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Editor Work2017 Vol. 25, No. 6
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2017, 25(6): 1395-1404.
Abstract
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This paper uses GCTS dynamic hollow cylindrical torsional shear apparatus and two cyclic loading waveform of sine wave and square wave. It considers the confining pressure, the influence of the vibration amplitude, frequency and the minor factors. It studies the dynamic characteristics of structural soft clay. The test results show the follows. When the dynamic stress is below the yield stress of soil structure, waveform's influence on the overall shape of the dynamic stress-strain relationship curve is very small. When dynamic stress exceeds the structure yield stress, stress-strain relationship is softening type. The softening degree of square wave is higher. Under the same conditions, square wave accumulated deformation is always greater than that of the sine wave. Waveform has an effect on pore pressure changes. The values of pore pressure under sinusoidal wave action is always greater than that of the square wave. Amplitude for the performance of pore pressure change is as follows:when the rising speed of stable amplitude is quick, the value is greater than the critical type amplitude under the action of pore pressure value. Namely the critical type amplitude under the action of pore pressure hysteresis phenomenon is serious. Yield strain and dynamic strength decrease with the increase of the vibration time trend, eventually tend to a certain value. Finally numerical size is related to the waveform. The sine wave is less than the square wave, which is contrary to the sine wave is greater than the square wave.
This paper uses GCTS dynamic hollow cylindrical torsional shear apparatus and two cyclic loading waveform of sine wave and square wave. It considers the confining pressure, the influence of the vibration amplitude, frequency and the minor factors. It studies the dynamic characteristics of structural soft clay. The test results show the follows. When the dynamic stress is below the yield stress of soil structure, waveform's influence on the overall shape of the dynamic stress-strain relationship curve is very small. When dynamic stress exceeds the structure yield stress, stress-strain relationship is softening type. The softening degree of square wave is higher. Under the same conditions, square wave accumulated deformation is always greater than that of the sine wave. Waveform has an effect on pore pressure changes. The values of pore pressure under sinusoidal wave action is always greater than that of the square wave. Amplitude for the performance of pore pressure change is as follows:when the rising speed of stable amplitude is quick, the value is greater than the critical type amplitude under the action of pore pressure value. Namely the critical type amplitude under the action of pore pressure hysteresis phenomenon is serious. Yield strain and dynamic strength decrease with the increase of the vibration time trend, eventually tend to a certain value. Finally numerical size is related to the waveform. The sine wave is less than the square wave, which is contrary to the sine wave is greater than the square wave.
2017, 25(6): 1405-1413.
According to the differences of pore structure characteristics between marine and continental shale in China, the Weiyuan and Jiao Shiba marine shale and Yaoqu continental shale are selected to test. The main test methods contain thin section analysis, mineral and main quantity analysis, low field scanning microscopy, mercury injection and gas adsorption. Based on the research results of pore structure characteristics and controlling factors, the new standards of pore size naming are put forward. The pores are divided into < 2nm, 2~100nm, 0.1~1μm, 1~10μm, 10~100μm, >100μm. They are respectively called ultramicropore, micropore, small hole, middle hole, big hole, and capillary hole. The sample porosity development degree from high to low in turn are 2#, 5#, 1#, 6#, 4# in 2~100nm pore range. The samples porosity development degree from high to low in turn are 2#, 1#, 4#, 6#, 5# in 10~100μm pore range. Pore distribution uniformity coefficient hu is proposed. Micro-nano pore of sample 2 and sample 5 are more development comparing to other samples. Also gas storage capacity of sample 2 and sample 5 are stronger. The test results of N2 adsorption, CO2 adsorption by using DFT model and mercury intrusion can be unified to attain continuous distribution of nanometer pore.
According to the differences of pore structure characteristics between marine and continental shale in China, the Weiyuan and Jiao Shiba marine shale and Yaoqu continental shale are selected to test. The main test methods contain thin section analysis, mineral and main quantity analysis, low field scanning microscopy, mercury injection and gas adsorption. Based on the research results of pore structure characteristics and controlling factors, the new standards of pore size naming are put forward. The pores are divided into < 2nm, 2~100nm, 0.1~1μm, 1~10μm, 10~100μm, >100μm. They are respectively called ultramicropore, micropore, small hole, middle hole, big hole, and capillary hole. The sample porosity development degree from high to low in turn are 2#, 5#, 1#, 6#, 4# in 2~100nm pore range. The samples porosity development degree from high to low in turn are 2#, 1#, 4#, 6#, 5# in 10~100μm pore range. Pore distribution uniformity coefficient hu is proposed. Micro-nano pore of sample 2 and sample 5 are more development comparing to other samples. Also gas storage capacity of sample 2 and sample 5 are stronger. The test results of N2 adsorption, CO2 adsorption by using DFT model and mercury intrusion can be unified to attain continuous distribution of nanometer pore.
2017, 25(6): 1414-1423.
The mechanical properties of shale gas reservoir have great influences on fracturing effect. It is of great necessity to investigate damage mechanism, mechanical properties and brittleness evaluation of shale rock and then to provide technical support for large-scale volume fracturing of shale gas exploitation. This paper conducts uniaxial compression tests on black carbonaceous shale of Lungmachi Formation. The test results indicate the follows. The black shale rock has obvious layered flake mineral structure. Its main mineral components are quartz and calcite, which causes the structure surface having high strength. Due to the effects of strong structure surface, shale rock with inclined bedding plane has larger values of elastic modulus and uniaxial tensile strength and the minimum total volumetric strains. However, when the bedding plan is parallel or vertical to the loading direction, the shale rock has smaller values of elastic modulus and uniaxial tensile strength and the maximum total volumetric strain. When the bedding angle β is increasing, the trend of crack initiation index behaves like a U-shaped curve, which is to say, the initiation crack indexes have smaller values at the β of 30° or 60° whereas bigger values at the β of 0° or 90°.It can be seen that brittleness is the key factor to rock fracturing. At the β of 30° or 60°, the rock has larger brittleness index with high fracturing variations of brittleness behave as an inverted U-shaped curve. The study of evaluating shale rock fracturing capability and improving the fracturing effect has important practical significance and application value.
The mechanical properties of shale gas reservoir have great influences on fracturing effect. It is of great necessity to investigate damage mechanism, mechanical properties and brittleness evaluation of shale rock and then to provide technical support for large-scale volume fracturing of shale gas exploitation. This paper conducts uniaxial compression tests on black carbonaceous shale of Lungmachi Formation. The test results indicate the follows. The black shale rock has obvious layered flake mineral structure. Its main mineral components are quartz and calcite, which causes the structure surface having high strength. Due to the effects of strong structure surface, shale rock with inclined bedding plane has larger values of elastic modulus and uniaxial tensile strength and the minimum total volumetric strains. However, when the bedding plan is parallel or vertical to the loading direction, the shale rock has smaller values of elastic modulus and uniaxial tensile strength and the maximum total volumetric strain. When the bedding angle β is increasing, the trend of crack initiation index behaves like a U-shaped curve, which is to say, the initiation crack indexes have smaller values at the β of 30° or 60° whereas bigger values at the β of 0° or 90°.It can be seen that brittleness is the key factor to rock fracturing. At the β of 30° or 60°, the rock has larger brittleness index with high fracturing variations of brittleness behave as an inverted U-shaped curve. The study of evaluating shale rock fracturing capability and improving the fracturing effect has important practical significance and application value.
2017, 25(6): 1424-1429.
Like most other soil layers, spatial variability of soil indexes also exists in the clayey layers. Such characteristic mainly results from geologic processes like deposition, diagenesis, et al. Determination of the scale of fluctuation is the key to know spatial variability of soil indexes. Therefore, this paper aims to analyze spatial variability of indexes of clayey soil in Nanjiang Port in Tianjin. It summarizes the spatial average method and its improved method at first. Combining geology data, the improved spatial average method is employed to analyze the scale of fluctuation of a typical soil layer in Tianjin Port in the vertical direction. The regional representative values are obtained, which are of high value on risk assessment in geotechnical engineering and determination of exploratory engineering intervals. In addition, the Bayesian inference is also discussed to revise the scale of fluctuation. Its results indicate that the Bayesian inference is much more reasonable. Furthermore, the scale of fluctuation of the mud and silt clay layer can be guidance for selection of sampling locations, and also valuable to reliability analysis of geotechnical engineering.
Like most other soil layers, spatial variability of soil indexes also exists in the clayey layers. Such characteristic mainly results from geologic processes like deposition, diagenesis, et al. Determination of the scale of fluctuation is the key to know spatial variability of soil indexes. Therefore, this paper aims to analyze spatial variability of indexes of clayey soil in Nanjiang Port in Tianjin. It summarizes the spatial average method and its improved method at first. Combining geology data, the improved spatial average method is employed to analyze the scale of fluctuation of a typical soil layer in Tianjin Port in the vertical direction. The regional representative values are obtained, which are of high value on risk assessment in geotechnical engineering and determination of exploratory engineering intervals. In addition, the Bayesian inference is also discussed to revise the scale of fluctuation. Its results indicate that the Bayesian inference is much more reasonable. Furthermore, the scale of fluctuation of the mud and silt clay layer can be guidance for selection of sampling locations, and also valuable to reliability analysis of geotechnical engineering.
2017, 25(6): 1430-1437.
Desiccation cracks can be formed in clay soil during drying, which connects with each other to generate a network. This process involves multi-field coupling effect, including water, thermal and stress. A close-packed model is used to simulate the formation of desiccation cracks. The simulation is based on the 3D discrete element modeling software MatDEM that is independently developed by Nanjing University. In the model, a discrete unit represents an assembly of soil particles, pore and pore water. Elements in the model are assigned moisture properties, where the transport of moisture can be simulated based on the Finite Difference Method. Furthermore, the coupling of moisture field and stress field is built, which considers the influence of moisture on the tensile strength of soil. In numerical simulation, assuming the water of soil surface evaporates at a certain rate, element diameters and mechanical parameters are calculated from moisture according the experimental data, so as to simulate evaporation, shrinkage and cracking processes of clay soil. Numerical simulation results coincide with the laboratory results, and each step of cracking process can be well simulated. This paper provides an alternative way for the numerical simulation of soil deformation and failure under multi-field effect.
Desiccation cracks can be formed in clay soil during drying, which connects with each other to generate a network. This process involves multi-field coupling effect, including water, thermal and stress. A close-packed model is used to simulate the formation of desiccation cracks. The simulation is based on the 3D discrete element modeling software MatDEM that is independently developed by Nanjing University. In the model, a discrete unit represents an assembly of soil particles, pore and pore water. Elements in the model are assigned moisture properties, where the transport of moisture can be simulated based on the Finite Difference Method. Furthermore, the coupling of moisture field and stress field is built, which considers the influence of moisture on the tensile strength of soil. In numerical simulation, assuming the water of soil surface evaporates at a certain rate, element diameters and mechanical parameters are calculated from moisture according the experimental data, so as to simulate evaporation, shrinkage and cracking processes of clay soil. Numerical simulation results coincide with the laboratory results, and each step of cracking process can be well simulated. This paper provides an alternative way for the numerical simulation of soil deformation and failure under multi-field effect.
2017, 25(6): 1438-1448.
This paper aims to study the contribution of halophytes roots in increasing shear strength of soil in cold and arid environments. The Gasikule Salt Lakes and the surrounding areas in the Qaidam Basin are selected as the test area. Five predominant halophytes(Triglochin maritimum Linn., Phragmites australis Trin., Carex enervis C.A.Mey., Leymus secalinus Tzvel., Koeleria cristata(L.)Pers.) are selected as test species. Direct shear tests are carried out to the samples of soil without roots and root-soil composite system collected in-situ by the method of digging soil from shallow layers to the deep layers of the ground, where layer-by-layer excavation is applied to investigate the effect of moisture content, vertical pressure, the pattern of roots arrangement, root content and root area ratio on shear strength of soil. Results exhibit the following results. With the increasing of soil moisture content, the cohesion force decline. The relationship between vertical pressure and shear strength satisfies Mohr-Coulomb law. The roots play a role in soil reinforcement in shallow layer. The increment amplitude of shear strength is 3.26%~57.18%.With decreasing in root area ratio(RAR)for T.maritimum Linn. and P.australis Trin. and the decreasing in root content for C.enervis C.A.Mey., L.secalinus Tzvel. and K.cristata(L.)Pers., the cohesion force of root-soil composite system decreases. Root area ratio(RAR)has a relatively larger effect on cohesion force of T.maritimum Linn. and P.australis Trin. root-soil composite system than soil moisture content. The effect of root content on cohesion force of C.enervis C.A.Mey., L.secalinus Tzvel. and K.cristata(L.)Pers. root-soil composite system is bigger than soil moisture content, too. The cohesion force of root-soil composite system at different depths is significantly larger than that of non-rooted soil, with the corresponding increment amplitude ranging from 9.61%~182.56%. In contrast, the variation in internal friction angle is relatively small. Reinforcement effect of shear strength for T.maritimum Linn.roots is relatively significant, followed by P.australis Trin., C.enervis C.A.Mey., L.secalinus Tzvel. and K.cristata(L.)Pers. The conclusion plays a role in assessing the reinforcement of roots in increasing shear strength and has an instructive meaning in implementing measures in soil erosion prevention and shallow landslide and other such geological hazards by halophytes in testing site and other regions with similar geological conditions.
This paper aims to study the contribution of halophytes roots in increasing shear strength of soil in cold and arid environments. The Gasikule Salt Lakes and the surrounding areas in the Qaidam Basin are selected as the test area. Five predominant halophytes(Triglochin maritimum Linn., Phragmites australis Trin., Carex enervis C.A.Mey., Leymus secalinus Tzvel., Koeleria cristata(L.)Pers.) are selected as test species. Direct shear tests are carried out to the samples of soil without roots and root-soil composite system collected in-situ by the method of digging soil from shallow layers to the deep layers of the ground, where layer-by-layer excavation is applied to investigate the effect of moisture content, vertical pressure, the pattern of roots arrangement, root content and root area ratio on shear strength of soil. Results exhibit the following results. With the increasing of soil moisture content, the cohesion force decline. The relationship between vertical pressure and shear strength satisfies Mohr-Coulomb law. The roots play a role in soil reinforcement in shallow layer. The increment amplitude of shear strength is 3.26%~57.18%.With decreasing in root area ratio(RAR)for T.maritimum Linn. and P.australis Trin. and the decreasing in root content for C.enervis C.A.Mey., L.secalinus Tzvel. and K.cristata(L.)Pers., the cohesion force of root-soil composite system decreases. Root area ratio(RAR)has a relatively larger effect on cohesion force of T.maritimum Linn. and P.australis Trin. root-soil composite system than soil moisture content. The effect of root content on cohesion force of C.enervis C.A.Mey., L.secalinus Tzvel. and K.cristata(L.)Pers. root-soil composite system is bigger than soil moisture content, too. The cohesion force of root-soil composite system at different depths is significantly larger than that of non-rooted soil, with the corresponding increment amplitude ranging from 9.61%~182.56%. In contrast, the variation in internal friction angle is relatively small. Reinforcement effect of shear strength for T.maritimum Linn.roots is relatively significant, followed by P.australis Trin., C.enervis C.A.Mey., L.secalinus Tzvel. and K.cristata(L.)Pers. The conclusion plays a role in assessing the reinforcement of roots in increasing shear strength and has an instructive meaning in implementing measures in soil erosion prevention and shallow landslide and other such geological hazards by halophytes in testing site and other regions with similar geological conditions.
2017, 25(6): 1449-1454.
Water-rock interaction is a main factor that weakens the rock mass strength of reservoir bank slope. Weaken strength for phyllite is especially obvious physical reacting with water. Taking the phyllite of a slope as example, this paper designs conventional triaxial compression tests under different saturated conditions and studies strength change law with saturated time. Results are obtained as follows:(1)the interaction between phyllite and water is strong. The rock strength parameters gradually decrease with the increase of water saturation time. For the first 60 days, the rock mass parameters linearly decrease with saturated time and tend to stable at 70 days. The mechanism gradually evolves elastic deformation to plastic deformation.(2)Weaken law of parameters shows obvious heterogeneity. The weaken degree is first large and then small, and finally tends to be stable.(3)According to shear failure mode, rock saturation is a cumulative process that from micro to macro. To sum up, the results of this paper have a certain reference value for studying the change law of mechanical property for rock mass of reservoir bank slopes.
Water-rock interaction is a main factor that weakens the rock mass strength of reservoir bank slope. Weaken strength for phyllite is especially obvious physical reacting with water. Taking the phyllite of a slope as example, this paper designs conventional triaxial compression tests under different saturated conditions and studies strength change law with saturated time. Results are obtained as follows:(1)the interaction between phyllite and water is strong. The rock strength parameters gradually decrease with the increase of water saturation time. For the first 60 days, the rock mass parameters linearly decrease with saturated time and tend to stable at 70 days. The mechanism gradually evolves elastic deformation to plastic deformation.(2)Weaken law of parameters shows obvious heterogeneity. The weaken degree is first large and then small, and finally tends to be stable.(3)According to shear failure mode, rock saturation is a cumulative process that from micro to macro. To sum up, the results of this paper have a certain reference value for studying the change law of mechanical property for rock mass of reservoir bank slopes.
2017, 25(6): 1455-1464.
Under the effect of intense exploitation of groundwater, the multi-layer soil of clayey soil and sandy soil is susceptible to be compressed, which causes the land subsidence disaster. To better understand the mechanism of land subsidence caused by groundwater withdrawal, a small-scale sand-clay interbred model box is built to carry out the consolidation and rebound tests. Distributed fiber optical sensing(DFOS)technologies are introduced for coupling monitoring of soil strain and water content to analyze the response characteristics of each layer to water level changes. The results indicate that soil layers are compressed during drainage while rebound during recharge. In addition, the deformation of clay layer is obvious than that of sand layer. The deformation of sand layer is synchronous with water content changes, while that of clay layer is slightly lagging behind the water content changes due to its lower coefficient of permeability. The segmented compression curve of clay layer shows that water content rapidly decreases when it is lower than its liquid limit, meanwhile the clay layer compression rate obviously accelerates during drainage. When water content is higher than that of its liquid limit during recharge, rebound rate significantly increases. The test results are of great significance to study the mechanism of land subsidence as well as to evaluate the compression potential of soil layers.
Under the effect of intense exploitation of groundwater, the multi-layer soil of clayey soil and sandy soil is susceptible to be compressed, which causes the land subsidence disaster. To better understand the mechanism of land subsidence caused by groundwater withdrawal, a small-scale sand-clay interbred model box is built to carry out the consolidation and rebound tests. Distributed fiber optical sensing(DFOS)technologies are introduced for coupling monitoring of soil strain and water content to analyze the response characteristics of each layer to water level changes. The results indicate that soil layers are compressed during drainage while rebound during recharge. In addition, the deformation of clay layer is obvious than that of sand layer. The deformation of sand layer is synchronous with water content changes, while that of clay layer is slightly lagging behind the water content changes due to its lower coefficient of permeability. The segmented compression curve of clay layer shows that water content rapidly decreases when it is lower than its liquid limit, meanwhile the clay layer compression rate obviously accelerates during drainage. When water content is higher than that of its liquid limit during recharge, rebound rate significantly increases. The test results are of great significance to study the mechanism of land subsidence as well as to evaluate the compression potential of soil layers.
2017, 25(6): 1465-1473.
Currently, there is a lack of experimental study and model prediction of thermal conductivity of soil under high temperature around the world. Tests are conducted through KD2 Pro on two kinds of lateritic clay within a wide range of temperatures(5~90℃) and water contents. Meanwhile, the IPCHT model is chosen to predict the variation of the volumetric water content and thermal conductivity under high temperature. The results of test indicate that the sensitivity of the thermal conductivity on the two kinds of lateritic clay to the volumetric water content is related to the temperature. The thermal conductivity increases with the increase of temperature. The thermal conductivity under 90℃ is 3 or 4 times as high as that under 5℃. The change of thermal conductivity with volumetric water content has obvious critical water content under 60~90℃(correspond to the plasticity index of soil). However, the latent heat transfer effect of water vapor in the lateritic clay of Liuzhou is more obvious than that in the lateritic clay of Guilin under the same temperature and volumetric water content. The results of model fit show that the prediction results of IPCHT model are not ideal except for the silty clay loam, after modification of the mass transfer enhancement factor ξ. The simulated values of the thermal conductivity of lateritic clay in Liuzhou and fine sand are in good agreement with the measured values(RMSE < 30%). However, the overall prediction effect of the lateritic clay in Guilin is still not ideal.
Currently, there is a lack of experimental study and model prediction of thermal conductivity of soil under high temperature around the world. Tests are conducted through KD2 Pro on two kinds of lateritic clay within a wide range of temperatures(5~90℃) and water contents. Meanwhile, the IPCHT model is chosen to predict the variation of the volumetric water content and thermal conductivity under high temperature. The results of test indicate that the sensitivity of the thermal conductivity on the two kinds of lateritic clay to the volumetric water content is related to the temperature. The thermal conductivity increases with the increase of temperature. The thermal conductivity under 90℃ is 3 or 4 times as high as that under 5℃. The change of thermal conductivity with volumetric water content has obvious critical water content under 60~90℃(correspond to the plasticity index of soil). However, the latent heat transfer effect of water vapor in the lateritic clay of Liuzhou is more obvious than that in the lateritic clay of Guilin under the same temperature and volumetric water content. The results of model fit show that the prediction results of IPCHT model are not ideal except for the silty clay loam, after modification of the mass transfer enhancement factor ξ. The simulated values of the thermal conductivity of lateritic clay in Liuzhou and fine sand are in good agreement with the measured values(RMSE < 30%). However, the overall prediction effect of the lateritic clay in Guilin is still not ideal.
2017, 25(6): 1474-1481.
The engineering properties of a rock are much dependent on the microscopic features of the minerals comprising the rock. The physical and mechanical features of various minerals(i.e. quartz, biotite and albite) in Beishan granite are investigated in a micro scale in the current study. The microscopic physical features of the minerals are characterized by volume and density, while the microscopic mechanical features of the minerals are characterized by Young modulus and Poisson ratio. The open database is used to obtain the initial crystal structure, initial cell parameters, and the unit and super cells of the minerals. The stable configurations of the mineral cells are obtained using the geometry optimization. The microscopic physical and mechanical parameters of the stable configurations are then computed using the molecular mechanics simulation. The effects of temperature and pressure on these microscopic physical and mechanical parameters are furthermore examined using the molecular dynamics simulation. It shows that in the main minerals included in granite, the great-small sequence of the cell volume is albite, biotite, and quartz, while that of the cell density is biotite, quartz, and albite. The Young modulus values of quartz, biotite and albite are 161.70 to 168.78GPa, 164.85 to 579.93GPa and 110.72 to 112.49GPa, respectively. The Poisson ratio values of quartz, biotite and albite are 0.25, 0.16 to 0.31, and 0.27, respectively. When the temperature changes from 300K to 500K under the pressure of 100kPa, the volume increases 0.17% and the density decreases 0.15%with no obvious changes in the Young modulus and Poisson's ratio for the quartz cell; the volume increases 0.24% and the density decreases 0.26%with the Young modulus increased 140.55% and the Poisson's ratio decreased 26.92%for the biotite cell; and the volume decreases 3.76% and the density increases 3.91%with the Young modulus increased 319.71% and the Poisson's ratio decreased 7.41%for the albite cell. When the pressure changes from 0.010 to 0.020GPa at the temperature of 298 K, the volume, density, Young modulus and Poisson's ratio have no obvious changes for the quartz cell; the volume and density have no obvious changes with the Young modulus increased 53.79% and the Poisson's ratio decreased 23.81%for the biotite cell; and the volume and density have no obvious changes with the Young modulus decreased 36.24% and the Poisson's ratio increased 29.41%for the albite cell. These theoretical results can be referable in analyzing the macroscopic physical and mechanical properties of the rock materials in a micro scale.
The engineering properties of a rock are much dependent on the microscopic features of the minerals comprising the rock. The physical and mechanical features of various minerals(i.e. quartz, biotite and albite) in Beishan granite are investigated in a micro scale in the current study. The microscopic physical features of the minerals are characterized by volume and density, while the microscopic mechanical features of the minerals are characterized by Young modulus and Poisson ratio. The open database is used to obtain the initial crystal structure, initial cell parameters, and the unit and super cells of the minerals. The stable configurations of the mineral cells are obtained using the geometry optimization. The microscopic physical and mechanical parameters of the stable configurations are then computed using the molecular mechanics simulation. The effects of temperature and pressure on these microscopic physical and mechanical parameters are furthermore examined using the molecular dynamics simulation. It shows that in the main minerals included in granite, the great-small sequence of the cell volume is albite, biotite, and quartz, while that of the cell density is biotite, quartz, and albite. The Young modulus values of quartz, biotite and albite are 161.70 to 168.78GPa, 164.85 to 579.93GPa and 110.72 to 112.49GPa, respectively. The Poisson ratio values of quartz, biotite and albite are 0.25, 0.16 to 0.31, and 0.27, respectively. When the temperature changes from 300K to 500K under the pressure of 100kPa, the volume increases 0.17% and the density decreases 0.15%with no obvious changes in the Young modulus and Poisson's ratio for the quartz cell; the volume increases 0.24% and the density decreases 0.26%with the Young modulus increased 140.55% and the Poisson's ratio decreased 26.92%for the biotite cell; and the volume decreases 3.76% and the density increases 3.91%with the Young modulus increased 319.71% and the Poisson's ratio decreased 7.41%for the albite cell. When the pressure changes from 0.010 to 0.020GPa at the temperature of 298 K, the volume, density, Young modulus and Poisson's ratio have no obvious changes for the quartz cell; the volume and density have no obvious changes with the Young modulus increased 53.79% and the Poisson's ratio decreased 23.81%for the biotite cell; and the volume and density have no obvious changes with the Young modulus decreased 36.24% and the Poisson's ratio increased 29.41%for the albite cell. These theoretical results can be referable in analyzing the macroscopic physical and mechanical properties of the rock materials in a micro scale.
2017, 25(6): 1482-1490.
Structural plane plays an important role in stability of rock mass. Many engineering accidents are caused by structural planes. This phenomenon has attracted enough attention. Up to now, the related researches on structural plane mainly include shearing curve description, impact of roughness, combination, filling and other factors on shear strength. In general, these researches are based on that the structural plane bears static load. In fact, it is very common for structural planes to bear cyclic shear load under conditions of dynamic load of earthquake, water level rise and fall, explosion and so on. However, there is less study on mechanical property of structural plane when it is under cyclic shear load. The paper is based on direct shear test. Influence of filled state on deformation and strength of structural plane is studied. Structural planes of four aspertity inclination angles are made using steel mould and concrete. Then several times direct shear tests are conducted under same normal stresses and two filled states. At the same time, shear stress and normal displacement are recorded. The analysis on shear stress-shear displacement and normal displacement-shear displacement curve shows that the asperity inclination angle become larger firstly and structural plane is easier to be cut. For the same shear failure style, if the normal stress increases, the structural plane will be worn or cut more serious, and the maximum normal displacement is lower. If the asperity inclination angle increases, the zig-zag pattern will be worn or cut more. From the second shear time, the structural plane is worn every time and not be affected by asperity inclination angle. After the filling, the structural plane is damaged like before. However, this factor makes the structural plane climbing further, weakens the cutting or wearing degree, and adds the normal displacement meanwhile.
Structural plane plays an important role in stability of rock mass. Many engineering accidents are caused by structural planes. This phenomenon has attracted enough attention. Up to now, the related researches on structural plane mainly include shearing curve description, impact of roughness, combination, filling and other factors on shear strength. In general, these researches are based on that the structural plane bears static load. In fact, it is very common for structural planes to bear cyclic shear load under conditions of dynamic load of earthquake, water level rise and fall, explosion and so on. However, there is less study on mechanical property of structural plane when it is under cyclic shear load. The paper is based on direct shear test. Influence of filled state on deformation and strength of structural plane is studied. Structural planes of four aspertity inclination angles are made using steel mould and concrete. Then several times direct shear tests are conducted under same normal stresses and two filled states. At the same time, shear stress and normal displacement are recorded. The analysis on shear stress-shear displacement and normal displacement-shear displacement curve shows that the asperity inclination angle become larger firstly and structural plane is easier to be cut. For the same shear failure style, if the normal stress increases, the structural plane will be worn or cut more serious, and the maximum normal displacement is lower. If the asperity inclination angle increases, the zig-zag pattern will be worn or cut more. From the second shear time, the structural plane is worn every time and not be affected by asperity inclination angle. After the filling, the structural plane is damaged like before. However, this factor makes the structural plane climbing further, weakens the cutting or wearing degree, and adds the normal displacement meanwhile.
2017, 25(6): 1491-1500.
Many causative factors have changed acutely after the Wenchuan earthquake. They included the loose material, micro-topography and hydrological environment. Hence, the earthquake-induced debris flows are different from the general one. A whole debris flow process mechanism is developed and analyzed quantitatively using initiation discrimination model, bed-matrix erosion model and outburst-discharge enlargement model. It includes the initiation, transition and deposition phases. Moreover, the failure mechanism of the erosion-outburst-induced debris flow is illustrated clearly with an example. The result indicates that bed-matrix entrainment mechanism is the comprehensive outcome of the stress enlargement, strength degradation and material basis. The landslide dam outburst-induced discharge enlargement and the above-mentioned erosion mechanism are contributed to the large-scale debris flow. The case study of Hongchun catchment indicates that debris-flow discharge increases to 800.80m3·s-1 due to H02-03 landslide-dam outburst, and the entrainment-induced solid materials are half of the total magnitude, about 34.72×104m3.
Many causative factors have changed acutely after the Wenchuan earthquake. They included the loose material, micro-topography and hydrological environment. Hence, the earthquake-induced debris flows are different from the general one. A whole debris flow process mechanism is developed and analyzed quantitatively using initiation discrimination model, bed-matrix erosion model and outburst-discharge enlargement model. It includes the initiation, transition and deposition phases. Moreover, the failure mechanism of the erosion-outburst-induced debris flow is illustrated clearly with an example. The result indicates that bed-matrix entrainment mechanism is the comprehensive outcome of the stress enlargement, strength degradation and material basis. The landslide dam outburst-induced discharge enlargement and the above-mentioned erosion mechanism are contributed to the large-scale debris flow. The case study of Hongchun catchment indicates that debris-flow discharge increases to 800.80m3·s-1 due to H02-03 landslide-dam outburst, and the entrainment-induced solid materials are half of the total magnitude, about 34.72×104m3.
2017, 25(6): 1501-1508.
The mechanism and evolution of toppling in interbedded rock slopes in upstream of Yalong River are analyzed with the typical case of Jaxi toppling. The analysis covers the aspects of geological background, development characteristics and formation conditions. This comprehensive study points out that the large-scale toppling in research area is developed by the unique structure of slopes in gravity stress field. The slopes are consisted of a pervasive foliation dipping steeply into the slope, have soft layer and hard layer interbedded and a set of well-developed cross-joints. A model illustrates a typical feature of toppling failure of interbedded rock slope. It is recombination of block-flexure toppling in hard rock and flexural toppling in soft rock, respectively. With the evolution of Yalong River, the deformation of the slope experiences four steps:unloading and rebound, initial deformation, breaking in flexure, and failure as landslide. The sliding surface can be developed along the cross-joints, rather than the maximum bending zone.
The mechanism and evolution of toppling in interbedded rock slopes in upstream of Yalong River are analyzed with the typical case of Jaxi toppling. The analysis covers the aspects of geological background, development characteristics and formation conditions. This comprehensive study points out that the large-scale toppling in research area is developed by the unique structure of slopes in gravity stress field. The slopes are consisted of a pervasive foliation dipping steeply into the slope, have soft layer and hard layer interbedded and a set of well-developed cross-joints. A model illustrates a typical feature of toppling failure of interbedded rock slope. It is recombination of block-flexure toppling in hard rock and flexural toppling in soft rock, respectively. With the evolution of Yalong River, the deformation of the slope experiences four steps:unloading and rebound, initial deformation, breaking in flexure, and failure as landslide. The sliding surface can be developed along the cross-joints, rather than the maximum bending zone.
2017, 25(6): 1509-1517.
This paper uses an indoor modeling test and simulates the sliding and accumulation process of landslide debris avalanches. Then, the paper acquires and further analyzes the deposit position of each granule of landslide-debris avalanches. In addition, this paper briefly analyzes the motion mechanism of landslide-debris avalanches. The result shows the follows. The deposit position of the slide-debris is of both randomness and regularity. These particles that are symmetrical on the central axis of slope board are still symmetrical after the slide. The deposit position of these granules in consecutive region previously is not continuous after the slide. The deposit position of the particles is affected by its initial positon conspicuously. The inside holistic rolling of slide-debris is founded in the process of slide. The result of the experiment provides reliable reference for the research of motion mechanism of landslide-debris and for backtracking the initial state of slopes.
This paper uses an indoor modeling test and simulates the sliding and accumulation process of landslide debris avalanches. Then, the paper acquires and further analyzes the deposit position of each granule of landslide-debris avalanches. In addition, this paper briefly analyzes the motion mechanism of landslide-debris avalanches. The result shows the follows. The deposit position of the slide-debris is of both randomness and regularity. These particles that are symmetrical on the central axis of slope board are still symmetrical after the slide. The deposit position of these granules in consecutive region previously is not continuous after the slide. The deposit position of the particles is affected by its initial positon conspicuously. The inside holistic rolling of slide-debris is founded in the process of slide. The result of the experiment provides reliable reference for the research of motion mechanism of landslide-debris and for backtracking the initial state of slopes.
2017, 25(6): 1518-1526.
The zoning of regional slope stability has very important significance for the landslide disaster prevention. In order to study regional slope stability, this study provides a regional slop stability zoning method in loess areas based on typical profiles. At first, the whole study area is divided into slope units using hydrology tool in ArcGIS.The raster data of the slope unit distribution and the DEM are imported into MATLAB.Secondly, the slope profiles in each unit are extracted along the average aspect calculated using least squares method. One profile represents one slope unit. Thirdly, MATLAB is used to formulate the command line files of FLAC2D, including all the information of each profile, material parameters of soil, initial saturation, pore pressure conditions, constraint boundary and so on. Then all the command line files of FLAC2D are executed automatically. The strength reduction method is induced to calculate the stability of each typical profile. Finally, the distribution of safety factor is mapped on the study area. In order to evaluate regional stability intuitively, we make the regional slope stability partitions for further assessment. We select Yaoxian as the study area and divide 946 typical profiles to calculate the stability of every slop unit. The study area is divided to three zones:unstable region, fundamental stable region and stable region. The zoning result is consistent with the actual survey. We can apply a single slope quantitative calculation to the whole region and combine the GIS analysis with external program calculation. This method improves the computation efficiency and accuracy effectively and can find potential sliding surface of the landslide. It is a new thought for prediction of regional slop stability in loess area.
The zoning of regional slope stability has very important significance for the landslide disaster prevention. In order to study regional slope stability, this study provides a regional slop stability zoning method in loess areas based on typical profiles. At first, the whole study area is divided into slope units using hydrology tool in ArcGIS.The raster data of the slope unit distribution and the DEM are imported into MATLAB.Secondly, the slope profiles in each unit are extracted along the average aspect calculated using least squares method. One profile represents one slope unit. Thirdly, MATLAB is used to formulate the command line files of FLAC2D, including all the information of each profile, material parameters of soil, initial saturation, pore pressure conditions, constraint boundary and so on. Then all the command line files of FLAC2D are executed automatically. The strength reduction method is induced to calculate the stability of each typical profile. Finally, the distribution of safety factor is mapped on the study area. In order to evaluate regional stability intuitively, we make the regional slope stability partitions for further assessment. We select Yaoxian as the study area and divide 946 typical profiles to calculate the stability of every slop unit. The study area is divided to three zones:unstable region, fundamental stable region and stable region. The zoning result is consistent with the actual survey. We can apply a single slope quantitative calculation to the whole region and combine the GIS analysis with external program calculation. This method improves the computation efficiency and accuracy effectively and can find potential sliding surface of the landslide. It is a new thought for prediction of regional slop stability in loess area.
2017, 25(6): 1527-1536.
The evolution of collision-fragmentation-disintegration has a significant control effect on the motional characteristics of large-scale high-speed rockslides, and affects the geological structure characteristics and the stability of accumulation body. This paper takes Tangjiashan high-speed rockslide as research object. It relies on the geological analysis principle. It interprets the fragmentation process and characteristics of collided sliding body. It further carries out the falling-collision experiments of cylindrical rock blocks drilled from the deposits. The weight loss induced by collision is quantified and the grading size of fragments is analyzed. In term of observation, it is shown that the higher the impacting velocities, the more mass loss, the finer the fragments tend to be, of which the friction coefficient is usually lower than the initial intact rocks. Moreover, the conventional mechanics experiment of impacted rock before and after collision is carried out to obtain the correlation between the impacting velocity and the mechanical parameters of rock blocks. The result shows that collision could greatly reduce the mechanical indexes of rock masses. Considering the macroscopic condition, the physical collision model experiment along a designed channel is implemented to acquire the relationship between the velocity and pattern of collision and the runout of landslide, as well as the accumulation form. The conclusion could provide some reference for the scope prediction of high-speed rockslide.
The evolution of collision-fragmentation-disintegration has a significant control effect on the motional characteristics of large-scale high-speed rockslides, and affects the geological structure characteristics and the stability of accumulation body. This paper takes Tangjiashan high-speed rockslide as research object. It relies on the geological analysis principle. It interprets the fragmentation process and characteristics of collided sliding body. It further carries out the falling-collision experiments of cylindrical rock blocks drilled from the deposits. The weight loss induced by collision is quantified and the grading size of fragments is analyzed. In term of observation, it is shown that the higher the impacting velocities, the more mass loss, the finer the fragments tend to be, of which the friction coefficient is usually lower than the initial intact rocks. Moreover, the conventional mechanics experiment of impacted rock before and after collision is carried out to obtain the correlation between the impacting velocity and the mechanical parameters of rock blocks. The result shows that collision could greatly reduce the mechanical indexes of rock masses. Considering the macroscopic condition, the physical collision model experiment along a designed channel is implemented to acquire the relationship between the velocity and pattern of collision and the runout of landslide, as well as the accumulation form. The conclusion could provide some reference for the scope prediction of high-speed rockslide.
2017, 25(6): 1537-1546.
This paper aims to study the failure characteristics of the soil slope under the earthquake. It uses particle flow code(PFC2D), simulates the failure process of the soil slopes with different inclinations and micro-parameters under a Wenchuan horizontal seismic wave. The results show that the slope angle mainly affects the failure extent. The steeper the slope is, the deeper the sliding surface is.The micro-parameters control the failure type of the slope. The slide body of the cohesive slope can move as a whole with an arc-shaped sliding surface. Yet the failure of non-cohesive slope is rheologically behaved with a polyline sliding surface whose upper part is steep and lower part is flat.
This paper aims to study the failure characteristics of the soil slope under the earthquake. It uses particle flow code(PFC2D), simulates the failure process of the soil slopes with different inclinations and micro-parameters under a Wenchuan horizontal seismic wave. The results show that the slope angle mainly affects the failure extent. The steeper the slope is, the deeper the sliding surface is.The micro-parameters control the failure type of the slope. The slide body of the cohesive slope can move as a whole with an arc-shaped sliding surface. Yet the failure of non-cohesive slope is rheologically behaved with a polyline sliding surface whose upper part is steep and lower part is flat.
2017, 25(6): 1547-1556.
Jinpingzi landslide is the nearest deep-seated colluvial debris landslide to the arch dam of Wudongde hydropower station in the downstream direction in lower reaches of Jinsha River. Its active zone Ⅱ was studied. Based on geotechnical investigation and long-term monitoring, the physical and mechanical property of the landslide materials and the long-term kinematics, especially the relationships among the landslide movement, rainfall and the groundwater were analysed. The response of the groundwater regime to the precipitation was further analyzed under different initial water content conditions based on the Green-Ampt infiltration model. Relationships between resisting forces and driving forces were discussed by limit equilibrium method assuming rigid-plastic frictional slip. Results showed that the long-term continuous movement was mostly due to the viscous component of the slip zone. Surface and subsurface displacement both showed a retrogressive type with average surface displacement rate 0.19~0.87mm·d-1 from 2005 to 2016. Basal sliding accounted for most of the deformation with different degrees of internal deformation in different parts. Rainfall was the predominant factor affecting the landslide activity but it is hard for rainfall water infiltrating to the deeply buried groundwater regime. Unlike some shallow landslides, the mechanism of Jinpingzi zone Ⅱ slow moving landslide was more likely to be the formation of transient saturated zone in shallow depth. The change of unit weight of the sliding mass and the effect of seepage affected the kinematics of the landslide.
Jinpingzi landslide is the nearest deep-seated colluvial debris landslide to the arch dam of Wudongde hydropower station in the downstream direction in lower reaches of Jinsha River. Its active zone Ⅱ was studied. Based on geotechnical investigation and long-term monitoring, the physical and mechanical property of the landslide materials and the long-term kinematics, especially the relationships among the landslide movement, rainfall and the groundwater were analysed. The response of the groundwater regime to the precipitation was further analyzed under different initial water content conditions based on the Green-Ampt infiltration model. Relationships between resisting forces and driving forces were discussed by limit equilibrium method assuming rigid-plastic frictional slip. Results showed that the long-term continuous movement was mostly due to the viscous component of the slip zone. Surface and subsurface displacement both showed a retrogressive type with average surface displacement rate 0.19~0.87mm·d-1 from 2005 to 2016. Basal sliding accounted for most of the deformation with different degrees of internal deformation in different parts. Rainfall was the predominant factor affecting the landslide activity but it is hard for rainfall water infiltrating to the deeply buried groundwater regime. Unlike some shallow landslides, the mechanism of Jinpingzi zone Ⅱ slow moving landslide was more likely to be the formation of transient saturated zone in shallow depth. The change of unit weight of the sliding mass and the effect of seepage affected the kinematics of the landslide.
2017, 25(6): 1557-1565.
Recent studies were based on the small samples which were as big as core samples to get the fracture propagation features. However, the small samples had many limitations. For example, continuous fracture propagation characteristics were difficult to get, which means it was a tough work to analyze the relationship between in-situ stress and fracture distribution. Hence, fracture propagation characteristics were gathered from a 2m×3m×0.7m samples from Shizhu County, Chongqin. The sample was cut into several cubic samples whose lengths of the sides were 30cm. At the same time, every surface of the cubic sample is numbered. Then the fracture distribution characteristics on each surface of the samples is obtained. The 3D fracture network is rebuilt according to the surface number. The fracture network shows the obvious rules that there are more fractures on the surface in the principle stress direction in contrast to other directions. The fractures on the surface perpendicular to the principle stress are 62°to the principle stress direction. Research on the fractal dimension proves that fractures on the different surfaces conform to the fractal dimension feature, which indicates that fractures' structure in small scale and big scale have similar regularity. In addition, fracture density and fractal dimension number in the maximum principle stress direction are bigger than other directions, which means fracture network structure is more complex. And fracture network structure in the surface perpendicular to the principle stress is less complex than that in the minimum horizontal stress direction. There are more bedding fractures in the horizontal stress direction while more shear fractures in the vertical direction, which are-62°to the minimum horizontal principle stress direction.
Recent studies were based on the small samples which were as big as core samples to get the fracture propagation features. However, the small samples had many limitations. For example, continuous fracture propagation characteristics were difficult to get, which means it was a tough work to analyze the relationship between in-situ stress and fracture distribution. Hence, fracture propagation characteristics were gathered from a 2m×3m×0.7m samples from Shizhu County, Chongqin. The sample was cut into several cubic samples whose lengths of the sides were 30cm. At the same time, every surface of the cubic sample is numbered. Then the fracture distribution characteristics on each surface of the samples is obtained. The 3D fracture network is rebuilt according to the surface number. The fracture network shows the obvious rules that there are more fractures on the surface in the principle stress direction in contrast to other directions. The fractures on the surface perpendicular to the principle stress are 62°to the principle stress direction. Research on the fractal dimension proves that fractures on the different surfaces conform to the fractal dimension feature, which indicates that fractures' structure in small scale and big scale have similar regularity. In addition, fracture density and fractal dimension number in the maximum principle stress direction are bigger than other directions, which means fracture network structure is more complex. And fracture network structure in the surface perpendicular to the principle stress is less complex than that in the minimum horizontal stress direction. There are more bedding fractures in the horizontal stress direction while more shear fractures in the vertical direction, which are-62°to the minimum horizontal principle stress direction.
2017, 25(6): 1566-1573.
The geological environment of the northern South China Sea is complex and rich in oil and gas resources. It is necessary to examine the physical and mechanical properties of seafloor sediments. Hence, this paper reports a preliminary study of the geological environment. In this study, a series of tests to determine various factors including water content, density, and specific gravity, are conducted in conjunction with miniature vane shear, micro penetration, and compression tests on samples collected in June 2015. The study includes investigating types of seafloor sediments and index parameters of the physical and mechanical properties of soil in the northern South China Sea. The results of the investigation indicate that the surficial seafloor sediment in the study area is mainly composed of silty clay and clayey silt with high moisture content, low density, and low mechanical strength. The variation in the fore-mentioned parameters is generally correlated with the depth of the seabed. Additionally, sedimentary environment, grain size composition, and age are determined as important factors controlling the properties of the sediments to a significant extent.
The geological environment of the northern South China Sea is complex and rich in oil and gas resources. It is necessary to examine the physical and mechanical properties of seafloor sediments. Hence, this paper reports a preliminary study of the geological environment. In this study, a series of tests to determine various factors including water content, density, and specific gravity, are conducted in conjunction with miniature vane shear, micro penetration, and compression tests on samples collected in June 2015. The study includes investigating types of seafloor sediments and index parameters of the physical and mechanical properties of soil in the northern South China Sea. The results of the investigation indicate that the surficial seafloor sediment in the study area is mainly composed of silty clay and clayey silt with high moisture content, low density, and low mechanical strength. The variation in the fore-mentioned parameters is generally correlated with the depth of the seabed. Additionally, sedimentary environment, grain size composition, and age are determined as important factors controlling the properties of the sediments to a significant extent.
2017, 25(6): 1574-1582.
Bearing behaviour of the pile in the beaded karst cave is very complex. It is of great significant to study the response characteristics coupling the load transfer of the pile and the stability of karst cave. Calculation on the bearing characteristics of the pile and the stability of beaded karst cave is made with the Plaxis 2D and Abaqus 3D.The numerical results show that the punching failure happens in the top rock when the ratio of the top rock thickness vs the cave span is small, while punching shear failure happens at larger ratio. There are multiple maxima of the side resistance around the pile because of the existence of the beaded karst carve. The number of the points is related to the top rock thickness, number of the karst carves and the floor rock thickness. The side resistance will fall down quickly around the free face of the top rock. The area size is related to the thickness of the surrounding rock and its displacement. The difference will become small under larger load. The maximum of the side resistance around the middle rock layer locates at the middle, and the maximum value declines with the increase of the middle rock layer thickness. Besides, the side resistance distributes as the isosceles triangle with the thin middle rock layer, while it distributes as ladder shape with thick middle rock layer. The thicker the middle rock layer, the greater the ladder span, and the more uniform distribution of the side resistance. However, the side resistance distribution around the middle rock layer is not related to the length of the pile. Only the side resistance around the floor rock layer is related to the length of the pile and the load value. The curve of load vs displacement of the middle rock layer is parabolic shape, and there is an obvious inflection point in the load-displacement curve. The vertical displacement of the middle rock layer grows with the increase of the length of the pile and the decrease of the thickness of middle rock layer. The greater the diameter of the pile, the greater the external load corresponding to the inflection point of the load-displacement curve, and the greater the vertical displacement of the middle rock layer. However, the influence of the pile diameter changing to the curve will become smaller when the pile diameter is large enough.
Bearing behaviour of the pile in the beaded karst cave is very complex. It is of great significant to study the response characteristics coupling the load transfer of the pile and the stability of karst cave. Calculation on the bearing characteristics of the pile and the stability of beaded karst cave is made with the Plaxis 2D and Abaqus 3D.The numerical results show that the punching failure happens in the top rock when the ratio of the top rock thickness vs the cave span is small, while punching shear failure happens at larger ratio. There are multiple maxima of the side resistance around the pile because of the existence of the beaded karst carve. The number of the points is related to the top rock thickness, number of the karst carves and the floor rock thickness. The side resistance will fall down quickly around the free face of the top rock. The area size is related to the thickness of the surrounding rock and its displacement. The difference will become small under larger load. The maximum of the side resistance around the middle rock layer locates at the middle, and the maximum value declines with the increase of the middle rock layer thickness. Besides, the side resistance distributes as the isosceles triangle with the thin middle rock layer, while it distributes as ladder shape with thick middle rock layer. The thicker the middle rock layer, the greater the ladder span, and the more uniform distribution of the side resistance. However, the side resistance distribution around the middle rock layer is not related to the length of the pile. Only the side resistance around the floor rock layer is related to the length of the pile and the load value. The curve of load vs displacement of the middle rock layer is parabolic shape, and there is an obvious inflection point in the load-displacement curve. The vertical displacement of the middle rock layer grows with the increase of the length of the pile and the decrease of the thickness of middle rock layer. The greater the diameter of the pile, the greater the external load corresponding to the inflection point of the load-displacement curve, and the greater the vertical displacement of the middle rock layer. However, the influence of the pile diameter changing to the curve will become smaller when the pile diameter is large enough.
2017, 25(6): 1583-1592.
An indoor slope model is designed and constructed for experimental test. A sliding surface is pre-installed in the slope model. The slope is reinforced with pile and sheet pile wall respectively. The geometry dimensional similarity ratio of the indoor slope model to the actual slope size is 1:25. The model is horizontally loaded step by step. Comparative analysis on the force and deformation characteristics of the two different supporting structures under horizontal load is conducted. The results show that the failure process of the slope-support structure system is divided into three stages. They are the sliding soil compaction stage, the main deformation stage of supporting structure, and the failure stage of supporting structure stage respectively. Transfer efficiency of soil pressure behind the piles is relatively low at the same horizontal position of pile 14cm below the pile top, which is inversely proportional to the position of the loading plate and in exponential variation law. Anti-slide pile is the main bearing component of the two supporting structures, and the retaining plank extends the main deformation stage of model damage. The reinforcement effect is obvious. Compared with the anti-slide pile supporting structure, the ultimate load of pile supporting structure is 0.5kN more than that of anti-slide pile, and the bearing capacity of pile supporting structure increases by 14.29%.Distribution form of soil pressure behind the piles is optimized by adopting retaining plank, which makes the soil pressure closer to the end of the anchor and is propitious to resist the flexure deformation of the pile body. This research can provide references for selecting the two different slope supporting structures.
An indoor slope model is designed and constructed for experimental test. A sliding surface is pre-installed in the slope model. The slope is reinforced with pile and sheet pile wall respectively. The geometry dimensional similarity ratio of the indoor slope model to the actual slope size is 1:25. The model is horizontally loaded step by step. Comparative analysis on the force and deformation characteristics of the two different supporting structures under horizontal load is conducted. The results show that the failure process of the slope-support structure system is divided into three stages. They are the sliding soil compaction stage, the main deformation stage of supporting structure, and the failure stage of supporting structure stage respectively. Transfer efficiency of soil pressure behind the piles is relatively low at the same horizontal position of pile 14cm below the pile top, which is inversely proportional to the position of the loading plate and in exponential variation law. Anti-slide pile is the main bearing component of the two supporting structures, and the retaining plank extends the main deformation stage of model damage. The reinforcement effect is obvious. Compared with the anti-slide pile supporting structure, the ultimate load of pile supporting structure is 0.5kN more than that of anti-slide pile, and the bearing capacity of pile supporting structure increases by 14.29%.Distribution form of soil pressure behind the piles is optimized by adopting retaining plank, which makes the soil pressure closer to the end of the anchor and is propitious to resist the flexure deformation of the pile body. This research can provide references for selecting the two different slope supporting structures.
2017, 25(6): 1593-1602.
The short rigid piles are located on the top of slope and subjected to the incline load. Both the cross effects produced by horizontal and vertical loads and the effect of the slope are needed to be considered in the design. Because of several factors interacting each other, far more complex than that of piles installed in horizontal ground. This paper adopts three-dimensional finite element software and carries out numerical simulation analysis of composite piles by taking into account of many factors. The study finds that under the same load and with the increase of the angle of the composite load, the ultimate bearing capacity firstly decreases and then increases. The influence of the vertical load on the horizontal displacement of the pile is greater than that of the internal force. Increasing the pressure of soil around piles will lead to the promotion of pile displacement and internal force. With increasing of edge distance from the slope crest, the effect will decrease.
The short rigid piles are located on the top of slope and subjected to the incline load. Both the cross effects produced by horizontal and vertical loads and the effect of the slope are needed to be considered in the design. Because of several factors interacting each other, far more complex than that of piles installed in horizontal ground. This paper adopts three-dimensional finite element software and carries out numerical simulation analysis of composite piles by taking into account of many factors. The study finds that under the same load and with the increase of the angle of the composite load, the ultimate bearing capacity firstly decreases and then increases. The influence of the vertical load on the horizontal displacement of the pile is greater than that of the internal force. Increasing the pressure of soil around piles will lead to the promotion of pile displacement and internal force. With increasing of edge distance from the slope crest, the effect will decrease.
2017, 25(6): 1603-1609.
In recent years, with the development of global marine strategies, engineering construction and experimental studies have been increasingly carried out in both offshore and onshore. In order to evaluate the soil properties on the seabed, the cone penetration test(CPT)technology has become much more important in the domestic and international marine engineering. This paper summarizes the development of marine cone penetration test according to extensive literatures domestic and oversea. Besides, the relevant research contents of the ball penetrometer are summarized. The ball penetrometer is now used oversea for offshore site characterization in soft sediments as an alternative or supplement to conventional CPT tests. The analytical results show that the ball penetrometer is superior to the cone in quantifying the strength of soft clay, as well as evaluating the remoulded strength and the effect of penetration velocity by means of cyclic remoulding tests and variable rate penetrometer tests. Based on the full-flow mechanism, it is worthwhile to compare the in situ testing data between ball penetrometer and CPT.Furthermore given the nature of soft soil at seabed, this paper introduces a stoppable piezoprobe at shallow depths for offshore engineering.
In recent years, with the development of global marine strategies, engineering construction and experimental studies have been increasingly carried out in both offshore and onshore. In order to evaluate the soil properties on the seabed, the cone penetration test(CPT)technology has become much more important in the domestic and international marine engineering. This paper summarizes the development of marine cone penetration test according to extensive literatures domestic and oversea. Besides, the relevant research contents of the ball penetrometer are summarized. The ball penetrometer is now used oversea for offshore site characterization in soft sediments as an alternative or supplement to conventional CPT tests. The analytical results show that the ball penetrometer is superior to the cone in quantifying the strength of soft clay, as well as evaluating the remoulded strength and the effect of penetration velocity by means of cyclic remoulding tests and variable rate penetrometer tests. Based on the full-flow mechanism, it is worthwhile to compare the in situ testing data between ball penetrometer and CPT.Furthermore given the nature of soft soil at seabed, this paper introduces a stoppable piezoprobe at shallow depths for offshore engineering.
2017, 25(6): 1617-1623.
In the construction process of city metro shield, the ground surface subsidence is one of the most important engineering problems, which not only affects the safety of the subway tunnel construction, but also directly relates to the normal operation of the surrounding buildings. The compressive modulus of generation zone is one of the key shield parameters that control the ground surface subsidence, especially to the shield tunneling in soft soil zone. The mixing proportion of the generation zone grouting material and the soil, and the waiting time after grouting are the important factors that affect the compressive modulus. This paper is based on the cumulosol shield tunneling project of Kunming Metro Line 3 Shiju section, with a compressive modulus test of mixtures which have different proportions of grouting materials and cumulosol and different curing times. The reasonable proportion relationship between the shield generation zone paste in the cumulosol zone and the soil are explored. The time to get expected compressive modulus of generation zone after grouting is put forward, which can provide reference for the shield tunneling construction in the cumulosol area.
In the construction process of city metro shield, the ground surface subsidence is one of the most important engineering problems, which not only affects the safety of the subway tunnel construction, but also directly relates to the normal operation of the surrounding buildings. The compressive modulus of generation zone is one of the key shield parameters that control the ground surface subsidence, especially to the shield tunneling in soft soil zone. The mixing proportion of the generation zone grouting material and the soil, and the waiting time after grouting are the important factors that affect the compressive modulus. This paper is based on the cumulosol shield tunneling project of Kunming Metro Line 3 Shiju section, with a compressive modulus test of mixtures which have different proportions of grouting materials and cumulosol and different curing times. The reasonable proportion relationship between the shield generation zone paste in the cumulosol zone and the soil are explored. The time to get expected compressive modulus of generation zone after grouting is put forward, which can provide reference for the shield tunneling construction in the cumulosol area.
2017, 25(6): 1633-1639.
Tunneling with neighboring soil void is a particular challenge for underground railway construction in karst terrain. To reduce the disturbance to neighboring soil voids generated by the TBM and to secure the TBM from sudden settlement, axis deviation and ground collapse, it's necessary to conduct TBM tunneling parameters optimization. Aiming at the existing circumstances that TBM tunneling parameters are mostly determined by engineering experiences, a mechanical model based on Mindlin solution is built and an optimal control problem about excavation rate is proposed using the excavation rate regarded as a controlled variable, and the variation of energy density is regarded as the performance index. The problem is then solved using Gradient method. This optimization method has been introduced to the construction of a TBM tunnel in Line 9, Guangzhou Railway System. The results indicate that the model proposed in this study can effectively reflect the disturbance at the top of neighboring soil voids caused by bulkhead thrust in TBM tunneling. The optimization based on optimal excavation rate control problem agrees with engineering experiences.
Tunneling with neighboring soil void is a particular challenge for underground railway construction in karst terrain. To reduce the disturbance to neighboring soil voids generated by the TBM and to secure the TBM from sudden settlement, axis deviation and ground collapse, it's necessary to conduct TBM tunneling parameters optimization. Aiming at the existing circumstances that TBM tunneling parameters are mostly determined by engineering experiences, a mechanical model based on Mindlin solution is built and an optimal control problem about excavation rate is proposed using the excavation rate regarded as a controlled variable, and the variation of energy density is regarded as the performance index. The problem is then solved using Gradient method. This optimization method has been introduced to the construction of a TBM tunnel in Line 9, Guangzhou Railway System. The results indicate that the model proposed in this study can effectively reflect the disturbance at the top of neighboring soil voids caused by bulkhead thrust in TBM tunneling. The optimization based on optimal excavation rate control problem agrees with engineering experiences.
2017, 25(6): 1610-1616.
A large amount of test data can be generated when the distributed optical fiber is used to detection of pile foundation. Therefore, the fast and accurate processing of these data has become an urgent problem to be re-solved. But there is no corresponding data processing software specialized in distributed optical fiber data. This paper introduces the embedded technics and key problems faced now when optical fiber is used to the detection of pile. It examines the characteristics of sensing fiber layout, the pressure bearing characteristics of pile and the main process of data processing for distributed optical fiber detection of pile foundation. It first puts forward a plan to realize the intelligent processing of detection data. Then the distributed optical fiber data processing system can be independently generated using computer programming language based on the plan. Finally, actual engineering datum is used to verify the practical application of the software. The results show that the distributed optical fiber pile testing data processing software is easy to use, can fast and intelligently process detected data. The results can truly reflect the actual situation and meet the requirements of pile detection data processing. This software can be applied to the distributed optical fiber pile detection data processing.
A large amount of test data can be generated when the distributed optical fiber is used to detection of pile foundation. Therefore, the fast and accurate processing of these data has become an urgent problem to be re-solved. But there is no corresponding data processing software specialized in distributed optical fiber data. This paper introduces the embedded technics and key problems faced now when optical fiber is used to the detection of pile. It examines the characteristics of sensing fiber layout, the pressure bearing characteristics of pile and the main process of data processing for distributed optical fiber detection of pile foundation. It first puts forward a plan to realize the intelligent processing of detection data. Then the distributed optical fiber data processing system can be independently generated using computer programming language based on the plan. Finally, actual engineering datum is used to verify the practical application of the software. The results show that the distributed optical fiber pile testing data processing software is easy to use, can fast and intelligently process detected data. The results can truly reflect the actual situation and meet the requirements of pile detection data processing. This software can be applied to the distributed optical fiber pile detection data processing.
2017, 25(6): 1624-1632.
Piedmont fracture of Mount Li that Xi'an metro tunnel pass through was taken as research prototype, and the activity characteristics were analyzed, and the biggest vertical displacement of the ground surface by the fault sticky slip activity was forecast based on the risk analysis results of earthquake in near field. The responsive deformation and failure characteristics of stratum and subway tunnel caused by fracture dislocation were studied by using numerical simulation method, and the critical dislocation amount of section tunnel structure damaged was analyzed and verified; the influence range of fracture activity were calculated, and the main fortification area of the subway tunnel crossing the fault zone was determined. Research result shows that the settlement response of stratum on the hanging wall is more obvious with the increase of the amount of fracture dislocation, differential settlement areas of stratum between the hanging wall and foot wall are concentrate near the fracture zone, which extend to both sides taking on the shape of "inverted triangle" gradually. When the amount of dislocation is greater than 20cm, the differential settlement of metro tunnel between the hanging wall and foot wall is particularly serious; the adjacent sectional tunnels appear tension and dislocation phenomena when the dislocation of hanging wall is 50cm. Based on the changing characteristics of the stratum vertical displacement at the tunnel vault, the least longitudinal fortified lengths of subway tunnel passing through the fault zone are get, which are 40m on the hanging wall and 15m on the footwall. The experimental results are consistent with the field investigation results after contrasting and verifying. Finally, corresponding proposed measures for fortification are put forward.
Piedmont fracture of Mount Li that Xi'an metro tunnel pass through was taken as research prototype, and the activity characteristics were analyzed, and the biggest vertical displacement of the ground surface by the fault sticky slip activity was forecast based on the risk analysis results of earthquake in near field. The responsive deformation and failure characteristics of stratum and subway tunnel caused by fracture dislocation were studied by using numerical simulation method, and the critical dislocation amount of section tunnel structure damaged was analyzed and verified; the influence range of fracture activity were calculated, and the main fortification area of the subway tunnel crossing the fault zone was determined. Research result shows that the settlement response of stratum on the hanging wall is more obvious with the increase of the amount of fracture dislocation, differential settlement areas of stratum between the hanging wall and foot wall are concentrate near the fracture zone, which extend to both sides taking on the shape of "inverted triangle" gradually. When the amount of dislocation is greater than 20cm, the differential settlement of metro tunnel between the hanging wall and foot wall is particularly serious; the adjacent sectional tunnels appear tension and dislocation phenomena when the dislocation of hanging wall is 50cm. Based on the changing characteristics of the stratum vertical displacement at the tunnel vault, the least longitudinal fortified lengths of subway tunnel passing through the fault zone are get, which are 40m on the hanging wall and 15m on the footwall. The experimental results are consistent with the field investigation results after contrasting and verifying. Finally, corresponding proposed measures for fortification are put forward.
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