; (4)compared with the model,the error value of landfill software settlement calculation is smaller,and the average error is less than 4.5%,which shows that the calculation of landfill settlement by LANDFILL is more practical. The research results provide both data and engineering references for the expansion design,safe operation and landfill construction of engineering muck field. The unreasonable storage capacity design can lead to a low utilization rate of site storage capacity. The simple dumping measures adopted at present would also cause potential safety hazards such as collapse and landslide. This paper aims to explore reasonable landfill method,increase landfill capacity and prevent safety accidents. This paper studies the capacity utilization of Lijia'ao landfill site in Longwei District of Wuzhou City for 4 years. The mechanical properties of engineering muck are studied by in-situ test and laboratory test. The process of filling is simulated by 3D geological modeling and LANDFILL. The site is calculated by LANDFILL and Sowers consolidation model. The settlement and capacity change are compared and analyzed. The results show that:(1)the composition of engineering muck is uneven due to the large disturbance,and are mainly composed of sandy fine grain soil(CLS) and low liquid limit clay(CL)in the half-saturated and-saturated states; (2)the engineering muck are mostly in fluid-plastic state and soft-plastic state,with low compacting degree and low average foundation bearing capacity; (3)the simulation results show that the expansion rate can be increased from 8.9%to 25.1%after the drainage measures and the landfill technology are improved. The capacity can be effectively improved; (4)compared with the model,the error value of landfill software settlement calculation is smaller,and the average error is less than 4.5%,which shows that the calculation of landfill settlement by LANDFILL is more practical. The research results provide both data and engineering references for the expansion design,safe operation and landfill construction of engineering muck field.
The widely-graded gravelly soil is widely distributed in the prone area of debris flow. Its strength characteristics are the key to correctly evaluate the startup and prevention design of debris flow. This paper aims to explore the relationship between the strength parameters and the maximum particle size and particle grading of widely-graded gravelly soil. It carries out the triaxial consolidated undrained strength tests for three kinds of the widely-graded gravelly soil with the maximum particle size of 30mm,20mm,10mm,5mm,respectively. The results show that the widely-graded gravelly soil has liquefaction characteristics. The test curves show three forms including strain softening,strain hardening and strain softening hardening. The effective internal friction angle of all liquefaction or effective liquefaction failure specimens increases linearly with the increase of maximum particle size. The effective internal friction angle increases quadratic polynomial with the increase of uniformity coefficient and increases piecewise linearly with the increase of characteristic particle size. The research results provide some reference support for the selection of parameters of the prediction of debris flow startup and the design of debris flow control engineering. The widely-graded gravelly soil is widely distributed in the prone area of debris flow. Its strength characteristics are the key to correctly evaluate the startup and prevention design of debris flow. This paper aims to explore the relationship between the strength parameters and the maximum particle size and particle grading of widely-graded gravelly soil. It carries out the triaxial consolidated undrained strength tests for three kinds of the widely-graded gravelly soil with the maximum particle size of 30mm,20mm,10mm,5mm,respectively. The results show that the widely-graded gravelly soil has liquefaction characteristics. The test curves show three forms including strain softening,strain hardening and strain softening hardening. The effective internal friction angle of all liquefaction or effective liquefaction failure specimens increases linearly with the increase of maximum particle size. The effective internal friction angle increases quadratic polynomial with the increase of uniformity coefficient and increases piecewise linearly with the increase of characteristic particle size. The research results provide some reference support for the selection of parameters of the prediction of debris flow startup and the design of debris flow control engineering.
The creep and progressive failure of loess induced by the time effect of the load can significantly affect the long-term service performance of its engineering structures. Especially in Northwest China,loess is widely distributed. Under the long-term action of the load,some typical engineering structures(such as the loess tunnel project excavated by Xi'an Metro) may be unstable due to loess creep and progressive failure,which can have an extremely negative impact on the smooth implementation of the project construction and its safe operation and maintenance after the completion of the project construction. It is of great theoretical and practical significance to analyze the rheological properties of loess and to reveal its rheological mechanism and then to establish its constitutive model. For this purpose,taking Q3 loess as the research object,based on the fractional derivative theory,the typical creep deformation process is analyzed. The fractional element model that can simulate the non-linear change characteristics of the accelerated creep stage is proposed. After theoretical analysis,the fractional-order improved Nishihara model is established and the constitutive equation is derived. On this basis,in order to verify the effectiveness of the fractional-order improved Nishihara model,the original and reshaped samples of Q3 loess triaxial hierarchical cyclic loading-unloading rheological test is carried out. The corresponding theoretical calculation results show that the fractional-order improved Nishihara model not only can simulate the three rheological stages of Q3 loess deceleration creep,constant velocity creep and accelerated creep,but also can make up for the inability of the integer-order improved Nishihara model to describe the accelerated creep stage. Compared to the integer-order improved Nishihara model,its prediction effect is better in the deceleration creep and unloading stages. The research results provide an important theoretical basis for the safe operation and maintenance design and construction plan of buildings considering the rheology of loess. The creep and progressive failure of loess induced by the time effect of the load can significantly affect the long-term service performance of its engineering structures. Especially in Northwest China,loess is widely distributed. Under the long-term action of the load,some typical engineering structures(such as the loess tunnel project excavated by Xi'an Metro) may be unstable due to loess creep and progressive failure,which can have an extremely negative impact on the smooth implementation of the project construction and its safe operation and maintenance after the completion of the project construction. It is of great theoretical and practical significance to analyze the rheological properties of loess and to reveal its rheological mechanism and then to establish its constitutive model. For this purpose,taking Q3 loess as the research object,based on the fractional derivative theory,the typical creep deformation process is analyzed. The fractional element model that can simulate the non-linear change characteristics of the accelerated creep stage is proposed. After theoretical analysis,the fractional-order improved Nishihara model is established and the constitutive equation is derived. On this basis,in order to verify the effectiveness of the fractional-order improved Nishihara model,the original and reshaped samples of Q3 loess triaxial hierarchical cyclic loading-unloading rheological test is carried out. The corresponding theoretical calculation results show that the fractional-order improved Nishihara model not only can simulate the three rheological stages of Q3 loess deceleration creep,constant velocity creep and accelerated creep,but also can make up for the inability of the integer-order improved Nishihara model to describe the accelerated creep stage. Compared to the integer-order improved Nishihara model,its prediction effect is better in the deceleration creep and unloading stages. The research results provide an important theoretical basis for the safe operation and maintenance design and construction plan of buildings considering the rheology of loess.
Engineering geology issues raised by earthquake-induced soil liquefaction have been drawn particular public attention. Studies focused on the formation mechanism of impact load-induced liquefaction and associated influencing factors are remarkably limited. This study conducts a series of impact load liquefaction tests on the sandy silt and its micro structure analyses towards revealing the development of pore pressure and the change in micro structure. The results indicate that impact load aggravates the development of pore pressure and its magnitude decreases with increase of impact energy. The micro structure analyses showed that impact load also causes a change in interparticle contact,particle morphology,and pore structure. Soil skeleton damages and pore shrinkage are deemed as the main cause to lead to soil liquefaction when subjected to impact load. The formation mechanism varies depending on the level of soil skeleton damage and pore shrinkage. Engineering geology issues raised by earthquake-induced soil liquefaction have been drawn particular public attention. Studies focused on the formation mechanism of impact load-induced liquefaction and associated influencing factors are remarkably limited. This study conducts a series of impact load liquefaction tests on the sandy silt and its micro structure analyses towards revealing the development of pore pressure and the change in micro structure. The results indicate that impact load aggravates the development of pore pressure and its magnitude decreases with increase of impact energy. The micro structure analyses showed that impact load also causes a change in interparticle contact,particle morphology,and pore structure. Soil skeleton damages and pore shrinkage are deemed as the main cause to lead to soil liquefaction when subjected to impact load. The formation mechanism varies depending on the level of soil skeleton damage and pore shrinkage.
Karst rock mass are widely developed in Southwest China. Due to the karstification of rock mass,the physical and mechanical properties of the karst rock mass are different from fractured rock mass in nature. The research has great significance on mechanical properties of karst fractured rock mass. It provides reasonable basis for engineering design,accurate and reliable parameters for the evaluation and prevention of karst collapse and landslide disasters,and modifies the stability evaluation model. Karst fractured rock mass in nature can be considered as rock mass with initial damage. In order to study the damage characteristics of karst fissure rock mass,this paper takes karst rock mass in Guizhou Province as research object. The Weibull distribution and equivalent strain principle is used to establish the damage evolution equation of karst fractured rock mass with initial damage. Meanwhile,the theory of rock strain strength is used establish the constitutive equation of karst fractured rock mass damage under uniaxial compression. The two equations provide a basis for studying the characteristics of dissolved rock mass with initial damage. Furthermore,the discrete element numerical software is used to carry out uniaxial compression numerical tests to study the evolution characteristics of karst fissure rock specimens under uniaxial compression conditions. In order to determine the microscopic parameters of the limestone,the uniaxial compression test of intact rock and the direct shear test of the structural plane are carried out. In addition,the random distribution of fracture in rock mass is obtained using field survey and statistics method. Finally,fractured rock mass model is constructed using particle flow discrete element software according to experiments and field investigation. The results show that the initial damage of karst fractured rock mass mainly includes erosion damage and crack damage. The initial damage of karst fractured rocks increases with the increase of the dissolution rate,and the final increase rate tends to flatten. The damage evolution curve of karst fractured rock mass all show the "S" behavior of slowly rising firstly,then rapidly growing,and finally slowly increasing to a damage value of 1. For fractured limestones with different karst rates,the compressive strength generally decreases as the dissolution rate increases. As the karst rate of fractured rock masses increases,the destruction of fractured limestone is mainly concentrated around the karst cavities,and the fragmentation characteristics after failure are also weakened. Local damage of sample can cause entire damage. In the initial stage of loading,the karst fractured limestone is mainly destroyed along the fractures. When the fractures are partially destroyed,the fractured limestones have a certain strength. While the residual rock blocks are destroyed,and the sample can be destroyed wholly. The heterogeneous characteristics of karst fissure rock masses leads to the failure originating from the dissolved pores and fractures with initial damage. Then the fractures undergo macroscopic damages after four stages of fissure initiation,expansion and shear,increase in number and length,and fissure penetration. The research results provide a scientific basis for parameter selection,optimal design and construction of engineering rock masses in karst areas. Karst rock mass are widely developed in Southwest China. Due to the karstification of rock mass,the physical and mechanical properties of the karst rock mass are different from fractured rock mass in nature. The research has great significance on mechanical properties of karst fractured rock mass. It provides reasonable basis for engineering design,accurate and reliable parameters for the evaluation and prevention of karst collapse and landslide disasters,and modifies the stability evaluation model. Karst fractured rock mass in nature can be considered as rock mass with initial damage. In order to study the damage characteristics of karst fissure rock mass,this paper takes karst rock mass in Guizhou Province as research object. The Weibull distribution and equivalent strain principle is used to establish the damage evolution equation of karst fractured rock mass with initial damage. Meanwhile,the theory of rock strain strength is used establish the constitutive equation of karst fractured rock mass damage under uniaxial compression. The two equations provide a basis for studying the characteristics of dissolved rock mass with initial damage. Furthermore,the discrete element numerical software is used to carry out uniaxial compression numerical tests to study the evolution characteristics of karst fissure rock specimens under uniaxial compression conditions. In order to determine the microscopic parameters of the limestone,the uniaxial compression test of intact rock and the direct shear test of the structural plane are carried out. In addition,the random distribution of fracture in rock mass is obtained using field survey and statistics method. Finally,fractured rock mass model is constructed using particle flow discrete element software according to experiments and field investigation. The results show that the initial damage of karst fractured rock mass mainly includes erosion damage and crack damage. The initial damage of karst fractured rocks increases with the increase of the dissolution rate,and the final increase rate tends to flatten. The damage evolution curve of karst fractured rock mass all show the "S" behavior of slowly rising firstly,then rapidly growing,and finally slowly increasing to a damage value of 1. For fractured limestones with different karst rates,the compressive strength generally decreases as the dissolution rate increases. As the karst rate of fractured rock masses increases,the destruction of fractured limestone is mainly concentrated around the karst cavities,and the fragmentation characteristics after failure are also weakened. Local damage of sample can cause entire damage. In the initial stage of loading,the karst fractured limestone is mainly destroyed along the fractures. When the fractures are partially destroyed,the fractured limestones have a certain strength. While the residual rock blocks are destroyed,and the sample can be destroyed wholly. The heterogeneous characteristics of karst fissure rock masses leads to the failure originating from the dissolved pores and fractures with initial damage. Then the fractures undergo macroscopic damages after four stages of fissure initiation,expansion and shear,increase in number and length,and fissure penetration. The research results provide a scientific basis for parameter selection,optimal design and construction of engineering rock masses in karst areas.
Gypsum-Slag(GS) soil hardening agent is a new type of soil curing material composed of cement,steel slag,mineral slag,desulfurization gypsum and other additives. This study focused on the GS soil hardening agent and cement and carries out a series of laboratory unconfined compressive strength tests and scanning electron microscope tests. Test results include the stabilized soil stress-strain curves and the effects of soil type,the amount of admixture and age on the mechanical properties of stabilized soil as well as its microstructure. The test program also includes a series of field tests designed to verify the laboratory data. The results indicate that the stress-strain curve of GS curing soil has obvious peak value,while that of soil-cement soil is relatively flat. The strength of the both curing soils increase with the increasement of proportion and age. However,the growth of GS curing soil strength is more uniform which is extremely different from cement curing soil. The deformation modulus of GS curing soil is 31.11~77.24 times the compressive strength,while that of cement curing soil is 23.24~71.62. In the field test,the integrity of pile formed by GS hardener is better than that of soil-cement pile. Based on the characteristics of quick increasing strength,high intensity in later period and good economic benefit,the GS agent is competent with cement in soil stabilization in underground,subgrade and other engineering. Gypsum-Slag(GS) soil hardening agent is a new type of soil curing material composed of cement,steel slag,mineral slag,desulfurization gypsum and other additives. This study focused on the GS soil hardening agent and cement and carries out a series of laboratory unconfined compressive strength tests and scanning electron microscope tests. Test results include the stabilized soil stress-strain curves and the effects of soil type,the amount of admixture and age on the mechanical properties of stabilized soil as well as its microstructure. The test program also includes a series of field tests designed to verify the laboratory data. The results indicate that the stress-strain curve of GS curing soil has obvious peak value,while that of soil-cement soil is relatively flat. The strength of the both curing soils increase with the increasement of proportion and age. However,the growth of GS curing soil strength is more uniform which is extremely different from cement curing soil. The deformation modulus of GS curing soil is 31.11~77.24 times the compressive strength,while that of cement curing soil is 23.24~71.62. In the field test,the integrity of pile formed by GS hardener is better than that of soil-cement pile. Based on the characteristics of quick increasing strength,high intensity in later period and good economic benefit,the GS agent is competent with cement in soil stabilization in underground,subgrade and other engineering.
This paper explores the evolution law of frost heaving pressure in ice crack of rock mass under freezing-thawing cycles,and reveals the influence mechanism of fatigue freezing-thawing on the deterioration of rock structure. It presents a self-made 8-channel real-time frost heaving pressure monitoring system and uses it to test the frost heaving pressure under different conditions of lithology and fracture geometry. It obtains the evolution curve of frost heaving pressure in multiple freezing-thawing cycles,and analyzes the influence of lithology and fracture geometry on the evolution law of frost heaving force. The results show the following three findings. (1)The process of deterioration of rock mass structure caused by feezing-thawing cycles is the process of fatigue damage caused by frost heaving force. The evolution of frost heaving pressure during each freezing-thawing cycle goes through the stages of incubation,explosion,fall back to stability,rise again and dissipation. It is found that the phenomenon of frost heaving pressure can rise again. The peak value of initial frost heaving force can be used as the index of frost thaw damage of fractured rock mass; (2)Under the action of multiple freezing-thawing cycles,the frost heaving pressure of rock fracture continuously erupts,accumulates and releases,during which the cumulative damage of fracture drives the continuous expansion of fracture,causing further fatigue deterioration of rock mass. Under the action of fatigue freezing-thawing cycles,the change trend of the peak value of initial frost heaving pressure and the peak value of secondary frost heaving pressure can be used as the judgment basis for the damage deterioration degree of fractured rock mass affected by freezing-thawing. (3)Structural characteristics of rock mass affect the evolution law of frost heaving pressure. The micro structure of rock mass matrix affects the water migration in the process of freezing. The macro pre-set fracture geometry affects the evolution law of frost heaving pressure. The larger the expansion degree,the greater the frost heaving pressure accumulation. The research on the evolution law of frost heaving pressure under fatigue freezing-thawing can provide theoretical basis for the long-term freezing-thawing stability prediction and engineering construction of rock mass engineering in cold region. This paper explores the evolution law of frost heaving pressure in ice crack of rock mass under freezing-thawing cycles,and reveals the influence mechanism of fatigue freezing-thawing on the deterioration of rock structure. It presents a self-made 8-channel real-time frost heaving pressure monitoring system and uses it to test the frost heaving pressure under different conditions of lithology and fracture geometry. It obtains the evolution curve of frost heaving pressure in multiple freezing-thawing cycles,and analyzes the influence of lithology and fracture geometry on the evolution law of frost heaving force. The results show the following three findings. (1)The process of deterioration of rock mass structure caused by feezing-thawing cycles is the process of fatigue damage caused by frost heaving force. The evolution of frost heaving pressure during each freezing-thawing cycle goes through the stages of incubation,explosion,fall back to stability,rise again and dissipation. It is found that the phenomenon of frost heaving pressure can rise again. The peak value of initial frost heaving force can be used as the index of frost thaw damage of fractured rock mass; (2)Under the action of multiple freezing-thawing cycles,the frost heaving pressure of rock fracture continuously erupts,accumulates and releases,during which the cumulative damage of fracture drives the continuous expansion of fracture,causing further fatigue deterioration of rock mass. Under the action of fatigue freezing-thawing cycles,the change trend of the peak value of initial frost heaving pressure and the peak value of secondary frost heaving pressure can be used as the judgment basis for the damage deterioration degree of fractured rock mass affected by freezing-thawing. (3)Structural characteristics of rock mass affect the evolution law of frost heaving pressure. The micro structure of rock mass matrix affects the water migration in the process of freezing. The macro pre-set fracture geometry affects the evolution law of frost heaving pressure. The larger the expansion degree,the greater the frost heaving pressure accumulation. The research on the evolution law of frost heaving pressure under fatigue freezing-thawing can provide theoretical basis for the long-term freezing-thawing stability prediction and engineering construction of rock mass engineering in cold region.
The main objective of the present study is to verify the applicability of binary-media model to remolded loess. To this end,triaxial compression tests are carried out. The stress-strain relationships and failure modes of specimen are obtained. The effects of confining pressure on the deformation behavior of specimen are analyzed. Moreover,we compare the characteristics of deformation behavior of remolded loess and the basic assumptions of binary-media model. The binary-media model is supposed to be a suitable approach to describe the mechanic behavior of remolded loess. Therefore,we proposed a parameter determination rule based on the characteristics of each parameter. The validity is further verified through the comparison between the fitting curves and the testing data. The suggest order of parameter determination is 'the elastic modulus of the bonded element → the breakage ratio → the parameters of frictional element → local strain coefficient'. The results indicate that double bear state is found in remolded loess sample and the stress-strain relationships of sample can be precisely described by the binary-media model. The higher the confining pressure,the faster the structural damage. Moreover,the frictional element shares most of the axial load in the late period of loading regarding the softening curve. With the transition of the stress-strain curve to the hardening type,load shared by the friction element decreases gradually at the late period of loading. The main objective of the present study is to verify the applicability of binary-media model to remolded loess. To this end,triaxial compression tests are carried out. The stress-strain relationships and failure modes of specimen are obtained. The effects of confining pressure on the deformation behavior of specimen are analyzed. Moreover,we compare the characteristics of deformation behavior of remolded loess and the basic assumptions of binary-media model. The binary-media model is supposed to be a suitable approach to describe the mechanic behavior of remolded loess. Therefore,we proposed a parameter determination rule based on the characteristics of each parameter. The validity is further verified through the comparison between the fitting curves and the testing data. The suggest order of parameter determination is 'the elastic modulus of the bonded element → the breakage ratio → the parameters of frictional element → local strain coefficient'. The results indicate that double bear state is found in remolded loess sample and the stress-strain relationships of sample can be precisely described by the binary-media model. The higher the confining pressure,the faster the structural damage. Moreover,the frictional element shares most of the axial load in the late period of loading regarding the softening curve. With the transition of the stress-strain curve to the hardening type,load shared by the friction element decreases gradually at the late period of loading.
Expansive soil is multi-cracked and has unfavorable engineering characteristics,which poses a potential threat to projects in expansive soil areas such as slopes. Regenerated rubber reinforced expansive soil(ESR)has good improvement effect on dynamic,static and expansion characteristics of expansive soil. The crack evolution pattern of expansive soil can be affected by the thickness of soil sample. In this paper,rubber-reinforced expansive soil is used to explore the effect of rubber powder on crack evolution of expansive soil and thickness effect of ESR crack. Four groups of samples with different thicknesses without adding rubber expansive soil and ESR are designed for the test. The results are as follows: (1)Water content of expansive soil during natural drying can be divided into three stages. The change of water content of ESR is more rapid. (2)There is obvious thickness effect in the cracking process of expansive soil. But the thickness effect of ESR is less obvious and the crack evolution is more uniform. (3)The total length and total area of cracks during cracking of expansive soils are seriously affected by thickness effect. Rubber reinforcement can restrain the length and area of cracks in expansive soils and reduce the difference between samples of different thicknesses. (4)The fractal dimension of crack development of expansive soil eventually ranges from 1.4 to 1.5. The change of fractal dimension of rubber-reinforced expansive soil with different thicknesses is closer. Expansive soil is multi-cracked and has unfavorable engineering characteristics,which poses a potential threat to projects in expansive soil areas such as slopes. Regenerated rubber reinforced expansive soil(ESR)has good improvement effect on dynamic,static and expansion characteristics of expansive soil. The crack evolution pattern of expansive soil can be affected by the thickness of soil sample. In this paper,rubber-reinforced expansive soil is used to explore the effect of rubber powder on crack evolution of expansive soil and thickness effect of ESR crack. Four groups of samples with different thicknesses without adding rubber expansive soil and ESR are designed for the test. The results are as follows: (1)Water content of expansive soil during natural drying can be divided into three stages. The change of water content of ESR is more rapid. (2)There is obvious thickness effect in the cracking process of expansive soil. But the thickness effect of ESR is less obvious and the crack evolution is more uniform. (3)The total length and total area of cracks during cracking of expansive soils are seriously affected by thickness effect. Rubber reinforcement can restrain the length and area of cracks in expansive soils and reduce the difference between samples of different thicknesses. (4)The fractal dimension of crack development of expansive soil eventually ranges from 1.4 to 1.5. The change of fractal dimension of rubber-reinforced expansive soil with different thicknesses is closer.
In arid and semi-arid loess regions, the water retention and permeability characteristics of compacted soil roadbed and loess overburden layer of landfill are all affected by temperature variation. To investigate the influence of temperature variations on the hydraulic properties of compacted loess in a full suction range, we measured the soil-water characteristic curve(SWCC) and hydraulic conductivity curve(HCC) of compacted loess in Yan'an city with different temperatures using the filter paper method and the self-developed soil column instantaneous profile method. The results show that in the high suction range of compacted loess SWCC, the volumetric water content of soil decreases as temperature increases. While in the low suction range, the temperature effect on water retention capacity of soil is not obvious. The HCC of loess in the low suction range is significantly affected by temperature. The higher the temperature, the stronger the permeability. As the suction increases or the volumetric water content decreases to a specific value, the influence of temperature on soil permeability can be ignored. Based on the results, the modified van Genuchten(VG)model is used as the prediction function of SWCC with the temperature effect taken into account. The parameters related to temperature are obtained by fitting the measured data. For the HCC, the 90 kPa matric suction is taken as the subsection point. The statistical model and power function are respectively used for the subsection prediction in the low suction range and high suction range. The prediction results are in good agreement with the measured data. In arid and semi-arid loess regions, the water retention and permeability characteristics of compacted soil roadbed and loess overburden layer of landfill are all affected by temperature variation. To investigate the influence of temperature variations on the hydraulic properties of compacted loess in a full suction range, we measured the soil-water characteristic curve(SWCC) and hydraulic conductivity curve(HCC) of compacted loess in Yan'an city with different temperatures using the filter paper method and the self-developed soil column instantaneous profile method. The results show that in the high suction range of compacted loess SWCC, the volumetric water content of soil decreases as temperature increases. While in the low suction range, the temperature effect on water retention capacity of soil is not obvious. The HCC of loess in the low suction range is significantly affected by temperature. The higher the temperature, the stronger the permeability. As the suction increases or the volumetric water content decreases to a specific value, the influence of temperature on soil permeability can be ignored. Based on the results, the modified van Genuchten(VG)model is used as the prediction function of SWCC with the temperature effect taken into account. The parameters related to temperature are obtained by fitting the measured data. For the HCC, the 90 kPa matric suction is taken as the subsection point. The statistical model and power function are respectively used for the subsection prediction in the low suction range and high suction range. The prediction results are in good agreement with the measured data.
The Hipparion red clay in Neogene in Northwest China has high clay content and is easy to crack due to drying. In order to study the effect of dry density on the cracking behavior of the compacted Hipparion red clay, a drying test is carried out by a self-made drying device, and the crack evolution process was analyzed by digital image correlation(DIC)method. The results show that: (1)cracking of samples with different initial dry densities occurs during drying process. The cracking process can be divided into four stages including crack initiation, crack propagation, crack self-healing and crack stabilization. The smaller the dry density, the denser and more uniform the desiccation crack network. (2)The change of strain field on the sample surface can better reflect the evolution process of desiccation crack. The blue compressive strain zone represents the shrinkage produced by water loss of sample. The red strain band represents the desiccation crack produced by tension. During drying process, the blue compressive strain area on the sample surface continues to expand and the width of the red tensile strain area decreases, indicating that the crack is pulled by the overall shrinkage of the sample and generate "self-healing" shrinkage. The smaller the dry density, the denser the tensile strain network, the higher the self-healing degree of desiccation crack. (3)The variation of the surface strain field of the sample shows that all cracks show self-healing phenomenon, but the main strain of main crack decreases the fast, and the self-healing phenomenon is the most significant, which plays a leading role in the self-healing of the crack. When the dry density of the sample is small, the larger the crack strain rate of all cracks, the higher the self-healing strain rate in the self-healing process, which indicates that the shrinkage of the sample due to water loss is more obvious. The Hipparion red clay in Neogene in Northwest China has high clay content and is easy to crack due to drying. In order to study the effect of dry density on the cracking behavior of the compacted Hipparion red clay, a drying test is carried out by a self-made drying device, and the crack evolution process was analyzed by digital image correlation(DIC)method. The results show that: (1)cracking of samples with different initial dry densities occurs during drying process. The cracking process can be divided into four stages including crack initiation, crack propagation, crack self-healing and crack stabilization. The smaller the dry density, the denser and more uniform the desiccation crack network. (2)The change of strain field on the sample surface can better reflect the evolution process of desiccation crack. The blue compressive strain zone represents the shrinkage produced by water loss of sample. The red strain band represents the desiccation crack produced by tension. During drying process, the blue compressive strain area on the sample surface continues to expand and the width of the red tensile strain area decreases, indicating that the crack is pulled by the overall shrinkage of the sample and generate "self-healing" shrinkage. The smaller the dry density, the denser the tensile strain network, the higher the self-healing degree of desiccation crack. (3)The variation of the surface strain field of the sample shows that all cracks show self-healing phenomenon, but the main strain of main crack decreases the fast, and the self-healing phenomenon is the most significant, which plays a leading role in the self-healing of the crack. When the dry density of the sample is small, the larger the crack strain rate of all cracks, the higher the self-healing strain rate in the self-healing process, which indicates that the shrinkage of the sample due to water loss is more obvious.
With the development of engineering activities such as exploitation of shale gas, waste water injection and carbon dioxide geological sequestration, the issue of induced seismicity due to the change of stress state of reservoir rocks has aroused wide attention, the investigation of failure process and acoustic emission characteristics is of great significance for the understanding of induced seismicity. A series of triaxial compression acoustic emission(AE)tests were conducted on shale, tight sandstone and dolomite, the spatial fracture geometry were obtained, and the failure process of different reservoir rocks were characterized by using acoustic emission monitoring method. The results suggested that: (1)the ratio of dilation stress to peak stress is highest for shale, followed by dolomite and tight sandstone, indicating that the breakdown of shale is dominated by brittle failure. (2)The rock fabric significantly affects fracture propagation and strength, shale typically has developed laminar structure, the compressive strength and failure types present strong anisotropy. Shear-tensile compound failure occurs and massive shear microfractures tend to form when bedding plane inclination is 0°. For shale samples with bedding plane inclinations of 30°and 60°, shear failure tends to occur during compression process. When bedding plane inclination increases to 90°, tensile fractures are likely to create. Tight sandstone sample produces a relative simple shear fracture, and dolomite sample develops two main shear fractures and multiple microfractures. (3)The acoustic emission characteristics of different reservoir rocks vary significantly during the failure process. The acoustic emission activities of shale samples begin to increase near the dilatation stress point, and the number and energy of acoustic emission events increase rapidly when the peak stress is reached. The tight sandstone sample only has a small amount of acoustic emission activity at the moment of breakdown. By comparison, the acoustic emission activities of dolomite samples are obvious in unstable fracture growth stage and post-peak stage, the amplitude, energy and number of events are relative large. Therefore, construction measures should be adjusted according to the microseismic monitoring results in practical engineering to avoid the brittle failure of shale when served as the cap rock and alleviate the induced earthquakes in the stimulation of dolomite formation. With the development of engineering activities such as exploitation of shale gas, waste water injection and carbon dioxide geological sequestration, the issue of induced seismicity due to the change of stress state of reservoir rocks has aroused wide attention, the investigation of failure process and acoustic emission characteristics is of great significance for the understanding of induced seismicity. A series of triaxial compression acoustic emission(AE)tests were conducted on shale, tight sandstone and dolomite, the spatial fracture geometry were obtained, and the failure process of different reservoir rocks were characterized by using acoustic emission monitoring method. The results suggested that: (1)the ratio of dilation stress to peak stress is highest for shale, followed by dolomite and tight sandstone, indicating that the breakdown of shale is dominated by brittle failure. (2)The rock fabric significantly affects fracture propagation and strength, shale typically has developed laminar structure, the compressive strength and failure types present strong anisotropy. Shear-tensile compound failure occurs and massive shear microfractures tend to form when bedding plane inclination is 0°. For shale samples with bedding plane inclinations of 30°and 60°, shear failure tends to occur during compression process. When bedding plane inclination increases to 90°, tensile fractures are likely to create. Tight sandstone sample produces a relative simple shear fracture, and dolomite sample develops two main shear fractures and multiple microfractures. (3)The acoustic emission characteristics of different reservoir rocks vary significantly during the failure process. The acoustic emission activities of shale samples begin to increase near the dilatation stress point, and the number and energy of acoustic emission events increase rapidly when the peak stress is reached. The tight sandstone sample only has a small amount of acoustic emission activity at the moment of breakdown. By comparison, the acoustic emission activities of dolomite samples are obvious in unstable fracture growth stage and post-peak stage, the amplitude, energy and number of events are relative large. Therefore, construction measures should be adjusted according to the microseismic monitoring results in practical engineering to avoid the brittle failure of shale when served as the cap rock and alleviate the induced earthquakes in the stimulation of dolomite formation.
The loess plateau possesses the largest loess area in the world. Its ecological environment is extremely fragile, with serious soil erosion and disasters. In recent years, as the key area of the Belt-Road initiative and western development, a series of major national strategies and engineering projects have started construction in this region. How to deal with the relationship between project construction and ecological environment protection, and keep the coordination between man and land is a significance issue of theoretical and practical approach. This paper proposes that the Natural-Based Solutions(NBS)should be used throughout the life cycle of major project construction in the Loess area. (1)In the site selection planning stage, we should make full use of and comply with nature, and arrange different types of major projects in suitable landform areas. At the same time, a sponge system can be constructed to turn rainwater, sewage and other wastewater into water resources for effective use. (2)In the design and construction stage, the nature should be fully protected and appropriately transformed. The "three controls"(water control, deformation control, and erosion control) measures should be adopted to achieve the "three defences"(settling defence, skid defence, erosion defence) disaster reduction goals. (3)In the project operation stage, it is necessary to build a 3S(Space-Sky-Surface) integrated multi-source coordinated observation system to fully grasp the project and the relevant regional ecological environment dynamically, take the initiative to prevent the occurrence of catastrophes. At the same time, through the combination of natural restoration and moderate artificial restoration, the natural environment disturbed by the construction of the project should be restored as soon as possible. The loess plateau possesses the largest loess area in the world. Its ecological environment is extremely fragile, with serious soil erosion and disasters. In recent years, as the key area of the Belt-Road initiative and western development, a series of major national strategies and engineering projects have started construction in this region. How to deal with the relationship between project construction and ecological environment protection, and keep the coordination between man and land is a significance issue of theoretical and practical approach. This paper proposes that the Natural-Based Solutions(NBS)should be used throughout the life cycle of major project construction in the Loess area. (1)In the site selection planning stage, we should make full use of and comply with nature, and arrange different types of major projects in suitable landform areas. At the same time, a sponge system can be constructed to turn rainwater, sewage and other wastewater into water resources for effective use. (2)In the design and construction stage, the nature should be fully protected and appropriately transformed. The "three controls"(water control, deformation control, and erosion control) measures should be adopted to achieve the "three defences"(settling defence, skid defence, erosion defence) disaster reduction goals. (3)In the project operation stage, it is necessary to build a 3S(Space-Sky-Surface) integrated multi-source coordinated observation system to fully grasp the project and the relevant regional ecological environment dynamically, take the initiative to prevent the occurrence of catastrophes. At the same time, through the combination of natural restoration and moderate artificial restoration, the natural environment disturbed by the construction of the project should be restored as soon as possible.
Based on the observation of the core of a well in the shale gas field in southern Sichuan at the mesoscale and the construction of a two-dimensional fracture model, displacement discontinuity method was used to simulate the physical and mechanical process of the interaction between hydraulic fractures and natural fractures in deep shale hydraulic fracturing. The influence of principal stress, stress difference and fracturing fluid injection rate on fracture propagation were discussed. The results show that under high stress difference, the length of the fracture decreases, the average width of the fracture increases and the increasing of fracture average width due to the increase of injection rate becomes limited. New fractures prevail in the increase of fracture length with the injection rate increases, so as to improve the activation of natural fractures, but the effect is limited. The generation of shear fracture is more affected by principal stress and injection rate, and its length decreases significantly under high stress difference. The fracture length under low injection rate is gradually larger than that under high injection rate during the fracturing process, under the condition of lower stress difference and the same injection volume. Fracture propagation rate decreases under high stress difference and generating more new fractures due to increasing the injection rate becomes limited. The modeling results based on the microscope observation meet the actual site better, and provide a reference for the design and construction of deep hydraulic fracturing in shale gas reservoir. Based on the observation of the core of a well in the shale gas field in southern Sichuan at the mesoscale and the construction of a two-dimensional fracture model, displacement discontinuity method was used to simulate the physical and mechanical process of the interaction between hydraulic fractures and natural fractures in deep shale hydraulic fracturing. The influence of principal stress, stress difference and fracturing fluid injection rate on fracture propagation were discussed. The results show that under high stress difference, the length of the fracture decreases, the average width of the fracture increases and the increasing of fracture average width due to the increase of injection rate becomes limited. New fractures prevail in the increase of fracture length with the injection rate increases, so as to improve the activation of natural fractures, but the effect is limited. The generation of shear fracture is more affected by principal stress and injection rate, and its length decreases significantly under high stress difference. The fracture length under low injection rate is gradually larger than that under high injection rate during the fracturing process, under the condition of lower stress difference and the same injection volume. Fracture propagation rate decreases under high stress difference and generating more new fractures due to increasing the injection rate becomes limited. The modeling results based on the microscope observation meet the actual site better, and provide a reference for the design and construction of deep hydraulic fracturing in shale gas reservoir.
The engineering characteristic of round gravel soil is very special. We usually use elastic subgrade reaction method to design excavation engineering. However, the elastic subgrade calculation mode of excavation engineering in round gravel soil is not clear. This paper uses the setting in Guangxi University Station deep excavation of Nanning rail transit line 1. It carries out a centrifuge test to simulate the deep excavation engineering in gravel area, and also makes a Plaxis numerical simulating for comparation. We obtain the deformation of retaining wall and distribution of lateral earth pressure separately. Based on the data, also according to the principle of elastic subgrade reaction method, we futher analyze and examine the elastic subgrade calculation mode in active and passive areas of the deep excavation retaining wall. The results show that the magnitude of soil pressure in active area is related to the wall deformation. The necessary wall deformation value S/h to reach active soil pressure is about 0.1%. And the soil pressure distribution shape in active area is triangle on the top and rectangle on the bottom, which coincide the mode in elastic subgrade reaction method. And the subgrade horizontal coefficient 'K' in passive area increases approximately linearly with the depth. The elastic subgrade mode in passive area is similar to the 'm' method. The engineering characteristic of round gravel soil is very special. We usually use elastic subgrade reaction method to design excavation engineering. However, the elastic subgrade calculation mode of excavation engineering in round gravel soil is not clear. This paper uses the setting in Guangxi University Station deep excavation of Nanning rail transit line 1. It carries out a centrifuge test to simulate the deep excavation engineering in gravel area, and also makes a Plaxis numerical simulating for comparation. We obtain the deformation of retaining wall and distribution of lateral earth pressure separately. Based on the data, also according to the principle of elastic subgrade reaction method, we futher analyze and examine the elastic subgrade calculation mode in active and passive areas of the deep excavation retaining wall. The results show that the magnitude of soil pressure in active area is related to the wall deformation. The necessary wall deformation value S/h to reach active soil pressure is about 0.1%. And the soil pressure distribution shape in active area is triangle on the top and rectangle on the bottom, which coincide the mode in elastic subgrade reaction method. And the subgrade horizontal coefficient 'K' in passive area increases approximately linearly with the depth. The elastic subgrade mode in passive area is similar to the 'm' method.
This paper studies the mechanical properties and failure mechanism of the soft and hard interbedded rock mass in the subway tunnel. It is based on the acquisition of physical and mechanical parameters of Urumqi mudstone and sandstone. It uses the microscopic parameter to calibrate the physical and mechanical parameters of the interbedded rock mass. It uses the particle flow numerical simulation uniaxial compression test to analyze the interbedded rock mass layer thickness, the layer thickness ratio, and the inclination angle of the interbedded rock mass. The analysis results show that as the layer thickness of the interbedded rock mass increases, its uniaxial compressive strength decreases, the number of cracks also decreases, and the crack development speed increases. As the layer thickness ratio of the interbedded rock mass increases, its uniaxial compressive strength is continuously decreasing. When the layer thickness ratio is greater than 1, the uniaxial compressive strength is relatively stable, and the crack development trend is faster when the layer thickness ratio is less than 0.6. The crack development trend is slower when the layer thickness ratio is greater than 0.6. The increase of the inclination of the interbedded rock mass makes the uniaxial compressive strength show a U-shaped change trend. The uniaxial compressive strength is the lowest at the inclination 40°, the number of cracks is the largest at the inclination 90°, and the development trend is slowest. According to the orthogonal test analysis, the layer thickness ratio is the most sensitive to the uniaxial compressive strength. The optimal combination is obtained by analysis as follows: layer thickness 6 cm, layer thickness ratio 0.1, and rock layer inclination angle 0°. This paper studies the mechanical properties and failure mechanism of the soft and hard interbedded rock mass in the subway tunnel. It is based on the acquisition of physical and mechanical parameters of Urumqi mudstone and sandstone. It uses the microscopic parameter to calibrate the physical and mechanical parameters of the interbedded rock mass. It uses the particle flow numerical simulation uniaxial compression test to analyze the interbedded rock mass layer thickness, the layer thickness ratio, and the inclination angle of the interbedded rock mass. The analysis results show that as the layer thickness of the interbedded rock mass increases, its uniaxial compressive strength decreases, the number of cracks also decreases, and the crack development speed increases. As the layer thickness ratio of the interbedded rock mass increases, its uniaxial compressive strength is continuously decreasing. When the layer thickness ratio is greater than 1, the uniaxial compressive strength is relatively stable, and the crack development trend is faster when the layer thickness ratio is less than 0.6. The crack development trend is slower when the layer thickness ratio is greater than 0.6. The increase of the inclination of the interbedded rock mass makes the uniaxial compressive strength show a U-shaped change trend. The uniaxial compressive strength is the lowest at the inclination 40°, the number of cracks is the largest at the inclination 90°, and the development trend is slowest. According to the orthogonal test analysis, the layer thickness ratio is the most sensitive to the uniaxial compressive strength. The optimal combination is obtained by analysis as follows: layer thickness 6 cm, layer thickness ratio 0.1, and rock layer inclination angle 0°.
This paper aims to reduce the ground surface settlement and control the construction risk of excavating shallow buried tunnel in aeolian sandy loess. It adopts the self-drilling pipe roof pre-reinforcement technology to control the surrounding rock deformation. The mechanical effect and deformation features is predicted by numerical simulation method before the excavation. Then, the mechanical parameters of the intrusion section were obtained by inversion calculation method using deformation monitoring data, which provides the reference for whole-process numerical simulation and comprehensive deformation control. The simulation finds that the maximum ground settlement at the intrusion section is 11.4 mm, the maximum vault sinking is 30.4 mm, and the maximum horizontal convergence is 48.5 mm. The self-drilling pipe roof pre-reinforcement technology can provide continuous longitudinal support, withstand the pressure of invading rock, and control surface settlement. The radial self-drilling anchor and pipe roof, along with the annular steel arch and feet-lock anchor, constitute the active and passive protection system for controlling rock deformation, which is proven to be an effective system to solve the problem of pre-reinforcement for the weak surrounding rock of the tunnel. This paper aims to reduce the ground surface settlement and control the construction risk of excavating shallow buried tunnel in aeolian sandy loess. It adopts the self-drilling pipe roof pre-reinforcement technology to control the surrounding rock deformation. The mechanical effect and deformation features is predicted by numerical simulation method before the excavation. Then, the mechanical parameters of the intrusion section were obtained by inversion calculation method using deformation monitoring data, which provides the reference for whole-process numerical simulation and comprehensive deformation control. The simulation finds that the maximum ground settlement at the intrusion section is 11.4 mm, the maximum vault sinking is 30.4 mm, and the maximum horizontal convergence is 48.5 mm. The self-drilling pipe roof pre-reinforcement technology can provide continuous longitudinal support, withstand the pressure of invading rock, and control surface settlement. The radial self-drilling anchor and pipe roof, along with the annular steel arch and feet-lock anchor, constitute the active and passive protection system for controlling rock deformation, which is proven to be an effective system to solve the problem of pre-reinforcement for the weak surrounding rock of the tunnel.
This paper aims to clarify the intrinsic relationship between the deformation behaviors of dynamic compaction gravel columns and the stability of the embankment under the load of the embankment. It examines an example of embankment failure of a high-speed railway station located in mountainous type soft soil. It is based on the field measured data and the three-dimensional numerical analysis model. It studies the bulging deformation and lateral deformation of the gravel columns. It further defines the bulging ratio and maximum lateral deformation of the gravel columns to describe their deformation characteristics. The results show that the gravel columns at different positions under the embankment have different degrees of bulging deformation and lateral bending deformation. The bulging deformation is mainly composed of the compression bulging caused by embankment load and the shear bulging caused by lateral sliding of embankment. The maximum bulging deformation area is concentrated in the range of 1~2 times of the pile diameter from the tip of pile. Especially, the bulging ratio of the gravel column near the entrance of the potential slip surface of the composite foundation is the largest(0.75%), which is about 1.5 times the bulging ratio of the gravel columns at the center of the embankment. The bulging deformation is mainly due to sliding shear. The growing trend of the maximum lateral deformation for dynamic compaction of gravel columns at different locations along the centerline of the embankment is approximately the three segment line mode. The lateral deformation of gravel columns begins to increase sharply from the 17th gravel column, which indicates that the 17th and its adjacent gravel columns are the key components for controlling the lateral deformation and stability of the embankment. The reason for the occurrence of several cracks in the embankment filling process may be caused by the shear failure of the dynamic compaction of gravel columns. Additional reinforcement measures should be adopted to ensure the stability of the filling embankment when granular columns are used to treat the mountainous type soft soil. This paper aims to clarify the intrinsic relationship between the deformation behaviors of dynamic compaction gravel columns and the stability of the embankment under the load of the embankment. It examines an example of embankment failure of a high-speed railway station located in mountainous type soft soil. It is based on the field measured data and the three-dimensional numerical analysis model. It studies the bulging deformation and lateral deformation of the gravel columns. It further defines the bulging ratio and maximum lateral deformation of the gravel columns to describe their deformation characteristics. The results show that the gravel columns at different positions under the embankment have different degrees of bulging deformation and lateral bending deformation. The bulging deformation is mainly composed of the compression bulging caused by embankment load and the shear bulging caused by lateral sliding of embankment. The maximum bulging deformation area is concentrated in the range of 1~2 times of the pile diameter from the tip of pile. Especially, the bulging ratio of the gravel column near the entrance of the potential slip surface of the composite foundation is the largest(0.75%), which is about 1.5 times the bulging ratio of the gravel columns at the center of the embankment. The bulging deformation is mainly due to sliding shear. The growing trend of the maximum lateral deformation for dynamic compaction of gravel columns at different locations along the centerline of the embankment is approximately the three segment line mode. The lateral deformation of gravel columns begins to increase sharply from the 17th gravel column, which indicates that the 17th and its adjacent gravel columns are the key components for controlling the lateral deformation and stability of the embankment. The reason for the occurrence of several cracks in the embankment filling process may be caused by the shear failure of the dynamic compaction of gravel columns. Additional reinforcement measures should be adopted to ensure the stability of the filling embankment when granular columns are used to treat the mountainous type soft soil.
The instability of tunnel face is quite common in weak surrounding rock tunnels. The advanced rock bolts are effective supporting structure for the tunnel face. According to the conventional installation scheme, the advanced rock bolts have to be cut off and shortened with the excavation of tunnel, and their supporting effect can become weaker and weaker. The rock bolts can not be reinstalled until their length is cut to a predetermined value. The discontinuous installing of rock bolts leads to significant fluctuations in the supporting effect. In order to solve this problem, a continuous-alternative design scheme is proposed for advanced rock bolts on tunnel face. In the new scheme, the rock bolts on tunnel face are divided into several parts equally. The rock bolts are successively installed during the tunnel advancing process, so that the rock bolts supporting state can be more uniform and stable. In order to evaluate the feasibility of the new scheme systematically, a case analysis is carried out based on the Muzhailing Tunnel Project of the Weiwu Expressway. First, both conventional discontinuous scheme and continuous-alternative scheme are designed under the condition of the same amount of rock bolt. The finite difference software FLAC3D is used to establish numerical model. In this way, the deformations of tunnel face and ground are compared for two different design schemes. The results show that the supporting effect of rock bolts is greatly influenced by the changes of the supporting states in the conventional discontinuous installation scheme. The continuous-alternative installation scheme can contribute a stable supporting effect on tunnel face without increasing the cost. Moreover, the supporting effect is much higher than the minimum level of conventional installation scheme. This study provides a new method for the arrangement of the advanced rock bolts on tunnel face. The instability of tunnel face is quite common in weak surrounding rock tunnels. The advanced rock bolts are effective supporting structure for the tunnel face. According to the conventional installation scheme, the advanced rock bolts have to be cut off and shortened with the excavation of tunnel, and their supporting effect can become weaker and weaker. The rock bolts can not be reinstalled until their length is cut to a predetermined value. The discontinuous installing of rock bolts leads to significant fluctuations in the supporting effect. In order to solve this problem, a continuous-alternative design scheme is proposed for advanced rock bolts on tunnel face. In the new scheme, the rock bolts on tunnel face are divided into several parts equally. The rock bolts are successively installed during the tunnel advancing process, so that the rock bolts supporting state can be more uniform and stable. In order to evaluate the feasibility of the new scheme systematically, a case analysis is carried out based on the Muzhailing Tunnel Project of the Weiwu Expressway. First, both conventional discontinuous scheme and continuous-alternative scheme are designed under the condition of the same amount of rock bolt. The finite difference software FLAC3D is used to establish numerical model. In this way, the deformations of tunnel face and ground are compared for two different design schemes. The results show that the supporting effect of rock bolts is greatly influenced by the changes of the supporting states in the conventional discontinuous installation scheme. The continuous-alternative installation scheme can contribute a stable supporting effect on tunnel face without increasing the cost. Moreover, the supporting effect is much higher than the minimum level of conventional installation scheme. This study provides a new method for the arrangement of the advanced rock bolts on tunnel face.
Understanding the flow behavior in fractured rocks is of great importance for the development and construction of deep geological engineering projects. Using temperature-depth profiles in the subsurface to characterize groundwater flow is becoming increasingly popular. Not only because the heat transport process is sensitive to groundwater flow(flow rates,preferential flow paths et al.),but also the temperature can be easily measured by Fiber-Optic Distributed Temperature Sensing(FO-DTS)with low costs. In this study,FO-DTS is used to conduct fully distributed space-time measurements of groundwater temperature in two boreholes. These boreholes(BSQ02 and BSQ03)locate at Xinchang Site in Gansu Province,where is the first underground laboratory site in China. The borehole temperature profiles are measured with FO-DTS under pumping conditions to find potential flow path through fractures. Through analyzing these profiles,location of hydraulically active fractures has been determined to be distributed around 40 m depth in BSQ02,and the main flow path is considered to be fracture B2-2. In order to further investigate the groundwater flow fields,measured temperature profiles are then interpreted with inverse numerical modeling of flow-heat transfer processes. Average groundwater flow rate in borehole under pumping condition is estimated to be 0.01 m·s-1 from inverse models. The temperature of groundwater flowing into the borehole through fracture B2-2 is around 13.65 ℃,which is estimated to be 0.7 ℃lower than the original groundwater(14.35 ℃)in borehole. The velocity of groundwater through B2-2 was estimated to be 1×10-5 m·s-1. This study succeeds in characterizing groundwater flow rates and flow paths using temperature data based on FO-DTS technology,which can be a promising method for understanding groundwater flow in fractured rocks. Understanding the flow behavior in fractured rocks is of great importance for the development and construction of deep geological engineering projects. Using temperature-depth profiles in the subsurface to characterize groundwater flow is becoming increasingly popular. Not only because the heat transport process is sensitive to groundwater flow(flow rates,preferential flow paths et al.),but also the temperature can be easily measured by Fiber-Optic Distributed Temperature Sensing(FO-DTS)with low costs. In this study,FO-DTS is used to conduct fully distributed space-time measurements of groundwater temperature in two boreholes. These boreholes(BSQ02 and BSQ03)locate at Xinchang Site in Gansu Province,where is the first underground laboratory site in China. The borehole temperature profiles are measured with FO-DTS under pumping conditions to find potential flow path through fractures. Through analyzing these profiles,location of hydraulically active fractures has been determined to be distributed around 40 m depth in BSQ02,and the main flow path is considered to be fracture B2-2. In order to further investigate the groundwater flow fields,measured temperature profiles are then interpreted with inverse numerical modeling of flow-heat transfer processes. Average groundwater flow rate in borehole under pumping condition is estimated to be 0.01 m·s-1 from inverse models. The temperature of groundwater flowing into the borehole through fracture B2-2 is around 13.65 ℃,which is estimated to be 0.7 ℃lower than the original groundwater(14.35 ℃)in borehole. The velocity of groundwater through B2-2 was estimated to be 1×10-5 m·s-1. This study succeeds in characterizing groundwater flow rates and flow paths using temperature data based on FO-DTS technology,which can be a promising method for understanding groundwater flow in fractured rocks.
In certain cases,residual soils appear to have high shear strength. But as they reach saturation,their shear strength reduces significantly to zero or very small. The measured data of the Shigu Mountain west passage project in Xiamen shows that the precipitation infiltration causes a significant increase in the deformation of the retaining piles of the foundation pit in the residual soil. This paper aims to explore the mechanism of precipitation intensification of the foundation pit deformation in unsaturated residual soil. It develops a numerical model in FE software PLAXIS and studies the responses of internal force of structure and stress stage of soil. The results show that rainfall infiltration can significantly increase the deformation of foundation pit in unsaturated residual soil and reduce the stability of the foundation pit. The reason is that rainfall infiltration increases the soil saturation,reduces the matrix suction. This leads to a reduction in shear strength. At the same time,rainfall infiltration leads to the increase of active earth pressure. Compared with the low permeability soil,the strength of the foundation pit bearing stratum in the residual soil with high permeability is more affected by rainfall infiltration. The stress path of the soil behind the wall shows that the shear force of the soil remains basically the same during the rainfall process,and the deformation of the foundation pit increases slightly. The dredging excavation after the rainfall makes the soil behind the pile reach the critical shear strength,which leads to the sharp increase of the deformation of the foundation pit. In certain cases,residual soils appear to have high shear strength. But as they reach saturation,their shear strength reduces significantly to zero or very small. The measured data of the Shigu Mountain west passage project in Xiamen shows that the precipitation infiltration causes a significant increase in the deformation of the retaining piles of the foundation pit in the residual soil. This paper aims to explore the mechanism of precipitation intensification of the foundation pit deformation in unsaturated residual soil. It develops a numerical model in FE software PLAXIS and studies the responses of internal force of structure and stress stage of soil. The results show that rainfall infiltration can significantly increase the deformation of foundation pit in unsaturated residual soil and reduce the stability of the foundation pit. The reason is that rainfall infiltration increases the soil saturation,reduces the matrix suction. This leads to a reduction in shear strength. At the same time,rainfall infiltration leads to the increase of active earth pressure. Compared with the low permeability soil,the strength of the foundation pit bearing stratum in the residual soil with high permeability is more affected by rainfall infiltration. The stress path of the soil behind the wall shows that the shear force of the soil remains basically the same during the rainfall process,and the deformation of the foundation pit increases slightly. The dredging excavation after the rainfall makes the soil behind the pile reach the critical shear strength,which leads to the sharp increase of the deformation of the foundation pit.
The 3D information model is the foundation of the whole life cycle management of the engineering projects. However,at present,the 3D geological model and the 3D information model of the projects are usually difficult to be unified due to the differences of data structure. Most of models only can be used for "visualization". They are difficult for "simulation" and "analyzation". In addition,due to the complexity of geological structures,a lot of simplifications are usually used in 3D geological modeling. Based on the advanced 3D modeling technology,this paper proposes a modeling method of 3D geological model and 3D model of building structure,realizing fast and refined modeling of 3D model. The established models are unified under standardized 3D model files such as*.stl,*.obj and*.igs,which can be conveniently used for 3D model visualization,analyzation and subsequent numerical simulation in different scenarios. For the construction of large hydropower projects,the framework of hydropower project information model(HIM) is proposed and applied to Suofengying Hydropower Project. The fromwork realizes the fusion and information of the BIM of the dam and the refined 3D geological model of the four landslides. The studies in this paper are of great significance for the realization of information management,stability analysis,potential disaster assessment and prediction of hydropower projects. The 3D information model is the foundation of the whole life cycle management of the engineering projects. However,at present,the 3D geological model and the 3D information model of the projects are usually difficult to be unified due to the differences of data structure. Most of models only can be used for "visualization". They are difficult for "simulation" and "analyzation". In addition,due to the complexity of geological structures,a lot of simplifications are usually used in 3D geological modeling. Based on the advanced 3D modeling technology,this paper proposes a modeling method of 3D geological model and 3D model of building structure,realizing fast and refined modeling of 3D model. The established models are unified under standardized 3D model files such as*.stl,*.obj and*.igs,which can be conveniently used for 3D model visualization,analyzation and subsequent numerical simulation in different scenarios. For the construction of large hydropower projects,the framework of hydropower project information model(HIM) is proposed and applied to Suofengying Hydropower Project. The fromwork realizes the fusion and information of the BIM of the dam and the refined 3D geological model of the four landslides. The studies in this paper are of great significance for the realization of information management,stability analysis,potential disaster assessment and prediction of hydropower projects.
In this paper,the overburden karst soil cave is taken as the research object. Through modeling and analysis,the mathematical model of the collapse caused by vacuum erosion caused by groundwater sudden drop is established. The stability coefficient expression of the excavated cave is obtained according to the Boyle's law,and the calculation formula of the negative pressure of the excavated cave is derived. The influence of the initial groundwater level,the depth of water level and the thickness of soil overburden on the stability coefficient of subsidence is analyzed by numerical examples,and the internal influence law is discussed. The results show that the collapse stability coefficient K is inversely proportional to the negative pressure ΔP of soil cave under the condition of underground water sag. The size and position of initial water level h' and the depth of water level drop ΔH are related to the formation of negative pressure ΔP of soil cavity(vacuum) and the change of stability coefficient K of soil cavity collapse. When the initial water level is h' and the depth of water level is ΔH,the thickness of overburden has an obvious influence on the stability coefficient of collapse. When the initial water level is medium high and the depth of water level is medium high,the stability coefficient of collapse is positively correlated with the thickness of overburden. In this paper,the overburden karst soil cave is taken as the research object. Through modeling and analysis,the mathematical model of the collapse caused by vacuum erosion caused by groundwater sudden drop is established. The stability coefficient expression of the excavated cave is obtained according to the Boyle's law,and the calculation formula of the negative pressure of the excavated cave is derived. The influence of the initial groundwater level,the depth of water level and the thickness of soil overburden on the stability coefficient of subsidence is analyzed by numerical examples,and the internal influence law is discussed. The results show that the collapse stability coefficient K is inversely proportional to the negative pressure ΔP of soil cave under the condition of underground water sag. The size and position of initial water level h' and the depth of water level drop ΔH are related to the formation of negative pressure ΔP of soil cavity(vacuum) and the change of stability coefficient K of soil cavity collapse. When the initial water level is h' and the depth of water level is ΔH,the thickness of overburden has an obvious influence on the stability coefficient of collapse. When the initial water level is medium high and the depth of water level is medium high,the stability coefficient of collapse is positively correlated with the thickness of overburden.
Failure of a hanging cavity cliff is a rock fall geological hazard,which affects safety of road projects and housing environment. Therefore,it is critical to understand its stability and factors controlling its failures. We proposed an approach for assessing the rock mass stability of a hanging cavity cliff based on an assumption of a linear triangle distribution of the tensile stress along the wall. First,we calculated the tensile moment based on the moment balance among tensile and compression forces and in turn derived the total tensile force on the wall surface. Then we obtained the maximum tensile stress by using principle of the linear distribution of tensile stress along the wall. The failure of a hanging cavity cliff attributes to the tensile failure of rock at the top of the cliff when the maximum tensile stress exceeds the tensile strength of rock. To assess the stability of a hanging cliff,we calculated the safety factor as the ratio of the tensile strength and the maximum tensile stress. The result of the proposed approach is different from the solution for a cantilever beam from mechanics of elasticity,which demonstrates potential limitations of mechanics of elasticity in analysis of an overhanging cliff. We used a case study to assess factors that determined the magnitude of the tensile stress in a hanging cliff,including the thickness(height) H of the hanging cliff body,unit weight of rock(γ),and length(depth)(L) of the hanging cavity. The results show that the maximum resulting tensile stress is proportional to L and φ,but inversely proportional to H. A deeper/longer wall tends to have a greater possibility of tensile failure than a shallower/shorter one. As the tensile stress decreases when the wall becomes thicker,the shear failure becomes more likely than the tensile failure for a thicker wall. We also made recommendations for future studies and its applications in engineering projects and prevention of geological hazards. Failure of a hanging cavity cliff is a rock fall geological hazard,which affects safety of road projects and housing environment. Therefore,it is critical to understand its stability and factors controlling its failures. We proposed an approach for assessing the rock mass stability of a hanging cavity cliff based on an assumption of a linear triangle distribution of the tensile stress along the wall. First,we calculated the tensile moment based on the moment balance among tensile and compression forces and in turn derived the total tensile force on the wall surface. Then we obtained the maximum tensile stress by using principle of the linear distribution of tensile stress along the wall. The failure of a hanging cavity cliff attributes to the tensile failure of rock at the top of the cliff when the maximum tensile stress exceeds the tensile strength of rock. To assess the stability of a hanging cliff,we calculated the safety factor as the ratio of the tensile strength and the maximum tensile stress. The result of the proposed approach is different from the solution for a cantilever beam from mechanics of elasticity,which demonstrates potential limitations of mechanics of elasticity in analysis of an overhanging cliff. We used a case study to assess factors that determined the magnitude of the tensile stress in a hanging cliff,including the thickness(height) H of the hanging cliff body,unit weight of rock(γ),and length(depth)(L) of the hanging cavity. The results show that the maximum resulting tensile stress is proportional to L and φ,but inversely proportional to H. A deeper/longer wall tends to have a greater possibility of tensile failure than a shallower/shorter one. As the tensile stress decreases when the wall becomes thicker,the shear failure becomes more likely than the tensile failure for a thicker wall. We also made recommendations for future studies and its applications in engineering projects and prevention of geological hazards.
Taihang Mountain Grand Canyon is located in Huguan County,Shanxi Province,which is a part of the South Taihang Mountain in China. After hundreds of millions of years,it has formed a large alpine canyon landscape system represented by canyon groups,peak forest stone pillars,river waterfalls,caves and so on,which has now been built into a "5A" Scenic spot and has the title of "National Geopark" in China. Meantime,the Taihang Mountain Grand Canyon is situated at the surface transition zone between the second and third topography ladders in China. Due to strong tectonic activities and serious surface erosion,as well as unique climate changes in this area,a series of collapse disasters occur frequently,damaging roads and facilities,which often endanger the safety of residents and tourists. Through geological disaster investigation,318 collapse disasters have been identified in the grand canyon area,which are dominated by high-level small-scale rock collapses. They are mainly distributed between 700 and 1100 meters above sea level,with an average drop of about 120 meters and a maximum of more than 300 meters. These collapses are mostly developed in areas where faults and weak rock strata are dense,and are distributed in bands along both sides of the canyon,showing the characteristics of cluster,multiple occurrence and recurrence when rainfall is concentrated in this canyon. Based on the analysis of the disaster-pregnant environment for the collapse of the scenic spot,it is found that under the action of the major disaster factors such as topographic landform,stratigraphic lithology,rock mass structure,surface agency and human activities,the collapse disaster-forming patterns consist of steep collapse zone,ladder-shaped collapsed rock chain,catastrophic collapse and sliding zone,and waterfront collapse zone. Finally,this paper summarizes four collapse types including collapse rolling stone type,collapse chain type,fragmentation type and falling rock surge type,and then puts on the related prevention and control suggestions for these disaster types. This study can provide reference and support for geological disaster prevention and mitigation in canyon areas,development and construction of scenic spots in Taihang Mountain,geological environmental protection and community safety. Taihang Mountain Grand Canyon is located in Huguan County,Shanxi Province,which is a part of the South Taihang Mountain in China. After hundreds of millions of years,it has formed a large alpine canyon landscape system represented by canyon groups,peak forest stone pillars,river waterfalls,caves and so on,which has now been built into a "5A" Scenic spot and has the title of "National Geopark" in China. Meantime,the Taihang Mountain Grand Canyon is situated at the surface transition zone between the second and third topography ladders in China. Due to strong tectonic activities and serious surface erosion,as well as unique climate changes in this area,a series of collapse disasters occur frequently,damaging roads and facilities,which often endanger the safety of residents and tourists. Through geological disaster investigation,318 collapse disasters have been identified in the grand canyon area,which are dominated by high-level small-scale rock collapses. They are mainly distributed between 700 and 1100 meters above sea level,with an average drop of about 120 meters and a maximum of more than 300 meters. These collapses are mostly developed in areas where faults and weak rock strata are dense,and are distributed in bands along both sides of the canyon,showing the characteristics of cluster,multiple occurrence and recurrence when rainfall is concentrated in this canyon. Based on the analysis of the disaster-pregnant environment for the collapse of the scenic spot,it is found that under the action of the major disaster factors such as topographic landform,stratigraphic lithology,rock mass structure,surface agency and human activities,the collapse disaster-forming patterns consist of steep collapse zone,ladder-shaped collapsed rock chain,catastrophic collapse and sliding zone,and waterfront collapse zone. Finally,this paper summarizes four collapse types including collapse rolling stone type,collapse chain type,fragmentation type and falling rock surge type,and then puts on the related prevention and control suggestions for these disaster types. This study can provide reference and support for geological disaster prevention and mitigation in canyon areas,development and construction of scenic spots in Taihang Mountain,geological environmental protection and community safety.
At mountainous tourist attractions,casualties caused by block instability and slope instability continue to occur,which seriously affects the safe operation of tourist attractions. In order to ensure tourism safety,this paper takes the import and export slope of a mountain tourist scenic spot in Zhejiang as the research background. It scans the slope rock mass with 3D laser scanner,combines the rocky slope engineering block stability evaluation and visualization software(CPG program) already developed based on coordinate projection method to analyze the rocky slope block stability. It uses the FLAC3D numerical analysis method to analyze the overall stability of the rock slope,and finally uses the finite element to analyze the proposed corresponding preventive measures. The research results show that the stability coefficient of some typical blocks is lower than the safety factor of 1.2. Due to the influence of weak interlayer,there is a large shear stress and transverse stress at the foot of the slope. The maximum tensile stress area of the steel trestle is small,and the stress value is about 1 MPa. On this basis,a number of comprehensive measures such as block removal,drainage,anchor spraying and avoidance are proposed,forming a prevention and control countermeasure with the characteristics of mountainous tourist scenery. At mountainous tourist attractions,casualties caused by block instability and slope instability continue to occur,which seriously affects the safe operation of tourist attractions. In order to ensure tourism safety,this paper takes the import and export slope of a mountain tourist scenic spot in Zhejiang as the research background. It scans the slope rock mass with 3D laser scanner,combines the rocky slope engineering block stability evaluation and visualization software(CPG program) already developed based on coordinate projection method to analyze the rocky slope block stability. It uses the FLAC3D numerical analysis method to analyze the overall stability of the rock slope,and finally uses the finite element to analyze the proposed corresponding preventive measures. The research results show that the stability coefficient of some typical blocks is lower than the safety factor of 1.2. Due to the influence of weak interlayer,there is a large shear stress and transverse stress at the foot of the slope. The maximum tensile stress area of the steel trestle is small,and the stress value is about 1 MPa. On this basis,a number of comprehensive measures such as block removal,drainage,anchor spraying and avoidance are proposed,forming a prevention and control countermeasure with the characteristics of mountainous tourist scenery.
During the 2018 rainy season,a huge 7~8 km long earth fissure suddenly appeared on the surface of the Kenya Rift Valley,east African. The fissure directly caused the destruction of the B3 highway(this is called B3 earth fissure),the main road connecting the east and west regions of Kenya. However,the "Nairobi-Malaba Standard Gauge Railway",a key project of China's "One Belt One Road" initiative,is only a few kilometers away from this earth fissure. Scientific explanation of the mechanism and dynamic process of earth fissures is an important guarantee for the safe operation of railways. This paper focuses on the study of the spatial distribution and formation mechanism of the B3 earth fissure. The spatial position of the earth fissures is obtained by using satellite image interpretation and field surveys. The high-resolution numerical value of the fissure zone is established using structure for motion technology. Detailed measurements are performed on this basis. Field investigations reveal that the B3 earth fissure is developed on the F4 active fault at the eastern boundary of the Kenya rift,and its spatial position is controlled by the F4 fault. The vertical profile of the earth fissure reveals that the Holocene sediments are obviously faulted and there are multiple fractured planes running through it. The pyroclastic rock layers under the earth fissures have obvious tensile cracks. The cracks become channels for surface water to seep downward during the rainy period,and cause the loose sediments on the shallow surface to migrate downwards. The north-south active faults system developed in the Kenya Rift Valley is the main channel for groundwater flow during the rainy period. These processes cause groundwater runoff to continuously erode the subsurface layer,surface materials to be transported downwards,which results in large-scale surface cracking and collapse. As a result,earth fissures in the Kenya Rift Valley are controlled by the spatial distribution of active faults in this area. During the 2018 rainy season,a huge 7~8 km long earth fissure suddenly appeared on the surface of the Kenya Rift Valley,east African. The fissure directly caused the destruction of the B3 highway(this is called B3 earth fissure),the main road connecting the east and west regions of Kenya. However,the "Nairobi-Malaba Standard Gauge Railway",a key project of China's "One Belt One Road" initiative,is only a few kilometers away from this earth fissure. Scientific explanation of the mechanism and dynamic process of earth fissures is an important guarantee for the safe operation of railways. This paper focuses on the study of the spatial distribution and formation mechanism of the B3 earth fissure. The spatial position of the earth fissures is obtained by using satellite image interpretation and field surveys. The high-resolution numerical value of the fissure zone is established using structure for motion technology. Detailed measurements are performed on this basis. Field investigations reveal that the B3 earth fissure is developed on the F4 active fault at the eastern boundary of the Kenya rift,and its spatial position is controlled by the F4 fault. The vertical profile of the earth fissure reveals that the Holocene sediments are obviously faulted and there are multiple fractured planes running through it. The pyroclastic rock layers under the earth fissures have obvious tensile cracks. The cracks become channels for surface water to seep downward during the rainy period,and cause the loose sediments on the shallow surface to migrate downwards. The north-south active faults system developed in the Kenya Rift Valley is the main channel for groundwater flow during the rainy period. These processes cause groundwater runoff to continuously erode the subsurface layer,surface materials to be transported downwards,which results in large-scale surface cracking and collapse. As a result,earth fissures in the Kenya Rift Valley are controlled by the spatial distribution of active faults in this area.
According to physical model tests,we discuss the dynamic process and accumulation characteristics of landslide dams formed under three different slope features including uniform slope(slope compositions mixed uniformly,parallel slope(soil layer surface parallel to the sliding surface) and intersecting slope(soil layer surface intersecting with the sliding surface). The material distribution and morphological characteristics of the landslide dams are studied by sub-regional sampling and 3D scanning technology. The results demonstrate that the accumulation characteristics of landslide dam are closely related with the slope body. The material distribution in the longitudinal direction(along the main river) and cross-sectional direction(along the sliding direction) of the dam are basically corresponded with that of the slope body,but different in vertical direction due to the differences in dynamic process and accumulation mechanism of the landslide dam under different slope conditions. The uniform slope and parallel slopes are initiated in an overall-starting mode. Obvious vertical infiltration effect and material exchange are present during the movement process,leading to the inverse grading distribution of sediment in the vertical direction of the dams. And the cross-sectional shapes of the dam are mostly flat and inclined. The intersecting slopes present a layered-starting mode. The original sequences are maintained during the movement and accumulation process. The pushing-climbing effect and horizontal infiltration can occur under some conditions,accounting for the inverse grading characteristic of sediment distribution in the vertical direction and undulating cross-sectional shape of the dam. This study promotes a better understanding of the relationship between slope body and landslide dam and provides a basis for rapid assessment of the stability of landslide dam and restoration of the initial state of the slope. According to physical model tests,we discuss the dynamic process and accumulation characteristics of landslide dams formed under three different slope features including uniform slope(slope compositions mixed uniformly,parallel slope(soil layer surface parallel to the sliding surface) and intersecting slope(soil layer surface intersecting with the sliding surface). The material distribution and morphological characteristics of the landslide dams are studied by sub-regional sampling and 3D scanning technology. The results demonstrate that the accumulation characteristics of landslide dam are closely related with the slope body. The material distribution in the longitudinal direction(along the main river) and cross-sectional direction(along the sliding direction) of the dam are basically corresponded with that of the slope body,but different in vertical direction due to the differences in dynamic process and accumulation mechanism of the landslide dam under different slope conditions. The uniform slope and parallel slopes are initiated in an overall-starting mode. Obvious vertical infiltration effect and material exchange are present during the movement process,leading to the inverse grading distribution of sediment in the vertical direction of the dams. And the cross-sectional shapes of the dam are mostly flat and inclined. The intersecting slopes present a layered-starting mode. The original sequences are maintained during the movement and accumulation process. The pushing-climbing effect and horizontal infiltration can occur under some conditions,accounting for the inverse grading characteristic of sediment distribution in the vertical direction and undulating cross-sectional shape of the dam. This study promotes a better understanding of the relationship between slope body and landslide dam and provides a basis for rapid assessment of the stability of landslide dam and restoration of the initial state of the slope.
InSAR technology is based on a single satellite platform or orbit and can derive only one-dimensional deformation information of the landslide in the direction of the line of sight(LOS) of the radar satellite. It cannot derive the deformation along its aspect direction and cannot meet well the engineering requirements for landslide monitoring. To obtain more direct landslide deformation information of interest,we develop the model and algorithm for extracting the deformation velocity field of landslides in the aspect direction from ascending and descending Sentinel-1A data. Our method includes the following steps:(1)deriving LOS deformation velocity fields,(2)defining the slope-based coordinate system,(3)modeling the LOS deformation according to the configuration between the satellites and surface slopes and (4)solving for the displacements of landslides in the aspect and aspect-perpendicular directions with the assumption of no deformation in the slope surface-normal direction. We conduct a case study of an ancient landslide at Taoping Village,Li County in Sichuan Province and verify the accuracy of the model and algorithm through simulation experiments. The results show that,in contrast with the LOS deformation,the derived deformation in the aspect and aspect-perpendicular directions can display clearer deformation patterns and high-susceptibility areas. According to the results of the simulation experiments,the calculation error of the model and algorithm increases approximately linearly with the noise level. When the noise level reaches 10 mm·a-1,the calculation errors of the deformation velocity field in the aspect and aspect-perpendicular directions are 14.1 and 11.9mm·a-1,respectively. This proves the reliability of our method and results. InSAR technology is based on a single satellite platform or orbit and can derive only one-dimensional deformation information of the landslide in the direction of the line of sight(LOS) of the radar satellite. It cannot derive the deformation along its aspect direction and cannot meet well the engineering requirements for landslide monitoring. To obtain more direct landslide deformation information of interest,we develop the model and algorithm for extracting the deformation velocity field of landslides in the aspect direction from ascending and descending Sentinel-1A data. Our method includes the following steps:(1)deriving LOS deformation velocity fields,(2)defining the slope-based coordinate system,(3)modeling the LOS deformation according to the configuration between the satellites and surface slopes and (4)solving for the displacements of landslides in the aspect and aspect-perpendicular directions with the assumption of no deformation in the slope surface-normal direction. We conduct a case study of an ancient landslide at Taoping Village,Li County in Sichuan Province and verify the accuracy of the model and algorithm through simulation experiments. The results show that,in contrast with the LOS deformation,the derived deformation in the aspect and aspect-perpendicular directions can display clearer deformation patterns and high-susceptibility areas. According to the results of the simulation experiments,the calculation error of the model and algorithm increases approximately linearly with the noise level. When the noise level reaches 10 mm·a-1,the calculation errors of the deformation velocity field in the aspect and aspect-perpendicular directions are 14.1 and 11.9mm·a-1,respectively. This proves the reliability of our method and results.
Large landslides often cause huge human casualties and property losses. It is of great significance to carry out numerical simulation of the entire process of landslide for quantitative landslide risk assessment. This paper establishes a two-dimensional material point method(MPM)numerical model for Shenzhen"12 ·20"landslide. This model incorporates the updated Lagrangian governing equation with the ideal elastoplastic model under the Drucker-Prager yield criterion. The equivalent internal friction angle is derived by considering the effect of pore water pressure. The K-means clustering algorithm is used to identify the potential slip surface in combination with the relative displacement of the material points. The computed results show that the landslide slip surface,instability and movement characteristics,impact strength,and deposition feature of the Shenzhen landslide obtained by the MPM simulation analysis are in good agreement with the actual observation results,which implies that MPM is a reliable numerical simulation tool to reproduce the entire life cycle of landslide stability,instability,movement,impact and deposition process. Large landslides often cause huge human casualties and property losses. It is of great significance to carry out numerical simulation of the entire process of landslide for quantitative landslide risk assessment. This paper establishes a two-dimensional material point method(MPM)numerical model for Shenzhen"12 ·20"landslide. This model incorporates the updated Lagrangian governing equation with the ideal elastoplastic model under the Drucker-Prager yield criterion. The equivalent internal friction angle is derived by considering the effect of pore water pressure. The K-means clustering algorithm is used to identify the potential slip surface in combination with the relative displacement of the material points. The computed results show that the landslide slip surface,instability and movement characteristics,impact strength,and deposition feature of the Shenzhen landslide obtained by the MPM simulation analysis are in good agreement with the actual observation results,which implies that MPM is a reliable numerical simulation tool to reproduce the entire life cycle of landslide stability,instability,movement,impact and deposition process.
To study the relationship between dynamic failure characteristics and acceleration response of loess-covered slopes,a 1∶20 shaking table test is set up. The amplitude of the input seismic wave is gradually increased. The development law of slope cracks in the whole cycle is tested in real time during the test. The MATLAB dynamic failure feature detection system is used to obtain the basic information of the surface cracks. The dynamic failure features of the slope surface are proposed. The peak acceleration change law of the monitoring points of each working condition is also analyzed. The results are as follows: (1)The crack width and crack area of the slope top and toe have a jumping growth when the input peak acceleration is 0.6g,indicating that the soil at the soil-rock contact surface has undergone progressive shear failure. The acceleration peak response on the sliding surface and the slope surface has a sudden significant change,indicating that the slope has been damaged. (2)The acceleration magnification coefficients along both the slope and sliding surfaces increase non-linearly. Additionally,the magnification coefficients along the slope surface are obviously larger than those along the sliding surface under various working conditions,indicating that the acceleration magnification effect along the elevation is obvious. (3)The sudden increase of tensile and shear cracks area is an important feature of slope failure. The generation of through cracks and the sudden change of acceleration response can be used as the basis for slope dynamic failure. Furthermore,the generation of through cracks and the sudden change of acceleration response can be used as the basis for the dynamic failure of the slope. To study the relationship between dynamic failure characteristics and acceleration response of loess-covered slopes,a 1∶20 shaking table test is set up. The amplitude of the input seismic wave is gradually increased. The development law of slope cracks in the whole cycle is tested in real time during the test. The MATLAB dynamic failure feature detection system is used to obtain the basic information of the surface cracks. The dynamic failure features of the slope surface are proposed. The peak acceleration change law of the monitoring points of each working condition is also analyzed. The results are as follows: (1)The crack width and crack area of the slope top and toe have a jumping growth when the input peak acceleration is 0.6g,indicating that the soil at the soil-rock contact surface has undergone progressive shear failure. The acceleration peak response on the sliding surface and the slope surface has a sudden significant change,indicating that the slope has been damaged. (2)The acceleration magnification coefficients along both the slope and sliding surfaces increase non-linearly. Additionally,the magnification coefficients along the slope surface are obviously larger than those along the sliding surface under various working conditions,indicating that the acceleration magnification effect along the elevation is obvious. (3)The sudden increase of tensile and shear cracks area is an important feature of slope failure. The generation of through cracks and the sudden change of acceleration response can be used as the basis for slope dynamic failure. Furthermore,the generation of through cracks and the sudden change of acceleration response can be used as the basis for the dynamic failure of the slope.