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Editor Work2015 Vol. 23, No. 4
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2015, 23(4): 589-596.
Abstract
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The most important engineering properties of coarse granular materials such as stress-strain and strength behavior, volume change and shear strength depend on the amount of grain breakages that occur when the stresses imposed on soil particles exceed their strength. Grain breakages(such as granite grains may occur even at relatively low compressive stresses) depend on the character of the individual rock grains. Experiments of grain breakages usually lead scatter data, and are time consuming to perform. A good method based on discrete element method(DEM)gives a potentially useful tool to study single grain breakage. A number of basical particles with diameters of 0.075～0.1245mm are bundled up a grain aggregate using PFC2D.Grain aggregates are used to simulate rock grain. Fractal model and size effect of breakage strength are analysed using grain aggregate based on PFC2D.Experimental data of basalt grain crushing are cited to verify the DEM simulation of the size effect of crushing strength and the modified Weibull modle.
The most important engineering properties of coarse granular materials such as stress-strain and strength behavior, volume change and shear strength depend on the amount of grain breakages that occur when the stresses imposed on soil particles exceed their strength. Grain breakages(such as granite grains may occur even at relatively low compressive stresses) depend on the character of the individual rock grains. Experiments of grain breakages usually lead scatter data, and are time consuming to perform. A good method based on discrete element method(DEM)gives a potentially useful tool to study single grain breakage. A number of basical particles with diameters of 0.075～0.1245mm are bundled up a grain aggregate using PFC2D.Grain aggregates are used to simulate rock grain. Fractal model and size effect of breakage strength are analysed using grain aggregate based on PFC2D.Experimental data of basalt grain crushing are cited to verify the DEM simulation of the size effect of crushing strength and the modified Weibull modle.
2015, 23(4): 597-603.
The shear strength envelope is linear in some range of stress. The commonly used 0～400kPa vertical stress for direct shear tests and confining pressure for triaxial tests can meet many engineering soil stress state of interest. And the shear strength envelope can be linear, designated by cohesion c and internal friction angle .In loess area, high loess slope over 100m is common, and the stress state of soil on the potential failure surface varies greatly from the low to the high. It is necessary to consider the shear strength parameters changing with the stress state. The research herein firstly utilizes a linear elastic finite method to figure out the stress field of a high loess slope. It then consolidates soil samples at the stress state of some key point on the potential sliding surface and performs triaxial compression tests(NCTC).Triaxial compression tests with 100kPa, 200kPa, 300kPa, 400kPa confining pressure are also performed for comparison. Results show that when considering the stress state of high loess slope, the shear strength envelope yielded by the total stress Mohr circle is not linear and the linear M-C criterion is not effective. But that yielded by the effective stress Mohr circles is linear, and the strength parameters are higher than CTC tests. In - space, the shear strength envelope(total and effective) of NCTC is higher than that of CTC, which is related to the high consolidated stress.
The shear strength envelope is linear in some range of stress. The commonly used 0～400kPa vertical stress for direct shear tests and confining pressure for triaxial tests can meet many engineering soil stress state of interest. And the shear strength envelope can be linear, designated by cohesion c and internal friction angle .In loess area, high loess slope over 100m is common, and the stress state of soil on the potential failure surface varies greatly from the low to the high. It is necessary to consider the shear strength parameters changing with the stress state. The research herein firstly utilizes a linear elastic finite method to figure out the stress field of a high loess slope. It then consolidates soil samples at the stress state of some key point on the potential sliding surface and performs triaxial compression tests(NCTC).Triaxial compression tests with 100kPa, 200kPa, 300kPa, 400kPa confining pressure are also performed for comparison. Results show that when considering the stress state of high loess slope, the shear strength envelope yielded by the total stress Mohr circle is not linear and the linear M-C criterion is not effective. But that yielded by the effective stress Mohr circles is linear, and the strength parameters are higher than CTC tests. In - space, the shear strength envelope(total and effective) of NCTC is higher than that of CTC, which is related to the high consolidated stress.
2015, 23(4): 604-608.
Moving mountains to fill out the ditch is a new measure to deal with the shortage of construction land in loess areas. Conducting dynamic strength characteristics research on compacted loess has important theoretical and practical significance for large-scale site formation of moving mountains to fill out the ditches in loess areas of high seismic intensity. This paper uses GDS vibrating triaxial to study the dynamic strength characteristics of Lvliang compacted loess under different conditions of the moisture content, dry density and loading frequency. The results show that the dynamic strength reduces with the increasing of moisture content and increases with the increasing of dry density and loading frequency. The moisture content has significant effect on the dynamic strength of compacted loess. The dynamic strength of compacted loess decreases with the increasing of vibration times. Linear equations under a semi-logarithmic coordinate can be used to fit their relationship.
Moving mountains to fill out the ditch is a new measure to deal with the shortage of construction land in loess areas. Conducting dynamic strength characteristics research on compacted loess has important theoretical and practical significance for large-scale site formation of moving mountains to fill out the ditches in loess areas of high seismic intensity. This paper uses GDS vibrating triaxial to study the dynamic strength characteristics of Lvliang compacted loess under different conditions of the moisture content, dry density and loading frequency. The results show that the dynamic strength reduces with the increasing of moisture content and increases with the increasing of dry density and loading frequency. The moisture content has significant effect on the dynamic strength of compacted loess. The dynamic strength of compacted loess decreases with the increasing of vibration times. Linear equations under a semi-logarithmic coordinate can be used to fit their relationship.
2015, 23(4): 609-615.
The micromechanical parameters of numerical model are obtained by repeated tests. Researches on particle material based on DEM are done. This article builds a numerical model of soil using LMGC, an open source software. And the 25 groups of macromechanical and micromechanical parameters calculated by the numerical model build a BP neural network. The BP neural network can back-calculates the micromechanical parameters if the macromechanical parameters of real physical tests are inputted into the neutral network. The numerical model can get the stress-strain line, stress train and particle rotation graph if the micromechanical parameters are set. The results show that the numerical model can well simulate the soil destruction process. The stress-strain line of numerical model matches well with the result of physical test. And error of macromechanical parameters calculated by BP neural network is about 10%.Besides, the stress train and particle rotation graph reveal the mechanism of soil destruction process.
The micromechanical parameters of numerical model are obtained by repeated tests. Researches on particle material based on DEM are done. This article builds a numerical model of soil using LMGC, an open source software. And the 25 groups of macromechanical and micromechanical parameters calculated by the numerical model build a BP neural network. The BP neural network can back-calculates the micromechanical parameters if the macromechanical parameters of real physical tests are inputted into the neutral network. The numerical model can get the stress-strain line, stress train and particle rotation graph if the micromechanical parameters are set. The results show that the numerical model can well simulate the soil destruction process. The stress-strain line of numerical model matches well with the result of physical test. And error of macromechanical parameters calculated by BP neural network is about 10%.Besides, the stress train and particle rotation graph reveal the mechanism of soil destruction process.
2015, 23(4): 616-623.
Heavy rainfall can change the permeability characteristics of aggregate gravel soil, which is the key factor triggering landslides, mudslides and other type of rainfall-induced disasters. This paper explores the dynamic mechanism of landslide induced by rainfall infiltration. Self-made one-dimensional permeameter and two-dimensional slope model are used for the representative gradation gravel soil test close to Shuizuwan Tunnel. Then, further research focuses on the seepage regulation of aggregate through Seep/w software. The results show that: there is a step-ladder trend between wetting front and time curve. More specifically, wetting front migration rate can rapidly increase with the sudden increase of the topsoil moisture to a maximum. It can slowly decrease with increased pressure. Finally the wetting front migration rate can slightly increase with the decreased pressure. The average rate of wetting front migration approaches a linear growth with the increased rainfall intensity. Development of soil settlement deformation passes through three stages. They are slow growth, sharply rises and gradually stagnation. The one-dimensional infiltration rate has a power, logarithmic and linear relations with the slope infiltration rates at top, middle and toe of the slope, respectively. The final depth of rainwater infiltration is the toe of slope, the top of slope and mid-slop in order descending.
Heavy rainfall can change the permeability characteristics of aggregate gravel soil, which is the key factor triggering landslides, mudslides and other type of rainfall-induced disasters. This paper explores the dynamic mechanism of landslide induced by rainfall infiltration. Self-made one-dimensional permeameter and two-dimensional slope model are used for the representative gradation gravel soil test close to Shuizuwan Tunnel. Then, further research focuses on the seepage regulation of aggregate through Seep/w software. The results show that: there is a step-ladder trend between wetting front and time curve. More specifically, wetting front migration rate can rapidly increase with the sudden increase of the topsoil moisture to a maximum. It can slowly decrease with increased pressure. Finally the wetting front migration rate can slightly increase with the decreased pressure. The average rate of wetting front migration approaches a linear growth with the increased rainfall intensity. Development of soil settlement deformation passes through three stages. They are slow growth, sharply rises and gradually stagnation. The one-dimensional infiltration rate has a power, logarithmic and linear relations with the slope infiltration rates at top, middle and toe of the slope, respectively. The final depth of rainwater infiltration is the toe of slope, the top of slope and mid-slop in order descending.
2015, 23(4): 624-633.
Large-scale rock landslides always are accompanied by thermal effect. Reduction of friction coefficient caused by the thermal effect can be used to explain the phenomenon of high-speed and long travel distance of landslide debris. The objective of this study is to understand the characteristics of heat generating on the rock joint surface after shear failure. First, the temperature and geometric data with respect to discontinuities surface are investigated using infrared thermal radiation imager and three-dimensional(3D)laser scanner respectively. Secondly, based on the statistical methods, the surface temperature distribution of rock joint after shear failure is obtained. On the other hand, the improved 2D divider method is employed to estimate the rock joint surface roughness through calculation of fractal dimension value for each sample. Thirdly, combined with the direct shear tests, multiple regression analysis is conducted among average temperature, normal stress, and roughness on the surface of rock joint. Under the condition of low shear speed( at the primary stage of sliding), the following results are found that:(1)The average temperature on the surface increases with the roughness of rock joint. The heat is mainly concentrated in the convex parts of rock joint surface; (2)The average temperature on the surface is directly proportional to the normal stress loaded on the rock joint; (3)The effect of rock joint surface roughness on the heat generation after shear failure is slightly larger than that of the normal stress. The testing results can provide technical parameters and theoretical help for investigation of energy during failure of large-scale rock landslides.
Large-scale rock landslides always are accompanied by thermal effect. Reduction of friction coefficient caused by the thermal effect can be used to explain the phenomenon of high-speed and long travel distance of landslide debris. The objective of this study is to understand the characteristics of heat generating on the rock joint surface after shear failure. First, the temperature and geometric data with respect to discontinuities surface are investigated using infrared thermal radiation imager and three-dimensional(3D)laser scanner respectively. Secondly, based on the statistical methods, the surface temperature distribution of rock joint after shear failure is obtained. On the other hand, the improved 2D divider method is employed to estimate the rock joint surface roughness through calculation of fractal dimension value for each sample. Thirdly, combined with the direct shear tests, multiple regression analysis is conducted among average temperature, normal stress, and roughness on the surface of rock joint. Under the condition of low shear speed( at the primary stage of sliding), the following results are found that:(1)The average temperature on the surface increases with the roughness of rock joint. The heat is mainly concentrated in the convex parts of rock joint surface; (2)The average temperature on the surface is directly proportional to the normal stress loaded on the rock joint; (3)The effect of rock joint surface roughness on the heat generation after shear failure is slightly larger than that of the normal stress. The testing results can provide technical parameters and theoretical help for investigation of energy during failure of large-scale rock landslides.
2015, 23(4): 634-640.
This paper investigate the characteristics of salt single well solution mining, and analyzed the key stratum of salt single well solution mining cavity by the theory of elastic thin circle plate. This study provides theoretical basis for the key stratum theory applying to the moving law research of salt cavity overlying strata, and it is a new supplement research result of key stratum theory. This paper put the subsidence differential equation of salt solution mining cavity overlying strata, the stress and the first breaking distance calculation formula on the key stratum of cavity overlying strata, and analyzed the stress characteristics of the key stratum of cavity overlying strata. This paper also put the criterion equation which suitable for distinguishing the key stratum of salt single well solution mining cavity overlying strata. Finally, this paper proposed the key stratum theory in the application of the cavity overlying strata control for salt single well solution mining.
This paper investigate the characteristics of salt single well solution mining, and analyzed the key stratum of salt single well solution mining cavity by the theory of elastic thin circle plate. This study provides theoretical basis for the key stratum theory applying to the moving law research of salt cavity overlying strata, and it is a new supplement research result of key stratum theory. This paper put the subsidence differential equation of salt solution mining cavity overlying strata, the stress and the first breaking distance calculation formula on the key stratum of cavity overlying strata, and analyzed the stress characteristics of the key stratum of cavity overlying strata. This paper also put the criterion equation which suitable for distinguishing the key stratum of salt single well solution mining cavity overlying strata. Finally, this paper proposed the key stratum theory in the application of the cavity overlying strata control for salt single well solution mining.
2015, 23(4): 641-645.
In recent years, groundwater contamination can be caused by deep geological disposal of nuclear waste, CO2 deep geological disposal, landfills, hydroelectric reservoir leakage, oil pipeline leakage, which is attracted much attentions. The safety and reliability of these projects are closely related with the low-permeability rock. For this problem, the low permeability of shale is studied with hydraulic fracturing method to measure stress and water pressure test method for measuring rock permeability. The results show that: (1)Stress value of the study area shows an increasing trend with the depth of the hole, in line with the general distribution of stress; (2)Rock permeability decreases with depth. From 0 to 100m deep, water permeability changes greatly. From 100 to 400m deep, water permeability changes little. From 400 to 600m deep, the rock permeability rate remains at a relatively stable order of magnitude. According to regression analysis, the rock permeability rate and depth of the hole have a good negative exponential relationship. (3)Rock permeability and geo-stress have a negative exponential relationship. The impact of geo-stress on the rock permeability is a certain difference at different regions. This is consistent with the findings of other scholars. It forms the foundation for future research on seepage of low-permeability rock.
In recent years, groundwater contamination can be caused by deep geological disposal of nuclear waste, CO2 deep geological disposal, landfills, hydroelectric reservoir leakage, oil pipeline leakage, which is attracted much attentions. The safety and reliability of these projects are closely related with the low-permeability rock. For this problem, the low permeability of shale is studied with hydraulic fracturing method to measure stress and water pressure test method for measuring rock permeability. The results show that: (1)Stress value of the study area shows an increasing trend with the depth of the hole, in line with the general distribution of stress; (2)Rock permeability decreases with depth. From 0 to 100m deep, water permeability changes greatly. From 100 to 400m deep, water permeability changes little. From 400 to 600m deep, the rock permeability rate remains at a relatively stable order of magnitude. According to regression analysis, the rock permeability rate and depth of the hole have a good negative exponential relationship. (3)Rock permeability and geo-stress have a negative exponential relationship. The impact of geo-stress on the rock permeability is a certain difference at different regions. This is consistent with the findings of other scholars. It forms the foundation for future research on seepage of low-permeability rock.
2015, 23(4): 646-653.
This paper uses scanning electron microscope and optical digital microscope to analyzes the relationship between the structure changes of surface micro-area on loess sample and its collapsibility, the soil samples microstructures at different depths influenced by both water and load before and after loess collapse. The image of microstructure is studied by image processing software. The number variation of large pores, medium pores, small pores and micro-pores before and after the loess collapses are analyzed. The results show that after collapse of the loess, the micro pores increase by 31.18%, small pores increase by 54.07%, medium pores decrease by 30.49%, large pores decrease by 90.14%.This shows that with increasing of pressure, the pores of loess are gradually compressed. The numbers of medium pores and large pores gradually decrease while the numbers of small pores and micro-pores gradually increase, which provide sufficient space for collapsible deformation of loess. The contribution of the four types of porosity to loess collapsibility is discussed to comprehensively analyze the formation mechanism of loess collapsibility form the micro perspective.
This paper uses scanning electron microscope and optical digital microscope to analyzes the relationship between the structure changes of surface micro-area on loess sample and its collapsibility, the soil samples microstructures at different depths influenced by both water and load before and after loess collapse. The image of microstructure is studied by image processing software. The number variation of large pores, medium pores, small pores and micro-pores before and after the loess collapses are analyzed. The results show that after collapse of the loess, the micro pores increase by 31.18%, small pores increase by 54.07%, medium pores decrease by 30.49%, large pores decrease by 90.14%.This shows that with increasing of pressure, the pores of loess are gradually compressed. The numbers of medium pores and large pores gradually decrease while the numbers of small pores and micro-pores gradually increase, which provide sufficient space for collapsible deformation of loess. The contribution of the four types of porosity to loess collapsibility is discussed to comprehensively analyze the formation mechanism of loess collapsibility form the micro perspective.
2015, 23(4): 654-659.
Geotechnical model featured by vivid and visualized research method of rock physical and mechanical property is widely used in the field of geotechnical engineering both at home and abroad. In geotechnical model tests, the speed of accuracy of material ration selection plays a pivotal part to the success of the prototype. With the wider spread application of dynamical model in geotechnical model experience, the study of similar material ratio also converts its direction from statics to dynamics. Similar material is the mixture of aggregate and cement, and the change of their ratio exerts a great influence on the property of similar material selecting river sand as the aggregate, cement and plaster as the cementing agent. This paper studies the physics and mechanical property under different ratio conditions by the elastic wave speed simulation measurement and uniaxial compressive test. Experimental results show that on the condition that the cement or plaster alone serves as cementing agent and the amount of aggregate and cement remains constant, the mass, dynamic and static elasticity modulus of the specimen will climb up and then decline with the increase of sand-binder ratio, while when the mixture of cement and plaster serve as cementing agent and the amount of cementing agent and sand-binder ratio remain constant, the dynamic and static elasticity modulus of the specimen will decline followed by a climb with an increase of cement and plaster-use ration.
Geotechnical model featured by vivid and visualized research method of rock physical and mechanical property is widely used in the field of geotechnical engineering both at home and abroad. In geotechnical model tests, the speed of accuracy of material ration selection plays a pivotal part to the success of the prototype. With the wider spread application of dynamical model in geotechnical model experience, the study of similar material ratio also converts its direction from statics to dynamics. Similar material is the mixture of aggregate and cement, and the change of their ratio exerts a great influence on the property of similar material selecting river sand as the aggregate, cement and plaster as the cementing agent. This paper studies the physics and mechanical property under different ratio conditions by the elastic wave speed simulation measurement and uniaxial compressive test. Experimental results show that on the condition that the cement or plaster alone serves as cementing agent and the amount of aggregate and cement remains constant, the mass, dynamic and static elasticity modulus of the specimen will climb up and then decline with the increase of sand-binder ratio, while when the mixture of cement and plaster serve as cementing agent and the amount of cementing agent and sand-binder ratio remain constant, the dynamic and static elasticity modulus of the specimen will decline followed by a climb with an increase of cement and plaster-use ration.
2015, 23(4): 660-667.
Triaxial compression tests with constant-strain-rate are performed on samples retrieved from a slope with slow movement experience. The viscous properties of the fine sand under air-dried condition are observed. The results include: (1)The rate effect, showing by the increase in strength with strain rate, is quantified by rate sensitivity coefficient. (2)The research focuses on the viscous properties at residual state, which shown by partially decay of stress jump induced by a sudden change of strain rate with the increase in displacement. The decay is quantified by using the rate sensitivity coefficient. (3)The effect of viscous property on the residual strength is shown by the rate effect and relaxation.
Triaxial compression tests with constant-strain-rate are performed on samples retrieved from a slope with slow movement experience. The viscous properties of the fine sand under air-dried condition are observed. The results include: (1)The rate effect, showing by the increase in strength with strain rate, is quantified by rate sensitivity coefficient. (2)The research focuses on the viscous properties at residual state, which shown by partially decay of stress jump induced by a sudden change of strain rate with the increase in displacement. The decay is quantified by using the rate sensitivity coefficient. (3)The effect of viscous property on the residual strength is shown by the rate effect and relaxation.
2015, 23(4): 668-674.
The stress-dependent pressure plate extractor system is used to study the residual soil SWCC curve of different vertical stresses, drying and wetting cycles and different types of natural residual cohesive soil and residual sandy clay. Then the laws of SWCC hysteresis loop area with and without volume change and AEV and AexV of residual soils are analyzed and compared. Results show that not only the ability of soil to resist deformation can be overestimated by the traditional method of SWCC curve, but also the underlying cause of SWCC curve changing is due to soil internal structure change constantly; Meanwhile, the higher net stress levels are, the larger size pores are much more influenced by the net stress. Thus the wetting branch is much more affected. The observed unequal change in the shape of drying and wetting branches of SWCC at higher net stress values brings them close to each other, and reduces the SWCC hysteresis as the net stress level increasing. Finally, according the simplicity of model parameters and the goodness-of-fit analysis results of the 3 kinds of improved SWCC models, the improved VG model has been found to be the most suitable model for all SWCC of the natural residual soil in southeast of Fujian. The above research is useful and meaningful as reference for the engineering characteristics and governance of the residual slope.
The stress-dependent pressure plate extractor system is used to study the residual soil SWCC curve of different vertical stresses, drying and wetting cycles and different types of natural residual cohesive soil and residual sandy clay. Then the laws of SWCC hysteresis loop area with and without volume change and AEV and AexV of residual soils are analyzed and compared. Results show that not only the ability of soil to resist deformation can be overestimated by the traditional method of SWCC curve, but also the underlying cause of SWCC curve changing is due to soil internal structure change constantly; Meanwhile, the higher net stress levels are, the larger size pores are much more influenced by the net stress. Thus the wetting branch is much more affected. The observed unequal change in the shape of drying and wetting branches of SWCC at higher net stress values brings them close to each other, and reduces the SWCC hysteresis as the net stress level increasing. Finally, according the simplicity of model parameters and the goodness-of-fit analysis results of the 3 kinds of improved SWCC models, the improved VG model has been found to be the most suitable model for all SWCC of the natural residual soil in southeast of Fujian. The above research is useful and meaningful as reference for the engineering characteristics and governance of the residual slope.
2015, 23(4): 675-680.
Creep and consolidation of soft soil are key issues in soil mechanics research and engineering construction. But the traditional consolidation theory cannot consider the rheological properties of soft soil. The secondary consolidation settlement of soft soil cannot be explained accurately. In order to research the consolidation and creep characteristics of soft soil, the secondary consolidation settlement and the rule of stress and deformation, this paper improves the traditional consolidation theory. On the basis of Terzaghi one-dimensional consolidation theory, one-dimensional rheological consolidation differential equation considering the effect of secondary consolidation is established. It uses the coefficient of secondary consolidation and modified Singh-Mitchell's experience creep model. On the basis of Terzaghi three-dimensional consolidation theory and Biot consolidation theory, three-dimensional rheological consolidation differential equation considering the effect of secondary consolidation is also established. It uses the modified Singh-Mitchell experience creep model. The new rheological consolidation differential equation can reflect the consolidation and creep character of soft soil and the stress-strain-time relationship more accurately. It can provide new theoretical basis for the study of the soft soil consolidation settlement.
Creep and consolidation of soft soil are key issues in soil mechanics research and engineering construction. But the traditional consolidation theory cannot consider the rheological properties of soft soil. The secondary consolidation settlement of soft soil cannot be explained accurately. In order to research the consolidation and creep characteristics of soft soil, the secondary consolidation settlement and the rule of stress and deformation, this paper improves the traditional consolidation theory. On the basis of Terzaghi one-dimensional consolidation theory, one-dimensional rheological consolidation differential equation considering the effect of secondary consolidation is established. It uses the coefficient of secondary consolidation and modified Singh-Mitchell's experience creep model. On the basis of Terzaghi three-dimensional consolidation theory and Biot consolidation theory, three-dimensional rheological consolidation differential equation considering the effect of secondary consolidation is also established. It uses the modified Singh-Mitchell experience creep model. The new rheological consolidation differential equation can reflect the consolidation and creep character of soft soil and the stress-strain-time relationship more accurately. It can provide new theoretical basis for the study of the soft soil consolidation settlement.
2015, 23(4): 681-686.
Most analytical solutions of sand and wick drains are combined with one-dimensional consolidation theory. The soil is considered as a linear poroelastic solid. But researches show that, under the isotropic consolidation, the average effective stress and permeability coefficient both have semi-logarithmic relationships with the void ratio. At the same time, experiments show that the permeability around PVD in smear zone is distributed in parabolic form. Therefore, to consider the effects of these three non-linear relationships, the analytical solution to this problem is derived in this paper. Correctness of this analytical solution is verified through degradation method. In addition, effects of parameters of Cc/Ck and on consolidation are analyzed. The results show that the rate of consolidation under Cc/Ck1 is faster than that of Cc/Ck1; and the rate of consolidation decreases with the growth of .
Most analytical solutions of sand and wick drains are combined with one-dimensional consolidation theory. The soil is considered as a linear poroelastic solid. But researches show that, under the isotropic consolidation, the average effective stress and permeability coefficient both have semi-logarithmic relationships with the void ratio. At the same time, experiments show that the permeability around PVD in smear zone is distributed in parabolic form. Therefore, to consider the effects of these three non-linear relationships, the analytical solution to this problem is derived in this paper. Correctness of this analytical solution is verified through degradation method. In addition, effects of parameters of Cc/Ck and on consolidation are analyzed. The results show that the rate of consolidation under Cc/Ck1 is faster than that of Cc/Ck1; and the rate of consolidation decreases with the growth of .
2015, 23(4): 687-694.
A large amount of sludge is often produced in the environment regulation and dredging process of urban river. It has important significance for improving the urban ecological environment and economic sustainable development to safely and efficiently dispose this kind of municipal sludge. Municipal sludge usually has high moisture content, void ratio and compressibility. More importantly, it has a very high fraction of organic and fine particles. It is therefore hard to reduce the total volume through mechanical dehydration. For this reason, accelerating the mechanical dehydration rate and improving the consolidation properties are the top priority during disposing and utilizing the sludge, which is also one of the most significant issues in this subject. In this investigation, the method of discrete short fiber reinforcement technique is proposed and applied to deal with municipal sludge. In order to study the effect of fiber reinforcement on sludge consolidation properties, a series of oedometer tests are conducted on sludge with different fiber contents(0, 0.05%, 0.1%, 0.2%, 0.4% and 0.8%).The effect of fiber addition on the coefficient of consolidation and permeability is analyzed. The results show that the deformation and void ratio of sample increase significantly with increasing fiber content while the consolidation time and coefficient of compressibility decrease with increasing fiber content under the same load conditions. When the fiber content is 0.1%, these changes are most significant, which can be considered as the optimal fiber content. In addition, the results prove that the inclusion of fiber can increase the consolidation coefficient and hydraulic conductivity of sludge. The corresponding consolidation efficiency and mechanical properties are also improved.
A large amount of sludge is often produced in the environment regulation and dredging process of urban river. It has important significance for improving the urban ecological environment and economic sustainable development to safely and efficiently dispose this kind of municipal sludge. Municipal sludge usually has high moisture content, void ratio and compressibility. More importantly, it has a very high fraction of organic and fine particles. It is therefore hard to reduce the total volume through mechanical dehydration. For this reason, accelerating the mechanical dehydration rate and improving the consolidation properties are the top priority during disposing and utilizing the sludge, which is also one of the most significant issues in this subject. In this investigation, the method of discrete short fiber reinforcement technique is proposed and applied to deal with municipal sludge. In order to study the effect of fiber reinforcement on sludge consolidation properties, a series of oedometer tests are conducted on sludge with different fiber contents(0, 0.05%, 0.1%, 0.2%, 0.4% and 0.8%).The effect of fiber addition on the coefficient of consolidation and permeability is analyzed. The results show that the deformation and void ratio of sample increase significantly with increasing fiber content while the consolidation time and coefficient of compressibility decrease with increasing fiber content under the same load conditions. When the fiber content is 0.1%, these changes are most significant, which can be considered as the optimal fiber content. In addition, the results prove that the inclusion of fiber can increase the consolidation coefficient and hydraulic conductivity of sludge. The corresponding consolidation efficiency and mechanical properties are also improved.
2015, 23(4): 695-699.
Marble under the environment of high water pressure and high stress are present in the deep buried tunnel of Jinping-II Hydropower Station. Several serious tunnel gushing hazards occurred at the marble sections during the construction process of the deep buried tunnel. Marble mechanical test under high water pressure indicates that a flat section appears near peak stress on the stress-strain curve. The stress drop is very big. Rock peak strength and degree of crushing after brittle failure increase with the increasing of water pressure. Compression cracking is the main failure pattern of marble samples. Stress analysis around cracks suggests that high water pressure in cracks reduces the stress concentration effects near crack tip, and the approximately equal concentration effects of maximum tensile stress near crack tips within a small angle range from loading direction. Therefore, the strain energy and the compression-cracking micro-crack quantity in the marble can further increase. The brittle failure can be developed. The degree of crushing of rock is significantly increased. This study has important academic and practical significances for the prevention of deep buried tunnel gushing hazards and high speed landslide hazards induced by heavy rainfall.
Marble under the environment of high water pressure and high stress are present in the deep buried tunnel of Jinping-II Hydropower Station. Several serious tunnel gushing hazards occurred at the marble sections during the construction process of the deep buried tunnel. Marble mechanical test under high water pressure indicates that a flat section appears near peak stress on the stress-strain curve. The stress drop is very big. Rock peak strength and degree of crushing after brittle failure increase with the increasing of water pressure. Compression cracking is the main failure pattern of marble samples. Stress analysis around cracks suggests that high water pressure in cracks reduces the stress concentration effects near crack tip, and the approximately equal concentration effects of maximum tensile stress near crack tips within a small angle range from loading direction. Therefore, the strain energy and the compression-cracking micro-crack quantity in the marble can further increase. The brittle failure can be developed. The degree of crushing of rock is significantly increased. This study has important academic and practical significances for the prevention of deep buried tunnel gushing hazards and high speed landslide hazards induced by heavy rainfall.
2015, 23(4): 700-705.
The safety situation of retaining wall is directly related to the safety of railway transportation system. Evaluation of the safety of the retaining wall is a problem urgently to be solved in. In this paper, the safety evaluation index system of retaining wall on the existing railway is established. It includes surface view of status, material status, and force status. These status are level indicators. It also includes wall body, wall, cracks, mortar and other six projects. They are the secondary indicators. The index system has the advantages of distinct, and the combination of qualitative and quantitative. In order to overcome the subjectivity of traditional safety assessment methods, the analysis hierarchy process and fuzzy mathematical comprehensive safety assessment method are put forward. The method quantifies evaluation results. The result of the research of safety assessment system of retaining wall combining practical engineering shows that the method can give the retaining wall a more objective overall evaluation.
The safety situation of retaining wall is directly related to the safety of railway transportation system. Evaluation of the safety of the retaining wall is a problem urgently to be solved in. In this paper, the safety evaluation index system of retaining wall on the existing railway is established. It includes surface view of status, material status, and force status. These status are level indicators. It also includes wall body, wall, cracks, mortar and other six projects. They are the secondary indicators. The index system has the advantages of distinct, and the combination of qualitative and quantitative. In order to overcome the subjectivity of traditional safety assessment methods, the analysis hierarchy process and fuzzy mathematical comprehensive safety assessment method are put forward. The method quantifies evaluation results. The result of the research of safety assessment system of retaining wall combining practical engineering shows that the method can give the retaining wall a more objective overall evaluation.
2015, 23(4): 706-711.
Drainage is an effective method for landslide control. Siphon with free power can realize water transport and the flow process controlled by liquid level change. It is very suitable for the need of slope groundwater control. But the highest siphon head 10m and intermittent drainage may produce siphon top air accumulation, which restricts the application of landslide drainage. Using declined drilling into the deep slope, and keeping the difference between the groundwater level control point height and the orifice height less than 10m, can realize the landslide deep groundwater descending requirements. Controlling the siphon drainage pipe diameter, the siphon tube to form a stable slug flow can prevent air accumulation. So, it can realize the continuous siphon process. Based on a thin seam model, it has proved that the maximum diameter of the siphon to form stable slug flow is about 4mm by energy method derived. The long-term static model also verified that 4mm diameter PA tube can form a complete slug flow. Examples are given to demonstrate the drainage project selection 4mm siphon, which can realize the landslide deep drainage and automatic restoration of siphon in intermittent process.
Drainage is an effective method for landslide control. Siphon with free power can realize water transport and the flow process controlled by liquid level change. It is very suitable for the need of slope groundwater control. But the highest siphon head 10m and intermittent drainage may produce siphon top air accumulation, which restricts the application of landslide drainage. Using declined drilling into the deep slope, and keeping the difference between the groundwater level control point height and the orifice height less than 10m, can realize the landslide deep groundwater descending requirements. Controlling the siphon drainage pipe diameter, the siphon tube to form a stable slug flow can prevent air accumulation. So, it can realize the continuous siphon process. Based on a thin seam model, it has proved that the maximum diameter of the siphon to form stable slug flow is about 4mm by energy method derived. The long-term static model also verified that 4mm diameter PA tube can form a complete slug flow. Examples are given to demonstrate the drainage project selection 4mm siphon, which can realize the landslide deep drainage and automatic restoration of siphon in intermittent process.
2015, 23(4): 712-718.
Based on geologic features of debris flow fan, combined with the engineering background of Futang tunnel in Dujiangyan to Wenchuan expressway, a 3D numerical model had been established to study tunnel excavation and support in debris flow fan. The paper presents different modelling conditions, including the non-support status, designed support status, optimizing support status as well as the deposition and erosion of debris flow fan. The study results show that, tunnel excavated in debris flow fan, the vault settlements are main controlling factor and lead to subsidence and side wall convergence; after pointed optimizing treatment to vault settlement using the advanced grouting and the systematical anchor lengthening, deformation of tunnel lining and subsidence are reduce markedly, it shows that the optimizations are effectual and reasonable. In addition, if the deposition thickness of debris flow above tunnel vault is less than 14 m, the tunnel is in obvious unsafe condition; if the debris flow thickness is more than 42 m, the stability of surrounding rock will become better and be easy to form a stabilizing system.
Based on geologic features of debris flow fan, combined with the engineering background of Futang tunnel in Dujiangyan to Wenchuan expressway, a 3D numerical model had been established to study tunnel excavation and support in debris flow fan. The paper presents different modelling conditions, including the non-support status, designed support status, optimizing support status as well as the deposition and erosion of debris flow fan. The study results show that, tunnel excavated in debris flow fan, the vault settlements are main controlling factor and lead to subsidence and side wall convergence; after pointed optimizing treatment to vault settlement using the advanced grouting and the systematical anchor lengthening, deformation of tunnel lining and subsidence are reduce markedly, it shows that the optimizations are effectual and reasonable. In addition, if the deposition thickness of debris flow above tunnel vault is less than 14 m, the tunnel is in obvious unsafe condition; if the debris flow thickness is more than 42 m, the stability of surrounding rock will become better and be easy to form a stabilizing system.
2015, 23(4): 719-724.
The risk evaluation of debris flow on reservoir bank is a very complicated problem because the influence factors are random, nonlinear and uncertainty. The Wudongde reservoir area is located at the lower reaches of the Jinsha River. It is selected as a case study. The ten impact factors covering history of outbreak, geological condition, terrain condition and hazard inducing factors, are chosen according to the geological and environmental conditions of reservoir area. Furthermore, the debris flow risk classification is established and divided into four grades of extremely severe, severe, moderate and mild. The set pair analysis theory is used to analyze the impact factors represented by the interval number. A new model of connectional expectation for debris flow risk evaluation is introduced. This model can be used to analyze variation trend of debris flow impact factors. The case study shows that the new method is reliable and can simplify the analysis process of the relationship between interval numbers.
The risk evaluation of debris flow on reservoir bank is a very complicated problem because the influence factors are random, nonlinear and uncertainty. The Wudongde reservoir area is located at the lower reaches of the Jinsha River. It is selected as a case study. The ten impact factors covering history of outbreak, geological condition, terrain condition and hazard inducing factors, are chosen according to the geological and environmental conditions of reservoir area. Furthermore, the debris flow risk classification is established and divided into four grades of extremely severe, severe, moderate and mild. The set pair analysis theory is used to analyze the impact factors represented by the interval number. A new model of connectional expectation for debris flow risk evaluation is introduced. This model can be used to analyze variation trend of debris flow impact factors. The case study shows that the new method is reliable and can simplify the analysis process of the relationship between interval numbers.
2015, 23(4): 725-730.
The erosion is the main cause of natural disasters of the loess highway slope. This paper uses the slope erosion experiment with simulated rainfall model. It can reproduce the splash erosion slope, sheet erosion, gully erosion, and collapse of basic failure process of slope. It can make detailed description and analysis of the process of erosion. The experiment shows that erosion sediment per unit area increase gradually with the increase of experiment slope and total runoff. The erosion sediment decreases gradually with the increase of experiment slope. Meanwhile, there is a corresponding relationship among the main parameters of loess slope erosion such as total erosion runoff, confluence sediment, erosion sediment, and rainfall intensity.
The erosion is the main cause of natural disasters of the loess highway slope. This paper uses the slope erosion experiment with simulated rainfall model. It can reproduce the splash erosion slope, sheet erosion, gully erosion, and collapse of basic failure process of slope. It can make detailed description and analysis of the process of erosion. The experiment shows that erosion sediment per unit area increase gradually with the increase of experiment slope and total runoff. The erosion sediment decreases gradually with the increase of experiment slope. Meanwhile, there is a corresponding relationship among the main parameters of loess slope erosion such as total erosion runoff, confluence sediment, erosion sediment, and rainfall intensity.
2015, 23(4): 731-737.
Darong landslide in Cengong county happened on June 29, 2012. It is a large-scale gentle inclined landslide accumulation deposits. The gradient of slope in the main accumulation area is between 8to 20.The dip angle of the interface between the bedrock and accumulation layer in main sliding area is between 4to 11.Strongly weathered layer distributes in the underlying bedrock. Since 2009, artificial soil has been continuously piled up on the catchment area on the left of accumulation area. Based on characteristics and 3D numerical simulation analysis, the artificial soil and heavy rainfall are the common inducing factor of Darong landslide. They firstly locally made the artificial soil area unstable. Its foot is therefore damaged, and gradually leads to the slope failure. The sliding surface is in the strongly weathered layer. In combination with other typical cases, the structure characteristics of the large gentle inclined accumulation landslide are summarized. Heavy rainfall is the necessary inducing factor of this landslide. When these landslides occur, the local underlying bedrock is often driven.
Darong landslide in Cengong county happened on June 29, 2012. It is a large-scale gentle inclined landslide accumulation deposits. The gradient of slope in the main accumulation area is between 8to 20.The dip angle of the interface between the bedrock and accumulation layer in main sliding area is between 4to 11.Strongly weathered layer distributes in the underlying bedrock. Since 2009, artificial soil has been continuously piled up on the catchment area on the left of accumulation area. Based on characteristics and 3D numerical simulation analysis, the artificial soil and heavy rainfall are the common inducing factor of Darong landslide. They firstly locally made the artificial soil area unstable. Its foot is therefore damaged, and gradually leads to the slope failure. The sliding surface is in the strongly weathered layer. In combination with other typical cases, the structure characteristics of the large gentle inclined accumulation landslide are summarized. Heavy rainfall is the necessary inducing factor of this landslide. When these landslides occur, the local underlying bedrock is often driven.
2015, 23(4): 738-746.
Early-warning of geo-hazards in China, refers to analyze and forecast the probability of regional geo-hazards induced by meteorological factors(mainly rainfall).It has gradually formed a grading business model since 2003, and is classified into national level, provincial level, city and county level. The technological keys and research difficulties of the business are the study on early-warning model and its reliability problem. Considering time-space scale and technical difficulty, early warning models are modeled mainly on the basis of statistical method. Up to now, two generation models have been formed and include mutually calculation, checking and supply. This paper systematically presents the principle, technical method, business application and improved technique of two generation models. The first generation model is named the implicit statistics models, and also named the critical rainfall criterion. It is established on the basis of different rainfalls in different geological environment areas. The model is widely used for involving only one or a group of parameters. It has been improved in model parameters and correcting criterion recently. But, it has difficulty in showing changes of geo-environment and causes of geo-hazards. The first model is also limited by improvement of warning division, accuracy and renewal of criteria. The second generation model is named explicit statistics models and established by taking into consideration of geo-environment and rainfall multi-parameters. In the model, explicit expression of geo-environmental factors, and the advantages of model principle, spatial precision and improving ability are shown. It significantly improves precision and accuracy of early-warning. The second generation model was developed in 2008 and used in national early-warning business, gradually to provincial business. Both are established on statistical method. The two generation early-warning models were influenced by selection of statistical samples, knowing degree of geological environmental conditions and accurate matching of rainfall data in some degree. Over years, the two generation models are operated successfully and improved continuously. Important contributions to geo-hazards mitigation have been made.
Early-warning of geo-hazards in China, refers to analyze and forecast the probability of regional geo-hazards induced by meteorological factors(mainly rainfall).It has gradually formed a grading business model since 2003, and is classified into national level, provincial level, city and county level. The technological keys and research difficulties of the business are the study on early-warning model and its reliability problem. Considering time-space scale and technical difficulty, early warning models are modeled mainly on the basis of statistical method. Up to now, two generation models have been formed and include mutually calculation, checking and supply. This paper systematically presents the principle, technical method, business application and improved technique of two generation models. The first generation model is named the implicit statistics models, and also named the critical rainfall criterion. It is established on the basis of different rainfalls in different geological environment areas. The model is widely used for involving only one or a group of parameters. It has been improved in model parameters and correcting criterion recently. But, it has difficulty in showing changes of geo-environment and causes of geo-hazards. The first model is also limited by improvement of warning division, accuracy and renewal of criteria. The second generation model is named explicit statistics models and established by taking into consideration of geo-environment and rainfall multi-parameters. In the model, explicit expression of geo-environmental factors, and the advantages of model principle, spatial precision and improving ability are shown. It significantly improves precision and accuracy of early-warning. The second generation model was developed in 2008 and used in national early-warning business, gradually to provincial business. Both are established on statistical method. The two generation early-warning models were influenced by selection of statistical samples, knowing degree of geological environmental conditions and accurate matching of rainfall data in some degree. Over years, the two generation models are operated successfully and improved continuously. Important contributions to geo-hazards mitigation have been made.
2015, 23(4): 747-754.
The continuing heavy precipitation is the most trigger factor for loess landslide. Continued heavy precipitation in the summer of 2011 in Guanzhong region caused the accumulation of rainfall up to the 50-return years, which triggered landslides resulting in many traffic disruptions and bringing a serious disaster. In particular, the Baqiao landslide occurred on the September 17(917Baqiao landslide) at the edge of Bailu highland. It had a total of 32 casualties. In order to reveal the causes and mechanism of the landslide and process motion, investigation and analysis of the917Baqiao landslide were implement to reveal disaster characteristics, triggered factors and formation mechanism. The landslide movement simulation was used to restore the process motion and disaster range. The results show that:(1)The landslide relative height is about 90m. The wide is 170m. Initiation average thickness is about 10m. The sliding direction is 55.The sliding distance is 150m. The total volume is about 15104m3. There is the three sliding cases with the sliding volumes are 9.5104m3, 3.5104m3 and 2104m3, respectively. The average deposit thickness is 12m. (2)It appears that the factors behind the 9.17 landslide in Bailu tableland are numerous and can be classified into three main categories. They are the long periods of heavy precipitation, slope cutting results in steepening of the slopes and the vertical joints in the loess. (3)According to the simulation results, the sliding process can be divided into 3 stages: the first stage is the start and accelerate stage(0～7.5s). The velocity is up to 4.9ms-1 and 8.4ms-1 form 0 in x-direction and y-direction, respectively. The sliding distance is 65m. The second stage is a speed reduction sliding(7.5～14s).The velocity is reduce to 1.5ms-1 and 2.5ms-1 in x-direction and y-direction, respectively. The sliding distance is 50m. The last stage is deposited and stoppage. The velocity is reduced to 0 and the deposited change to thin gradually. The sliding distance is 175m and the maximum deposit thickness is 14m. The simulation results are consistent with the field survey. The results provide important reference for understanding and studying mechanism of this type of landslide and also provide guidance for future disaster prevention and mitigation in this region.
The continuing heavy precipitation is the most trigger factor for loess landslide. Continued heavy precipitation in the summer of 2011 in Guanzhong region caused the accumulation of rainfall up to the 50-return years, which triggered landslides resulting in many traffic disruptions and bringing a serious disaster. In particular, the Baqiao landslide occurred on the September 17(917Baqiao landslide) at the edge of Bailu highland. It had a total of 32 casualties. In order to reveal the causes and mechanism of the landslide and process motion, investigation and analysis of the917Baqiao landslide were implement to reveal disaster characteristics, triggered factors and formation mechanism. The landslide movement simulation was used to restore the process motion and disaster range. The results show that:(1)The landslide relative height is about 90m. The wide is 170m. Initiation average thickness is about 10m. The sliding direction is 55.The sliding distance is 150m. The total volume is about 15104m3. There is the three sliding cases with the sliding volumes are 9.5104m3, 3.5104m3 and 2104m3, respectively. The average deposit thickness is 12m. (2)It appears that the factors behind the 9.17 landslide in Bailu tableland are numerous and can be classified into three main categories. They are the long periods of heavy precipitation, slope cutting results in steepening of the slopes and the vertical joints in the loess. (3)According to the simulation results, the sliding process can be divided into 3 stages: the first stage is the start and accelerate stage(0～7.5s). The velocity is up to 4.9ms-1 and 8.4ms-1 form 0 in x-direction and y-direction, respectively. The sliding distance is 65m. The second stage is a speed reduction sliding(7.5～14s).The velocity is reduce to 1.5ms-1 and 2.5ms-1 in x-direction and y-direction, respectively. The sliding distance is 50m. The last stage is deposited and stoppage. The velocity is reduced to 0 and the deposited change to thin gradually. The sliding distance is 175m and the maximum deposit thickness is 14m. The simulation results are consistent with the field survey. The results provide important reference for understanding and studying mechanism of this type of landslide and also provide guidance for future disaster prevention and mitigation in this region.
2015, 23(4): 755-759.
The 2014 Ludian MS 6.5/MW 6.1 earthquake in Yunnan, China caused significant causalities and serious disasters. It also triggered at least 1024 landslides with areas equal to 100m2 or larger. The purpose of this study is to utilize the spatial distribution and scale-changes of coseismic landslides to analyze the source and rupturing process of the 2014 Ludian earthquake. Base on the northwest strike direction of the long axis of the landslide-distribution area and the regional tectonic distribution of the earthquake affected area, the seismogenic fault of the Ludian earthquake is considered to be the Baogunao-Xiaohe fault. Most of the landslides occurred in the areas southeast to the epicenter, which indicates the rupturing direction is from northwest to southeast. The landslides in the northwest part of the affected area is characterized by more, smaller-scales, and larger distribution area, whereas those of the southeast part are few, larger-scales, and distributed in a smaller area. Landslides triggered by blind-ruptured earthquakes always show more quantity, smaller-scale, and larger distribution-area than those of surface-ruptured earthquakes. It can be inferred that the rupturing plane is relatively deep in the northwest section of the seismogenic fault and probably did not generate surface ruptures. The southeast section of the seismogenic fault should be relatively shallower and rupture the ground surface. These inferences have been validated by field investigations. It is concluded the seismic rupturing started from depth in northwest, then spread upward to the shallow subsurface in the southeast, which produced the surface rupture at the terminal of the rupture plane. Such a rupturing process can also explain the unusually serious disasters caused by the Ludian earthquake.
The 2014 Ludian MS 6.5/MW 6.1 earthquake in Yunnan, China caused significant causalities and serious disasters. It also triggered at least 1024 landslides with areas equal to 100m2 or larger. The purpose of this study is to utilize the spatial distribution and scale-changes of coseismic landslides to analyze the source and rupturing process of the 2014 Ludian earthquake. Base on the northwest strike direction of the long axis of the landslide-distribution area and the regional tectonic distribution of the earthquake affected area, the seismogenic fault of the Ludian earthquake is considered to be the Baogunao-Xiaohe fault. Most of the landslides occurred in the areas southeast to the epicenter, which indicates the rupturing direction is from northwest to southeast. The landslides in the northwest part of the affected area is characterized by more, smaller-scales, and larger distribution area, whereas those of the southeast part are few, larger-scales, and distributed in a smaller area. Landslides triggered by blind-ruptured earthquakes always show more quantity, smaller-scale, and larger distribution-area than those of surface-ruptured earthquakes. It can be inferred that the rupturing plane is relatively deep in the northwest section of the seismogenic fault and probably did not generate surface ruptures. The southeast section of the seismogenic fault should be relatively shallower and rupture the ground surface. These inferences have been validated by field investigations. It is concluded the seismic rupturing started from depth in northwest, then spread upward to the shallow subsurface in the southeast, which produced the surface rupture at the terminal of the rupture plane. Such a rupturing process can also explain the unusually serious disasters caused by the Ludian earthquake.
2015, 23(4): 760-768.
The Baishi landslide is located at the west of Beichuan county, Mianyang, Sichuan Province. The landslide was detected due to fast deformation that caused several small collapses and falls in the front of the unstable slope as well as densely distributed tensile cracks in the slope. In order to better understand the stability status and estimate the failure time of the unstable slope, a comprehensive monitoring system was carried out after the deformation was reported. The monitoring was continued till the slope failed. This study analyzes the landslide deformation phases and failure mechanism using the monitoring data. The result shows that the failure mode of the Baishi landslide is bending-tensile(toppling).The failure has both the retrogressive and advancing features. The landslide is divided into several zones according to the spatial variation of deformation characteristics over the slope. The monitoring results indicate that the front part of the slope(Zone I-3)plays a key role in controlling landslide stability. Therefore, the monitoring data of this zone is significantly important for predicting the failure time of the whole landslide.
The Baishi landslide is located at the west of Beichuan county, Mianyang, Sichuan Province. The landslide was detected due to fast deformation that caused several small collapses and falls in the front of the unstable slope as well as densely distributed tensile cracks in the slope. In order to better understand the stability status and estimate the failure time of the unstable slope, a comprehensive monitoring system was carried out after the deformation was reported. The monitoring was continued till the slope failed. This study analyzes the landslide deformation phases and failure mechanism using the monitoring data. The result shows that the failure mode of the Baishi landslide is bending-tensile(toppling).The failure has both the retrogressive and advancing features. The landslide is divided into several zones according to the spatial variation of deformation characteristics over the slope. The monitoring results indicate that the front part of the slope(Zone I-3)plays a key role in controlling landslide stability. Therefore, the monitoring data of this zone is significantly important for predicting the failure time of the whole landslide.
2015, 23(4): 769-777.
Earth fissures are one of the geohazards in Linfen Basin. They firstly occurred here in 1970s.86 earth fissures were found in Linfen Basin in August, 2012. This paper examines the Guochang earth fissure. It expounds in detail the geological environment of Linfen Basin. The geological investigation, measurement, trenching, drilling and geophysical exploration are used to study the characteristics of earth fissure. They include the planes, damages, shallow sectional structure, deep features. It then summarizes the activity of earth fissure. Finally, this paper discovers the main characteristics of Guochang earth fissure. It has planar long extend, fat width, stability of trend, and severe damages. The shallow section is wide at the top and narrow at the bottom, which look likestrumpet.The deep features show the extractive activity existed in the lower part of earth fissure. The activity of ground fissure is controlled by rainfall. The effects of different factors on Guochang earth fissure are analyzed. The factors include tectonic activity, excessive extraction of groundwater and heavy rains. The formation of Guochang earth fissure is divided into the three steps of inoculation, formation and expansion. At last, the formation mechanism of Guochang earth fissure is acquired. The mechanism includes that (1)tectonic activity inoculates the fissure, (2)pumping groundwater triggers the fissure and (3)heavy rainfalls extend the fissure.
Earth fissures are one of the geohazards in Linfen Basin. They firstly occurred here in 1970s.86 earth fissures were found in Linfen Basin in August, 2012. This paper examines the Guochang earth fissure. It expounds in detail the geological environment of Linfen Basin. The geological investigation, measurement, trenching, drilling and geophysical exploration are used to study the characteristics of earth fissure. They include the planes, damages, shallow sectional structure, deep features. It then summarizes the activity of earth fissure. Finally, this paper discovers the main characteristics of Guochang earth fissure. It has planar long extend, fat width, stability of trend, and severe damages. The shallow section is wide at the top and narrow at the bottom, which look likestrumpet.The deep features show the extractive activity existed in the lower part of earth fissure. The activity of ground fissure is controlled by rainfall. The effects of different factors on Guochang earth fissure are analyzed. The factors include tectonic activity, excessive extraction of groundwater and heavy rains. The formation of Guochang earth fissure is divided into the three steps of inoculation, formation and expansion. At last, the formation mechanism of Guochang earth fissure is acquired. The mechanism includes that (1)tectonic activity inoculates the fissure, (2)pumping groundwater triggers the fissure and (3)heavy rainfalls extend the fissure.
2015, 23(4): 778-783.
This paper examines advanced geological forecasting of landslide about one tunnel body during construction. It takes an expressway tunnel as an example for technology and evaluation. It introduces the general situation of the tunnel engineering and the basic engineering geological condition of the landslide. Several methods including trend extrapolation of geology, reflection wave of geological radar, and advanced borehole are adopted for analytical prediction about the features of landslide. These features include the extension, scale, material composition, engineering and physical and mechanical properties, and the spatial location-relation with the tunnel. A comprehensive conclusion is obtained about advanced geological forecasting. It can reduce and /or even avoid the defects of the single method, and put forward the corresponding construction treatment ideas.
This paper examines advanced geological forecasting of landslide about one tunnel body during construction. It takes an expressway tunnel as an example for technology and evaluation. It introduces the general situation of the tunnel engineering and the basic engineering geological condition of the landslide. Several methods including trend extrapolation of geology, reflection wave of geological radar, and advanced borehole are adopted for analytical prediction about the features of landslide. These features include the extension, scale, material composition, engineering and physical and mechanical properties, and the spatial location-relation with the tunnel. A comprehensive conclusion is obtained about advanced geological forecasting. It can reduce and /or even avoid the defects of the single method, and put forward the corresponding construction treatment ideas.
2015, 23(4): 784-789.
This paper is based on the detailed investigation of roadway water flowing fractures for the water seepage. It analyzes the connectivity advantage of orientation and mine water seepage and surface water bodies of two gold mines at Sanshadao. It summarizes the distribution of crack occurrence, and gushing water sample temperature, salinity and dynamic monitoring of the results of hydrogen and oxygen isotope. The study shows that the water-seepage dominant orientation in the district of Xishan mine is parallel to the maximum horizontal principal stress. The optimal direction of Xinli mine water seepage is nearly perpendicular to the maximum horizontal principal stress. The Xishan mine has stable recharge of seawater, rock saline, and Quaternary fresh water. In the Xinli mine, the proportions of saline and fresh water in inrushing water in mine pits are diminishing gradually, as the seawater increases. The role of neotectonic fractures in controlling the dominant orientations of mine water seepage is stronger than that of fractures developed by excavation. The neotectonic fractures make the Xishan mine have well connectivity with surface waters and control the recharge process of the seawater. There is weaker connectedness between pits and surface waters in the Xinli mine which attributes to the mining-induced fractures.
This paper is based on the detailed investigation of roadway water flowing fractures for the water seepage. It analyzes the connectivity advantage of orientation and mine water seepage and surface water bodies of two gold mines at Sanshadao. It summarizes the distribution of crack occurrence, and gushing water sample temperature, salinity and dynamic monitoring of the results of hydrogen and oxygen isotope. The study shows that the water-seepage dominant orientation in the district of Xishan mine is parallel to the maximum horizontal principal stress. The optimal direction of Xinli mine water seepage is nearly perpendicular to the maximum horizontal principal stress. The Xishan mine has stable recharge of seawater, rock saline, and Quaternary fresh water. In the Xinli mine, the proportions of saline and fresh water in inrushing water in mine pits are diminishing gradually, as the seawater increases. The role of neotectonic fractures in controlling the dominant orientations of mine water seepage is stronger than that of fractures developed by excavation. The neotectonic fractures make the Xishan mine have well connectivity with surface waters and control the recharge process of the seawater. There is weaker connectedness between pits and surface waters in the Xinli mine which attributes to the mining-induced fractures.
2015, 23(4): 790-794.
Susceptibility analysis is an effective method to obtain characteristics of developments of catchment. There is a concomitant or alternate pattern of flash flood and debris flow in the mountainous area of Beijing. Consideration of hazard of debris flow alone cannot match the requirement of disaster prevention and control in the mountainous area of Beijing if causing factors of flash flood are neglected. In this research, we adopt the evaluation factors of flash flood in the susceptibility analysis of debris flow. Ten catchments in Beijing mountainous area are investigated. Analytic hierarchy process and entropy method are used for subjective and objective weighting. Combination weighting is calculated by game theory. The susceptibility of catchments is divided into slight, moderate and severe scale by K-means algorithm. Field investigation is used to check the results of scaling. The result shows that susceptibility analysis considering factors of flash flow fits the characteristics of disasters in the mountainous area of Beijing.
Susceptibility analysis is an effective method to obtain characteristics of developments of catchment. There is a concomitant or alternate pattern of flash flood and debris flow in the mountainous area of Beijing. Consideration of hazard of debris flow alone cannot match the requirement of disaster prevention and control in the mountainous area of Beijing if causing factors of flash flood are neglected. In this research, we adopt the evaluation factors of flash flood in the susceptibility analysis of debris flow. Ten catchments in Beijing mountainous area are investigated. Analytic hierarchy process and entropy method are used for subjective and objective weighting. Combination weighting is calculated by game theory. The susceptibility of catchments is divided into slight, moderate and severe scale by K-means algorithm. Field investigation is used to check the results of scaling. The result shows that susceptibility analysis considering factors of flash flow fits the characteristics of disasters in the mountainous area of Beijing.
2015, 23(4): 795-800.
The three dimensional high density resistivity method has been popularized and widely applied in engineering. It is very important to improve the resolution of the data processing and interpreting. This paper is based on the theory of three-dimensional high density resistivity method and proposed to set up the different geoelectric models. It utilizes the finite difference method and the least-squares method to process the data. And then, the paper uses the results of the interpretation to analyze spatial orientation and morphological effect in order to obtain the change rules of the abnormal body. Simulation and analysis results show that the three-dimensional high density resistivity method has a good accuracy in detecting the position of abnormal body.
The three dimensional high density resistivity method has been popularized and widely applied in engineering. It is very important to improve the resolution of the data processing and interpreting. This paper is based on the theory of three-dimensional high density resistivity method and proposed to set up the different geoelectric models. It utilizes the finite difference method and the least-squares method to process the data. And then, the paper uses the results of the interpretation to analyze spatial orientation and morphological effect in order to obtain the change rules of the abnormal body. Simulation and analysis results show that the three-dimensional high density resistivity method has a good accuracy in detecting the position of abnormal body.
2015, 23(4): 801-808.
Underground water-sealed oil storage caverns are the preferred way to national petroleum reserve because of its advantages in economy, environmental protection, safety, suitability for strategic reserves, and convenience. Construction of the underground water-sealed oil storage caverns is growing rapidly in China. Its construction site selection plays a decisive role in smooth construction and safe operation. This paper selects the east coast of China as the study area. The seismic intensity, active fault, maximum horizontal stress, lithology, groundwater level, average annual rainfall and the distribution of large-scale wharf and oil refinery eight factors are selected as indexes that constitute an evaluation index system of the construction suitability of underground water-sealed oil storage caverns. The system is also based on the analysis of the principle of underground water-sealed oil storage caverns and the location factor. Then, the analytic hierarchy process is applied to determining the weight of each indexes. The space analysis function of ArcGIS is applied to evaluating the suitability of the construction of underground water-sealed oil storage caverns in the study zone. The result of construction suitability evaluation of underground water-sealed oil storage caverns in the east coast of China is obtained in the end. It provides a reference to the scientific site selection of underground water-sealed oil storage caverns in the east coast of China.
Underground water-sealed oil storage caverns are the preferred way to national petroleum reserve because of its advantages in economy, environmental protection, safety, suitability for strategic reserves, and convenience. Construction of the underground water-sealed oil storage caverns is growing rapidly in China. Its construction site selection plays a decisive role in smooth construction and safe operation. This paper selects the east coast of China as the study area. The seismic intensity, active fault, maximum horizontal stress, lithology, groundwater level, average annual rainfall and the distribution of large-scale wharf and oil refinery eight factors are selected as indexes that constitute an evaluation index system of the construction suitability of underground water-sealed oil storage caverns. The system is also based on the analysis of the principle of underground water-sealed oil storage caverns and the location factor. Then, the analytic hierarchy process is applied to determining the weight of each indexes. The space analysis function of ArcGIS is applied to evaluating the suitability of the construction of underground water-sealed oil storage caverns in the study zone. The result of construction suitability evaluation of underground water-sealed oil storage caverns in the east coast of China is obtained in the end. It provides a reference to the scientific site selection of underground water-sealed oil storage caverns in the east coast of China.
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