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Editor Work2022 Vol. 30, No. 1
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2022, 30(1): 1-20.
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This is the keynote speech for the 5th Gu Dezhen Lecture co-sponsored by the Engineering Geology Commission,China Geological Society and the Key Laboratory of Engineering Geomechanics,Chinese Academy of Sciences. The paper briefly recalls the core value and historical contribution of the"Engineering Geomechanics of Rock Masses(EGRM)"founded by Professor Gu Dezhen,and introduces the Statistical Mechanics of Rock Masses(SMRM) and its inheriting and developing to the EGRM in the past 30 years. Referring to the ideology of Statistical Physics,the SMRM has proposed geometric probability models for rock mass structure,the energy principle of fracture mechanics for continuity equivalent of discontinuous rock mass,the principle of structure-stress control to the behavior of rock mass,the principle of weak link control to rock mass strength,and the seepage mechanical principle of discontinuity network. The SMRM has established the constitutive model,the analytical method for complete deformation of rock mass,the model for characteristics and rock burst mechanism of high energy-store rock mass,the analytical solution of circular tunnel in elastic rock mass. The SMRM also has developed the technology and equipment for in situ data acquisition,computational methods for full directional parameters of structure,deformation,compressive strength and shear strength,permeability of rock mass,and anisotropic quality rating and active reinforcement of rock masses,and the module for numerical analysis,i.e. JointModel. The SMRM has strongly promoted the advances of the theory and technology of EGRM and rock mass mechanics.
This is the keynote speech for the 5th Gu Dezhen Lecture co-sponsored by the Engineering Geology Commission,China Geological Society and the Key Laboratory of Engineering Geomechanics,Chinese Academy of Sciences. The paper briefly recalls the core value and historical contribution of the"Engineering Geomechanics of Rock Masses(EGRM)"founded by Professor Gu Dezhen,and introduces the Statistical Mechanics of Rock Masses(SMRM) and its inheriting and developing to the EGRM in the past 30 years. Referring to the ideology of Statistical Physics,the SMRM has proposed geometric probability models for rock mass structure,the energy principle of fracture mechanics for continuity equivalent of discontinuous rock mass,the principle of structure-stress control to the behavior of rock mass,the principle of weak link control to rock mass strength,and the seepage mechanical principle of discontinuity network. The SMRM has established the constitutive model,the analytical method for complete deformation of rock mass,the model for characteristics and rock burst mechanism of high energy-store rock mass,the analytical solution of circular tunnel in elastic rock mass. The SMRM also has developed the technology and equipment for in situ data acquisition,computational methods for full directional parameters of structure,deformation,compressive strength and shear strength,permeability of rock mass,and anisotropic quality rating and active reinforcement of rock masses,and the module for numerical analysis,i.e. JointModel. The SMRM has strongly promoted the advances of the theory and technology of EGRM and rock mass mechanics.
2022, 30(1): 21-36.
A framework of three-dimensional network structural rock mechanics has been proposed by author recently. It is a new branch of rock mechanics. Main characteristics of research object,basic framework,main research content and future prospection are explained according to author's research experience on fractured rock mass for more than 20 years. It is concluded that rock mass structure control theory consists of four aspects: material strength control,structure type control,seepage path control and geometric boundary control. The main technical contents include three-dimensional RQD estimation,rock mass representative elements estimation technology,structure block search technology,directional projection rock mass discontinuity three-dimensional connectivity estimation technology and rock mass three-dimensional seepage path search technology. The theory is mainly composed of spherical projection theory,probability and statistics theory,stochastics dynamics,geometric topology theory,block theory,nonlinear system theory and multiscale equivalent structure model of fractured rock mass. A large amount of geological data of discontinuities in the sampling window of rock mass investigation is statistically emphasized as a foundation. Rock mass random discontinuities based three dimensional network numerical modelling technique is the kernel of the three-dimensional network structural rock mechanics.
A framework of three-dimensional network structural rock mechanics has been proposed by author recently. It is a new branch of rock mechanics. Main characteristics of research object,basic framework,main research content and future prospection are explained according to author's research experience on fractured rock mass for more than 20 years. It is concluded that rock mass structure control theory consists of four aspects: material strength control,structure type control,seepage path control and geometric boundary control. The main technical contents include three-dimensional RQD estimation,rock mass representative elements estimation technology,structure block search technology,directional projection rock mass discontinuity three-dimensional connectivity estimation technology and rock mass three-dimensional seepage path search technology. The theory is mainly composed of spherical projection theory,probability and statistics theory,stochastics dynamics,geometric topology theory,block theory,nonlinear system theory and multiscale equivalent structure model of fractured rock mass. A large amount of geological data of discontinuities in the sampling window of rock mass investigation is statistically emphasized as a foundation. Rock mass random discontinuities based three dimensional network numerical modelling technique is the kernel of the three-dimensional network structural rock mechanics.
2022, 30(1): 37-52.
Heterogeneity is one of the important properties of rock mass. Heterogeneity is widespread in rock mass from the material composition to structural characteristics to micro-macro mechanical behavior. On the basis of reviewing the existing researches,the causes,characteristics,mechanical effects and temporal and spatial evolution of rock mass heterogeneity are described from three different scales including micro heterogeneity,structural heterogeneity and macro heterogeneity. The relevant study methods and the different manifestations of heterogeneity at different scales are introduced. The study of rock mass heterogeneity is an extension of the theoretical system of engineering geomechanics of rock mass. The multi-scale research method has also become an effective means to fully reveal the deformation and failure mechanism of rock mass.
Heterogeneity is one of the important properties of rock mass. Heterogeneity is widespread in rock mass from the material composition to structural characteristics to micro-macro mechanical behavior. On the basis of reviewing the existing researches,the causes,characteristics,mechanical effects and temporal and spatial evolution of rock mass heterogeneity are described from three different scales including micro heterogeneity,structural heterogeneity and macro heterogeneity. The relevant study methods and the different manifestations of heterogeneity at different scales are introduced. The study of rock mass heterogeneity is an extension of the theoretical system of engineering geomechanics of rock mass. The multi-scale research method has also become an effective means to fully reveal the deformation and failure mechanism of rock mass.
2022, 30(1): 53-58.
This paper describes briefly the main contents of the Rock Mass Structure Control Theory put forward by Gu Dezhen in the 1970s,the Geological Environment Theory put forward by Wang Sijing in the 1990s and the Engineering Geology Coupling Theory put forward by Li Guangcheng at the beginning of this century. It expounds the relations of the inheritance and development of the three theories. The three theories are compared in terms of put forward time,objects of study,contents of study,controlling factors,basic ideas,disciplines involved and thought categories. According to the three theories,the paper finally analyzes two engineering cases. One case is the selection of underground powerhouse location of Ming Tombs pumped storage power station. The second is the selection of Zipingpu dam location and its axis direction as well as the adopted engineering measures.
This paper describes briefly the main contents of the Rock Mass Structure Control Theory put forward by Gu Dezhen in the 1970s,the Geological Environment Theory put forward by Wang Sijing in the 1990s and the Engineering Geology Coupling Theory put forward by Li Guangcheng at the beginning of this century. It expounds the relations of the inheritance and development of the three theories. The three theories are compared in terms of put forward time,objects of study,contents of study,controlling factors,basic ideas,disciplines involved and thought categories. According to the three theories,the paper finally analyzes two engineering cases. One case is the selection of underground powerhouse location of Ming Tombs pumped storage power station. The second is the selection of Zipingpu dam location and its axis direction as well as the adopted engineering measures.
2022, 30(1): 59-70.
Brittleness is one of the most important mechanical properties of rock materials. Accurate evaluation of rock brittleness has extremely high practical value and plays a crucial role in underground engineering and slope stability,rock drillability and cutability analysis in water conservancy,hydropower,transportation,energy exploration and development. Researchers from all over the world have established many brittleness evaluation indexes from physical parameters,mechanical parameters,and elastic parameters. However,there is no unified recognition and definition of rock brittleness yet. This article systematically reviews the methods of rock brittleness evaluation at home and abroad,classifies dozens of commonly used brittleness evaluation indicators,summarizes the basic principles and application status of existing brittleness indicators,and discusses the adaptability,advantages and existing problems of brittleness indicators. Finally,the future research direction of rock brittleness evaluation method is discussed.
Brittleness is one of the most important mechanical properties of rock materials. Accurate evaluation of rock brittleness has extremely high practical value and plays a crucial role in underground engineering and slope stability,rock drillability and cutability analysis in water conservancy,hydropower,transportation,energy exploration and development. Researchers from all over the world have established many brittleness evaluation indexes from physical parameters,mechanical parameters,and elastic parameters. However,there is no unified recognition and definition of rock brittleness yet. This article systematically reviews the methods of rock brittleness evaluation at home and abroad,classifies dozens of commonly used brittleness evaluation indicators,summarizes the basic principles and application status of existing brittleness indicators,and discusses the adaptability,advantages and existing problems of brittleness indicators. Finally,the future research direction of rock brittleness evaluation method is discussed.
2022, 30(1): 71-82.
In the high-level radioactive waste deep geological disposal,the properties of engineering barrier made up of bentonite are probably weakened under chemical effects originating from natural groundwater and possible leaked nuclides. This paper aims to summarize the latest researches about the evolution of barrier properties for Gaomiaozi(GMZ)bentonite under chemical effects. The basic physical properties of GMZ bentonite and the chemical environment in Beishan China are introduced first. Subsequently,the barrier properties involving hydraulic,mechanical and retardant under chemical effects are analyzed systematically. Results show that the chemical effects on the water retention and permeability relate to osmotic suction and diffuse double layer theory respectively. The attenuation of swelling pressure under chemical effects can be explained by the hydration mechanism of bentonite. The deformation properties under the chemical-mechanical coupling or chemical-hydraulic-mechanical coupling conditions would change owing to osmotic consolidation and chemical softening effect. The adsorption and diffusion properties of bentonite are affected by nuclide concentration,ionic environment,pH value and other factors. Finally,we summary the key research challenges and suggest directions for future works.
In the high-level radioactive waste deep geological disposal,the properties of engineering barrier made up of bentonite are probably weakened under chemical effects originating from natural groundwater and possible leaked nuclides. This paper aims to summarize the latest researches about the evolution of barrier properties for Gaomiaozi(GMZ)bentonite under chemical effects. The basic physical properties of GMZ bentonite and the chemical environment in Beishan China are introduced first. Subsequently,the barrier properties involving hydraulic,mechanical and retardant under chemical effects are analyzed systematically. Results show that the chemical effects on the water retention and permeability relate to osmotic suction and diffuse double layer theory respectively. The attenuation of swelling pressure under chemical effects can be explained by the hydration mechanism of bentonite. The deformation properties under the chemical-mechanical coupling or chemical-hydraulic-mechanical coupling conditions would change owing to osmotic consolidation and chemical softening effect. The adsorption and diffusion properties of bentonite are affected by nuclide concentration,ionic environment,pH value and other factors. Finally,we summary the key research challenges and suggest directions for future works.
2022, 30(1): 83-100.
This study reveals the different contributions of soil cohesion and internal friction angle on factor of safety(FOS) of soil slope. It shows the existence and reason of a critical slip surface with a global minimum factor of safety(FOS)value in soil slopes. It selects a large number of potential slip surfaces in soil slopes,and then defines four types of FOS values(FOSc×φ,FOSc,FOSφ and FOSc+φ)for each potential slip surface. It calculates these FOS values by conventional slice methods under the limited equilibrium principle,and then plots these FOS values against their associated slip depths and finds their variation features in terms of the slip depth d. The FOSc×φ is defined as the conventional FOS value contributed by both soil cohesion and internal frictional angle of a soil slope. The plots show that local FOSc×φ value decreases and then increases as slip depth increases. Therefore,FOSc×φ have a global minimum value. The FOSc is defined as the FOS value contributed by only the internal cohesion of a soil slope. The plots show that local minimum FOSc value decreases as slip depth increases. The FOSφ is defined as the FOS value contributed by only internal friction angle of a soil slope. The plots show that local minimum FOSφ value always near-linearly increases as slip depth increases. The FOSc+φ is defined as the sum of FOSc and FOSφ. The results show FOSc+φ value is approximately equal to FOSc×φ value for each potential slip surface. The above four features are further shown in the results of the five conventional slice methods,the slopes with ground water effect,and the slopes comprising of heterogeneous soils. Hence,this paper shows that a general soil slope has a global minimum value among its numerous FOS values associated with numerous potential slip surfaces. The reasons for the existence of a global minimum FOS value are (1)the individual contributions of the cohesion and friction angle to FOS values against the depth d and (2)the approximate equal values of FOSc+φ to FOSc×φ for any potential slip surface.
This study reveals the different contributions of soil cohesion and internal friction angle on factor of safety(FOS) of soil slope. It shows the existence and reason of a critical slip surface with a global minimum factor of safety(FOS)value in soil slopes. It selects a large number of potential slip surfaces in soil slopes,and then defines four types of FOS values(FOSc×φ,FOSc,FOSφ and FOSc+φ)for each potential slip surface. It calculates these FOS values by conventional slice methods under the limited equilibrium principle,and then plots these FOS values against their associated slip depths and finds their variation features in terms of the slip depth d. The FOSc×φ is defined as the conventional FOS value contributed by both soil cohesion and internal frictional angle of a soil slope. The plots show that local FOSc×φ value decreases and then increases as slip depth increases. Therefore,FOSc×φ have a global minimum value. The FOSc is defined as the FOS value contributed by only the internal cohesion of a soil slope. The plots show that local minimum FOSc value decreases as slip depth increases. The FOSφ is defined as the FOS value contributed by only internal friction angle of a soil slope. The plots show that local minimum FOSφ value always near-linearly increases as slip depth increases. The FOSc+φ is defined as the sum of FOSc and FOSφ. The results show FOSc+φ value is approximately equal to FOSc×φ value for each potential slip surface. The above four features are further shown in the results of the five conventional slice methods,the slopes with ground water effect,and the slopes comprising of heterogeneous soils. Hence,this paper shows that a general soil slope has a global minimum value among its numerous FOS values associated with numerous potential slip surfaces. The reasons for the existence of a global minimum FOS value are (1)the individual contributions of the cohesion and friction angle to FOS values against the depth d and (2)the approximate equal values of FOSc+φ to FOSc×φ for any potential slip surface.
2022, 30(1): 101-109.
The practice of hydrogeology and water hazards prevention and control technology in China's mines in the new century urgently needs to establish its own theoretical guidance. This paper puts forward the idea of establishing Structural Hydrogeology under the guidance of Professor Gu Dezhen's academic thinking of "Hydrogeological Structure",and discusses its basic theoretical framework. From the perspective of methodology,the prevention and control of water disaster in mines are divided into two methods: passive and active prevention and control. Structural Hydrogeology can guide the prevention and control of water-sand mixture inrush in coal mines. The mechanism of water-sand mixture inrush disaster with high potential energy from the passive prevention and control is analyzed. The idea of structural hydrogeology can also be used to guide the active geological engineering prevention and control of the water-sand mixture inrush with high potential energy. Combined with typical cases,specific methods are put forward from the transformation of geological material properties,structure reconstruction of water-separating properties,transformation of hydrodynamic storage environment,and mitigation of mining-induced rock mass damages. The main purpose of this work is to spawn an innovative theory and technology for water prevention and control with the characteristics of Chinese mines.
The practice of hydrogeology and water hazards prevention and control technology in China's mines in the new century urgently needs to establish its own theoretical guidance. This paper puts forward the idea of establishing Structural Hydrogeology under the guidance of Professor Gu Dezhen's academic thinking of "Hydrogeological Structure",and discusses its basic theoretical framework. From the perspective of methodology,the prevention and control of water disaster in mines are divided into two methods: passive and active prevention and control. Structural Hydrogeology can guide the prevention and control of water-sand mixture inrush in coal mines. The mechanism of water-sand mixture inrush disaster with high potential energy from the passive prevention and control is analyzed. The idea of structural hydrogeology can also be used to guide the active geological engineering prevention and control of the water-sand mixture inrush with high potential energy. Combined with typical cases,specific methods are put forward from the transformation of geological material properties,structure reconstruction of water-separating properties,transformation of hydrodynamic storage environment,and mitigation of mining-induced rock mass damages. The main purpose of this work is to spawn an innovative theory and technology for water prevention and control with the characteristics of Chinese mines.
2022, 30(1): 110-116.
In order to analyze the stability of slope,a method based on limit equilibrium theory is proposed. Assuming that the slope is made up with elastomer only affected by gravity,the stress distribution can be obtained by analytical solution of elastic mechanics. The sliding surface is described by piecewise quadratic polynomial function. When the piecewise interval is short enough,this description method can reflect arbitrary curved shape. According to the Mohr-Coulomb criterion,the factor of safety is defined,which can be expressed as a function of polynomial coefficient. The polynomial coefficient of the most dangerous sliding surface can be obtained by using the mixed penalty function optimization method,then the factor of safety can be obtained to analyze the stability of the slope. The proposed method is different from the previous methods. It does not need to divide the landslide body into vertical slices and to assume the normal stress distribution form on the sliding surface. It directly uses the existing slope body elastic stress solution. The results of the calculation examples show that the factor of safety obtained by the method in the paper is very close to the results obtained by the simplified Bishop method and the finite element strength reduction method. They are basically between the finite element method and the simplified Bishop method.
In order to analyze the stability of slope,a method based on limit equilibrium theory is proposed. Assuming that the slope is made up with elastomer only affected by gravity,the stress distribution can be obtained by analytical solution of elastic mechanics. The sliding surface is described by piecewise quadratic polynomial function. When the piecewise interval is short enough,this description method can reflect arbitrary curved shape. According to the Mohr-Coulomb criterion,the factor of safety is defined,which can be expressed as a function of polynomial coefficient. The polynomial coefficient of the most dangerous sliding surface can be obtained by using the mixed penalty function optimization method,then the factor of safety can be obtained to analyze the stability of the slope. The proposed method is different from the previous methods. It does not need to divide the landslide body into vertical slices and to assume the normal stress distribution form on the sliding surface. It directly uses the existing slope body elastic stress solution. The results of the calculation examples show that the factor of safety obtained by the method in the paper is very close to the results obtained by the simplified Bishop method and the finite element strength reduction method. They are basically between the finite element method and the simplified Bishop method.
2022, 30(1): 117-126.
As subgrade filler,municipal sludge solidified soil is of great significance for saving engineering cost and protecting environment. This paper takes the municipal sludge solidified soil as the research object and uses DDS dynamic triaxial apparatus to study the influence on cumulative plastic strain and dynamic strength characteristics. It considers the three aspects of number of dry and wet cycles,initial static deviator stress and dynamic stress. The experimental results show that the accumulative plastic strain of soil increases first and then becomes stable with the increase of dry-wet cycles under the action of dry-wet cycles alone,but the change of accumulative plastic strain of soil is not obvious under the coupling action of dry-wet cycle and initial static deviator stress. The dynamic stress has a great influence on the cumulative plastic strain and there is a critical value. when the dynamic stress is less than the critical value. The cumulative plastic strain increases first and then becomes stable gradually. When the dynamic stress is greater than the critical value,the cumulative plastic strain increases rapidly after reaching a certain vibration time,which causes rapid deformation and damage of soil. Both the dry-wet cycle and the initial static deviator stress can reduce the dynamic strength of soil. But after the dry-wet cycle reaches 10 times,the dynamic strength can tend to be stable and not be affected by them. By means of regression analysis,we establish a stable cumulative plastic strain model of the municipal sludge solidified soil,which takes into account the influences of the number of dry-wet cycles,the initial static deviator stress and the dynamic stress. We verify its feasibility.
As subgrade filler,municipal sludge solidified soil is of great significance for saving engineering cost and protecting environment. This paper takes the municipal sludge solidified soil as the research object and uses DDS dynamic triaxial apparatus to study the influence on cumulative plastic strain and dynamic strength characteristics. It considers the three aspects of number of dry and wet cycles,initial static deviator stress and dynamic stress. The experimental results show that the accumulative plastic strain of soil increases first and then becomes stable with the increase of dry-wet cycles under the action of dry-wet cycles alone,but the change of accumulative plastic strain of soil is not obvious under the coupling action of dry-wet cycle and initial static deviator stress. The dynamic stress has a great influence on the cumulative plastic strain and there is a critical value. when the dynamic stress is less than the critical value. The cumulative plastic strain increases first and then becomes stable gradually. When the dynamic stress is greater than the critical value,the cumulative plastic strain increases rapidly after reaching a certain vibration time,which causes rapid deformation and damage of soil. Both the dry-wet cycle and the initial static deviator stress can reduce the dynamic strength of soil. But after the dry-wet cycle reaches 10 times,the dynamic strength can tend to be stable and not be affected by them. By means of regression analysis,we establish a stable cumulative plastic strain model of the municipal sludge solidified soil,which takes into account the influences of the number of dry-wet cycles,the initial static deviator stress and the dynamic stress. We verify its feasibility.
2022, 30(1): 127-143.
The huge potential of shale oil makes this resource an important energy alternative to improve the balance between energy supply and demand. In this sense,its development and economic utilization have regained significant attention. The in-situ conversion is the best technology recommended for the exploitation of continental shale oil in China. However,the current low-maturity shale oil and underground in-situ conversion/modification methods of oil shale mainly face bottlenecks such as low thermal efficiency,high pollution risk,and reservoir subsidence instability. Therefore,on the basis of analyzing the advantages and disadvantages of various in-situ conversion/modification methods of shale oil,the temperature,time conditions,and structural evolution characteristics of hydrocarbon generation from shale oil cracking are summarized. Consequently,a thermal in-situ mining theory of shale oil chemicals is suggested. This theory uses the reaction of calcium oxide and water to provide heat for the in-situ conversion of organic matter. Hence,considering the principle of material and energy balance,the theory and method of this thermal in-situ conversion for shale oil chemical production are proposed. And the technical feasibility of the method is demonstrated by analyzing temperature level,heat supply,and solid-phase volume change. The results of the heat-solid-phase material balance analysis and the high-pressure calcium oxide hydrolysis test show the technology is efficient theoretically. Therefore,some mining methods using calcium oxide are proposed such as surface coating modification of calcium oxide powder,calcium oxide microspheres,calcium oxide hydroxyl injection liquid,and high-pressure air calcium oxide powder injection.
The huge potential of shale oil makes this resource an important energy alternative to improve the balance between energy supply and demand. In this sense,its development and economic utilization have regained significant attention. The in-situ conversion is the best technology recommended for the exploitation of continental shale oil in China. However,the current low-maturity shale oil and underground in-situ conversion/modification methods of oil shale mainly face bottlenecks such as low thermal efficiency,high pollution risk,and reservoir subsidence instability. Therefore,on the basis of analyzing the advantages and disadvantages of various in-situ conversion/modification methods of shale oil,the temperature,time conditions,and structural evolution characteristics of hydrocarbon generation from shale oil cracking are summarized. Consequently,a thermal in-situ mining theory of shale oil chemicals is suggested. This theory uses the reaction of calcium oxide and water to provide heat for the in-situ conversion of organic matter. Hence,considering the principle of material and energy balance,the theory and method of this thermal in-situ conversion for shale oil chemical production are proposed. And the technical feasibility of the method is demonstrated by analyzing temperature level,heat supply,and solid-phase volume change. The results of the heat-solid-phase material balance analysis and the high-pressure calcium oxide hydrolysis test show the technology is efficient theoretically. Therefore,some mining methods using calcium oxide are proposed such as surface coating modification of calcium oxide powder,calcium oxide microspheres,calcium oxide hydroxyl injection liquid,and high-pressure air calcium oxide powder injection.
2022, 30(1): 144-153.
This paper aims to clarify the microstructure characteristics and damage mechanism of paleosol with different water contents under freeze-thaw cycles. It uses the nuclear magnetic resonance scanner to test the paleosol samples with different water contents after freeze-thaw cycles. It studies the combination of freeze-thaw cycles and water content on the microstructure of the paleosol and the internal damage changes of the soil. The results show that the different water contents under freeze-thaw cycles cause different degrees of damage to the interior of the soil. The damage degree is that the soil with high water content is greater than that with low water content. As the number of freeze-thaw cycles increases,the signal amplitude of the T2 spectrum curve increases,the pore structure changes,the content of macropores and maximum pores increase,and the content of mesopores decreases. At the same time,the increase in pore volume of soils with larger water content is greater than that of soil with lower water content. These results show that the greater the water content in construction projects in seasonal frozen soil areas,the more likely the soil mass is to be destroyed. So the waterproof and drainage problems should be paid attention in the project. According to the principle of damage mechanics,the relationship between soil particle continuity and porosity is obtained. Then the relationship between effective stress and porosity is obtained. According to the results of nuclear magnetic resonance scanning,this paper establishes the relationship between porosity and the number of freeze-thaw cycles,and finally derives the expression of the relationship between the effective stress of the paleosol and the number of freeze-thaw cycles. The research results provide theoretical guidance for the construction projects of paleosol strata in seasonally frozen soil regions.
This paper aims to clarify the microstructure characteristics and damage mechanism of paleosol with different water contents under freeze-thaw cycles. It uses the nuclear magnetic resonance scanner to test the paleosol samples with different water contents after freeze-thaw cycles. It studies the combination of freeze-thaw cycles and water content on the microstructure of the paleosol and the internal damage changes of the soil. The results show that the different water contents under freeze-thaw cycles cause different degrees of damage to the interior of the soil. The damage degree is that the soil with high water content is greater than that with low water content. As the number of freeze-thaw cycles increases,the signal amplitude of the T2 spectrum curve increases,the pore structure changes,the content of macropores and maximum pores increase,and the content of mesopores decreases. At the same time,the increase in pore volume of soils with larger water content is greater than that of soil with lower water content. These results show that the greater the water content in construction projects in seasonal frozen soil areas,the more likely the soil mass is to be destroyed. So the waterproof and drainage problems should be paid attention in the project. According to the principle of damage mechanics,the relationship between soil particle continuity and porosity is obtained. Then the relationship between effective stress and porosity is obtained. According to the results of nuclear magnetic resonance scanning,this paper establishes the relationship between porosity and the number of freeze-thaw cycles,and finally derives the expression of the relationship between the effective stress of the paleosol and the number of freeze-thaw cycles. The research results provide theoretical guidance for the construction projects of paleosol strata in seasonally frozen soil regions.
2022, 30(1): 154-163.
The upper soft and lower hard double-layer soft clay foundation in reclamation land of costal area in Tianjin has complicated physical properties and engineering characteristics. Its deformation characteristics are different under different loading modes. This phenomenon can result in large post-construction settlement and uneven settlement in engineering practice. It can further lead to many engineering problems such as economic losses and even casualties. At present,most of the recent studies focus on the upper hard and lower soft double-layer soft clay foundation under constant loading mode. However,non-negligible settlement can happen due to some foundation under repeated loading. So far,the consolidation deformation mechanism of the double-layer soft clay foundation under different loading modes is deficient. The theoretical research lags far behind the engineering practice,which restricts the development of economic construction in relevant area. Therefore,it is particularly significant to study the deformation characteristics of double-layer soft clay foundation. This paper conducts one-dimensional consolidation test and Scanning Electron Microscope(SEM)test on the double-layer soft clay foundation in reclamation land,and then obtained compression characteristics and microcosmic mechanism of the soil sample. Applying one-dimensional consolidation test,this paper studies the deformation differences of double-layer soft clay foundation under repeated loading mode and constant loading mode. Furthermore,it discusses the micro-deformation mechanism of double-layer soft clay foundation under different loading modes based on the SEM test. The experimental results provide theoretical basis to establish deformation model and predict long-term settlement of the double-layer soft clay foundation. The results show the follows:(1)Under repeated loading mode,the compression coefficient and consolidation coefficient of double-layer soft clay foundation decrease obviously at the initial stage and then slowly decrease until stable. (2)Under different loading modes,the variation tendencies of compression coefficient and consolidation coefficient of the soil sample are different. (3)Compared with repeated loading mode,the initial value of compression coefficient is higher while the value of consolidation coefficient is lower under constant loading mode,and the variable quantity ranges from 30% to 45%. (4)When the loading grade is invariable,the settlement of double-layer soft clay foundation caused by repeated loading exceeds 30% to 45% than that caused by constant loading. (5)Moreover,increasing loading grades squeezes and reduces soil internal macropore,and can improve the roundness,orientation and the degree of homogenization of pores. Comparably,the repeated loading mode has the same effect on soil internal pores' roundness,orientation,and internal structure,which has relatively poor orderliness.
The upper soft and lower hard double-layer soft clay foundation in reclamation land of costal area in Tianjin has complicated physical properties and engineering characteristics. Its deformation characteristics are different under different loading modes. This phenomenon can result in large post-construction settlement and uneven settlement in engineering practice. It can further lead to many engineering problems such as economic losses and even casualties. At present,most of the recent studies focus on the upper hard and lower soft double-layer soft clay foundation under constant loading mode. However,non-negligible settlement can happen due to some foundation under repeated loading. So far,the consolidation deformation mechanism of the double-layer soft clay foundation under different loading modes is deficient. The theoretical research lags far behind the engineering practice,which restricts the development of economic construction in relevant area. Therefore,it is particularly significant to study the deformation characteristics of double-layer soft clay foundation. This paper conducts one-dimensional consolidation test and Scanning Electron Microscope(SEM)test on the double-layer soft clay foundation in reclamation land,and then obtained compression characteristics and microcosmic mechanism of the soil sample. Applying one-dimensional consolidation test,this paper studies the deformation differences of double-layer soft clay foundation under repeated loading mode and constant loading mode. Furthermore,it discusses the micro-deformation mechanism of double-layer soft clay foundation under different loading modes based on the SEM test. The experimental results provide theoretical basis to establish deformation model and predict long-term settlement of the double-layer soft clay foundation. The results show the follows:(1)Under repeated loading mode,the compression coefficient and consolidation coefficient of double-layer soft clay foundation decrease obviously at the initial stage and then slowly decrease until stable. (2)Under different loading modes,the variation tendencies of compression coefficient and consolidation coefficient of the soil sample are different. (3)Compared with repeated loading mode,the initial value of compression coefficient is higher while the value of consolidation coefficient is lower under constant loading mode,and the variable quantity ranges from 30% to 45%. (4)When the loading grade is invariable,the settlement of double-layer soft clay foundation caused by repeated loading exceeds 30% to 45% than that caused by constant loading. (5)Moreover,increasing loading grades squeezes and reduces soil internal macropore,and can improve the roundness,orientation and the degree of homogenization of pores. Comparably,the repeated loading mode has the same effect on soil internal pores' roundness,orientation,and internal structure,which has relatively poor orderliness.
2022, 30(1): 164-176.
The Jiangdingya ancient landslide is a huge scale landslide located in the Bailong River fault zone,in Zhouqu County,Gansu Province. Affected by fault activities,rainfall,river erosion,and human engineering activities,it has repeatedly revived and blocked the Bailong River,causing great disasters. In order to study the resurrection mechanism of Jiangdingya ancient landslide,based on the field geological survey,we focus on the centrifuge model test under the conditions of 10%,15% and 20% water content. The test shows that when the water content is 10%,only a few cracks are generated in the middle and rear part of the slope,but the landslide is still in a stable state as a whole. In the case of 15% and 20% water content,the landslide body is damaged. When the water content is 15% and 20%,the centrifugal acceleration required for the slope instability is 100g and 50g respectively. The test analysis shows that the Jiangdingya ancient landslide is a thrust-type landslide. Its deformation starts from the middle and rear part of the slope,where cracks are generated. Then the cracks gradually expand to the front edge and finally penetrate and cause the landslide damage. The deformation process of the landslide body is mainly divided into three stages: ①deformation initiation stage(crack formation stage); ②deformation acceleration stage(crack acceleration development stage); ③instability stage. The centrifugal simulation test and field investigation and analysis show that the factors for the resurrection of the Jiangdingya ancient landslide are mainly affected by rainfall and pore water pressure. It is a coupling sliding caused by the erosion of the front river and the movement of the middle and rear parts of the landslide caused by rainfall.
The Jiangdingya ancient landslide is a huge scale landslide located in the Bailong River fault zone,in Zhouqu County,Gansu Province. Affected by fault activities,rainfall,river erosion,and human engineering activities,it has repeatedly revived and blocked the Bailong River,causing great disasters. In order to study the resurrection mechanism of Jiangdingya ancient landslide,based on the field geological survey,we focus on the centrifuge model test under the conditions of 10%,15% and 20% water content. The test shows that when the water content is 10%,only a few cracks are generated in the middle and rear part of the slope,but the landslide is still in a stable state as a whole. In the case of 15% and 20% water content,the landslide body is damaged. When the water content is 15% and 20%,the centrifugal acceleration required for the slope instability is 100g and 50g respectively. The test analysis shows that the Jiangdingya ancient landslide is a thrust-type landslide. Its deformation starts from the middle and rear part of the slope,where cracks are generated. Then the cracks gradually expand to the front edge and finally penetrate and cause the landslide damage. The deformation process of the landslide body is mainly divided into three stages: ①deformation initiation stage(crack formation stage); ②deformation acceleration stage(crack acceleration development stage); ③instability stage. The centrifugal simulation test and field investigation and analysis show that the factors for the resurrection of the Jiangdingya ancient landslide are mainly affected by rainfall and pore water pressure. It is a coupling sliding caused by the erosion of the front river and the movement of the middle and rear parts of the landslide caused by rainfall.
2022, 30(1): 177-186.
It is always a difficult and hot issue to study the critical-sliding warning. In this paper,we use the mechanical monitoring method(Newton force monitoring) to monitor the slope of a mountain side highway in Baoxing County,Ya'an. The slope is located at the lower edge of the old landslide of Tangbao landslide. After 4 months of continuous monitoring,we obtain a large number of monitoring data,and two local landslides are successfully predicted during the monitoring period. We first integrate the Newton force monitoring data and rainfall monitoring data,and then compare the monitoring curve with the landslide evolution process,reveal the mechanical evolution law in the process of landslide,and analyze the causes of landslide induced by rainfall. Then,we fit the relationship between the critical-sliding warning time and the landslide volume of the successful cases,and find that there is an obvious positive correlation. Finally,we discuss the relationship between Newton force monitoring method and Saito model,and put forward the idea of monitoring and critical-sliding warning from surface to point. According to the analysis,the Newton force monitoring curve can well correspond with the landslide evolution process. The soil landslide can be divided into three stages: a)the rising stage of Newton force; b) the drop stage of Newton force; c) landslide stage. This paper provides practical experience for the popularization of Newton force monitoring system,and provides a new idea for the research of the combination of mechanical monitoring and displacement monitoring.
It is always a difficult and hot issue to study the critical-sliding warning. In this paper,we use the mechanical monitoring method(Newton force monitoring) to monitor the slope of a mountain side highway in Baoxing County,Ya'an. The slope is located at the lower edge of the old landslide of Tangbao landslide. After 4 months of continuous monitoring,we obtain a large number of monitoring data,and two local landslides are successfully predicted during the monitoring period. We first integrate the Newton force monitoring data and rainfall monitoring data,and then compare the monitoring curve with the landslide evolution process,reveal the mechanical evolution law in the process of landslide,and analyze the causes of landslide induced by rainfall. Then,we fit the relationship between the critical-sliding warning time and the landslide volume of the successful cases,and find that there is an obvious positive correlation. Finally,we discuss the relationship between Newton force monitoring method and Saito model,and put forward the idea of monitoring and critical-sliding warning from surface to point. According to the analysis,the Newton force monitoring curve can well correspond with the landslide evolution process. The soil landslide can be divided into three stages: a)the rising stage of Newton force; b) the drop stage of Newton force; c) landslide stage. This paper provides practical experience for the popularization of Newton force monitoring system,and provides a new idea for the research of the combination of mechanical monitoring and displacement monitoring.
2022, 30(1): 187-196.
The Cretaceous sandstone has a short sedimentation time and a poor degree of cementation. It is easy to disintegrate under hydration. The Cretaceous Wulong Formation sandstone in Yichang, Hubei is selected to carry out laboratory static and dynamic disintegration tests. The variation law of the Cretaceous sandstone's disintegration resistance index under static and dynamic disintegration methods is analyzed. The disintegration process of Cretaceous sandstone is analyzed by measuring the change in the mass percentage of disintegrated particles in different particle size ranges after the disintegration cycle. The microscopic characteristics of the Cretaceous sandstone before and after the disintegration is observed by scanning electron microscope tests. The morphological characteristics of post-disintegration residues is analyzed for the disintegration failure mode of Cretaceous sandstone. The disintegration mechanism of Cretaceous sandstone is examined. Starting from the perspective of energy dissipation, the surface energy increment is used to quantitatively describe the process of Cretaceous sandstone disintegration degree of fragmentation. The results show that the Cretaceous sandstone under static disintegration has a lower disintegration resistance index than that of dynamic disintegration. As the number of disintegration increases, the mass percentage of small particles(0.25~0.075 mm) gradually increases, and eventually stabilizes. The disintegration of Cretaceous sandstone mainly spreads along the joint fracture surface, particle cementation surface and micro-cracks. As the particle size of the disintegrated material becomes smaller, the chance of contact with water increases, and the corresponding crack propagation path becomes shorter. The degree of disintegration is increased. The cumulative increase in surface energy can better reflect the degree of fragmentation of the Cretaceous sandstone during the disintegration process. The greater the cumulative increase in surface energy, the more broken the disintegration residue and the higher the degree of disintegration. The research results can provide a theoretical reference for the evaluation of the engineering properties of the rock and soil mass in the soft rock area.
The Cretaceous sandstone has a short sedimentation time and a poor degree of cementation. It is easy to disintegrate under hydration. The Cretaceous Wulong Formation sandstone in Yichang, Hubei is selected to carry out laboratory static and dynamic disintegration tests. The variation law of the Cretaceous sandstone's disintegration resistance index under static and dynamic disintegration methods is analyzed. The disintegration process of Cretaceous sandstone is analyzed by measuring the change in the mass percentage of disintegrated particles in different particle size ranges after the disintegration cycle. The microscopic characteristics of the Cretaceous sandstone before and after the disintegration is observed by scanning electron microscope tests. The morphological characteristics of post-disintegration residues is analyzed for the disintegration failure mode of Cretaceous sandstone. The disintegration mechanism of Cretaceous sandstone is examined. Starting from the perspective of energy dissipation, the surface energy increment is used to quantitatively describe the process of Cretaceous sandstone disintegration degree of fragmentation. The results show that the Cretaceous sandstone under static disintegration has a lower disintegration resistance index than that of dynamic disintegration. As the number of disintegration increases, the mass percentage of small particles(0.25~0.075 mm) gradually increases, and eventually stabilizes. The disintegration of Cretaceous sandstone mainly spreads along the joint fracture surface, particle cementation surface and micro-cracks. As the particle size of the disintegrated material becomes smaller, the chance of contact with water increases, and the corresponding crack propagation path becomes shorter. The degree of disintegration is increased. The cumulative increase in surface energy can better reflect the degree of fragmentation of the Cretaceous sandstone during the disintegration process. The greater the cumulative increase in surface energy, the more broken the disintegration residue and the higher the degree of disintegration. The research results can provide a theoretical reference for the evaluation of the engineering properties of the rock and soil mass in the soft rock area.
2022, 30(1): 197-204.
At present,the research on the internal force and deformation of landslide anti-slide pile under complex geological condition is still insufficient. In order to study the response of the anti-slide pile for Jiangdingya talus landslide,string wire stress gauges and the embedded strain gauges were installed in the anti-slide piles to monitor the stress and strain. A new calculation model based on monitoring data and a FE model in PLAXIS 3D were established for further study. The results show that the maximum stress of a single steel bar monitored is 112.5 MPa,which is much smaller than the design value,and the maximum stain is 34 με. The calculated model introduced in this paper is reliable and can be used on actual project. The bending moment calculated by the FE model is much smaller than the design value,but their change trends are consistent,which can prove that the monitored data are authentic and the FE model is reliable. The anti-slide piles are currently in a safe state and the treatment effect of Jiangdingya talus landslide is remarkable.
At present,the research on the internal force and deformation of landslide anti-slide pile under complex geological condition is still insufficient. In order to study the response of the anti-slide pile for Jiangdingya talus landslide,string wire stress gauges and the embedded strain gauges were installed in the anti-slide piles to monitor the stress and strain. A new calculation model based on monitoring data and a FE model in PLAXIS 3D were established for further study. The results show that the maximum stress of a single steel bar monitored is 112.5 MPa,which is much smaller than the design value,and the maximum stain is 34 με. The calculated model introduced in this paper is reliable and can be used on actual project. The bending moment calculated by the FE model is much smaller than the design value,but their change trends are consistent,which can prove that the monitored data are authentic and the FE model is reliable. The anti-slide piles are currently in a safe state and the treatment effect of Jiangdingya talus landslide is remarkable.
2022, 30(1): 205-215.
Shale gas,as efficient and clean energy,plays a significant role in the energy mix nowadays. The 30% of hydrogen peroxide is used to immerse the shale sample(Niutitang Formation,Hunan Province) in order to increase the porosity and gas transportability. The variation of microscopic pore structure is observed by the super depth of field microscope and mercury injection experiment. Also,the variations of the microstructure of natural and oxidized fractures before and post immersion determined are determined by scanning electron microscopy. The three results are found. (1)Lots of bubbles and adhesions appear on the surface of the samples leading to the reduction of mechanical strength and breakage of the sample. (2)The observation of scanning electron microscope shows that iron element is attached to the surface of clay in the form of pyrite. The sulfur in pyrite is replaced by oxygen after oxidation. (3)After immersion the pore volume is increased from 0.041 mL·g-1 to 0.137 mL·g-1 with porosity from 9.35% to 25.35%. Based on the above results,it can be concluded that oxidation can significantly change the pore structure of organic-rich shale enhancing the migration ability of gas.
Shale gas,as efficient and clean energy,plays a significant role in the energy mix nowadays. The 30% of hydrogen peroxide is used to immerse the shale sample(Niutitang Formation,Hunan Province) in order to increase the porosity and gas transportability. The variation of microscopic pore structure is observed by the super depth of field microscope and mercury injection experiment. Also,the variations of the microstructure of natural and oxidized fractures before and post immersion determined are determined by scanning electron microscopy. The three results are found. (1)Lots of bubbles and adhesions appear on the surface of the samples leading to the reduction of mechanical strength and breakage of the sample. (2)The observation of scanning electron microscope shows that iron element is attached to the surface of clay in the form of pyrite. The sulfur in pyrite is replaced by oxygen after oxidation. (3)After immersion the pore volume is increased from 0.041 mL·g-1 to 0.137 mL·g-1 with porosity from 9.35% to 25.35%. Based on the above results,it can be concluded that oxidation can significantly change the pore structure of organic-rich shale enhancing the migration ability of gas.
2022, 30(1): 216-222.
It is of great significance to obtain accurate mineral composition of rock and the meso-structure of minerals to study the macroscopic mechanical properties of rock from the meso-level. CT scanning technology is a powerful tool for studying the meso-structure of rocks. In this paper,we use a high-resolution 3D CT scanning system to obtain CT images of granite. We determine reasonable segmentation thresholds by considering the results of X-ray diffraction test. And then,we realize the three-valued analysis of CT grayscale images of granite by threshold segmentation method. Finally,we obtain the main mineral content and meso-structure characteristics of granite. The results show that the main minerals of granite,i.e.,quartz,feldspar,and mica can be identified and quantitatively determined by using reasonable segmentation thresholds. Based on the 3D reconstruction model,we can obtain the shape,the particle size,and the spatial distribution characteristics of different minerals. The method proposed in this paper can provide some references for testing the rock mineral composition quantitatively and understanding their meso-structures.
It is of great significance to obtain accurate mineral composition of rock and the meso-structure of minerals to study the macroscopic mechanical properties of rock from the meso-level. CT scanning technology is a powerful tool for studying the meso-structure of rocks. In this paper,we use a high-resolution 3D CT scanning system to obtain CT images of granite. We determine reasonable segmentation thresholds by considering the results of X-ray diffraction test. And then,we realize the three-valued analysis of CT grayscale images of granite by threshold segmentation method. Finally,we obtain the main mineral content and meso-structure characteristics of granite. The results show that the main minerals of granite,i.e.,quartz,feldspar,and mica can be identified and quantitatively determined by using reasonable segmentation thresholds. Based on the 3D reconstruction model,we can obtain the shape,the particle size,and the spatial distribution characteristics of different minerals. The method proposed in this paper can provide some references for testing the rock mineral composition quantitatively and understanding their meso-structures.
2022, 30(1): 223-233.
The dynamic change of lattice spacing of rock minerals reflects the process of inner stress storage and release in rock. X ray diffraction is a major approach to determine minerals crystal structure parameters,including lattice spacing. It is difficult to inverse detailed structure of minerals by X ray due to restrictions of information presented by X ray attenuation,which are statistically average. Fine mineral structures and element location could be obtained by neutron rays because of high-energy and thick penetration depth. The measurement of lattice spacing of rock minerals is the most pressing problem in understanding of rock inner stress storage and release. In this work,a novel method for determination of rock inner stress based on X-ray and neutron diffraction is proposed. The basic principle of the method is analyzed,and the key technology and research prospects of the method are proposed. The following conclusions are drawn: taking the advantage of X-rays in determining the lattice parameters of rock minerals,we can achieve the dating of the lattice spacing of rock minerals combined with heat treatment technology. The diffraction deviation peaks of rock minerals then can be accurately measured by neutron diffraction technology,aiming at achieving the accurate depiction of the depth profile of the stress in the rock. The absolute measurement of the absolute value of the stress in the rock can be achieved by combining X-rays and neutrons. The methods proposed in this paper are helpful to reveal the microscopic storage and release process of the stress in the rock,as well as the long-term remaining material conditions and physical mechanical mechanisms,and are expected to provide a new technical solution for the study of rock mineral composition and microstructure.
The dynamic change of lattice spacing of rock minerals reflects the process of inner stress storage and release in rock. X ray diffraction is a major approach to determine minerals crystal structure parameters,including lattice spacing. It is difficult to inverse detailed structure of minerals by X ray due to restrictions of information presented by X ray attenuation,which are statistically average. Fine mineral structures and element location could be obtained by neutron rays because of high-energy and thick penetration depth. The measurement of lattice spacing of rock minerals is the most pressing problem in understanding of rock inner stress storage and release. In this work,a novel method for determination of rock inner stress based on X-ray and neutron diffraction is proposed. The basic principle of the method is analyzed,and the key technology and research prospects of the method are proposed. The following conclusions are drawn: taking the advantage of X-rays in determining the lattice parameters of rock minerals,we can achieve the dating of the lattice spacing of rock minerals combined with heat treatment technology. The diffraction deviation peaks of rock minerals then can be accurately measured by neutron diffraction technology,aiming at achieving the accurate depiction of the depth profile of the stress in the rock. The absolute measurement of the absolute value of the stress in the rock can be achieved by combining X-rays and neutrons. The methods proposed in this paper are helpful to reveal the microscopic storage and release process of the stress in the rock,as well as the long-term remaining material conditions and physical mechanical mechanisms,and are expected to provide a new technical solution for the study of rock mineral composition and microstructure.
2022, 30(1): 234-241.
Because of the limitations in traditional acoustic emission positioning algorithms of rock mechanics experiments,we introduce the gray wolf algorithm(GWO)into the acoustic emission positioning research. This algorithm imitates the leadership and hunting mechanism of wolves through simulating head wolf leadership. On the basis of the original gray wolf algorithm,aiming at the defect of its poor local search ability,we propose an improved gray wolf algorithm(BGWO)based on the population memory elimination system. The BGWO algorithm modifies the method of decreasing the convergence factor and eliminates the worst individual. We compare and analyze the performance of five positioning algorithms. They are BGWO,GWO,Gravity search algorithm(GSA),Geiger algorithm and LS algorithm in the experimental of uniaxial compression acoustic emission of prefabricated fractured rock specimen. We find out that the BGWO algorithm is better than other algorithms in terms of acoustic emission positioning search efficiency,search accuracy,stability and simulation of experimental results.
Because of the limitations in traditional acoustic emission positioning algorithms of rock mechanics experiments,we introduce the gray wolf algorithm(GWO)into the acoustic emission positioning research. This algorithm imitates the leadership and hunting mechanism of wolves through simulating head wolf leadership. On the basis of the original gray wolf algorithm,aiming at the defect of its poor local search ability,we propose an improved gray wolf algorithm(BGWO)based on the population memory elimination system. The BGWO algorithm modifies the method of decreasing the convergence factor and eliminates the worst individual. We compare and analyze the performance of five positioning algorithms. They are BGWO,GWO,Gravity search algorithm(GSA),Geiger algorithm and LS algorithm in the experimental of uniaxial compression acoustic emission of prefabricated fractured rock specimen. We find out that the BGWO algorithm is better than other algorithms in terms of acoustic emission positioning search efficiency,search accuracy,stability and simulation of experimental results.
2022, 30(1): 242-253.
During the field survey in 2016,48 earth fissures were discovered in the Anren county,North-East of the Wei River Basin. These fissures have resulted in severe geo-hazards. To determine the characteristics and the formation mechanism of these earth fissures,a series of geological investigation methods,such as field investi￣gations,measurements,seismic exploration,geological drilling,and trench excavation were employed. Field investigations and measurements indicated that these earth fissures were distributed along the geomorphic boundary and developed on the hanging wall of Shuangquan-Linyi fault. They were found to be trending in 60°~80°direction and were divided into five groups. Searches across the earth fissures revealed that multiple secondary fissures existed on both sides of these earth fissures,indicating that earth fissures caused severe soil ruptures in the shallow earth surfaces. Geological drilling profiles revealed that earth fissures dislocate several stratums and reflected that they possess the characteristics of syn-sedimentary faults. Seismic reflection profiles revealed that buried faults existed under the earth fissures,which showed that earth fissures were outcrops of buried faults. Regarding their genesis,these fissures were formed owing to the coupling action of multiple factors. The earth fissures forming process at Anren area can be divided into three stages. The regional extension first generated multiple buried faults. Then,the seismic activity ruptured multiple strata near the buried faults and formed multiple buried fractures. Finally,erosion process resulting from water infiltration caused the buried fractures to propagate to the surface and promote the formation of current earth fissures.
During the field survey in 2016,48 earth fissures were discovered in the Anren county,North-East of the Wei River Basin. These fissures have resulted in severe geo-hazards. To determine the characteristics and the formation mechanism of these earth fissures,a series of geological investigation methods,such as field investi￣gations,measurements,seismic exploration,geological drilling,and trench excavation were employed. Field investigations and measurements indicated that these earth fissures were distributed along the geomorphic boundary and developed on the hanging wall of Shuangquan-Linyi fault. They were found to be trending in 60°~80°direction and were divided into five groups. Searches across the earth fissures revealed that multiple secondary fissures existed on both sides of these earth fissures,indicating that earth fissures caused severe soil ruptures in the shallow earth surfaces. Geological drilling profiles revealed that earth fissures dislocate several stratums and reflected that they possess the characteristics of syn-sedimentary faults. Seismic reflection profiles revealed that buried faults existed under the earth fissures,which showed that earth fissures were outcrops of buried faults. Regarding their genesis,these fissures were formed owing to the coupling action of multiple factors. The earth fissures forming process at Anren area can be divided into three stages. The regional extension first generated multiple buried faults. Then,the seismic activity ruptured multiple strata near the buried faults and formed multiple buried fractures. Finally,erosion process resulting from water infiltration caused the buried fractures to propagate to the surface and promote the formation of current earth fissures.
2022, 30(1): 254-264.
The faults along the Shangri-La-Bangda section of Yunnan-Tibet railway are well developed. The tectonic movement is strong. Research on the present in-situ stress field in this area is conducive to the construction of the Yunnan-Tibet railway. A multisource comprehensive analysis method based on geomechanical trace analysis,focal mechanism solution,and measured data is utilized to analyze the orientation of in-situ stress field of the Shangri-La-Bangda Railway. Based on the Hoek-Brown strength criterion,the modified Sheorey theory and the measured data,the rock mass strength parameters and in-situ stress values along Shangri-La-Bangda section of Yunnan-Tibet railway are estimated and predicted respectively. And the characteristics of in-situ stress field and its engineering effect in the research area are analyzed. The results show that the orientation of the maximum horizontal principal stress is in the range of N0°W~N40°W in the Shangri-La-Deqin stress district while it turns into N60°E~N80°E in the Mangkang-Bangda stress district. The maximum and minimum horizontal principal stresses ranges are 24.23~37.30 MPa and 14.81~22.79 MPa,respectively when the buried depth is about 1 000 m. Their ranges are 47.29~66.69 MPa and 28.90~40.76 MPa when the buried depth is about 2 000 m. The tunnel axes are N80°W~N40°E and N10°E~S50°E in Shangri-La-Deqin stress district and Mangkang-Bangda stress district,which are conducive to the stability of surrounding rock. The effect of high in-situ stress is obvious when the buried depth is more than 400 m. Rockburst risk is high when the depth of hard rock is more than 700 m. Large deformation risk is high when the depth of soft rock is more than 1400 m.
The faults along the Shangri-La-Bangda section of Yunnan-Tibet railway are well developed. The tectonic movement is strong. Research on the present in-situ stress field in this area is conducive to the construction of the Yunnan-Tibet railway. A multisource comprehensive analysis method based on geomechanical trace analysis,focal mechanism solution,and measured data is utilized to analyze the orientation of in-situ stress field of the Shangri-La-Bangda Railway. Based on the Hoek-Brown strength criterion,the modified Sheorey theory and the measured data,the rock mass strength parameters and in-situ stress values along Shangri-La-Bangda section of Yunnan-Tibet railway are estimated and predicted respectively. And the characteristics of in-situ stress field and its engineering effect in the research area are analyzed. The results show that the orientation of the maximum horizontal principal stress is in the range of N0°W~N40°W in the Shangri-La-Deqin stress district while it turns into N60°E~N80°E in the Mangkang-Bangda stress district. The maximum and minimum horizontal principal stresses ranges are 24.23~37.30 MPa and 14.81~22.79 MPa,respectively when the buried depth is about 1 000 m. Their ranges are 47.29~66.69 MPa and 28.90~40.76 MPa when the buried depth is about 2 000 m. The tunnel axes are N80°W~N40°E and N10°E~S50°E in Shangri-La-Deqin stress district and Mangkang-Bangda stress district,which are conducive to the stability of surrounding rock. The effect of high in-situ stress is obvious when the buried depth is more than 400 m. Rockburst risk is high when the depth of hard rock is more than 700 m. Large deformation risk is high when the depth of soft rock is more than 1400 m.
2022, 30(1): 265-269.
In the process of design and construction,integration of permanent and temporary structures means to combine the water sealing and dropping structure、the temporary support structure with the permanent structure. It can maximize the role of the temporary structure,or minimize the waste of temporary structures. For the first time,the author puts forward the permanent and temporary combination of the underground project. Combined with the scientific research work in recent years,the author systematically sorts out the scientific attempts and technical practices in this field in China. Under the Carbon peaking and Carbon neutrality background,the author put forward that we should vigorously advocate permanent and temporary combination of the underground project,aiming to reduce the waste of materials,the impact on the surrounding environment,and speed up the construction.
In the process of design and construction,integration of permanent and temporary structures means to combine the water sealing and dropping structure、the temporary support structure with the permanent structure. It can maximize the role of the temporary structure,or minimize the waste of temporary structures. For the first time,the author puts forward the permanent and temporary combination of the underground project. Combined with the scientific research work in recent years,the author systematically sorts out the scientific attempts and technical practices in this field in China. Under the Carbon peaking and Carbon neutrality background,the author put forward that we should vigorously advocate permanent and temporary combination of the underground project,aiming to reduce the waste of materials,the impact on the surrounding environment,and speed up the construction.
2022, 30(1): 270-280.
Piezocone penetration test(CPTU) is one of the most widely used in-situ testing methods at present,but CPTU cannot in-situ measure the soil density,which is the most basic physical index of soil. Density piezocone penetration test(DCPTU),incorporating the nuclear densitometer into the piezocone penetration system,is a new in-situ testing method that can simultaneously measure the cone resistance,sleeve friction,pore water pressure and density during the penetration. In this paper,the testing apparatus and density testing theory of DCPTU are introduced firstly. Then,the reliability of measuring density of sand,clay,lumpy fill and seabed sediments by DCPTU is evaluated by comparing with laboratory test results. The difference between measured and actual density of heterogeneous strata is analyzed and a method for deducing the actual density profile is proposed. The engineering applications of DCPTU,including identification of soft interlayer,evaluation of liquefaction potential of sand,examination of the effect of ground improvement,detection of spaces of lumpy fill,and investigation of the thickness and density distribution of fluid mud layer,were summarized. Finally,the development trend and application prospect of DCPTU in measuring maximum shear modulus of soil,in situ evaluating soil structure and in situ testing physical and mechanical properties of unfavorable ground are forecasted.
Piezocone penetration test(CPTU) is one of the most widely used in-situ testing methods at present,but CPTU cannot in-situ measure the soil density,which is the most basic physical index of soil. Density piezocone penetration test(DCPTU),incorporating the nuclear densitometer into the piezocone penetration system,is a new in-situ testing method that can simultaneously measure the cone resistance,sleeve friction,pore water pressure and density during the penetration. In this paper,the testing apparatus and density testing theory of DCPTU are introduced firstly. Then,the reliability of measuring density of sand,clay,lumpy fill and seabed sediments by DCPTU is evaluated by comparing with laboratory test results. The difference between measured and actual density of heterogeneous strata is analyzed and a method for deducing the actual density profile is proposed. The engineering applications of DCPTU,including identification of soft interlayer,evaluation of liquefaction potential of sand,examination of the effect of ground improvement,detection of spaces of lumpy fill,and investigation of the thickness and density distribution of fluid mud layer,were summarized. Finally,the development trend and application prospect of DCPTU in measuring maximum shear modulus of soil,in situ evaluating soil structure and in situ testing physical and mechanical properties of unfavorable ground are forecasted.
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