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Editor Work2019 Vol. 27, No. 2
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2019, 27(2): 219-229.
Abstract
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2019, 27(2): 230-238.
The places in Gansu Bailong, Sichuan Jialing and Yunan Xiaojiang river basin have complex dry-wet climate characteristics. Phyllite slope in debris flow gully is easily affected by dry-wet climate, which can cause the collapse of the slopes. The slope collapses provide rich source materials for debris flow in such areas. After investigated the climate conditions in the study area, we select 3 kinds of conditions:common condition, dry-wet condition and extreme dry-wet condition. These three conditions are very beneficial to rock breaking. The phyllite in the surface of debris flow is the research object. And these three kinds of condition are taken as the experimental conditions. After dry-wet cycles maintenance, we carry out macroscopic observation of samples. We also test their quality-rate of change, elastic wave velocity, uniaxial compressive strength, analyzed new components of phyllite. After the observation and tests, we get some results. They explain that under different dry-wet circulations the degradation behavior and mechanism of phyllite are different. These results also reveal that the best influent factor is the extreme dry-wet. It provides a useful reference for regional evaluation and prevention of debris flow disaster in the study area.
The places in Gansu Bailong, Sichuan Jialing and Yunan Xiaojiang river basin have complex dry-wet climate characteristics. Phyllite slope in debris flow gully is easily affected by dry-wet climate, which can cause the collapse of the slopes. The slope collapses provide rich source materials for debris flow in such areas. After investigated the climate conditions in the study area, we select 3 kinds of conditions:common condition, dry-wet condition and extreme dry-wet condition. These three conditions are very beneficial to rock breaking. The phyllite in the surface of debris flow is the research object. And these three kinds of condition are taken as the experimental conditions. After dry-wet cycles maintenance, we carry out macroscopic observation of samples. We also test their quality-rate of change, elastic wave velocity, uniaxial compressive strength, analyzed new components of phyllite. After the observation and tests, we get some results. They explain that under different dry-wet circulations the degradation behavior and mechanism of phyllite are different. These results also reveal that the best influent factor is the extreme dry-wet. It provides a useful reference for regional evaluation and prevention of debris flow disaster in the study area.
2019, 27(2): 239-249.
Carbon dioxide geological storage technology is an effective way to reduce carbon dioxide emissions. The sandstone lens is an ideal site for carbon dioxide storage because of its good combination of reservoir cover. During the supercritical carbon dioxide injected into sandstone lens, a series of complex problems including fracture initiation, extension and evolution directly determine the safety of storage. The numerical simulation software ABAQUS that is based on the extended finite element method(XFEM) is used in this study. The study uses the changes of the main keywords to set up fluid-solid coupling model. Then the process of injecting supercritical carbon dioxide into sandstone lens is observed to find out the fracture failure process in the internal sandstone lens reservoir. Several conclusions are drawn from the simulation as follows. Under the condition of different lens shapes, the velocity of the inclined lens is faster than that of the horizontal lens, and the pore pressure at fracture initiation is much larger. The propagation time is short, and the CO2 storage ability is poor. As three different kinds of CO2 injection flowing rates increase, the pressure increase is more obvious, the initiating cracking time is shorter, the fracture propagation time is shorter and the speed of propagation is faster. However, the length and shape of the fracture do not change significantly. In the process of the fracture propagation, the fracture widens firstly and becomes the diversion channel, and then grows. The stress at the fracture tip increases first and then decreases gradually. The fracture stops expanding at last.
Carbon dioxide geological storage technology is an effective way to reduce carbon dioxide emissions. The sandstone lens is an ideal site for carbon dioxide storage because of its good combination of reservoir cover. During the supercritical carbon dioxide injected into sandstone lens, a series of complex problems including fracture initiation, extension and evolution directly determine the safety of storage. The numerical simulation software ABAQUS that is based on the extended finite element method(XFEM) is used in this study. The study uses the changes of the main keywords to set up fluid-solid coupling model. Then the process of injecting supercritical carbon dioxide into sandstone lens is observed to find out the fracture failure process in the internal sandstone lens reservoir. Several conclusions are drawn from the simulation as follows. Under the condition of different lens shapes, the velocity of the inclined lens is faster than that of the horizontal lens, and the pore pressure at fracture initiation is much larger. The propagation time is short, and the CO2 storage ability is poor. As three different kinds of CO2 injection flowing rates increase, the pressure increase is more obvious, the initiating cracking time is shorter, the fracture propagation time is shorter and the speed of propagation is faster. However, the length and shape of the fracture do not change significantly. In the process of the fracture propagation, the fracture widens firstly and becomes the diversion channel, and then grows. The stress at the fracture tip increases first and then decreases gradually. The fracture stops expanding at last.
2019, 27(2): 250-259.
Some geological prediction methods e.g. geological sketch, explosive seismic method and electromagnetic method cannot be used in tunnel construction by double shield TBM, because of the impact of shield, segment and electromagnetic interference. According to the characteristics of double shield TBM, we put forward comprehensive advanced geological prediction methods including geological analysis, geophysical prospecting and advance drilling, based on CCS Hydropower Station Diversion Tunnel. The guide lines of comprehensive advanced geological prediction are from rough to fine and combine points and areas. The geological analysis includes geological analysis along the tunnel, observation of rock mucks and tunneling parameters. It does not occupy the tunneling time and its cost is low. So it can be used along whole tunnel. ISIS seismic method and BEAM electric method are used as geophysical prospecting. Geophysical prospecting and advanced drilling method need some tunneling time and their cost is higher. The advanced prediction methods should be determined after considering accuracy, cost and time occupation integratedly. The corresponding measurements to deal with the adverse geological conditions are given based on the results of comprehensive advanced geological predictions. The research results show that comprehensive advanced geological methods can meet the characteristics of double shield TBM, and identify the adverse geological conditions effectively. Additionally, it can supply basic references for treatments, and then reduce and even avoid the influence of the adverse geological conditions.
Some geological prediction methods e.g. geological sketch, explosive seismic method and electromagnetic method cannot be used in tunnel construction by double shield TBM, because of the impact of shield, segment and electromagnetic interference. According to the characteristics of double shield TBM, we put forward comprehensive advanced geological prediction methods including geological analysis, geophysical prospecting and advance drilling, based on CCS Hydropower Station Diversion Tunnel. The guide lines of comprehensive advanced geological prediction are from rough to fine and combine points and areas. The geological analysis includes geological analysis along the tunnel, observation of rock mucks and tunneling parameters. It does not occupy the tunneling time and its cost is low. So it can be used along whole tunnel. ISIS seismic method and BEAM electric method are used as geophysical prospecting. Geophysical prospecting and advanced drilling method need some tunneling time and their cost is higher. The advanced prediction methods should be determined after considering accuracy, cost and time occupation integratedly. The corresponding measurements to deal with the adverse geological conditions are given based on the results of comprehensive advanced geological predictions. The research results show that comprehensive advanced geological methods can meet the characteristics of double shield TBM, and identify the adverse geological conditions effectively. Additionally, it can supply basic references for treatments, and then reduce and even avoid the influence of the adverse geological conditions.
2019, 27(2): 260-266.
The deformation, movement and destroying of the surrounding rock in the laneway can happen during the mining of coal stratum. The dynamic change characteristics have important reference significance to the selection of the technical parameters such as laneway design and support. In the paper, combining the mining process of one working face in Huainan mine area, the testing section is laid in the coal laneway. Through laying the distributed fiber sensors in the drill hole, the strain parameters of rock stratum can be detected and analyzed during the deformation and failure processing of coal and rock strata. The law of deformation development of rock stratum in the section space and characteristics affected by mining can be discussed. The analysis results through the 16 groups monitoring data from 2 monitoring drill hole indicate that the producing shifting characteristics affected by mining in the floor rock stratum are obvious during the mining process of working face, and the development of the deformation locations often start from bedding plane because of interface control of rock stratum. The maximum deformation depth of the floor rock stratum is 14.1 m in the detection field, the results are basically consistent with the resistivity CT, and its appearing ahead of stress is very clear. All of the monitoring effect is well. The distributed fiber testing technology can be used as an effective method to distinguish accurately the evolutionary process of rock stratum deformation. It can make for studying deformation and destroy rules of rock stratum after stress in different conditions.
The deformation, movement and destroying of the surrounding rock in the laneway can happen during the mining of coal stratum. The dynamic change characteristics have important reference significance to the selection of the technical parameters such as laneway design and support. In the paper, combining the mining process of one working face in Huainan mine area, the testing section is laid in the coal laneway. Through laying the distributed fiber sensors in the drill hole, the strain parameters of rock stratum can be detected and analyzed during the deformation and failure processing of coal and rock strata. The law of deformation development of rock stratum in the section space and characteristics affected by mining can be discussed. The analysis results through the 16 groups monitoring data from 2 monitoring drill hole indicate that the producing shifting characteristics affected by mining in the floor rock stratum are obvious during the mining process of working face, and the development of the deformation locations often start from bedding plane because of interface control of rock stratum. The maximum deformation depth of the floor rock stratum is 14.1 m in the detection field, the results are basically consistent with the resistivity CT, and its appearing ahead of stress is very clear. All of the monitoring effect is well. The distributed fiber testing technology can be used as an effective method to distinguish accurately the evolutionary process of rock stratum deformation. It can make for studying deformation and destroy rules of rock stratum after stress in different conditions.
2019, 27(2): 267-276.
Most of the underground water-sealed oil storage caverns in China are built in coastal areas and within the continental coastline. There are few studies about the construction of underground water-sealed oil storage cavern in island. Seawater surrounds the island, and the excavation of underground caverns can lead to seawater intrusion, affecting the service life of underground water-sealed oil storage cavern. In order to ensure the water-sealed reliability of underground cavern, it is necessary to arrange the water curtain system. Nowadays, underground water-sealed oil storage cavern is mostly equipped with horizontal water curtain system. There are few researches on water-sealed reliability of vertical water curtain system. Compared to horizontal water curtain system, vertical water curtain system has advantages of easy to drill and small disturbance on original rock. In addition, vertical water curtain system can weaken the seawater intrusion. Therefore, the study on water-sealed reliability of vertical water curtain system has great significance. In this paper, we use numerical simulation to research the arrangement methods of vertical water curtain system. According to the orthogonal design, we obtain the best arrangement parameters of the vertical water curtain boreholes. Based on the underground water-sealed oil storage cavern of an island in Zhejiang province, we study the water-sealed reliability of vertical water curtain system by comparing the results of cavern without water curtain system, cavern with horizontal water curtain system and cavern with vertical water curtain system. The results show that in the case of only setting vertical water curtain system, it can satisfy the water-sealed reliability. Moreover, compared with horizontal water curtain system, vertical water curtain system can better prevent the flow of oil from one cavern to another. The results provide theoretical basis for the water-sealed reliability of vertical water curtain system in underground water-sealed oil storage cavern in island environment.
Most of the underground water-sealed oil storage caverns in China are built in coastal areas and within the continental coastline. There are few studies about the construction of underground water-sealed oil storage cavern in island. Seawater surrounds the island, and the excavation of underground caverns can lead to seawater intrusion, affecting the service life of underground water-sealed oil storage cavern. In order to ensure the water-sealed reliability of underground cavern, it is necessary to arrange the water curtain system. Nowadays, underground water-sealed oil storage cavern is mostly equipped with horizontal water curtain system. There are few researches on water-sealed reliability of vertical water curtain system. Compared to horizontal water curtain system, vertical water curtain system has advantages of easy to drill and small disturbance on original rock. In addition, vertical water curtain system can weaken the seawater intrusion. Therefore, the study on water-sealed reliability of vertical water curtain system has great significance. In this paper, we use numerical simulation to research the arrangement methods of vertical water curtain system. According to the orthogonal design, we obtain the best arrangement parameters of the vertical water curtain boreholes. Based on the underground water-sealed oil storage cavern of an island in Zhejiang province, we study the water-sealed reliability of vertical water curtain system by comparing the results of cavern without water curtain system, cavern with horizontal water curtain system and cavern with vertical water curtain system. The results show that in the case of only setting vertical water curtain system, it can satisfy the water-sealed reliability. Moreover, compared with horizontal water curtain system, vertical water curtain system can better prevent the flow of oil from one cavern to another. The results provide theoretical basis for the water-sealed reliability of vertical water curtain system in underground water-sealed oil storage cavern in island environment.
2019, 27(2): 277-285.
The present paper studies the deformation control of the soft surrounding rock tunnel caused by different excavation sequences of core-keeping ring cut method. The study is combined with engineering example of Dongtou Mountain tunnel. Firstly, with the tunnel model and various input parameters, the method of MIDAS numerical simulation is employed to analyze and compare the deformation of surrounding rock and maximum principal stress in different stages when the tunnel is under different excavation sequences. Finally the paper analyzes the combination of numerical simulation results and actual monitoring results. The results of the evaluation demonstrate that in the construction of Dongtou Mountain tunnel, the stability and deformation of surrounding rock are better guaranteed when the deeper side of the tunnel is first excavated rather than the shallower side. The reduction degrees of rock positions from large to small are shallow buried in the arch, shallow buried in the arch foot, deep buried in the waist, deep buried in the arch foot and vault in the descending order, respectively. The maximum principal stress decreases obviously in shallow buried side in the arch. Therefore, the better working condition is chosen and the effect of different excavation sequences on the deformation of surrounding rock of the tunnel is shown. The results provide references to the information-oriented construction of tunnel, and the guidance for design and construction of Dongtou Mountain and other tunnels in similar geological condition.
The present paper studies the deformation control of the soft surrounding rock tunnel caused by different excavation sequences of core-keeping ring cut method. The study is combined with engineering example of Dongtou Mountain tunnel. Firstly, with the tunnel model and various input parameters, the method of MIDAS numerical simulation is employed to analyze and compare the deformation of surrounding rock and maximum principal stress in different stages when the tunnel is under different excavation sequences. Finally the paper analyzes the combination of numerical simulation results and actual monitoring results. The results of the evaluation demonstrate that in the construction of Dongtou Mountain tunnel, the stability and deformation of surrounding rock are better guaranteed when the deeper side of the tunnel is first excavated rather than the shallower side. The reduction degrees of rock positions from large to small are shallow buried in the arch, shallow buried in the arch foot, deep buried in the waist, deep buried in the arch foot and vault in the descending order, respectively. The maximum principal stress decreases obviously in shallow buried side in the arch. Therefore, the better working condition is chosen and the effect of different excavation sequences on the deformation of surrounding rock of the tunnel is shown. The results provide references to the information-oriented construction of tunnel, and the guidance for design and construction of Dongtou Mountain and other tunnels in similar geological condition.
2019, 27(2): 286-293.
Stratum structure of gravel soil-bedrock slope foundation is common in southwest China. The upper layer is slightly crushed stone and the lower bedrock is mainly weathered-slightly weathered thick quartz sandstone. The weak interlayer is black phyllite. Rock quality is good. For a rock-socketed pile foundation built on slopes and subjected to horizontal loads, the bedrock of the overlying soil and embankment is often inclined. If structural inclination of the rock changes, the strength of the rock specimen would also change. If the bedrock of embedded section exists and the bedding plane has inclination angle, it often affects the horizontal bearing property of pile foundation greatly. Therefore, the bedrock level is one of the main factors affecting the horizontal bearing capacity of rock-socketed pile. At present, there is little research on the horizontal bearing capacity of piles for the level inclination of embedded section. This article digs deeper into this aspect of theory. The physical model test is carried out at Physical Simulation Laboratory, Chengdu University of Technology. It uses a single pile water static load test. It uses small blocks of masonry and polyethylene film to simulate the structural plane of the rock formation. Loading method maintains load slowly. Jack is placed at the back of the pile to apply horizontal load. Each level load is 0.3 kN. The rock-socketed piles under four conditions are simulated by changing the inclination of bedrock of the embedded section. Model pile length is 1 meter. The embedded depth of the model pile is three times of the pile diameter. The exposed pile top length is equal to the pile diameter. The top soil and bedrock slope are 30 degrees in gravel soil-bedrock slope foundation site. Bedrock is complete bedrock and bedding inclination respectively horizontal, forward 30 degrees, reverse 30 degrees. The test data are obtained as follows. The top displacement of pile top, the maximum value of bending moment of pile body and the maximum position of bending moment, the position of maximum shear force and the maximum shear value of pile body are obtained with the variation of loads. Then the bearing capacity of pile foundation under different inclinations is analyzed. The critical load, ultimate load, pile foundation horizontal bearing capacity characteristic value and the maximum pile bending moment value and the maximum pile shear force value of the piles at different grass-root levels are compared. Finally, the effect on the bearing capacity of horizontal loaded rock-socketed pile is studied. The results show that in the slope site, the existence of bedrock in embedded section can reduce the horizontal bearing capacity of rock-socketed pile. Compared with the intact bedrock, when the bedded bedrock in horizontal section exists, the critical load decreases by 17%, the maximum bending moment decreases by 23% and the maximum shear force decreases by 37.5%. However, the horizontal bearing capacity of rockfill piles drops more when the base level of the embankment is inclined. The influence of the maximum bending moment point and the position of the maximum shear point on the inclination change of bedrock inclination in the embedded section is relatively small. The location of the maximum bending moment is almost unchanged. The position of the maximum shear point is reduced by 1 times of pile diameter when the bedrock of the embedded section is forward 30 degrees and reverse 30 degrees. This study can be used as a reference for the design of rock-fill piles bearing horizontal loads on layered and slope rock mass foundations with different dip angles.
Stratum structure of gravel soil-bedrock slope foundation is common in southwest China. The upper layer is slightly crushed stone and the lower bedrock is mainly weathered-slightly weathered thick quartz sandstone. The weak interlayer is black phyllite. Rock quality is good. For a rock-socketed pile foundation built on slopes and subjected to horizontal loads, the bedrock of the overlying soil and embankment is often inclined. If structural inclination of the rock changes, the strength of the rock specimen would also change. If the bedrock of embedded section exists and the bedding plane has inclination angle, it often affects the horizontal bearing property of pile foundation greatly. Therefore, the bedrock level is one of the main factors affecting the horizontal bearing capacity of rock-socketed pile. At present, there is little research on the horizontal bearing capacity of piles for the level inclination of embedded section. This article digs deeper into this aspect of theory. The physical model test is carried out at Physical Simulation Laboratory, Chengdu University of Technology. It uses a single pile water static load test. It uses small blocks of masonry and polyethylene film to simulate the structural plane of the rock formation. Loading method maintains load slowly. Jack is placed at the back of the pile to apply horizontal load. Each level load is 0.3 kN. The rock-socketed piles under four conditions are simulated by changing the inclination of bedrock of the embedded section. Model pile length is 1 meter. The embedded depth of the model pile is three times of the pile diameter. The exposed pile top length is equal to the pile diameter. The top soil and bedrock slope are 30 degrees in gravel soil-bedrock slope foundation site. Bedrock is complete bedrock and bedding inclination respectively horizontal, forward 30 degrees, reverse 30 degrees. The test data are obtained as follows. The top displacement of pile top, the maximum value of bending moment of pile body and the maximum position of bending moment, the position of maximum shear force and the maximum shear value of pile body are obtained with the variation of loads. Then the bearing capacity of pile foundation under different inclinations is analyzed. The critical load, ultimate load, pile foundation horizontal bearing capacity characteristic value and the maximum pile bending moment value and the maximum pile shear force value of the piles at different grass-root levels are compared. Finally, the effect on the bearing capacity of horizontal loaded rock-socketed pile is studied. The results show that in the slope site, the existence of bedrock in embedded section can reduce the horizontal bearing capacity of rock-socketed pile. Compared with the intact bedrock, when the bedded bedrock in horizontal section exists, the critical load decreases by 17%, the maximum bending moment decreases by 23% and the maximum shear force decreases by 37.5%. However, the horizontal bearing capacity of rockfill piles drops more when the base level of the embankment is inclined. The influence of the maximum bending moment point and the position of the maximum shear point on the inclination change of bedrock inclination in the embedded section is relatively small. The location of the maximum bending moment is almost unchanged. The position of the maximum shear point is reduced by 1 times of pile diameter when the bedrock of the embedded section is forward 30 degrees and reverse 30 degrees. This study can be used as a reference for the design of rock-fill piles bearing horizontal loads on layered and slope rock mass foundations with different dip angles.
2019, 27(2): 294-301.
Hornito, formed by cooled lava, is a key protection of lava landform in active Wudalianchi volcano geopark. At present, a lot of cracks are developed on the surfaces of hornitos and are responsible to hornito damage. Based on forming process of hornitos, the paper analyzes temperature changes of lava during cooling. A 3D model of a hornito is established and the thermal stress distribution is calculated through numerical simulation. On this basis, this paper uses fracture mechanics to analyse crack morphology and distribution of the hornito. The study shows that thermal stress is generated in hornito during lava cooling. The maximum principal stress trace presents circumferential distribution. Moreover, the cracks are vertical and parallel. Adjacent cracks have approximate equidistance. Besides, the width of some cracks on the outer side is larger. Crack tips are sharp or blunt. The density of crack distribution is different. The vertical cracks observed at the scene conform to these characteristics. According to this, this paper points out that vertical cracks are the primary cracks produced during the forming process of hornito.
Hornito, formed by cooled lava, is a key protection of lava landform in active Wudalianchi volcano geopark. At present, a lot of cracks are developed on the surfaces of hornitos and are responsible to hornito damage. Based on forming process of hornitos, the paper analyzes temperature changes of lava during cooling. A 3D model of a hornito is established and the thermal stress distribution is calculated through numerical simulation. On this basis, this paper uses fracture mechanics to analyse crack morphology and distribution of the hornito. The study shows that thermal stress is generated in hornito during lava cooling. The maximum principal stress trace presents circumferential distribution. Moreover, the cracks are vertical and parallel. Adjacent cracks have approximate equidistance. Besides, the width of some cracks on the outer side is larger. Crack tips are sharp or blunt. The density of crack distribution is different. The vertical cracks observed at the scene conform to these characteristics. According to this, this paper points out that vertical cracks are the primary cracks produced during the forming process of hornito.
2019, 27(2): 302-310.
This paper investigates the micro-mechanical response of supported joint under direct shear loading with the particle flow code. It builts the supported joint and unsupported joint numerical model successfully. It investigates the mechanical properties and failure mode of supported joint under direct shear tests and under different normal stresses. At the same time, based on the shear-displacement curve and peak shear strength of the numerical model, it investigates the macro-mechanical properties. Moreover, the failure characteristics of the bolted joint are also analyzed via the micro-cracks distribution. Detailed results are given as follows:(1)Compared to the unsupported joint, the shear stress curve of the supported joint shows obvious increasing trend at the post-peak phase. There is obvious difference between the shear stresses for unsupported and supported joints. (2)Due to the different inclination angles, the supported joint exhibits different failure modes. When the inclination angle equals to 90°, the failure of the joint concentrates at the contact point of the joint and bolt. While, with increases of the inclination angle, the failure of the joint gradually turns to tensile failure along the bolt and the tensile crack propagation in the rock. (3)With different joint roughness value, the influence of bolt angel on the shear strength is different. When JRC value is small, the bolt shown a great influence on the peak shear stress, but when the JRC is larger, the influence is weaken.
This paper investigates the micro-mechanical response of supported joint under direct shear loading with the particle flow code. It builts the supported joint and unsupported joint numerical model successfully. It investigates the mechanical properties and failure mode of supported joint under direct shear tests and under different normal stresses. At the same time, based on the shear-displacement curve and peak shear strength of the numerical model, it investigates the macro-mechanical properties. Moreover, the failure characteristics of the bolted joint are also analyzed via the micro-cracks distribution. Detailed results are given as follows:(1)Compared to the unsupported joint, the shear stress curve of the supported joint shows obvious increasing trend at the post-peak phase. There is obvious difference between the shear stresses for unsupported and supported joints. (2)Due to the different inclination angles, the supported joint exhibits different failure modes. When the inclination angle equals to 90°, the failure of the joint concentrates at the contact point of the joint and bolt. While, with increases of the inclination angle, the failure of the joint gradually turns to tensile failure along the bolt and the tensile crack propagation in the rock. (3)With different joint roughness value, the influence of bolt angel on the shear strength is different. When JRC value is small, the bolt shown a great influence on the peak shear stress, but when the JRC is larger, the influence is weaken.
2019, 27(2): 311-316.
In this paper, stone columns are encased with three types of biaxial geogrid such as stretch plastic geogrid, welded polyester geogrid and knitted polyester geogrid. Uniaxial compression tests are conducted on the geogrid-encased stone columns to study their deformation and strength characteristics. The results show that there are good linear relationships between column strength and encasement strength both in stretch plastic geogrid and knitted polyester geogrid encased columns, while the linear relationship is not good in welded polyester geogrid encased columns. Stretch plastic geogrid encased column is damaged when the strength of geogrid reaches, while welded polyester and knitted polyester encased columns are damaged due to the breakage of welding or knitting nodes when the strength of geogrid are far from reaching. Therefore, the strength of stretch plastic geogrid encased column is significantly higher than that of welded polyester geogrid and knitted polyester geogrid encased columns. In practical engineering, stretch plastic geogrid is recommended for encasing the stone columns, and the strength of plastic geogrid-encased stone columns can be calculated by using a corrected theoretic formula for polypropylene geotextile encased stone columns.
In this paper, stone columns are encased with three types of biaxial geogrid such as stretch plastic geogrid, welded polyester geogrid and knitted polyester geogrid. Uniaxial compression tests are conducted on the geogrid-encased stone columns to study their deformation and strength characteristics. The results show that there are good linear relationships between column strength and encasement strength both in stretch plastic geogrid and knitted polyester geogrid encased columns, while the linear relationship is not good in welded polyester geogrid encased columns. Stretch plastic geogrid encased column is damaged when the strength of geogrid reaches, while welded polyester and knitted polyester encased columns are damaged due to the breakage of welding or knitting nodes when the strength of geogrid are far from reaching. Therefore, the strength of stretch plastic geogrid encased column is significantly higher than that of welded polyester geogrid and knitted polyester geogrid encased columns. In practical engineering, stretch plastic geogrid is recommended for encasing the stone columns, and the strength of plastic geogrid-encased stone columns can be calculated by using a corrected theoretic formula for polypropylene geotextile encased stone columns.
2019, 27(2): 317-324.
A large amount of tailings are produced after mining and beneficiation process of copper ore and tungsten ore. The stability safety of tailing dams largely depends on the shear strength characteristics of tailings. And the shear strength properties can also determine the innovative utilization of the tailings in future. The gradation curve of tailings obtained by means of tailing pond site sampling is different from the gradation curve of unclassified tailings produced by beneficiation process of ores. Selection of suitable shear strength parameters of tailings and comparative analysis of the shear strength of different tailings can be helpful to evaluate the dam break safety of tailings pond. In order to study the shear strength characteristics of copper tailings and tungsten tailings as well as the main differences and similarities between two kinds of tailings, a series of direct shear tests are carried out for copper tailings and tungsten tailings with different particle size ranges. Besides, X diffraction analysis and scanning electron microscope(SEM)analysis are conducted to study the intrinsic micro mechanism. The direct shear testing results demonstrate that dry copper tailings and dry tungsten tailings behave the strength properties of cohesionless soil. In the case of the same particle size range condition, the shear strength of the copper tailings is higher than that of the tungsten tailings. Both the copper tailings and tungsten tailings show a certain value of cohesion when the water content is 15%. The shear strength of hydrated tailings with water content of 15% increases by 16.7%~83.8% relative to the dry condition. With the increase of water content from 10% to 20%, no obvious change is shown to the internal friction angle of fine grained tungsten tailings. However, the cohesion decreases obviously with the increase of water content, which reduces the shear strength of tailings. The results of X-ray diffraction analysis show that both copper tailings and tungsten tailings are mainly quartz crystal phases and the other mineral components are mostly silicate secondary minerals. The 5000 times magnified SEM photos display that a certain amount of clay minerals can be observed on the surface of fine tailings particles. It is due to the effect of clay minerals that the shear strength of tailings changes with the increase of water content.
A large amount of tailings are produced after mining and beneficiation process of copper ore and tungsten ore. The stability safety of tailing dams largely depends on the shear strength characteristics of tailings. And the shear strength properties can also determine the innovative utilization of the tailings in future. The gradation curve of tailings obtained by means of tailing pond site sampling is different from the gradation curve of unclassified tailings produced by beneficiation process of ores. Selection of suitable shear strength parameters of tailings and comparative analysis of the shear strength of different tailings can be helpful to evaluate the dam break safety of tailings pond. In order to study the shear strength characteristics of copper tailings and tungsten tailings as well as the main differences and similarities between two kinds of tailings, a series of direct shear tests are carried out for copper tailings and tungsten tailings with different particle size ranges. Besides, X diffraction analysis and scanning electron microscope(SEM)analysis are conducted to study the intrinsic micro mechanism. The direct shear testing results demonstrate that dry copper tailings and dry tungsten tailings behave the strength properties of cohesionless soil. In the case of the same particle size range condition, the shear strength of the copper tailings is higher than that of the tungsten tailings. Both the copper tailings and tungsten tailings show a certain value of cohesion when the water content is 15%. The shear strength of hydrated tailings with water content of 15% increases by 16.7%~83.8% relative to the dry condition. With the increase of water content from 10% to 20%, no obvious change is shown to the internal friction angle of fine grained tungsten tailings. However, the cohesion decreases obviously with the increase of water content, which reduces the shear strength of tailings. The results of X-ray diffraction analysis show that both copper tailings and tungsten tailings are mainly quartz crystal phases and the other mineral components are mostly silicate secondary minerals. The 5000 times magnified SEM photos display that a certain amount of clay minerals can be observed on the surface of fine tailings particles. It is due to the effect of clay minerals that the shear strength of tailings changes with the increase of water content.
2019, 27(2): 325-332.
The permeability and permeability coefficient of landslide bodies are great importance to the calculation of the seepage and stability of the reservoir landslides. This paper analyses the test data of 1188 test pits(samples) from 396 landslides in the Three Gorges Reservoir Area. It gets the following conclusions:(1)According to provenance lithology of landslides in Three Gorges Reservoir Area, landslide bodies can be divided into dolomite and limestone, marlite, sand shale interbed. According to the composition structure, landslide bodies can be divided into the homogeneous fine-grained soil, soil containing gravel stone, soil clip gravel stone, crushed rock soil and fractured rock mass. (2)The permeability of landslide bodies is mainly medium and good. Moreover, it has certain regional distribution characteristics. The permeability of landslide bodies in Fengjie, Wuxi and Zhongxian is medium. And the permeability of landslide bodies in other districts is good. The permeability coefficient is positively correlated with the content of gravel stone of landslide body. The permeability of the fractured rock mass is lower than that of the crushed rock soil. (3)The average permeability coefficient of different components of landslide bodies are as follows. The permeability coefficient of homogeneous fine-grained soil is 1.28 m·d-1. The soil containing gravel stone is 1.41 m·d-1. The soil clip gravel stone is 2.56 m·d-1. The crushed rock soil is 3.84 m·d-1. And the fractured rock mass is 3.24 m·d-1.
The permeability and permeability coefficient of landslide bodies are great importance to the calculation of the seepage and stability of the reservoir landslides. This paper analyses the test data of 1188 test pits(samples) from 396 landslides in the Three Gorges Reservoir Area. It gets the following conclusions:(1)According to provenance lithology of landslides in Three Gorges Reservoir Area, landslide bodies can be divided into dolomite and limestone, marlite, sand shale interbed. According to the composition structure, landslide bodies can be divided into the homogeneous fine-grained soil, soil containing gravel stone, soil clip gravel stone, crushed rock soil and fractured rock mass. (2)The permeability of landslide bodies is mainly medium and good. Moreover, it has certain regional distribution characteristics. The permeability of landslide bodies in Fengjie, Wuxi and Zhongxian is medium. And the permeability of landslide bodies in other districts is good. The permeability coefficient is positively correlated with the content of gravel stone of landslide body. The permeability of the fractured rock mass is lower than that of the crushed rock soil. (3)The average permeability coefficient of different components of landslide bodies are as follows. The permeability coefficient of homogeneous fine-grained soil is 1.28 m·d-1. The soil containing gravel stone is 1.41 m·d-1. The soil clip gravel stone is 2.56 m·d-1. The crushed rock soil is 3.84 m·d-1. And the fractured rock mass is 3.24 m·d-1.
2019, 27(2): 333-340.
The correlations of physical index and mechanical parameters, according to experimental data of Yangzhou clays, are investigated in this paper. The statistical results show that there is a positive correlation between the plasticity index and compressibility or bulk compressibility, while there is a negative correlation with internal friction angle or effective internal friction angle. Also, the cohesion decreases with the increase of liquid index, while it increases with the increase of the difference between liquid limit and water content. And the correlation coefficient of cohesion and liquid index is higher. However, if the water content is higher than the liquid limit, the cohesion is independent of the liquidity index or the difference value. In addition, the samples of Yangzhou clays exhibit obviously unimodal pore-size distribution(PSD), obtained from the mercury intrusion porosimetry tests on undisturbed clays. The volume of the inter-particle pores increases, while pore diameter corresponding to the peak of PSD decreases with the increase of the plasticity index. The above results provide a simple method for estimating the mechanical parameters of clay in Yangzhou area.
The correlations of physical index and mechanical parameters, according to experimental data of Yangzhou clays, are investigated in this paper. The statistical results show that there is a positive correlation between the plasticity index and compressibility or bulk compressibility, while there is a negative correlation with internal friction angle or effective internal friction angle. Also, the cohesion decreases with the increase of liquid index, while it increases with the increase of the difference between liquid limit and water content. And the correlation coefficient of cohesion and liquid index is higher. However, if the water content is higher than the liquid limit, the cohesion is independent of the liquidity index or the difference value. In addition, the samples of Yangzhou clays exhibit obviously unimodal pore-size distribution(PSD), obtained from the mercury intrusion porosimetry tests on undisturbed clays. The volume of the inter-particle pores increases, while pore diameter corresponding to the peak of PSD decreases with the increase of the plasticity index. The above results provide a simple method for estimating the mechanical parameters of clay in Yangzhou area.
2019, 27(2): 341-349.
The Jinpingzi landslide is a typical creep landslide with total volume of about 6.25×108 m3 on the right bank of the Jinsha River, about 900 m from dam of Wudongde hydropower Station. This paper further clarifies the internal mechanism controlling the activity pattern of the landslide, the characteristics of residual strength and the peak strength of slip zone. It provides references for the protection and management of similar landslides. It employs a series of repeated shear tests under different clay contents. It is found that the strain-softening phenomenon of sliding zone soil is becoming more obvious as clay content increases. The residual strength and peak strength of sliding zone soil show a nonlinear decrease law as clay content increases, but the decreased degree increases as normal stress increases. Meanwhile, the residual internal friction angle and peak internal friction angle have a good linear negative correlation with the clay content. The peak cohesion and residual cohesion increase as clay content increases, but there is a decrease at clay content 40%. The reason for the decreasing tendency of the cohesion may be that the distribution of bound water around the clay particles has a critical effect on the strength characteristics of the slip zone, especially for the cohesion. Data and results of this paper have important significance to the protection and management of Jingpingzi landslide and the evolution process of creep landslides under different particle sizes.
The Jinpingzi landslide is a typical creep landslide with total volume of about 6.25×108 m3 on the right bank of the Jinsha River, about 900 m from dam of Wudongde hydropower Station. This paper further clarifies the internal mechanism controlling the activity pattern of the landslide, the characteristics of residual strength and the peak strength of slip zone. It provides references for the protection and management of similar landslides. It employs a series of repeated shear tests under different clay contents. It is found that the strain-softening phenomenon of sliding zone soil is becoming more obvious as clay content increases. The residual strength and peak strength of sliding zone soil show a nonlinear decrease law as clay content increases, but the decreased degree increases as normal stress increases. Meanwhile, the residual internal friction angle and peak internal friction angle have a good linear negative correlation with the clay content. The peak cohesion and residual cohesion increase as clay content increases, but there is a decrease at clay content 40%. The reason for the decreasing tendency of the cohesion may be that the distribution of bound water around the clay particles has a critical effect on the strength characteristics of the slip zone, especially for the cohesion. Data and results of this paper have important significance to the protection and management of Jingpingzi landslide and the evolution process of creep landslides under different particle sizes.
2019, 27(2): 350-359.
In this paper, the polymer curing agent and polypropylene fiber are used to reinforce sand in compound. The pull-out test is carried out on the remolded samples with different polypropylene fiber contents, curing agent contents and dry density to measure its tensile strength. The study compares the change regulation of tensile strength of sand before and after improvement, then analyzes its mechanism of composite reinforcement with scanning electron microscope(SEM). The experimental results show that the composite reinforcement of polymer curing agent and polypropylene fiber can significantly improve the tensile strength of sand. Fiber content, curing agent content and dry density have great influences on the tensile strength of modified sand. For specimens with the same dry density and polymer curing agent content, the tensile strength gradually increases with the increase of fiber content. For the specimens with 4% curing agent content and 1.5 g·cm-3 dry density, as fiber content increases from 0.2% to 0.8%, the tensile strength increases from 79.06 kPa to 194.51 kPa. For the specimens with the same dry density and fiber content, the tensile strength increases as polymer curing agent content increasing. For the specimens with 0.8% fiber content and 1.5 g·cm-3 dry density, the tensile strength increases from 63.16 kPa to 194.51 kPa as polymer curing agent content increases from 1% to 4%. As the dry density increase, the tensile strength first increases and then decreases with the peak at approximately1.55 g·cm-3. Composite reinforcement has the advantages of physical and chemical reinforcement. Through the interaction force among fibers and sand particles and the bonding force of polymer among sand particles, tensile strength of the modified sand is greatly improved. The results of this study also provide some references for further research on composite reinforcement of sand soil and its engineering application.
In this paper, the polymer curing agent and polypropylene fiber are used to reinforce sand in compound. The pull-out test is carried out on the remolded samples with different polypropylene fiber contents, curing agent contents and dry density to measure its tensile strength. The study compares the change regulation of tensile strength of sand before and after improvement, then analyzes its mechanism of composite reinforcement with scanning electron microscope(SEM). The experimental results show that the composite reinforcement of polymer curing agent and polypropylene fiber can significantly improve the tensile strength of sand. Fiber content, curing agent content and dry density have great influences on the tensile strength of modified sand. For specimens with the same dry density and polymer curing agent content, the tensile strength gradually increases with the increase of fiber content. For the specimens with 4% curing agent content and 1.5 g·cm-3 dry density, as fiber content increases from 0.2% to 0.8%, the tensile strength increases from 79.06 kPa to 194.51 kPa. For the specimens with the same dry density and fiber content, the tensile strength increases as polymer curing agent content increasing. For the specimens with 0.8% fiber content and 1.5 g·cm-3 dry density, the tensile strength increases from 63.16 kPa to 194.51 kPa as polymer curing agent content increases from 1% to 4%. As the dry density increase, the tensile strength first increases and then decreases with the peak at approximately1.55 g·cm-3. Composite reinforcement has the advantages of physical and chemical reinforcement. Through the interaction force among fibers and sand particles and the bonding force of polymer among sand particles, tensile strength of the modified sand is greatly improved. The results of this study also provide some references for further research on composite reinforcement of sand soil and its engineering application.
2019, 27(2): 360-366.
Particles transport plays an important role in contaminants transport in groundwater. In this study, the case of red mud pond in Zhatang is taken to analyze the distribution characteristics and transport law of red mud particles by means of combining site sampling and laboratory analysis. The results suggest that red mud is a kind of back-fill material that is similar to clay with well-graded. The distribution characteristics of red mud particles tend to be consistent at different sampling depths. There are differences in the transport law of red mud particles between various particle sizes. Hydrodynamic conditions play a decisive role in the maximum particle size of red mud particles in transport process.
Particles transport plays an important role in contaminants transport in groundwater. In this study, the case of red mud pond in Zhatang is taken to analyze the distribution characteristics and transport law of red mud particles by means of combining site sampling and laboratory analysis. The results suggest that red mud is a kind of back-fill material that is similar to clay with well-graded. The distribution characteristics of red mud particles tend to be consistent at different sampling depths. There are differences in the transport law of red mud particles between various particle sizes. Hydrodynamic conditions play a decisive role in the maximum particle size of red mud particles in transport process.
2019, 27(2): 367-375.
There are some problems in traditional predictions of slope displacement when we take a relatively long monitoring cycle and the difficulty in monitoring dependent variables into consideration. Three kinds of problems may be caused. Firstly, models are often difficult to be built. Besides, the number of models is too large. Last but not least, spatial prediction can not be carried out. A semi-filled and semi-excavated subgrade slope is taken as the research object. The spatial correlation between different measuring points is taken into account. Based on the monitoring data of slope displacement, the basic theory of spatial econometrics and dynamic panel data are introduced. After testing and quantifying the spatial relationship between different measuring points, a dynamic spatial panel data model of slope displacement is established. The prediction results of the model is tested. Results show that the proposed model is more concise in terms of parameters, compared with traditional time series models. In addition, all monitoring points in the slope can be predicted in one model at the same time. Finally, the prediction of this model can be effective not only in time scale but also in space scale.
There are some problems in traditional predictions of slope displacement when we take a relatively long monitoring cycle and the difficulty in monitoring dependent variables into consideration. Three kinds of problems may be caused. Firstly, models are often difficult to be built. Besides, the number of models is too large. Last but not least, spatial prediction can not be carried out. A semi-filled and semi-excavated subgrade slope is taken as the research object. The spatial correlation between different measuring points is taken into account. Based on the monitoring data of slope displacement, the basic theory of spatial econometrics and dynamic panel data are introduced. After testing and quantifying the spatial relationship between different measuring points, a dynamic spatial panel data model of slope displacement is established. The prediction results of the model is tested. Results show that the proposed model is more concise in terms of parameters, compared with traditional time series models. In addition, all monitoring points in the slope can be predicted in one model at the same time. Finally, the prediction of this model can be effective not only in time scale but also in space scale.
2019, 27(2): 376-389.
Rubber-Sand Mixture(RSM)has recently been demonstrated to be a new type of low cost isolation material with wide application. The mechanics and deformation characteristics of RSM can vary with mix ratio and particle size ratio of the two base materials. In order to promote the engineering application of RSM, a series of biaxial compression tests are conducted numerically on three kinds of particle size ratio and six kinds of mix ratio based on DEM simulation. Influence mechanisms of particle size ratio on macroscopic and mesoscopic characteristics are analyzed. Results indicate that:(1)The stress-strain curves of RSM show a linear growth relationship under small strain. With the increase of rubber content, the deviator stress and its degree decrease with increase of particle size ratio. (2)With the increase of rubber content, the modulus of RSM decreases, and the hardening characteristics of specimen is enhanced. The larger the particle size ratio, the more evident the degree of hardening. (3)With the increase of rubber content, volumetric expansion of RSM is decreased, and the contraction characteristics of specimen is enhanced. The larger the particle size ratio, the more evident the degree of contraction. (4)The stress-strain behavior of RSM can be simulated well with the extended Duncan-Chang hyperbola model, and the influence of particle size ratio and rubber particle content on model parameters is obvious. (5)The mesoscopic mechanism of the effect of particle size ratio on RSM can be described by these factors including particle contact characteristics, particle coordination number, force chain distribution, and energy consumption development.
Rubber-Sand Mixture(RSM)has recently been demonstrated to be a new type of low cost isolation material with wide application. The mechanics and deformation characteristics of RSM can vary with mix ratio and particle size ratio of the two base materials. In order to promote the engineering application of RSM, a series of biaxial compression tests are conducted numerically on three kinds of particle size ratio and six kinds of mix ratio based on DEM simulation. Influence mechanisms of particle size ratio on macroscopic and mesoscopic characteristics are analyzed. Results indicate that:(1)The stress-strain curves of RSM show a linear growth relationship under small strain. With the increase of rubber content, the deviator stress and its degree decrease with increase of particle size ratio. (2)With the increase of rubber content, the modulus of RSM decreases, and the hardening characteristics of specimen is enhanced. The larger the particle size ratio, the more evident the degree of hardening. (3)With the increase of rubber content, volumetric expansion of RSM is decreased, and the contraction characteristics of specimen is enhanced. The larger the particle size ratio, the more evident the degree of contraction. (4)The stress-strain behavior of RSM can be simulated well with the extended Duncan-Chang hyperbola model, and the influence of particle size ratio and rubber particle content on model parameters is obvious. (5)The mesoscopic mechanism of the effect of particle size ratio on RSM can be described by these factors including particle contact characteristics, particle coordination number, force chain distribution, and energy consumption development.
2019, 27(2): 390-397.
Former researches of unsaturated drainage well foundations always treated the foundations with ideal radial boundaries, but did not consider the smearing effect. The construction disturbance can affect the speed of consolidation by decreasing the soil permeability near the inside of a drainage well foundation. In this case, the smearing effect is illustrated with the semi-permeable boundary and is included in a new modeling of drainage well foundation in unsaturated soils. By introducing Bessel functions, analytical solutions with respect to excess pore pressures are achieved in the Laplace domain according to the governing equations. Secondly, by utilizing the Crump's method, the inverse Laplace transform to obtain semi-analytical solutions to excess pore pressures in the time domain is performed. It is shown that the present solutions are in good agreement with the previous solutions in the literature and more reliable. Finally, parametric studies are conducted by the variations of excess pore pressures at different ratios of air-water permeability coefficient and the radius. Results indicate that the semi-permeability coefficients have significant influence on the consolidation, and excess pore pressures dissipate faster with the increase of semi-permeability coefficient.
Former researches of unsaturated drainage well foundations always treated the foundations with ideal radial boundaries, but did not consider the smearing effect. The construction disturbance can affect the speed of consolidation by decreasing the soil permeability near the inside of a drainage well foundation. In this case, the smearing effect is illustrated with the semi-permeable boundary and is included in a new modeling of drainage well foundation in unsaturated soils. By introducing Bessel functions, analytical solutions with respect to excess pore pressures are achieved in the Laplace domain according to the governing equations. Secondly, by utilizing the Crump's method, the inverse Laplace transform to obtain semi-analytical solutions to excess pore pressures in the time domain is performed. It is shown that the present solutions are in good agreement with the previous solutions in the literature and more reliable. Finally, parametric studies are conducted by the variations of excess pore pressures at different ratios of air-water permeability coefficient and the radius. Results indicate that the semi-permeability coefficients have significant influence on the consolidation, and excess pore pressures dissipate faster with the increase of semi-permeability coefficient.
2019, 27(2): 398-407.
The reinforced protecting wall is a composite structure located around the oil tank. It is consisted of three parts which are the backfill soil, reinforcements arranged in the soil and geogrid panels respectively. The reinforced protecting wall has received very few attentions of researchers. Related researches haven't taken the influence of spatial character on the reinforced protecting wall into consideration. As a result, its theoretical researches lag behind its engineering application currently. Due to the fact that the circular geosynthetics-reinforced protection walls cannot ignore the influence of its space characteristics, the numerical analysis is carried out with Plaxis3D finite element software. The reinforced concrete protection wall and the reinforced concrete dome are simulated with the slab unit. The geotextiles are made of geosynthetics. In order to better simulate the actual working conditions, interface units are set up at the interfaces of soil, concrete and geotextiles. The tank body is simulated with the plate element, and the oil in the tank is simulated by the entity unit. Because the tank and internal fuel use entity modeling, the interaction between soil and superstructure can be considered, and the rationality and accuracy of numerical simulation can be improved. The deformation characteristics of circular geosynthetics-reinforced protection walls located around oil tank and mechanical characteristics of reinforced materials are investigated with developing a three-dimensional numerical model. The model uses the hardening soil model with small-stain stiffness(HSS models) as reinforced soil constitutive model. By changing geosynthetics-reinforced protection wall height, thickness, gradient of wall space, geogrid stiffness and reinforcement spacing, the effects of these factors on the wall deformation characteristics are explored. This paper conducts a detail study on the influence of the size of reinforced protecting wall on the serviceability limit state. The study is composed of deformation behavior, the foundation settlement, and the distribution of strains and tensile in the reinforcement. According to the above analysis, this paper puts forward some suggestions to optimize shape and size of reinforced protecting wall. The results show that the wall lateral displacement decreases with the decrease in the wall thickness, height and gradient of wall space. Also, too small wall thickness and too large reinforcement spacing can lead to the increase of the overturning trend of protection wall, and smaller stiffness of geogrid results in excessive lateral displacement of wall. Thus, these parameters should be taken into account in practice. The construction of reinforced wall can increase the settlement of foundation on the edge of storage tank. The loading state of the fuel in the storage tank does not affect the settlement of the reinforced protective wall foundation. However, the maximum settlement difference of the tank foundation decreases with the increase of fuel oil in the storage tank. Further, the potential failure surface of the geosynthetics-reinforced protection walls according to the position of maximum tensile stress of geogrid is a curve going through wall toe. The soil pressure behind the wall is greatly affected by the wall gradient. So the gradient should be considered when choosing a appropriate design method.
The reinforced protecting wall is a composite structure located around the oil tank. It is consisted of three parts which are the backfill soil, reinforcements arranged in the soil and geogrid panels respectively. The reinforced protecting wall has received very few attentions of researchers. Related researches haven't taken the influence of spatial character on the reinforced protecting wall into consideration. As a result, its theoretical researches lag behind its engineering application currently. Due to the fact that the circular geosynthetics-reinforced protection walls cannot ignore the influence of its space characteristics, the numerical analysis is carried out with Plaxis3D finite element software. The reinforced concrete protection wall and the reinforced concrete dome are simulated with the slab unit. The geotextiles are made of geosynthetics. In order to better simulate the actual working conditions, interface units are set up at the interfaces of soil, concrete and geotextiles. The tank body is simulated with the plate element, and the oil in the tank is simulated by the entity unit. Because the tank and internal fuel use entity modeling, the interaction between soil and superstructure can be considered, and the rationality and accuracy of numerical simulation can be improved. The deformation characteristics of circular geosynthetics-reinforced protection walls located around oil tank and mechanical characteristics of reinforced materials are investigated with developing a three-dimensional numerical model. The model uses the hardening soil model with small-stain stiffness(HSS models) as reinforced soil constitutive model. By changing geosynthetics-reinforced protection wall height, thickness, gradient of wall space, geogrid stiffness and reinforcement spacing, the effects of these factors on the wall deformation characteristics are explored. This paper conducts a detail study on the influence of the size of reinforced protecting wall on the serviceability limit state. The study is composed of deformation behavior, the foundation settlement, and the distribution of strains and tensile in the reinforcement. According to the above analysis, this paper puts forward some suggestions to optimize shape and size of reinforced protecting wall. The results show that the wall lateral displacement decreases with the decrease in the wall thickness, height and gradient of wall space. Also, too small wall thickness and too large reinforcement spacing can lead to the increase of the overturning trend of protection wall, and smaller stiffness of geogrid results in excessive lateral displacement of wall. Thus, these parameters should be taken into account in practice. The construction of reinforced wall can increase the settlement of foundation on the edge of storage tank. The loading state of the fuel in the storage tank does not affect the settlement of the reinforced protective wall foundation. However, the maximum settlement difference of the tank foundation decreases with the increase of fuel oil in the storage tank. Further, the potential failure surface of the geosynthetics-reinforced protection walls according to the position of maximum tensile stress of geogrid is a curve going through wall toe. The soil pressure behind the wall is greatly affected by the wall gradient. So the gradient should be considered when choosing a appropriate design method.
2019, 27(2): 408-414.
The upper bound method of limit analysis has received extensive attention in the stability assessment of submarine slopes. However, the method has not take into account the seismic load and the possible local failure mechanism of multi-layered submarine slopes. Based on the upper bound theorem, we derive the equilibrium equation of power dissipation and internal energy dissipation rate of multi-layered submarine slopes under horizontal pseudo-static earthquake load. Combined with the strength reduction technique and the optimization method, we solve the global and local factors of safety of submarine slopes under different horizontal seismic coefficients, and successfully search the local sliding surfaces of multi-layered submarine slope. The analyses of typical examples verify the effectiveness of the proposed method. On this basis, we discuss the global and local stability of submarine slopes with two typical combined soil layers under different earthquake conditions. By comparing with the numerical solution, we can accurately evaluate the stability of submarine slopes and effectively predict the position of critical slip surfaces. Finally, the improved method is applied to one case of submarine slope.
The upper bound method of limit analysis has received extensive attention in the stability assessment of submarine slopes. However, the method has not take into account the seismic load and the possible local failure mechanism of multi-layered submarine slopes. Based on the upper bound theorem, we derive the equilibrium equation of power dissipation and internal energy dissipation rate of multi-layered submarine slopes under horizontal pseudo-static earthquake load. Combined with the strength reduction technique and the optimization method, we solve the global and local factors of safety of submarine slopes under different horizontal seismic coefficients, and successfully search the local sliding surfaces of multi-layered submarine slope. The analyses of typical examples verify the effectiveness of the proposed method. On this basis, we discuss the global and local stability of submarine slopes with two typical combined soil layers under different earthquake conditions. By comparing with the numerical solution, we can accurately evaluate the stability of submarine slopes and effectively predict the position of critical slip surfaces. Finally, the improved method is applied to one case of submarine slope.
2019, 27(2): 415-425.
On October 11, 2018, a massive landslide occurred in Baige Village, Boluo Town, Jiangdacounty, Changdu city, Tibet. About 3, 165×104 cubic meter of a mountain mass rushed into the Jinsha River at a high speed, thus forming a barrier dam. At 9:00 on October 13, the body of the barrier dam was washed away by natural aerial drainage and the threat of forming a barrier lake was resolved. On November 3, only 23 days later, the high slip mass of 215×104 cubic meter at the back edge of the landslide occurred sliding failure again. The high-speed slip mass scraped the slope along the way and then rushed into the Jinsha River, forming a barrier dam again. This paper held the view that the landslide happened in Baige Village was thought to be mainly controlled by the next branch margin thrust fault f2, then finally generated buckling failure of the overall instability of the landslide with the influence of a long-term gravity unloading, rainfall and repeated infiltration of groundwater. The process of slip deformation and failure can be divided into five stages:trailing creep and settlement under the fault phase(Ⅰ), slope crack development, penetration stage(Ⅱ), overall launch of the "locking-fix end" cutting stage(Ⅲ), a stage with high moving speed(Ⅳ), collided, crushing and dam accumulation stage(Ⅴ). The failure mode of the first-stage deformation and failure mechanism can be summed up as creep-slip type-down fault type-shearing type-ski-jump type, and the failure mode is shown as the thrust type. In the later stage, the free surface condition of the slope is better, and the traction type can remain as the main failure mode. On this basis, combined with the residual strong deformation block(K1, K2, K3) and morphological characteristics and deformation signs of the surrounding influence zone, this paper predicted and analyzed the deformation and failure characteristics and development trend of the block, deeming that strong deformation areas can be destroyed by gradual disintegration. And these research findings can provide some reference for the monitoring, survey and governance of the future plan making and implementation.
On October 11, 2018, a massive landslide occurred in Baige Village, Boluo Town, Jiangdacounty, Changdu city, Tibet. About 3, 165×104 cubic meter of a mountain mass rushed into the Jinsha River at a high speed, thus forming a barrier dam. At 9:00 on October 13, the body of the barrier dam was washed away by natural aerial drainage and the threat of forming a barrier lake was resolved. On November 3, only 23 days later, the high slip mass of 215×104 cubic meter at the back edge of the landslide occurred sliding failure again. The high-speed slip mass scraped the slope along the way and then rushed into the Jinsha River, forming a barrier dam again. This paper held the view that the landslide happened in Baige Village was thought to be mainly controlled by the next branch margin thrust fault f2, then finally generated buckling failure of the overall instability of the landslide with the influence of a long-term gravity unloading, rainfall and repeated infiltration of groundwater. The process of slip deformation and failure can be divided into five stages:trailing creep and settlement under the fault phase(Ⅰ), slope crack development, penetration stage(Ⅱ), overall launch of the "locking-fix end" cutting stage(Ⅲ), a stage with high moving speed(Ⅳ), collided, crushing and dam accumulation stage(Ⅴ). The failure mode of the first-stage deformation and failure mechanism can be summed up as creep-slip type-down fault type-shearing type-ski-jump type, and the failure mode is shown as the thrust type. In the later stage, the free surface condition of the slope is better, and the traction type can remain as the main failure mode. On this basis, combined with the residual strong deformation block(K1, K2, K3) and morphological characteristics and deformation signs of the surrounding influence zone, this paper predicted and analyzed the deformation and failure characteristics and development trend of the block, deeming that strong deformation areas can be destroyed by gradual disintegration. And these research findings can provide some reference for the monitoring, survey and governance of the future plan making and implementation.
2019, 27(2): 426-436.
The fill embankment has good stability under natural conditions after compaction. However, during the early construction and later road operation, a large number of deformation and damage phenomena could occur due to multiple factors such as engineering load and dynamic load. Aiming at this problem, this paper takes a fill embankment slope as an example, and uses indoor physical simulation technology to study the deformation and failure mechanism of the slope induced by the engineering load. The results show that after the pile is continuously applied in the upper part, the internal stress conditions of the slope change, resulting in uneven settlement. The deformation and failure of the fill slope is mainly controlled by the concentration of the tensile stress at the top of the slope during the loading process and the concentration of the shear stress in the slope. The direction of the crack extends and gradually changes to the pressure in the lower part of the pile carrier. The shear-shaped belt is gradually penetrated and extended to the lower portion to cause overall deformation and destruction of the slope. The deformation mechanism has the following process:from internal stress redistribution to tension crack formation and expansion then to tensile cracks to form a sliding surface, finally overall sliding. The deformation is a typical creep-pull cracked landslide. This study can provide reference for similar projects.
The fill embankment has good stability under natural conditions after compaction. However, during the early construction and later road operation, a large number of deformation and damage phenomena could occur due to multiple factors such as engineering load and dynamic load. Aiming at this problem, this paper takes a fill embankment slope as an example, and uses indoor physical simulation technology to study the deformation and failure mechanism of the slope induced by the engineering load. The results show that after the pile is continuously applied in the upper part, the internal stress conditions of the slope change, resulting in uneven settlement. The deformation and failure of the fill slope is mainly controlled by the concentration of the tensile stress at the top of the slope during the loading process and the concentration of the shear stress in the slope. The direction of the crack extends and gradually changes to the pressure in the lower part of the pile carrier. The shear-shaped belt is gradually penetrated and extended to the lower portion to cause overall deformation and destruction of the slope. The deformation mechanism has the following process:from internal stress redistribution to tension crack formation and expansion then to tensile cracks to form a sliding surface, finally overall sliding. The deformation is a typical creep-pull cracked landslide. This study can provide reference for similar projects.
2019, 27(2): 437-450.
Wenchuan earthquake ruptured the Yinxiu-Beichuan fault in Longmenshan thrust zone. More than 100 large-scale landslides were triggered during earthquake along the 300 km fault rupture. Three landslides with volume larger than 1000×104 m3 were developed within 5 km at the right bank of Huangdongzi River in Mianyan City. There are Daguangbao landslide, Hongshigou landslide and Laoyingyan landslide. The Daguangbao landslide was the largest landslide during the earthquake. Geological investigations were conducted in landslide areas and the results showed that the study area was located not only between imbricated thrust belts but also on an anticline. The Hongshigou landslide was close to its axis, while the others were on each wing. Several joint sets and weak interlayers were developed in slopes. The three landslides were triggered with special geology. A bedding fault with breccia rock formed landslide potential boundary. The shear resistance reduced rapidly during earthquake which triggered the landslide initiation. The Hongshigou landslide was located on a cataclastic slope with many breccia shear bands. The landslide was triggered resulting from the shear bands failure which formed the basal shear surface rapidly during the earthquake. A weak interlayer of almost 100 m developed in Laoyingyan slope. The weak layer tensioned rapidly due to strong horizontal seismic shaking which triggered the slope collapse.
Wenchuan earthquake ruptured the Yinxiu-Beichuan fault in Longmenshan thrust zone. More than 100 large-scale landslides were triggered during earthquake along the 300 km fault rupture. Three landslides with volume larger than 1000×104 m3 were developed within 5 km at the right bank of Huangdongzi River in Mianyan City. There are Daguangbao landslide, Hongshigou landslide and Laoyingyan landslide. The Daguangbao landslide was the largest landslide during the earthquake. Geological investigations were conducted in landslide areas and the results showed that the study area was located not only between imbricated thrust belts but also on an anticline. The Hongshigou landslide was close to its axis, while the others were on each wing. Several joint sets and weak interlayers were developed in slopes. The three landslides were triggered with special geology. A bedding fault with breccia rock formed landslide potential boundary. The shear resistance reduced rapidly during earthquake which triggered the landslide initiation. The Hongshigou landslide was located on a cataclastic slope with many breccia shear bands. The landslide was triggered resulting from the shear bands failure which formed the basal shear surface rapidly during the earthquake. A weak interlayer of almost 100 m developed in Laoyingyan slope. The weak layer tensioned rapidly due to strong horizontal seismic shaking which triggered the slope collapse.
2019, 27(2): 451-458.
This paper starts from plastic limit analysis and builds a reliability calculation model of limiting condition for slope on the basis of the upper bound theorem. As the limit state function of the slope was too complex to be solved by the common reliability method, the response surface method is introduced as the"bridge" between the limit state function and the reliability calculation. Sampling points are optimized using quadratic orthogonal principle. The quadratic response surface function is established, which considers the correlation between parameters. An upper bound solution of reliability is achieved directly using the J-C method. Influences of variability of parameter(s) on reliability of slope were discussed.
This paper starts from plastic limit analysis and builds a reliability calculation model of limiting condition for slope on the basis of the upper bound theorem. As the limit state function of the slope was too complex to be solved by the common reliability method, the response surface method is introduced as the"bridge" between the limit state function and the reliability calculation. Sampling points are optimized using quadratic orthogonal principle. The quadratic response surface function is established, which considers the correlation between parameters. An upper bound solution of reliability is achieved directly using the J-C method. Influences of variability of parameter(s) on reliability of slope were discussed.
2019, 27(2): 459-465.
Slope displacement is a macroscopic manifestation of landslide evolution. Analyzing and predicting landslide displacement are of great significance for disaster prevention and mitigation. Since the landslide displacement is obvious nonlinear characteristics, single model is often difficult to delineate the complexity and nonlinearity of landslide displacement. To find a universal method for predicting landslide displacement, a new method combined with multiple data-driven modeling methods is proposed to predict the landslide displacement. The new method is based on time series analysis. The landslide displacement sequence is decomposed into trend term and periodic term. The trend term is treated using parallel grey neural network, and uses the artificial bee conony(ABC)to find the optimal extreme learning machine model(ELM)to predict the periodic term. This paper takes Baishuihe landslide and Bazimen landslide for examples. After statistically analyzing the displacement data, the gray neural network model predicts trending displacement, and the optimized learning machine model train and predict the periodic term. The result shows that the optimized extreme learning machine model is better than the extreme learning machine model and wavelet neural network. Therefore, the proposed combination of grey neural network and ABC-ELM can be used as a reference for practical engineering.
Slope displacement is a macroscopic manifestation of landslide evolution. Analyzing and predicting landslide displacement are of great significance for disaster prevention and mitigation. Since the landslide displacement is obvious nonlinear characteristics, single model is often difficult to delineate the complexity and nonlinearity of landslide displacement. To find a universal method for predicting landslide displacement, a new method combined with multiple data-driven modeling methods is proposed to predict the landslide displacement. The new method is based on time series analysis. The landslide displacement sequence is decomposed into trend term and periodic term. The trend term is treated using parallel grey neural network, and uses the artificial bee conony(ABC)to find the optimal extreme learning machine model(ELM)to predict the periodic term. This paper takes Baishuihe landslide and Bazimen landslide for examples. After statistically analyzing the displacement data, the gray neural network model predicts trending displacement, and the optimized learning machine model train and predict the periodic term. The result shows that the optimized extreme learning machine model is better than the extreme learning machine model and wavelet neural network. Therefore, the proposed combination of grey neural network and ABC-ELM can be used as a reference for practical engineering.
2019, 27(2): 466-476.
The deformation and failure of the loess slopes is more likely to occur during the rainfall, and have caused significant losses. In order to reduce the impact of loess landslides induced by rainfall, it is of practical significance to carry out the field experimental study on rainfall-induced landslides. The natural loess slope chosen in this article is located at Jingyang. Based on the rainfall simulation system designed by us, we designed and conducted three groups of field tests of loess slope with different rainfall intensities, aiming at investigating osmotic law and deformation and failure mode of the natural loess slopes under the different rain fall intensity. By analyzing the changes of readout of soil moisture sensors, earth pressure cells and tensiometers buried in the slope and experimental phenomenon, we obtained the deformation and failure law of field test of large loess slope under the artificial rainfall condition, and the law of water infiltration, and meanwhile we summarized deformation and failure mode of this kind of slopes. The experimental results show that, the rainfall infiltration on the loess slope present certain rules during the tests, which are:the infiltration depth and seepage rate of slope shoulder are the largest under rainfall condition, followed by slope toe, and that of middle slope location are the smallest. Moreover, the greater the rainfall intensity is, the lager the infiltration rate of loess is, the longer the infiltration time is, and the bigger the increasing range of the soil pressure and volume moisture at the same position and the decrease magnitude of the matrix suction are. Under the condition of rainfall, the deformation and failure mode of natural loess slope is:①formation and extension of erosion at the shoulder of slope; ②emergence and development of fractures in the slope surface; ③occurrence and growth of fissures at the shoulder of slope; ④local caving of the slope. If it continues to rain, some cracks at the shoulder of slope will penetrate each other gradually, the sliding surface can be subsequently formed, and landslide can occur eventually.
The deformation and failure of the loess slopes is more likely to occur during the rainfall, and have caused significant losses. In order to reduce the impact of loess landslides induced by rainfall, it is of practical significance to carry out the field experimental study on rainfall-induced landslides. The natural loess slope chosen in this article is located at Jingyang. Based on the rainfall simulation system designed by us, we designed and conducted three groups of field tests of loess slope with different rainfall intensities, aiming at investigating osmotic law and deformation and failure mode of the natural loess slopes under the different rain fall intensity. By analyzing the changes of readout of soil moisture sensors, earth pressure cells and tensiometers buried in the slope and experimental phenomenon, we obtained the deformation and failure law of field test of large loess slope under the artificial rainfall condition, and the law of water infiltration, and meanwhile we summarized deformation and failure mode of this kind of slopes. The experimental results show that, the rainfall infiltration on the loess slope present certain rules during the tests, which are:the infiltration depth and seepage rate of slope shoulder are the largest under rainfall condition, followed by slope toe, and that of middle slope location are the smallest. Moreover, the greater the rainfall intensity is, the lager the infiltration rate of loess is, the longer the infiltration time is, and the bigger the increasing range of the soil pressure and volume moisture at the same position and the decrease magnitude of the matrix suction are. Under the condition of rainfall, the deformation and failure mode of natural loess slope is:①formation and extension of erosion at the shoulder of slope; ②emergence and development of fractures in the slope surface; ③occurrence and growth of fissures at the shoulder of slope; ④local caving of the slope. If it continues to rain, some cracks at the shoulder of slope will penetrate each other gradually, the sliding surface can be subsequently formed, and landslide can occur eventually.
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