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Editor Work2021 Vol. 29, No. 1
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2021, 29(1): 1-11.
Abstract
Using the sinusoid and triangular waves to simulate the loading form of ocean wave, we carried out a series of tests of cyclic rotation of principal stress axis with GCTS hollow cylindrical torsional apparatus for soft dredged fill of Tianjin Binhai under the condition of triaxial isobaric consolidation. The effects of cyclic shear stress amplitude and vibration wave on the generalized shear strain, dynamic strength and pore pressure of the dredged fill under the continuous rotation of dynamic principal stress direction were discussed. The test results indicate that when the amplitude of cyclic shear stress is less than the critical cyclic shear stress, the generalized shear strain has little change and grows slowly. The loading waveform has little influence on the deformation. When the amplitude of cyclic shear stress exceeds the critical cyclic shear stress, soil mass deforms greatly with less cyclic number. It is observed that the development rate of generalized shear strain under sinusoid wave is greater than that under triangular wave, and the corresponding generalized shear strain under sinusoid waves is always greater than that under triangular waves with the same cyclic number. Under the same waveform, the larger the value of failure criterion is, the larger the value of dynamic strength is. The dynamic strength decreases under different failure standards with the increase of failure cyclic number, and finally they tend to the same value. In the same conditions, sinusoid wave is more likely to cause soil damage than triangular wave under the effect of cyclic rotation of principal stress axis. Based on the analysis of the test data, we established the relationship between the dynamic strength and the failure cyclic number with the two kids of waveform under the different failure criteria. Under the same conditions, the growth rate of pore pressure of sinusoidal wave is higher than that of triangle wave. And the larger the amplitude of cyclic shear stress, the faster the rate of pore pressure growth. However, due to the hysteresis effect of pore pressure of cohesive soil, the value is relatively small when the failure strain is reached.
Using the sinusoid and triangular waves to simulate the loading form of ocean wave, we carried out a series of tests of cyclic rotation of principal stress axis with GCTS hollow cylindrical torsional apparatus for soft dredged fill of Tianjin Binhai under the condition of triaxial isobaric consolidation. The effects of cyclic shear stress amplitude and vibration wave on the generalized shear strain, dynamic strength and pore pressure of the dredged fill under the continuous rotation of dynamic principal stress direction were discussed. The test results indicate that when the amplitude of cyclic shear stress is less than the critical cyclic shear stress, the generalized shear strain has little change and grows slowly. The loading waveform has little influence on the deformation. When the amplitude of cyclic shear stress exceeds the critical cyclic shear stress, soil mass deforms greatly with less cyclic number. It is observed that the development rate of generalized shear strain under sinusoid wave is greater than that under triangular wave, and the corresponding generalized shear strain under sinusoid waves is always greater than that under triangular waves with the same cyclic number. Under the same waveform, the larger the value of failure criterion is, the larger the value of dynamic strength is. The dynamic strength decreases under different failure standards with the increase of failure cyclic number, and finally they tend to the same value. In the same conditions, sinusoid wave is more likely to cause soil damage than triangular wave under the effect of cyclic rotation of principal stress axis. Based on the analysis of the test data, we established the relationship between the dynamic strength and the failure cyclic number with the two kids of waveform under the different failure criteria. Under the same conditions, the growth rate of pore pressure of sinusoidal wave is higher than that of triangle wave. And the larger the amplitude of cyclic shear stress, the faster the rate of pore pressure growth. However, due to the hysteresis effect of pore pressure of cohesive soil, the value is relatively small when the failure strain is reached.
2021, 29(1): 12-24.
1703KB
The geological disasters caused by avalanche, large scale deformation, and flow slide of the geo-granular materials have brought massive destruction and potential threats to national economic development and security of lives and property of the people. Most of the geological materials causing those geological disasters can be classified as granular materials. The integration of geological disaster and granular material mechanics is always one of the most important directions for researchers in both soft matter and geological engineering. Granular materials are composited by many individual granules, the mechanical properties of which are extremely complicated. A granular system shows the characteristics of gas, liquid and solid depending on the kinstate of the granules. In the geological engineering field, some typical geological disasters, such as landslides, debris flows, are closely related to the mechanics of granular material. The key to seal with them lies in the phase transition of granular materials or geo-granular materials between solid state and fluid state. This paper first briefly introduced the fundamental characteristics of granular material. The jamming phase transition, local and non-local rheology, and couple typical experimental techniques. It also discussed the application prospect of the mechanics of granular material in geological engineering field. The success of integration of granular material mechanics and engineering geology would expand the research of physics and mechanics of granular matter and provide a theoretical basis for critical engineering and geological disaster prevention.
The geological disasters caused by avalanche, large scale deformation, and flow slide of the geo-granular materials have brought massive destruction and potential threats to national economic development and security of lives and property of the people. Most of the geological materials causing those geological disasters can be classified as granular materials. The integration of geological disaster and granular material mechanics is always one of the most important directions for researchers in both soft matter and geological engineering. Granular materials are composited by many individual granules, the mechanical properties of which are extremely complicated. A granular system shows the characteristics of gas, liquid and solid depending on the kinstate of the granules. In the geological engineering field, some typical geological disasters, such as landslides, debris flows, are closely related to the mechanics of granular material. The key to seal with them lies in the phase transition of granular materials or geo-granular materials between solid state and fluid state. This paper first briefly introduced the fundamental characteristics of granular material. The jamming phase transition, local and non-local rheology, and couple typical experimental techniques. It also discussed the application prospect of the mechanics of granular material in geological engineering field. The success of integration of granular material mechanics and engineering geology would expand the research of physics and mechanics of granular matter and provide a theoretical basis for critical engineering and geological disaster prevention.
2021, 29(1): 25-33.
In the stability analysis of rock engineering, the stiffness coefficient of fractures is a vital mechanical parameter that is related to the accuracy and reliability of the calculation and analysis. At the same time, it is still a tricky task to obtain the stiffness coefficient of fractures. When the stress wave propagates to the fracture in the rock mass, reflection and transmission phenomena can occur, which are closely related to the stiffness coefficient of fractures. The transmission coefficient of the stress wave can be employed to invert the dynamic stiffness coefficient of fracture. In this paper, based on the particle discrete element method, a piecewise linear contact model and an absorption boundary model of stress waves are developed, and a series of simulation of stress wave propagation in the macroscopic rock mass is carried out. The static and dynamic stiffness coefficients of the fracture are separately calculated according to its stress-deformation curve under the quasi-static compression test simulation and stress wave transmission coefficient. The simulation results show that: (1)The piecewise linear contact model developed by C++language is well used to simulate the nonlinear deformation characteristics of the fracture; (2)The particle discrete element method can accurately reflect the law of stress waves propagation in the rock mass, and the transmission coefficient of the stress wave through the fractures with variable stiffness is consistent with the theoretical solution; (3)Employing the viscous absorption boundary model to the discrete particle model, and we achieves the simulation of the far-field stress wave propagation in the finite model; (4)Based on the modeling the dynamic and static stiffness coefficients of the fracture with low JCR are obtained, and the ratio of the dynamic/static stiffness coefficients is about 1.0. This paper can have a significant meaning for the testing and value of the fracture stiffness in the rock mass.
In the stability analysis of rock engineering, the stiffness coefficient of fractures is a vital mechanical parameter that is related to the accuracy and reliability of the calculation and analysis. At the same time, it is still a tricky task to obtain the stiffness coefficient of fractures. When the stress wave propagates to the fracture in the rock mass, reflection and transmission phenomena can occur, which are closely related to the stiffness coefficient of fractures. The transmission coefficient of the stress wave can be employed to invert the dynamic stiffness coefficient of fracture. In this paper, based on the particle discrete element method, a piecewise linear contact model and an absorption boundary model of stress waves are developed, and a series of simulation of stress wave propagation in the macroscopic rock mass is carried out. The static and dynamic stiffness coefficients of the fracture are separately calculated according to its stress-deformation curve under the quasi-static compression test simulation and stress wave transmission coefficient. The simulation results show that: (1)The piecewise linear contact model developed by C++language is well used to simulate the nonlinear deformation characteristics of the fracture; (2)The particle discrete element method can accurately reflect the law of stress waves propagation in the rock mass, and the transmission coefficient of the stress wave through the fractures with variable stiffness is consistent with the theoretical solution; (3)Employing the viscous absorption boundary model to the discrete particle model, and we achieves the simulation of the far-field stress wave propagation in the finite model; (4)Based on the modeling the dynamic and static stiffness coefficients of the fracture with low JCR are obtained, and the ratio of the dynamic/static stiffness coefficients is about 1.0. This paper can have a significant meaning for the testing and value of the fracture stiffness in the rock mass.
2021, 29(1): 34-43.
Continuous distribution of weak expansive soil and collapsible sand soft sandstone exists in Jichao and Jianghuai connecting sections of the Yangtze River to Huaihe River(waterway) diversion project. In order to utilize river excavation waste to develop non-expansive soil, the feasibility of using collapsible soft sandstone to improve weak expansive soil is studied. The results show that the disintegrated sandstone is easy to become fines and has low natural water content without expansion. So it can be used as a modified material. The expansion rate, expansion force, optimum water content and the amount of incorporation are negatively related when the weak expansive soil is mixed with the disintegrated sandstone. The maximum dry density, permeability coefficient and the amount of incorporation are positively related. After the weak expansive soil is incorporated into the disintegrated sandstone, its internal friction angle develops with the inverse S-shaped curve law, and the cohesive force decreases approximately quadratic with the increase of the dosage. The shear strength of improved soil may be lower than that of natural weak expansive soil when the dosage is higher than 30%. The higher the content of coarse grains of disintegrated sandstone, the higher the cohesion and the lower the friction angle of the improved soil when the content and the size range of disintegrated sandstone are the same. The strength stability of sandstone improved soil under dry and wet cycling conditions is improved. The improvement effect of the hydrated disintegrated sandstone is better than that of the crushed disintegrated sandstone. According to the standard of no loss of strength after the improvement of weak expansive soil, the reasonable content of disintegrated sandstone is determined to be 30%. And the content of coarse-grained group in the machine crushed disintegrated sandstone has to be reasonably controlled during the construction of disintegrated sandstone improved soil.
Continuous distribution of weak expansive soil and collapsible sand soft sandstone exists in Jichao and Jianghuai connecting sections of the Yangtze River to Huaihe River(waterway) diversion project. In order to utilize river excavation waste to develop non-expansive soil, the feasibility of using collapsible soft sandstone to improve weak expansive soil is studied. The results show that the disintegrated sandstone is easy to become fines and has low natural water content without expansion. So it can be used as a modified material. The expansion rate, expansion force, optimum water content and the amount of incorporation are negatively related when the weak expansive soil is mixed with the disintegrated sandstone. The maximum dry density, permeability coefficient and the amount of incorporation are positively related. After the weak expansive soil is incorporated into the disintegrated sandstone, its internal friction angle develops with the inverse S-shaped curve law, and the cohesive force decreases approximately quadratic with the increase of the dosage. The shear strength of improved soil may be lower than that of natural weak expansive soil when the dosage is higher than 30%. The higher the content of coarse grains of disintegrated sandstone, the higher the cohesion and the lower the friction angle of the improved soil when the content and the size range of disintegrated sandstone are the same. The strength stability of sandstone improved soil under dry and wet cycling conditions is improved. The improvement effect of the hydrated disintegrated sandstone is better than that of the crushed disintegrated sandstone. According to the standard of no loss of strength after the improvement of weak expansive soil, the reasonable content of disintegrated sandstone is determined to be 30%. And the content of coarse-grained group in the machine crushed disintegrated sandstone has to be reasonably controlled during the construction of disintegrated sandstone improved soil.
2021, 29(1): 44-51.
Soil erosion and geological disasters in loess area of China are extremely serious, which is mainly related to the poor engineering geological properties of loess. Microbial induced calcium carbonate precipitation(MICP)was used in order to improve the mechanical behavior of loess. We sprayed the prepared bacterial solution and cementation solution to the surface of the soil sample for MICP treatment. Based on the penetration test and calcium carbonate content test, we analysed the influence of MICP-treated cycles(3, 5, 7 rounds) and cementation solution concentrations(0.5 M, 1 M, 5 M)on penetration strength and calcium carbonate content of MICP-treated samples. The results show that: (1)MICP technology can significantly improve the structure strength and form a hard crust with high strength on the surface of soil sample. (2)With the increase of MICP treatment cycles, the strength and thickness of hard crust, internal strength of soil and the content of calcium carbonate increase gradually. (3)The concentration of cementing solution has a significant influence. The sample treated by 1.5 M cementing solution performs the best treatment effect with structure strength of surface up to 600 kPa and good internal integrity. The effect of the sample treated by 1.5 M cementing solution is worse than 1.0 M. A thin hard crust is formed on the surface of it and the internal strength of it is low. The mechanical strength of soil sample treated by 0.5 M cementing solution is improved insignificantly. (4)The mechanism of MICP improvement on the structure strength of loess is mainly that calcium carbonate induced by microorganisms cements soil particles, which greatly improves the connection strength between soil particles and significantly improves the mechanical properties of soil.
Soil erosion and geological disasters in loess area of China are extremely serious, which is mainly related to the poor engineering geological properties of loess. Microbial induced calcium carbonate precipitation(MICP)was used in order to improve the mechanical behavior of loess. We sprayed the prepared bacterial solution and cementation solution to the surface of the soil sample for MICP treatment. Based on the penetration test and calcium carbonate content test, we analysed the influence of MICP-treated cycles(3, 5, 7 rounds) and cementation solution concentrations(0.5 M, 1 M, 5 M)on penetration strength and calcium carbonate content of MICP-treated samples. The results show that: (1)MICP technology can significantly improve the structure strength and form a hard crust with high strength on the surface of soil sample. (2)With the increase of MICP treatment cycles, the strength and thickness of hard crust, internal strength of soil and the content of calcium carbonate increase gradually. (3)The concentration of cementing solution has a significant influence. The sample treated by 1.5 M cementing solution performs the best treatment effect with structure strength of surface up to 600 kPa and good internal integrity. The effect of the sample treated by 1.5 M cementing solution is worse than 1.0 M. A thin hard crust is formed on the surface of it and the internal strength of it is low. The mechanical strength of soil sample treated by 0.5 M cementing solution is improved insignificantly. (4)The mechanism of MICP improvement on the structure strength of loess is mainly that calcium carbonate induced by microorganisms cements soil particles, which greatly improves the connection strength between soil particles and significantly improves the mechanical properties of soil.
2021, 29(1): 52-58.
Uncertainty exists in evaluation for anisotropy of a rock joint roughness. One can obtain different anisotropy evaluation of rock joint roughness via different methods even for the same sample, which makes anisotropy evaluation results inconsistent. To this end, this paper proposed a rotation sampling method to evaluate the anisotropy of rock joint roughness coefficient(JRC). The method uses the 3D point cloud data of a rock joint sample that obtained from high-precision 3D laser scanning technology. Based on the comparison analysis of a typical rock joint sample, the influences of the sampling method and the sampling size on the anisotropy evaluation results of JRC were investigated. The results show that the existing single profile sampling method makes the JRC anisotropy data discrete and therefore requires larger sampling size to improve its accuracy of the obtained JRC data. The proposed rotation sampling method can overcome this problem of JRC anisotropy data dispersion and obtain accurate and reliable JRC data for anisotropy evaluation. The method and the results can provide a reference for further studying the anisotropy of rock joint roughness.
Uncertainty exists in evaluation for anisotropy of a rock joint roughness. One can obtain different anisotropy evaluation of rock joint roughness via different methods even for the same sample, which makes anisotropy evaluation results inconsistent. To this end, this paper proposed a rotation sampling method to evaluate the anisotropy of rock joint roughness coefficient(JRC). The method uses the 3D point cloud data of a rock joint sample that obtained from high-precision 3D laser scanning technology. Based on the comparison analysis of a typical rock joint sample, the influences of the sampling method and the sampling size on the anisotropy evaluation results of JRC were investigated. The results show that the existing single profile sampling method makes the JRC anisotropy data discrete and therefore requires larger sampling size to improve its accuracy of the obtained JRC data. The proposed rotation sampling method can overcome this problem of JRC anisotropy data dispersion and obtain accurate and reliable JRC data for anisotropy evaluation. The method and the results can provide a reference for further studying the anisotropy of rock joint roughness.
2021, 29(1): 59-68.
The shape characteristics of mineral particles are conventionally evaluated by thin section observation and manual identification of rock samples,the results are often subject to subjective influence. The paper presented a method for quantifying the shape parameters of mineral particles in photomicrographs of rock slices based on an image processing technology. The shape parameters of mineral particles mainly includes sphericity,convexity,aspect ratio,and roundness. Firstly,the method distinguishes mineral particles in photomicrographs using image segmentation technology,then extracts the pixel contour coordinates of the particles for discrete geometric analysis,and finally calculates the shape parameters of mineral particles. In particular,since roundness was difficult to be calculate directly and accurately,the paper proposed a two-step method to calculate the roundness based on Fourier series fitting particle contour,which includes identification the key points in corners and grouping them. The identification of the key points includes two process,which are smoothing particle contour based on Fourier series and searching for the key points in corners. The grouping of the key points also includes two process. Firstly,the key points were preliminarily divided into several groups by statistical analysis,then,the dichotomy was adopted for the precise grouping of these key points. We analyzed the effects of image resolution Re,goodness of fitting Fourier series R2 of particle profile and grouping coefficient a of key points on the calculation results of particle shape parameters. We found that(1)the results of sphericity,convexity and aspect ratio are basically not affected by Re and R2; (2)the results of roundness are affected by Re and R2. It is suggested that the minimum circumscribed circle diameter of particles should be more than 200 pixels for roundness calculation,and there is an optimal R2 range,within which the calculated roundness is close to the theoretical value; (3)when a is accurate to the tenth,a=0.1 is the most reasonable during the process of grouping of the key points.
The shape characteristics of mineral particles are conventionally evaluated by thin section observation and manual identification of rock samples,the results are often subject to subjective influence. The paper presented a method for quantifying the shape parameters of mineral particles in photomicrographs of rock slices based on an image processing technology. The shape parameters of mineral particles mainly includes sphericity,convexity,aspect ratio,and roundness. Firstly,the method distinguishes mineral particles in photomicrographs using image segmentation technology,then extracts the pixel contour coordinates of the particles for discrete geometric analysis,and finally calculates the shape parameters of mineral particles. In particular,since roundness was difficult to be calculate directly and accurately,the paper proposed a two-step method to calculate the roundness based on Fourier series fitting particle contour,which includes identification the key points in corners and grouping them. The identification of the key points includes two process,which are smoothing particle contour based on Fourier series and searching for the key points in corners. The grouping of the key points also includes two process. Firstly,the key points were preliminarily divided into several groups by statistical analysis,then,the dichotomy was adopted for the precise grouping of these key points. We analyzed the effects of image resolution Re,goodness of fitting Fourier series R2 of particle profile and grouping coefficient a of key points on the calculation results of particle shape parameters. We found that(1)the results of sphericity,convexity and aspect ratio are basically not affected by Re and R2; (2)the results of roundness are affected by Re and R2. It is suggested that the minimum circumscribed circle diameter of particles should be more than 200 pixels for roundness calculation,and there is an optimal R2 range,within which the calculated roundness is close to the theoretical value; (3)when a is accurate to the tenth,a=0.1 is the most reasonable during the process of grouping of the key points.
2021, 29(1): 69-76.
Carbonate sand has the characteristics of irregular particle shape, high porosity and low particle strength, and thus exhibits more complicated liquefaction characteristics than silica sand. Physical property tests, undrained cyclic triaxial tests and light dynamic penetration tests are conducted to study the differences in physical properties, liquefaction resistance and penetration resistance between carbonate sand and silica sand. Carbonate sand is found to have larger void ratio and internal friction angle than silica sand, which is consistent with the characteristics of carbonate sand particles. The liquefaction resistance increases with increasing relative density for both sands, and it is found that under the same relative density, carbonate sand has higher liquefaction resistance than silica sand. The penetration resistance increases with increasing relative density for both sands, and it is also found that under the same relative density, carbonate sand has higher penetration resistance than silica sand. Combining the results of undrained cyclic triaxial tests and light dynamic penetration tests, it can be concluded preliminarily that the current liquefaction evaluation methods based on the empirical data on terrestrial silica sand foundations can be conservative for evaluating the liquefaction susceptibility of carbonate sand foundations.
Carbonate sand has the characteristics of irregular particle shape, high porosity and low particle strength, and thus exhibits more complicated liquefaction characteristics than silica sand. Physical property tests, undrained cyclic triaxial tests and light dynamic penetration tests are conducted to study the differences in physical properties, liquefaction resistance and penetration resistance between carbonate sand and silica sand. Carbonate sand is found to have larger void ratio and internal friction angle than silica sand, which is consistent with the characteristics of carbonate sand particles. The liquefaction resistance increases with increasing relative density for both sands, and it is found that under the same relative density, carbonate sand has higher liquefaction resistance than silica sand. The penetration resistance increases with increasing relative density for both sands, and it is also found that under the same relative density, carbonate sand has higher penetration resistance than silica sand. Combining the results of undrained cyclic triaxial tests and light dynamic penetration tests, it can be concluded preliminarily that the current liquefaction evaluation methods based on the empirical data on terrestrial silica sand foundations can be conservative for evaluating the liquefaction susceptibility of carbonate sand foundations.
2021, 29(1): 77-85.
It is difficult to characterize and determine the high heterogeneity of the internal structure and the strong variability of permeability in the fracture core and fracture fracture zone in the fault tectonic zone. The relationship between the permeability and internal structural characteristics of different structural units in Beishan fault zone was studied by observing the microscopic structure, grain size characteristics, pore characteristics, in-situ water pressure test and laboratory penetration test. The research results show that: It is concluded that fault gouge is developed in the fault core, and the structural plane of structural dislocation can be seen in the fault core of Shiyuejing. The laboratory permeability test shows that the permeability coefficient of fault gouge is about 2×10-11~5×10-11m·s-1. No anisotropy of the vertical and lateral permeability characteristics of fault gouge is found. The structure and geological origin of the Shiyuejing fault fracture zone and F4 fault zone are described with the method of three-dimensional fine trough. According to the borehole water pressure test, the permeability coefficient range of the core fracture zone of Shiyuejing is 1.32×10-5 m·s-1 to 1.94×10-5 m·s-1, and the permeability coefficient in the core of the F4 fault is generally greater than 2.4×10-6 m·s-1. Laboratory permeability tests of the samples in the Shiyuejing fault zone show that the permeability coefficient of the fracture damage zone is generally between 10-9~10-6 m·s-1, and its P-Q curves show typical laminar flow type, filling type and erosion property. The permeability capacity of the sample increases with the increase of the number of fractures contained in the zone.
It is difficult to characterize and determine the high heterogeneity of the internal structure and the strong variability of permeability in the fracture core and fracture fracture zone in the fault tectonic zone. The relationship between the permeability and internal structural characteristics of different structural units in Beishan fault zone was studied by observing the microscopic structure, grain size characteristics, pore characteristics, in-situ water pressure test and laboratory penetration test. The research results show that: It is concluded that fault gouge is developed in the fault core, and the structural plane of structural dislocation can be seen in the fault core of Shiyuejing. The laboratory permeability test shows that the permeability coefficient of fault gouge is about 2×10-11~5×10-11m·s-1. No anisotropy of the vertical and lateral permeability characteristics of fault gouge is found. The structure and geological origin of the Shiyuejing fault fracture zone and F4 fault zone are described with the method of three-dimensional fine trough. According to the borehole water pressure test, the permeability coefficient range of the core fracture zone of Shiyuejing is 1.32×10-5 m·s-1 to 1.94×10-5 m·s-1, and the permeability coefficient in the core of the F4 fault is generally greater than 2.4×10-6 m·s-1. Laboratory permeability tests of the samples in the Shiyuejing fault zone show that the permeability coefficient of the fracture damage zone is generally between 10-9~10-6 m·s-1, and its P-Q curves show typical laminar flow type, filling type and erosion property. The permeability capacity of the sample increases with the increase of the number of fractures contained in the zone.
2021, 29(1): 86-95.
The displacement-time curves published by Saito in 1960s imply landslide happening definitely in future, but actually, the gestation and development of landslide are of diversity and periodicity. For to walk out ties or limit from Saito's curves, the author puts forward that displacement-time curves of landsides can be classified as three types. They consist of change slowly to be stable, evolution in terraces and losing stability of slope. The stable type can transform to be terrace form in each other, and the latter transform to be failure type. In general, the type of losing stability can be not transform in reverse. Meanwhile, every type is interpreted with actual examples. Landslide occurs in the opening geological environmental systems. Landslide development is related intimately with its boundary conditions, constituents and structures, initial states and induced factors and their changes in time and space. Physical essence of landslide is out- of -balance of internal stress action in the slope which dynamic source is mainly from unbalance of gravity in slope. Losing stability of slope can be considered as it is into"automatic state" which means landslide would be happening inevitable. The type of evolution in terraces is susceptible with extraneous factor and the landslide is in the responding state or"passive state".The type to be stable landslide occurs only deformation adjustment in a local area which is in"weak dynamic state" unless it encounters extra-regular and extraneous factors. Because of the internal or external environments of landslides to be in the change endlessly, that scientists pursue"precise of early warning" of landslides would be impossible and unnecessary. The key problem is in the advance of service in disaster risk reduction.
The displacement-time curves published by Saito in 1960s imply landslide happening definitely in future, but actually, the gestation and development of landslide are of diversity and periodicity. For to walk out ties or limit from Saito's curves, the author puts forward that displacement-time curves of landsides can be classified as three types. They consist of change slowly to be stable, evolution in terraces and losing stability of slope. The stable type can transform to be terrace form in each other, and the latter transform to be failure type. In general, the type of losing stability can be not transform in reverse. Meanwhile, every type is interpreted with actual examples. Landslide occurs in the opening geological environmental systems. Landslide development is related intimately with its boundary conditions, constituents and structures, initial states and induced factors and their changes in time and space. Physical essence of landslide is out- of -balance of internal stress action in the slope which dynamic source is mainly from unbalance of gravity in slope. Losing stability of slope can be considered as it is into"automatic state" which means landslide would be happening inevitable. The type of evolution in terraces is susceptible with extraneous factor and the landslide is in the responding state or"passive state".The type to be stable landslide occurs only deformation adjustment in a local area which is in"weak dynamic state" unless it encounters extra-regular and extraneous factors. Because of the internal or external environments of landslides to be in the change endlessly, that scientists pursue"precise of early warning" of landslides would be impossible and unnecessary. The key problem is in the advance of service in disaster risk reduction.
2021, 29(1): 96-103.
To explore the monitoring sensitive parts of the rock tetrahedral wedge, we used our self-developed slope model test platform and carried out a physical simulation test of the tetrahedral wedge rock slope. We monitored the internal displacement and internal stress at the structural plane of the wedge in the whole process of sliding instability. The results show that with the increase of sliding displacement of the wedge, the difference of displacement change rate at each displacement monitoring point is smaller, and the overall sliding characteristics of wedge are more obvious. In the early stage of the wedge instability process, the sensitive parts of displacement monitoring and stress monitoring are in the lower part of the wedge. Near the instability, the upper part of the wedge is the sensitive part of displacement monitoring, and the upper middle part of the wedge is the stress monitoring sensitive part. In the early stage of the wedge instability process, the monitored stress value is significantly increased compared with the initial state, and compared with displacement monitoring, the feedback of stress monitoring is more advanced, and can respond to the change of slope more timely. The research results can provide reference for the safety monitoring of the rock slope wedge.
To explore the monitoring sensitive parts of the rock tetrahedral wedge, we used our self-developed slope model test platform and carried out a physical simulation test of the tetrahedral wedge rock slope. We monitored the internal displacement and internal stress at the structural plane of the wedge in the whole process of sliding instability. The results show that with the increase of sliding displacement of the wedge, the difference of displacement change rate at each displacement monitoring point is smaller, and the overall sliding characteristics of wedge are more obvious. In the early stage of the wedge instability process, the sensitive parts of displacement monitoring and stress monitoring are in the lower part of the wedge. Near the instability, the upper part of the wedge is the sensitive part of displacement monitoring, and the upper middle part of the wedge is the stress monitoring sensitive part. In the early stage of the wedge instability process, the monitored stress value is significantly increased compared with the initial state, and compared with displacement monitoring, the feedback of stress monitoring is more advanced, and can respond to the change of slope more timely. The research results can provide reference for the safety monitoring of the rock slope wedge.
2021, 29(1): 104-115.
To address the problems of huge areas, lack of data, and time urgency that are usually present in the Regional Crustal Stability(RCS)assessment, this paper presents the InSAR method to gain the elements of RCS and assess RCS. This method has the advantages of large area coverage, backtrack observation and high-efficiency. A major project in the Alxa area is used as example. We selected 25 periods of ASAR/ERS synthetic aperture radar data from 1996 to 2010. We recognize the geo-hazards and ground water fluctuation by D-InSAR centimeter-scale deformation. Then we analyze the tectonic activation by IPTA-InSAR millimeter-scale deformation. Furthermore, used the geological background, the RCS is assessed. Study results prove that InSAR is an effective new tool to assess the RCS under limited condition.
To address the problems of huge areas, lack of data, and time urgency that are usually present in the Regional Crustal Stability(RCS)assessment, this paper presents the InSAR method to gain the elements of RCS and assess RCS. This method has the advantages of large area coverage, backtrack observation and high-efficiency. A major project in the Alxa area is used as example. We selected 25 periods of ASAR/ERS synthetic aperture radar data from 1996 to 2010. We recognize the geo-hazards and ground water fluctuation by D-InSAR centimeter-scale deformation. Then we analyze the tectonic activation by IPTA-InSAR millimeter-scale deformation. Furthermore, used the geological background, the RCS is assessed. Study results prove that InSAR is an effective new tool to assess the RCS under limited condition.
2021, 29(1): 116-124.
The landslide disaster in China is serious, and early warning of regional landslide disaster is an important measure of disaster prevention and reduction. Then the study of the model is the key to carry out regional landslides warning successfully. This paper systematically proposes the construction method of the regional landslide disaster warning model based on machine learning, and takes Qingchuan County, Sichuan province as an example. Based on the geological and meteorological data of about ten years, the regional landslide disaster early warning model of Qingchuan County is built and an example verification is carried out. (1)The construction of regional landslide disaster warning model based on machine learning mainly includes several key steps including the construction of training sample set, sample training, parameter adjustment, model preservation and invocation. (2)A training sample set construction method for regional landslide early warning is proposed. That is, based on the positive samples, the negative samples are obtained by random sampling under spatial-temporal limitation, and the complete training sample set is finally obtained. (3)In the sample learning and training, 80% of the training sample set is taken as the training set, and 20% is taken as the test set, and 50-fold cross verification method is used. Then, Accuracy, ROC curve and AUC value verification model and model generalization ability are adopted. In order to achieve the optimal model, Bayesian Optimization Algorithm is used to optimize the model parameters. (4)In the early warning, the trained warning model is used to output the probability of landslide disaster. According to the probability, the early warning level is determined. When the output probability P≥40% and P < 60%, yellow alert can be issued; When the output probability P≥60% and P < 80%, an orange alert can be issued; and a red alert is issued when the output probability P≥80%. (5)Taking Qingchuan County as an example, six machine learning models were used for training. The results showed that the Random Forest model had the best performance, with the highest accuracy(0.963), no over-fitting phenomenon and the best generalization ability(AUC=0.986). The Second model is Logistic Regression model. Then, the model is artificial neural network model and decision tree model. We take the actual early-warning on June 26, 2018 as an example, load and call the pre-trained Random Forest model, calculate the output probability of the model, and divide the warning levels. According to the verification of the actual occurrence of landslide disasters, the result shows that all the landslides are within the warning area, among which 70.6% fall in the red warning area, 17.6% in the orange warning area and 11.8% in the yellow warning area.
The landslide disaster in China is serious, and early warning of regional landslide disaster is an important measure of disaster prevention and reduction. Then the study of the model is the key to carry out regional landslides warning successfully. This paper systematically proposes the construction method of the regional landslide disaster warning model based on machine learning, and takes Qingchuan County, Sichuan province as an example. Based on the geological and meteorological data of about ten years, the regional landslide disaster early warning model of Qingchuan County is built and an example verification is carried out. (1)The construction of regional landslide disaster warning model based on machine learning mainly includes several key steps including the construction of training sample set, sample training, parameter adjustment, model preservation and invocation. (2)A training sample set construction method for regional landslide early warning is proposed. That is, based on the positive samples, the negative samples are obtained by random sampling under spatial-temporal limitation, and the complete training sample set is finally obtained. (3)In the sample learning and training, 80% of the training sample set is taken as the training set, and 20% is taken as the test set, and 50-fold cross verification method is used. Then, Accuracy, ROC curve and AUC value verification model and model generalization ability are adopted. In order to achieve the optimal model, Bayesian Optimization Algorithm is used to optimize the model parameters. (4)In the early warning, the trained warning model is used to output the probability of landslide disaster. According to the probability, the early warning level is determined. When the output probability P≥40% and P < 60%, yellow alert can be issued; When the output probability P≥60% and P < 80%, an orange alert can be issued; and a red alert is issued when the output probability P≥80%. (5)Taking Qingchuan County as an example, six machine learning models were used for training. The results showed that the Random Forest model had the best performance, with the highest accuracy(0.963), no over-fitting phenomenon and the best generalization ability(AUC=0.986). The Second model is Logistic Regression model. Then, the model is artificial neural network model and decision tree model. We take the actual early-warning on June 26, 2018 as an example, load and call the pre-trained Random Forest model, calculate the output probability of the model, and divide the warning levels. According to the verification of the actual occurrence of landslide disasters, the result shows that all the landslides are within the warning area, among which 70.6% fall in the red warning area, 17.6% in the orange warning area and 11.8% in the yellow warning area.
2021, 29(1): 125-136.
Geological hazards usually resulted in varying degrees of damage to vegetation and infrastructure. Despite important research efforts such as physical modeling and numerical simulation, the mechanisms that govern the hazard process in a natural environment are still unclear due to a lack of instant on-site monitoring. Nonetheless, on-site monitoring instruments and equipment are still vulnerable to hazards and experienced destruction during the large hazard event, making it difficult for data collection and subsequent validation of numerical models. Therefore, it is urgent to find an effective method to reconstruct the hazards process. With the development of seismology, it is now possible to use the long-period seismic signals recorded by the seismic stations to provide a specific diagnostic of geological hazards. This study explores a set of new methods for the reconstruction of geological hazards based on the seismic signals and subsequent analyzing methods such as Band-Pass filter(BP-filter), Empirical mode decomposition(EMD), fast Fourier transform(FFT), short-time Fourier Transform(STFT), and power spectral density(PSD). The basic dynamic characteristics of geological hazards can then be revealed by comparing and analyzing the field survey results, together with the numerical simulations. Several case studies and analyses of dammed lakes, landslides, debris flows, and other hazards are then illustrated for validating the method. Results suggest the method may be a new way for the fast reconstruction of the evolution process of geological hazards for hazards warning and mitigation.
Geological hazards usually resulted in varying degrees of damage to vegetation and infrastructure. Despite important research efforts such as physical modeling and numerical simulation, the mechanisms that govern the hazard process in a natural environment are still unclear due to a lack of instant on-site monitoring. Nonetheless, on-site monitoring instruments and equipment are still vulnerable to hazards and experienced destruction during the large hazard event, making it difficult for data collection and subsequent validation of numerical models. Therefore, it is urgent to find an effective method to reconstruct the hazards process. With the development of seismology, it is now possible to use the long-period seismic signals recorded by the seismic stations to provide a specific diagnostic of geological hazards. This study explores a set of new methods for the reconstruction of geological hazards based on the seismic signals and subsequent analyzing methods such as Band-Pass filter(BP-filter), Empirical mode decomposition(EMD), fast Fourier transform(FFT), short-time Fourier Transform(STFT), and power spectral density(PSD). The basic dynamic characteristics of geological hazards can then be revealed by comparing and analyzing the field survey results, together with the numerical simulations. Several case studies and analyses of dammed lakes, landslides, debris flows, and other hazards are then illustrated for validating the method. Results suggest the method may be a new way for the fast reconstruction of the evolution process of geological hazards for hazards warning and mitigation.
2021, 29(1): 137-150.
The hill-canyon composite topography is a common site in Western China. A large number of infrastructures, such as bridges and dams, have been built in such a site. However, field investigations after earthquakes show that surface irregularities may cause seismic motions amplified in such a site. Seismic motion amplification has an adverse effect on the stability of slopes and the safety of buildings. Therefore, it is significant to investigate the seismic motion amplification effect of hill-canyon composite topography. In this paper, we focused on the seismic response of the shallow-cutting hill-canyon composite topography. In such a site, the relative height between the hill top and the base of canyon always ranges from 100 m to 500 m. Employing the boundary integral equation method, the seismic motion at every interesting position in such a site was obtained. Then, parametric studies were conducted, including the effects of the types of waves(P and SV waves), the frequencies of incident waves, the angles of incidence, and the geometry characteristics of the hills and canyons on the seismic motion amplification effect of hill-canyon composite topography. The results show that the existence of the hills clearly changes the spatial distribution of seismic motions. The surface seismic motion is either amplified or de-amplified, depending on the frequency of incident wave. Different types of waves determine different spatial distribution patterns of seismic motions. The influence of the depth of the canyon on amplification pattern depends on the types of waves. The geometric asymmetry contributes to the asymmetry of the spatial distribution of seismic motions. The asymmetry is much clearer in the case of SV wave incidence than that in the case of P wave incidence. In the case of oblique incidence, seismic motions near the slope facing away from the source are much larger than those near the slope facing towards the source in the canyon. The method in this paper is efficient to investigate the seismic motion amplification effect of hill-canyon composite topography, and capable to obtain the seismic motion at every position, which will be used in the stability analysis of slopes.
The hill-canyon composite topography is a common site in Western China. A large number of infrastructures, such as bridges and dams, have been built in such a site. However, field investigations after earthquakes show that surface irregularities may cause seismic motions amplified in such a site. Seismic motion amplification has an adverse effect on the stability of slopes and the safety of buildings. Therefore, it is significant to investigate the seismic motion amplification effect of hill-canyon composite topography. In this paper, we focused on the seismic response of the shallow-cutting hill-canyon composite topography. In such a site, the relative height between the hill top and the base of canyon always ranges from 100 m to 500 m. Employing the boundary integral equation method, the seismic motion at every interesting position in such a site was obtained. Then, parametric studies were conducted, including the effects of the types of waves(P and SV waves), the frequencies of incident waves, the angles of incidence, and the geometry characteristics of the hills and canyons on the seismic motion amplification effect of hill-canyon composite topography. The results show that the existence of the hills clearly changes the spatial distribution of seismic motions. The surface seismic motion is either amplified or de-amplified, depending on the frequency of incident wave. Different types of waves determine different spatial distribution patterns of seismic motions. The influence of the depth of the canyon on amplification pattern depends on the types of waves. The geometric asymmetry contributes to the asymmetry of the spatial distribution of seismic motions. The asymmetry is much clearer in the case of SV wave incidence than that in the case of P wave incidence. In the case of oblique incidence, seismic motions near the slope facing away from the source are much larger than those near the slope facing towards the source in the canyon. The method in this paper is efficient to investigate the seismic motion amplification effect of hill-canyon composite topography, and capable to obtain the seismic motion at every position, which will be used in the stability analysis of slopes.
2021, 29(1): 151-161.
Severe forest fire often greatly increases soil erosion rate. The existing methods to predict the soil loss on the slope are not suitable for the post-fire debris flow. However, the soil erosion prediction models are essential for planning post fire emergency responses. We attempt to use the RUSLE model to estimate the potential post fire soil loss for the D4 basin in Ba Jiaolou town, China, burnt in 2018. We comprehensively carry out the field investigation, indoor and outdoor experiments, and remote sensing interpretation. Results show that the total volume of the soil loss on the slope during the first five years post fire in D4 watershed is 3.28×104 m3, and the contribution from the heavy and moderate burnt area reaches up to 93.90%. By comparing the investigating data and the predicting data, we finally conclude that the RUSLE modle is effective for predicting the volume of the soil loss transported by the post-fire debris flow. It can provide some references for emergency response to the post-fire debris flow.
Severe forest fire often greatly increases soil erosion rate. The existing methods to predict the soil loss on the slope are not suitable for the post-fire debris flow. However, the soil erosion prediction models are essential for planning post fire emergency responses. We attempt to use the RUSLE model to estimate the potential post fire soil loss for the D4 basin in Ba Jiaolou town, China, burnt in 2018. We comprehensively carry out the field investigation, indoor and outdoor experiments, and remote sensing interpretation. Results show that the total volume of the soil loss on the slope during the first five years post fire in D4 watershed is 3.28×104 m3, and the contribution from the heavy and moderate burnt area reaches up to 93.90%. By comparing the investigating data and the predicting data, we finally conclude that the RUSLE modle is effective for predicting the volume of the soil loss transported by the post-fire debris flow. It can provide some references for emergency response to the post-fire debris flow.
2021, 29(1): 162-170.
Steering drilling technology is one of the most important technologies in the global petroleum industry in the 21st century, and it is also a key component of horizontal drilling, the core technology of the American "The Shale Gas Revolution". At present, the main research goal of steering drilling is to increase the drilling speed, reduce the drilling time and risk, and intelligence is an important way to achieve this goal. The article analyzes the application of big data and artificial intelligence in the petroleum industry at home and abroad, establishes a cloud big data intelligent steering drilling method framework, proposes an artificial intelligence inversion method for logging while drilling parameters, and points out the way to realize the management of cloud big data and intelligent algorithms, and draw the following conclusions: (1)The intelligent guided drilling method based on cloud big data mainly includes the things perception layer, the big data storage layer and the cloud platform decision layer. The things perception layer realizes the collection and transmission of key information of the wellsite to the big data center. The big data storage center is mainly responsible for data storage and cloud management. The cloud platform decision layer relies on the massive data in the big data center to perform cloud ground software control, artificial intelligence decision-making, and cloud platform management. (2)Select six geophysical parameters such as SP, GR, DEN, AC, CNL, and RT, and use different Machine Learning algorithms to build models to realize the independent identification of formation lithology. The Decision Tree model and the Random Forest model have an accuracy of 0.81 and 0.89 respectively, forming a set of schemes that can quickly and automatically describe the classification of lithological characteristics. (3)The cloud platform management decision is mainly used to decode real-time upload data downhole, and obtain drilling trajectories and logging curves. The cloud artificial intelligence decision-making module performs intelligent inversion and prediction of stratum and drilling parameters, realizes intelligent correction of drilling trajectories and intelligent optimization of drilling parameters, and ensures the accuracy and speed of drilling of intelligent steering engineering.
Steering drilling technology is one of the most important technologies in the global petroleum industry in the 21st century, and it is also a key component of horizontal drilling, the core technology of the American "The Shale Gas Revolution". At present, the main research goal of steering drilling is to increase the drilling speed, reduce the drilling time and risk, and intelligence is an important way to achieve this goal. The article analyzes the application of big data and artificial intelligence in the petroleum industry at home and abroad, establishes a cloud big data intelligent steering drilling method framework, proposes an artificial intelligence inversion method for logging while drilling parameters, and points out the way to realize the management of cloud big data and intelligent algorithms, and draw the following conclusions: (1)The intelligent guided drilling method based on cloud big data mainly includes the things perception layer, the big data storage layer and the cloud platform decision layer. The things perception layer realizes the collection and transmission of key information of the wellsite to the big data center. The big data storage center is mainly responsible for data storage and cloud management. The cloud platform decision layer relies on the massive data in the big data center to perform cloud ground software control, artificial intelligence decision-making, and cloud platform management. (2)Select six geophysical parameters such as SP, GR, DEN, AC, CNL, and RT, and use different Machine Learning algorithms to build models to realize the independent identification of formation lithology. The Decision Tree model and the Random Forest model have an accuracy of 0.81 and 0.89 respectively, forming a set of schemes that can quickly and automatically describe the classification of lithological characteristics. (3)The cloud platform management decision is mainly used to decode real-time upload data downhole, and obtain drilling trajectories and logging curves. The cloud artificial intelligence decision-making module performs intelligent inversion and prediction of stratum and drilling parameters, realizes intelligent correction of drilling trajectories and intelligent optimization of drilling parameters, and ensures the accuracy and speed of drilling of intelligent steering engineering.
2021, 29(1): 171-182.
There are huge reserves of shale gas resources in China, and the Sichuan Basin is the main production area. An important indicator in shale gas exploration and development is fracture characteristics and carries the two major functions of gas storage and transportation channels. Therefore, understanding the microscopic characteristics of reservoir fractures is of great significance for evaluating the gas content of the reservoir and the development prospects. In this paper, the main research object is the core of shale gas Well Lu 201. The well is located in the main shale gas production area in Southern Sichuan. With handheld microscope and stereo microscope as the main observation tools, observation experiments on the core were carried out. This paper also uses image software to reconstruct images of the core surface, statistically analyses the types, reservoir fracture characteristics, development characteristics and mineral characteristics, and successfully constructs two-dimensional shale fracture models. Through microscope observation this paper finds that: (1)Fractures in the 1st and 2nd sub-layers of the Longyi 1 sub-member of the Longmaxi Formation and Wufeng Formation shale reservoirs are mostly short fractures, accounting for 79.8% of the total fractures, with fracture length/core circumference less than 25%. (2)Fractures are well developed in the core of the Longyi 1 sub-member 1st small layer, and the fractures are mainly parallel to the bedding planes. The natural fracture number in the 2nd small layer of the Longyi 1 sub-member is slightly lower than that of the 1st small layer, while in the Wufeng formation only a very small number of natural fractures are observed. (3)The main minerals observed on the surface of the core are pyrite and calcite. The main innovation of this paper is the statistical analysis of the fracture characteristics of the Longmaxi Formation shale reservoir in Southern Sichuan through an intuitive method. and this research is of great significance for shale gas production and reservoir gas flow analysis.
There are huge reserves of shale gas resources in China, and the Sichuan Basin is the main production area. An important indicator in shale gas exploration and development is fracture characteristics and carries the two major functions of gas storage and transportation channels. Therefore, understanding the microscopic characteristics of reservoir fractures is of great significance for evaluating the gas content of the reservoir and the development prospects. In this paper, the main research object is the core of shale gas Well Lu 201. The well is located in the main shale gas production area in Southern Sichuan. With handheld microscope and stereo microscope as the main observation tools, observation experiments on the core were carried out. This paper also uses image software to reconstruct images of the core surface, statistically analyses the types, reservoir fracture characteristics, development characteristics and mineral characteristics, and successfully constructs two-dimensional shale fracture models. Through microscope observation this paper finds that: (1)Fractures in the 1st and 2nd sub-layers of the Longyi 1 sub-member of the Longmaxi Formation and Wufeng Formation shale reservoirs are mostly short fractures, accounting for 79.8% of the total fractures, with fracture length/core circumference less than 25%. (2)Fractures are well developed in the core of the Longyi 1 sub-member 1st small layer, and the fractures are mainly parallel to the bedding planes. The natural fracture number in the 2nd small layer of the Longyi 1 sub-member is slightly lower than that of the 1st small layer, while in the Wufeng formation only a very small number of natural fractures are observed. (3)The main minerals observed on the surface of the core are pyrite and calcite. The main innovation of this paper is the statistical analysis of the fracture characteristics of the Longmaxi Formation shale reservoir in Southern Sichuan through an intuitive method. and this research is of great significance for shale gas production and reservoir gas flow analysis.
2021, 29(1): 183-196.
Natural gas hydrate(NGH) is regarded as one of the most important clean energy in the 21st century. It is found that NGH is mostly stored in the porous media of submarine sediments, and some in permafrost zone. Safe and efficient utilization of NGH is important for solving current energy crisis. However, the NGH production is a complex process with many impact factors, especially the phase transition in porous media during exploitation. By comprehensively analyzing previous research results, we generalized the phase transition process of NGH into the change of equilibrium temperature and pressure, transition rate, transition stability, transformation efficiency and distribution pattern, which are significantly influenced by the characteristics of porous media. These influencing factors can be divided into pore diameter and particle size, wettability, thermal conductivity, temperature and pressure, water and gas conditions in porous media. We summarized the influence and its mechanisms as follows: 1)The pore diameter and particle size control the equilibrium temperature and pressure, the small particle size can accelerate the hydrate formation rate and decrease the transformation efficiency. 2)Wettability can determine the contact form between the hydrate and the porous media. The surface of the medium with strong hydrophilicity can speed up the formation rate of NGH. 3)The rate of NGH phase transition increases with the enhancement of the thermal conductivity. 4)The rate of NGH phase transition is positively related to the driving force of pressure and temperature, but this trend has not seen when the driving force of temperature and pressure is too large. 5)The water and gas conditions influence the equilibrium temperature and pressure, transition rate, transition stability and distribution pattern. With extensive literatures reviewed, this paper points out several key problems in current researches, gives some potential research methods and comes up with promising research directions, which is important for the extraction and exploration of NGH.
Natural gas hydrate(NGH) is regarded as one of the most important clean energy in the 21st century. It is found that NGH is mostly stored in the porous media of submarine sediments, and some in permafrost zone. Safe and efficient utilization of NGH is important for solving current energy crisis. However, the NGH production is a complex process with many impact factors, especially the phase transition in porous media during exploitation. By comprehensively analyzing previous research results, we generalized the phase transition process of NGH into the change of equilibrium temperature and pressure, transition rate, transition stability, transformation efficiency and distribution pattern, which are significantly influenced by the characteristics of porous media. These influencing factors can be divided into pore diameter and particle size, wettability, thermal conductivity, temperature and pressure, water and gas conditions in porous media. We summarized the influence and its mechanisms as follows: 1)The pore diameter and particle size control the equilibrium temperature and pressure, the small particle size can accelerate the hydrate formation rate and decrease the transformation efficiency. 2)Wettability can determine the contact form between the hydrate and the porous media. The surface of the medium with strong hydrophilicity can speed up the formation rate of NGH. 3)The rate of NGH phase transition increases with the enhancement of the thermal conductivity. 4)The rate of NGH phase transition is positively related to the driving force of pressure and temperature, but this trend has not seen when the driving force of temperature and pressure is too large. 5)The water and gas conditions influence the equilibrium temperature and pressure, transition rate, transition stability and distribution pattern. With extensive literatures reviewed, this paper points out several key problems in current researches, gives some potential research methods and comes up with promising research directions, which is important for the extraction and exploration of NGH.
2021, 29(1): 197-204.
In the construction of high dam reservoir, it is necessary to determine the permeability parameters of the rock and soil near the engineering area under the condition of high water head, and high-pressure packer test is one of the most commonly used methods. Compared with other tests, the water head and seepage velocity are very high during the high-pressure packer test, and the nonlinear flow is prone to show up. In this case, the Darcy's law is no longer applicable. Therefore, a method for determining nonlinear parameters based on the high-pressure packer test is urgently needed. In this paper, a nonlinear flow mathematical model of the high-pressure packer test is established. By using the finite difference method, the numerical solution of the nonlinear flow mathematical model under the condition of step head is obtained, and the accuracy of the numerical solution is verified. On this basis, the influence of nonlinear parameters on water head h and flow velocity v is discussed. Combining with the in-situ high-pressure packer test at Baihetan Hydropower Station, the nonlinear parameters are calculated to further verify the reliability of the method. The results show that when the nonlinear parameter k and the radial distance r remain unchanged, the larger the nonlinear parameter β, the smaller the h and the v during the test. When β and r remain unchanged, the larger the nonlinear parameter k, the higher the h and the smaller v during the test. Furthermore, larger β and k will make the packer test reach a steady state faster. If the calculation is still carried out according to the Darcy equation, the water head in the permeable medium will be overestimated, and then the ability of the structural surface to resist seepage damage will be overestimated, which will eventually have a negative impact on the stability of the project. Non-linear movement of groundwater occurred during the field high-pressure packer test at Baihetan Hydropower Station, and the nonlinear parameters of the C2 staggered zone as follows: β=1.62 min ·m-1, k=9.60×10-3m ·min-1, this method has good applicability for determining the nonlinear parameters of the staggered zone on site.
In the construction of high dam reservoir, it is necessary to determine the permeability parameters of the rock and soil near the engineering area under the condition of high water head, and high-pressure packer test is one of the most commonly used methods. Compared with other tests, the water head and seepage velocity are very high during the high-pressure packer test, and the nonlinear flow is prone to show up. In this case, the Darcy's law is no longer applicable. Therefore, a method for determining nonlinear parameters based on the high-pressure packer test is urgently needed. In this paper, a nonlinear flow mathematical model of the high-pressure packer test is established. By using the finite difference method, the numerical solution of the nonlinear flow mathematical model under the condition of step head is obtained, and the accuracy of the numerical solution is verified. On this basis, the influence of nonlinear parameters on water head h and flow velocity v is discussed. Combining with the in-situ high-pressure packer test at Baihetan Hydropower Station, the nonlinear parameters are calculated to further verify the reliability of the method. The results show that when the nonlinear parameter k and the radial distance r remain unchanged, the larger the nonlinear parameter β, the smaller the h and the v during the test. When β and r remain unchanged, the larger the nonlinear parameter k, the higher the h and the smaller v during the test. Furthermore, larger β and k will make the packer test reach a steady state faster. If the calculation is still carried out according to the Darcy equation, the water head in the permeable medium will be overestimated, and then the ability of the structural surface to resist seepage damage will be overestimated, which will eventually have a negative impact on the stability of the project. Non-linear movement of groundwater occurred during the field high-pressure packer test at Baihetan Hydropower Station, and the nonlinear parameters of the C2 staggered zone as follows: β=1.62 min ·m-1, k=9.60×10-3m ·min-1, this method has good applicability for determining the nonlinear parameters of the staggered zone on site.
2021, 29(1): 205-213.
As a significant source of uncertainty, the statistical uncertainty due to limited samples considerably affects the result of slope stability evaluation. In this paper, a conditional probability approach(CPA)was proposed to lower the effects of statistical uncertainty on slope stability evaluation without adding further samples. First, the bias between the mean (μ) of a Gaussian population and the averaged value (X) of a small sample ( X ) taken from the population obeys the t distribution. Based on this condition, given a set of survey sample data X , a series of potential mean values (μi*) of the corresponding unknown population with random deviations from the X can be created(denoted by event Bi, i=1, 2, …). The occurrence probability of each case is quantified and denoted by P(Bi). Then, the stability analysis for each case can be performed. The result(e.g., failure probability Pfi) is seen as the conditional probability of event Bi(denoted by P(A|Bi)), where A stands for the event of slope failure. Finally, from the law of total probability, the sum of the product of P(Bi) and P(A|Bi) for all cases is treated as the slope failure probability(denoted by P(A)). To investigate the established method, a series of case studies were carried out. The result indicates that the CPA can efficiently reduce the discretion of the stability analysis result (i.e. P(A)), thereby lead to a more precise outcome than the conventional analysis method where the sample mean is directly utilized.
As a significant source of uncertainty, the statistical uncertainty due to limited samples considerably affects the result of slope stability evaluation. In this paper, a conditional probability approach(CPA)was proposed to lower the effects of statistical uncertainty on slope stability evaluation without adding further samples. First, the bias between the mean (μ) of a Gaussian population and the averaged value (X) of a small sample ( X ) taken from the population obeys the t distribution. Based on this condition, given a set of survey sample data X , a series of potential mean values (μi*) of the corresponding unknown population with random deviations from the X can be created(denoted by event Bi, i=1, 2, …). The occurrence probability of each case is quantified and denoted by P(Bi). Then, the stability analysis for each case can be performed. The result(e.g., failure probability Pfi) is seen as the conditional probability of event Bi(denoted by P(A|Bi)), where A stands for the event of slope failure. Finally, from the law of total probability, the sum of the product of P(Bi) and P(A|Bi) for all cases is treated as the slope failure probability(denoted by P(A)). To investigate the established method, a series of case studies were carried out. The result indicates that the CPA can efficiently reduce the discretion of the stability analysis result (i.e. P(A)), thereby lead to a more precise outcome than the conventional analysis method where the sample mean is directly utilized.
2021, 29(1): 214-221.
Former researches of unsaturated vertical drain foundations mostly treated the foundations with ideal radial boundaries. The drain resistance and smear effect are important factors affecting the consolidation of unsaturated soil with vertical drain. This paper is based on Fredlund's one-dimensional consolidation theory for unsaturated soil mechanics and the equal strain hypothesis. The coupled governing equations of excess pore pressures are transformed into equivalent linear partial differential equations by introducing variables. This paper further takes into account the drain resistance and smear effect conditions in the analytical derivation. Separation of variables and the method of undetermined coefficients are mainly adopted to obtain the analytical solution to consolidation of unsaturated soils with vertical drain under instantaneous load. Moreover, the validity of the solution is verified by degenerating and comparing with the existing solution in saturated soils. A typical example is used to illustrate the influence of drain resistance and smear effect on consolidation of vertical drain foundation. The results show that the decrease of the smear effect-and drain resistance-related coefficients(i.e., drain resistance factor G, ratio of influence radius to vertical drain radius N, smear coefficient α, ratio of smear radius to vertical drain radius S)can lead to an obvious increase in the consolidation speed. When the drain resistance factor G is less than 0.1, the influence of the drain resistance can be neglected in practical engineering; When the ratio of smear radius to vertical drain radius S is bigger than 5, the influence of smear effect cannot cause much more remarkable difference than when S=5. It is expected that the permeability of vertical drain foundation in unsaturated soils should be improved and construction disturbance should be reduced to decrease the influence of drain resistance and smear effect in practical engineering.
Former researches of unsaturated vertical drain foundations mostly treated the foundations with ideal radial boundaries. The drain resistance and smear effect are important factors affecting the consolidation of unsaturated soil with vertical drain. This paper is based on Fredlund's one-dimensional consolidation theory for unsaturated soil mechanics and the equal strain hypothesis. The coupled governing equations of excess pore pressures are transformed into equivalent linear partial differential equations by introducing variables. This paper further takes into account the drain resistance and smear effect conditions in the analytical derivation. Separation of variables and the method of undetermined coefficients are mainly adopted to obtain the analytical solution to consolidation of unsaturated soils with vertical drain under instantaneous load. Moreover, the validity of the solution is verified by degenerating and comparing with the existing solution in saturated soils. A typical example is used to illustrate the influence of drain resistance and smear effect on consolidation of vertical drain foundation. The results show that the decrease of the smear effect-and drain resistance-related coefficients(i.e., drain resistance factor G, ratio of influence radius to vertical drain radius N, smear coefficient α, ratio of smear radius to vertical drain radius S)can lead to an obvious increase in the consolidation speed. When the drain resistance factor G is less than 0.1, the influence of the drain resistance can be neglected in practical engineering; When the ratio of smear radius to vertical drain radius S is bigger than 5, the influence of smear effect cannot cause much more remarkable difference than when S=5. It is expected that the permeability of vertical drain foundation in unsaturated soils should be improved and construction disturbance should be reduced to decrease the influence of drain resistance and smear effect in practical engineering.
2021, 29(1): 222-228.
In this paper, the self-designed system for ground vibration acceleration monitoring was used to monitor the ground vibration caused by steel sheet pile driving in three sites with different soil properties. The peak acceleration and frequency characteristics of ground vibration were analyzed. The vibration attenuation law and the influence on surrounding buildings were discussed. The results show that soil strength has significant influence on the vibration caused by steel sheet pile construction. The penetration rate of steel sheet pile in soil with low resistance is high, causing slight ground vibration response. While in soil with high resistance, the penetration rate is low and the ground vibration is relatively much more obvious. The ground longitudinal and tangential accelerations caused by steel sheet pile construction are close to each other at the same depth, and have a trend to increase with the depth. There is little influence of vibration source distance and soil property on the dominant frequency of ground vibration caused by steel sheet pile construction. A good positive linear correlation shows between the dominant frequency of ground vibration and the vibration frequency of pile construction. The construction vibration of steel sheet pile attenuates rapidly in the range of 4m from the vibration source. The minimum safety distance of steel sheet piles for surrounding buildings due to construction is far smaller than that of soil compaction pile.
In this paper, the self-designed system for ground vibration acceleration monitoring was used to monitor the ground vibration caused by steel sheet pile driving in three sites with different soil properties. The peak acceleration and frequency characteristics of ground vibration were analyzed. The vibration attenuation law and the influence on surrounding buildings were discussed. The results show that soil strength has significant influence on the vibration caused by steel sheet pile construction. The penetration rate of steel sheet pile in soil with low resistance is high, causing slight ground vibration response. While in soil with high resistance, the penetration rate is low and the ground vibration is relatively much more obvious. The ground longitudinal and tangential accelerations caused by steel sheet pile construction are close to each other at the same depth, and have a trend to increase with the depth. There is little influence of vibration source distance and soil property on the dominant frequency of ground vibration caused by steel sheet pile construction. A good positive linear correlation shows between the dominant frequency of ground vibration and the vibration frequency of pile construction. The construction vibration of steel sheet pile attenuates rapidly in the range of 4m from the vibration source. The minimum safety distance of steel sheet piles for surrounding buildings due to construction is far smaller than that of soil compaction pile.
2021, 29(1): 229-236.
At present, the improved incremental method is widespread in the study of the internal force and deformation of the pile anchor retaining structure for deep excavation. The precise calculation of load increment plays a key role in applying this method into practice. Most of the researchers focus on the reaction increment of the soil below the excavated surface and released due to the soil elastic resistance change caused by resistance coefficient change. However, there are few studies on the influencing factors of soil elastic resistance. Therefore, we used the earth pressure considering displacement and considered the influence of the change of the elastic resistance caused by the change of the resistance factor of the soil below the excavation surface. We proposed an incremental calculation method that was more in line with the actual engineering. Then we compiled a MATLAB calculation program based on the engineering example and compared the results of the program with those before consideration. Furthermore, we adopted PLAXIS to simulate the engineering example to verify the rationality of this method. The results show that the calculation method for displacement and internal force of pile anchor retaining structure based on improved incremental method is reasonable and feasible. Finally, we used the method of control variable to discuss two factors that affected the soil elastic resistance—the cohesion of soil and the internal friction angle of soil. The results show that as the decrease of the cohesion of soil and the internal friction angle of soil, the displacement of pile shows a trend of increasing, but the maximum displacement is always within the allowable range of deep excavation deformation.
At present, the improved incremental method is widespread in the study of the internal force and deformation of the pile anchor retaining structure for deep excavation. The precise calculation of load increment plays a key role in applying this method into practice. Most of the researchers focus on the reaction increment of the soil below the excavated surface and released due to the soil elastic resistance change caused by resistance coefficient change. However, there are few studies on the influencing factors of soil elastic resistance. Therefore, we used the earth pressure considering displacement and considered the influence of the change of the elastic resistance caused by the change of the resistance factor of the soil below the excavation surface. We proposed an incremental calculation method that was more in line with the actual engineering. Then we compiled a MATLAB calculation program based on the engineering example and compared the results of the program with those before consideration. Furthermore, we adopted PLAXIS to simulate the engineering example to verify the rationality of this method. The results show that the calculation method for displacement and internal force of pile anchor retaining structure based on improved incremental method is reasonable and feasible. Finally, we used the method of control variable to discuss two factors that affected the soil elastic resistance—the cohesion of soil and the internal friction angle of soil. The results show that as the decrease of the cohesion of soil and the internal friction angle of soil, the displacement of pile shows a trend of increasing, but the maximum displacement is always within the allowable range of deep excavation deformation.
2021, 29(1): 237-246.
In order to study the influencing factors and mechanism of basalt fiber-reinforced clay, the ABAQUS finite element software was used to establish the numerical analysis model of basalt fiber reinforced clay. The modeling was developed secondary based on Python language, according to the fiber percentage of dry soil mass 0, 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35% and 0.60%. The different fiber length and distribution modes were also considered. A series of unconfined compressive strength(UCS)models of basalt fiber-reinforced clay were established, and combined with the laboratory test results. The fiber reinforcement mechanism was analyzed. The results show that: (1)Based on fiber and soil separation theory, the simplified establishment of fiber reinforced soil model can be realized based on development secondary by Python language, and the simulation results are basically consistent with the laboratory tests; (2)The addition of basalt fiber can significantly improve the unconfined compressive strength and reduce the lateral bulging deformation of soil, and the fiber content, length and distribution mode have certain effects on the soil strength and lateral bulging deformation; (3)The fiber reinforcement mechanism is related to the fiber mechanics characteristic in soil. The influence rules of different fiber content, length and distribution modes can be explained by fiber mechanics characteristic analysis.
In order to study the influencing factors and mechanism of basalt fiber-reinforced clay, the ABAQUS finite element software was used to establish the numerical analysis model of basalt fiber reinforced clay. The modeling was developed secondary based on Python language, according to the fiber percentage of dry soil mass 0, 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35% and 0.60%. The different fiber length and distribution modes were also considered. A series of unconfined compressive strength(UCS)models of basalt fiber-reinforced clay were established, and combined with the laboratory test results. The fiber reinforcement mechanism was analyzed. The results show that: (1)Based on fiber and soil separation theory, the simplified establishment of fiber reinforced soil model can be realized based on development secondary by Python language, and the simulation results are basically consistent with the laboratory tests; (2)The addition of basalt fiber can significantly improve the unconfined compressive strength and reduce the lateral bulging deformation of soil, and the fiber content, length and distribution mode have certain effects on the soil strength and lateral bulging deformation; (3)The fiber reinforcement mechanism is related to the fiber mechanics characteristic in soil. The influence rules of different fiber content, length and distribution modes can be explained by fiber mechanics characteristic analysis.
2021, 29(1): 247-255.
In order to study the coordinated mechanism of subgrade scattered piles in soft soil subgrade, we put forward the synergistic model of subgrade scattered piles, as the compensation for soft soil foundation. We also clarified slope ratio of boundary load and hard-shell correlation mechanism of critical loading of soft soil foundation by using Mathematica software, and established the checking method of bearing capacity of the synergistic subgrade scattered piles, that based on critical loading of soft soil foundation through theoretical analysis. The instance analysis of the spacing between scattered piles associated with its length-designing verifies the feasibility of the method for checking the bearing capacity of the foundation piles in the soft soil foundation that is compensated by subgrade scattered piles. It further reveals the failure mechanism that the unfavorable terrain at the passive area of the roadbed scattered piles aggravates its destabilization. The results show that the proposed synergistic model and checking method for the bearing capacity of the foundation piles have good applicability in embankment. and the paper also proposes the necessity of overload preloading scheme that should be used with caution, emphasizes the importance of controlling the loading rate of the subgrade filling.
In order to study the coordinated mechanism of subgrade scattered piles in soft soil subgrade, we put forward the synergistic model of subgrade scattered piles, as the compensation for soft soil foundation. We also clarified slope ratio of boundary load and hard-shell correlation mechanism of critical loading of soft soil foundation by using Mathematica software, and established the checking method of bearing capacity of the synergistic subgrade scattered piles, that based on critical loading of soft soil foundation through theoretical analysis. The instance analysis of the spacing between scattered piles associated with its length-designing verifies the feasibility of the method for checking the bearing capacity of the foundation piles in the soft soil foundation that is compensated by subgrade scattered piles. It further reveals the failure mechanism that the unfavorable terrain at the passive area of the roadbed scattered piles aggravates its destabilization. The results show that the proposed synergistic model and checking method for the bearing capacity of the foundation piles have good applicability in embankment. and the paper also proposes the necessity of overload preloading scheme that should be used with caution, emphasizes the importance of controlling the loading rate of the subgrade filling.
2021, 29(1): 256-263.
The joint seepage is the most common disease of shield tunnel and takes an important impact on the service performance of lining. We propose the assumption of joint effective opening based on the scenario of gasket failure, and then propose the practical calculation formula for the seepage discharge estimation and the equivalent permeability coefficient for the tunnel lining. Taking the conventional shield tunnel common used in the metro line as example, we estimate the seepage discharge of shield tunnel by the proposed practical formula, which was verified by the numerical simulation based on block discrete element method. Taking three different types of shield tunnel as the prototype, furthermore, we calculate the seepage discharge under 135 different conditions. The influences of joint effective opening, external water pressure and lining geometry on the seepage discharge of shield tunnel and the equivalent permeability coefficient of lining are well discussed. It is suggested that the joint effective opening influences the seepage discharge and the equivalent permeability coefficient in a very significant way. The traditional calculation method neglects the influence of joint opening and underestimate the seepage discharge of shield tunnel. The practical calculation formula proposed in this study is readily to handle and can provide some qualitative and quantitative reference for the lining waterproof design as well as the service performance estimation of shield tunnels.
The joint seepage is the most common disease of shield tunnel and takes an important impact on the service performance of lining. We propose the assumption of joint effective opening based on the scenario of gasket failure, and then propose the practical calculation formula for the seepage discharge estimation and the equivalent permeability coefficient for the tunnel lining. Taking the conventional shield tunnel common used in the metro line as example, we estimate the seepage discharge of shield tunnel by the proposed practical formula, which was verified by the numerical simulation based on block discrete element method. Taking three different types of shield tunnel as the prototype, furthermore, we calculate the seepage discharge under 135 different conditions. The influences of joint effective opening, external water pressure and lining geometry on the seepage discharge of shield tunnel and the equivalent permeability coefficient of lining are well discussed. It is suggested that the joint effective opening influences the seepage discharge and the equivalent permeability coefficient in a very significant way. The traditional calculation method neglects the influence of joint opening and underestimate the seepage discharge of shield tunnel. The practical calculation formula proposed in this study is readily to handle and can provide some qualitative and quantitative reference for the lining waterproof design as well as the service performance estimation of shield tunnels.
2021, 29(1): 264-274.
The NSFC proposals and grants of engineering geology field in 2020 were analyzed. The field includes the engineering geological environment and disaster under the discipline of environmental geoscience and the engineering geology subordinate to the discipline of geology. The number of applications for funding projects in the field of engineering geology has increased steadily, mainly due to the continuous growing of applications for Key Programs and Young Scientist Funds. The number of applications for other types of programs is relatively stable. The statistics of the last ten years show that the peer-review referens well handled the peer-review scale on the proposals. The age structure of applicants for General Program tends to be younger, and that for the Youth Scientists Fund is reasonable. The field of engineering geology has been funded in several different project types, showing strong competitiveness.
The NSFC proposals and grants of engineering geology field in 2020 were analyzed. The field includes the engineering geological environment and disaster under the discipline of environmental geoscience and the engineering geology subordinate to the discipline of geology. The number of applications for funding projects in the field of engineering geology has increased steadily, mainly due to the continuous growing of applications for Key Programs and Young Scientist Funds. The number of applications for other types of programs is relatively stable. The statistics of the last ten years show that the peer-review referens well handled the peer-review scale on the proposals. The age structure of applicants for General Program tends to be younger, and that for the Youth Scientists Fund is reasonable. The field of engineering geology has been funded in several different project types, showing strong competitiveness.
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