2015 Vol. 37 No. 4
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Abstract：
The linear relation between shear strength and normal stress of failure plane shows the essential property of soil shear strength. The Mohr-Coulomb criterion, Drucker-Prager yield criterion and Matsuoka-Nakai criterion respectively respond to the linear relationship between shear stress and normal stress on different shear failure planes including shear failure plane with the angle of 45°+φ/2 relating to the plane of the main principal stress, the octahedral plane in the principal stress space of soil element and the spatially mobilized plane named also σ1/2 spatially mobilized plane. In this paper, new σ1/3 spatially mobilized plane is proposed using three points κσ11/3, κσ21/3, κσ31/3 in the soil element in the principal stress axes, named as the σ1/3 spatially mobilized plane. Furthermore, the new strength criterion is also proposed using the shear stress ratio on theσ1/3spatial mobilization plane being constant. The strength failure surface depicted in the principal stress space by this criterion is a smooth cone surface with the curved triangle shape onplane. The strength failure surfaces of Mohr-Coulomb criterion, Drucker-Prager yield criterion, Matsuoka-Nakai criterion, Lade-Duncan criterion and σ1/3 spatially mobilized plane criterion described in the stress space as well as the change laws of Lade-Duncan criterion and σ1/3 spatially mobilized plane criterion with parameter b on different π planes are comparatively analyzed. It is shown that the Lade-Duncan criterion and σ1/3 spatially mobilized plane strength criterion are approximate, which reveals the physical essence of Lade-Duncan strength criterion, that is, the former approximately obeys the linear relationship between shear stress and normal stress onσ1/3 spatially mobilized plane at failure of soils. The
The linear relation between shear strength and normal stress of failure plane shows the essential property of soil shear strength. The Mohr-Coulomb criterion, Drucker-Prager yield criterion and Matsuoka-Nakai criterion respectively respond to the linear relationship between shear stress and normal stress on different shear failure planes including shear failure plane with the angle of 45°+φ/2 relating to the plane of the main principal stress, the octahedral plane in the principal stress space of soil element and the spatially mobilized plane named also σ1/2 spatially mobilized plane. In this paper, new σ1/3 spatially mobilized plane is proposed using three points κσ11/3, κσ21/3, κσ31/3 in the soil element in the principal stress axes, named as the σ1/3 spatially mobilized plane. Furthermore, the new strength criterion is also proposed using the shear stress ratio on theσ1/3spatial mobilization plane being constant. The strength failure surface depicted in the principal stress space by this criterion is a smooth cone surface with the curved triangle shape on
Abstract：
The permeability coefficient of gas in municipal solid waste (MSW) is an important parameter for migration analysis and design of extraction well for gas in landfills. The permeability of MSW is mainly dependent on the void ratio, organic content, saturation degree and so on. In this study, the air permeability tests on unsaturated MSW are carried out under different influencing conditions by a new developed permeameter. It is found that there is a nonlinear relationship between permeability coefficient of MSW and seepage pressure of air, which can be better fitted by using the Forchheimer non-Darcy flow equation. With the increase of void ratio of MSW, the permeability coefficient increases, non-Darcy coefficient Ba decreases and the air pressure at demarcation point increases, respectively. With the increase of organic content in MSW, the permeability coefficient decreases and the air pressure at demarcation point increases, respectively. The flaky organic part will be spread and the connecting seepage path will be reduced in MSW, resulting in the attenuation of permeability for MSW. The higher the saturation degree in MSW, the smaller the permeability and the larger the air pressure at demarcation point. Within the effective porosity in the tests, there are better relationships among the permeability coefficient of MSW, the air pressure at demarcation point and the effective porosity, and the non-Darcy coefficients are changed in a narrow range.
The permeability coefficient of gas in municipal solid waste (MSW) is an important parameter for migration analysis and design of extraction well for gas in landfills. The permeability of MSW is mainly dependent on the void ratio, organic content, saturation degree and so on. In this study, the air permeability tests on unsaturated MSW are carried out under different influencing conditions by a new developed permeameter. It is found that there is a nonlinear relationship between permeability coefficient of MSW and seepage pressure of air, which can be better fitted by using the Forchheimer non-Darcy flow equation. With the increase of void ratio of MSW, the permeability coefficient increases, non-Darcy coefficient Ba decreases and the air pressure at demarcation point increases, respectively. With the increase of organic content in MSW, the permeability coefficient decreases and the air pressure at demarcation point increases, respectively. The flaky organic part will be spread and the connecting seepage path will be reduced in MSW, resulting in the attenuation of permeability for MSW. The higher the saturation degree in MSW, the smaller the permeability and the larger the air pressure at demarcation point. Within the effective porosity in the tests, there are better relationships among the permeability coefficient of MSW, the air pressure at demarcation point and the effective porosity, and the non-Darcy coefficients are changed in a narrow range.
Abstract：
In order to understand the mechanical properties and short-term self recovery features of salt rock with damage under constant temperature, the self recovery tests on the salt rock with shear damage are designed, and the variation laws of related mechanical parameters with the time for recovery are studied. The test results show that the recovery of internal friction angle is obvious, and that of cohesive force is not obvious. In the early recovery stage, the shear strength decreases and then relatively increases with the to recovery, and eventually enters into the long-term recovery phase. After recovery, with the increasing ability of resistance to deformation, the deformation ability of damaged salt rock also increases. The researches on the self recovery of salt rock with damage should be divided into long-term and short-term ones, and the dividing point is about 7 d. Through the discussion and analysis of the self-healing theory, it is known that the recovery is the strengthening of mechanical properties and improvement of comprehensive quality, sometimes along with degradation of some mechanical properties. By fitting the damage variables, the variation of damage values of damaged specimens in the process of self healing is released.
In order to understand the mechanical properties and short-term self recovery features of salt rock with damage under constant temperature, the self recovery tests on the salt rock with shear damage are designed, and the variation laws of related mechanical parameters with the time for recovery are studied. The test results show that the recovery of internal friction angle is obvious, and that of cohesive force is not obvious. In the early recovery stage, the shear strength decreases and then relatively increases with the to recovery, and eventually enters into the long-term recovery phase. After recovery, with the increasing ability of resistance to deformation, the deformation ability of damaged salt rock also increases. The researches on the self recovery of salt rock with damage should be divided into long-term and short-term ones, and the dividing point is about 7 d. Through the discussion and analysis of the self-healing theory, it is known that the recovery is the strengthening of mechanical properties and improvement of comprehensive quality, sometimes along with degradation of some mechanical properties. By fitting the damage variables, the variation of damage values of damaged specimens in the process of self healing is released.
Abstract：
Some properties of SH waves in layered media are analyzed such as propagating path, reflecting cofficent and travelling time in order to improve the accuracy and efficiency of 1-D finite element method dealing with seismic response problem of horizontal layered site for inclined SH waves in time domain. Based on the Huygens wave principle, impedance interfaces are regarded as the secondary sources or wavelet sources, which are called interfacial wavelets. The relation between interfacial wavelets can be expressed as a group of time delay equations, and the motion of interfaces can be obtained by solving the time delay equations. The earthquake motion can be ascertained from surface wavelets. The new method is called an interfacial wavelet algorithm and demonstrated by two corresponding numerical models. When using this method, mesh divisions and artificial boundary conditions need no treatment so that computing amount and transmission errors between nodes are reduced greatly. It is very fit to solve seismic response in layered media.
Some properties of SH waves in layered media are analyzed such as propagating path, reflecting cofficent and travelling time in order to improve the accuracy and efficiency of 1-D finite element method dealing with seismic response problem of horizontal layered site for inclined SH waves in time domain. Based on the Huygens wave principle, impedance interfaces are regarded as the secondary sources or wavelet sources, which are called interfacial wavelets. The relation between interfacial wavelets can be expressed as a group of time delay equations, and the motion of interfaces can be obtained by solving the time delay equations. The earthquake motion can be ascertained from surface wavelets. The new method is called an interfacial wavelet algorithm and demonstrated by two corresponding numerical models. When using this method, mesh divisions and artificial boundary conditions need no treatment so that computing amount and transmission errors between nodes are reduced greatly. It is very fit to solve seismic response in layered media.
Abstract：
For the promotion and application of coarse-grained soil fillings in the railway subgrade in frozen regions, the shear strength properties of coarse-grained soil with fines content under freeze-thaw cycles are directly related to the subgrade stability. The influencing rules of freeze-thaw cycles, fines content and confining pressure on the shear strength properties of coarse-grained soil are therefore thoroughly studied and analyzed in laboratory tests. The results show that with the increasing increment of fines content, the stress-strain curve of coarse-grained soil changes from strain-softening before freeze-thaw cycles to strain-hardening after freeze-thaw cycles. With the increasing of fines content, the cohesion function of fines effectively enhances the shear strength of coarse-grained soil before freeze-thaw cycles, but the frost heave properties of fines decrease the shear strength of coarse-grained soil after freeze-thaw cycles. The shear strength indexes of coarse-grained soil decrease and then are steady after 6 freeze-thaw cycles. The confining pressure effectively enhances the shear strength of coarse-grained soil. Finally, the reasonable fines content of 5% is recommended for the railway subgrade coarse-grained soil fillings in frozen regions, and the mechanical indexes of the 6th freeze-thaw cycle are suggested for the engineering design values.
For the promotion and application of coarse-grained soil fillings in the railway subgrade in frozen regions, the shear strength properties of coarse-grained soil with fines content under freeze-thaw cycles are directly related to the subgrade stability. The influencing rules of freeze-thaw cycles, fines content and confining pressure on the shear strength properties of coarse-grained soil are therefore thoroughly studied and analyzed in laboratory tests. The results show that with the increasing increment of fines content, the stress-strain curve of coarse-grained soil changes from strain-softening before freeze-thaw cycles to strain-hardening after freeze-thaw cycles. With the increasing of fines content, the cohesion function of fines effectively enhances the shear strength of coarse-grained soil before freeze-thaw cycles, but the frost heave properties of fines decrease the shear strength of coarse-grained soil after freeze-thaw cycles. The shear strength indexes of coarse-grained soil decrease and then are steady after 6 freeze-thaw cycles. The confining pressure effectively enhances the shear strength of coarse-grained soil. Finally, the reasonable fines content of 5% is recommended for the railway subgrade coarse-grained soil fillings in frozen regions, and the mechanical indexes of the 6th freeze-thaw cycle are suggested for the engineering design values.
Abstract：
Frost-heave damage is the main reason for the channels in seasonal frozen regions. A new device is developed for simulating the frost-heave phenomenon of channels. It mainly includes the freeze-thaw model container, the circulating cooling water system and the measurement control system. The freeze-thaw model container consists of internal and external structures, and thermal insulation materials are filled between them. The circulating cooling water system adopts 12 groups of semiconductor chilling plates, and cooling or heating is accomplished by the Peltier effects. The high-pressure pump combined with the air cooling radiator realizes a continuous cooling for the system without hydraulic rotating joints. The installation device for the direct rebound displacement sensors is developed to ensure the accurate measurement. The whole device is used to study the frost-heave damage of a channel. The test results show a good regularity with correct simulation of both the temperature and displacement fields, indicating that this facility is effective for the simulation tests on frost-heave of channels.
Frost-heave damage is the main reason for the channels in seasonal frozen regions. A new device is developed for simulating the frost-heave phenomenon of channels. It mainly includes the freeze-thaw model container, the circulating cooling water system and the measurement control system. The freeze-thaw model container consists of internal and external structures, and thermal insulation materials are filled between them. The circulating cooling water system adopts 12 groups of semiconductor chilling plates, and cooling or heating is accomplished by the Peltier effects. The high-pressure pump combined with the air cooling radiator realizes a continuous cooling for the system without hydraulic rotating joints. The installation device for the direct rebound displacement sensors is developed to ensure the accurate measurement. The whole device is used to study the frost-heave damage of a channel. The test results show a good regularity with correct simulation of both the temperature and displacement fields, indicating that this facility is effective for the simulation tests on frost-heave of channels.
Abstract：
The pile capacity degrades and the permanent settlement of pile accumulates when the pile is subjected to low-amplitude and long-term axial cyclic loading. The degradation of the pile capacity and the permanent accumulated settlement of the pile will greatly influence the service ability of settlement-sensitive superstructures, such as high-speed railway tracks, wind turbines and so on. The general design requirements of piles under cyclic axial loading and the key issues that are of great interest to the designers are introduced. The behaviors of piles under axial cyclic loading are presented and the main factors influencing them are discussed. The definitions of load ratios are given. The criteria for assessing pile response based on the limit cyclic loading ratio are proposed. The idea of a cyclic interaction diagram is developed. The design method and procedure for piles under cyclic axial loading are proposed. Finally, a case is given to verify the proposed design approach.
The pile capacity degrades and the permanent settlement of pile accumulates when the pile is subjected to low-amplitude and long-term axial cyclic loading. The degradation of the pile capacity and the permanent accumulated settlement of the pile will greatly influence the service ability of settlement-sensitive superstructures, such as high-speed railway tracks, wind turbines and so on. The general design requirements of piles under cyclic axial loading and the key issues that are of great interest to the designers are introduced. The behaviors of piles under axial cyclic loading are presented and the main factors influencing them are discussed. The definitions of load ratios are given. The criteria for assessing pile response based on the limit cyclic loading ratio are proposed. The idea of a cyclic interaction diagram is developed. The design method and procedure for piles under cyclic axial loading are proposed. Finally, a case is given to verify the proposed design approach.
Abstract：
During compression of unsaturated soils, the volume change and water content change interact simultaneously. The hydro-mechanical coupling effects on both of them are comprehensively investigated. For this purpose, tests on water density in soils and suction-controlled (0~1000 kPa) one-dimensional compression tests on saturated and unsaturated soils are carried out for Jingmen expansive soils. The conclusions are drawn as follows: (1) For the volume change behaviour, the yielding point can be observed on the load-compression curve, and the compression ones under higher suction intersect the curves under lower suction sequentially. The unloading curves appear to be linear, and the slopes of which decrease with the increasing suction. The volume change formula is presented, which is capable of predicting the shrinkage due to suction increase, volume compression/expansion due to loading/unloading, yielding, and the variety of compressibility due to suction change. (2) For the water retention behaviour during compression, the water content changes slightly under higher suction. When compressed to the net vertical pressure of 2941.8 kPa, the water contents under the four different suctions are similar. A three-parameter Logistic function is presented for simulating the coupling effects of suction and net vertical stress on water content. (3) The degree of saturation increases during both loading and unloading, both of which mean ‘wetting’. However, the water content decreases during loading, which means ‘drying’. The reason for this discrepancy is that the change of degree of saturation can be affected by change of the water content as well as that of void ratio.
During compression of unsaturated soils, the volume change and water content change interact simultaneously. The hydro-mechanical coupling effects on both of them are comprehensively investigated. For this purpose, tests on water density in soils and suction-controlled (0~1000 kPa) one-dimensional compression tests on saturated and unsaturated soils are carried out for Jingmen expansive soils. The conclusions are drawn as follows: (1) For the volume change behaviour, the yielding point can be observed on the load-compression curve, and the compression ones under higher suction intersect the curves under lower suction sequentially. The unloading curves appear to be linear, and the slopes of which decrease with the increasing suction. The volume change formula is presented, which is capable of predicting the shrinkage due to suction increase, volume compression/expansion due to loading/unloading, yielding, and the variety of compressibility due to suction change. (2) For the water retention behaviour during compression, the water content changes slightly under higher suction. When compressed to the net vertical pressure of 2941.8 kPa, the water contents under the four different suctions are similar. A three-parameter Logistic function is presented for simulating the coupling effects of suction and net vertical stress on water content. (3) The degree of saturation increases during both loading and unloading, both of which mean ‘wetting’. However, the water content decreases during loading, which means ‘drying’. The reason for this discrepancy is that the change of degree of saturation can be affected by change of the water content as well as that of void ratio.
Abstract：
The measured results of forces at pile top of tube frame structural system and large-scale model tests by applying the optimized design of pile foundation stiffness to reduce differential settlement show that the forces at pile top in different tube areas increase with the increase of loading level, and those under the tube and peripheral frame columns tend to be uniform under the working loads. The optimized design of pile foundation stiffness to reduce differential settlement can adjust distribution of forces and improve stress behavior of rafts. In model tests, the improvement ratio for tubes is in the decreasing order of angle pile, side pile and center pile. The corresponding pile butt force ratio of the forces to mean values is 1.15∶1.02∶0.83. The measured pile forces are in the decreasing order of peripheral frame columns, peripheral frame edge columns and piles under the tube. This is mainly due to the weakening of support stiffness caused by the vertical pile group effect. The pile group effect is weaker due to the fewer number of piles under the peripheral frame columns and angle piles.
The measured results of forces at pile top of tube frame structural system and large-scale model tests by applying the optimized design of pile foundation stiffness to reduce differential settlement show that the forces at pile top in different tube areas increase with the increase of loading level, and those under the tube and peripheral frame columns tend to be uniform under the working loads. The optimized design of pile foundation stiffness to reduce differential settlement can adjust distribution of forces and improve stress behavior of rafts. In model tests, the improvement ratio for tubes is in the decreasing order of angle pile, side pile and center pile. The corresponding pile butt force ratio of the forces to mean values is 1.15∶1.02∶0.83. The measured pile forces are in the decreasing order of peripheral frame columns, peripheral frame edge columns and piles under the tube. This is mainly due to the weakening of support stiffness caused by the vertical pile group effect. The pile group effect is weaker due to the fewer number of piles under the peripheral frame columns and angle piles.
Abstract：
The three-dimensional failure mechanism for the face stability of tunnel in pure clay under undrained condition is improved. As in the existing 3D translational multi-block collapse mechanism, the intersection of the circular truncated cylinder with the tunnel face is an ellipse surface that does not cover the entire circular face of the tunnel. The truncated elliptical cylinder is adapted to construct the 3D translational multi-block failure mechanism. In the present 3D mechanism, all the radial cross-sections of the rigid block are elliptical, and the intersection of the cylinder with the tunnel face is a circular face. The 3D collapse mechanism is further modified to intermix rotating multi-block and homogeneous shear zone, and the corresponding upper bound solution significantly improves the existing limit analysis. The validity of the combined upper bound solution for the tunnel stability in clays is demonstrated by comparing with the existing 3D finite element and centrifuge results.
The three-dimensional failure mechanism for the face stability of tunnel in pure clay under undrained condition is improved. As in the existing 3D translational multi-block collapse mechanism, the intersection of the circular truncated cylinder with the tunnel face is an ellipse surface that does not cover the entire circular face of the tunnel. The truncated elliptical cylinder is adapted to construct the 3D translational multi-block failure mechanism. In the present 3D mechanism, all the radial cross-sections of the rigid block are elliptical, and the intersection of the cylinder with the tunnel face is a circular face. The 3D collapse mechanism is further modified to intermix rotating multi-block and homogeneous shear zone, and the corresponding upper bound solution significantly improves the existing limit analysis. The validity of the combined upper bound solution for the tunnel stability in clays is demonstrated by comparing with the existing 3D finite element and centrifuge results.
Abstract：
Dynamic elastic modulus and damping ratio are the basic mechanical parameters for dynamic analysis of soils, which can be usually got by dynamic triaxial tests with small strain range. The reliability of test technology and the accuracy of the test parameters are the key to the aseismic safety assessment. Based on the results of the dynamic triaxial tests, the influences of several factors such as using internal or external sensors, relative position of force and displacement sensors on the hysteresis loop, dynamic elastic modulus and damping ratio are analyzed. A new method is proposed, which can be used to calculate the dynamic modulus and damping ratio when there is non-closed hysteresis loop of residual deformation, and the influence laws of the frequency, confining pressure, consolidation ratio and other factors on the test results and their characteristics are compared. The influence factor of power function is also added to the Janbu formula, and the normalized characteristics of dynamic elastic modulus and damping ratio with different confining pressures and consolidation ratios are studied. The research results will help improve the ability of domestic research institutions to test the dynamic parameters of soils, and this study also has a positive reference significance to the antiseismic engineering and scientific research.
Dynamic elastic modulus and damping ratio are the basic mechanical parameters for dynamic analysis of soils, which can be usually got by dynamic triaxial tests with small strain range. The reliability of test technology and the accuracy of the test parameters are the key to the aseismic safety assessment. Based on the results of the dynamic triaxial tests, the influences of several factors such as using internal or external sensors, relative position of force and displacement sensors on the hysteresis loop, dynamic elastic modulus and damping ratio are analyzed. A new method is proposed, which can be used to calculate the dynamic modulus and damping ratio when there is non-closed hysteresis loop of residual deformation, and the influence laws of the frequency, confining pressure, consolidation ratio and other factors on the test results and their characteristics are compared. The influence factor of power function is also added to the Janbu formula, and the normalized characteristics of dynamic elastic modulus and damping ratio with different confining pressures and consolidation ratios are studied. The research results will help improve the ability of domestic research institutions to test the dynamic parameters of soils, and this study also has a positive reference significance to the antiseismic engineering and scientific research.
Abstract：
In order to overcome the limitation of ABAQUS in simulating rainfall infiltration, Python language is used to modify the rainfall infiltration boundary in ABAQUS, the rainfall boundary is considered as an uncertain boundary and is solved by iterative algorithm, and then a rainfall module is developed. This module overcomes the unchanged infiltration rate which is adopted in ABAQUS, thus the ABAQUS’s function in rainfall infiltration analysis is improved. Compared with the column infiltration tests, the validity of this module is confirmed. On this basis, the rainfall infiltration process of anti-slide pile slope is studied. The results show that the anti-slide pile can improve slope stability, however, under rainfall conditions, the anti-slide pile will reduce the effective drainage section, the underground water from trailing of the slope cannot discharge in time, and this will have adverse effect on the slope stability. So, for pluvial regions, the adverse effect of rainfall should be considered in anti-slid pile design. With the aid of the powerful features of ABAQUS, the proposed module may provide a good research platform for more complicated rainfall problems in the future.
In order to overcome the limitation of ABAQUS in simulating rainfall infiltration, Python language is used to modify the rainfall infiltration boundary in ABAQUS, the rainfall boundary is considered as an uncertain boundary and is solved by iterative algorithm, and then a rainfall module is developed. This module overcomes the unchanged infiltration rate which is adopted in ABAQUS, thus the ABAQUS’s function in rainfall infiltration analysis is improved. Compared with the column infiltration tests, the validity of this module is confirmed. On this basis, the rainfall infiltration process of anti-slide pile slope is studied. The results show that the anti-slide pile can improve slope stability, however, under rainfall conditions, the anti-slide pile will reduce the effective drainage section, the underground water from trailing of the slope cannot discharge in time, and this will have adverse effect on the slope stability. So, for pluvial regions, the adverse effect of rainfall should be considered in anti-slid pile design. With the aid of the powerful features of ABAQUS, the proposed module may provide a good research platform for more complicated rainfall problems in the future.
Abstract：
Using the new shoulder balance weight retaining wall of an old embankment widening project of a mountainous highway as the prototype, four groups of geotechnical centrifugal model tests are designed based on the wall motions under translation (T), rotating around base (RB), rotation around top (RT) and T+RB modes, the impact of wall motion modes on earth pressure and deformation of the filling is discussed, and the process of soils at various depths entering in to the active earth pressure is analyzed. The results show that: (1) The wall motion modes almost have no influence on the values and distribution of earth pressure on the upper wall, but when the ratio of displacement to height of retaining wall is less than 0.3%~0.5%, the shallow layer fills behind the upper wall have soil arching effect which is caused by wall-soil friction, and the coefficient of horizontal earth pressure increases; (2) The equilibrator has a shadowing effect on the down wall earth pressure, and the influence area is about 1/3 height of the down wall below the equilibrator. The results reduce the position of the acting point of earth pressure resultant force; (3) The motion modes have obvious impact on the fill settlement. When the maximum wall displacements are the same, the fill settlement of the T mode is significantly larger than that of the RB and RT modes. Under the RT mode, although it has the same displacement area as the RT mode, the equilibrator deflects downward. The fill settlement is promoted, leading to that the fill settlement of the RT mode is larger than that of RB mode, and the second fracture surface occurs easier on the upper wall.
Using the new shoulder balance weight retaining wall of an old embankment widening project of a mountainous highway as the prototype, four groups of geotechnical centrifugal model tests are designed based on the wall motions under translation (T), rotating around base (RB), rotation around top (RT) and T+RB modes, the impact of wall motion modes on earth pressure and deformation of the filling is discussed, and the process of soils at various depths entering in to the active earth pressure is analyzed. The results show that: (1) The wall motion modes almost have no influence on the values and distribution of earth pressure on the upper wall, but when the ratio of displacement to height of retaining wall is less than 0.3%~0.5%, the shallow layer fills behind the upper wall have soil arching effect which is caused by wall-soil friction, and the coefficient of horizontal earth pressure increases; (2) The equilibrator has a shadowing effect on the down wall earth pressure, and the influence area is about 1/3 height of the down wall below the equilibrator. The results reduce the position of the acting point of earth pressure resultant force; (3) The motion modes have obvious impact on the fill settlement. When the maximum wall displacements are the same, the fill settlement of the T mode is significantly larger than that of the RB and RT modes. Under the RT mode, although it has the same displacement area as the RT mode, the equilibrator deflects downward. The fill settlement is promoted, leading to that the fill settlement of the RT mode is larger than that of RB mode, and the second fracture surface occurs easier on the upper wall.
Abstract：
The installation of bucket foundation is a vital construction procedure. The existing relative studies have mainly focused on the methods for calculating the penetration resistance and required suction. However, the understanding of the soil-skirt interaction during the installation is not clear yet due to inadequate test data. Model tests on the installation of bucket foundation are carried out in silt sand. The inner and outer soil pressures on the skirt are measured under both jacking installation and suction installation conditions. The jacking test results show that the inner soil pressures on the skirt are much larger than the outer ones. The compaction extent of the inner sand grows with the increase of the penetration depth, which is contrary to that of the outer sand. The suction test results show that the inner soil pressures decrease dramatically when the suction is applied. The outer soil pressures, however, increase firstly and then fall down to stable values rapidly. The inner friction and tip resistance are greatly reduced due to the seepage effects. The test results also indicate that the existing critical suction is too conservative. Based on the test results, the existing prediction method for the required suction is modified and evaluated, and a more accurate method is obtained.
The installation of bucket foundation is a vital construction procedure. The existing relative studies have mainly focused on the methods for calculating the penetration resistance and required suction. However, the understanding of the soil-skirt interaction during the installation is not clear yet due to inadequate test data. Model tests on the installation of bucket foundation are carried out in silt sand. The inner and outer soil pressures on the skirt are measured under both jacking installation and suction installation conditions. The jacking test results show that the inner soil pressures on the skirt are much larger than the outer ones. The compaction extent of the inner sand grows with the increase of the penetration depth, which is contrary to that of the outer sand. The suction test results show that the inner soil pressures decrease dramatically when the suction is applied. The outer soil pressures, however, increase firstly and then fall down to stable values rapidly. The inner friction and tip resistance are greatly reduced due to the seepage effects. The test results also indicate that the existing critical suction is too conservative. Based on the test results, the existing prediction method for the required suction is modified and evaluated, and a more accurate method is obtained.
Abstract：
Two models with the same dimension, bedding and count-tilt rock slopes with siltized intercalation are designed, and large-scale shaking table tests are performed to analyze the seismic response differences between bedding and count-tilt rock slopes with siltized intercalation. The research results show that the acceleration amplification coefficient in the bedding rock slope is smaller than that in the count-tilt rock slope. The acceleration amplification coefficient on slope face of the bedding rock slope is larger than that of the count-tilt rock slope at the middle and upper parts of slope, where the elevation height is not less than 0.4, while the acceleration amplification coefficient on slope face of the bedding rock slope is close to that of the count-tilt rock slope at the lower part of slope, where the elevation height is less than 0.4. The displacements on slope faces of both the bedding and count-tilt rock slopes increase with the increase of the amplitude of input seismic waves, but the displacement on slope face of bedding rock slope is larger than that of count-tilt rock slope, and the difference value between increases with the amplitude of input seismic waves. The seismic stability of the bedding rock slope is stronger than that of the count-tilt rock slope; the failure forms of bedding rock slope mainly include vertical tension crack at the back edge, bedding sliding at mud layer and caving rocks at slope top, while those of the count-tilt mainly include intersect of horizontal and vertical cracks, squeezed siltized intercalation and shattered slope top.
Two models with the same dimension, bedding and count-tilt rock slopes with siltized intercalation are designed, and large-scale shaking table tests are performed to analyze the seismic response differences between bedding and count-tilt rock slopes with siltized intercalation. The research results show that the acceleration amplification coefficient in the bedding rock slope is smaller than that in the count-tilt rock slope. The acceleration amplification coefficient on slope face of the bedding rock slope is larger than that of the count-tilt rock slope at the middle and upper parts of slope, where the elevation height is not less than 0.4, while the acceleration amplification coefficient on slope face of the bedding rock slope is close to that of the count-tilt rock slope at the lower part of slope, where the elevation height is less than 0.4. The displacements on slope faces of both the bedding and count-tilt rock slopes increase with the increase of the amplitude of input seismic waves, but the displacement on slope face of bedding rock slope is larger than that of count-tilt rock slope, and the difference value between increases with the amplitude of input seismic waves. The seismic stability of the bedding rock slope is stronger than that of the count-tilt rock slope; the failure forms of bedding rock slope mainly include vertical tension crack at the back edge, bedding sliding at mud layer and caving rocks at slope top, while those of the count-tilt mainly include intersect of horizontal and vertical cracks, squeezed siltized intercalation and shattered slope top.
Abstract：
Three-dimensional static and dynamic elasto-plastic finite element analyses are conducted on a concrete faced rock fill dam. Three different soil-structure interface models are used to simulate the interface between slab and cushion layer, including hyperbolic model (only for static analysis), ideal elasto-plastic model and ageneralized plastic model. The slab stresses are nearly the same among three interface models after construction. The slope-direction slab stresses are also slightly different among three interface models during impoundment, while the axial-direction slab stresses have clear differences. The stress path and shear deformation between slab and cushion layer calculated by the generalized plastic model are different from those by the hyperbolic and ideal elasto-plastic models during impoundment. The slope-direction stress induced by the residual deformation is slightly different between the generalized plastic and ideal elasto-plastic interface models, but the axial-direction stress is much larger for the ideal elasto-plastic model. The ideal elasto-plastic model can only produce plastic deformation when the stress reaches the peak strength, and the shear deformation of interface during earthquakes will be underestimated. The generalized plastic interface model can reflect the dilative and contractive responses, strain hardening, softening, particle breakage and cyclic residual deformation, which is more close to reality.
Three-dimensional static and dynamic elasto-plastic finite element analyses are conducted on a concrete faced rock fill dam. Three different soil-structure interface models are used to simulate the interface between slab and cushion layer, including hyperbolic model (only for static analysis), ideal elasto-plastic model and ageneralized plastic model. The slab stresses are nearly the same among three interface models after construction. The slope-direction slab stresses are also slightly different among three interface models during impoundment, while the axial-direction slab stresses have clear differences. The stress path and shear deformation between slab and cushion layer calculated by the generalized plastic model are different from those by the hyperbolic and ideal elasto-plastic models during impoundment. The slope-direction stress induced by the residual deformation is slightly different between the generalized plastic and ideal elasto-plastic interface models, but the axial-direction stress is much larger for the ideal elasto-plastic model. The ideal elasto-plastic model can only produce plastic deformation when the stress reaches the peak strength, and the shear deformation of interface during earthquakes will be underestimated. The generalized plastic interface model can reflect the dilative and contractive responses, strain hardening, softening, particle breakage and cyclic residual deformation, which is more close to reality.
Abstract：
The spatial structure of tunnel lining model is a typical stratiform distribution, so it is difficult to identify the void area if its height is less than tuning thickness when using ground penetrating radar (GPR) to detect the second lining of tunnel. In this paper, by establishing a geometrical model for the second lining layer of tunnel including void area and considering the spreading law of electromagnetic waves in tunnel lining, a reflection model for electromagnetic waves in tunnel lining detection is obtained, and the generalized reflection coefficient in spectrum expression is deduced as well as an inversion method to further estimate the lining thickness of tunnel and the height of void area according to the reflection coefficient sequence spectrum. By analyzing the amplitude spectrum properties of the reflection coefficient sequence, a quick method to estimate the height of void area is proposed, namely determining the two-way travel time of void area and leading to the height of void area according to the depressing period of the amplitude spectra. Finally, 1stopt mathematical optimization analysis software is adopted for the global optimization and calculation of parameters. The results of physical model experiments and field tests indicate that the spectrum inversion method can also estimate the lining thickness of tunnel and the height of void area accurately when the height of void area is less than 1/4 wavelength, consequently enhancing the vertical resolution of GPR data.
The spatial structure of tunnel lining model is a typical stratiform distribution, so it is difficult to identify the void area if its height is less than tuning thickness when using ground penetrating radar (GPR) to detect the second lining of tunnel. In this paper, by establishing a geometrical model for the second lining layer of tunnel including void area and considering the spreading law of electromagnetic waves in tunnel lining, a reflection model for electromagnetic waves in tunnel lining detection is obtained, and the generalized reflection coefficient in spectrum expression is deduced as well as an inversion method to further estimate the lining thickness of tunnel and the height of void area according to the reflection coefficient sequence spectrum. By analyzing the amplitude spectrum properties of the reflection coefficient sequence, a quick method to estimate the height of void area is proposed, namely determining the two-way travel time of void area and leading to the height of void area according to the depressing period of the amplitude spectra. Finally, 1stopt mathematical optimization analysis software is adopted for the global optimization and calculation of parameters. The results of physical model experiments and field tests indicate that the spectrum inversion method can also estimate the lining thickness of tunnel and the height of void area accurately when the height of void area is less than 1/4 wavelength, consequently enhancing the vertical resolution of GPR data.
Abstract：
The fiber reinforced polymer (FRP) bars have the behavior of strong corrosion resistance, high tensile strength and small elastic modulus, and can be used to replace steel bars, which undergo wearing due to rusting in slope reinforcement. The pre-stress FRP bars are reasonable, but the bars have low shear strength and cannot be pre-stressed using the traditional rigid clamp, lest they are crashed to failure. An end anchoring pre-stress locking device is designed for pre-stress application and retention in the FRP bars. Field tests are conducted to verify the stability of the device. The test results show that the device is practically feasible and convenient, and it can apply and retain pre-stress in basalt-glass fiber reinforced polymer (B-GFRP) bars well. Exposure to external factors such as heavy rains and blasting results in the loss of pre-stress. The pre-stress loss is caused by degeneration of the bonding resulting from external factors, but not by the invalidation of the device. The pre-stress retention by the device in the B-GFRP bars is 5%~35%, which conforms to the control criterion for the pre-stress loss of the steel pre-stressed soil nail reinforcement.
The fiber reinforced polymer (FRP) bars have the behavior of strong corrosion resistance, high tensile strength and small elastic modulus, and can be used to replace steel bars, which undergo wearing due to rusting in slope reinforcement. The pre-stress FRP bars are reasonable, but the bars have low shear strength and cannot be pre-stressed using the traditional rigid clamp, lest they are crashed to failure. An end anchoring pre-stress locking device is designed for pre-stress application and retention in the FRP bars. Field tests are conducted to verify the stability of the device. The test results show that the device is practically feasible and convenient, and it can apply and retain pre-stress in basalt-glass fiber reinforced polymer (B-GFRP) bars well. Exposure to external factors such as heavy rains and blasting results in the loss of pre-stress. The pre-stress loss is caused by degeneration of the bonding resulting from external factors, but not by the invalidation of the device. The pre-stress retention by the device in the B-GFRP bars is 5%~35%, which conforms to the control criterion for the pre-stress loss of the steel pre-stressed soil nail reinforcement.
Abstract：
There are many cracks in the natural rock mass and the majority of the cracks are unequal. The main control crack with a certain scale decides the stability of the rock mass. In order to study the interaction rules of the cracks with unequal length and the initiation rules of the main control crack, based on the Kachanov method, the expressions for the stress intensity factors of two collinear cracks with unequal length loaded by uniaxial tractions at infinity are derived, and the influence of the crack distance on the interaction is theoretically analyzed. The initiation angle of the main crack under uniaxial tension is calculated by the maximum circumferential stress criteria and the theoretical fracture criteria curves are drawn. The stress intensity factors of sliding close cracks are derived and the compression tests on rock-like specimens with two unequal collinear cracks are performed. The results show that the small crack almost has no effect on the initiation of the main control crack when the crack distance reaches the length of the small crack. The initiation angle of the main control crack is only related to the crack incline angle, and it decreases with the increase of the crack angle when the cracks are loaded by uniaxial tension and it increases with the increase of the crack angle when the cracks are loaded by uniaxial compression. The initial critical load increases rapidly when the crack incline angle is less than 30°.
There are many cracks in the natural rock mass and the majority of the cracks are unequal. The main control crack with a certain scale decides the stability of the rock mass. In order to study the interaction rules of the cracks with unequal length and the initiation rules of the main control crack, based on the Kachanov method, the expressions for the stress intensity factors of two collinear cracks with unequal length loaded by uniaxial tractions at infinity are derived, and the influence of the crack distance on the interaction is theoretically analyzed. The initiation angle of the main crack under uniaxial tension is calculated by the maximum circumferential stress criteria and the theoretical fracture criteria curves are drawn. The stress intensity factors of sliding close cracks are derived and the compression tests on rock-like specimens with two unequal collinear cracks are performed. The results show that the small crack almost has no effect on the initiation of the main control crack when the crack distance reaches the length of the small crack. The initiation angle of the main control crack is only related to the crack incline angle, and it decreases with the increase of the crack angle when the cracks are loaded by uniaxial tension and it increases with the increase of the crack angle when the cracks are loaded by uniaxial compression. The initial critical load increases rapidly when the crack incline angle is less than 30°.
Abstract：
By means of seism investigation, soil test and 14C dating, disaster phenomena about seismic subsidence of soft soils and some earthquake-induced association structures of soil layers are identified in soft soils of limnetic facies during the Mid-late Holocene in the Anqiu area of Yishu fault-seismic zone, including subsidence synform folds of soft soils, small scale co-seismic faults, pinch-and-swell structures and seismic fissures, in which subsidence synforms are vertical deformations that directly reflect the seismic subsidence disaster. Small scale co-seismic faults are some little faults caused by earthquakes, with vertical lengths of 0.5~1.8 m under the subsidence synform. A subsidence synform comes at first along with producing of co-seismic faults and developes downward treading on the heels of these faults extending to the even deeper place. The earthquake vibration causes the thixotropic deformation of saturated soft soils, and soil particles flow from the hinge zone to two wings of the synform, in which the seismic additional stresses act continually, resulting in formation of the narrow and deep-seated subsidence synform. The deepest seismic subsidence of soft soils is 1.08 m, and the average depth is 0.68 m. It is estimated that the seismic intensity is VIII degree, and the earthquake magnitude is over M6.0. The formation age of the mucky soils for 3901±33a B.P. is obtained by the14C dating, so the seismic event occurred in about 19th Century B.C.. The co-seismic fault is an important factor for forming the seismic subsidence of soft soils, which provides the new information for understanding the formation mechanism of the seismic subsidence of soft soils and the new revelation for preventing or mitigating the harm of the seismic subsidence. Therefore, attention should be paid to possible hidden troubles of co-seismic faults to be produced in the underlying layer of soft soils.
By means of seism investigation, soil test and 14C dating, disaster phenomena about seismic subsidence of soft soils and some earthquake-induced association structures of soil layers are identified in soft soils of limnetic facies during the Mid-late Holocene in the Anqiu area of Yishu fault-seismic zone, including subsidence synform folds of soft soils, small scale co-seismic faults, pinch-and-swell structures and seismic fissures, in which subsidence synforms are vertical deformations that directly reflect the seismic subsidence disaster. Small scale co-seismic faults are some little faults caused by earthquakes, with vertical lengths of 0.5~1.8 m under the subsidence synform. A subsidence synform comes at first along with producing of co-seismic faults and developes downward treading on the heels of these faults extending to the even deeper place. The earthquake vibration causes the thixotropic deformation of saturated soft soils, and soil particles flow from the hinge zone to two wings of the synform, in which the seismic additional stresses act continually, resulting in formation of the narrow and deep-seated subsidence synform. The deepest seismic subsidence of soft soils is 1.08 m, and the average depth is 0.68 m. It is estimated that the seismic intensity is VIII degree, and the earthquake magnitude is over M6.0. The formation age of the mucky soils for 3901±33a B.P. is obtained by the14C dating, so the seismic event occurred in about 19th Century B.C.. The co-seismic fault is an important factor for forming the seismic subsidence of soft soils, which provides the new information for understanding the formation mechanism of the seismic subsidence of soft soils and the new revelation for preventing or mitigating the harm of the seismic subsidence. Therefore, attention should be paid to possible hidden troubles of co-seismic faults to be produced in the underlying layer of soft soils.
Abstract：
The surrounding rock salt of underground gas storage cavern is subjected to long-term triaxial fatigue stress. The deformation property of rock salt under triaxial cyclic loading is of great importance to the stability of the rock salt cavity. A series of laboratory tests are performed to explore the deformation behavior of eight rock salt specimens under various confining pressures, stress levels and loading frequencies. The axial low-frequency cyclic stress is applied on each salt specimen while the confining pressure is kept steady. The test parameters are processed by the dimensionless method. The effects of the strength of stress ratio (ratio of generalized shear strength to spherical stress), amplitude of stress ratio, level of the maximum stress, loading frequency and loading cycles (N) on the volumetric strain (εv) of rock salt are analyzed. The nonlinear curve fitting is carried out using the function εv =λlgN+εv0 for a curve of each specimen on the volumetric strain with the cycles. Further, the expressions for the parameters λ and εv0 with the amplitude of stress ratio, the maximum stress and loading frequency are obtained, respectively. The analysis of standardization regression coefficient indicates that the maximum stress is the key factor that influences the volumetric deformation of rock salt, and the stress amplitude ratio comes the second. It is noted that the rock salt exhibits dilatancy under high maximum stress.
The surrounding rock salt of underground gas storage cavern is subjected to long-term triaxial fatigue stress. The deformation property of rock salt under triaxial cyclic loading is of great importance to the stability of the rock salt cavity. A series of laboratory tests are performed to explore the deformation behavior of eight rock salt specimens under various confining pressures, stress levels and loading frequencies. The axial low-frequency cyclic stress is applied on each salt specimen while the confining pressure is kept steady. The test parameters are processed by the dimensionless method. The effects of the strength of stress ratio (ratio of generalized shear strength to spherical stress), amplitude of stress ratio, level of the maximum stress, loading frequency and loading cycles (N) on the volumetric strain (εv) of rock salt are analyzed. The nonlinear curve fitting is carried out using the function εv =λlgN+εv0 for a curve of each specimen on the volumetric strain with the cycles. Further, the expressions for the parameters λ and εv0 with the amplitude of stress ratio, the maximum stress and loading frequency are obtained, respectively. The analysis of standardization regression coefficient indicates that the maximum stress is the key factor that influences the volumetric deformation of rock salt, and the stress amplitude ratio comes the second. It is noted that the rock salt exhibits dilatancy under high maximum stress.
Abstract：
The experimental research on the release characteristics of deposited particles in porous media plays an important role in the blocking process of the WSHP recharge. The release characteristics of deposited particles in porous media are studied by using the self-development sand deposition and release equipment. Two factors are taken into consideration, one is increasing the flow velocity, the other is changing the flow direction. The study shows that as the flow velocity increases, deposited particles are easier to release from the surface of porous media and it takes less time to reach the second peak of relative concentration, meanwhile, the water injected is almost of the same amount. Compared with the way of increasing the flow velocity, the way of changing the flow direction is more effective in the releasing process of deposited particles, and it takes less time and water to reach the second peak of relative concentration. With the increase of time, blocking will appear in porous media and change as it is before the flow direction. The initial phase after the flow condition changes plays an important role in the release of deposited particles. The research lays foundation for further studies on the deposition and release characteristics that suspended particles transport in layer, especially in the recharge process of WSHP.
The experimental research on the release characteristics of deposited particles in porous media plays an important role in the blocking process of the WSHP recharge. The release characteristics of deposited particles in porous media are studied by using the self-development sand deposition and release equipment. Two factors are taken into consideration, one is increasing the flow velocity, the other is changing the flow direction. The study shows that as the flow velocity increases, deposited particles are easier to release from the surface of porous media and it takes less time to reach the second peak of relative concentration, meanwhile, the water injected is almost of the same amount. Compared with the way of increasing the flow velocity, the way of changing the flow direction is more effective in the releasing process of deposited particles, and it takes less time and water to reach the second peak of relative concentration. With the increase of time, blocking will appear in porous media and change as it is before the flow direction. The initial phase after the flow condition changes plays an important role in the release of deposited particles. The research lays foundation for further studies on the deposition and release characteristics that suspended particles transport in layer, especially in the recharge process of WSHP.
Abstract：
In order to clearly comprehend the volume change law of sulphate saline soil in the intense reaction period of producing ice crystals and causing salt expansion, assuming that the ice crystals and the mirabilite in the soil exist independently and the volume change of soil is composed of three increased parts and three reduced parts, and based on the law of conservation of solute, an expression for the volume change of sulphate saline soil considering salt expansion and frost heave is proposed. It is found that the expression for the volume change in the intense reaction period is largely decided by the initial void ratio n, unfrozen water content θu1 and θu2 before and after being cooled, and solubility r1 and r2 before and after being cooled. The volume of artificial sulphate saline soil samples is investigated using the test system of soil under controlled temperature. The unfrozen water content in the process of freezing is determined by the freezing temperature tests, and the concept of no precipitated water content (NPWC) is given, and the cumulative volume change rate of soil samples during being cooled is calculated. The rationality and applicability of the proposed expression is verified through analysis and comparison between the measured and calculated volume change rates of soil samples.
In order to clearly comprehend the volume change law of sulphate saline soil in the intense reaction period of producing ice crystals and causing salt expansion, assuming that the ice crystals and the mirabilite in the soil exist independently and the volume change of soil is composed of three increased parts and three reduced parts, and based on the law of conservation of solute, an expression for the volume change of sulphate saline soil considering salt expansion and frost heave is proposed. It is found that the expression for the volume change in the intense reaction period is largely decided by the initial void ratio n, unfrozen water content θu1 and θu2 before and after being cooled, and solubility r1 and r2 before and after being cooled. The volume of artificial sulphate saline soil samples is investigated using the test system of soil under controlled temperature. The unfrozen water content in the process of freezing is determined by the freezing temperature tests, and the concept of no precipitated water content (NPWC) is given, and the cumulative volume change rate of soil samples during being cooled is calculated. The rationality and applicability of the proposed expression is verified through analysis and comparison between the measured and calculated volume change rates of soil samples.
Abstract：
Whether or not the dynamic parameters of earth rockfill determined in the laboratory or in situ are corresponding to the reality is a matter of concern. A back-analysis approach for the dynamic parameters of earth-rockfill based on response spectra and acceleration peak is presented. According to the acceleration response information of Liyutan Dam in the Chi-Chi earthquake, and by applying the back-calculation approach, the dynamic parameters are obtained. The results demonstrate that the proposed method is feasible, and the computational accuracy basically satisfies the practical engineering requirements. The dynamic shear modulus coefficient K of the dam materials obtained from the laboratory dynamic triaxial tests is small and should be revised.
Whether or not the dynamic parameters of earth rockfill determined in the laboratory or in situ are corresponding to the reality is a matter of concern. A back-analysis approach for the dynamic parameters of earth-rockfill based on response spectra and acceleration peak is presented. According to the acceleration response information of Liyutan Dam in the Chi-Chi earthquake, and by applying the back-calculation approach, the dynamic parameters are obtained. The results demonstrate that the proposed method is feasible, and the computational accuracy basically satisfies the practical engineering requirements. The dynamic shear modulus coefficient K of the dam materials obtained from the laboratory dynamic triaxial tests is small and should be revised.
