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Editor Work2017 Vol. 25, No. 1
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2017, 25(1): 1-10.
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This paper is to further explore the mechanical effects of plants in slope protection in cold and arid environments. It selects five kinds of native herbs and shrubs as the test samples. They are suitable for the local climate conditions. They are planted in the self-built test area in this research. The single tensile tests are carried out to systematically analyze the strength characteristics of plant roots of the five kinds of herbs and shrubs. The results show the follows. The single root tensile resistances increases with the diameter increasing. Power relations exist between single root tensile resistances and root diameters of the herbs and shrubs respectively. Meanwhile, the single root tensile strengths increase with the diameter decreasing. Power relations exist between single root tensile strengths and root diameters of five kinds of herbs and shrubs respectively. The single root tensile strength of Elymus nutans Griseb is bigger than that of Agropyron trachycaulum(Linn.) Gaertn, while the sequence of the single tensile strengths of shrubs from big to small is Caragana korshinskii Kom,Zygophyllum xanthoxylon(Bunge) Maxim. and Nitraria tangutorum Bobr. Besides, some phenomena are shown by comparing and analyzing the stress-strain relationship curves of tensile tests of three kinds of shrubs in the vegetative period of 1a and 2a. That is,in the early single root tensile test of shrubs, there is a linear relationship between stress and strain, which shows the elastic material properties. Until the middle and late stage of the test, the relationship between stress and strain is nonlinear and shows the elastic-plastic material properties. Further research shows a downward trend of the largest elongation of the shrub single root with the increasing of vegetative period. The results of the study have a theoretical researching and practical guiding significance in the prevention and treatment of geological disasters such as shallow landslide and soil erosion in the study area and in the protection of the regional ecological geological environment.
This paper is to further explore the mechanical effects of plants in slope protection in cold and arid environments. It selects five kinds of native herbs and shrubs as the test samples. They are suitable for the local climate conditions. They are planted in the self-built test area in this research. The single tensile tests are carried out to systematically analyze the strength characteristics of plant roots of the five kinds of herbs and shrubs. The results show the follows. The single root tensile resistances increases with the diameter increasing. Power relations exist between single root tensile resistances and root diameters of the herbs and shrubs respectively. Meanwhile, the single root tensile strengths increase with the diameter decreasing. Power relations exist between single root tensile strengths and root diameters of five kinds of herbs and shrubs respectively. The single root tensile strength of Elymus nutans Griseb is bigger than that of Agropyron trachycaulum(Linn.) Gaertn, while the sequence of the single tensile strengths of shrubs from big to small is Caragana korshinskii Kom,Zygophyllum xanthoxylon(Bunge) Maxim. and Nitraria tangutorum Bobr. Besides, some phenomena are shown by comparing and analyzing the stress-strain relationship curves of tensile tests of three kinds of shrubs in the vegetative period of 1a and 2a. That is,in the early single root tensile test of shrubs, there is a linear relationship between stress and strain, which shows the elastic material properties. Until the middle and late stage of the test, the relationship between stress and strain is nonlinear and shows the elastic-plastic material properties. Further research shows a downward trend of the largest elongation of the shrub single root with the increasing of vegetative period. The results of the study have a theoretical researching and practical guiding significance in the prevention and treatment of geological disasters such as shallow landslide and soil erosion in the study area and in the protection of the regional ecological geological environment.
2017, 25(1): 11-18.
According to conditions of the soft foundation and processing requirements, this paper introduces a new high vacuum densification method(HVDM).To exame the proposed method, tests are done before soft soil foundation treatment, at the end of the soft soil foundation treatment and 5months after the end of the soft soil foundation treatment, respectively. Plate load test on the hydraulic fill sand surface is done after the construction. The results show that, the foundation soil strength is greatly improved by using HVDM.The sand layer's cone tip resistance, the side friction, and the undrained shear strength of silt layer are increased by 406.3%, 360.8% and 60.3%,respectively. The treatment effect is more obvious in the range of 6~7m deep. The physical and mechanical properties are improved to varying degrees. The dry density, is increased by 6.08%. The pore compression coefficient decreased by 8.96%. The a1-2 decreased by 10.53%. The compression modulus of Es1-2 increased by 12.18%. Direct shear strength increased by 8.91%. The internal friction angle increased by 41.01%. The cohesion from triaxial(UU) test increased by 33.04%. The foundation bearing capacity increased from less than 50kPa to over 120kPa, which can meet the requirements of foundation treatment.
According to conditions of the soft foundation and processing requirements, this paper introduces a new high vacuum densification method(HVDM).To exame the proposed method, tests are done before soft soil foundation treatment, at the end of the soft soil foundation treatment and 5months after the end of the soft soil foundation treatment, respectively. Plate load test on the hydraulic fill sand surface is done after the construction. The results show that, the foundation soil strength is greatly improved by using HVDM.The sand layer's cone tip resistance, the side friction, and the undrained shear strength of silt layer are increased by 406.3%, 360.8% and 60.3%,respectively. The treatment effect is more obvious in the range of 6~7m deep. The physical and mechanical properties are improved to varying degrees. The dry density, is increased by 6.08%. The pore compression coefficient decreased by 8.96%. The a1-2 decreased by 10.53%. The compression modulus of Es1-2 increased by 12.18%. Direct shear strength increased by 8.91%. The internal friction angle increased by 41.01%. The cohesion from triaxial(UU) test increased by 33.04%. The foundation bearing capacity increased from less than 50kPa to over 120kPa, which can meet the requirements of foundation treatment.
2017, 25(1): 19-26.
Anchorage technology has been widely employed in the field of earthen sites' stability controlling. However, the lack of anchorage slurry is one of key problems in the development of anchorage technology and theory. Physical, mechanical and acoustic properties of the modified SH-(C+F) mortar specimens were tested. The specimens are composed of clay fly ash and SH whose concentrations are 0.5%, 1.0%, 1.5% respectively. In-situ anchoring, pull out tests and stress-strain monitoring of the interface between bolt and slurry of the anchoring systems are carried out. The systems are made up of mixed slurry and wood bolt, glass fiber reinforced plastic, and reinforced bar. The test results reveal the failure mode, anchorage performance, spatial and temporal distribution law of stress-strain on the blot-slurry interfaces of three types of anchorage systems. The test results show that SH-(C+F) mortar has better physical and mechanical properties, and better compatibility with earthen sites. The anchoring performance of the three kinds of anchorage systems with the full length grouting of SH anchorage system is excellent. Anchoring performance of wood bolt anchorage system achieves optimal when its concentration is 1%,while anchorage performance of glass fiber reinforced plastic and reinforced bar anchoring system behaves better with the increase of concentration of SH.The research findings provide a basis and a reference for the application of SH-based modified slurry in the field of earthen sites anchoring.
Anchorage technology has been widely employed in the field of earthen sites' stability controlling. However, the lack of anchorage slurry is one of key problems in the development of anchorage technology and theory. Physical, mechanical and acoustic properties of the modified SH-(C+F) mortar specimens were tested. The specimens are composed of clay fly ash and SH whose concentrations are 0.5%, 1.0%, 1.5% respectively. In-situ anchoring, pull out tests and stress-strain monitoring of the interface between bolt and slurry of the anchoring systems are carried out. The systems are made up of mixed slurry and wood bolt, glass fiber reinforced plastic, and reinforced bar. The test results reveal the failure mode, anchorage performance, spatial and temporal distribution law of stress-strain on the blot-slurry interfaces of three types of anchorage systems. The test results show that SH-(C+F) mortar has better physical and mechanical properties, and better compatibility with earthen sites. The anchoring performance of the three kinds of anchorage systems with the full length grouting of SH anchorage system is excellent. Anchoring performance of wood bolt anchorage system achieves optimal when its concentration is 1%,while anchorage performance of glass fiber reinforced plastic and reinforced bar anchoring system behaves better with the increase of concentration of SH.The research findings provide a basis and a reference for the application of SH-based modified slurry in the field of earthen sites anchoring.
2017, 25(1): 27-35.
In static-dynamic drainage consolidation method, the soil consolidation effect is strongly related to drainage body spacing. This paper studies the effect of different drainage body spacing on the energy transfer processes of soft soil under high-energy impacts. Static-dynamic consolidation model tests (1:30 similarity ratio) are performed on the muck soil where different drainage systems are installed using a self-developed high-energy electromagnetic impact testing system. The energy transferring processes in different drainage systems are characterized under repeated high-energy impacts. The experimental results show the follows. (1) The pore pressure in non-plastic drainage board(non-artificial vertical drains) area is hardly to disperse under impact load. Additional soil pressure is difficult to pass down along the depth direction. The board area can be, but the pass down needs to undergo certain impact passes. The pore pressure more easily dissipates. Larger settlement more easily takes place in the vertical drains dense area. (2) Soft soil in drain area is top-down gradually reinforced. The more dense drains, as the number of impact passes increase, the greater the proportion of the energy distribution in the deep soft ground, and the proportion becomes the largest in final impact. More obvious trend of the main compression zone moving downward is shown. Those results show that drainage setting is necessary, but should maintain a reasonable density. Under given conditions, the drains more dense, more conducive to strengthening the deep ground soil. Its important engineering significance is that the deep muck soil ground can be strengthened when impact applying sufficient number of times and with suitable drains, by using static-dynamic drainage consolidation method. The finding provides the basis for optimization of design and construction for high water content soft soil ground, and how to meet the reinforcement depth requirement as well.
In static-dynamic drainage consolidation method, the soil consolidation effect is strongly related to drainage body spacing. This paper studies the effect of different drainage body spacing on the energy transfer processes of soft soil under high-energy impacts. Static-dynamic consolidation model tests (1:30 similarity ratio) are performed on the muck soil where different drainage systems are installed using a self-developed high-energy electromagnetic impact testing system. The energy transferring processes in different drainage systems are characterized under repeated high-energy impacts. The experimental results show the follows. (1) The pore pressure in non-plastic drainage board(non-artificial vertical drains) area is hardly to disperse under impact load. Additional soil pressure is difficult to pass down along the depth direction. The board area can be, but the pass down needs to undergo certain impact passes. The pore pressure more easily dissipates. Larger settlement more easily takes place in the vertical drains dense area. (2) Soft soil in drain area is top-down gradually reinforced. The more dense drains, as the number of impact passes increase, the greater the proportion of the energy distribution in the deep soft ground, and the proportion becomes the largest in final impact. More obvious trend of the main compression zone moving downward is shown. Those results show that drainage setting is necessary, but should maintain a reasonable density. Under given conditions, the drains more dense, more conducive to strengthening the deep ground soil. Its important engineering significance is that the deep muck soil ground can be strengthened when impact applying sufficient number of times and with suitable drains, by using static-dynamic drainage consolidation method. The finding provides the basis for optimization of design and construction for high water content soft soil ground, and how to meet the reinforcement depth requirement as well.
2017, 25(1): 43-49.
Geomembrane has been commonly used as barriers in landfills in combination with soils. However, the soil-geomembrane interfaces may become the potential planes of weakness within the system along which failure may occur. Therefore, many laboratory tests have been conducted by researchers to investigate the interface shear behaviors. However, it is difficult to directly investigate the material interactions and mechanisms occurring at soil-geomembrane interfaces through common laboratory tests. In order to investigate the mesoscopical interface properties between geomembrane and soil, a serial of numerical direct shear tests are carried out using a modified three dimensional DEM code, EsyS-particle. In this paper, the sand is modeled with cohesionless frictional interactions, while the geomembrane is modeled with bonded particles. In order to precisely simulate the smooth surface of the geomembrane, the distance between two nearest bonded particles has been adjusted to a small value. Suitable mesoscopic discrete element parameters of the sand and geomembrane have been calibrated by numerical triaxial tests and tensile tests, respectively. The numerical interface direct shear tests are performed under the same conditions as the laboratory tests, and the simulation results are compared to experimental data. The DEM simulation result shows that the DEM simulation is capable of reasonably predicting interaction behavior between geomembrane and soil. The shear band thickness is approximately 2 times of the average particle diameters. During the shear process, the particles inside the band undergo large horizontal relative displacements, while particles outside the area are driven by an upward motion. And the void ratio inside the shear band sees an increasing trend during the shear process, whereas no obvious change is observed outside the area. The distributions of contact force chains are small and homogeneous at the beginning of the shear, during the shearing, the contact force chains are concentrating to the left part of the sample, and the orientations of the forces changed from nearly vertical to diagonal.
Geomembrane has been commonly used as barriers in landfills in combination with soils. However, the soil-geomembrane interfaces may become the potential planes of weakness within the system along which failure may occur. Therefore, many laboratory tests have been conducted by researchers to investigate the interface shear behaviors. However, it is difficult to directly investigate the material interactions and mechanisms occurring at soil-geomembrane interfaces through common laboratory tests. In order to investigate the mesoscopical interface properties between geomembrane and soil, a serial of numerical direct shear tests are carried out using a modified three dimensional DEM code, EsyS-particle. In this paper, the sand is modeled with cohesionless frictional interactions, while the geomembrane is modeled with bonded particles. In order to precisely simulate the smooth surface of the geomembrane, the distance between two nearest bonded particles has been adjusted to a small value. Suitable mesoscopic discrete element parameters of the sand and geomembrane have been calibrated by numerical triaxial tests and tensile tests, respectively. The numerical interface direct shear tests are performed under the same conditions as the laboratory tests, and the simulation results are compared to experimental data. The DEM simulation result shows that the DEM simulation is capable of reasonably predicting interaction behavior between geomembrane and soil. The shear band thickness is approximately 2 times of the average particle diameters. During the shear process, the particles inside the band undergo large horizontal relative displacements, while particles outside the area are driven by an upward motion. And the void ratio inside the shear band sees an increasing trend during the shear process, whereas no obvious change is observed outside the area. The distributions of contact force chains are small and homogeneous at the beginning of the shear, during the shearing, the contact force chains are concentrating to the left part of the sample, and the orientations of the forces changed from nearly vertical to diagonal.
2017, 25(1): 50-57.
Dynamic shear modulus and damping ratio test of fault gouge with different dry density values or water contents are performed using GDS resonant column system. The results show that the relationship between dynamic shear modulus and dynamic shear strain can be well fitted by Hardin-Drnevich hyperbolic model. The dynamic shear modulus and the damping ratio both increase with the dry density, while decrease with water content. Experimental points of normalized dynamic shear modulus are mainly located in the range of the G/Gmax~γ curve of sand which is proposed by Seed and Idriss, and in accordance with the trend of cohesive soil which is proposed by Sun and Seed. The damping ratio changes linearly with the dynamic shear strain under semilog coordination. The fitting formula is suggested.
Dynamic shear modulus and damping ratio test of fault gouge with different dry density values or water contents are performed using GDS resonant column system. The results show that the relationship between dynamic shear modulus and dynamic shear strain can be well fitted by Hardin-Drnevich hyperbolic model. The dynamic shear modulus and the damping ratio both increase with the dry density, while decrease with water content. Experimental points of normalized dynamic shear modulus are mainly located in the range of the G/Gmax~γ curve of sand which is proposed by Seed and Idriss, and in accordance with the trend of cohesive soil which is proposed by Sun and Seed. The damping ratio changes linearly with the dynamic shear strain under semilog coordination. The fitting formula is suggested.
2017, 25(1): 58-64.
Star-shaped pile is a new type of special-section pile. It is formed by cutting five circular arcs in a circle pile. This paper aims to explore the uplifting bearing capacity of star-shaped piles. For comparison, the experimental tests on four single piles in dry sand by sand pourer construction are carried out in model tank of independent research and development. The four tested piles are the maximum ratio of perimeter and area of the five-star-shaped pile F1,the maximum of the circumference of the five-star-shaped pile F2,the round pile C1 with the same section of F2, and the round pile C2 with the same cross-sectional area of F2. Test results show:(1) The uplifting bearing capacity values of the pile F1 and F2 are basically the same. The maximum is the pile C1. The minimum is the pile C2. (2) The uplifting bearing capacity value of the pile C1 is 1.73 times that of the pile F1. The uplifting side resistance is weakened because of star-shaped section. (3) The side area of the pile C2 is 0.66 times that of the pile F2,but its uplifting bearing capacity is 0.8 times of the pile F2. So it shows again that the star-shaped section weakens the uplifting side resistance. However, the uplifting bearing capacity value of the pile F2 is 1.25 times that of the pile C2,which shows that the circular section changing into the star-shaped section can improve the uplifting bearing capacity to some extent.(4) The distribution between uplifting side friction and displacement is hyperbolic. The side limiting friction is reached only by a little displacement.
Star-shaped pile is a new type of special-section pile. It is formed by cutting five circular arcs in a circle pile. This paper aims to explore the uplifting bearing capacity of star-shaped piles. For comparison, the experimental tests on four single piles in dry sand by sand pourer construction are carried out in model tank of independent research and development. The four tested piles are the maximum ratio of perimeter and area of the five-star-shaped pile F1,the maximum of the circumference of the five-star-shaped pile F2,the round pile C1 with the same section of F2, and the round pile C2 with the same cross-sectional area of F2. Test results show:(1) The uplifting bearing capacity values of the pile F1 and F2 are basically the same. The maximum is the pile C1. The minimum is the pile C2. (2) The uplifting bearing capacity value of the pile C1 is 1.73 times that of the pile F1. The uplifting side resistance is weakened because of star-shaped section. (3) The side area of the pile C2 is 0.66 times that of the pile F2,but its uplifting bearing capacity is 0.8 times of the pile F2. So it shows again that the star-shaped section weakens the uplifting side resistance. However, the uplifting bearing capacity value of the pile F2 is 1.25 times that of the pile C2,which shows that the circular section changing into the star-shaped section can improve the uplifting bearing capacity to some extent.(4) The distribution between uplifting side friction and displacement is hyperbolic. The side limiting friction is reached only by a little displacement.
2017, 25(1): 65-72.
Used as a modified material, the waste tire granulated rubber is expected to enhance the effectiveness of liner system in landfill and extend the utilization of the tire waste. The mechanical and hydraulic properties tests of waste tire ground rubber and Kaolin soil mixtures are conducted. The effects of ground rubber on the compressibility, shrinkage and hydraulic conductivity properties are studied. As the rubber mixing content increases, the hydraulic conductivity, coefficient of compressibility, swelling index, coefficient of consolidation, and volumetric shrinkage ratio increase. The Kaolin soil and the mixtures are medium compressibility soils. The unconfined compressive strengths are greater than 200kPa, and the volumetric shrinkage ratios are less than the threshold strain of 4%. Under the pressure of 50kPa and 200kPa, the hydraulic conductivities are less than 1.0×10-7cm·s-1,which meets the requirement of compacted clay liner in the specification. In contrast to the 30mesh ground rubber, the mixtures of 12mesh ground rubber and Kaolin soil have smaller compressibility and swelling index, and larger consolidation coefficient. It is also found out that the size of the ground rubber has insignificant effect on unconfined compressive strength, shrinkage and hydraulic conductivity of the mixtures. Overall, the mixture with the size of 12-mesh and the rubber content of 25% is the optimal design scheme for using as a landfill liner material.
Used as a modified material, the waste tire granulated rubber is expected to enhance the effectiveness of liner system in landfill and extend the utilization of the tire waste. The mechanical and hydraulic properties tests of waste tire ground rubber and Kaolin soil mixtures are conducted. The effects of ground rubber on the compressibility, shrinkage and hydraulic conductivity properties are studied. As the rubber mixing content increases, the hydraulic conductivity, coefficient of compressibility, swelling index, coefficient of consolidation, and volumetric shrinkage ratio increase. The Kaolin soil and the mixtures are medium compressibility soils. The unconfined compressive strengths are greater than 200kPa, and the volumetric shrinkage ratios are less than the threshold strain of 4%. Under the pressure of 50kPa and 200kPa, the hydraulic conductivities are less than 1.0×10-7cm·s-1,which meets the requirement of compacted clay liner in the specification. In contrast to the 30mesh ground rubber, the mixtures of 12mesh ground rubber and Kaolin soil have smaller compressibility and swelling index, and larger consolidation coefficient. It is also found out that the size of the ground rubber has insignificant effect on unconfined compressive strength, shrinkage and hydraulic conductivity of the mixtures. Overall, the mixture with the size of 12-mesh and the rubber content of 25% is the optimal design scheme for using as a landfill liner material.
2017, 25(1): 73-79.
The soil water characteristic curves of sand, silty clay and clay are measured by axis translation technique. The T2 distribution curve of specimens are tested under different matric suction loading steps combining with nuclear magnetic resonance(NMR) technique. The distribution of pore water in soil is discussed with the T2 distribution curve from the microscopic point of view during drying process. The results show that volumetric water content gradually reduces with the increase of the suction. The drying curve can be divided into three sections:boundary effect zone, transition zone and residual zone. In addition, the clay water-holding capacity is obviously higher than that of silt and sand. The tests of NMR are corresponded with drying process in the pressure plate apparatus. The results of NMR tests further show the drainage process of soil from the microscopic of perspective. On the whole, the large pore water with large potential energy is discharged first in the drainage process of soil, and then the water in small pores begins to drain. However, this rule is not absolute, because of the complexity of the soil pore structure. There will be a phenomenon of simultaneous discharge of different size porosity of pore water and the redistribution of pore water in soil occurred during the drying process.
The soil water characteristic curves of sand, silty clay and clay are measured by axis translation technique. The T2 distribution curve of specimens are tested under different matric suction loading steps combining with nuclear magnetic resonance(NMR) technique. The distribution of pore water in soil is discussed with the T2 distribution curve from the microscopic point of view during drying process. The results show that volumetric water content gradually reduces with the increase of the suction. The drying curve can be divided into three sections:boundary effect zone, transition zone and residual zone. In addition, the clay water-holding capacity is obviously higher than that of silt and sand. The tests of NMR are corresponded with drying process in the pressure plate apparatus. The results of NMR tests further show the drainage process of soil from the microscopic of perspective. On the whole, the large pore water with large potential energy is discharged first in the drainage process of soil, and then the water in small pores begins to drain. However, this rule is not absolute, because of the complexity of the soil pore structure. There will be a phenomenon of simultaneous discharge of different size porosity of pore water and the redistribution of pore water in soil occurred during the drying process.
2017, 25(1): 80-87.
Studies on the properties and improvements of expansive soil have drawn more and more attentions because of many engineering accidents caused by deformation of expansive soil. In order to investigate the creep characteristics of fiber reinforced expansive soil, unsaturated triaxial creep tests are carried out with the consideration of the influence of water content and reinforcement ratio of basalt fiber mixed into the expansive soil. Long-term strength of the fiber reinforced expensive soil is analyzed through isochronous stress-strain curves. Meanwhile, Mesri creep model is established and verified. The main conclusions are as follows:By comparing strain-time curve, it finds that the fiber reinforced expansive soil has an obvious role on reducing creep deformation. However, there exists an optimal reinforcement rate. If fiber content surpasses the optimal reinforcement rate, the creep effect cannot be significantly decreased. The creep properties of the fiber reinforced expansive soil increase as the moisture content decreases. They have the optimum moisture content. If less than the optimum moisture content, the creep effect cannot be significantly increased. Isochronous stress-strain curves can be obtained from the strain-time curve at different load levels. The long-term strength of the samples can be figured out according to the inflexion point of isochronous stress-strain curves. Long-term strength of expansive soil can be significantly improved by fiber reinforcement. In the test, the long-term strength of 0.4% reinforced expansive soil is improved by 26.7% compared with pure soil under the same condition. The long-term strength of 0.6% reinforced expansive soil is improved by 23.3%. Mesri creep model can generally reflect the triaxial creep characteristics of fiber reinforced expansive soil.
Studies on the properties and improvements of expansive soil have drawn more and more attentions because of many engineering accidents caused by deformation of expansive soil. In order to investigate the creep characteristics of fiber reinforced expansive soil, unsaturated triaxial creep tests are carried out with the consideration of the influence of water content and reinforcement ratio of basalt fiber mixed into the expansive soil. Long-term strength of the fiber reinforced expensive soil is analyzed through isochronous stress-strain curves. Meanwhile, Mesri creep model is established and verified. The main conclusions are as follows:By comparing strain-time curve, it finds that the fiber reinforced expansive soil has an obvious role on reducing creep deformation. However, there exists an optimal reinforcement rate. If fiber content surpasses the optimal reinforcement rate, the creep effect cannot be significantly decreased. The creep properties of the fiber reinforced expansive soil increase as the moisture content decreases. They have the optimum moisture content. If less than the optimum moisture content, the creep effect cannot be significantly increased. Isochronous stress-strain curves can be obtained from the strain-time curve at different load levels. The long-term strength of the samples can be figured out according to the inflexion point of isochronous stress-strain curves. Long-term strength of expansive soil can be significantly improved by fiber reinforcement. In the test, the long-term strength of 0.4% reinforced expansive soil is improved by 26.7% compared with pure soil under the same condition. The long-term strength of 0.6% reinforced expansive soil is improved by 23.3%. Mesri creep model can generally reflect the triaxial creep characteristics of fiber reinforced expansive soil.
2017, 25(1): 88-94.
Hydraulic fracturing is a well-stimulation technique and has been used as one of the key methods of extracting unconventional oil and unconventional gas resources. Uniaxial hydraulic fracturing experiments are carried out in order to study the effect of shale bedding plane orientation with respect to loading direction on breakdown pressure and hydraulic fracture propagation. Fracturing is completed on cylindrical samples containing a single blind axial borehole under simple uniaxial conditions with axial stress of 10MPa. The results show that the effect of bedding plane orientation with respect to principal stress on the breakdown pressure of shale is obvious. Under the same applied stress conditions, 90° sample returns the highest breakdown pressure, followed by 0° sample, while 30° sample returns the lowest. As the result, the breakdown pressure curve shows a U-like shape. In terms of fracture morphology, there are two types of fracturing patterns founded in samples. One type is the cracks extending along the loading direction and the other is the crack extending along the loading direction at first and then turning to the bedding plane direction. Fracture propagation by hydraulic fracturing is induced by both shear and tensile stresses, which means the failure modes are tensile splitting, sliding failure or both. The experiment result has a significant impact on understanding mechanism of fracture extension and provides references for fracture optimization design in exploiting shale gas.
Hydraulic fracturing is a well-stimulation technique and has been used as one of the key methods of extracting unconventional oil and unconventional gas resources. Uniaxial hydraulic fracturing experiments are carried out in order to study the effect of shale bedding plane orientation with respect to loading direction on breakdown pressure and hydraulic fracture propagation. Fracturing is completed on cylindrical samples containing a single blind axial borehole under simple uniaxial conditions with axial stress of 10MPa. The results show that the effect of bedding plane orientation with respect to principal stress on the breakdown pressure of shale is obvious. Under the same applied stress conditions, 90° sample returns the highest breakdown pressure, followed by 0° sample, while 30° sample returns the lowest. As the result, the breakdown pressure curve shows a U-like shape. In terms of fracture morphology, there are two types of fracturing patterns founded in samples. One type is the cracks extending along the loading direction and the other is the crack extending along the loading direction at first and then turning to the bedding plane direction. Fracture propagation by hydraulic fracturing is induced by both shear and tensile stresses, which means the failure modes are tensile splitting, sliding failure or both. The experiment result has a significant impact on understanding mechanism of fracture extension and provides references for fracture optimization design in exploiting shale gas.
2017, 25(1): 102-109.
In order to gain the creep laws of light weight soil which is in the central part of the subgrade under long-term loading, the creep properties of light weight soil and remolded soil with different water contents and axial compression force were analyzed by one-dimensional compression tests. The results show that when other factors are the same, the higher the axial compression force and water content are,the greater the creep deformation of soil samples is.The deformation of light weight soil under loading for one day can basically reach 93%~98% of the whole deformation, and the attenuating creep is obvious. Light weight soil is a kind of structural soil, and it has different creep mechanism with remolded soil. When the axial compression force is no more than the compressed yield stress, the creep deformation is mainly from holes closure, drainage water, solid particles' movement. When the axial compression force is more than the compressed yield stress, the original structure of the light weight soil will be destroyed and EPS beads will be compressed. Based on the attenuation creep characteristics of light weight soil, an empirical creep model is established base on the hyperbolic model. When the axial compression force is less than the compressed yield stress, it can basically reflect the creep laws of light weight soil which is in the central part of the subgrade. By the experiments and theoretical calculation analysis, it is found that the consolidation characteristic of light weight soil is better than that of remolded soil. So the subgrade settlement can reach a stable value after the construction, and the post-construction settlement can almost be neglected during the operation.
In order to gain the creep laws of light weight soil which is in the central part of the subgrade under long-term loading, the creep properties of light weight soil and remolded soil with different water contents and axial compression force were analyzed by one-dimensional compression tests. The results show that when other factors are the same, the higher the axial compression force and water content are,the greater the creep deformation of soil samples is.The deformation of light weight soil under loading for one day can basically reach 93%~98% of the whole deformation, and the attenuating creep is obvious. Light weight soil is a kind of structural soil, and it has different creep mechanism with remolded soil. When the axial compression force is no more than the compressed yield stress, the creep deformation is mainly from holes closure, drainage water, solid particles' movement. When the axial compression force is more than the compressed yield stress, the original structure of the light weight soil will be destroyed and EPS beads will be compressed. Based on the attenuation creep characteristics of light weight soil, an empirical creep model is established base on the hyperbolic model. When the axial compression force is less than the compressed yield stress, it can basically reflect the creep laws of light weight soil which is in the central part of the subgrade. By the experiments and theoretical calculation analysis, it is found that the consolidation characteristic of light weight soil is better than that of remolded soil. So the subgrade settlement can reach a stable value after the construction, and the post-construction settlement can almost be neglected during the operation.
2017, 25(1): 110-116.
The physical and mechanical parameters of ore body and surface clay are measured. Then these parameters are inputted into SoilVision software to analyze seepage process and calculate slope stability coefficients of ion-absorpted type rare earth mine. The phreatic line and development of crack width of test ore block are monitored. The monitoring results show that the numerical calculation model is reasonable. The simplified model of slope is established in terms of the slope section shape and in-situ leaching mining technology features. The effect of deflector hole and collect liquid roadway to slope stability is discussed. The simulation calculations and experimental results indicate that the effect of deflector hole to slope safety factor is very small when charge liquid rate of deflector hole is less than 13.35%.The slope safety factor almost increases linearly with increasing charge liquid rate if charge liquid rate of deflector hole is 13.35% to 15.8%.For 42m horizontal long slope, collect liquid roadway plays an important role in controlling the slope instability if the distance between collect liquid roadway and seepage face is 12m to 24m.
The physical and mechanical parameters of ore body and surface clay are measured. Then these parameters are inputted into SoilVision software to analyze seepage process and calculate slope stability coefficients of ion-absorpted type rare earth mine. The phreatic line and development of crack width of test ore block are monitored. The monitoring results show that the numerical calculation model is reasonable. The simplified model of slope is established in terms of the slope section shape and in-situ leaching mining technology features. The effect of deflector hole and collect liquid roadway to slope stability is discussed. The simulation calculations and experimental results indicate that the effect of deflector hole to slope safety factor is very small when charge liquid rate of deflector hole is less than 13.35%.The slope safety factor almost increases linearly with increasing charge liquid rate if charge liquid rate of deflector hole is 13.35% to 15.8%.For 42m horizontal long slope, collect liquid roadway plays an important role in controlling the slope instability if the distance between collect liquid roadway and seepage face is 12m to 24m.
2017, 25(1): 117-122.
Due to the collapsibility, porous and water sensitivity of loess, geological disasters are widely distributed in loess area in northwest of China and show the characteristic of disaster chains. In this paper, several typical geological disasters in loess area are analyzed and the developmental states of geological disasters are concluded. Furthermore, the structures of two typical disaster chains are well described. In the geological disaster chains, the scale amplification is obvious, which is elaborated according to the 7.23 debris flow in Dagou gully in Tianshui City, Gansu Province. According to current research progress in geological disasters, three key issues are concluded and then the research ideas are given respectively. The research on risk assessment and chain scission about disaster chains should pay more attention to the future research. All and all, the preliminary research on geological disaster chains would be provide scientific reference to the future study.
Due to the collapsibility, porous and water sensitivity of loess, geological disasters are widely distributed in loess area in northwest of China and show the characteristic of disaster chains. In this paper, several typical geological disasters in loess area are analyzed and the developmental states of geological disasters are concluded. Furthermore, the structures of two typical disaster chains are well described. In the geological disaster chains, the scale amplification is obvious, which is elaborated according to the 7.23 debris flow in Dagou gully in Tianshui City, Gansu Province. According to current research progress in geological disasters, three key issues are concluded and then the research ideas are given respectively. The research on risk assessment and chain scission about disaster chains should pay more attention to the future research. All and all, the preliminary research on geological disaster chains would be provide scientific reference to the future study.
2017, 25(1): 123-131.
Large mudstone landslides are one of the main geological disasters in Huangshui River Basin in Qinghai Province. In the paper, the sliding zones of two typical large mudstone landslides in the area are taken as examples. Ring shear tests with different shear rates are conducted on the soils. The dynamic shear characteristics of the soils with different moisture contents in the sliding zones are revealed. The test results show that the soils in the sliding zones are expansive mudstone, and have obvious strain softening characteristics. The stress rapidly and significantly dropped from the peak stress to the residual stress (stress drop rang focused on 30%~40%). The shear strength has a negative relation with shear rate and moisture content. The response of the residual stress to these factors is less than the peak stress. The greater the moisture content (shear rate), the greater the change extent of shear stress and shear strength. The findings provide reasonable evidence for mechanism analysis and stability evaluation of landslide deformation in Huangshui River Basin.
Large mudstone landslides are one of the main geological disasters in Huangshui River Basin in Qinghai Province. In the paper, the sliding zones of two typical large mudstone landslides in the area are taken as examples. Ring shear tests with different shear rates are conducted on the soils. The dynamic shear characteristics of the soils with different moisture contents in the sliding zones are revealed. The test results show that the soils in the sliding zones are expansive mudstone, and have obvious strain softening characteristics. The stress rapidly and significantly dropped from the peak stress to the residual stress (stress drop rang focused on 30%~40%). The shear strength has a negative relation with shear rate and moisture content. The response of the residual stress to these factors is less than the peak stress. The greater the moisture content (shear rate), the greater the change extent of shear stress and shear strength. The findings provide reasonable evidence for mechanism analysis and stability evaluation of landslide deformation in Huangshui River Basin.
2017, 25(1): 132-138.
Due to the characteristics of low cohension and poor water stability, the silt using in the civil engineering is limited. Corn straw can have high tensile strength and is known as a good natural and enviromental protection fiber. This paper examines the reinforcement effect of the corn straw after preservation treatment in silt. It applies the antiseptic treatment to corn straw. It proposes a new concept of utilizing corn straw to reinforce soil. A series of tests are conducted to verify this idea. Fristly the tensile strength of corn straw is tested and the straw barks without stem node is selected to be samples because of its higher strength. Then the samples are soaked into the Kathan, Sodium diacetate and Polyvinyl alcohol solutions individually for some time. Their tensile strength are tested to compared their antiseptic ability. Test results show that the straw which soaked in the three antiseptic solutions and after waterlogged have higher tensile strength than that of natural straw. The antiseptic effect of polyvinyl alcohol is the best. The sample at 12 weeks after the treatment with polyvinyl alcohol has the tensile strength of about 160% of the nature straw. Microscope photographs and weighing test are carried out on the samples soaked into the polyvinyl alcoho. The results show that the straw can reach saturation after three days of immersion. The corn straw antiseptically treated with polyvinyl alcohol is then added into the silt and the triaxial tests are tested for the compacted silt samples. The strength increasing of silt reinforced with corn straw is mainly embodied in the cohesion. The increase is about 100% as much as pure soil, which contribute to water stability of silt; the curves of stress-strain relationship of reinforced soil come to exhibit a hardening character, which is different to the softening character of pure soil. The failure mode of reinforced soil is comparatively complete, which is different to shear failure modes of pure soil. These kind of phenomena show that the ability of silt to resist the external load is improved by corn straw fiber.
Due to the characteristics of low cohension and poor water stability, the silt using in the civil engineering is limited. Corn straw can have high tensile strength and is known as a good natural and enviromental protection fiber. This paper examines the reinforcement effect of the corn straw after preservation treatment in silt. It applies the antiseptic treatment to corn straw. It proposes a new concept of utilizing corn straw to reinforce soil. A series of tests are conducted to verify this idea. Fristly the tensile strength of corn straw is tested and the straw barks without stem node is selected to be samples because of its higher strength. Then the samples are soaked into the Kathan, Sodium diacetate and Polyvinyl alcohol solutions individually for some time. Their tensile strength are tested to compared their antiseptic ability. Test results show that the straw which soaked in the three antiseptic solutions and after waterlogged have higher tensile strength than that of natural straw. The antiseptic effect of polyvinyl alcohol is the best. The sample at 12 weeks after the treatment with polyvinyl alcohol has the tensile strength of about 160% of the nature straw. Microscope photographs and weighing test are carried out on the samples soaked into the polyvinyl alcoho. The results show that the straw can reach saturation after three days of immersion. The corn straw antiseptically treated with polyvinyl alcohol is then added into the silt and the triaxial tests are tested for the compacted silt samples. The strength increasing of silt reinforced with corn straw is mainly embodied in the cohesion. The increase is about 100% as much as pure soil, which contribute to water stability of silt; the curves of stress-strain relationship of reinforced soil come to exhibit a hardening character, which is different to the softening character of pure soil. The failure mode of reinforced soil is comparatively complete, which is different to shear failure modes of pure soil. These kind of phenomena show that the ability of silt to resist the external load is improved by corn straw fiber.
2017, 25(1): 154-163.
Prediction model for movement distance of rock avalanches has important theoretical significance and practical significance due to the characteristic of difficult detection, complex mechanism and high risk of gully-type rock avalanches. This study selects 38 typical rock avalanches induced by Wenchuan earthquake, and obtains their basic data based on the remote sensing and GIS technology combining with field investigation. Through correlation analysis, the results indicate that the influence factors of the maximum horizontal movement distance of rock avalanches (L) are landslide volume (V), the maximum vertical movement distance H, the elevation difference of slip source area (Hs), and the mean slope angle of the lower channel (β). Then a stepwise regression method is adapted to build optimal multiple regression model for the prediction of L. The validation shows that the multiple regression model is suitable for predicting rock avalanche hazardous zones in Wenchuan earthquake areas. The optimal multiple regression model and other internationally common-used prediction models are compared for the movement distance of landslides and debris flows. The result indicates that the forecast index system is suitable for the rock avalanches risk assessment in mountainous areas. The system considers the volume, drop height, the mean slope of the channel, with better goodness of fit index and physical meaning.
Prediction model for movement distance of rock avalanches has important theoretical significance and practical significance due to the characteristic of difficult detection, complex mechanism and high risk of gully-type rock avalanches. This study selects 38 typical rock avalanches induced by Wenchuan earthquake, and obtains their basic data based on the remote sensing and GIS technology combining with field investigation. Through correlation analysis, the results indicate that the influence factors of the maximum horizontal movement distance of rock avalanches (L) are landslide volume (V), the maximum vertical movement distance H, the elevation difference of slip source area (Hs), and the mean slope angle of the lower channel (β). Then a stepwise regression method is adapted to build optimal multiple regression model for the prediction of L. The validation shows that the multiple regression model is suitable for predicting rock avalanche hazardous zones in Wenchuan earthquake areas. The optimal multiple regression model and other internationally common-used prediction models are compared for the movement distance of landslides and debris flows. The result indicates that the forecast index system is suitable for the rock avalanches risk assessment in mountainous areas. The system considers the volume, drop height, the mean slope of the channel, with better goodness of fit index and physical meaning.
2017, 25(1): 164-170.
The flood discharge inlet of Lianghekou hydropower station could decorate at the left bank slope of Qingdahe River. A new deformation rock mass (Ⅳ) is found after three were identified in the previous stages. The construction safety is largely dependent on the stability of the deformation rock mass. On the basis of engineering geological methods such as exploratory tunneling and stereographic projection, the deformation mechanism is analyzed. The rock slope is toppling with thin and medium-thickness rock stratum. As the uplift of Qinghai-Tibet Plateau and incision of Qingdahe River, the slope is unloaded at the free face. The thin rock stratum is toppling and buckling at the slope toe and then the upper location. The deformation is aggravated with river erosion and a slip plane could be formed gradually. Landslide tends to occur with external disturbances e.g.rainstorm or earthquake. The deformation mass at the upper slope could get further damaged after slope toe failure. Because the thickness of rock stratum is small, the joint group nearly vertical to the bedding plane is developed well and the rock mass is strongly toppling, buckling and fragmentized. The stability is studied quantitatively with Geo-slope software. The results show that the deformation mass Ⅳ is in the limit equilibrium state and could get unstable after the deformation masses located at the lower part of the slope is clear off. Some proper treatment measures are then suggested.
The flood discharge inlet of Lianghekou hydropower station could decorate at the left bank slope of Qingdahe River. A new deformation rock mass (Ⅳ) is found after three were identified in the previous stages. The construction safety is largely dependent on the stability of the deformation rock mass. On the basis of engineering geological methods such as exploratory tunneling and stereographic projection, the deformation mechanism is analyzed. The rock slope is toppling with thin and medium-thickness rock stratum. As the uplift of Qinghai-Tibet Plateau and incision of Qingdahe River, the slope is unloaded at the free face. The thin rock stratum is toppling and buckling at the slope toe and then the upper location. The deformation is aggravated with river erosion and a slip plane could be formed gradually. Landslide tends to occur with external disturbances e.g.rainstorm or earthquake. The deformation mass at the upper slope could get further damaged after slope toe failure. Because the thickness of rock stratum is small, the joint group nearly vertical to the bedding plane is developed well and the rock mass is strongly toppling, buckling and fragmentized. The stability is studied quantitatively with Geo-slope software. The results show that the deformation mass Ⅳ is in the limit equilibrium state and could get unstable after the deformation masses located at the lower part of the slope is clear off. Some proper treatment measures are then suggested.
2017, 25(1): 171-179.
Stress-induced failure of rock mass due to the conflicts between rock mass strength and relatively high in-situ stresses, has commonly occurred during the developments of hydropower projects in western China. Estimates of rock mass properties have thus become one of the important tasks in the engineering practice, which can have significant influence on decision-making for engineering problems. This paper examines the differences of considerations in two empirical methods of the Hydro-engineering approach and the Hoek-Brown method. It addresses the influences of three main factors on rock mass strengths. They include lithology, confinement level, and damage of intact rock. Then, it examines the applicability of the two empirical approaches to the condition where the three parameters soundly present. The findings suggest that (1) the influence of these three factors cannot be ignored on estimating rock mass properties; (2) the Hydro-engineering approach is applicable to low-stress conditions whereas less suitable in western area where stress appears relatively high; (3) the Hoek-Brown method is applicable to both circumstances, i.e., low stress condition typically in the areas of central and eastern China as well as complex geological conditions with high in-situ stresses represented with the area of western China.
Stress-induced failure of rock mass due to the conflicts between rock mass strength and relatively high in-situ stresses, has commonly occurred during the developments of hydropower projects in western China. Estimates of rock mass properties have thus become one of the important tasks in the engineering practice, which can have significant influence on decision-making for engineering problems. This paper examines the differences of considerations in two empirical methods of the Hydro-engineering approach and the Hoek-Brown method. It addresses the influences of three main factors on rock mass strengths. They include lithology, confinement level, and damage of intact rock. Then, it examines the applicability of the two empirical approaches to the condition where the three parameters soundly present. The findings suggest that (1) the influence of these three factors cannot be ignored on estimating rock mass properties; (2) the Hydro-engineering approach is applicable to low-stress conditions whereas less suitable in western area where stress appears relatively high; (3) the Hoek-Brown method is applicable to both circumstances, i.e., low stress condition typically in the areas of central and eastern China as well as complex geological conditions with high in-situ stresses represented with the area of western China.
2017, 25(1): 180-189.
This paper aims to capture the evolution rules of fracture-inflowing water at the shallow depth of Xinli gold deposit exploited under seawater. From a hydrogeochemical point of view, it uses the principal component analysis and maximum likelihood method to identify the water-recharging sources of the inflowing water and estimate their mixing ratios. Using numerical modeling, the paper verifies indirectly the inflowing water evolutionary character and calculates it with the proposed method. The research shows that the method can effectively identify the combined patterns and variations of end-members of mine inflowing water, and calculate the most possible mixing ratios. The end-member model of the fracture-inflowing water of the Xinli gold mine has been changed from the type Ⅰ bedrock saline water+seabottom groundwater to the type Ⅰ bedrock saline water+seabottom groundwater+seawater. The sea bottom groundwater and seawater are prone to percolating into the mine pit from the shoulders of its both sides. The seawater percentage of the mine inflowing water goes through an increasing first and decreasing history.
This paper aims to capture the evolution rules of fracture-inflowing water at the shallow depth of Xinli gold deposit exploited under seawater. From a hydrogeochemical point of view, it uses the principal component analysis and maximum likelihood method to identify the water-recharging sources of the inflowing water and estimate their mixing ratios. Using numerical modeling, the paper verifies indirectly the inflowing water evolutionary character and calculates it with the proposed method. The research shows that the method can effectively identify the combined patterns and variations of end-members of mine inflowing water, and calculate the most possible mixing ratios. The end-member model of the fracture-inflowing water of the Xinli gold mine has been changed from the type Ⅰ bedrock saline water+seabottom groundwater to the type Ⅰ bedrock saline water+seabottom groundwater+seawater. The sea bottom groundwater and seawater are prone to percolating into the mine pit from the shoulders of its both sides. The seawater percentage of the mine inflowing water goes through an increasing first and decreasing history.
2017, 25(1): 190-198.
As one of the main recharge sources of the Jinan karst groundwater, the Yufu River plays an important role in spring protection in Jinan. In this paper, hydrochemistry and isotope are used to analyze variation of ions and mineral dissolutin/precipitation, flow path and scope due to river infiltration. The results indicate the SO4-Ca-Mg type of river water gradually turns into HCO3-Ca type of groundwater toward central city springs. Saturation indices of calcite and dolomite decrease, while saturation index of gypsum remains constant due to river infiltration. The data of hydrochemistry and isotope show that fraction of river water in karst aquifer reaches to 48%in the area from the Cuima to Manzizhuang. The river water occupies respectively 50% and 5% at 3 and 8 kilometers east to the Yufu River, showing less effect on the spring areas.
As one of the main recharge sources of the Jinan karst groundwater, the Yufu River plays an important role in spring protection in Jinan. In this paper, hydrochemistry and isotope are used to analyze variation of ions and mineral dissolutin/precipitation, flow path and scope due to river infiltration. The results indicate the SO4-Ca-Mg type of river water gradually turns into HCO3-Ca type of groundwater toward central city springs. Saturation indices of calcite and dolomite decrease, while saturation index of gypsum remains constant due to river infiltration. The data of hydrochemistry and isotope show that fraction of river water in karst aquifer reaches to 48%in the area from the Cuima to Manzizhuang. The river water occupies respectively 50% and 5% at 3 and 8 kilometers east to the Yufu River, showing less effect on the spring areas.
2017, 25(1): 199-208.
This paper is based on the engineering geological and hydrogeological conditions of Nanjing and the long-term monitoring data on the deformation of structures. The tunnel deformation characteristics in various geomorphic units are analyzed systematically. The effects of soft soil on shield tunnels and the hydrogeological conditions on mining tunnels are determined as the major engineering geological factors dominating the deformation of Nanjing metro tunnel. There are various kinds of soft soils in Nanjing. They are formed in different sedimentary conditions. Those soft soils, typically those in the valley plain area of Yangtze River, are of high void ratio, great water content, high compressibility and sensitive structure. These properties can easily lead to uneven settlements of the shield tunnels. As to the mining tunnels through the hilly area, the lining structure can be uplifted by the groundwater gradually when the groundwater exceeds the normal water table. As a result, the operation of metro tunnels can be disrupted seriously. This study fosters the understanding of the deformation of metro tunnels from the engineering geological perspective, and offers a theoretical basis to monitor and control the deformation and ensuring the safety of the tunnels in operating.
This paper is based on the engineering geological and hydrogeological conditions of Nanjing and the long-term monitoring data on the deformation of structures. The tunnel deformation characteristics in various geomorphic units are analyzed systematically. The effects of soft soil on shield tunnels and the hydrogeological conditions on mining tunnels are determined as the major engineering geological factors dominating the deformation of Nanjing metro tunnel. There are various kinds of soft soils in Nanjing. They are formed in different sedimentary conditions. Those soft soils, typically those in the valley plain area of Yangtze River, are of high void ratio, great water content, high compressibility and sensitive structure. These properties can easily lead to uneven settlements of the shield tunnels. As to the mining tunnels through the hilly area, the lining structure can be uplifted by the groundwater gradually when the groundwater exceeds the normal water table. As a result, the operation of metro tunnels can be disrupted seriously. This study fosters the understanding of the deformation of metro tunnels from the engineering geological perspective, and offers a theoretical basis to monitor and control the deformation and ensuring the safety of the tunnels in operating.
2017, 25(1): 209-214.
In the platform of FLAC3D software, how to build the three-dimensional models of complex geological bodies is always a difficulty encountered by many numerical simulation operators. On the other hand, the three-dimensional laser scanning technique presents a unique advantage in obtaining the fine spatial data of complex objects. Therefore, by the aid of reverse engineering, a new modeling method of complex geological bodies in FLAC3D platform is proposed. The accurate spatial and geometric information of complex geological bodies is firstly obtained by employing three-dimensional laser scanning technique. The point cloud data describing surface characteristics of complex geological bodies is processed and its surface model is then reconstructed in CAD format. Using the formidable geometry cleanup and mesh generation function of Hypermesh software, the surface model is transformed into three-dimensional finite element model. The node and element information can be translated into the format which can be received by FLAC3D. According to the above processes, the model data for FLAC3D is generated and the refined model of complex geological bodies is created in the pre-processing of FLAC3D.the feasibility and practicability of this approach is verified by combining practical project.
In the platform of FLAC3D software, how to build the three-dimensional models of complex geological bodies is always a difficulty encountered by many numerical simulation operators. On the other hand, the three-dimensional laser scanning technique presents a unique advantage in obtaining the fine spatial data of complex objects. Therefore, by the aid of reverse engineering, a new modeling method of complex geological bodies in FLAC3D platform is proposed. The accurate spatial and geometric information of complex geological bodies is firstly obtained by employing three-dimensional laser scanning technique. The point cloud data describing surface characteristics of complex geological bodies is processed and its surface model is then reconstructed in CAD format. Using the formidable geometry cleanup and mesh generation function of Hypermesh software, the surface model is transformed into three-dimensional finite element model. The node and element information can be translated into the format which can be received by FLAC3D. According to the above processes, the model data for FLAC3D is generated and the refined model of complex geological bodies is created in the pre-processing of FLAC3D.the feasibility and practicability of this approach is verified by combining practical project.
2017, 25(1): 215-221.
Liquid CO2 phase transition characteristics and coal to gas phase CO2 and CH4adsorption regularity are researched. Experiment finds out that under different coal quality, temperature and equilibrium pressure, the adsorption ability of CO2 in coking coal and anthracite coal is as 1.8~2.4 times to that of CH4. The volume of CO2 phase transition expands to 794 times instantaneously within 0.2 s. Theoretical studies are carried out to establish a mathematical model for the non-coupling fracturing under the condition of blasting hole initial shock pressure peak, fissured circle effective radius and blasting induced cracking borehole three main blasting parameters. Blasting machine is used and has 200MPa outlet pressure when the liquid CO2 phase transition instantaneously. According to on-site experiment research of the coal seam, its permeability improvement leads to bursting. The control hole has 2m and 3m distance to the blasting hole. After blasting the one drilling gas extraction from scalar increases up to 6 times and 4 times, the one drilling gas extraction concentration up to 5 times and 4 times. The one drilling gas extraction concentration is in 35%~55%.The control hole has 4m distance from the blasting hole after five days, the gas extraction effect attenuates to the level before blasting. The field test shows that under the initial impact pressure peak value of 200MPa and the borehole diameter of 0.094m, the effective radius of the fracture zone of the coal seam is 3m.
Liquid CO2 phase transition characteristics and coal to gas phase CO2 and CH4adsorption regularity are researched. Experiment finds out that under different coal quality, temperature and equilibrium pressure, the adsorption ability of CO2 in coking coal and anthracite coal is as 1.8~2.4 times to that of CH4. The volume of CO2 phase transition expands to 794 times instantaneously within 0.2 s. Theoretical studies are carried out to establish a mathematical model for the non-coupling fracturing under the condition of blasting hole initial shock pressure peak, fissured circle effective radius and blasting induced cracking borehole three main blasting parameters. Blasting machine is used and has 200MPa outlet pressure when the liquid CO2 phase transition instantaneously. According to on-site experiment research of the coal seam, its permeability improvement leads to bursting. The control hole has 2m and 3m distance to the blasting hole. After blasting the one drilling gas extraction from scalar increases up to 6 times and 4 times, the one drilling gas extraction concentration up to 5 times and 4 times. The one drilling gas extraction concentration is in 35%~55%.The control hole has 4m distance from the blasting hole after five days, the gas extraction effect attenuates to the level before blasting. The field test shows that under the initial impact pressure peak value of 200MPa and the borehole diameter of 0.094m, the effective radius of the fracture zone of the coal seam is 3m.
2017, 25(1): 222-229.
Water absorption experiments are carried out on three different types of surrounding rocks collected from Mogao Grottoes at Dunhuang. It uses a self-developed intelligent water absorption equipment. Its objective is to investigate their water absorption characteristics and underlying key influencing factors. The water absorption characteristics of the three types of rocks are analyzed and compared based on their water absorption curves obtained from the water absorption experiments. Meanwhile, the mineral components, microstructure features and pore structure parameters are determined by multiple means of X-ray diffraction, scanning electron microscopy and mercury intrusion porosimetry. Finally, the effects of clay minerals and micropore structure on water absorption of the investigated three typical rocks from Mogao Grottoes are comprehensively discussed. Results show that the patterns of the water absorption curves of the three types of rocks are very similar and all characterized by a similar kind of dynamic process with decreasing water absorption rate that can be well fitted by a negative exponential function. However, significant differences are found in water absorption ability among the three types of rock samples which can be sorted in an order of black sandstone > mudstone > siltstone. Finally, it concludes that for the three different types of rock samples investigated in this study, the content of clay minerals (mainly illite) is not the main factor restricting its water absorption, whereas the key factor determining the water-absorption capacity and rate is the pore structure especially porosity.
Water absorption experiments are carried out on three different types of surrounding rocks collected from Mogao Grottoes at Dunhuang. It uses a self-developed intelligent water absorption equipment. Its objective is to investigate their water absorption characteristics and underlying key influencing factors. The water absorption characteristics of the three types of rocks are analyzed and compared based on their water absorption curves obtained from the water absorption experiments. Meanwhile, the mineral components, microstructure features and pore structure parameters are determined by multiple means of X-ray diffraction, scanning electron microscopy and mercury intrusion porosimetry. Finally, the effects of clay minerals and micropore structure on water absorption of the investigated three typical rocks from Mogao Grottoes are comprehensively discussed. Results show that the patterns of the water absorption curves of the three types of rocks are very similar and all characterized by a similar kind of dynamic process with decreasing water absorption rate that can be well fitted by a negative exponential function. However, significant differences are found in water absorption ability among the three types of rock samples which can be sorted in an order of black sandstone > mudstone > siltstone. Finally, it concludes that for the three different types of rock samples investigated in this study, the content of clay minerals (mainly illite) is not the main factor restricting its water absorption, whereas the key factor determining the water-absorption capacity and rate is the pore structure especially porosity.
2017, 25(1): 230-236.
High-density resistivity method is effective in searching for water in karst areas. Due to complex topography condition in karst area, the high density resistivity method can be greatly influenced by the terrain fluctuation. In order to improve the prospecting its effect in water exploration, and mastering the regularity of the influence of the terrain fluctuation, this work uses a high-density micro-electrical measurement system and the copper cylinder model to simulate the karst pipe underground. It then studies the influence of terrain fluctuation on the high density resistivity method to detect the karst pipes. The results indicate that high density composite profile method and α2 device are greatly influenced by the valley topography. False low resistance anomaly can be easily appeared in the middle valley. Rectangular AMN and rolling MNB device are less affected by terrain. The exploration depth of high density resistivity method about the anomaly can be reduced by the valley topography. When the electrode spacing is fixed, the top depth of the inversion about the flat model and valley model is less than the true anomaly, but the transverse width is greater than the true anomaly. Otherwise, the top depth the inversion about the flat model is greater than the valley model, the transverse width of the inversion about the flat model is less than the valley model.
High-density resistivity method is effective in searching for water in karst areas. Due to complex topography condition in karst area, the high density resistivity method can be greatly influenced by the terrain fluctuation. In order to improve the prospecting its effect in water exploration, and mastering the regularity of the influence of the terrain fluctuation, this work uses a high-density micro-electrical measurement system and the copper cylinder model to simulate the karst pipe underground. It then studies the influence of terrain fluctuation on the high density resistivity method to detect the karst pipes. The results indicate that high density composite profile method and α2 device are greatly influenced by the valley topography. False low resistance anomaly can be easily appeared in the middle valley. Rectangular AMN and rolling MNB device are less affected by terrain. The exploration depth of high density resistivity method about the anomaly can be reduced by the valley topography. When the electrode spacing is fixed, the top depth of the inversion about the flat model and valley model is less than the true anomaly, but the transverse width is greater than the true anomaly. Otherwise, the top depth the inversion about the flat model is greater than the valley model, the transverse width of the inversion about the flat model is less than the valley model.
2017, 25(1): 237-245.
Based on the system investigation and mapping of loess engineering slope protection in the areas of Baoji, Shanxi Province, the prevalent problem of prevention and mitigation failure of anti-sliding retaining wall is studied. In this paper, three anti-sliding retaining wall failure modes, loess mud over wall, shear failure and "retaining wall traveling by ship", are put forward. To analyze the relationship between modes and different mechanisms, the authors conducted a loess soil mechanics test and calculated the landslide thrust using the limit equilibrium mehtod with the Lingnan landslide as an example. The results show that:(1) Both engineering slope cutting and rainfall cause slopes instability. (2) Imperfect slope drainage system, incompact surface soil, rainfall and local existence water depression are the leading cause of loess mud flow disaster. The burial depth of anti-sliding retaining wall foundation is the main reason of retaining wall traveling by ship. (3) Finally, the article discusses how to solve the problem of prevention and mitigation failure of anti-sliding retaining wall of loess engineering slope.
Based on the system investigation and mapping of loess engineering slope protection in the areas of Baoji, Shanxi Province, the prevalent problem of prevention and mitigation failure of anti-sliding retaining wall is studied. In this paper, three anti-sliding retaining wall failure modes, loess mud over wall, shear failure and "retaining wall traveling by ship", are put forward. To analyze the relationship between modes and different mechanisms, the authors conducted a loess soil mechanics test and calculated the landslide thrust using the limit equilibrium mehtod with the Lingnan landslide as an example. The results show that:(1) Both engineering slope cutting and rainfall cause slopes instability. (2) Imperfect slope drainage system, incompact surface soil, rainfall and local existence water depression are the leading cause of loess mud flow disaster. The burial depth of anti-sliding retaining wall foundation is the main reason of retaining wall traveling by ship. (3) Finally, the article discusses how to solve the problem of prevention and mitigation failure of anti-sliding retaining wall of loess engineering slope.
2017, 25(1): 246-256.
From October 13 to 21, 2016, the 10th Congress of Engineering Geology of China was successfully held in Chengdu, Sichuan Province, China. It was participated by nearly 1, 500 delegates. It is the first time for the Congress to have had more than one thousand participants. The Congress set up six sub-venues, one special lecture and one youth-exclusive lecture. The topics include transportation, energy, ocean, city and other major engineering geology problems in the One Belt and One Road Initiative, new theories and technology of engineering geology, education and development of engineering geology. It had 21 specially invited reports, 58 keynote reports, 220 group reports and 19 youth-exclusive reports. It provided a board platform for domestic and foreign experts to communicate with each other widely and deeply. This Congress demonstrated the rich achievements of engineering geology fundamental research in China, embodied the innovative and practical application of engineering geological technology, and highlighted the development of engineering practice which serves for the national strategy and sprints to difficulties and hotspots. China's engineering geology is developing prosperously, and making more and more international influence.
From October 13 to 21, 2016, the 10th Congress of Engineering Geology of China was successfully held in Chengdu, Sichuan Province, China. It was participated by nearly 1, 500 delegates. It is the first time for the Congress to have had more than one thousand participants. The Congress set up six sub-venues, one special lecture and one youth-exclusive lecture. The topics include transportation, energy, ocean, city and other major engineering geology problems in the One Belt and One Road Initiative, new theories and technology of engineering geology, education and development of engineering geology. It had 21 specially invited reports, 58 keynote reports, 220 group reports and 19 youth-exclusive reports. It provided a board platform for domestic and foreign experts to communicate with each other widely and deeply. This Congress demonstrated the rich achievements of engineering geology fundamental research in China, embodied the innovative and practical application of engineering geological technology, and highlighted the development of engineering practice which serves for the national strategy and sprints to difficulties and hotspots. China's engineering geology is developing prosperously, and making more and more international influence.
2017, 25(1): 36-42.
The study on strength theory of unsaturated soil and the determination of related parameters are the core of the research in unsaturated soil mechanics. At present, Bishop's single-variable strength theory, Fredlund's double-variables strength theory, and Lu Ning's suction stress strength theory are generally accepted. Lu Ning introduced the concept of suction stress and the suction stress characteristic curve(the relationship between the suction stress and the volumetric water content).This theory avoids the determination of matric suction and it is convenient for widely promotion in engineering practice. This paper tests the effective strength parameters based on the conventional triaxial CD test with different water contents. Results show that the effective internal friction angles with different water contents are basically same. The effective cohesion increases with the water content. When the water content increases to the plastic water content, the cohesion reaches a constant value. According to the relationship between effective cohesion and the stress suction, suction stress characteristic curve can be obtained and then fit the stress suction function. The function can explain unsaturated strength combined with the effective internal friction angle and saturated effective cohesion.
The study on strength theory of unsaturated soil and the determination of related parameters are the core of the research in unsaturated soil mechanics. At present, Bishop's single-variable strength theory, Fredlund's double-variables strength theory, and Lu Ning's suction stress strength theory are generally accepted. Lu Ning introduced the concept of suction stress and the suction stress characteristic curve(the relationship between the suction stress and the volumetric water content).This theory avoids the determination of matric suction and it is convenient for widely promotion in engineering practice. This paper tests the effective strength parameters based on the conventional triaxial CD test with different water contents. Results show that the effective internal friction angles with different water contents are basically same. The effective cohesion increases with the water content. When the water content increases to the plastic water content, the cohesion reaches a constant value. According to the relationship between effective cohesion and the stress suction, suction stress characteristic curve can be obtained and then fit the stress suction function. The function can explain unsaturated strength combined with the effective internal friction angle and saturated effective cohesion.
2017, 25(1): 95-101.
This paper aims to explore the effects of different grille intensities to the variation of pile-soil stress ratio of pile-net composite foundations. On the basis of pile-net composite working mechanism foundation, it derives analytically the pile-soil stress ratio. Then it takes the net composite foundation of Ganlong(Ganzhou-Longyan) and Harbin-Dalian(Harbin-Dalian) high-speed rail piles as an engineering examples. It carries out a comparative analysis of the measured data from the pile under the grille strength 100kN·m-1 and 300kN·m-1 conditions to understand the pile-soil stress ratio variation. Finally it establishes a three-dimensional numerical model and further analyses the pile-soil stress ratio variation for the grid strength between 100kN·m-1~400kN·m-1. The results show that:as the grid strength increases from 100kN·m-1 to 300kN·m-1, the pile-soil stress ratio increased considerably. When the grid intensity exceeds 300kN·m-1, the pile-soil stress ratio increases to a lesser extent. By considering the characteristics of the greatest contribution composite foundation bearing, it is recommended to select the grid strength 200kN·m-1~300kN·m-1. Under this condition, the pile-soil stress ratio is from 3.8 to 4.5.
This paper aims to explore the effects of different grille intensities to the variation of pile-soil stress ratio of pile-net composite foundations. On the basis of pile-net composite working mechanism foundation, it derives analytically the pile-soil stress ratio. Then it takes the net composite foundation of Ganlong(Ganzhou-Longyan) and Harbin-Dalian(Harbin-Dalian) high-speed rail piles as an engineering examples. It carries out a comparative analysis of the measured data from the pile under the grille strength 100kN·m-1 and 300kN·m-1 conditions to understand the pile-soil stress ratio variation. Finally it establishes a three-dimensional numerical model and further analyses the pile-soil stress ratio variation for the grid strength between 100kN·m-1~400kN·m-1. The results show that:as the grid strength increases from 100kN·m-1 to 300kN·m-1, the pile-soil stress ratio increased considerably. When the grid intensity exceeds 300kN·m-1, the pile-soil stress ratio increases to a lesser extent. By considering the characteristics of the greatest contribution composite foundation bearing, it is recommended to select the grid strength 200kN·m-1~300kN·m-1. Under this condition, the pile-soil stress ratio is from 3.8 to 4.5.
2017, 25(1): 139-146.
Geological disasters such as slope failure, caused by earthquake, are very common in meizoseismal area. The dual structure slope is composed of underlying rock mass and overlying soil mass. The seismic responses of dual structure slope with anchor-frame reinforcement remain unclear. Based on the prototype slope with dual structure at the ZK132+300 of Fuyong Expressway, a 1/20 downscale model slope is designed and built. Shaking table tests with 20 loading cases are then conducted in the key laboratory of disaster prevention of Fujian Province. The influences of slope elevation, seismic wave amplitude and seismic wave spectrum on the PGA amplification coefficients are focused in this article. Some conclusions can be drawn as follows. The PGA amplification coefficients inside and upon the slope increase with the slope elevation and magnify dramatically at the top of slope. The anchor-frame support restrains the PGA amplification coefficients upon the slope, comparing with their counterparts inside the slope. Due to the plasticity of soil, the PGA amplification coefficients decease linearly or exponentially with the seismic wave amplitude. Excited by the seismic waves with same amplitude and different spectrums, there exists some difference among the PGA amplification coefficients upon the slope. However, the distinction due to seismic wave spectrum fades away with the slope elevation and vanishes at the top of slope. The failure characteristic of model slope during shaking table tests is carefully inspected and described. The cracks only occur near the free face of slope top and slope shoulder, and no interconnected crack and overall instability occur during tests. It is concluded that the anchor-frame reinforcement can improve the seismic performance of soil slope significantly.
Geological disasters such as slope failure, caused by earthquake, are very common in meizoseismal area. The dual structure slope is composed of underlying rock mass and overlying soil mass. The seismic responses of dual structure slope with anchor-frame reinforcement remain unclear. Based on the prototype slope with dual structure at the ZK132+300 of Fuyong Expressway, a 1/20 downscale model slope is designed and built. Shaking table tests with 20 loading cases are then conducted in the key laboratory of disaster prevention of Fujian Province. The influences of slope elevation, seismic wave amplitude and seismic wave spectrum on the PGA amplification coefficients are focused in this article. Some conclusions can be drawn as follows. The PGA amplification coefficients inside and upon the slope increase with the slope elevation and magnify dramatically at the top of slope. The anchor-frame support restrains the PGA amplification coefficients upon the slope, comparing with their counterparts inside the slope. Due to the plasticity of soil, the PGA amplification coefficients decease linearly or exponentially with the seismic wave amplitude. Excited by the seismic waves with same amplitude and different spectrums, there exists some difference among the PGA amplification coefficients upon the slope. However, the distinction due to seismic wave spectrum fades away with the slope elevation and vanishes at the top of slope. The failure characteristic of model slope during shaking table tests is carefully inspected and described. The cracks only occur near the free face of slope top and slope shoulder, and no interconnected crack and overall instability occur during tests. It is concluded that the anchor-frame reinforcement can improve the seismic performance of soil slope significantly.
2017, 25(1): 147-153.
Heifangtai is located in Yongjing County, Gansu province. The loess landslide is very developed due to irrigation. One of the most typical landslides is the gradual retreat of the loess landslide caused by long-term irrigation. This paper compares the Google images and the field survey of representative landslide occurred in recent years. It shows that the loess landslides have the characteristics of gradual recession. It further investigates and analyze the water content of the loess landslide profile. It finds that the main reason for loess landslide occurred continuously are soft base effect formed by long-term soaking of groundwater. The arc groove of the landslide often becomes the concentration of groundwater and drainage points. The residual landslide accumulation in slide source area rises the local underground water. It is the main reason to make the same position more and more gradual retreat type landslide.
Heifangtai is located in Yongjing County, Gansu province. The loess landslide is very developed due to irrigation. One of the most typical landslides is the gradual retreat of the loess landslide caused by long-term irrigation. This paper compares the Google images and the field survey of representative landslide occurred in recent years. It shows that the loess landslides have the characteristics of gradual recession. It further investigates and analyze the water content of the loess landslide profile. It finds that the main reason for loess landslide occurred continuously are soft base effect formed by long-term soaking of groundwater. The arc groove of the landslide often becomes the concentration of groundwater and drainage points. The residual landslide accumulation in slide source area rises the local underground water. It is the main reason to make the same position more and more gradual retreat type landslide.
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