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Editor Work2019 Vol. 27, No. 3
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DISCUSSION ON ENERGY DISSIPATION MECHANISM IN SEEPAGE-CHEMICAL DAMAGE-SOFTENING PROCESS OF SOFT ROCK
2019, 27(3): 477-486.
Abstract
2397KB
Red bed soft rock has the characteristics of softening when it encounters water. The comprehensive effects of seepage, chemical and mechanical damage under rainfall conditions result in engineering geological hazards, which is one of the hot and difficult issues in geotechnical engineering field. Based on the principle of energy dissipation, the seepage, chemical and damage effects in the softening process of soft rock are studied. The main seepage, chemical and damage energy variables are extracted. The effect of seepage-chemical-damage on the softening process of soft rock and the mechanism of energy dissipation are discussed. The energy dissipation process is analyzed with triaxial test of soft rock. The results show that under the combined action of seepage-chemical-damage effect, water forms seepage in soft rock, which accelerates the softening process. The chemical interaction between soft rock and seepage accelerates the development of fracture-pore damage. The development of fracture-pore damage in soft rock in turn promotes the seepage and chemical action. From the energy point of view, the ultimate strain energy of soft rock can be reduced after softening. Seepage provides energy, but also consumes the energy of soft rock itself through chemical effect, which reduces strength and caused damage. Therefore, the softening process of soft rock is a process of energy dissipation. In this process, the fluctuation and dissipation of seepage, chemical and mechanical damage energy, material exchange and non-linear positive feedback make soft rock undergo phase transition from equilibrium to non-equilibrium, and finally soften and destroy intact soft rock to form dissipative structure.
Red bed soft rock has the characteristics of softening when it encounters water. The comprehensive effects of seepage, chemical and mechanical damage under rainfall conditions result in engineering geological hazards, which is one of the hot and difficult issues in geotechnical engineering field. Based on the principle of energy dissipation, the seepage, chemical and damage effects in the softening process of soft rock are studied. The main seepage, chemical and damage energy variables are extracted. The effect of seepage-chemical-damage on the softening process of soft rock and the mechanism of energy dissipation are discussed. The energy dissipation process is analyzed with triaxial test of soft rock. The results show that under the combined action of seepage-chemical-damage effect, water forms seepage in soft rock, which accelerates the softening process. The chemical interaction between soft rock and seepage accelerates the development of fracture-pore damage. The development of fracture-pore damage in soft rock in turn promotes the seepage and chemical action. From the energy point of view, the ultimate strain energy of soft rock can be reduced after softening. Seepage provides energy, but also consumes the energy of soft rock itself through chemical effect, which reduces strength and caused damage. Therefore, the softening process of soft rock is a process of energy dissipation. In this process, the fluctuation and dissipation of seepage, chemical and mechanical damage energy, material exchange and non-linear positive feedback make soft rock undergo phase transition from equilibrium to non-equilibrium, and finally soften and destroy intact soft rock to form dissipative structure.
2019, 27(3): 487-496.
This paper studies the variation of acoustic emission(AE)characteristics during dacite failure and the rules of AE b value in rock failure precursor. We carry out tests of dacite samples under uniaxial loading, triaxial loading and triaxial unloading conditions. The AE is detected at the same time. The results show that:the change of AE b value is closely related to the stress path. There are significant differences between loading and unloading paths, but the uniaxial loading and the triaxial loading are similar. In uniaxial and triaxial loading tests, the confining pressure has great influence on the change of AE b value. Before rock failure, for the overall AE b value, the higher the confining pressure, the bigger the value. When rock is damaged, the higher the confining pressure, the greater the decline of b value, dropping more rapidly. The b value also reaches its minimum in the whole process. In triaxial unloading test, the effects of confining pressure on the b value is not obvious. Compared with the triaxial loading test, when triaxial unloading tests reach a certain unloading level, the overall b value is lower, and the minimum value of b value is smaller at last. We propose that when rocks reach peak strength and there is a significant stress drop subsequently. The rapid dropping of b value can be used as a precursor to damage. The threshold of b value is determined by a large number of indoor rock AE test results. Rapid drop of the AE b value and b value breaking through 0.6 can be used as the precursors of rock failure.
This paper studies the variation of acoustic emission(AE)characteristics during dacite failure and the rules of AE b value in rock failure precursor. We carry out tests of dacite samples under uniaxial loading, triaxial loading and triaxial unloading conditions. The AE is detected at the same time. The results show that:the change of AE b value is closely related to the stress path. There are significant differences between loading and unloading paths, but the uniaxial loading and the triaxial loading are similar. In uniaxial and triaxial loading tests, the confining pressure has great influence on the change of AE b value. Before rock failure, for the overall AE b value, the higher the confining pressure, the bigger the value. When rock is damaged, the higher the confining pressure, the greater the decline of b value, dropping more rapidly. The b value also reaches its minimum in the whole process. In triaxial unloading test, the effects of confining pressure on the b value is not obvious. Compared with the triaxial loading test, when triaxial unloading tests reach a certain unloading level, the overall b value is lower, and the minimum value of b value is smaller at last. We propose that when rocks reach peak strength and there is a significant stress drop subsequently. The rapid dropping of b value can be used as a precursor to damage. The threshold of b value is determined by a large number of indoor rock AE test results. Rapid drop of the AE b value and b value breaking through 0.6 can be used as the precursors of rock failure.
2019, 27(3): 497-504.
The whole world has paid more attention to the geological disposal of high-level radioactive waste. Granite is the candidate surrounding rock of high-level radioactive waste disposal project in China. It is very important to understand the strength and destructive characteristics of granite in the design and performance evaluation of disposal system. As aggregates of mineral grains, granite is a heterogeneous rock composed of minerals such as quartz, feldspar and biotite, and the macroscopic mechanical behaviors of rock is obviously affected by mineral grain size. Taking the granites in pre-selected Alxa area of China's high-level geological repository as example, the rock samples have obvious difference in grain size. The effect of grain size on granite mechanical properties is studied using uniaxial compression experiments with the combination of numerical simulation. Uniaxial compression experiments are conducted on MTS815 rock mechanics test system and numerical simulations are based on the particle flow code PFC2D. In the process of numerical simulation, the actual spatial distribution of various components within the rock ISS obtained by image processing based on the surface image of the specimen. The particle flow model of granite based on the actual distributions is thereafter established. The model is used to simulate the uniaxial compression test of granite, and the reliability of the model is demonstrated by comparison with the experimental results. Experiment and simulation results show that the failure mode of Alxa granite is brittle and tensional. Most failure is parallel to the direction of compressive stress. Numerical simulation based on digital image processing method can be used to calculate the mechanical responses of rock materials with high efficiency and accuracy. Mineral grain size has little effect on elastic modulus and Poisson's ratio of the rock, but peak strength is obviously affected by the grain size. The main results are as follows:The strength of rock with fine grained and equigranular texture is high, and the strength of rock with coarse grained and inequigranular texture is low.
The whole world has paid more attention to the geological disposal of high-level radioactive waste. Granite is the candidate surrounding rock of high-level radioactive waste disposal project in China. It is very important to understand the strength and destructive characteristics of granite in the design and performance evaluation of disposal system. As aggregates of mineral grains, granite is a heterogeneous rock composed of minerals such as quartz, feldspar and biotite, and the macroscopic mechanical behaviors of rock is obviously affected by mineral grain size. Taking the granites in pre-selected Alxa area of China's high-level geological repository as example, the rock samples have obvious difference in grain size. The effect of grain size on granite mechanical properties is studied using uniaxial compression experiments with the combination of numerical simulation. Uniaxial compression experiments are conducted on MTS815 rock mechanics test system and numerical simulations are based on the particle flow code PFC2D. In the process of numerical simulation, the actual spatial distribution of various components within the rock ISS obtained by image processing based on the surface image of the specimen. The particle flow model of granite based on the actual distributions is thereafter established. The model is used to simulate the uniaxial compression test of granite, and the reliability of the model is demonstrated by comparison with the experimental results. Experiment and simulation results show that the failure mode of Alxa granite is brittle and tensional. Most failure is parallel to the direction of compressive stress. Numerical simulation based on digital image processing method can be used to calculate the mechanical responses of rock materials with high efficiency and accuracy. Mineral grain size has little effect on elastic modulus and Poisson's ratio of the rock, but peak strength is obviously affected by the grain size. The main results are as follows:The strength of rock with fine grained and equigranular texture is high, and the strength of rock with coarse grained and inequigranular texture is low.
2019, 27(3): 505-515.
At present, the application of energy principle to study the failure, deformation and stability of rock mass is the focus of rock mechanics research. This paper aims to study the response laws of three kinds of energy of argillaceous sandstone. They are the volumetric energy per unit, the volumetric elastic energy per unit and the volumetric dissipated energy per unit under cyclic loading. The loading and unloading test is carried out considering different frequencies, confining pressures and stress amplitudes. The test results show that the three kinds of energy response to number of cycles have the same performance with different pressures and same frequency. With the increase of frequency, the three kinds of energy response laws to number of cycles show regular volatility. Performance among accumulated volumetric energy, accumulated volumetric elastic energy and number of cycles is approximately linear. The accumulated volumetric dissipated energy is strongly characterized by nonlinearity. The energy rate index is used to measure the degree of energy change. The higher the frequency, the greater the change of the energy rate. There are sudden change points in the curve of volumetric dissipated energy rate versus time, preliminary speculated to be the threshold point for the development of cracks in the inner or surface of the rock sample. Through the analysis of the factors affecting dissipated energy, we can find that the positive increasing trends are shown among confining pressure, frequency, dynamic stress amplitude and dissipated energy respectively. Based on the analysis results of relevant literatures, three kinds of energy response laws are comprehensively analyzed from the beginning of the cycle to the final failure of the rock. The energy response laws of the rock sample under cyclic loading are clarified. It is helpful to deepen the understanding of the energy response law, damage and failure of argillaceous sandstone, and provide experimental basis and application guidance for analyzing the stability of rock mass engineering using energy principle.
At present, the application of energy principle to study the failure, deformation and stability of rock mass is the focus of rock mechanics research. This paper aims to study the response laws of three kinds of energy of argillaceous sandstone. They are the volumetric energy per unit, the volumetric elastic energy per unit and the volumetric dissipated energy per unit under cyclic loading. The loading and unloading test is carried out considering different frequencies, confining pressures and stress amplitudes. The test results show that the three kinds of energy response to number of cycles have the same performance with different pressures and same frequency. With the increase of frequency, the three kinds of energy response laws to number of cycles show regular volatility. Performance among accumulated volumetric energy, accumulated volumetric elastic energy and number of cycles is approximately linear. The accumulated volumetric dissipated energy is strongly characterized by nonlinearity. The energy rate index is used to measure the degree of energy change. The higher the frequency, the greater the change of the energy rate. There are sudden change points in the curve of volumetric dissipated energy rate versus time, preliminary speculated to be the threshold point for the development of cracks in the inner or surface of the rock sample. Through the analysis of the factors affecting dissipated energy, we can find that the positive increasing trends are shown among confining pressure, frequency, dynamic stress amplitude and dissipated energy respectively. Based on the analysis results of relevant literatures, three kinds of energy response laws are comprehensively analyzed from the beginning of the cycle to the final failure of the rock. The energy response laws of the rock sample under cyclic loading are clarified. It is helpful to deepen the understanding of the energy response law, damage and failure of argillaceous sandstone, and provide experimental basis and application guidance for analyzing the stability of rock mass engineering using energy principle.
2019, 27(3): 516-524.
Carbonate rock can be easily corroded in natural environment. Water is an important factor that causes carbonate rock erosion. The pure water was used to wash the surface of oolitic limestone specimens in the experimental tank. The mechanism of rain or dynamic water on the dissolution of oolitic limestone was studied. The experiment of simulated rain was carried out for 1200 h. After each 120 h(i.e. a cycle), specimens were dried and the surface mico-topography, weight and ultrasonic wave velocity of specimens were measured, and the dissolution rate was calculated based on the change of the micro-topography. The results show that rain can cause calcite matrix dissolution and oolitic detachment on the surface of specimens. During the first to the fourth rain cycles, the calcite matrix on the surface of specimens slowly dissolved and the dissolution rate was 0~0.05 μm·h-1. During the fifth rain cycle, oolitic detachment occurred on the surface of specimens and the dissolution rate was 0.08~0.47 μm·h-1. During the sixth to the tenth rain cycles, the calcite matrix on the surface of specimens slowly dissolved and the dissolution rate was 0~0.06 μm·h-1. Elastic wave velocity did not change during the whole cycling process, indicating that there is no degradation inside specimens.
Carbonate rock can be easily corroded in natural environment. Water is an important factor that causes carbonate rock erosion. The pure water was used to wash the surface of oolitic limestone specimens in the experimental tank. The mechanism of rain or dynamic water on the dissolution of oolitic limestone was studied. The experiment of simulated rain was carried out for 1200 h. After each 120 h(i.e. a cycle), specimens were dried and the surface mico-topography, weight and ultrasonic wave velocity of specimens were measured, and the dissolution rate was calculated based on the change of the micro-topography. The results show that rain can cause calcite matrix dissolution and oolitic detachment on the surface of specimens. During the first to the fourth rain cycles, the calcite matrix on the surface of specimens slowly dissolved and the dissolution rate was 0~0.05 μm·h-1. During the fifth rain cycle, oolitic detachment occurred on the surface of specimens and the dissolution rate was 0.08~0.47 μm·h-1. During the sixth to the tenth rain cycles, the calcite matrix on the surface of specimens slowly dissolved and the dissolution rate was 0~0.06 μm·h-1. Elastic wave velocity did not change during the whole cycling process, indicating that there is no degradation inside specimens.
2019, 27(3): 525-531.
Direct shearing tests of pre-split structural plane filled with clay films are conducted on the slate specimens using a microprocessor servo-controlled shearing tester under various normal stresses. After that, two experimental phenomena are found as follows. (1)During the process of direct shearing test of structural plane, the areas which bored the shearing force were not the whole structural plane, but were partial structural plane. (2)The values of effective frictional areas which bored the shearing force during every shearing process, could increase with the increasing of normal stress, but the increasing rate decreased gradually. In this paper, to analyze the changing law of shear strength parameters of filled structural plane, the apparent shear strength parameters and effective shear strength parameters were proposed. The apparent shear strength parameters were calculated according to the assumption that the shearing force was borne by the whole structural plane. And then, curves of relation between apparent shear stress and shear displacement were obtained. And apparent shear strength parameters were achieved by fitting the apparent shear stresses under various apparent normal stresses. The effective shear strength parameters were calculated according to the assumption of effective frictional areas. In the same way, the curves of relation between the effective shear stress and the shear displacement, and effective shear strength parameters were obtained. Comparing the apparent shear strength parameters with effective shear strength parameters, we find that:(1)the frictional angle has no relationship with the choice of structural plane which bears the shearing force. But the cohesion is influenced by the choice of structural plane. (2)Comparing with the apparent cohesion, the value of effective cohesion is improved by 95%. This paper may contribute to the assessment and selection of the treatment plan of landslide engineering.
Direct shearing tests of pre-split structural plane filled with clay films are conducted on the slate specimens using a microprocessor servo-controlled shearing tester under various normal stresses. After that, two experimental phenomena are found as follows. (1)During the process of direct shearing test of structural plane, the areas which bored the shearing force were not the whole structural plane, but were partial structural plane. (2)The values of effective frictional areas which bored the shearing force during every shearing process, could increase with the increasing of normal stress, but the increasing rate decreased gradually. In this paper, to analyze the changing law of shear strength parameters of filled structural plane, the apparent shear strength parameters and effective shear strength parameters were proposed. The apparent shear strength parameters were calculated according to the assumption that the shearing force was borne by the whole structural plane. And then, curves of relation between apparent shear stress and shear displacement were obtained. And apparent shear strength parameters were achieved by fitting the apparent shear stresses under various apparent normal stresses. The effective shear strength parameters were calculated according to the assumption of effective frictional areas. In the same way, the curves of relation between the effective shear stress and the shear displacement, and effective shear strength parameters were obtained. Comparing the apparent shear strength parameters with effective shear strength parameters, we find that:(1)the frictional angle has no relationship with the choice of structural plane which bears the shearing force. But the cohesion is influenced by the choice of structural plane. (2)Comparing with the apparent cohesion, the value of effective cohesion is improved by 95%. This paper may contribute to the assessment and selection of the treatment plan of landslide engineering.
2019, 27(3): 532-538.
There is a plenty of stone relics in Beijing built with Beijing marble(mainly used white marble and green marble). Due to the need of restoration and protection, it is necessary to figure out the physical and mechanical properties of these marbles. In practice, the physical parameters of stone relics can be obtained easily. But it is hard to sample stone relics for mechanical experiment. So in this study, we used Schmidt hardness, Leeb hardness, P-wave velocity, uniaxial compressive strength and modulus of elasticity to obtain the physical and mechanical properties of these marbles. In order to find out the relationship between physical parameters(including Schmidt hardness, Leeb hardness, P-wave velocity) and mechanical parameters(including uniaxial compressive strength and modulus of elasticity), the univariate and binary linear regression analysis was performed among the test results. Depending on the correlation coefficient, the results of regression analysis indicate that the Leeb hardness with D-type probe is more reliable in evaluating the uniaxial compressive strength. The results also reveal that Schmidt hardness is more suitable in predicting the modulus of elasticity. In addition, it will be more reliable to use both of the Leeb hardness with D-type probe and Schmidt hardness to evaluate uniaxial compressive strength or modulus of elasticity.
There is a plenty of stone relics in Beijing built with Beijing marble(mainly used white marble and green marble). Due to the need of restoration and protection, it is necessary to figure out the physical and mechanical properties of these marbles. In practice, the physical parameters of stone relics can be obtained easily. But it is hard to sample stone relics for mechanical experiment. So in this study, we used Schmidt hardness, Leeb hardness, P-wave velocity, uniaxial compressive strength and modulus of elasticity to obtain the physical and mechanical properties of these marbles. In order to find out the relationship between physical parameters(including Schmidt hardness, Leeb hardness, P-wave velocity) and mechanical parameters(including uniaxial compressive strength and modulus of elasticity), the univariate and binary linear regression analysis was performed among the test results. Depending on the correlation coefficient, the results of regression analysis indicate that the Leeb hardness with D-type probe is more reliable in evaluating the uniaxial compressive strength. The results also reveal that Schmidt hardness is more suitable in predicting the modulus of elasticity. In addition, it will be more reliable to use both of the Leeb hardness with D-type probe and Schmidt hardness to evaluate uniaxial compressive strength or modulus of elasticity.
2019, 27(3): 539-549.
Cement-based curing agent blocking is one of the main technology for the remediation of heavy metal contaminated soils in recent years. Freeze and thaw cycles(FTcs) is an important external agent affecting the mechanical properties of cement solidified heavy metal contaminated soil. In present study, the artificial lead-contaminated soil is prepared using a systematic design. FTcs tests and laboratory soil tests are employed to reveal the influence of freeze and thaw cycle on the unconfined compression strength of lead-contaminated soil. The results show that:with the increasing of the proportion of cement, the unconfined compression strength(qu) of cement solidified lead-contaminated soil increases, while failure strain decreases. With the increasing of the proportion of lead ion(higher pollution level), the unconfined compression strength(qu) of cement solidified lead-contaminated soil decreases. However, the trend of stress-strain curves is similar. The unconfined compressive strength of cement solidified lead-contaminated soil decreases with the increasing of freeze-thaw times. When the freeze-thaw times is the same, the loss rate of unconfined compressive strength of cement solidified lead-contaminated soil decreases with the increasing of the proportion of cement. The microstructure of solidified lead contaminated soil is quantitatively analyzed using SEM image. It is found that the proportion of fine particles(< 1 μm) and fine pores(< 2 μm) in the samples increases with the increasing of freeze-thaw times. It may be the main reasons leading to the decreasing of unconfined compressive strength of the soil that failure of freeze and thaw cycles on soil structure.
Cement-based curing agent blocking is one of the main technology for the remediation of heavy metal contaminated soils in recent years. Freeze and thaw cycles(FTcs) is an important external agent affecting the mechanical properties of cement solidified heavy metal contaminated soil. In present study, the artificial lead-contaminated soil is prepared using a systematic design. FTcs tests and laboratory soil tests are employed to reveal the influence of freeze and thaw cycle on the unconfined compression strength of lead-contaminated soil. The results show that:with the increasing of the proportion of cement, the unconfined compression strength(qu) of cement solidified lead-contaminated soil increases, while failure strain decreases. With the increasing of the proportion of lead ion(higher pollution level), the unconfined compression strength(qu) of cement solidified lead-contaminated soil decreases. However, the trend of stress-strain curves is similar. The unconfined compressive strength of cement solidified lead-contaminated soil decreases with the increasing of freeze-thaw times. When the freeze-thaw times is the same, the loss rate of unconfined compressive strength of cement solidified lead-contaminated soil decreases with the increasing of the proportion of cement. The microstructure of solidified lead contaminated soil is quantitatively analyzed using SEM image. It is found that the proportion of fine particles(< 1 μm) and fine pores(< 2 μm) in the samples increases with the increasing of freeze-thaw times. It may be the main reasons leading to the decreasing of unconfined compressive strength of the soil that failure of freeze and thaw cycles on soil structure.
2019, 27(3): 550-558.
There are some differences in the physical and mechanical properties of the same saturated soft soil under different sampling methods. Relying on geotechnical engineering survey projects for rail transit in soft soils, three sampling methods were adopted to carry out indoor comparative test on soft soil samples. The methods were the core tube sampler, the thick-wall sampler and the open thin-wall sampler. Based on the laboratory test results, the regularity and difference between the same indicators under the three sampling methods were compared and analyzed from the perspective of physical and mechanical properties. Based on the comprehensive analysis of the test results, combined with the changes of saturated soft soil structure under different sampling methods, the internal mechanism of index difference was analyzed. The results show that the physical properties of the core tube sample and thick-wall samples are basically the same, and the shear strength index is 2.1%~20.3% higher than these of the thin-wall samples. Compared with those of the thin-wall samples, the water content and porosity ratio of the core tube sample and thick-wall samples are reduced by about 10%, density has a small increase, about 3%, and the shear strength index has improved, an increase of 6.9%~68.3%. The change of solid and liquid composition in saturated soft soils caused by sampling method is the root cause of the difference in physical and mechanical properties.
There are some differences in the physical and mechanical properties of the same saturated soft soil under different sampling methods. Relying on geotechnical engineering survey projects for rail transit in soft soils, three sampling methods were adopted to carry out indoor comparative test on soft soil samples. The methods were the core tube sampler, the thick-wall sampler and the open thin-wall sampler. Based on the laboratory test results, the regularity and difference between the same indicators under the three sampling methods were compared and analyzed from the perspective of physical and mechanical properties. Based on the comprehensive analysis of the test results, combined with the changes of saturated soft soil structure under different sampling methods, the internal mechanism of index difference was analyzed. The results show that the physical properties of the core tube sample and thick-wall samples are basically the same, and the shear strength index is 2.1%~20.3% higher than these of the thin-wall samples. Compared with those of the thin-wall samples, the water content and porosity ratio of the core tube sample and thick-wall samples are reduced by about 10%, density has a small increase, about 3%, and the shear strength index has improved, an increase of 6.9%~68.3%. The change of solid and liquid composition in saturated soft soils caused by sampling method is the root cause of the difference in physical and mechanical properties.
2019, 27(3): 559-568.
The lateral loading capacity of various foundations are facing different requirements when they are applied to more and more fields. As the widespread usage of foundation forms, pile foundation plays an important role in various engineering. The two kinds of bearing capacity of pile foundation include vertical bearing capacity and lateral bearing capacity. Lateral capacity plays a crucial role in many situations in order to determine the stability under the seismic load and wind load specially. The lateral bearing capacity of pile foundation is mainly affected by pile and soil properties while the compactness and stone content of soil are the major factors to influence the lateral bearing capacity of the pile foundation on the gravel soil. This paper aims to clarify the influence of soil properties from the gravel soils on the lateral bearing capacity of pile foundations. It carries out 5 groups of indoor tests on static lateral loading test of single piles under different soil compactness and stone content. To achieve the expectation of the test, the relationship of piles' top displacement and lateral load is recorded. Their curves are plotted for the relationship with different compactness and stone content. Furthermore, critical load and ultimate load are found from these curves. As the load increases, the development of soil fissures surrounding the pile is recorded by taking photos and sketching in the progress of loading and writing explanations. The stress-strain process is divided into three parts according to the curve of piles' top displacement and lateral load and the development of soil fissure surrounding the pile. Lateral radial angle is obtained from the soil fissure angle surrounding the pile and is another important index to explain the lateral bearing capacity of pile foundation. According to the principle of horizontal diffusion, the effective calculating width in different soil properties is calculated using the lateral radial angle. Finally, the formulation of effective calculating width which provided by specification is adopted to calculate the proportional coefficient of lateral resistance coefficient-m value. It is proved that when the soil compactness is increased by 20%the critical and ultimate load growths are about 1.5 KN and 1.7 KN respectively, the horizontal diffusion angle growth is about 13ånd the m value growth is about 120 MN/m4. When the soil stone content is increased by 20%critical and ultimate load growths are about 0.6 KN and 0.5 KN, respectively, the horizontal diffusion angle growth is about 3°, the m value growth is about 50 MN/m4. The experiments show that the increasing of compactness and stone content has an improvement on each index. But by contrast, the effect of compactness on various indexes is obviously better than that of stone content. Under comprehensive consideration, the increasing of compactness and stone content of gravel soil can enhance the lateral bearing capacity of pile foundation, but the effect of soil compactness is more obvious. Therefore, as for the site selection of pile foundation engineering on gravel soil which requires higher horizontal bearing capacity, the site with higher compactness should be preferentially selected.
The lateral loading capacity of various foundations are facing different requirements when they are applied to more and more fields. As the widespread usage of foundation forms, pile foundation plays an important role in various engineering. The two kinds of bearing capacity of pile foundation include vertical bearing capacity and lateral bearing capacity. Lateral capacity plays a crucial role in many situations in order to determine the stability under the seismic load and wind load specially. The lateral bearing capacity of pile foundation is mainly affected by pile and soil properties while the compactness and stone content of soil are the major factors to influence the lateral bearing capacity of the pile foundation on the gravel soil. This paper aims to clarify the influence of soil properties from the gravel soils on the lateral bearing capacity of pile foundations. It carries out 5 groups of indoor tests on static lateral loading test of single piles under different soil compactness and stone content. To achieve the expectation of the test, the relationship of piles' top displacement and lateral load is recorded. Their curves are plotted for the relationship with different compactness and stone content. Furthermore, critical load and ultimate load are found from these curves. As the load increases, the development of soil fissures surrounding the pile is recorded by taking photos and sketching in the progress of loading and writing explanations. The stress-strain process is divided into three parts according to the curve of piles' top displacement and lateral load and the development of soil fissure surrounding the pile. Lateral radial angle is obtained from the soil fissure angle surrounding the pile and is another important index to explain the lateral bearing capacity of pile foundation. According to the principle of horizontal diffusion, the effective calculating width in different soil properties is calculated using the lateral radial angle. Finally, the formulation of effective calculating width which provided by specification is adopted to calculate the proportional coefficient of lateral resistance coefficient-m value. It is proved that when the soil compactness is increased by 20%the critical and ultimate load growths are about 1.5 KN and 1.7 KN respectively, the horizontal diffusion angle growth is about 13ånd the m value growth is about 120 MN/m4. When the soil stone content is increased by 20%critical and ultimate load growths are about 0.6 KN and 0.5 KN, respectively, the horizontal diffusion angle growth is about 3°, the m value growth is about 50 MN/m4. The experiments show that the increasing of compactness and stone content has an improvement on each index. But by contrast, the effect of compactness on various indexes is obviously better than that of stone content. Under comprehensive consideration, the increasing of compactness and stone content of gravel soil can enhance the lateral bearing capacity of pile foundation, but the effect of soil compactness is more obvious. Therefore, as for the site selection of pile foundation engineering on gravel soil which requires higher horizontal bearing capacity, the site with higher compactness should be preferentially selected.
2019, 27(3): 569-576.
We used CT scanning and PFC3D to establish the gravel-bearing slip soil model in three dimensions. Firstly, we obtained the point cloud data of the gravels through binarization processing and boundary identifying technology based on a series of two-dimensional CT images. Then, according to the boundary point cloud data, we established the three-dimensional model of every gravel by inverse reconstruction method. Finally, we imported the reconstructive model into PFC3D. The simulated results show that Euler angles of the gravels changed with the development of shearing deformation of the triaxial sample. Compared with the sample without gravels, the movement of balls around the gravels is more non-orientable, which indicates that the existence of the gravel has remarkable influence on the development of shearing zones. We verified the feasibility of this method through analyzing the moving regulation of the gravels in triaxial test. In brief, the study on the movement of gravels has great meaning to reveal the development of shear failure in gravel-bearing slip soil using CT and PFC.
We used CT scanning and PFC3D to establish the gravel-bearing slip soil model in three dimensions. Firstly, we obtained the point cloud data of the gravels through binarization processing and boundary identifying technology based on a series of two-dimensional CT images. Then, according to the boundary point cloud data, we established the three-dimensional model of every gravel by inverse reconstruction method. Finally, we imported the reconstructive model into PFC3D. The simulated results show that Euler angles of the gravels changed with the development of shearing deformation of the triaxial sample. Compared with the sample without gravels, the movement of balls around the gravels is more non-orientable, which indicates that the existence of the gravel has remarkable influence on the development of shearing zones. We verified the feasibility of this method through analyzing the moving regulation of the gravels in triaxial test. In brief, the study on the movement of gravels has great meaning to reveal the development of shear failure in gravel-bearing slip soil using CT and PFC.
2019, 27(3): 577-584.
Hazard assessment and prediction are the important contents of prevention and control of disasters. This paper attempts to solve the shortcomings of the method for determining the weight of indicators in traditional hazard assessment and the uncertainty of influencing factors. It takes the collapses in Wenchuan-Lixian highway of G4217 line as an example. Twelve factors including slope and aspect are selected as indicators of collapse hazard assessment. Hazard grading standards are established according to its unique geological environment conditions. The entropy weight method and analytical hierarchy process are coupled to determine the weights of the factors affecting collapse. A comprehensive evaluation model is established using EW-AHP and unascertained measure theory. Hazard assessment is carried out for 20 collapses in the study area and compared with the results of the field survey and assessment results using EW. Results show that the assessment results of the model are more in line with the actual situation and assessment method is reasonable and effective. It can provide a new idea for the prediction of the hazard of collapse in the future.
Hazard assessment and prediction are the important contents of prevention and control of disasters. This paper attempts to solve the shortcomings of the method for determining the weight of indicators in traditional hazard assessment and the uncertainty of influencing factors. It takes the collapses in Wenchuan-Lixian highway of G4217 line as an example. Twelve factors including slope and aspect are selected as indicators of collapse hazard assessment. Hazard grading standards are established according to its unique geological environment conditions. The entropy weight method and analytical hierarchy process are coupled to determine the weights of the factors affecting collapse. A comprehensive evaluation model is established using EW-AHP and unascertained measure theory. Hazard assessment is carried out for 20 collapses in the study area and compared with the results of the field survey and assessment results using EW. Results show that the assessment results of the model are more in line with the actual situation and assessment method is reasonable and effective. It can provide a new idea for the prediction of the hazard of collapse in the future.
2019, 27(3): 585-591.
Draining slope groundwater in real time can reduce the occurrence of landslides. The inclined drainage hole is an important method for landslide treatment. However, the clogging problem of the method restricts the effect of drainage, and the durability is not guaranteed. This paper proposes a negative pressure drainage technique for the downdip drainage hole. The lower part of hole is a permeable hole section, and the upper part is a grouting closed hole section. A slurry stopper is provided between the permeable hole section and the grouting closed hole section. The siphon pipe is placed at the bottom of the permeable hole section through the grouting closed hole section. When the water level in the slope rises and the water head height of the drain inlet is greater than the height of the borehole orifice, the siphon drainage starts naturally under the effect of height difference, resulting in the generation of the vacuum pressure in the permeable hole section, and thus the drainage rate is accelerated. The suction effect of the negative pressure drainage can discharge the silt in the hole. Moreover, the closed hole section isolates the water-air connection between the permeable hole section and the atmosphere, which is helpful to solve the problems of chemical and biological clogging. In this study, the principle and application feasibility of the proposed method is qualitatively analyzed. In addition, the physical model test of negative pressure and drainage capacity under constant head conditions is carried out. The model test material is fine sand. The results demonstrate that:(1)The drainage process can produce the necessary negative pressure conditions in the hole. (2)After draining for a period of time, the pressure value in the permeable cavity no longer changes, and the drainage flow is basically stable. (3)Increasing the diameter of the drainage pipe or the height difference between the drain outlet and the permeable cavity can generate a larger negative pressure value in the permeable cavity, thereby improving the drainage effect. Therefore, the proposed method is a new and effective drainage method and has a good engineering application value.
Draining slope groundwater in real time can reduce the occurrence of landslides. The inclined drainage hole is an important method for landslide treatment. However, the clogging problem of the method restricts the effect of drainage, and the durability is not guaranteed. This paper proposes a negative pressure drainage technique for the downdip drainage hole. The lower part of hole is a permeable hole section, and the upper part is a grouting closed hole section. A slurry stopper is provided between the permeable hole section and the grouting closed hole section. The siphon pipe is placed at the bottom of the permeable hole section through the grouting closed hole section. When the water level in the slope rises and the water head height of the drain inlet is greater than the height of the borehole orifice, the siphon drainage starts naturally under the effect of height difference, resulting in the generation of the vacuum pressure in the permeable hole section, and thus the drainage rate is accelerated. The suction effect of the negative pressure drainage can discharge the silt in the hole. Moreover, the closed hole section isolates the water-air connection between the permeable hole section and the atmosphere, which is helpful to solve the problems of chemical and biological clogging. In this study, the principle and application feasibility of the proposed method is qualitatively analyzed. In addition, the physical model test of negative pressure and drainage capacity under constant head conditions is carried out. The model test material is fine sand. The results demonstrate that:(1)The drainage process can produce the necessary negative pressure conditions in the hole. (2)After draining for a period of time, the pressure value in the permeable cavity no longer changes, and the drainage flow is basically stable. (3)Increasing the diameter of the drainage pipe or the height difference between the drain outlet and the permeable cavity can generate a larger negative pressure value in the permeable cavity, thereby improving the drainage effect. Therefore, the proposed method is a new and effective drainage method and has a good engineering application value.
2019, 27(3): 592-600.
At the beginning of 2011, affected by multi-periods of heavy rainfall, many geohazards were developed on the accumulated layer slopes in Shuimatuo Town, Sinan County. They include ground surface rupture, wall inclination, deformation aggravation of fissures on ground and walls. Once influenced by the heavy rainfall and other unfavorable factors, the unstable slopes would slide continuously, posing a serious threat to the 509 persons and 556 houses of Datong Community, and a significantly negative impact to the local society. Based on the field survey and indoor analysis, this paper elaborates the geo-environmental characteristics of the Shuimatuo landslide region and clarifies the important effects of geological structures and topographic conditions to the seepage field of the slope. With the help of local meteorological data, we continue to research the deformation and failure process of the slope under the rainfall condition with the SEEP/W module and the FLAC3D software. We preliminarily expound the formation mechanism of the thrust-type landslide(H1) and secondary tractive landslide(H2)triggered by the multi-period of rainfall. The preliminary research results believe that induced by the rare heavy rainfall in the history, the major landslide begins to deform, but limited by the terrain condition, showing characteristics of part and progressive failure. During the long-term creep deformation process of landslide, rainfall causes a fluctuation of the groundwater level, strengthening the creep of sliding mass. Controlled by the free surface condition, the evolutionary process of secondary tractive landslide shows obvious correlation and certain lag comparing to the major landslide. For the thrust-type accumulated layer landslide, affected by the terrain, groundwater and loading conditions, it takes a long time from strength decrease of sliding belt to the formation of sliding plane. While tractive accumulated layer landslide lasts shortly as it is a backward movement generated by slope stress redistribution due to the lack of key anti-slide body.
At the beginning of 2011, affected by multi-periods of heavy rainfall, many geohazards were developed on the accumulated layer slopes in Shuimatuo Town, Sinan County. They include ground surface rupture, wall inclination, deformation aggravation of fissures on ground and walls. Once influenced by the heavy rainfall and other unfavorable factors, the unstable slopes would slide continuously, posing a serious threat to the 509 persons and 556 houses of Datong Community, and a significantly negative impact to the local society. Based on the field survey and indoor analysis, this paper elaborates the geo-environmental characteristics of the Shuimatuo landslide region and clarifies the important effects of geological structures and topographic conditions to the seepage field of the slope. With the help of local meteorological data, we continue to research the deformation and failure process of the slope under the rainfall condition with the SEEP/W module and the FLAC3D software. We preliminarily expound the formation mechanism of the thrust-type landslide(H1) and secondary tractive landslide(H2)triggered by the multi-period of rainfall. The preliminary research results believe that induced by the rare heavy rainfall in the history, the major landslide begins to deform, but limited by the terrain condition, showing characteristics of part and progressive failure. During the long-term creep deformation process of landslide, rainfall causes a fluctuation of the groundwater level, strengthening the creep of sliding mass. Controlled by the free surface condition, the evolutionary process of secondary tractive landslide shows obvious correlation and certain lag comparing to the major landslide. For the thrust-type accumulated layer landslide, affected by the terrain, groundwater and loading conditions, it takes a long time from strength decrease of sliding belt to the formation of sliding plane. While tractive accumulated layer landslide lasts shortly as it is a backward movement generated by slope stress redistribution due to the lack of key anti-slide body.
2019, 27(3): 601-607.
Considering the horizontal seismic action and the anchor-frame reinforcement, we propose a seismic stability analysis method on the basis of general slice principle for the anchor-frame reinforced slope. The equilibrium of single slice in differential form is analyzed firstly. Then the limit equilibrium equations of sliding body in integral form are deduced. Finally the equations are solved with programming of ergodic searching. Taking the anchor-frame reinforced slope on an expressway as a prototype, both of the proposed analysis method and the numerical simulation method are used to calculate the safety factor of slope under the designed seismic action. The results calculated by these two methods fit each other well, which implies the validity of the proposed method. We also discuss the influences of average anchoring force and seismic action coefficient on the safety factor of seismic stability. The proposed analysis method associated with the general slice principle can provide an efficient means not only for the seismic stability analysis, but also for the preliminary design of anchor-frame reinforced slope.
Considering the horizontal seismic action and the anchor-frame reinforcement, we propose a seismic stability analysis method on the basis of general slice principle for the anchor-frame reinforced slope. The equilibrium of single slice in differential form is analyzed firstly. Then the limit equilibrium equations of sliding body in integral form are deduced. Finally the equations are solved with programming of ergodic searching. Taking the anchor-frame reinforced slope on an expressway as a prototype, both of the proposed analysis method and the numerical simulation method are used to calculate the safety factor of slope under the designed seismic action. The results calculated by these two methods fit each other well, which implies the validity of the proposed method. We also discuss the influences of average anchoring force and seismic action coefficient on the safety factor of seismic stability. The proposed analysis method associated with the general slice principle can provide an efficient means not only for the seismic stability analysis, but also for the preliminary design of anchor-frame reinforced slope.
2019, 27(3): 608-622.
The evaluation targets of geological hazard susceptibility and risk assessment are the same but the evaluation contents including time, space and intensity information of geological disasters are different. This paper combines the statistical model in the susceptibility with the physical model in the risk assessment on collapse landslides, and combines the advantages of statistical model predicting spatial location information objectively with the advantages of physical model simulation including geological disaster occurrence mechanisms. It makes up for the insufficiency of regional statistical model predicting the disaster intensity information. It also effectively controls or corrects the spatial position of the physical model simulation. Then a comprehensive analysis is completed on the susceptibility and risk level of the collapse and landslide, which achieves a refined assessment of the potential high-risk location of the regional collapse and landslide. This paper takes the Longshan community in Fuding County, Fujian Province as an example. It uses data from high-definition images, terrain, boreholes and geological disasters acquired in the field. With the combination of statistical model and physical model, the refined evaluation of potential high-risk locations is completed. The research results show that:the area that needs to be focused on governance is about 26.92% of the total area of the mountain near the community. There are five areas in the community that require centralized investigation and governance. Three of them need to be focused on key governance. The potential high-risk areas coincide with the hidden danger points in the investigation area. The five high-risk areas directly threaten the safety of 180 buildings(about 360 householders). Refining the large-scale high-risk areas is delineated in field research. The feasibility of the evaluation method system is verified. The evaluation method system provides working ideas and guidance for the refined investigation and governance of regional collapse and landslide disasters.
The evaluation targets of geological hazard susceptibility and risk assessment are the same but the evaluation contents including time, space and intensity information of geological disasters are different. This paper combines the statistical model in the susceptibility with the physical model in the risk assessment on collapse landslides, and combines the advantages of statistical model predicting spatial location information objectively with the advantages of physical model simulation including geological disaster occurrence mechanisms. It makes up for the insufficiency of regional statistical model predicting the disaster intensity information. It also effectively controls or corrects the spatial position of the physical model simulation. Then a comprehensive analysis is completed on the susceptibility and risk level of the collapse and landslide, which achieves a refined assessment of the potential high-risk location of the regional collapse and landslide. This paper takes the Longshan community in Fuding County, Fujian Province as an example. It uses data from high-definition images, terrain, boreholes and geological disasters acquired in the field. With the combination of statistical model and physical model, the refined evaluation of potential high-risk locations is completed. The research results show that:the area that needs to be focused on governance is about 26.92% of the total area of the mountain near the community. There are five areas in the community that require centralized investigation and governance. Three of them need to be focused on key governance. The potential high-risk areas coincide with the hidden danger points in the investigation area. The five high-risk areas directly threaten the safety of 180 buildings(about 360 householders). Refining the large-scale high-risk areas is delineated in field research. The feasibility of the evaluation method system is verified. The evaluation method system provides working ideas and guidance for the refined investigation and governance of regional collapse and landslide disasters.
2019, 27(3): 623-631.
The study on the deformation and failure mechanism of loess slope is of great significance for the prevention and control of loess landslides. Slope with loess-mudstone interface is one of the loess landslides types. Researchers have clearly understood its basic failure process and mechanism. However, its deformation and failure process under different rainfall patterns, especially under heavy rainfall conditions, need to be further studied. Therefore, this paper conducts a laboratory rainfall experiment of the loess-mudstone interface slope model and studies its deformation and failure mode under heavy rainfall conditions. It designs two kinds of rainfall patterns. They are the continuous strong rainfall and the intermittent strong rainfall. It compares and analyzes the infiltration characteristics and failure modes. The results show that the rainfall infiltration rate gradually decreases from the leading edge to the trailing edge of the slope under two rainfall conditions. In the surface of the slope, the infiltration rate gradually increases with the intermittent to continuous transition of rainfall. In the deep parts of the slope, the slope structure affects the infiltration rate. The slope under intermittent rainfall appears as sliding and fracturing instability, while in the continuous rainfall condition, it behaves as creeping and fracturing failure.
The study on the deformation and failure mechanism of loess slope is of great significance for the prevention and control of loess landslides. Slope with loess-mudstone interface is one of the loess landslides types. Researchers have clearly understood its basic failure process and mechanism. However, its deformation and failure process under different rainfall patterns, especially under heavy rainfall conditions, need to be further studied. Therefore, this paper conducts a laboratory rainfall experiment of the loess-mudstone interface slope model and studies its deformation and failure mode under heavy rainfall conditions. It designs two kinds of rainfall patterns. They are the continuous strong rainfall and the intermittent strong rainfall. It compares and analyzes the infiltration characteristics and failure modes. The results show that the rainfall infiltration rate gradually decreases from the leading edge to the trailing edge of the slope under two rainfall conditions. In the surface of the slope, the infiltration rate gradually increases with the intermittent to continuous transition of rainfall. In the deep parts of the slope, the slope structure affects the infiltration rate. The slope under intermittent rainfall appears as sliding and fracturing instability, while in the continuous rainfall condition, it behaves as creeping and fracturing failure.
2019, 27(3): 632-639.
The long-term deformation and stability of gravity anchorage slope is one of the most important problems affecting the natural serviceability of the suspension bridge engineering. In order to discuss the problem reasonably, the gravity anchorage slope on Kangding Bank of Dadu River Bridge in Luding is taken as an engineering example. Firstly, in-situ shear and compression tests of the slope soil are carried out. The stress field of the gravity anchorage slope is obtained with three-dimensional elastoplastic numerical simulation method. Based on these results, the loading conditions of the direct shear creep test are determined. Then the direct shear creep test is carried out for the slope mainly composed of moraine soil. The creep test results show creep behaviour of the moraine soil decreases with time. In light of the creep characteristics of the soil, time-dependent combination constitutive models consist of Burgers and general Kelvin model individually with Mohr-Coulomb strength principle is proposed and applied in visco-elastic-plastic numerical simulation analysis of the slope. Considering the requirements of natural serviceability of the anchorage, the criterion of allowable displacement at its unique point(saddle point of the anchorage) is applied. The shear strength reduction method for long-term deformation and stability analysis of the slope is also used. The results of the practical example obtained using the present method show horizontal displacement towards the river of the saddle point is 13.19 cm when the anchorage-slope system has naturally served for 100 years. The long-term stability coefficient of the system is 1.71 to meet the requirement of its natural serviceability limit state.
The long-term deformation and stability of gravity anchorage slope is one of the most important problems affecting the natural serviceability of the suspension bridge engineering. In order to discuss the problem reasonably, the gravity anchorage slope on Kangding Bank of Dadu River Bridge in Luding is taken as an engineering example. Firstly, in-situ shear and compression tests of the slope soil are carried out. The stress field of the gravity anchorage slope is obtained with three-dimensional elastoplastic numerical simulation method. Based on these results, the loading conditions of the direct shear creep test are determined. Then the direct shear creep test is carried out for the slope mainly composed of moraine soil. The creep test results show creep behaviour of the moraine soil decreases with time. In light of the creep characteristics of the soil, time-dependent combination constitutive models consist of Burgers and general Kelvin model individually with Mohr-Coulomb strength principle is proposed and applied in visco-elastic-plastic numerical simulation analysis of the slope. Considering the requirements of natural serviceability of the anchorage, the criterion of allowable displacement at its unique point(saddle point of the anchorage) is applied. The shear strength reduction method for long-term deformation and stability analysis of the slope is also used. The results of the practical example obtained using the present method show horizontal displacement towards the river of the saddle point is 13.19 cm when the anchorage-slope system has naturally served for 100 years. The long-term stability coefficient of the system is 1.71 to meet the requirement of its natural serviceability limit state.
2019, 27(3): 640-650.
The geological environment is complex and fragile in the upper reaches of Minjiang River. Geological hazards mainly landslides, collapses and debris flows in these areas are characterized by large quantity, large scale and serious harm. Especially, many geological hazards were triggered by the Wenchuan Earthquake. This study is based on the geological survey reports before and after the Wenchuan Earthquake, and uses GIS technology and programming computing technology. It makes the point density map, surface density map and volume density map of the upper reaches of Minjiang River with suitable control-points space and searching radius. It is proposed that geohazard intensity can be divided into 8 grades from weak to strong using the point density map, surface density map and volume density map. So, its analysis shows that the geohazard intensity is high in the upper reaches of Minjiang River. The accumulative geohazard intensity before the Wenchuan Earthquake is up to the highest 8th grade(extremely intense activity). The highest geohazard intensity triggered by Wenchuan Earthquake is the 7th grade, and most are the 2th to the 6th. The main reason of the high cumulative geohazard intensity in the upper reaches of Minjiang River is the frequent occurrence of extreme events such as historical strong earthquake and rainstorms. Generally, the geohazard intensity triggered by the Wenchuan Earthquake is high, and mainly along the Longmen Mountain fault zone and the southern valley area.
The geological environment is complex and fragile in the upper reaches of Minjiang River. Geological hazards mainly landslides, collapses and debris flows in these areas are characterized by large quantity, large scale and serious harm. Especially, many geological hazards were triggered by the Wenchuan Earthquake. This study is based on the geological survey reports before and after the Wenchuan Earthquake, and uses GIS technology and programming computing technology. It makes the point density map, surface density map and volume density map of the upper reaches of Minjiang River with suitable control-points space and searching radius. It is proposed that geohazard intensity can be divided into 8 grades from weak to strong using the point density map, surface density map and volume density map. So, its analysis shows that the geohazard intensity is high in the upper reaches of Minjiang River. The accumulative geohazard intensity before the Wenchuan Earthquake is up to the highest 8th grade(extremely intense activity). The highest geohazard intensity triggered by Wenchuan Earthquake is the 7th grade, and most are the 2th to the 6th. The main reason of the high cumulative geohazard intensity in the upper reaches of Minjiang River is the frequent occurrence of extreme events such as historical strong earthquake and rainstorms. Generally, the geohazard intensity triggered by the Wenchuan Earthquake is high, and mainly along the Longmen Mountain fault zone and the southern valley area.
2019, 27(3): 651-658.
High-speed remote landslide has become a hotspot in geological disasters due to the strong disaster. During the process of large-scale landslide, the heat generated by friction of the sliding zone increases the temperature of the local area, which changes the mechanical properties of the rock and soil. In order to explore the heat generated and accumulated in the sliding zone quantitatively, this paper developes a slope model of 230, 000 particles by using the MatDEM discrete element software. It simulates the sliding process of landslide. The results show that MatDEM simulates the typical characteristics of landslide accurately and shows the law of heat in discrete element model. The simulation results show that the "kerosene" high heat zone is formed near the sliding zone. With the highest heat at 3×105J in sliding zone cause the temperature increase 545.5℃ with heat capacity of 550J/kg·℃ when the slope heights 100 m. The high speed is caused by high temperature in the slidezone. High-calorie belt attaching to the sliding zone occur displacement accompanying the thickest sliding body. Morever, it is proved that the MatDEM can use unit connection state and the thermal field demonstrate the development law of cracks directly in the sliding body and sliding bed, which provides a new numerical calculation in landslides.
High-speed remote landslide has become a hotspot in geological disasters due to the strong disaster. During the process of large-scale landslide, the heat generated by friction of the sliding zone increases the temperature of the local area, which changes the mechanical properties of the rock and soil. In order to explore the heat generated and accumulated in the sliding zone quantitatively, this paper developes a slope model of 230, 000 particles by using the MatDEM discrete element software. It simulates the sliding process of landslide. The results show that MatDEM simulates the typical characteristics of landslide accurately and shows the law of heat in discrete element model. The simulation results show that the "kerosene" high heat zone is formed near the sliding zone. With the highest heat at 3×105J in sliding zone cause the temperature increase 545.5℃ with heat capacity of 550J/kg·℃ when the slope heights 100 m. The high speed is caused by high temperature in the slidezone. High-calorie belt attaching to the sliding zone occur displacement accompanying the thickest sliding body. Morever, it is proved that the MatDEM can use unit connection state and the thermal field demonstrate the development law of cracks directly in the sliding body and sliding bed, which provides a new numerical calculation in landslides.
2019, 27(3): 659-667.
In order to study the variation of pore water pressure and settlement of karst cave under water-level fluctuation, the laboratory physical model experiment is adopted in this paper. The geological disaster spot of the karst collapse in Longyan City of Fujian Province is taken as the research object. The results show that:(1)The response of pore water pressure is closely related to the fluctuation of the water level. According to the change of pore water pressure, the collapse development of the soil inside karst caves can be roughly determined. (2)The internal collapse of soil caves spread to the upper and horizontal directions simultaneously, but the expansion speed of the upper direction is greater than that of the horizontal direction. (3)The development of subsidence is irregular, and the center of the approximately circular subsidence pit formed in the surface is not on the same vertical line as that of the original cavity. Besides, the collapse model of the covered karst under the cyclic fluctuation of the water level is summarized according to the analysis of the development characteristics of karst caves. At last, the three development stages of the development of the karst cave subsidence are presented:the development of the soil cave, the expansion of the soil cave and the surface collapse. The results of this research can be applied in monitoring and detecting early warning signs of karst cave collapse.
In order to study the variation of pore water pressure and settlement of karst cave under water-level fluctuation, the laboratory physical model experiment is adopted in this paper. The geological disaster spot of the karst collapse in Longyan City of Fujian Province is taken as the research object. The results show that:(1)The response of pore water pressure is closely related to the fluctuation of the water level. According to the change of pore water pressure, the collapse development of the soil inside karst caves can be roughly determined. (2)The internal collapse of soil caves spread to the upper and horizontal directions simultaneously, but the expansion speed of the upper direction is greater than that of the horizontal direction. (3)The development of subsidence is irregular, and the center of the approximately circular subsidence pit formed in the surface is not on the same vertical line as that of the original cavity. Besides, the collapse model of the covered karst under the cyclic fluctuation of the water level is summarized according to the analysis of the development characteristics of karst caves. At last, the three development stages of the development of the karst cave subsidence are presented:the development of the soil cave, the expansion of the soil cave and the surface collapse. The results of this research can be applied in monitoring and detecting early warning signs of karst cave collapse.
2019, 27(3): 668-675.
The wireless electromagnetic method is a new geophysical method developed in recent years. It can be applied to resources, energy and deep engineering geological exploration. Its characteristic is that two directions long bipole near-south-north and near-east-west are established in high-resistance areas. With hundreds of kilometers of emission sources, high-power electromagnetic signals can cover the whole country. After the project of transmitter station being completed at the end of November 2015, the first signal test was carried out in the Renqiu Basin of the North China Oilfield, which is 960 kilometers away from the transmitter source. The signal was collected by high-precision acquisition system, and then the frequency spectrum was obtained by performing segmentation spectrum transformation. At last, the transmitted signal was evaluated through analyzing the signal-to-noise ratio and spectrum amplitude. Before the test, the optimal transmit duration was determined by a few uniformly distributed frequencies to save time. Other frequencies transmit duration can be obtained by interpolation. Through experiments, the electromagnetic field signal was successfully detected. When the frequency is greater than 0.353 78 Hz with east-west bipole source, and the frequency is higher than 1.4151 Hz with north-south bipole, source, the signal-noise-ratio is greater than 3 and considered being measurable. The test showed that the transmitter station can transmit effective signals, and other tests and joint test studies could be carry out in the whole country.
The wireless electromagnetic method is a new geophysical method developed in recent years. It can be applied to resources, energy and deep engineering geological exploration. Its characteristic is that two directions long bipole near-south-north and near-east-west are established in high-resistance areas. With hundreds of kilometers of emission sources, high-power electromagnetic signals can cover the whole country. After the project of transmitter station being completed at the end of November 2015, the first signal test was carried out in the Renqiu Basin of the North China Oilfield, which is 960 kilometers away from the transmitter source. The signal was collected by high-precision acquisition system, and then the frequency spectrum was obtained by performing segmentation spectrum transformation. At last, the transmitted signal was evaluated through analyzing the signal-to-noise ratio and spectrum amplitude. Before the test, the optimal transmit duration was determined by a few uniformly distributed frequencies to save time. Other frequencies transmit duration can be obtained by interpolation. Through experiments, the electromagnetic field signal was successfully detected. When the frequency is greater than 0.353 78 Hz with east-west bipole source, and the frequency is higher than 1.4151 Hz with north-south bipole, source, the signal-noise-ratio is greater than 3 and considered being measurable. The test showed that the transmitter station can transmit effective signals, and other tests and joint test studies could be carry out in the whole country.
2019, 27(3): 676-681.
With the development of dynamic model test such as centrifuge and shaking table, the requirement for dynamic similar material is more detailed. On the basis of dynamic similitude theory of model test, how to select the ratio of raw materials accurately plays an important role in the model test. This paper selects river sand with different particle gradations, iron powder, barite powder and mica sheet as the raw materials, and jet cement as the cementing agent. It then studies the physical and mechanical property of the similar materials with the elastic wave speed simulation measurement and uniaxial compressive test. The results show the follows. (1)The density, dynamic and static elasticity modulus of the specimens with better particle gradation are bigger and the sand-blinder ratio has a greater influence on the density of similar material as the gap gradation enlarges. (2)The dynamic similar material can be obtained whose density is between 1.5-2.2g·cm-3, dynamic Poisson's ratio is between 0.2-0.4 and dynamic elasticity modulus is between 2.5-5.5Gpa if we choose the river sand as aggregate and cement as cementing agent. (3)Iron powder has better effect on gaining weight than the barite powder. The dynamic and static elasticity modulus of the barite specimen have no obvious changes with the change of barite powder content. Therefore, barite powder is an ideal raw material to make dynamic similar material with high-density and low-strength. (4)With the increase of mica sheet content, the dynamic Poisson's ratio, dynamic and static elasticity modulus of specimen can reduce evidently. As a result, the mica sheet is not suitable for similar material with high density but it can make similar material of weak intercalation or structural plane.
With the development of dynamic model test such as centrifuge and shaking table, the requirement for dynamic similar material is more detailed. On the basis of dynamic similitude theory of model test, how to select the ratio of raw materials accurately plays an important role in the model test. This paper selects river sand with different particle gradations, iron powder, barite powder and mica sheet as the raw materials, and jet cement as the cementing agent. It then studies the physical and mechanical property of the similar materials with the elastic wave speed simulation measurement and uniaxial compressive test. The results show the follows. (1)The density, dynamic and static elasticity modulus of the specimens with better particle gradation are bigger and the sand-blinder ratio has a greater influence on the density of similar material as the gap gradation enlarges. (2)The dynamic similar material can be obtained whose density is between 1.5-2.2g·cm-3, dynamic Poisson's ratio is between 0.2-0.4 and dynamic elasticity modulus is between 2.5-5.5Gpa if we choose the river sand as aggregate and cement as cementing agent. (3)Iron powder has better effect on gaining weight than the barite powder. The dynamic and static elasticity modulus of the barite specimen have no obvious changes with the change of barite powder content. Therefore, barite powder is an ideal raw material to make dynamic similar material with high-density and low-strength. (4)With the increase of mica sheet content, the dynamic Poisson's ratio, dynamic and static elasticity modulus of specimen can reduce evidently. As a result, the mica sheet is not suitable for similar material with high density but it can make similar material of weak intercalation or structural plane.
2019, 27(3): 682-690.
Based on the metro Lintong line passing through the active fault of Lishan Mountain on Xi'an metro Lintong line, the three-dimensional finite element model of metro tunnel-active fault-stratum was built. Deformation and stress characteristics of metro tunnel crossing the piedmont fault of Lishan Mountain, effect mechanism and key fortification positions of metro tunnel are revealed. The fortification range of the subway Lintong line crossing piedmont fault of Lishan Mountain is determined, and the corresponding measures for prevention and control are put forward. Research result shows that active fault ruptures caused bending deformation along the longitudinal metro tunnel. The tunnel can be divided into three deformation areas:stability section in the footwall, shear tension section in the fault zone and settlement section in the hanging wall. The vertical stratum stress near the fault zone decreases in the hanging wall and increases in the footwall. In addition, the contact pressure at the bottom of the tunnel decreases in the hanging wall and increases in the footwall. Vault contact pressure increases in the hanging wall and decreases in the footwall. And the top of tunnel is in compression at the hanging wall and in tension at the footwall. The bottom of tunnel was in tension at the hanging wall and in compression at the footwall. The shear scope of the tunnel remains unchanged with the variation of fault dislocation. The maximum shear force occurs at the intersection with the fault. Finally, it is confirmed that the fortification length of Lintong line across the fault is at least 80 m. The measures for prevention and control measures are put forward. The conclusions can be presented as the reference for the design and disease control of Xi'an LinTong Line passing through the piedmont active fault of Lishan Mountain.
Based on the metro Lintong line passing through the active fault of Lishan Mountain on Xi'an metro Lintong line, the three-dimensional finite element model of metro tunnel-active fault-stratum was built. Deformation and stress characteristics of metro tunnel crossing the piedmont fault of Lishan Mountain, effect mechanism and key fortification positions of metro tunnel are revealed. The fortification range of the subway Lintong line crossing piedmont fault of Lishan Mountain is determined, and the corresponding measures for prevention and control are put forward. Research result shows that active fault ruptures caused bending deformation along the longitudinal metro tunnel. The tunnel can be divided into three deformation areas:stability section in the footwall, shear tension section in the fault zone and settlement section in the hanging wall. The vertical stratum stress near the fault zone decreases in the hanging wall and increases in the footwall. In addition, the contact pressure at the bottom of the tunnel decreases in the hanging wall and increases in the footwall. Vault contact pressure increases in the hanging wall and decreases in the footwall. And the top of tunnel is in compression at the hanging wall and in tension at the footwall. The bottom of tunnel was in tension at the hanging wall and in compression at the footwall. The shear scope of the tunnel remains unchanged with the variation of fault dislocation. The maximum shear force occurs at the intersection with the fault. Finally, it is confirmed that the fortification length of Lintong line across the fault is at least 80 m. The measures for prevention and control measures are put forward. The conclusions can be presented as the reference for the design and disease control of Xi'an LinTong Line passing through the piedmont active fault of Lishan Mountain.
2019, 27(3): 691-698.
Tamusu, located in Alex, Inner Monglia, northwestern China, is one of the preselected area for high-level radioactive waste geologic disposal of China. Carrying out hydrogeological assessment at potential disposal sites of interest is particularly important for getting scientific results of suitability. In particular, knowing about recharge sources and evolution processes of groundwater will help to further understand the formation and renewal of groundwater. Combining the hydrogeological conditions in Tamusu area, using hydrogeochemical and isotopic techniques to get the results of 26 specimens which were collected from the study area. The results show that groundwater in the study area mainly originated from local precipitation because there was similar isotopic characteristics between them. It is also consistent with the hydrogeological conditions in the study area. The typical feature of groundwater is high salinity and the TDS average value is about 2.9 g·L-1. Meanwhile, almost all samples were Na+-Cl- type. This is a common phenomenon in arid regions. Moreover, two chloroalkaline indices of groundwater are positive and there are good linear relationship between Mg2++Ca2+-HCO3--SO42- and Na++K+-Cl- with a slope of-1. This indicates that ion exchange is a significant geochemical process for controlling the composition of groundwater. The groundwater in study area is not fit to drink due to high salinity and the age of deep groundwater older than 5000 a because of weak renewal. This cognition provides crucial hydrogeological evidences for site selection and evaluation in the area.
Tamusu, located in Alex, Inner Monglia, northwestern China, is one of the preselected area for high-level radioactive waste geologic disposal of China. Carrying out hydrogeological assessment at potential disposal sites of interest is particularly important for getting scientific results of suitability. In particular, knowing about recharge sources and evolution processes of groundwater will help to further understand the formation and renewal of groundwater. Combining the hydrogeological conditions in Tamusu area, using hydrogeochemical and isotopic techniques to get the results of 26 specimens which were collected from the study area. The results show that groundwater in the study area mainly originated from local precipitation because there was similar isotopic characteristics between them. It is also consistent with the hydrogeological conditions in the study area. The typical feature of groundwater is high salinity and the TDS average value is about 2.9 g·L-1. Meanwhile, almost all samples were Na+-Cl- type. This is a common phenomenon in arid regions. Moreover, two chloroalkaline indices of groundwater are positive and there are good linear relationship between Mg2++Ca2+-HCO3--SO42- and Na++K+-Cl- with a slope of-1. This indicates that ion exchange is a significant geochemical process for controlling the composition of groundwater. The groundwater in study area is not fit to drink due to high salinity and the age of deep groundwater older than 5000 a because of weak renewal. This cognition provides crucial hydrogeological evidences for site selection and evaluation in the area.
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