2018 Vol. 26, No. 6

Others
PFC2D code is used to simulate the direct shear tests of rockfills, taking into consideration of the particle crushing. The methods to establish the model of the rockfill sample and conduct the tests are given. The results obtained from the numerical simulation are analyzed from several aspects, such as the characteristics of stress-strain relationship, volume strain and shear strength. The effect of the contact-bond strength between basic particles, the porosity of the single rock particle and the porosity of the rockfill material on the shear strength of the rockfills are also discussed. PFC2D code is used to simulate the direct shear tests of rockfills, taking into consideration of the particle crushing. The methods to establish the model of the rockfill sample and conduct the tests are given. The results obtained from the numerical simulation are analyzed from several aspects, such as the characteristics of stress-strain relationship, volume strain and shear strength. The effect of the contact-bond strength between basic particles, the porosity of the single rock particle and the porosity of the rockfill material on the shear strength of the rockfills are also discussed.
A series of gas permeability and saturated penetration tests on Malan loess are accomplished by using the improved ZC-2015 air permeameter and TST-55 permeameter. We obtain two permeability parameters of gas permeability ka and saturation permeability coefficient Kw respectively. The void ratio e is acquired by laboratory normal experiment. And the planar void ratio e0 is obtained from electron microscopy(SEM)which is analyzed by image-pro plus(IPP). Then combining with the test results and using mathematical model, the relationship between macroscopic and microcosmic pore parameters and infiltration parameters are established. The results show that dry density of remolded soils increases, the number of particles per unit volume increases, porosity area decreases. The buried depth of undisturbed dry loess samples increases. Soil pore area and pore number, the average pore diameter of macropores and mesopores in loess significantly decrease. The semi-logarithmic linear model can eliminate the magnitude difference between Kw, ka and the pore structure parameters, and the fitting results is better. lgKw and lgka with e, e0 show a good linear relationships. When the water content changes, the regulation of slope and intercept about the gas permeability fit lines change obviously. Due to uniform sample preparation, fitting curves of remolded soils show the high fitting degree. Comparing with the remolded loess, fitting degree of undisturbed loess in different depth is low because of structural difference of deposition process. A series of gas permeability and saturated penetration tests on Malan loess are accomplished by using the improved ZC-2015 air permeameter and TST-55 permeameter. We obtain two permeability parameters of gas permeability ka and saturation permeability coefficient Kw respectively. The void ratio e is acquired by laboratory normal experiment. And the planar void ratio e0 is obtained from electron microscopy(SEM)which is analyzed by image-pro plus(IPP). Then combining with the test results and using mathematical model, the relationship between macroscopic and microcosmic pore parameters and infiltration parameters are established. The results show that dry density of remolded soils increases, the number of particles per unit volume increases, porosity area decreases. The buried depth of undisturbed dry loess samples increases. Soil pore area and pore number, the average pore diameter of macropores and mesopores in loess significantly decrease. The semi-logarithmic linear model can eliminate the magnitude difference between Kw, ka and the pore structure parameters, and the fitting results is better. lgKw and lgka with e, e0 show a good linear relationships. When the water content changes, the regulation of slope and intercept about the gas permeability fit lines change obviously. Due to uniform sample preparation, fitting curves of remolded soils show the high fitting degree. Comparing with the remolded loess, fitting degree of undisturbed loess in different depth is low because of structural difference of deposition process.
From a geotechnical perspective, residual soil derived from the mudstone in Zimbabwe is often viewed as a regional problematic soil, indicating that their behavior can deviate from traditional rules of soil behavior. Thus it appears especially important to accurately assess its engineering characteristics, which can provide theoretical guidance to engineering investigation and construction. In this study, a laboratory study is conducted to investigate the physical and mechanical properties of the soils, and then the special characteristics in mechanics are explained from the aspects of mineral composition, chemical components, and microstructures. The results show that this residual soil is termed hard clayey soil with low expansibility and compaction. For undisturbed soil, it is unsaturated and possessed the high strength because of structural strength inherited from parent rock. The soil shows an aggregate structure which contains a highly orientated kaolin aggregation and many fissures according to the result of SEM. In addition, the ferrous cementing effect can result in a high strength between the aggregations, which is monitored. Because of strong water sensitivity and disintegration, the cohesion can be remarkably reduced after soaking and the internal friction angle can also be reduced under wetting and drying cycle. The high collapsible deformation is not founded. Therefore, geotechnical engineers should pay close attention to engineering disasters due to meteoric water. From a geotechnical perspective, residual soil derived from the mudstone in Zimbabwe is often viewed as a regional problematic soil, indicating that their behavior can deviate from traditional rules of soil behavior. Thus it appears especially important to accurately assess its engineering characteristics, which can provide theoretical guidance to engineering investigation and construction. In this study, a laboratory study is conducted to investigate the physical and mechanical properties of the soils, and then the special characteristics in mechanics are explained from the aspects of mineral composition, chemical components, and microstructures. The results show that this residual soil is termed hard clayey soil with low expansibility and compaction. For undisturbed soil, it is unsaturated and possessed the high strength because of structural strength inherited from parent rock. The soil shows an aggregate structure which contains a highly orientated kaolin aggregation and many fissures according to the result of SEM. In addition, the ferrous cementing effect can result in a high strength between the aggregations, which is monitored. Because of strong water sensitivity and disintegration, the cohesion can be remarkably reduced after soaking and the internal friction angle can also be reduced under wetting and drying cycle. The high collapsible deformation is not founded. Therefore, geotechnical engineers should pay close attention to engineering disasters due to meteoric water.
Hydraulic conductivity is an important parameter to describe the permeability characterization of fractured rock mass. It is often determined using the water pressure tests of borehole in hydraulic and hydro-power engineering. When the water pressure is very low, the permeability variation of rock mass is not obvious owing to its integrity and strength. But under high water pressure, its permeability would change obviously. The main reasons are that fractured apertures can be increased, some close fractures may be re-opened, and the small and unconnected fractures are penetrated between each other under the action of high water pressure. Changes of permeability would lead to some difficulties for seepage analysis, because hydraulic conductivity is often considered to be constant. The calculated hydraulic head and flux have great errors if the variation of permeability coefficient hasn't been considered. On the condition of high water pressure, the relationship between hydraulic conductivity of fractured rock mass and water pressure is deduced according to the Non-Darcy flow equation in this paper. Three equations for calculating hydraulic conductivity are provided here. The first equation is applied to the condition for low water pressure. The results of field water pressure test show that when the hydraulic fracturing of rock mass occurs, hydraulic conductivity increases obviously. It can be calculated through the variation of water flux and water pressure. In this paper, variation characteristics of permeability coefficient before and after hydraulic fracturing are verified using the results of high pressure water test from pumped storage power stations. Field test results are used to calculate hydraulic conductivity of rock mass. A comparison is conducted for measured and calculated hydraulic conductivity values to validate the rationality of deduced equation. The errors between measured and calculated values are less than 15 percent and the average error is about 10 percent, which show the calculated hydraulic conductivity is basically in agreement with measured value. Expressions of hydraulic conductivity provide selection criteria of seepage analysis for hydraulic and hydro-power engineering or large deep tunnel project. Hydraulic conductivity is an important parameter to describe the permeability characterization of fractured rock mass. It is often determined using the water pressure tests of borehole in hydraulic and hydro-power engineering. When the water pressure is very low, the permeability variation of rock mass is not obvious owing to its integrity and strength. But under high water pressure, its permeability would change obviously. The main reasons are that fractured apertures can be increased, some close fractures may be re-opened, and the small and unconnected fractures are penetrated between each other under the action of high water pressure. Changes of permeability would lead to some difficulties for seepage analysis, because hydraulic conductivity is often considered to be constant. The calculated hydraulic head and flux have great errors if the variation of permeability coefficient hasn't been considered. On the condition of high water pressure, the relationship between hydraulic conductivity of fractured rock mass and water pressure is deduced according to the Non-Darcy flow equation in this paper. Three equations for calculating hydraulic conductivity are provided here. The first equation is applied to the condition for low water pressure. The results of field water pressure test show that when the hydraulic fracturing of rock mass occurs, hydraulic conductivity increases obviously. It can be calculated through the variation of water flux and water pressure. In this paper, variation characteristics of permeability coefficient before and after hydraulic fracturing are verified using the results of high pressure water test from pumped storage power stations. Field test results are used to calculate hydraulic conductivity of rock mass. A comparison is conducted for measured and calculated hydraulic conductivity values to validate the rationality of deduced equation. The errors between measured and calculated values are less than 15 percent and the average error is about 10 percent, which show the calculated hydraulic conductivity is basically in agreement with measured value. Expressions of hydraulic conductivity provide selection criteria of seepage analysis for hydraulic and hydro-power engineering or large deep tunnel project.
Soil moisture content has a great influence on the strength, deformation and permeability of soils. How to measure soil moisture content rapidly is an important subject in foundation engineering. Aiming at the problems such as poor real-time ability in existing measurements, a new method based on fiber Bragg grating(FBG)technique for rapid determination of soil moisture content is proposed in this paper. By using free-fall balls, impact loads are applied to FBG strain sensors embedded in sandy soil. The strains and their variation of sensors in this process are measured. Based on the analysis of the variation of strain, the concept of peak strain is introduced. By controlling variable method, an indoor test on sandy soil is carried out under the condition of different moisture contents. The experimental results show that peak strain decreases with increasing of moisture content. There is a nearly linear relationship between the moisture content and the peak strain. Therefore, soil moisture content can be estimated by an empirical calculation formula. The possible errors in the method are analyzed, and the methods for reducing errors are given. Soil moisture content has a great influence on the strength, deformation and permeability of soils. How to measure soil moisture content rapidly is an important subject in foundation engineering. Aiming at the problems such as poor real-time ability in existing measurements, a new method based on fiber Bragg grating(FBG)technique for rapid determination of soil moisture content is proposed in this paper. By using free-fall balls, impact loads are applied to FBG strain sensors embedded in sandy soil. The strains and their variation of sensors in this process are measured. Based on the analysis of the variation of strain, the concept of peak strain is introduced. By controlling variable method, an indoor test on sandy soil is carried out under the condition of different moisture contents. The experimental results show that peak strain decreases with increasing of moisture content. There is a nearly linear relationship between the moisture content and the peak strain. Therefore, soil moisture content can be estimated by an empirical calculation formula. The possible errors in the method are analyzed, and the methods for reducing errors are given.
Study on secondary consolidation characteristics and mechanism of structured loess has become an effective means of calculating and controlling post-construction settlement in loess high fill foundation. In this paper, the secondary consolidation characteristics and deformation mechanism are studied by means of compression test of structured loess. Then the formula describing the time effect of secondary settlement coefficient is established. The test results show that an obvious secondary-consolidation effect exists in structured loess. The load coefficient of secondary consolidation curve(P-Cα)increases first and then decreases, and it finally tends to be stable. The peak of Cα corresponding to the loading value is greater than Pc. High stress loads are not major controlling factor of the secondary consolidation coefficient. The influence mechanism of load and water content on secondary settlement coefficient is analyzed based on geotechnical mechanics. The P-Cα curve of structured loess in high water content only decreases and tends to be a stable period by weakening effect of water on soil particles. Establishing the formula describing the time effect of secondary settlement coefficient can provide help for post-construction calculation of the covered original loess foundation in high fill engineering. Study on secondary consolidation characteristics and mechanism of structured loess has become an effective means of calculating and controlling post-construction settlement in loess high fill foundation. In this paper, the secondary consolidation characteristics and deformation mechanism are studied by means of compression test of structured loess. Then the formula describing the time effect of secondary settlement coefficient is established. The test results show that an obvious secondary-consolidation effect exists in structured loess. The load coefficient of secondary consolidation curve(P-Cα)increases first and then decreases, and it finally tends to be stable. The peak of Cα corresponding to the loading value is greater than Pc. High stress loads are not major controlling factor of the secondary consolidation coefficient. The influence mechanism of load and water content on secondary settlement coefficient is analyzed based on geotechnical mechanics. The P-Cα curve of structured loess in high water content only decreases and tends to be a stable period by weakening effect of water on soil particles. Establishing the formula describing the time effect of secondary settlement coefficient can provide help for post-construction calculation of the covered original loess foundation in high fill engineering.
This paper aims to study the density, strength and deformation characteristics of soil and EPS particles mixtures that is a type of light weight soil. It carried out the density tests and unconfined compressive strength tests of the mixed soil with different cement content, EPS content, age and water content. The results show the following findings. When volume ratio of EPS particals is 20% to 60%, the density range of the light weight soil is about 0.64g·cm-3~1.46g·cm-3. The amount of EPS particles has the greatest impact on the light weight soil density. When the volume rate of EPS particles is increased by 10%, the density of EPS particles light weight soil is decreased by about 0.15g·cm-3~0.23g·cm-3, which shows that it is feasible to realize the light weight of mixed soil by adding EPS particles. Cement content and water content have less influence on density of light weight soil. But age has little effect on density of light weight soil. In addition, when the volume ratio of EPS is 50%, the density of light weight soil is similar to that of water. The range of unconfined compressive strength of EPS particles light weight soil in this test is 103.2 kPa~1359.0 kPa, while the unconfined compressive strength of plain soil is 79.98 kPa. So it can be stated that the light soil in the proportioning of this test has better strength properties relative to the plain soil. The unconfined compressive strength of light weight soil increases exponentially with the increase of cement content. However, the larger the volume ratio of EPS particles, the smaller the unconfined compressive strength and the linear relationship between them. In the case of more than the optimal water content, with the increase of water content, the relationship between the unconfined compressive strength is reduced exponentially. The increase of age makes the unconfined compressive strength increase in hyperbolic form. The stress-strain relationship characteristics of EPS particles light weight soil are mainly characterized by strain softening type. However, the increase of water content and the increase of the content of EPS particles can make the stress-strain relationship curves of the light weight soil change gradually to the hardening type. Damage strain and average deformation model are used to describe the deformation characteristics of soil. The damage strain of light weight soil decreases with the increase of cement content, but the volume ratio of EPS particle is opposite. The greater the water content, the greater the damage strain of light weight soil. However, the increase of the age makes the damage strain of the sample decrease. When the volume ratio of EPS particles is more than 50%, the damage strain of light weight soil is greatly increased, and its brittleness is obviously weakened. The average deformation modulus is a parameter to characterize the stiffness of EPS particles light weight soil. The larger the cement content, the larger the average deformation modulus of light weight soil. However, the average deformation modulus of light weight soil decreases linearly with the increase of the volume ratio of EPS particles. The increase of water content can reduce the stiffness of light weight soil, and the longer the age, the greater the stiffness. This paper aims to study the density, strength and deformation characteristics of soil and EPS particles mixtures that is a type of light weight soil. It carried out the density tests and unconfined compressive strength tests of the mixed soil with different cement content, EPS content, age and water content. The results show the following findings. When volume ratio of EPS particals is 20% to 60%, the density range of the light weight soil is about 0.64g·cm-3~1.46g·cm-3. The amount of EPS particles has the greatest impact on the light weight soil density. When the volume rate of EPS particles is increased by 10%, the density of EPS particles light weight soil is decreased by about 0.15g·cm-3~0.23g·cm-3, which shows that it is feasible to realize the light weight of mixed soil by adding EPS particles. Cement content and water content have less influence on density of light weight soil. But age has little effect on density of light weight soil. In addition, when the volume ratio of EPS is 50%, the density of light weight soil is similar to that of water. The range of unconfined compressive strength of EPS particles light weight soil in this test is 103.2 kPa~1359.0 kPa, while the unconfined compressive strength of plain soil is 79.98 kPa. So it can be stated that the light soil in the proportioning of this test has better strength properties relative to the plain soil. The unconfined compressive strength of light weight soil increases exponentially with the increase of cement content. However, the larger the volume ratio of EPS particles, the smaller the unconfined compressive strength and the linear relationship between them. In the case of more than the optimal water content, with the increase of water content, the relationship between the unconfined compressive strength is reduced exponentially. The increase of age makes the unconfined compressive strength increase in hyperbolic form. The stress-strain relationship characteristics of EPS particles light weight soil are mainly characterized by strain softening type. However, the increase of water content and the increase of the content of EPS particles can make the stress-strain relationship curves of the light weight soil change gradually to the hardening type. Damage strain and average deformation model are used to describe the deformation characteristics of soil. The damage strain of light weight soil decreases with the increase of cement content, but the volume ratio of EPS particle is opposite. The greater the water content, the greater the damage strain of light weight soil. However, the increase of the age makes the damage strain of the sample decrease. When the volume ratio of EPS particles is more than 50%, the damage strain of light weight soil is greatly increased, and its brittleness is obviously weakened. The average deformation modulus is a parameter to characterize the stiffness of EPS particles light weight soil. The larger the cement content, the larger the average deformation modulus of light weight soil. However, the average deformation modulus of light weight soil decreases linearly with the increase of the volume ratio of EPS particles. The increase of water content can reduce the stiffness of light weight soil, and the longer the age, the greater the stiffness.
As a natural geologic disaster, soil landslide is affected by natural factors and human activities. It brings a great threat to the safety of the surrounding residents' life and property, attracting more worries from people. Landslide prevention and control are also one of the hot spots in engineering research. Soil is essentially a kind of deposits consists of granular material with complicated composition and structure. By means of numerical simulation of granular material flows, we can well understand the phenomena of soil flows in the nature, such as landslide and debris flows. It is therefore possible to predict the landslide hazard zone and to improve the design of engineering protection measurements. However, the finite element method(FEM) is not suitable for simulating soil flow with large deformation and large displacement due to the finite element method is sensitive to mesh distortion. In this paper, we simulate the soil flows using the material point method(MPM). MPM is a mesh-free method and originating from the particle-in-cell(PIC)method. It combines the Eulerian description and Lagrangian description and has distinct advantages in solving the large deformation and large displacement problem. Currently, there have been many studies on the simulation of slope sliding using MPM, but less attentions has paid to sensitivity analysis on relevant parameters. In this paper, the large deformations of the cohesive soil and the non-cohesive soil slopes due to gravity are numerically investigated with MPM.The influence of the internal friction angle, the cohesive force, the aspect ratio and bottom surface gradient on the landslide run-out are analysed. In this MPM simulation, the elasto-palstic constitutive models based on the Drucker-Prager(DP)yield criterion is used for modeling nonlinear characters of soil flows. The Drucker-Prager yield criterion is a pressure-dependent model for determining whether a material has failed or undergone plastic yielding. The yielding surface of the Drucker-Prager criterion may be considered depending on the internal friction angle of the material and its cohesion. The simulated results show the following featurs. (a) There are well agreements in the flow pattern, the sliding distance and natural angle of repose between the simulated results and the corresponding experimental results, which validates the ability of MPM to modeling soil flows. (b) The sliding distance decreases with the increase of the internal friction angle and cohesive force. (c) The steepness of the soil slope has significant influence on its stability. The sliding distance increases with the increase of the steepness of the soil slope. (d) For a comparatively small aspect ratio, the sliding distance increases linearly with aspect ratio. It is noteworthy that the internal friction angle and cohesive force of soil reflect its shear resistance. Therefore, the damage due to landslide can be reduced by improving the shear resistance of soil through engineering measurements. The results of the simulation provide a reliable reference to explore the law of the soil sliding hazardous behavior and reduce the sliding damage range. As a natural geologic disaster, soil landslide is affected by natural factors and human activities. It brings a great threat to the safety of the surrounding residents' life and property, attracting more worries from people. Landslide prevention and control are also one of the hot spots in engineering research. Soil is essentially a kind of deposits consists of granular material with complicated composition and structure. By means of numerical simulation of granular material flows, we can well understand the phenomena of soil flows in the nature, such as landslide and debris flows. It is therefore possible to predict the landslide hazard zone and to improve the design of engineering protection measurements. However, the finite element method(FEM) is not suitable for simulating soil flow with large deformation and large displacement due to the finite element method is sensitive to mesh distortion. In this paper, we simulate the soil flows using the material point method(MPM). MPM is a mesh-free method and originating from the particle-in-cell(PIC)method. It combines the Eulerian description and Lagrangian description and has distinct advantages in solving the large deformation and large displacement problem. Currently, there have been many studies on the simulation of slope sliding using MPM, but less attentions has paid to sensitivity analysis on relevant parameters. In this paper, the large deformations of the cohesive soil and the non-cohesive soil slopes due to gravity are numerically investigated with MPM.The influence of the internal friction angle, the cohesive force, the aspect ratio and bottom surface gradient on the landslide run-out are analysed. In this MPM simulation, the elasto-palstic constitutive models based on the Drucker-Prager(DP)yield criterion is used for modeling nonlinear characters of soil flows. The Drucker-Prager yield criterion is a pressure-dependent model for determining whether a material has failed or undergone plastic yielding. The yielding surface of the Drucker-Prager criterion may be considered depending on the internal friction angle of the material and its cohesion. The simulated results show the following featurs. (a) There are well agreements in the flow pattern, the sliding distance and natural angle of repose between the simulated results and the corresponding experimental results, which validates the ability of MPM to modeling soil flows. (b) The sliding distance decreases with the increase of the internal friction angle and cohesive force. (c) The steepness of the soil slope has significant influence on its stability. The sliding distance increases with the increase of the steepness of the soil slope. (d) For a comparatively small aspect ratio, the sliding distance increases linearly with aspect ratio. It is noteworthy that the internal friction angle and cohesive force of soil reflect its shear resistance. Therefore, the damage due to landslide can be reduced by improving the shear resistance of soil through engineering measurements. The results of the simulation provide a reliable reference to explore the law of the soil sliding hazardous behavior and reduce the sliding damage range.
Oil contamination in soil is instability and easy to migrate again under the action of environment. It then contaminates surrounding soil and even water. Experiments are undertaken on saline soil in inshore area. Variable parameters of pollution intensity, residual time of oil contamination in soil, and soil density are considered. Migration law of two-dimensional space under immediate filter and outdated filter condition are studied. Results indicate the following feature. (ⅰ) In the case of immediate filter condition, the migration depth of oil in saline soil is deeper with the increasing of oil contaminated lever, and the maximum migration depth is 6 cm. Dry density(1.2g·cm-3-1.4g·cm-3) has little effect on migration depth, but oil entrapment increases as dry density intensifies. The concentration of oil contamination on same depth is lower with the increasing dry density. As to horizontal direction, the concentration distribution of oil contamination decreases steeply with the increasing of oil contaminated lever and soil density. (ⅱ) In the case of outdated filter condition, the migration law of oil contamination in vertical direction is similar to that of immediate condition, but oil entrapment of soil surface enhances, and the maximum migration depth in saline soil is 4 cm. The maximum oil entrapment rate(0~2 cm) is 99.98%. In the horizontal direction, the concentration distribution of oil contamination decreases largely with the increasing of oil contaminated lever and the decreasing of soil density. Saline soil has good ability to adsorb oil contamination and can be improved by increasing soil density. Oil contamination in soil is instability and easy to migrate again under the action of environment. It then contaminates surrounding soil and even water. Experiments are undertaken on saline soil in inshore area. Variable parameters of pollution intensity, residual time of oil contamination in soil, and soil density are considered. Migration law of two-dimensional space under immediate filter and outdated filter condition are studied. Results indicate the following feature. (ⅰ) In the case of immediate filter condition, the migration depth of oil in saline soil is deeper with the increasing of oil contaminated lever, and the maximum migration depth is 6 cm. Dry density(1.2g·cm-3-1.4g·cm-3) has little effect on migration depth, but oil entrapment increases as dry density intensifies. The concentration of oil contamination on same depth is lower with the increasing dry density. As to horizontal direction, the concentration distribution of oil contamination decreases steeply with the increasing of oil contaminated lever and soil density. (ⅱ) In the case of outdated filter condition, the migration law of oil contamination in vertical direction is similar to that of immediate condition, but oil entrapment of soil surface enhances, and the maximum migration depth in saline soil is 4 cm. The maximum oil entrapment rate(0~2 cm) is 99.98%. In the horizontal direction, the concentration distribution of oil contamination decreases largely with the increasing of oil contaminated lever and the decreasing of soil density. Saline soil has good ability to adsorb oil contamination and can be improved by increasing soil density.
Based on one-dimensional consolidation theory of Terzaghi, this paper studies the one-dimensional consolidation problem of saturated soil layer with fractional viscoelastic model under symmetric semi-permeable boundaries subjected to arbitrary loading. By using the Laplace transform upon the one-dimensional consolidation equation of saturated soils and the fractional Kelvin-Voigt viscoelastic constitutive equation, the analytical solutions of effective stress and settlement in the Laplace transform domain are obtained. Crump's method is adopted to perform the inverse Laplace transform in order to obtain semi-analytical solutions in the time domain. It is shown that the present solution is reliable and in a good agreement with the existing solutions from literatures by reducing the proposed solution. Last, several numerical examples are provided to investigate the consolidation behavior of saturated soils with the fractional viscoelastic model under symmetric semi-permeable boundaries subjected to arbitrary loading. The results illustrate that, in the case of arbitrary loading, the consolidation rate is affected by the semi-permeable boundary parameters, fractional order, viscosity coefficient and load parameters. The final settlement of saturated soil layer is affected by the modulus of compressibility. In addition, the consolidation behavior of soil layer is consistent with the characteristics of loadings. Based on one-dimensional consolidation theory of Terzaghi, this paper studies the one-dimensional consolidation problem of saturated soil layer with fractional viscoelastic model under symmetric semi-permeable boundaries subjected to arbitrary loading. By using the Laplace transform upon the one-dimensional consolidation equation of saturated soils and the fractional Kelvin-Voigt viscoelastic constitutive equation, the analytical solutions of effective stress and settlement in the Laplace transform domain are obtained. Crump's method is adopted to perform the inverse Laplace transform in order to obtain semi-analytical solutions in the time domain. It is shown that the present solution is reliable and in a good agreement with the existing solutions from literatures by reducing the proposed solution. Last, several numerical examples are provided to investigate the consolidation behavior of saturated soils with the fractional viscoelastic model under symmetric semi-permeable boundaries subjected to arbitrary loading. The results illustrate that, in the case of arbitrary loading, the consolidation rate is affected by the semi-permeable boundary parameters, fractional order, viscosity coefficient and load parameters. The final settlement of saturated soil layer is affected by the modulus of compressibility. In addition, the consolidation behavior of soil layer is consistent with the characteristics of loadings.
The increasingly severe weathering erosion affects the stability of surrounding rocks and the preserving environment of wall paintings, which has become a great threat to the security of the grotto relics. A cliff located at the north of the Mogao grottoes is selected as the research site. The method of gradual dissection is adopted, and samples are numbered in sequence along the horizontal direction from the surface. A series of experiments are conducted and include size distribution test, field acoustic wave test, soluble salt test and X-Ray diffraction test. The results illustrate that the grain composition of the cliff have an effect on weather resistance. The curve of wave velocity fluctuates along the excavation depth. The content of sodium feldspar decreases within depth of 0.7 m as Quartz increases. As one of the main contribution to weathering of rock mass, soluble salts accumulate within the depth ranging from 0.4 m to 1.0 m. By comprehensive analysis on experimental results, depths in 1.0 m, 0.6 m and 0.4 m are respectively regarded as the weathering depths of No.1, No.2 and No.3 horizontal testing caves. As for the variation among cliff space, the heaviest weathering happening at upper part and weakest weathering lies at lower part. The increasingly severe weathering erosion affects the stability of surrounding rocks and the preserving environment of wall paintings, which has become a great threat to the security of the grotto relics. A cliff located at the north of the Mogao grottoes is selected as the research site. The method of gradual dissection is adopted, and samples are numbered in sequence along the horizontal direction from the surface. A series of experiments are conducted and include size distribution test, field acoustic wave test, soluble salt test and X-Ray diffraction test. The results illustrate that the grain composition of the cliff have an effect on weather resistance. The curve of wave velocity fluctuates along the excavation depth. The content of sodium feldspar decreases within depth of 0.7 m as Quartz increases. As one of the main contribution to weathering of rock mass, soluble salts accumulate within the depth ranging from 0.4 m to 1.0 m. By comprehensive analysis on experimental results, depths in 1.0 m, 0.6 m and 0.4 m are respectively regarded as the weathering depths of No.1, No.2 and No.3 horizontal testing caves. As for the variation among cliff space, the heaviest weathering happening at upper part and weakest weathering lies at lower part.
For the fractured rock slope and complex stratums, the grouting is a well-known crush rock treatment method in geotechnical engineering. However, the grout stone body usually face the damage of dramatic freezing-thawing cycles. In this paper, the freezing-thawing cycle test and SEM test are used to study the stone body of self-developed viscosity time-varying grout(SJP). The strength properties of SJP and blank cement stone body are study through compression test and wave test. According to the results of experiments, the mechanism of freezing and thawing damage is also discussed. The result shows that under the condition of freezing and thawing, the durability of SJP grout stone body is obviously better than blank cement stones. The compressive strength and relative dynamic elastic modulus of SJP grout stone decrease continuously with the increase of freeze-thaw cycles. But the tensile strength shows a trend of increasing firstly and then decreasing. All the decreasing rate of strengths of SJP is slower than the blank cement. When 2# added amount to 2.0, 3# added amount is 1.5%, SJP slurry stone body has the best frost resistance. The damage mechanism can be illustrated as follows. The production of C-S-H in SJP grout increases under the action of SJP additives, and combined with the fiber needle hydration derivatives, that make the pore structure of stone body becomes denser than the blank cement. This characteristic slows the freeze-thaw damage accumulation effectively, thus its durability under the condition of freezing and thawing is improved effectively. Therefore, the SJP stone body is more suitable for application in alpine mountain area engineering construction. For the fractured rock slope and complex stratums, the grouting is a well-known crush rock treatment method in geotechnical engineering. However, the grout stone body usually face the damage of dramatic freezing-thawing cycles. In this paper, the freezing-thawing cycle test and SEM test are used to study the stone body of self-developed viscosity time-varying grout(SJP). The strength properties of SJP and blank cement stone body are study through compression test and wave test. According to the results of experiments, the mechanism of freezing and thawing damage is also discussed. The result shows that under the condition of freezing and thawing, the durability of SJP grout stone body is obviously better than blank cement stones. The compressive strength and relative dynamic elastic modulus of SJP grout stone decrease continuously with the increase of freeze-thaw cycles. But the tensile strength shows a trend of increasing firstly and then decreasing. All the decreasing rate of strengths of SJP is slower than the blank cement. When 2# added amount to 2.0, 3# added amount is 1.5%, SJP slurry stone body has the best frost resistance. The damage mechanism can be illustrated as follows. The production of C-S-H in SJP grout increases under the action of SJP additives, and combined with the fiber needle hydration derivatives, that make the pore structure of stone body becomes denser than the blank cement. This characteristic slows the freeze-thaw damage accumulation effectively, thus its durability under the condition of freezing and thawing is improved effectively. Therefore, the SJP stone body is more suitable for application in alpine mountain area engineering construction.
In the field of hydraulic fracturing for shale gas production, the pump rate has a significant effect on fracture network propagation. The random natural fractures in shale reservoir lead to confusion of parametric sensitivity analysis in hydraulic fracturing. Firstly, based on the fracture characteristic in shale reservoir, concrete specimens with three sets of orthogonal pre-existed fractures are prepared. Then, with true triaxial fracturing simulation experimental system, the fluid with constant pump rate is injected into the specimens under true triaxial loading. Finally, the area of fractures per unit volume(P32) is employed to analyse the effect of pump rate on fracture network propagation. The results show as follows. (1)In the specimens with small dimension of block element(high pre-existed fractures density), the phenomenon of stimulation reservoir volume is more significant. (2)The fluid with low pump rate can stimulate only pre-fractures in specimens. The fluid with medium and high pump rate can not only stimulate the pre-fractures, but also divert the direction of stimulated pre-fractures and open new hydraulic fractures in concrete, which increases the complexity of fracture network. (3)With the increase of injection rate, the P32 value of specimen after fracturing increases. However, when the injection rate increases to a certain value, the P32 value doesn't increase, or even decreases. In the field of hydraulic fracturing for shale gas production, the pump rate has a significant effect on fracture network propagation. The random natural fractures in shale reservoir lead to confusion of parametric sensitivity analysis in hydraulic fracturing. Firstly, based on the fracture characteristic in shale reservoir, concrete specimens with three sets of orthogonal pre-existed fractures are prepared. Then, with true triaxial fracturing simulation experimental system, the fluid with constant pump rate is injected into the specimens under true triaxial loading. Finally, the area of fractures per unit volume(P32) is employed to analyse the effect of pump rate on fracture network propagation. The results show as follows. (1)In the specimens with small dimension of block element(high pre-existed fractures density), the phenomenon of stimulation reservoir volume is more significant. (2)The fluid with low pump rate can stimulate only pre-fractures in specimens. The fluid with medium and high pump rate can not only stimulate the pre-fractures, but also divert the direction of stimulated pre-fractures and open new hydraulic fractures in concrete, which increases the complexity of fracture network. (3)With the increase of injection rate, the P32 value of specimen after fracturing increases. However, when the injection rate increases to a certain value, the P32 value doesn't increase, or even decreases.
Natural fracture in shale formation is very developed. During fracking treatment, the natural fractures can be reactivated to form a complex network. In addition, the natural fracture is the medium for gas storage. Lots of gas exists in natural fractures in the form of free gas. Numerical simulation was used to study the interaction between hydraulic fracture(HF) and natural fracture(NF). The paper mainly focused on the reactivation and extension of NF caused by HF. The model includes three and single NF, respectively, and simulation variables corresponding to different angles of approach, differential stress and elastic parameters of formation. Results show that:(1)Formation breakdown stress is changing with corresponding angles of approach. When angle of approach is 90°, the water pressure for formation breakdown is the largest, and formation breakdown stress increase with increasing of differential stress. (2)Whether single or three natural fracture, after reinstating of natural fractures, the extension direction of branch fracture resume to the maximum horizontal principal stress. When angle of approach is 90°, the reactivated effect is best. (3)The branching HF presented double shift at tip of NF when angle of approach is 90°. It is helpful to form fracture network and large number of element burst in the model. The fracking effect is the best. (4)The critical water pressure for the reactivation of NF decrease with increasing of elastic modulus and deceasing of Poisson's ratio. The elastic properties of gas formation has a great influence on the formation of a fracture network. The fracking effect is good in formation with high elastic modulus and low Poisson's ratio. Natural fracture in shale formation is very developed. During fracking treatment, the natural fractures can be reactivated to form a complex network. In addition, the natural fracture is the medium for gas storage. Lots of gas exists in natural fractures in the form of free gas. Numerical simulation was used to study the interaction between hydraulic fracture(HF) and natural fracture(NF). The paper mainly focused on the reactivation and extension of NF caused by HF. The model includes three and single NF, respectively, and simulation variables corresponding to different angles of approach, differential stress and elastic parameters of formation. Results show that:(1)Formation breakdown stress is changing with corresponding angles of approach. When angle of approach is 90°, the water pressure for formation breakdown is the largest, and formation breakdown stress increase with increasing of differential stress. (2)Whether single or three natural fracture, after reinstating of natural fractures, the extension direction of branch fracture resume to the maximum horizontal principal stress. When angle of approach is 90°, the reactivated effect is best. (3)The branching HF presented double shift at tip of NF when angle of approach is 90°. It is helpful to form fracture network and large number of element burst in the model. The fracking effect is the best. (4)The critical water pressure for the reactivation of NF decrease with increasing of elastic modulus and deceasing of Poisson's ratio. The elastic properties of gas formation has a great influence on the formation of a fracture network. The fracking effect is good in formation with high elastic modulus and low Poisson's ratio.
A large-scale landslide occurred in Baige village, at the border between Tibet Autonomous Region and Sichuan Province, on October 11, 2018. The sliding mass detached from a high-elevation mountain ridge, then dammed the Jinsha River impounding a barrier lake. This initial lake drained naturally. Afterwards, on November 3, a second landslide involved with a large mass of loose material from the first event blocked the river again, inducing a 50 m high dam and a barrier lake with a capacity of 500 million cubic meters. In order to alleviate the dangers of potential dam-breach flood, the artificial spillway was constructed allowing controlled breaching until November 13. However, downstream flooding still cause a major loss of property and damage, covering a large area of Sichuan Province and Yunnan Province. Extensive on-site investigation, combined with historical satellite images interpretation, InSAR monitoring, UAV aerial photography and ground deformation monitoring techniques, was conducted in this paper, to analyze the historical deformation of the study area and the evolutional characteristics of these two events. Based on that, the emergency measurements after each event have been developed, and the implementation of spillway was secured by monitoring and early-warning work at site. The successive landslides damming the Jinsha River presents a good example to study the emergency response and mitigation plan for similar cases in the future. A large-scale landslide occurred in Baige village, at the border between Tibet Autonomous Region and Sichuan Province, on October 11, 2018. The sliding mass detached from a high-elevation mountain ridge, then dammed the Jinsha River impounding a barrier lake. This initial lake drained naturally. Afterwards, on November 3, a second landslide involved with a large mass of loose material from the first event blocked the river again, inducing a 50 m high dam and a barrier lake with a capacity of 500 million cubic meters. In order to alleviate the dangers of potential dam-breach flood, the artificial spillway was constructed allowing controlled breaching until November 13. However, downstream flooding still cause a major loss of property and damage, covering a large area of Sichuan Province and Yunnan Province. Extensive on-site investigation, combined with historical satellite images interpretation, InSAR monitoring, UAV aerial photography and ground deformation monitoring techniques, was conducted in this paper, to analyze the historical deformation of the study area and the evolutional characteristics of these two events. Based on that, the emergency measurements after each event have been developed, and the implementation of spillway was secured by monitoring and early-warning work at site. The successive landslides damming the Jinsha River presents a good example to study the emergency response and mitigation plan for similar cases in the future.
We used Landsat and other high-moderate space resolution images to analysis the glacial retreat in the recent 40 years of Sedongpu Basin, and combed the eight times debris flow blocking Yarlung Zangbo river incidents of Sedongpu Basin after 2014. Combined with the radar and meteorological data, we analyzed the reasons of frequent collapse disasters occurred in the basin. Then we found the following factors. First, the "steep-gentle-relative steep" ladder terrain is the foundation of the frequent occurrence of the debris flows in Sedongpu Basin. Second, the debris flow always block the channel at a large extent. Third, there are lots of crevasses in the glacier trailing edge. Fourth, earthquake and abundant rainfalls also lead to the frequent debris flow of Sedongpu Basin. Combined the above factors, we speculate the glacier avalanche induced debris flow(GAIDF) of Sedongpu Basin will happen frequently for a long time with typical periodicity. So, we suggested to establish a long-time monitoring and warning system for the Yarlung Zangbo Grand Canyon in order to provide effective support to the emergency work of Sedongpu Basin glacier debrisflow. We used Landsat and other high-moderate space resolution images to analysis the glacial retreat in the recent 40 years of Sedongpu Basin, and combed the eight times debris flow blocking Yarlung Zangbo river incidents of Sedongpu Basin after 2014. Combined with the radar and meteorological data, we analyzed the reasons of frequent collapse disasters occurred in the basin. Then we found the following factors. First, the "steep-gentle-relative steep" ladder terrain is the foundation of the frequent occurrence of the debris flows in Sedongpu Basin. Second, the debris flow always block the channel at a large extent. Third, there are lots of crevasses in the glacier trailing edge. Fourth, earthquake and abundant rainfalls also lead to the frequent debris flow of Sedongpu Basin. Combined the above factors, we speculate the glacier avalanche induced debris flow(GAIDF) of Sedongpu Basin will happen frequently for a long time with typical periodicity. So, we suggested to establish a long-time monitoring and warning system for the Yarlung Zangbo Grand Canyon in order to provide effective support to the emergency work of Sedongpu Basin glacier debrisflow.
The post-fire debris flow is another special type of debris flows that closely related to forest fire and generate in burned area. Obvious difference in term of the initiation mechanism has been find between post-fire debris flows and general debris flows. Fire combusts the surface vegetation and furtherly destroys the texture of underlying soil for the high temperature of fire. The unit weight, pore porosity, permeability and other physical and hydrological properties of the fire-infected soil are changed dramatically in fire, and abundant residual ash layer and loose debris accumulated on the slope after fire. Therefore, post-fire debris flows usually have the characteristics of high unit weight and viscosity. A review of research on the generation mode, kinetic mechanism, influence factors, debris flow forecasting and mitigation measures of this kind of debris flows is put forward, referring to relevant literature at home and abroad. Post-fire debris flows are first studied in 1936, detailed study on which is mostly conducted in America, Australian and Spain. But few can been find in China, except the researches in agroforestry, in which the study are mainly about water and soil loss, vegetation combust and recovery. As another special type of debris flow hazards, systematic study of post-fire debris flows has not attracted enough attention in China, which reflects the poor study of this kind of debris flows. Based on the key problem mentioned above, some suggestions are came up with to enhance the research on the generation and spatial-temporal evolution mechanism and effective protection of post-fire debris flows. The post-fire debris flow is another special type of debris flows that closely related to forest fire and generate in burned area. Obvious difference in term of the initiation mechanism has been find between post-fire debris flows and general debris flows. Fire combusts the surface vegetation and furtherly destroys the texture of underlying soil for the high temperature of fire. The unit weight, pore porosity, permeability and other physical and hydrological properties of the fire-infected soil are changed dramatically in fire, and abundant residual ash layer and loose debris accumulated on the slope after fire. Therefore, post-fire debris flows usually have the characteristics of high unit weight and viscosity. A review of research on the generation mode, kinetic mechanism, influence factors, debris flow forecasting and mitigation measures of this kind of debris flows is put forward, referring to relevant literature at home and abroad. Post-fire debris flows are first studied in 1936, detailed study on which is mostly conducted in America, Australian and Spain. But few can been find in China, except the researches in agroforestry, in which the study are mainly about water and soil loss, vegetation combust and recovery. As another special type of debris flow hazards, systematic study of post-fire debris flows has not attracted enough attention in China, which reflects the poor study of this kind of debris flows. Based on the key problem mentioned above, some suggestions are came up with to enhance the research on the generation and spatial-temporal evolution mechanism and effective protection of post-fire debris flows.
Shallow tunnels in ancient granites are often in tensile stress state and have the challenges of instability in vault faces and local ground collapse. This paper takes the Jining Tunnel as one example and carries out the engineering geological survey, laboratory tests and surrounding rock stability simulation. It analyzes the stability of the surrounding rock from three aspects of granite weathering zoning, rock structure controlling and rock mass qualifying. Surrounded by slightly-moderaltely weathered granites, most of the tunnel is located below the groundwater level. The rock joints are extensively filled with mud. Deformation and damage in forms of block down and cave was often occur. The differential deformation and uneven settlement occurred at the junction of the paleo-weathering granite crusts with the upper Tertiary mudstone. Four collapse pits are emerged due to collapse of caves in shallow depths. The stress monitoring results show that the contact pressure of the top arch is less than the gravity stress, and the lateral pressure is smaller, which is unfavorable to the vault stability. In order to ensure the safety of personnel and machinery equipment, supporting measures with strengthening are undertaken, which prove to be of positive engineering significance. Shallow tunnels in ancient granites are often in tensile stress state and have the challenges of instability in vault faces and local ground collapse. This paper takes the Jining Tunnel as one example and carries out the engineering geological survey, laboratory tests and surrounding rock stability simulation. It analyzes the stability of the surrounding rock from three aspects of granite weathering zoning, rock structure controlling and rock mass qualifying. Surrounded by slightly-moderaltely weathered granites, most of the tunnel is located below the groundwater level. The rock joints are extensively filled with mud. Deformation and damage in forms of block down and cave was often occur. The differential deformation and uneven settlement occurred at the junction of the paleo-weathering granite crusts with the upper Tertiary mudstone. Four collapse pits are emerged due to collapse of caves in shallow depths. The stress monitoring results show that the contact pressure of the top arch is less than the gravity stress, and the lateral pressure is smaller, which is unfavorable to the vault stability. In order to ensure the safety of personnel and machinery equipment, supporting measures with strengthening are undertaken, which prove to be of positive engineering significance.
To fully consider the slid characters from shake table tests, we put forward an estimation method for the permanent displacement based on the basic earthquake landslide model. (1)we calculate the yield accelerations of slide downward and upward with considering the combined control effect of seismic and gravity, in order to show the behavior that the slide-body may slide downward and upward along the slide-belt. (2)We evaluate the local acceleration close to the slid-body because of the amplification effect of vibration characteristics of slope and height of the slide-body based on a simplified dynamic model of slope. (3)We calculate the maximum velocity of slide in every seismic wave period and then give the kinetic energy dissipated by sliding along the slide-belt with considering the control role of yield accelerations and local acceleration close to the slid-body. (4)We calculate the permanent displacement in per seismic wave period through the way that divide the kinetic energy by friction force based on the fact that the energy is dissipated by frictions at the slid-belt and the principle of conservation of energy. (5)Finally we get the overall permanent displacement by accumulating the permanent displacements in every seismic wave period. Through comparing the results from experiments and calculation, we have found that the method in this paper has high accuracy and reliability in estimating the permanent displacement. The idea of this article is adoptable to the present of vertical seismic by reckoning in vertical seismic inertial force though it comes from the scene that horizontal seismic present only. To fully consider the slid characters from shake table tests, we put forward an estimation method for the permanent displacement based on the basic earthquake landslide model. (1)we calculate the yield accelerations of slide downward and upward with considering the combined control effect of seismic and gravity, in order to show the behavior that the slide-body may slide downward and upward along the slide-belt. (2)We evaluate the local acceleration close to the slid-body because of the amplification effect of vibration characteristics of slope and height of the slide-body based on a simplified dynamic model of slope. (3)We calculate the maximum velocity of slide in every seismic wave period and then give the kinetic energy dissipated by sliding along the slide-belt with considering the control role of yield accelerations and local acceleration close to the slid-body. (4)We calculate the permanent displacement in per seismic wave period through the way that divide the kinetic energy by friction force based on the fact that the energy is dissipated by frictions at the slid-belt and the principle of conservation of energy. (5)Finally we get the overall permanent displacement by accumulating the permanent displacements in every seismic wave period. Through comparing the results from experiments and calculation, we have found that the method in this paper has high accuracy and reliability in estimating the permanent displacement. The idea of this article is adoptable to the present of vertical seismic by reckoning in vertical seismic inertial force though it comes from the scene that horizontal seismic present only.
Clear water flow is one of the main conditions for debris flow to start. Different water flows can cause debris flow on different scales. Using the indoor flume model experiment, the pore water pressure was measured with piezometer tube at three cross-sections. High resolution camera technology was used to record the movement of engineering slag and the collapse of skeleton particles. The results are used to analyze the phenomenon of slag in the process of debris flow formation. Based on the analysis, the experiment was conducted with fixing the slope angle of flume device of 8 degree. The clear water flow discharge was of 0.083 and 0.409 L·s-1 respectively. The test results were used to analyze the effect of the flow state on soil particles failure and debris flow initiation under different clear water flow discharges. Under the action of the same clear water flow, the failure mode of the accumulated slag was mainly affected by the content of gravel particles. And the particle size of 2 mm in the slag had a greater influence on the content of gravel. When the particle size was larger than 2 mm and the content of gravel was greater than 50%, the failure mode of slag was mainly the undercut caused by erosion. The pore water pressure appeared increasing at beginning, and then stable. When the particle size was less than 2 mm and the content of gravel was greater than 65%, the failure mode of slag was mainly the bottom erosion caused by seepage. The pore water pressure was characterized by an arc-shaped rising with time. Clear water flow is one of the main conditions for debris flow to start. Different water flows can cause debris flow on different scales. Using the indoor flume model experiment, the pore water pressure was measured with piezometer tube at three cross-sections. High resolution camera technology was used to record the movement of engineering slag and the collapse of skeleton particles. The results are used to analyze the phenomenon of slag in the process of debris flow formation. Based on the analysis, the experiment was conducted with fixing the slope angle of flume device of 8 degree. The clear water flow discharge was of 0.083 and 0.409 L·s-1 respectively. The test results were used to analyze the effect of the flow state on soil particles failure and debris flow initiation under different clear water flow discharges. Under the action of the same clear water flow, the failure mode of the accumulated slag was mainly affected by the content of gravel particles. And the particle size of 2 mm in the slag had a greater influence on the content of gravel. When the particle size was larger than 2 mm and the content of gravel was greater than 50%, the failure mode of slag was mainly the undercut caused by erosion. The pore water pressure appeared increasing at beginning, and then stable. When the particle size was less than 2 mm and the content of gravel was greater than 65%, the failure mode of slag was mainly the bottom erosion caused by seepage. The pore water pressure was characterized by an arc-shaped rising with time.
In recent years, the occurrence of geological fracture disaster has increased at the Beijing Plain. The geological crack disaster accelerates soil erosion and impacts negatively on infrastructure construction in the area. This paper aims to analyze the generation of geological cracks and reduce the potential losses of economy and property. With geological survey, InSAR monitoring, trenching and drilling methods, the spatial characteristics of ground fissures at Shongzhuang Village are investigated. The factors responsible for the ground fissures and the occurrence mechanism are analyzed based on geological structure, lithology and land subsidence. The conclusions are as follows. (1)The ground fissures at Songzhuang Viallge are sourced at Xiaozhong River, extend along the way through the Shuangbutou Village quay, Gouqu Village, Dapang Village, and end at the Pingjiatuan Village. Its influencing length is up to 8.7 kilometers and extends to the NEE direction. The houses, walls and pavements along the fissures have been damaged to varying degree. The affected objects exhibit tensile deformation. (2)Under the influence of tectonics, the thickness of the Quaternary sedimentary strata is different in two sides of the fissures. The difference in regional sedimentary environment leads to the heterogeneity of stratum lithology. Both of them are the important geological background for the formation of the fissures. (3)Nanyuan-Tongxian fault zone, conceals in the lower part of the ground fissure turn out to be a tensional fracture. Although moving under the ground, it provides the geological conditions for the accumulation and transmission of stress for the formation of the fissures. (4)The long-term and excessive exploitation of groundwater resources has changed the stable environment of the soil, and caused the horizontal and vertical deformation of the soil. The two kinds of deformations altogether caused the ground fissure. The superimposed effects of extensional deformation basement, buried fracture and groundwater overexploitation are the causes of horizontally or vertically compression of soils. The tensile stress concentrated zone is formed near the fault zone in the unsaturated zone. When the stress reaches the tensile strength of the soil, a blind crack is formed. The blind crack is extended to the surface due to rain erosion or of phreatic water table going up and developed to geological cracks and beads-like collapses. In recent years, the occurrence of geological fracture disaster has increased at the Beijing Plain. The geological crack disaster accelerates soil erosion and impacts negatively on infrastructure construction in the area. This paper aims to analyze the generation of geological cracks and reduce the potential losses of economy and property. With geological survey, InSAR monitoring, trenching and drilling methods, the spatial characteristics of ground fissures at Shongzhuang Village are investigated. The factors responsible for the ground fissures and the occurrence mechanism are analyzed based on geological structure, lithology and land subsidence. The conclusions are as follows. (1)The ground fissures at Songzhuang Viallge are sourced at Xiaozhong River, extend along the way through the Shuangbutou Village quay, Gouqu Village, Dapang Village, and end at the Pingjiatuan Village. Its influencing length is up to 8.7 kilometers and extends to the NEE direction. The houses, walls and pavements along the fissures have been damaged to varying degree. The affected objects exhibit tensile deformation. (2)Under the influence of tectonics, the thickness of the Quaternary sedimentary strata is different in two sides of the fissures. The difference in regional sedimentary environment leads to the heterogeneity of stratum lithology. Both of them are the important geological background for the formation of the fissures. (3)Nanyuan-Tongxian fault zone, conceals in the lower part of the ground fissure turn out to be a tensional fracture. Although moving under the ground, it provides the geological conditions for the accumulation and transmission of stress for the formation of the fissures. (4)The long-term and excessive exploitation of groundwater resources has changed the stable environment of the soil, and caused the horizontal and vertical deformation of the soil. The two kinds of deformations altogether caused the ground fissure. The superimposed effects of extensional deformation basement, buried fracture and groundwater overexploitation are the causes of horizontally or vertically compression of soils. The tensile stress concentrated zone is formed near the fault zone in the unsaturated zone. When the stress reaches the tensile strength of the soil, a blind crack is formed. The blind crack is extended to the surface due to rain erosion or of phreatic water table going up and developed to geological cracks and beads-like collapses.
The research group, just in the next day after the "8·8" Jiuzhaigou earthquake, installed microseismic monitoring instruments at the bottom(1# monitoring point) and the top(2# monitoring point) of the Jubao Mountain in the Jiuzhaigou county. They collected a good amount of seismic data during aftershocks. The paper seeks to research the seismic response characteristics through analysis of the monitoring data of 1# monitoring point at the elevation of 1414 m and 2# monitoring point at the elevatoion of 1551 m above mean sea level. The earthquake monitoring data show the follow features. (1)Compared with the low elevation monitoring point, the peak acceleration of the ground motion in all directions of the high elevation monitoring point show an increasing trend. The horizontal acceleration amplitude of each monitoring point is generally larger than the vertical direction. And the topographic amplification effect is remarkable. (2)During the aftershocks, near SN trending ridge of the Jubao Mountain quaked more fiercely along the east-west direction, which swung violently along the East and West sides of ridge, formed seismic fractures that developed along the ridge. The study of the aftershock monitoring data confirms the existence of the directional effect of the slope ground motion. The peak acceleration amplification effect of 2# monitoring station in horizontal East-West direction is obviously stronger than that in other directions. Seismic wave energy significantly magnified at the horizontal east-west direction. So, the top buildings were more easily damaged along this direction. These results proved that the local terrain had a controlling effect on slope seismic response. (3)The vertical main frequency of the amplitude spectrum of 2# monitoring point focused on the range between 6 Hz and 12 Hz. The horizontal East-West frequency focused on the lower frequency range between 5 Hz and 8 Hz. And the main frequency of horizontal north-south direction was mainly 5~10 Hz. Compared with the 1# monitoring point, the main frequency in all directions of the 2# monitoring point had obvious attenuation. That is, with the increase of the elevation, the main frequency of the seismic vibration showed a decreasing trend. And the seismic wave in the upper part of the slope was dominated by medium and low frequency. Further calculation and analysis showed that the topographic amplification effect of the thin ridge, the strip-type mountain and multiple free surfaces mountain were closely related to the half wave length of the seismic wave. Under the coupling effect of local topographic dimensions and the rich wavelength components of seismic waves, the topographic amplification effect was remarkable, and the seismic damage of the mountain was developed. The research group, just in the next day after the "8·8" Jiuzhaigou earthquake, installed microseismic monitoring instruments at the bottom(1# monitoring point) and the top(2# monitoring point) of the Jubao Mountain in the Jiuzhaigou county. They collected a good amount of seismic data during aftershocks. The paper seeks to research the seismic response characteristics through analysis of the monitoring data of 1# monitoring point at the elevation of 1414 m and 2# monitoring point at the elevatoion of 1551 m above mean sea level. The earthquake monitoring data show the follow features. (1)Compared with the low elevation monitoring point, the peak acceleration of the ground motion in all directions of the high elevation monitoring point show an increasing trend. The horizontal acceleration amplitude of each monitoring point is generally larger than the vertical direction. And the topographic amplification effect is remarkable. (2)During the aftershocks, near SN trending ridge of the Jubao Mountain quaked more fiercely along the east-west direction, which swung violently along the East and West sides of ridge, formed seismic fractures that developed along the ridge. The study of the aftershock monitoring data confirms the existence of the directional effect of the slope ground motion. The peak acceleration amplification effect of 2# monitoring station in horizontal East-West direction is obviously stronger than that in other directions. Seismic wave energy significantly magnified at the horizontal east-west direction. So, the top buildings were more easily damaged along this direction. These results proved that the local terrain had a controlling effect on slope seismic response. (3)The vertical main frequency of the amplitude spectrum of 2# monitoring point focused on the range between 6 Hz and 12 Hz. The horizontal East-West frequency focused on the lower frequency range between 5 Hz and 8 Hz. And the main frequency of horizontal north-south direction was mainly 5~10 Hz. Compared with the 1# monitoring point, the main frequency in all directions of the 2# monitoring point had obvious attenuation. That is, with the increase of the elevation, the main frequency of the seismic vibration showed a decreasing trend. And the seismic wave in the upper part of the slope was dominated by medium and low frequency. Further calculation and analysis showed that the topographic amplification effect of the thin ridge, the strip-type mountain and multiple free surfaces mountain were closely related to the half wave length of the seismic wave. Under the coupling effect of local topographic dimensions and the rich wavelength components of seismic waves, the topographic amplification effect was remarkable, and the seismic damage of the mountain was developed.
In order to research the seismic response laws of a mountain at different depths of a slope, a seismic monitoring array was installed in the Xuejiaba slope of Jiuzhaigou county. Four monitoring instruments at the foot and top of the mountain were triggered by a MS3.2 aftershock. The data reveal the following feature. The terrain of the hill, which is located at the protruding position on the surface of the slope, has obvious amplification effect. At the same time, the horizontal acceleration peak is greater than the vertical direction. Comparing with the another monitoring at the foot of the mountain, the PGA at the 2#-1 monitoring point on the surface of slope is maximum. Its arias intensity enlarges more than five times. The largest amplification effect is obvious in the vertical direction. The acceleration is 2.48 times and the alias intensity is 5.24 times. The amplification effect of acceleration at each monitoring gradually attenuates with the deepening of the horizontal depth of the mountain. The value of PGA decreases from 2.48 to the inner of 2.03, and the Alias intensity is reduced from 5.84 to 3.92. The peak acceleration decreases greatly within the surface range of 0 to 25 m and at the inner slope falls at a slow rate. Fourier spectrum indications the following features. The frequency range get from the foot of mountains is 0-50 Hz. The main frequency value is about 23 Hz. The frequency range of the 2#-1 monitoring point has not changed significantly compared with the data from the foot of the mountain. But the main frequency value is obviously reduced about 5 Hz. Spectral frequency components are complex, with the depth of the hole deeper in horizontal direction, the amplitude and frequency components of each monitoring point gradually decrease. Through the analysis of all of the data, it is confirmed that under the earthquake, with the increasing of the amplitude of acceleration, the energy of the ground vibration can increase geometrically, and the surface of the mountain can be the most powerful position. If accumulation of the vibration energy excesses the strength of the rock mass in short time, it is easy to trigger collapse and landslide, which have a great impact on the safety of the construction. In order to research the seismic response laws of a mountain at different depths of a slope, a seismic monitoring array was installed in the Xuejiaba slope of Jiuzhaigou county. Four monitoring instruments at the foot and top of the mountain were triggered by a MS3.2 aftershock. The data reveal the following feature. The terrain of the hill, which is located at the protruding position on the surface of the slope, has obvious amplification effect. At the same time, the horizontal acceleration peak is greater than the vertical direction. Comparing with the another monitoring at the foot of the mountain, the PGA at the 2#-1 monitoring point on the surface of slope is maximum. Its arias intensity enlarges more than five times. The largest amplification effect is obvious in the vertical direction. The acceleration is 2.48 times and the alias intensity is 5.24 times. The amplification effect of acceleration at each monitoring gradually attenuates with the deepening of the horizontal depth of the mountain. The value of PGA decreases from 2.48 to the inner of 2.03, and the Alias intensity is reduced from 5.84 to 3.92. The peak acceleration decreases greatly within the surface range of 0 to 25 m and at the inner slope falls at a slow rate. Fourier spectrum indications the following features. The frequency range get from the foot of mountains is 0-50 Hz. The main frequency value is about 23 Hz. The frequency range of the 2#-1 monitoring point has not changed significantly compared with the data from the foot of the mountain. But the main frequency value is obviously reduced about 5 Hz. Spectral frequency components are complex, with the depth of the hole deeper in horizontal direction, the amplitude and frequency components of each monitoring point gradually decrease. Through the analysis of all of the data, it is confirmed that under the earthquake, with the increasing of the amplitude of acceleration, the energy of the ground vibration can increase geometrically, and the surface of the mountain can be the most powerful position. If accumulation of the vibration energy excesses the strength of the rock mass in short time, it is easy to trigger collapse and landslide, which have a great impact on the safety of the construction.
Debris flow is a devastating geological disaster due to the destructive power of large-sized particles. The large-sized particles have greater power than the liquid at the same volume and velocity. In order to investigate the starting mechanism of large-sized particles in viscous debris flow, a reasonable and simple calculation model is developed. The flow condition is the key factor of the debris flow outburst. Considering the random distribution of relative position between supporting and starting particles, the critical hydraulic condition of upstream is achieved by analyzing the particle forces under the impact of slurry. The forces include the lift force, drag force, effective gravity. The particles' moment equilibrium equation of staring condition is solved. The proposed formula of critical starting velocity is consistent with universal laws. The theoretical results by proposed formula are in good agreement with numerical simulation results of three typical cases made by CFD software FLUENT. The proposed formula has significance for preventing and controlling debris flow, especially in the calculation of the discharge in separation of water and solid. Debris flow is a devastating geological disaster due to the destructive power of large-sized particles. The large-sized particles have greater power than the liquid at the same volume and velocity. In order to investigate the starting mechanism of large-sized particles in viscous debris flow, a reasonable and simple calculation model is developed. The flow condition is the key factor of the debris flow outburst. Considering the random distribution of relative position between supporting and starting particles, the critical hydraulic condition of upstream is achieved by analyzing the particle forces under the impact of slurry. The forces include the lift force, drag force, effective gravity. The particles' moment equilibrium equation of staring condition is solved. The proposed formula of critical starting velocity is consistent with universal laws. The theoretical results by proposed formula are in good agreement with numerical simulation results of three typical cases made by CFD software FLUENT. The proposed formula has significance for preventing and controlling debris flow, especially in the calculation of the discharge in separation of water and solid.
The weak intercalation forms a sliding zone after long-term geological evolution and plays an important role in controlling the stability of massive layered rockslides. In order to determine the formation process of the sliding zone, we take the Jiweishan Landslide as an example and analyze the developmental regularities of the weak intercalation. The weak intercalation can be divided into three stages including the original soft rock, the interlayer shear zone and the sliding zone. In addition, we have comparatively studied the evolutionary characteristics of weak intercalation through the laboratory test of the physical properties, physicochemical properties, and physical mechanics properties. As a result, from the view of the mineral composition, the mean value of the clay mineral content is increased from 4.4% to 16.9%. From the view of the physical properties and the microstructure, the density is decreased from 5% to 6%, and the porosity is increased by 108%. It reflects the decreased density and loose structure due to long-term evolution. From the view of the physicochemical properties, the total content of exchangeable salt is the highest in the original soft rock, followed by the sliding zone, whereas the interlayer shear zone exhibited the lowest value. The organic matter content is gradually increased in the alkalescence evolutionary environment. From the view of the shear creep strength, the internal friction angle is decreased from 57.58°to 29.63°, and the cohesion decreased from 585 kPa to 96 kPa. Based on these data, we analyze the change of the residual sliding thrust of the main section of the Jiweishan Landslide driving block. The residual sliding thrust increases with a decrease in the long-term strength parameter. When the internal friction angle φ < 25° and cohesion c < 129 kPa, the residual sliding thrust of the driving block is greater than zero, and then the driving block is sliding. The conclusions provide an important reference for the study of the development and mechanism of layered rockslides controlled by weak intercalations. The weak intercalation forms a sliding zone after long-term geological evolution and plays an important role in controlling the stability of massive layered rockslides. In order to determine the formation process of the sliding zone, we take the Jiweishan Landslide as an example and analyze the developmental regularities of the weak intercalation. The weak intercalation can be divided into three stages including the original soft rock, the interlayer shear zone and the sliding zone. In addition, we have comparatively studied the evolutionary characteristics of weak intercalation through the laboratory test of the physical properties, physicochemical properties, and physical mechanics properties. As a result, from the view of the mineral composition, the mean value of the clay mineral content is increased from 4.4% to 16.9%. From the view of the physical properties and the microstructure, the density is decreased from 5% to 6%, and the porosity is increased by 108%. It reflects the decreased density and loose structure due to long-term evolution. From the view of the physicochemical properties, the total content of exchangeable salt is the highest in the original soft rock, followed by the sliding zone, whereas the interlayer shear zone exhibited the lowest value. The organic matter content is gradually increased in the alkalescence evolutionary environment. From the view of the shear creep strength, the internal friction angle is decreased from 57.58°to 29.63°, and the cohesion decreased from 585 kPa to 96 kPa. Based on these data, we analyze the change of the residual sliding thrust of the main section of the Jiweishan Landslide driving block. The residual sliding thrust increases with a decrease in the long-term strength parameter. When the internal friction angle φ < 25° and cohesion c < 129 kPa, the residual sliding thrust of the driving block is greater than zero, and then the driving block is sliding. The conclusions provide an important reference for the study of the development and mechanism of layered rockslides controlled by weak intercalations.
In the northwest, a lot of multi-stage high slopes with loess have been encountered in the construction of basic engineering. Slope engineering belongs to permanent project. So it is unavoidable to meet the conditions of rainfall. Under rainfall infiltration, the degree of saturation and mass of soil slope increase, which can further cause the change of slope matric suction and effective stress. As a result, the stability of the slope can be greatly influenced. In this paper, the coupling calculation model of seepage field and stress field is established. It considers the changes of the matrix suction as the rain water infiltration at the different depths of the slope body. Then, the stability of the multi-stage high slope with loess under the condition of rainfall infiltration can be analyzed. Then, according to an actual engineering and using the PLAXIS 3D geotechnical finite element software, the calculation model of slope stability is established. By setting the variation function of rainfall with the time and boundary condition, the stability calculation of multi-stage high slope with loess is carried out under the condition of rainfall infiltration. And then, The numerical calculation results are compared with the theoretical calculation results. According to the numerical calculation results, the changes of the deformation, matrix suction, effective stress, potential slip surface and safety factor of the multi-stage high slope with loess under the condition of rainfall infiltration are obtained. And the stability of the multi-stage high slope with loess under the condition of rainfall infiltration are analyzed. The study results can provide some guidance for the design of the multi-stage high slope with loess under the rainfall infiltration. In the northwest, a lot of multi-stage high slopes with loess have been encountered in the construction of basic engineering. Slope engineering belongs to permanent project. So it is unavoidable to meet the conditions of rainfall. Under rainfall infiltration, the degree of saturation and mass of soil slope increase, which can further cause the change of slope matric suction and effective stress. As a result, the stability of the slope can be greatly influenced. In this paper, the coupling calculation model of seepage field and stress field is established. It considers the changes of the matrix suction as the rain water infiltration at the different depths of the slope body. Then, the stability of the multi-stage high slope with loess under the condition of rainfall infiltration can be analyzed. Then, according to an actual engineering and using the PLAXIS 3D geotechnical finite element software, the calculation model of slope stability is established. By setting the variation function of rainfall with the time and boundary condition, the stability calculation of multi-stage high slope with loess is carried out under the condition of rainfall infiltration. And then, The numerical calculation results are compared with the theoretical calculation results. According to the numerical calculation results, the changes of the deformation, matrix suction, effective stress, potential slip surface and safety factor of the multi-stage high slope with loess under the condition of rainfall infiltration are obtained. And the stability of the multi-stage high slope with loess under the condition of rainfall infiltration are analyzed. The study results can provide some guidance for the design of the multi-stage high slope with loess under the rainfall infiltration.
The corner effect is one of the important forms of the spatial effect in deep excavations. However, the corner effects of the deep excavation with multi exposed corners have not been widely investigated and addressed in the previous literature. Based on the long and narrow deep excavation project of two square crossing of utility tunnels in a soft ground of Hainan, three dimensional numerical models of two typical construction programs are established using a commercial finite element software Plaxis 3D. Comparison and analysis of ground settlement caused by excavation, the deformation of the support structure, and the supporting axial force are performed. At the same time, the impacts of the corner effect on the distribution characteristics of these aforementioned studies are further discussed. The calculated results show that the maximum ground surface settlement of the long and narrow deep excavation for the utility tunnel varies between 0.11% He~0.67% He(He is excavation depth) under the two typical construction modes. The reasonable upper and lower bounds among the maximum lateral displacement of the steel sheet pile and excavation depth are 0.25% He and 1.35% He, respectively. On the whole, the maximum ground settlement of the soil around the excavation and lateral deformation of the supporting structure under the circumstance of construction program Ⅱ are lower than that in the condition of construction program Ⅰ. During the excavation process, it is worth noting that both two free surfaces of the exposed corner all have the remarkable corner effects under the circumstance of construction program Ⅱ, while the exposed corners in only one direction show the obvious corner effects under the circumstance of the construction program Ⅰ after their formation. The range of influence of the corner effects is approximately 2 times excavation depths. Within that range, the ground settlement, the deformation of the supporting structure and strut axial forces are all significantly lower than those in areas exceeding the coverage of the corner effects. The study suggests that if the influence of the corner effects and the degree of exertion are properly considered in the design of deep foundation pits with multi exposed corners at the intersections of utility tunnels, the project cost can be reduced to some extent. The corner effect is one of the important forms of the spatial effect in deep excavations. However, the corner effects of the deep excavation with multi exposed corners have not been widely investigated and addressed in the previous literature. Based on the long and narrow deep excavation project of two square crossing of utility tunnels in a soft ground of Hainan, three dimensional numerical models of two typical construction programs are established using a commercial finite element software Plaxis 3D. Comparison and analysis of ground settlement caused by excavation, the deformation of the support structure, and the supporting axial force are performed. At the same time, the impacts of the corner effect on the distribution characteristics of these aforementioned studies are further discussed. The calculated results show that the maximum ground surface settlement of the long and narrow deep excavation for the utility tunnel varies between 0.11% He~0.67% He(He is excavation depth) under the two typical construction modes. The reasonable upper and lower bounds among the maximum lateral displacement of the steel sheet pile and excavation depth are 0.25% He and 1.35% He, respectively. On the whole, the maximum ground settlement of the soil around the excavation and lateral deformation of the supporting structure under the circumstance of construction program Ⅱ are lower than that in the condition of construction program Ⅰ. During the excavation process, it is worth noting that both two free surfaces of the exposed corner all have the remarkable corner effects under the circumstance of construction program Ⅱ, while the exposed corners in only one direction show the obvious corner effects under the circumstance of the construction program Ⅰ after their formation. The range of influence of the corner effects is approximately 2 times excavation depths. Within that range, the ground settlement, the deformation of the supporting structure and strut axial forces are all significantly lower than those in areas exceeding the coverage of the corner effects. The study suggests that if the influence of the corner effects and the degree of exertion are properly considered in the design of deep foundation pits with multi exposed corners at the intersections of utility tunnels, the project cost can be reduced to some extent.
The practical research show that the conductivity of expansive soil has a linear relationship with the free expansion rate at the middle route of the south-to-north water diversion project. This paper aims to develop a rapid method for the discrimination of expansive soils at the Yangtze-to-Huai Water Diversion project and to present the standard for the electrical conductivity of soil of Yangtze-to-Huai area. It examines the electrical conductivity characteristics of expansive soils. It investigates the relationship between the conductivity of expansive soil and water content and free expansion rate in this area. Basic properties, swelling index and electrical conductivity tests are conducted on multi-group soil samples with varying water content obtained from the project field. The study shows that the lead rate increases with the increase of soil moisture content and then decreases. The soil has the highest electrical conductivity in the vicinity of its liquid limit. The electrical conductivity shows peak characteristics and increases with the swelling index of the soil under the same moisture content. The conductivity and the free swell index are linearly correlated in general. The correlation reaches a maximum in the vicinity of the liquid limit of the soil. The precision of the linear empirical model is controlled by the correlation coefficient. For weakly expansive soils, the model can achieve a high accuracy level of the free swell index when the R2 value is equal or greater than 0.78. and the findings have practical value in predicting the free swell index of soils. The practical research show that the conductivity of expansive soil has a linear relationship with the free expansion rate at the middle route of the south-to-north water diversion project. This paper aims to develop a rapid method for the discrimination of expansive soils at the Yangtze-to-Huai Water Diversion project and to present the standard for the electrical conductivity of soil of Yangtze-to-Huai area. It examines the electrical conductivity characteristics of expansive soils. It investigates the relationship between the conductivity of expansive soil and water content and free expansion rate in this area. Basic properties, swelling index and electrical conductivity tests are conducted on multi-group soil samples with varying water content obtained from the project field. The study shows that the lead rate increases with the increase of soil moisture content and then decreases. The soil has the highest electrical conductivity in the vicinity of its liquid limit. The electrical conductivity shows peak characteristics and increases with the swelling index of the soil under the same moisture content. The conductivity and the free swell index are linearly correlated in general. The correlation reaches a maximum in the vicinity of the liquid limit of the soil. The precision of the linear empirical model is controlled by the correlation coefficient. For weakly expansive soils, the model can achieve a high accuracy level of the free swell index when the R2 value is equal or greater than 0.78. and the findings have practical value in predicting the free swell index of soils.
Sichuan power transmission lines pass through the mountain area with a wide distribution of gravel soil. The gravel soil is a special rock and soil between the rock body and the soil body. There are different types of the gravel soil classification. For the gravel soil foundation pile under horizontal with different stone content, the horizontal bearing characteristics have a big difference. The current standards give a quite wide range of the proportional coefficient m of ground horizontal resistance coefficient. In practical application, we evaluate the m value too random. At present, there are some researches on the soil properties of gravel soil with different stone content, however, there are few researches on the characteristics of pile-soil horizontal interaction for gravelly soils with different stone content. Therefore, evaluating the characteristics of pile-soil horizontal interaction and m value on the gravel soil foundation under different stone content is a task to be resolved for the design of transmission tower pile foundation. In this paper, single pile static lateral loading tests are conducted in State Key Laboratory of Geohazard Prevention and Geoenvironment Protection of Chengdu University of Technology. We obtained three gravel soil with different stone content by conducting sizing test. We carried out three sets of physical simulation tests with different stone contents respectively, and obtained the mechanical parameters of gravelly soil with different stone contents. Then we got the effects of the displacement of pile top, the internal force of the pile, the proportional coefficient m of ground horizontal resistance coefficient with different stone content. We got the variation tendency of the m value with different stone contents. According to comparative analysis, we got the experiment characteristics and laws, and studied the bending moment value of pile curve, shear force curve, soil pressure curve on the pile side, and the variation tendency of the m value with different stone contents. The results indicate that pile bending moment first increases and then decreases from pile top to pile bottom. As the stone content of the gravel soil foundation grows, the maximum bending moment value of pile grows nonlinearity. The maximum bending moment value is buried approximately at 0.3 meter depth location of the section. At the condition of high stone content, bending stiffness can be properly increased at the position of the section at design time. As horizontal force increases, soil pressure on the pile is nonlinearly increase, too. As the stone content of the gravel soil foundation grows, the ground horizontal resistance increases, the position of zero of soil pressure on the pile side can also improve. This is due to the improvement of the horizontal resistance of the gravel soil and the simultaneous increase of the earth pressure before and after the pile. The stone content increase every 10%, the m value would also increase about 1.15~1.40 times. This research fill the application blank which does not address the different stone contents of the gravel soil affecting m value. It can also be used as a reference of the proportional coefficient m of ground horizontal resistance coefficient. Sichuan power transmission lines pass through the mountain area with a wide distribution of gravel soil. The gravel soil is a special rock and soil between the rock body and the soil body. There are different types of the gravel soil classification. For the gravel soil foundation pile under horizontal with different stone content, the horizontal bearing characteristics have a big difference. The current standards give a quite wide range of the proportional coefficient m of ground horizontal resistance coefficient. In practical application, we evaluate the m value too random. At present, there are some researches on the soil properties of gravel soil with different stone content, however, there are few researches on the characteristics of pile-soil horizontal interaction for gravelly soils with different stone content. Therefore, evaluating the characteristics of pile-soil horizontal interaction and m value on the gravel soil foundation under different stone content is a task to be resolved for the design of transmission tower pile foundation. In this paper, single pile static lateral loading tests are conducted in State Key Laboratory of Geohazard Prevention and Geoenvironment Protection of Chengdu University of Technology. We obtained three gravel soil with different stone content by conducting sizing test. We carried out three sets of physical simulation tests with different stone contents respectively, and obtained the mechanical parameters of gravelly soil with different stone contents. Then we got the effects of the displacement of pile top, the internal force of the pile, the proportional coefficient m of ground horizontal resistance coefficient with different stone content. We got the variation tendency of the m value with different stone contents. According to comparative analysis, we got the experiment characteristics and laws, and studied the bending moment value of pile curve, shear force curve, soil pressure curve on the pile side, and the variation tendency of the m value with different stone contents. The results indicate that pile bending moment first increases and then decreases from pile top to pile bottom. As the stone content of the gravel soil foundation grows, the maximum bending moment value of pile grows nonlinearity. The maximum bending moment value is buried approximately at 0.3 meter depth location of the section. At the condition of high stone content, bending stiffness can be properly increased at the position of the section at design time. As horizontal force increases, soil pressure on the pile is nonlinearly increase, too. As the stone content of the gravel soil foundation grows, the ground horizontal resistance increases, the position of zero of soil pressure on the pile side can also improve. This is due to the improvement of the horizontal resistance of the gravel soil and the simultaneous increase of the earth pressure before and after the pile. The stone content increase every 10%, the m value would also increase about 1.15~1.40 times. This research fill the application blank which does not address the different stone contents of the gravel soil affecting m value. It can also be used as a reference of the proportional coefficient m of ground horizontal resistance coefficient.
The key features for highway extension along river are occupation of the widening road on the original river, deep marine clay, and oblique intersection of deep marine clay with weathered rock layer. Therefore, the foundation is necessary to be reinforced. In addition, the opposite riverbank requires to be expanded and excavated which would have bad influence on the effect of ground improvement. Thus, modification method must be determined carefully. Based on numerical analysis with ABAQUS software and field measurements, the economy and reinforcement effect of the Bidirectional Dry Jet Mixing Method(BDJMM) and Concrete Prefabricated Square Pile are compared. Research results indicate that(1)the reinforcement effect of combination of BDJM and plastic drainage plate is better than that of traditional DJM method. (2)For the oblique intersection of soft clay layer with weathered rock layer, a significant sliding shearing interface at certain depth of the pile body can be formed. Concrete Prefabricated Square Pile would not meet with such kind of problem. So the Concrete Prefabricated Square Pile is the best choice in the ground improvement with the condition of oblique intersection of soft soil layer and rock layer. The key features for highway extension along river are occupation of the widening road on the original river, deep marine clay, and oblique intersection of deep marine clay with weathered rock layer. Therefore, the foundation is necessary to be reinforced. In addition, the opposite riverbank requires to be expanded and excavated which would have bad influence on the effect of ground improvement. Thus, modification method must be determined carefully. Based on numerical analysis with ABAQUS software and field measurements, the economy and reinforcement effect of the Bidirectional Dry Jet Mixing Method(BDJMM) and Concrete Prefabricated Square Pile are compared. Research results indicate that(1)the reinforcement effect of combination of BDJM and plastic drainage plate is better than that of traditional DJM method. (2)For the oblique intersection of soft clay layer with weathered rock layer, a significant sliding shearing interface at certain depth of the pile body can be formed. Concrete Prefabricated Square Pile would not meet with such kind of problem. So the Concrete Prefabricated Square Pile is the best choice in the ground improvement with the condition of oblique intersection of soft soil layer and rock layer.
Tamusu pre-selected area of Alxa pre-selected region for geological disposal of high-level nuclear waste is located in North Alxa Block. The crust consists of Permian and Triassic granite and is stable. There are a few faults, three ductile shear zones and one ductile-brittle deformation zone in the area. And the joints are controlled by regional tectonics. The classification of ground rock mass mainly is Ⅲ, and secondly is Ⅳ. According to core logging and mechanical test, the classifications of TMS01 and TMS02 drill cores are mainly Ⅴ and Ⅲ, respectively. From comparison of rock mass quality and well logging data, obvious correlation between quality and physical parameters of rock mass is found. Therefore, the relationship between rock mass quality and resistivity is established. Combining with the quality of surface rock mass and drilling core and geophysical prospecting section, the quality of rock mass in target depth is predicted as follows:the main rock mass is grade Ⅱ and Ⅲ, and some is grade Ⅰ and Ⅳ. Tamusu pre-selected area of Alxa pre-selected region for geological disposal of high-level nuclear waste is located in North Alxa Block. The crust consists of Permian and Triassic granite and is stable. There are a few faults, three ductile shear zones and one ductile-brittle deformation zone in the area. And the joints are controlled by regional tectonics. The classification of ground rock mass mainly is Ⅲ, and secondly is Ⅳ. According to core logging and mechanical test, the classifications of TMS01 and TMS02 drill cores are mainly Ⅴ and Ⅲ, respectively. From comparison of rock mass quality and well logging data, obvious correlation between quality and physical parameters of rock mass is found. Therefore, the relationship between rock mass quality and resistivity is established. Combining with the quality of surface rock mass and drilling core and geophysical prospecting section, the quality of rock mass in target depth is predicted as follows:the main rock mass is grade Ⅱ and Ⅲ, and some is grade Ⅰ and Ⅳ.
There are plenty saline soil distributed in Da'an area, Jilin Province. Those soils show frost heave deformation due to the low temperature in winter, which can cause serious damage to construction projects and building structures. This paper takes field sampling collections of saline soil in Da'an area, Jilin Province. The physical and chemical property, soil grain composition of the soil samples are tested. The frost heave properties are studied using indoor frost heaving simulation experiment. The experiment results show that the salinization type of soil samples is carbonic acid type. Soil samples of research area have high exchangeable cation content and sodion content. The water content, salt content and compaction degree of soil samples all show imparity influence to the frost heaving results during frost heaving process. Frost heaving tests are carried out. The results show that with the temperature decreasing the frost heaving ratio increases. Only the frost heaving ration does not change much nearby the-10℃. For most of soil samples, with the compaction degree increasing the frost heaving ratio basically increases. The compaction degree affects frost heaving ration more obviously at low water contents soil samples. The soil samples of high salt content show lager frost heaving ratio than the low salt content samples. Besides, the frost heaving ratio take longer time to be stabilized than the low salt content samples. According to the test results, the largest frost heaving ratio is 3.5%. It ends up at soil samples with 26% water content, 1.5% salt content and 90%compaction degree. There is a best compaction degree of different salt content soil samples. The heaving ratio is increased by compaction degree of low salt content samples. But for high salt content samples, it shows inhibiting effect to soil if the compaction degree is too high or too low. For very low water content samples, high salt content shows inhibiting effect to soil samples. The soil samples show frost heaving only when the salt content is high enough. Soil has a frost heaving beginning water content, the frost heaving beginning water content of Da'an saline soil is 21%. This research provides theoretical basis to preventative mature of frost heaving damage in west Jilin Province. There are plenty saline soil distributed in Da'an area, Jilin Province. Those soils show frost heave deformation due to the low temperature in winter, which can cause serious damage to construction projects and building structures. This paper takes field sampling collections of saline soil in Da'an area, Jilin Province. The physical and chemical property, soil grain composition of the soil samples are tested. The frost heave properties are studied using indoor frost heaving simulation experiment. The experiment results show that the salinization type of soil samples is carbonic acid type. Soil samples of research area have high exchangeable cation content and sodion content. The water content, salt content and compaction degree of soil samples all show imparity influence to the frost heaving results during frost heaving process. Frost heaving tests are carried out. The results show that with the temperature decreasing the frost heaving ratio increases. Only the frost heaving ration does not change much nearby the-10℃. For most of soil samples, with the compaction degree increasing the frost heaving ratio basically increases. The compaction degree affects frost heaving ration more obviously at low water contents soil samples. The soil samples of high salt content show lager frost heaving ratio than the low salt content samples. Besides, the frost heaving ratio take longer time to be stabilized than the low salt content samples. According to the test results, the largest frost heaving ratio is 3.5%. It ends up at soil samples with 26% water content, 1.5% salt content and 90%compaction degree. There is a best compaction degree of different salt content soil samples. The heaving ratio is increased by compaction degree of low salt content samples. But for high salt content samples, it shows inhibiting effect to soil if the compaction degree is too high or too low. For very low water content samples, high salt content shows inhibiting effect to soil samples. The soil samples show frost heaving only when the salt content is high enough. Soil has a frost heaving beginning water content, the frost heaving beginning water content of Da'an saline soil is 21%. This research provides theoretical basis to preventative mature of frost heaving damage in west Jilin Province.
Application of large-diameter long piles and super long piles in large thickness loess foundation has increased sharply. However, bearing deformation mechanism, lateral resistance and end bearing capacity of super long piles in loess foundation differ from those of the ordinary piles. Vertical compression static load tests of super long single pile and pile group are conducted respectively. The similar material is applied as filling of model test. Laws of development of load settlement, pile shaft force, lateral resistance and soil plastic zone at the end of pile under the vertical load are analysed. Test results show that load of super long single pile is mainly undertaken by lateral resistance of pile under the vertical load, which is gradually developed from top to bottom. It belongs to pure friction pile, and the failure mode of single pile is punching failure. The influence scope of plastic deformation of pile end soil is about 1.1 times of pile diameter. Compared with the single pile, the end bearing capacity of super long pile group is greatly improved, and pile shaft force attenuation depth of the pile has decreased, and lateral resistance increases gradually along the pile body. Influence scope of the pile end soil layer is about 1.25 times of diameter, which is close to the influence scope of super long single pile. Research method and results in this paper can provide reference for research on bearing characteristics of super long piles in large thickness loess foundation. Application of large-diameter long piles and super long piles in large thickness loess foundation has increased sharply. However, bearing deformation mechanism, lateral resistance and end bearing capacity of super long piles in loess foundation differ from those of the ordinary piles. Vertical compression static load tests of super long single pile and pile group are conducted respectively. The similar material is applied as filling of model test. Laws of development of load settlement, pile shaft force, lateral resistance and soil plastic zone at the end of pile under the vertical load are analysed. Test results show that load of super long single pile is mainly undertaken by lateral resistance of pile under the vertical load, which is gradually developed from top to bottom. It belongs to pure friction pile, and the failure mode of single pile is punching failure. The influence scope of plastic deformation of pile end soil is about 1.1 times of pile diameter. Compared with the single pile, the end bearing capacity of super long pile group is greatly improved, and pile shaft force attenuation depth of the pile has decreased, and lateral resistance increases gradually along the pile body. Influence scope of the pile end soil layer is about 1.25 times of diameter, which is close to the influence scope of super long single pile. Research method and results in this paper can provide reference for research on bearing characteristics of super long piles in large thickness loess foundation.
High level radioactive waste is the inevitable product of nuclear power development. The whole world has paid more attention to the safe disposal of the waste so as to maintain the sustainable development of nuclear power. Regional suitability assessment of engineering geology is one of the key tasks when siting the repository of high-radioactive waste disposal. Alxa area is one of the pre-selected areas for high level radioactive waste disposal in China. In order to identify pre-selected sites with good engineering geology in this area, the regional suitability assessment of engineering geology is necessary. Based on comprehensive index model and ArcGIS system, the regional engineering geology suitability of pre-selected Alxa region for high-level radioactive waste disposal is assessed. In comprehensive index model, the selection of assessment factors and determination of the weight value of factors are important. Due to the special purpose and requirements of high-radioactive waste site selection, the selection of assessment factors is different from that surface engineering. For example, the topography and rainfall factors are not in the consideration of high-radioactive waste site selection. According to field engineering geological survey and comprehensive data collection, lithology, faults, seismic, tectonic stress and tectonic terrain are selected as assessment factors. Considering the characteristics of multi-objective and fuzziness in suitability evaluation of high-radioactive waste disposal, analytic hierarchy process is used to determine the weight of each factor. On the basis of these factors, the comprehensive index is obtained. Then engineering geology suitability of Alxa region is classified into five levels according to the comprehensive index. They are respectively the better suitability, the good suitability, the moderate suitability, the poor suitability and the worse suitability. Evaluation results can provide reference for siting the repository of high-radioactive waste disposal. It is considered that the better suitability area and good suitability area in the assessment map can be considered as the site area. Among these area, Tamusu and Nuorigong are two sections with the level of the better to good suitability. Further site selection work can carried out in these two sections. High level radioactive waste is the inevitable product of nuclear power development. The whole world has paid more attention to the safe disposal of the waste so as to maintain the sustainable development of nuclear power. Regional suitability assessment of engineering geology is one of the key tasks when siting the repository of high-radioactive waste disposal. Alxa area is one of the pre-selected areas for high level radioactive waste disposal in China. In order to identify pre-selected sites with good engineering geology in this area, the regional suitability assessment of engineering geology is necessary. Based on comprehensive index model and ArcGIS system, the regional engineering geology suitability of pre-selected Alxa region for high-level radioactive waste disposal is assessed. In comprehensive index model, the selection of assessment factors and determination of the weight value of factors are important. Due to the special purpose and requirements of high-radioactive waste site selection, the selection of assessment factors is different from that surface engineering. For example, the topography and rainfall factors are not in the consideration of high-radioactive waste site selection. According to field engineering geological survey and comprehensive data collection, lithology, faults, seismic, tectonic stress and tectonic terrain are selected as assessment factors. Considering the characteristics of multi-objective and fuzziness in suitability evaluation of high-radioactive waste disposal, analytic hierarchy process is used to determine the weight of each factor. On the basis of these factors, the comprehensive index is obtained. Then engineering geology suitability of Alxa region is classified into five levels according to the comprehensive index. They are respectively the better suitability, the good suitability, the moderate suitability, the poor suitability and the worse suitability. Evaluation results can provide reference for siting the repository of high-radioactive waste disposal. It is considered that the better suitability area and good suitability area in the assessment map can be considered as the site area. Among these area, Tamusu and Nuorigong are two sections with the level of the better to good suitability. Further site selection work can carried out in these two sections.
The presence of middle-lower dip joints is one of the important geological defects in dam foundation. Analysis of development mode and formation mechanism provides an important foundation for the stability of slopes. This paper is based on detailed analysis of the spatial distribution, combined with geological analysis, SEM and numerical simulation. It interprets the formation mechanism of middle-lower dip joints at a large hydropower station dam site. The results are as follows:(1)Intermittent rapid down-cutting of the river is the main reason for the alternative distribution of middle-lower dip joints; (2)Main fracture mechanism is coexist of tension and shear, a small number of samples show the shear fracture; (3)If faults and dykes exist in slopes and their widths are large, relaxation effect along the whole weak belt is obvious and the distribution of shear strain increment belt is not obvious.(4)If the width of weak belt and distance to the slope surface are both small, on the one hand, shear strain increment is concentrated along the dip direction of weak belt, on the other hand, concentrated degree and number of middle-lower dip joints increased. In addition, density of middle-lower dip joints also increased. The presence of middle-lower dip joints is one of the important geological defects in dam foundation. Analysis of development mode and formation mechanism provides an important foundation for the stability of slopes. This paper is based on detailed analysis of the spatial distribution, combined with geological analysis, SEM and numerical simulation. It interprets the formation mechanism of middle-lower dip joints at a large hydropower station dam site. The results are as follows:(1)Intermittent rapid down-cutting of the river is the main reason for the alternative distribution of middle-lower dip joints; (2)Main fracture mechanism is coexist of tension and shear, a small number of samples show the shear fracture; (3)If faults and dykes exist in slopes and their widths are large, relaxation effect along the whole weak belt is obvious and the distribution of shear strain increment belt is not obvious.(4)If the width of weak belt and distance to the slope surface are both small, on the one hand, shear strain increment is concentrated along the dip direction of weak belt, on the other hand, concentrated degree and number of middle-lower dip joints increased. In addition, density of middle-lower dip joints also increased.
The loess has strong collapsibility in Heifangtai Platform, Yongjing Country, Gansu Province which belongs to a typical loess platform. Collapsible loess of thick layer caused by long-term flood irrigation has induced many loess landslides and severe ground deformations. We selected ground deformations in Heifangtai Platform as research object. The descending data of Sentinel-1 A satellite in three different orbits were processed using PS-InSAR technique between 2014 and 2017, and the deformation in different line of sight(LOS) is obtained. In addition, 3 D ground surface deformations was obtained by inversion and calculation in the area. Ground surface deformations of LOS direction, vertical and horizontal direction was analyzed, and the development trend of ground surface deformation was predicted. The results show there are differential settlements in study area. The deformation rates of LOS direction are larger in some area including closing to central area of platform and the part of area on the edge of platform. The range of settlement is 4~13 mm·a-1. A region with large vertical deformation is near the middle of platform. The average rate of deformation is-20~-6 mm·a-1. The North-South deformations are small. The average rate of deformation is-5~5 mm·a-1. However, the West-East deformations are large. The average rate of deformation is mostly more than 20 mm·a-1. Ground surface deformations are still at a slow acceleration stage in short term as a whole. With continuous development of agricultural irrigation, the rate of ground surface deformation will gradually decrease after rising a certain value. The loess has strong collapsibility in Heifangtai Platform, Yongjing Country, Gansu Province which belongs to a typical loess platform. Collapsible loess of thick layer caused by long-term flood irrigation has induced many loess landslides and severe ground deformations. We selected ground deformations in Heifangtai Platform as research object. The descending data of Sentinel-1 A satellite in three different orbits were processed using PS-InSAR technique between 2014 and 2017, and the deformation in different line of sight(LOS) is obtained. In addition, 3 D ground surface deformations was obtained by inversion and calculation in the area. Ground surface deformations of LOS direction, vertical and horizontal direction was analyzed, and the development trend of ground surface deformation was predicted. The results show there are differential settlements in study area. The deformation rates of LOS direction are larger in some area including closing to central area of platform and the part of area on the edge of platform. The range of settlement is 4~13 mm·a-1. A region with large vertical deformation is near the middle of platform. The average rate of deformation is-20~-6 mm·a-1. The North-South deformations are small. The average rate of deformation is-5~5 mm·a-1. However, the West-East deformations are large. The average rate of deformation is mostly more than 20 mm·a-1. Ground surface deformations are still at a slow acceleration stage in short term as a whole. With continuous development of agricultural irrigation, the rate of ground surface deformation will gradually decrease after rising a certain value.
The 10th China Youth's Symposium on Engineering Geology(CYSEG)was successfully held at China Three Gorges University from 7th to 9th in September 2018. The CYSEG mainly focused on "Engineering geology and geotechnical engineering problems in water conservancy and hydropower engineering", which is jointly organized by Committee of Engineering Geology in China, China Three Gorges University with other organizations, and co-organized by China University of Geosciences with other organizations. There were more than 300 participants from 78 organizations including domestic universities, research institutes and the industries. The CYSEG was composed of two parts:academic seminar and field geological survey. Among them, 55 young scholars' lectures and 12 graduate students' reports were presented. In a harmonious atmosphere, all the attendees discussed the issues around symposium theme. In the CYSEG, new academic sparks were collided, and new academic thoughts were produced. It plays a positive role in promoting the development for CYSEG, fresh blood and power keep pouring into. The 10th China Youth's Symposium on Engineering Geology(CYSEG)was successfully held at China Three Gorges University from 7th to 9th in September 2018. The CYSEG mainly focused on "Engineering geology and geotechnical engineering problems in water conservancy and hydropower engineering", which is jointly organized by Committee of Engineering Geology in China, China Three Gorges University with other organizations, and co-organized by China University of Geosciences with other organizations. There were more than 300 participants from 78 organizations including domestic universities, research institutes and the industries. The CYSEG was composed of two parts:academic seminar and field geological survey. Among them, 55 young scholars' lectures and 12 graduate students' reports were presented. In a harmonious atmosphere, all the attendees discussed the issues around symposium theme. In the CYSEG, new academic sparks were collided, and new academic thoughts were produced. It plays a positive role in promoting the development for CYSEG, fresh blood and power keep pouring into.
The crushing of particles is one of the important factors that cause change of the sand mechanical properties, in particular the fragile material calcareous sand. This paper aims to further understand the effect of particle crushing on the stress-strain and shear strength of calcareous sand. It carries out a series of triaxial shear tests on calcareous sand with different relative densities under different confining pressures. It analyzes the particle size distribution curves of calcareous sand samples before and after tests. It discusses the particle breakage rules of calcareous sand as well as their influencing factors. Through triaxial tests the stress-strain curve of the calcareous sand is obtained. The relationship between relative density and particle crushing, confining pressure and particle crushing, and the effect of particle crushing on stress-strain and shear strength of calcareous sand were analyzed by introducing Hardin's relative breaking ratio Br. The results show that with the increase of confining pressure, the increment of particle shrinkage decreases gradually until the crushing reaches an upper limit. Then the confining pressure and relative density have little effect on the particle crushing. The influence degree of relative density on particle crushing is less than confining pressure. Sliding friction can bring about the stress increase to a limit state. The particle crushing result in the stress cannot reach the state. In the experimental condition, particles are less broken under low confining pressure and the relative motion form among particles is slip, so the stress-strain curve is soften strain type. Under high confining pressure the particles crushing becomes serious and occurs throughout the shear process. So the stress-strain curve is hardening strain type. Particle breakage makes the volume gradually change from the dilatancy to the shrinkage. The more serious the breakage is, the more obvious the shrinkage is. Under low confining pressure the strength of calcareous sand is mainly provided by dilatancy and interlocking. Due to the serious particles breakage under high confining pressure, the dilatancy disappears and the interlocking decreases, so the peak friction angle decreases and the shear strength reduces. The crushing of particles is one of the important factors that cause change of the sand mechanical properties, in particular the fragile material calcareous sand. This paper aims to further understand the effect of particle crushing on the stress-strain and shear strength of calcareous sand. It carries out a series of triaxial shear tests on calcareous sand with different relative densities under different confining pressures. It analyzes the particle size distribution curves of calcareous sand samples before and after tests. It discusses the particle breakage rules of calcareous sand as well as their influencing factors. Through triaxial tests the stress-strain curve of the calcareous sand is obtained. The relationship between relative density and particle crushing, confining pressure and particle crushing, and the effect of particle crushing on stress-strain and shear strength of calcareous sand were analyzed by introducing Hardin's relative breaking ratio Br. The results show that with the increase of confining pressure, the increment of particle shrinkage decreases gradually until the crushing reaches an upper limit. Then the confining pressure and relative density have little effect on the particle crushing. The influence degree of relative density on particle crushing is less than confining pressure. Sliding friction can bring about the stress increase to a limit state. The particle crushing result in the stress cannot reach the state. In the experimental condition, particles are less broken under low confining pressure and the relative motion form among particles is slip, so the stress-strain curve is soften strain type. Under high confining pressure the particles crushing becomes serious and occurs throughout the shear process. So the stress-strain curve is hardening strain type. Particle breakage makes the volume gradually change from the dilatancy to the shrinkage. The more serious the breakage is, the more obvious the shrinkage is. Under low confining pressure the strength of calcareous sand is mainly provided by dilatancy and interlocking. Due to the serious particles breakage under high confining pressure, the dilatancy disappears and the interlocking decreases, so the peak friction angle decreases and the shear strength reduces.
2018, 26(6): 1748-1758.
Abstract(1365)
567KB(58)