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Editor Work2015 Vol. 23, No. 2
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2015, 23(2): 187-193.
Abstract
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Landslides that are occurred during the earthquake are called seismic-landslides. This paper discusses the difference between the earthquake-induced landslide risk zonation and the general landslide risk zonation. It considers that some factors related to earthquake should be taken into the consideration in earthquake-induced landslide risk zonation. They include the distance between the landslide location and epicenter and the fault's buffer distance. They can reflect the role of earthquake dynamic energy to landslide formation. However, it is hard to reflect the earthquake effect in the vulnerability assessment. Five factors including landslide density, population density, road density, building density, and cultivated land density are adopted to evaluate the study area vulnerability. Finally, the contributing weight model is adopted to evaluate the landslide risk. The result shows that the higher and the high risk region are accounting for 9.03% and 14.61% of the whole study area respectively. This demonstrates that the disaster area after the Wenchuan Earthquake is still facing the landslide hazard threats. In the meizoseismal area, the counties of Beichuan, Qiangchuan, Dujiangyan, and Pengzhou should be regarded as the main landslide risk prevention areas. After field sampling and validation, the results are proved to be consistent with the actual Wenchuan earthquake regions. Thus, the method in this paper is reliable.
Landslides that are occurred during the earthquake are called seismic-landslides. This paper discusses the difference between the earthquake-induced landslide risk zonation and the general landslide risk zonation. It considers that some factors related to earthquake should be taken into the consideration in earthquake-induced landslide risk zonation. They include the distance between the landslide location and epicenter and the fault's buffer distance. They can reflect the role of earthquake dynamic energy to landslide formation. However, it is hard to reflect the earthquake effect in the vulnerability assessment. Five factors including landslide density, population density, road density, building density, and cultivated land density are adopted to evaluate the study area vulnerability. Finally, the contributing weight model is adopted to evaluate the landslide risk. The result shows that the higher and the high risk region are accounting for 9.03% and 14.61% of the whole study area respectively. This demonstrates that the disaster area after the Wenchuan Earthquake is still facing the landslide hazard threats. In the meizoseismal area, the counties of Beichuan, Qiangchuan, Dujiangyan, and Pengzhou should be regarded as the main landslide risk prevention areas. After field sampling and validation, the results are proved to be consistent with the actual Wenchuan earthquake regions. Thus, the method in this paper is reliable.
2015, 23(2): 194-202.
Xiangshuping landslide is located at the Qixin couple of Daping county in Dejiang county, Tongren prefecture, Guizhou province. It is a large ancient landslide. There are several pull trap slots in the boundary of the landslide and the front of the lower slope. Sliding direction of the landslide is 310～335.On the basis of the Engineering geological conditions and deformation and failure characteristics of landslide area, this paper builds the conceptual model of the formation mechanism. In the valley formation and evolution, Xiangshuping landslide evolves in the forms of sliding and bending. The pull slot LC6# and pull slot LC3# in front of the slope are sequentially formed. Their unloading and overhead effects lead to further deformation in upper slope and causes stress concentration at the base of slope and drop of overall slope stability. Landslide occurs while the base of slope is unstable. Numerical analysis well reproduces the landslide evolution and mechanism. The result of the research can provide reference for analogous landslide developmental conditions and identifications of the western mountains.
Xiangshuping landslide is located at the Qixin couple of Daping county in Dejiang county, Tongren prefecture, Guizhou province. It is a large ancient landslide. There are several pull trap slots in the boundary of the landslide and the front of the lower slope. Sliding direction of the landslide is 310～335.On the basis of the Engineering geological conditions and deformation and failure characteristics of landslide area, this paper builds the conceptual model of the formation mechanism. In the valley formation and evolution, Xiangshuping landslide evolves in the forms of sliding and bending. The pull slot LC6# and pull slot LC3# in front of the slope are sequentially formed. Their unloading and overhead effects lead to further deformation in upper slope and causes stress concentration at the base of slope and drop of overall slope stability. Landslide occurs while the base of slope is unstable. Numerical analysis well reproduces the landslide evolution and mechanism. The result of the research can provide reference for analogous landslide developmental conditions and identifications of the western mountains.
2015, 23(2): 203-210.
This paper takes Pengkeng landslide as a case study on the basis of the theory of unsaturated soil mechanics. The finite element method is used to calculate and analyze the slope seepage, deformation properties and stability under rainfall infiltration. The calculation results are utilized to study dynamic response mechanism of landslide due to rainfall and the relationship between safety factor and displacement under different real working conditions. Results show that the loose structure of the slip mass has provided a convenient condition for rainwater infiltrated. Thus it changes the spatial distribution of matrix suction and weakens the rock-soil mass parameters. The ground water level is risen under sustained rainfall. Deformation instability occurs in the zone of slope toe, then pulls the slope rear edge and causes the tensile fissures, which forms partial landslide in unsaturated area during rainfall period. In the initial stage of the heavy rainfall, the safety factor of the slope drops rapidly, which easily causes the landslide. The safety coefficient reduces further due to the continued infiltration of rainwater. Landslide occurrence after rainfall should be paid more attention. Safety factor is affected and vibrated with water in different parts of the slope. Finally, the concept of risk factor is proposed to reflect the harmful degree of slope under groundwater level and rainfall condition variation. The relationship between the risk factor and incremental displacement is established to describe the changes of surface displacement of slope measure point at different time periods. The above research and method will be useful and meaningful as reference for the management and early warning of the similar projects.
This paper takes Pengkeng landslide as a case study on the basis of the theory of unsaturated soil mechanics. The finite element method is used to calculate and analyze the slope seepage, deformation properties and stability under rainfall infiltration. The calculation results are utilized to study dynamic response mechanism of landslide due to rainfall and the relationship between safety factor and displacement under different real working conditions. Results show that the loose structure of the slip mass has provided a convenient condition for rainwater infiltrated. Thus it changes the spatial distribution of matrix suction and weakens the rock-soil mass parameters. The ground water level is risen under sustained rainfall. Deformation instability occurs in the zone of slope toe, then pulls the slope rear edge and causes the tensile fissures, which forms partial landslide in unsaturated area during rainfall period. In the initial stage of the heavy rainfall, the safety factor of the slope drops rapidly, which easily causes the landslide. The safety coefficient reduces further due to the continued infiltration of rainwater. Landslide occurrence after rainfall should be paid more attention. Safety factor is affected and vibrated with water in different parts of the slope. Finally, the concept of risk factor is proposed to reflect the harmful degree of slope under groundwater level and rainfall condition variation. The relationship between the risk factor and incremental displacement is established to describe the changes of surface displacement of slope measure point at different time periods. The above research and method will be useful and meaningful as reference for the management and early warning of the similar projects.
2015, 23(2): 211-218.
This paper investigates the effect of matric suction on the shear strength and deformation mechanical properties of unsaturated sliding-zone soil. It uses the undisturbed sliding-zone soil samples from the Huangtupo riverside slump-mass No. I for the tests. A series of consolidated drained direct shear tests are carried out under different combination of net normal stresses and matric suctions with GDS direct shear system. The experimental results show that an increase in net normal stress results in a higher shear strength under constant matric suction conditions. The stress-strain curve appears strain-hardening behavior as net normal stress increases when matric suction is 50kPa. As matric suction increases and exceeds net normal stress, the stress-strain curve appears a peak shear strength followed by a strain-softening behavior apparently. Or the stress-strain curve appears strain-hardening behavior. Under constant net normal stress conditions, an increase in matric suction results in a higher shear strength. The stress-strain curve changes from a peak shear strength followed by a strain-softening behavior under lower normal stress to a strain-hardening behavior under higher normal stress. The vertical displacement during shearing appears shear dilation when matric suction is greater than net normal stress. Otherwise, the curve appears shear compression. Under consolidation and drain condition, the cohesion of sliding-zone soil increases with matric suction linearly. The unsaturated shear coefficient b is calculated to be 13.7according to the relationship between cohesion versus matric suction. The effective friction angle increases with matric suction slightly. The average effective friction angle is 15.9.
This paper investigates the effect of matric suction on the shear strength and deformation mechanical properties of unsaturated sliding-zone soil. It uses the undisturbed sliding-zone soil samples from the Huangtupo riverside slump-mass No. I for the tests. A series of consolidated drained direct shear tests are carried out under different combination of net normal stresses and matric suctions with GDS direct shear system. The experimental results show that an increase in net normal stress results in a higher shear strength under constant matric suction conditions. The stress-strain curve appears strain-hardening behavior as net normal stress increases when matric suction is 50kPa. As matric suction increases and exceeds net normal stress, the stress-strain curve appears a peak shear strength followed by a strain-softening behavior apparently. Or the stress-strain curve appears strain-hardening behavior. Under constant net normal stress conditions, an increase in matric suction results in a higher shear strength. The stress-strain curve changes from a peak shear strength followed by a strain-softening behavior under lower normal stress to a strain-hardening behavior under higher normal stress. The vertical displacement during shearing appears shear dilation when matric suction is greater than net normal stress. Otherwise, the curve appears shear compression. Under consolidation and drain condition, the cohesion of sliding-zone soil increases with matric suction linearly. The unsaturated shear coefficient b is calculated to be 13.7according to the relationship between cohesion versus matric suction. The effective friction angle increases with matric suction slightly. The average effective friction angle is 15.9.
2015, 23(2): 219-226.
Effectiveness post-evaluation of prevention engineering is an important link in debris flow control. It can be used in inspecting prevention engineering quality, discrimination of formation mechanism. It also can provide reference to debris flow prevention and control in the future. This paper refers to post-evaluation theory on construction projects and combines with many examples of debris flow control projects. Three primary indicators and ten secondary indices are selected to build effectiveness post-evaluation indices system of debris flow control. The three primary indicators include control effectiveness, beneficial result and rationality of control scheme. The ten secondary indices include change of topography, control of solid matter and effectiveness of guide control engineering, economic benefit mobilization of environmental benefit, social benefit, recognition of debris flow mechanism, parameters security, coordination among each control engineering and difficulty of implementation process. Then, effectiveness post-evaluation model of debris flow control project is established on the basis of fuzzy comprehensive evaluation and analytic hierarchy process. At last, the model is applied to the verification and analysis of Dashuigou debris flow control project in Lintong, Xi'an.It concludes that the effectiveness of this model is fine and has the certain promotion application value.
Effectiveness post-evaluation of prevention engineering is an important link in debris flow control. It can be used in inspecting prevention engineering quality, discrimination of formation mechanism. It also can provide reference to debris flow prevention and control in the future. This paper refers to post-evaluation theory on construction projects and combines with many examples of debris flow control projects. Three primary indicators and ten secondary indices are selected to build effectiveness post-evaluation indices system of debris flow control. The three primary indicators include control effectiveness, beneficial result and rationality of control scheme. The ten secondary indices include change of topography, control of solid matter and effectiveness of guide control engineering, economic benefit mobilization of environmental benefit, social benefit, recognition of debris flow mechanism, parameters security, coordination among each control engineering and difficulty of implementation process. Then, effectiveness post-evaluation model of debris flow control project is established on the basis of fuzzy comprehensive evaluation and analytic hierarchy process. At last, the model is applied to the verification and analysis of Dashuigou debris flow control project in Lintong, Xi'an.It concludes that the effectiveness of this model is fine and has the certain promotion application value.
2015, 23(2): 227-232.
Multi-stage intrusions of dikes can change the rock and slope structures greatly, and further change the deformation and failure mode and the stability of the slope. This paper examines the Gaxiapa slope in the dam area of the Lenggu waterpower station at the midstream of the Yalongjiang River as a case study. Before dike intrusions, Gaxiapa slope was a stable slope with thin-middle layer sandstone. The bedding dip direction is opposite to the slope dip direction. After intrusions, the slope constitutes interbedded sandstone and granite dike. The rock was cracked by crushing of the dikes. The original deformation mode bending-dumping changes into outburst of retaining wall.The comparatively intact sandstone in the middle became the retaining wall, which blocks the sliding of the cracked rock at the back, together with the front dike. However, the front dike is deforming severely and in a critical steady state now. If the front dike fails, the Gaxiapa slope is likely to slide down entirely. The result of the failure mode analysis is validated using 3DEC numerical simulation software. The conclusions of the study can be of some value for the similar study, and provide the theoretical support for the stability analysis and prevention of the landslide with the similar structures.
Multi-stage intrusions of dikes can change the rock and slope structures greatly, and further change the deformation and failure mode and the stability of the slope. This paper examines the Gaxiapa slope in the dam area of the Lenggu waterpower station at the midstream of the Yalongjiang River as a case study. Before dike intrusions, Gaxiapa slope was a stable slope with thin-middle layer sandstone. The bedding dip direction is opposite to the slope dip direction. After intrusions, the slope constitutes interbedded sandstone and granite dike. The rock was cracked by crushing of the dikes. The original deformation mode bending-dumping changes into outburst of retaining wall.The comparatively intact sandstone in the middle became the retaining wall, which blocks the sliding of the cracked rock at the back, together with the front dike. However, the front dike is deforming severely and in a critical steady state now. If the front dike fails, the Gaxiapa slope is likely to slide down entirely. The result of the failure mode analysis is validated using 3DEC numerical simulation software. The conclusions of the study can be of some value for the similar study, and provide the theoretical support for the stability analysis and prevention of the landslide with the similar structures.
2015, 23(2): 233-244.
This paper aims to perfect the overall stability of grillage flexible supporting structure with prestressed anchors. According to the actuality, the stability analysis and design of the structure have not considered rainfall infiltration effect. Using the GeoStudio software, the overall stability parameters is analyzed for the grillage flexible supporting structure with prestressed anchors under the heavy rainfall conditions in loess area. It considers the soil moisture content influence of the ultimate uplift capacity of friction type grouting anchor. The result shows the following aspects. The rainfall duration, rainfall intensity and underground water level have obvious influence on the frame prestressed anchor flexible retaining structure. The influence of permeability anisotropy can be ignored. The safety factor of frame prestressed anchor flexible retaining structure under the condition of rainfall has lag effect. The greater the rainfall duration and saturated permeability coefficient are, the weaker the lag effect is. The greater the rainfall intensity and the higher the initial groundwater level are, the greater the lag effect is. The results of this study can be used as the guidance of the design and construction of grillage flexible supporting structure with prestressed anchors considering the influence of rainfall in unsaturated loess area.
This paper aims to perfect the overall stability of grillage flexible supporting structure with prestressed anchors. According to the actuality, the stability analysis and design of the structure have not considered rainfall infiltration effect. Using the GeoStudio software, the overall stability parameters is analyzed for the grillage flexible supporting structure with prestressed anchors under the heavy rainfall conditions in loess area. It considers the soil moisture content influence of the ultimate uplift capacity of friction type grouting anchor. The result shows the following aspects. The rainfall duration, rainfall intensity and underground water level have obvious influence on the frame prestressed anchor flexible retaining structure. The influence of permeability anisotropy can be ignored. The safety factor of frame prestressed anchor flexible retaining structure under the condition of rainfall has lag effect. The greater the rainfall duration and saturated permeability coefficient are, the weaker the lag effect is. The greater the rainfall intensity and the higher the initial groundwater level are, the greater the lag effect is. The results of this study can be used as the guidance of the design and construction of grillage flexible supporting structure with prestressed anchors considering the influence of rainfall in unsaturated loess area.
2015, 23(2): 245-251.
According to Mengzi expansive soil, consolidated drained tests and undrained tests are carried on under the saturated and remolded condition. The stress-strain characteristics of saturated soil are researched systematically under different consolidation pressure, initial dry density, initial water content, shearing rate and drainage condition. The inherent unity of diversity of shearing strength for the same samples is measured by different experimental methods and is indicated according to the normalization of critical state test results. The failure lines in p'-q- space of remolded saturated expansive soil under consolidated drained and undrained condition are attained. The hyperbolic curve model can fit well the inferior hardening stress-strain curve. The exponential curve model can fit the inferior soft stress-strain curve. The test results can provide technical parameters and theoretical help for shearing strength variation of slope during rainfall and strength state of soil structure in normal water level.
According to Mengzi expansive soil, consolidated drained tests and undrained tests are carried on under the saturated and remolded condition. The stress-strain characteristics of saturated soil are researched systematically under different consolidation pressure, initial dry density, initial water content, shearing rate and drainage condition. The inherent unity of diversity of shearing strength for the same samples is measured by different experimental methods and is indicated according to the normalization of critical state test results. The failure lines in p'-q- space of remolded saturated expansive soil under consolidated drained and undrained condition are attained. The hyperbolic curve model can fit well the inferior hardening stress-strain curve. The exponential curve model can fit the inferior soft stress-strain curve. The test results can provide technical parameters and theoretical help for shearing strength variation of slope during rainfall and strength state of soil structure in normal water level.
2015, 23(2): 252-259.
The study on strength theory of unsaturated soil is the core of the research in the field of unsaturated soil mechanics. In the early time, Bishop's univariate strength theory and Fredlund's bivariate strength theory are the most classical strength theories for unsaturated soil. Both introduce the matric suction as stress parameter. However, it attributes to effective stress in the former and it is an independent variable in the latter. Matric suction controlled unsaturated triaxial or direct shear apparatus are needed in order to get the related parameters in the two formulas. The controlling of matric suction needs synchronized increase of pore air pressure and pore water pressure so as to keep the matric suction constant, which is so called axis-translation technique. However, problems such as long process and its feasibility doubts still exist in axis parallel translation technique. Therefore, conventional triaxial CU test with different moisture content is used to get the effective steady state strength parameters. Then the suction stress characteristic curve is obtained on the basis of the suction stress concept. The shear strength formula is expressed as a function of suction stress which significantly avoids the determination of matric suction. Therefore, it is convenient for widely application in engineering practice. In order to make a further compare with the unsaturated strength of Bishop and Fredlund, the soil water characteristic curve of the same sample determined by tensiometer is used to get their strength parameters. In theory, these three strength theories are different in the mechanism explanation, but they can transform to each other in mathematics. From the perspective of engineering applications, shear strength theory, based on suction stress, is more convenient to apply in engineering.
The study on strength theory of unsaturated soil is the core of the research in the field of unsaturated soil mechanics. In the early time, Bishop's univariate strength theory and Fredlund's bivariate strength theory are the most classical strength theories for unsaturated soil. Both introduce the matric suction as stress parameter. However, it attributes to effective stress in the former and it is an independent variable in the latter. Matric suction controlled unsaturated triaxial or direct shear apparatus are needed in order to get the related parameters in the two formulas. The controlling of matric suction needs synchronized increase of pore air pressure and pore water pressure so as to keep the matric suction constant, which is so called axis-translation technique. However, problems such as long process and its feasibility doubts still exist in axis parallel translation technique. Therefore, conventional triaxial CU test with different moisture content is used to get the effective steady state strength parameters. Then the suction stress characteristic curve is obtained on the basis of the suction stress concept. The shear strength formula is expressed as a function of suction stress which significantly avoids the determination of matric suction. Therefore, it is convenient for widely application in engineering practice. In order to make a further compare with the unsaturated strength of Bishop and Fredlund, the soil water characteristic curve of the same sample determined by tensiometer is used to get their strength parameters. In theory, these three strength theories are different in the mechanism explanation, but they can transform to each other in mathematics. From the perspective of engineering applications, shear strength theory, based on suction stress, is more convenient to apply in engineering.
2015, 23(2): 260-264.
Based on the one-dimensional consolidation theory, this paper examines the consolidation problem for the saturated non-homogeneous foundation whose physical and mechanical properties are variation along the depth. Firstly, the analytical solutions to the governing equation of a saturated soil layer is obtained using the method of separation of variables. The laws of soil permeability and compressibility coefficients with depth can be expressed as exponential functions. In addition, the analogous transformation relationships between two solutions of excess pore pressure and degree of consolidation are given through comparison of the present solution with the classical solutions of Terzaghi consolidation theory. The consolidation of non-homogenous foundation can be expressed by that of homogenous foundation with the same loading and boundary conditions. Consequently, the non-homogeneous foundation consolidation problem can be reduced to the calculation of the transition parameters and the factor concentrically reflecting the effects of non-homogeneous on consolidation. This method can provide a simple and convenient approach in analyzing and solving the non-homogeneous foundation consolidation.
Based on the one-dimensional consolidation theory, this paper examines the consolidation problem for the saturated non-homogeneous foundation whose physical and mechanical properties are variation along the depth. Firstly, the analytical solutions to the governing equation of a saturated soil layer is obtained using the method of separation of variables. The laws of soil permeability and compressibility coefficients with depth can be expressed as exponential functions. In addition, the analogous transformation relationships between two solutions of excess pore pressure and degree of consolidation are given through comparison of the present solution with the classical solutions of Terzaghi consolidation theory. The consolidation of non-homogenous foundation can be expressed by that of homogenous foundation with the same loading and boundary conditions. Consequently, the non-homogeneous foundation consolidation problem can be reduced to the calculation of the transition parameters and the factor concentrically reflecting the effects of non-homogeneous on consolidation. This method can provide a simple and convenient approach in analyzing and solving the non-homogeneous foundation consolidation.
2015, 23(2): 265-271.
Dredger fill of soft ground can't be put into engineering until foundation treatment is finished. Shallow foundation treatment such as vacuum preloading is generally utilized to improve the strength of foundation.But for a large area loading ground, shallow foundation treatment is not sufficient to ensure the stability of the foundation. Therefore, a deep foundation reinforcement is needed. Three plans of deep foundation reinforcement are the mixing pile foundation, micro-pile foundation and the mixture of the two piles. They are proposed after vacuum preloading treatment for the dredger fill of soft ground of the shipbuilding base in this paper. Besides, the finite element method software PLAXIS is utilized to simulate the proposed plans in the framework of the Biot's consolidation theory and the effective stress theory. Soft Soil Model based on the modified Cam-clay Model is selected for muck and mucky soil. Mohr-Coulomb Model is selected for sand, clay and silty clay. Linear elastic model and elastic model are respectively for mixing piles and micro piles. Settlements of different plans are obtained by the calculation. Further analysis on the different types of foundation reinforcement is made with different mechanism. For this deep dredger fill of soft ground, the mixing pile foundation is better than the micro-pile foundation with the same length in improving the ground strength. Additionally, settlements of mixing pile foundation with different lengths are calculated. The mixing pile foundation with the length from 10m to 15m can improve the ground strength. However, the effect is not improved obviously as the length increases. The results can provide some basis for the design of a deep dredger fill of soft ground reinforcement.
Dredger fill of soft ground can't be put into engineering until foundation treatment is finished. Shallow foundation treatment such as vacuum preloading is generally utilized to improve the strength of foundation.But for a large area loading ground, shallow foundation treatment is not sufficient to ensure the stability of the foundation. Therefore, a deep foundation reinforcement is needed. Three plans of deep foundation reinforcement are the mixing pile foundation, micro-pile foundation and the mixture of the two piles. They are proposed after vacuum preloading treatment for the dredger fill of soft ground of the shipbuilding base in this paper. Besides, the finite element method software PLAXIS is utilized to simulate the proposed plans in the framework of the Biot's consolidation theory and the effective stress theory. Soft Soil Model based on the modified Cam-clay Model is selected for muck and mucky soil. Mohr-Coulomb Model is selected for sand, clay and silty clay. Linear elastic model and elastic model are respectively for mixing piles and micro piles. Settlements of different plans are obtained by the calculation. Further analysis on the different types of foundation reinforcement is made with different mechanism. For this deep dredger fill of soft ground, the mixing pile foundation is better than the micro-pile foundation with the same length in improving the ground strength. Additionally, settlements of mixing pile foundation with different lengths are calculated. The mixing pile foundation with the length from 10m to 15m can improve the ground strength. However, the effect is not improved obviously as the length increases. The results can provide some basis for the design of a deep dredger fill of soft ground reinforcement.
2015, 23(2): 272-278.
Hydrated geosynthetic clay liners(GCls) are the excellence anti-seepage material. But they exhibit extremely low shear strength at the same time. To improved the disadvantage, a protector that adequately backfill over the GCL is set so as to consist of composite liners system. The artificially graded gravel soils are taken from natural sediment. The compacted gravel soils instead of clay are as a protective layer of GCls liner. The compacted gravel soils are selected according to the requirement of the code. They are put into the direct shear apparatus under the GCL with a hydration degree of, respectively, 50% and complete saturation. The direct shear friction tensile tester(TGH) is used in this paper. The experiments are performed. The results show that the shear strength of compacted gravel soils is far more than the contact surfaces that are consisted of compacted gravel soils with hydrated GCL.The shear strength of the contact surfaces is decreasing with the increasing of GCls' moisture content. So it is effective to release the pressure of GCls with the help from high bearing capacity of wide grading gravel soils according to the principle of stress diffusion in soil.
Hydrated geosynthetic clay liners(GCls) are the excellence anti-seepage material. But they exhibit extremely low shear strength at the same time. To improved the disadvantage, a protector that adequately backfill over the GCL is set so as to consist of composite liners system. The artificially graded gravel soils are taken from natural sediment. The compacted gravel soils instead of clay are as a protective layer of GCls liner. The compacted gravel soils are selected according to the requirement of the code. They are put into the direct shear apparatus under the GCL with a hydration degree of, respectively, 50% and complete saturation. The direct shear friction tensile tester(TGH) is used in this paper. The experiments are performed. The results show that the shear strength of compacted gravel soils is far more than the contact surfaces that are consisted of compacted gravel soils with hydrated GCL.The shear strength of the contact surfaces is decreasing with the increasing of GCls' moisture content. So it is effective to release the pressure of GCls with the help from high bearing capacity of wide grading gravel soils according to the principle of stress diffusion in soil.
2015, 23(2): 279-286.
Marbles, quarried from Dashiwo town of Fangshan district in Beijing, are employed by many famous stone cultural relics in Beijing. Microscopic characteristics of petrography of white marble and greenish white marble are studied, using the methods of thin section microscopic observation, X-ray diffraction(XRD), X-ray fluorescence(XRF), scanning electron microscopy(SEM) and electron probe test. The fresh marble samples are taken from the quarry. The weathered samples are the debris of broken stones from the historic buildings. Results confirm that the main mineral of the marble is dolomite. Part of the marble contains quartz. Based on image processing software, the particle size distribution of the white marble and greenish white marble are calculated after statistical analysis. On this basis, the weathering mechanism of the marble is analyzed from the view of the temperature change, dissolution due to acid rain, water erosion and the salt crystals along microcracks. The above study can provide a scientific basis for restoration and protection of the marble cultural relics.
Marbles, quarried from Dashiwo town of Fangshan district in Beijing, are employed by many famous stone cultural relics in Beijing. Microscopic characteristics of petrography of white marble and greenish white marble are studied, using the methods of thin section microscopic observation, X-ray diffraction(XRD), X-ray fluorescence(XRF), scanning electron microscopy(SEM) and electron probe test. The fresh marble samples are taken from the quarry. The weathered samples are the debris of broken stones from the historic buildings. Results confirm that the main mineral of the marble is dolomite. Part of the marble contains quartz. Based on image processing software, the particle size distribution of the white marble and greenish white marble are calculated after statistical analysis. On this basis, the weathering mechanism of the marble is analyzed from the view of the temperature change, dissolution due to acid rain, water erosion and the salt crystals along microcracks. The above study can provide a scientific basis for restoration and protection of the marble cultural relics.
2015, 23(2): 287-300.
When the ultrasonic wave propagates in rock and soil, it carries lots of information related to the physical and mechanical properties of geotechnical medium. The information can be integrated and reflected in change of a series of acoustic parameters including ultrasonic velocity, attenuation coefficient, waveform, frequency, frequency spectrum and amplitude. Based on these parameters, the physical and mechanical properties of rock mass and mesoscopic structure characteristics can be investigated indirectly, so as to solve a series of geotechnical engineering problems. In this paper, the geotechnical problems which can be resolved by ultrasonic nondestructive testing are summarized. A systematic review is performed on the progresses of ultrasonic testing in soil and rock, which include the work of soil strength parameters, the microstructure of soil parameters, the obtaining of rock strength parameters by ultrasonic test, the rock fracturing mechanism, the application of ultrasonic wave attenuation in rock materials, the anisotropy of ultrasonic velocity and attenuation and research of ultrasonic test in flow test. Finally, the ultrasonic test is broadened in the research field of rock and soil aggregate. Wave velocity and attenuation law with specimens of different rock percentage are discussed. Also during compressive test, the meso-damage characteristics are analyzed with acoustic parameters, to illustrate that the rock and soil aggregate which is not only different from soil but also different from rock. Based on the above research, the development tendency of ultrasonic test is also prospected.
When the ultrasonic wave propagates in rock and soil, it carries lots of information related to the physical and mechanical properties of geotechnical medium. The information can be integrated and reflected in change of a series of acoustic parameters including ultrasonic velocity, attenuation coefficient, waveform, frequency, frequency spectrum and amplitude. Based on these parameters, the physical and mechanical properties of rock mass and mesoscopic structure characteristics can be investigated indirectly, so as to solve a series of geotechnical engineering problems. In this paper, the geotechnical problems which can be resolved by ultrasonic nondestructive testing are summarized. A systematic review is performed on the progresses of ultrasonic testing in soil and rock, which include the work of soil strength parameters, the microstructure of soil parameters, the obtaining of rock strength parameters by ultrasonic test, the rock fracturing mechanism, the application of ultrasonic wave attenuation in rock materials, the anisotropy of ultrasonic velocity and attenuation and research of ultrasonic test in flow test. Finally, the ultrasonic test is broadened in the research field of rock and soil aggregate. Wave velocity and attenuation law with specimens of different rock percentage are discussed. Also during compressive test, the meso-damage characteristics are analyzed with acoustic parameters, to illustrate that the rock and soil aggregate which is not only different from soil but also different from rock. Based on the above research, the development tendency of ultrasonic test is also prospected.
2015, 23(2): 301-310.
Hydraulic fracturing technology is the core technology in the oil and gas production, especially for the shale gas extraction. Numerical simulation for optimization design of fracking and productivity prediction is a key factor in successful hydraulic fracturing. This paper introduces the history of hydraulic fracturing technology. It reviews the computer simulation techniques of hydraulic fracturing in the oil and gas field. It covers the following two aspects: computing models(2D model, P3D model and fully 3D model) and numerical methods(continuum-based numerical methods and discontinuum-based numerical methods).Finally, the limitation of current study and the further studies needed are put forward, from the following three aspects.(1)Improvement of the fully 3D model. The combination of fully 3D model, treatment parameter and monitoring data can calibrate the model itself. The calibrated model can well predict and optimize the real hydraulic fracturing operation.(2)Selection of numerical methods. There are many methods for hydraulic fracturing. The methods should be comprehensively compared and optimized, in order to verify their applicable scope, computional efficiency and simulation effect.(3)Numerical simulation of the reservoir with natural fracture network. Natural fracture network increases the anisotropy of rock mechanical property. The interaction between natural further and hydraulic fracture benefits the reservoir stimulation, plays an important role in the geometry, dimension and connectivity rate of hydraulic fracture network. The simulation of the reservoir with natural fracture network will be the hotspot in future study.
Hydraulic fracturing technology is the core technology in the oil and gas production, especially for the shale gas extraction. Numerical simulation for optimization design of fracking and productivity prediction is a key factor in successful hydraulic fracturing. This paper introduces the history of hydraulic fracturing technology. It reviews the computer simulation techniques of hydraulic fracturing in the oil and gas field. It covers the following two aspects: computing models(2D model, P3D model and fully 3D model) and numerical methods(continuum-based numerical methods and discontinuum-based numerical methods).Finally, the limitation of current study and the further studies needed are put forward, from the following three aspects.(1)Improvement of the fully 3D model. The combination of fully 3D model, treatment parameter and monitoring data can calibrate the model itself. The calibrated model can well predict and optimize the real hydraulic fracturing operation.(2)Selection of numerical methods. There are many methods for hydraulic fracturing. The methods should be comprehensively compared and optimized, in order to verify their applicable scope, computional efficiency and simulation effect.(3)Numerical simulation of the reservoir with natural fracture network. Natural fracture network increases the anisotropy of rock mechanical property. The interaction between natural further and hydraulic fracture benefits the reservoir stimulation, plays an important role in the geometry, dimension and connectivity rate of hydraulic fracture network. The simulation of the reservoir with natural fracture network will be the hotspot in future study.
2015, 23(2): 311-319.
The stability analysis of surrounding rock and the measure of support control for the part of the loose sandstones layer in the water conveyance tunnel are difficult problems, because there is no perfect excavation and supporting control method. The evolution of the mechanical properties of the loose sandstones and the supporting force mechanism is analyzed under the engineering background of a domestic water conveyance tunnel. Sub-step supporting method and optimized supporting method for the frozen construction part across the loose sandstones layer are raised through theoretic and finite element simulation. The study shows that step by step combined support method can get ideal supporting effect. The disturbance attenuation should be considered during freezing and thawing process in carrying on the supporting structure stiffness design and numerical analysis. Supporting methods should consider geological conditions and make all of the supporting measures to achieve effective integration so as to make the supporting mechanism clear.
The stability analysis of surrounding rock and the measure of support control for the part of the loose sandstones layer in the water conveyance tunnel are difficult problems, because there is no perfect excavation and supporting control method. The evolution of the mechanical properties of the loose sandstones and the supporting force mechanism is analyzed under the engineering background of a domestic water conveyance tunnel. Sub-step supporting method and optimized supporting method for the frozen construction part across the loose sandstones layer are raised through theoretic and finite element simulation. The study shows that step by step combined support method can get ideal supporting effect. The disturbance attenuation should be considered during freezing and thawing process in carrying on the supporting structure stiffness design and numerical analysis. Supporting methods should consider geological conditions and make all of the supporting measures to achieve effective integration so as to make the supporting mechanism clear.
2015, 23(2): 320-327.
According to the regional TM and SPOT vision, the scope of hydraulic fill region can be decided with embracing strong, information-rich, clear linear imaging features and other characteristics. The hydraulic fill region should be combined with the results of field prospecting and indoor test. Mapping technology can make work fast, high quality and low cost. In addition, the second level evaluating influence factors include field surroundings, project property, mechanics property and consolidation time, and relatively. Another 13 first level single-factor evaluating indicators include groundwater level and quality, type of cause's combination, salinization, type of rock and soil mass, clay content, liquidity index, water content, porosity ratio, cohesion, internal friction, compressibility, compression modulus and consolidation time. They are chosen for the system comprehensive evaluation. The evaluation index weight is determined by AHP.They are normalized for hydraulic fill project of Liaodong Bay. The engineering suitability remote sensing zoning is used to make the zones Ⅰ, Ⅱ and Ⅲ. The results are used to propose zone of the result of hydraulic fill region suitability, to provide the reference for the engineering construction of this region and for engineering suitability zoning of other hydraulic fill region and to improve the economic and social benefits.
According to the regional TM and SPOT vision, the scope of hydraulic fill region can be decided with embracing strong, information-rich, clear linear imaging features and other characteristics. The hydraulic fill region should be combined with the results of field prospecting and indoor test. Mapping technology can make work fast, high quality and low cost. In addition, the second level evaluating influence factors include field surroundings, project property, mechanics property and consolidation time, and relatively. Another 13 first level single-factor evaluating indicators include groundwater level and quality, type of cause's combination, salinization, type of rock and soil mass, clay content, liquidity index, water content, porosity ratio, cohesion, internal friction, compressibility, compression modulus and consolidation time. They are chosen for the system comprehensive evaluation. The evaluation index weight is determined by AHP.They are normalized for hydraulic fill project of Liaodong Bay. The engineering suitability remote sensing zoning is used to make the zones Ⅰ, Ⅱ and Ⅲ. The results are used to propose zone of the result of hydraulic fill region suitability, to provide the reference for the engineering construction of this region and for engineering suitability zoning of other hydraulic fill region and to improve the economic and social benefits.
2015, 23(2): 328-334.
The noise signal of ground penetrating radar(GPR)usually has the unsteady and nonlinear characteristics. To remove these noises and improve the accuracy of GPR image interpretation, denoising with HHT method is studied. Firstly, the basic theory of the HHT is described. Then the feasibility of HHT method is verified with numerical simulation of GPR data denoising. Finally, the method is used in the tunnel geological advanced prediction of GPR data processing. The research shows that the method can be used in GPR signal denoising and that the precision of GPR signal interpretation can be improved by contrasting three characteristic parameters images obtained by Hilbert transform with EMD composite images.
The noise signal of ground penetrating radar(GPR)usually has the unsteady and nonlinear characteristics. To remove these noises and improve the accuracy of GPR image interpretation, denoising with HHT method is studied. Firstly, the basic theory of the HHT is described. Then the feasibility of HHT method is verified with numerical simulation of GPR data denoising. Finally, the method is used in the tunnel geological advanced prediction of GPR data processing. The research shows that the method can be used in GPR signal denoising and that the precision of GPR signal interpretation can be improved by contrasting three characteristic parameters images obtained by Hilbert transform with EMD composite images.
2015, 23(2): 335-343.
This paper is to decrease the tentative calculations and get the global optimum in higher possibility. The temperature global optimization is employed to locate the concentrated seepage pipes in rock-soil body of the dam or abutment. Global search(GS), Multistart(MS) and Genetic algorithm(GA) are selected to estimate the positions of the concentrated seepage pipes with the discontinuous objective function associated with cooperation and complementarity of these algorithms. Firstly, the local optima are searched by GS.Then in the consequent MS optimization, the local optima are inputted as the initial starts to increase the probability of searching the global optima. Finally, the result is verified or improved by genetic algorithm and its hybrid algorithm. According to the characteristics of concentrated leakage passage recharged by water in lower temperature, the objective function in the optimization is modified with this specific physical meaning. The step-by-step optimization is set up to reduce the parameter amount in each iteration. The number of the concentrated seepage pipes is ascertained by the attraction basins composed by temperature datum or their residuals. The optimization is terminated when the modified residual is less than the data detection precision. The real solution for the locations of the concentrated passages is the iteration result with the least residual. In the case study, two intense concentrated seepage pipes and three minor ones are estimated by step-by-step and direct optimizations in the left leaky dam abutment of Douhe reservoir, where the locations of the multi-seepages are firmed by engineering practice partly.
This paper is to decrease the tentative calculations and get the global optimum in higher possibility. The temperature global optimization is employed to locate the concentrated seepage pipes in rock-soil body of the dam or abutment. Global search(GS), Multistart(MS) and Genetic algorithm(GA) are selected to estimate the positions of the concentrated seepage pipes with the discontinuous objective function associated with cooperation and complementarity of these algorithms. Firstly, the local optima are searched by GS.Then in the consequent MS optimization, the local optima are inputted as the initial starts to increase the probability of searching the global optima. Finally, the result is verified or improved by genetic algorithm and its hybrid algorithm. According to the characteristics of concentrated leakage passage recharged by water in lower temperature, the objective function in the optimization is modified with this specific physical meaning. The step-by-step optimization is set up to reduce the parameter amount in each iteration. The number of the concentrated seepage pipes is ascertained by the attraction basins composed by temperature datum or their residuals. The optimization is terminated when the modified residual is less than the data detection precision. The real solution for the locations of the concentrated passages is the iteration result with the least residual. In the case study, two intense concentrated seepage pipes and three minor ones are estimated by step-by-step and direct optimizations in the left leaky dam abutment of Douhe reservoir, where the locations of the multi-seepages are firmed by engineering practice partly.
2015, 23(2): 344-351.
This paper studies the comprehensive geophysical detection method and evaluation standard of karst roadbed grouting effect. The typical test areas of Nanning-Guangzhou railway karst roadbed are selected. The field test research of detection standard and characteristics are studied using resistivity method, transient surface wave method and electromagnetic wave CT method. The applicability and economy of the above geophysical detection methods are evaluated. The comprehensive geophysical detection method of variety methods combination in different engineering conditions is proposed. The differential values of resistivity, surface wave velocity and electromagnetic wave absorption coefficient are statistically analyzed using the test data of grouting. The grouting is qualified, and preliminarily obtained in the karst roadbed. The grouting effect detection standards are proposed for the above three geophysical methods. The resistivity method detection standard is that the resistivity differential values of karst cave is more than 20%, and the pebble soil is more than 10%.The transient surface wave method detection standard is that the wave velocity of clay is more than 20.6h+130.3, and the karst cave is more than 17.1h+236.9. The electromagnetic wave CT method detection standard is that the electromagnetic wave absorption coefficient differential values of karst cave is more than 0.4dB m-1, and the pebble soil is more than 0.1dB m-1.
This paper studies the comprehensive geophysical detection method and evaluation standard of karst roadbed grouting effect. The typical test areas of Nanning-Guangzhou railway karst roadbed are selected. The field test research of detection standard and characteristics are studied using resistivity method, transient surface wave method and electromagnetic wave CT method. The applicability and economy of the above geophysical detection methods are evaluated. The comprehensive geophysical detection method of variety methods combination in different engineering conditions is proposed. The differential values of resistivity, surface wave velocity and electromagnetic wave absorption coefficient are statistically analyzed using the test data of grouting. The grouting is qualified, and preliminarily obtained in the karst roadbed. The grouting effect detection standards are proposed for the above three geophysical methods. The resistivity method detection standard is that the resistivity differential values of karst cave is more than 20%, and the pebble soil is more than 10%.The transient surface wave method detection standard is that the wave velocity of clay is more than 20.6h+130.3, and the karst cave is more than 17.1h+236.9. The electromagnetic wave CT method detection standard is that the electromagnetic wave absorption coefficient differential values of karst cave is more than 0.4dB m-1, and the pebble soil is more than 0.1dB m-1.
2015, 23(2): 352-360.
This is a summary report for the 5th International Forum on Opto-electronic Sensor-based Monitoring in Geo-engineering(5th OSMG-2014). This forum was held in Nanjing University in Oct 2014. The forum shows the following features in recent research:(1)The opto-electronic demodulation technologies are undergoing numerous developments and the monitoring accuracy and reliability are significant enhanced.(2)More and more sensors for geo-engineering monitoring have been developed recently, which can meet nearly all the requirements of engineering monitoring.(3)The performance testing and installation techniques of the opto-electronic sensors have become a hot research topic.(4)The opto-electronic sensor-based health diagnosis and monitoring theories have become more mature recently.(5)The applications of distributed sensing technologies in monitoring engineering structures have been advocated extensively and the sensor systems have been introduced into a variety of disciplines. The future research can focus on the following aspects:(1)Development of cost-effective demodulation techniques for distributed fiber optic sensing technology. (2)Development of fiber optic sensors for geo-engineering monitoring. (3)The field installation methods of fiber optic sensors in harsh environments. (4)Real-time processing, error analysis and anomaly recognition of huge monitoring data. (5)Transmission technologies of huge monitoring data. (6)Early warning and stability assessment methods in geo-engineering based on distributed monitoring technologies.
This is a summary report for the 5th International Forum on Opto-electronic Sensor-based Monitoring in Geo-engineering(5th OSMG-2014). This forum was held in Nanjing University in Oct 2014. The forum shows the following features in recent research:(1)The opto-electronic demodulation technologies are undergoing numerous developments and the monitoring accuracy and reliability are significant enhanced.(2)More and more sensors for geo-engineering monitoring have been developed recently, which can meet nearly all the requirements of engineering monitoring.(3)The performance testing and installation techniques of the opto-electronic sensors have become a hot research topic.(4)The opto-electronic sensor-based health diagnosis and monitoring theories have become more mature recently.(5)The applications of distributed sensing technologies in monitoring engineering structures have been advocated extensively and the sensor systems have been introduced into a variety of disciplines. The future research can focus on the following aspects:(1)Development of cost-effective demodulation techniques for distributed fiber optic sensing technology. (2)Development of fiber optic sensors for geo-engineering monitoring. (3)The field installation methods of fiber optic sensors in harsh environments. (4)Real-time processing, error analysis and anomaly recognition of huge monitoring data. (5)Transmission technologies of huge monitoring data. (6)Early warning and stability assessment methods in geo-engineering based on distributed monitoring technologies.
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