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Editor Work2020 Vol. 28, No. 4
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2020, 28(4): 677-684.
Abstract
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The excavation of underground rock masses in high-stress region often produces the tensile-compressive stress state in surrounding rock, which leads to the tensile failure hazard of rock masses. The traditional parallel bond model in PFC, however, cannot simulate the high ratio between uniaxial compressive strength and tensile strength of brittle rocks. To solve this problem, a new parallel bond failure criterion considering two tensile strength parameters is established and a series of numerical simulation tests under tensile-compressive stress condition are conducted in this paper. The simulated tensile-compressive strengths are close to that tested by physical experiments. A high ratio between uniaxial compressive strength and tensile strength is achieved. The failure mechanism is analyzed in detail. With the increase of confining pressure, the inclination angle of fracture surface increases gradually and the fracture transforms from tensile fracture to tensile-shear fracture. Echelon cracks are found at the fracture region under tensile-compressive stress state. The mechanical properties of fracture surfaces are revealed according to the mesoscopic particle displacement fields. The tension property decreases and shear property increases gradually with the increase of confining pressure(i.e. with the increase of the inclination angle of fracture surface). The evolution process of rock damage under tensile-compressive stress state can be divided into the following four stages. They are elastic deformation stage, stable rupture development stage, unstable rupture development stage and overall rupture stage(post-peak stress drop and residue stage). When the confining pressure is larger, the elastic deformation stage and stable rupture development stage are more short, the unstable rupture development stage is more long and intensive, the fracture surface friction is stronger, and the stress fluctuation is greater at post-peak residue stage.
The excavation of underground rock masses in high-stress region often produces the tensile-compressive stress state in surrounding rock, which leads to the tensile failure hazard of rock masses. The traditional parallel bond model in PFC, however, cannot simulate the high ratio between uniaxial compressive strength and tensile strength of brittle rocks. To solve this problem, a new parallel bond failure criterion considering two tensile strength parameters is established and a series of numerical simulation tests under tensile-compressive stress condition are conducted in this paper. The simulated tensile-compressive strengths are close to that tested by physical experiments. A high ratio between uniaxial compressive strength and tensile strength is achieved. The failure mechanism is analyzed in detail. With the increase of confining pressure, the inclination angle of fracture surface increases gradually and the fracture transforms from tensile fracture to tensile-shear fracture. Echelon cracks are found at the fracture region under tensile-compressive stress state. The mechanical properties of fracture surfaces are revealed according to the mesoscopic particle displacement fields. The tension property decreases and shear property increases gradually with the increase of confining pressure(i.e. with the increase of the inclination angle of fracture surface). The evolution process of rock damage under tensile-compressive stress state can be divided into the following four stages. They are elastic deformation stage, stable rupture development stage, unstable rupture development stage and overall rupture stage(post-peak stress drop and residue stage). When the confining pressure is larger, the elastic deformation stage and stable rupture development stage are more short, the unstable rupture development stage is more long and intensive, the fracture surface friction is stronger, and the stress fluctuation is greater at post-peak residue stage.
2020, 28(4): 685-696.
In order to investigate the effect of ultra-fine cement on the early compressive strength development of cement stabilized soil, the composite cement binder is proposed by adding different contents of ultrafine cement into ordinary cement binder. Factors influencing the early strength of the composite cement stabilized soft soil were investigated. They include the content of the ultra-fine cement, the water content of soft soil and the curing stress. The curing equipment was designed and fabricated to apply the curing stress on the composite cement stabilized soil sample. The mechanical and micro-structural properties of the composite cement stabilized soft soil were obtained and analyzed via the unconfined compressive strength(UCS)test, the X-ray diffractometer(XRD)test, electron microscopy scanner(SEM)test, and proton nuclear magnetic resonance(NMR)test. The experimental results showed that at the same curing stress, the early compressive strength and the stiffness of the composite cement stabilized soft soil increased with the higher replacement contents of ultra-fine cement, regardless of the initial water content in the soft soil. The active particles with the smaller size in the composite cement binder could hydrate with free water in the stabilized soil, and then form the gelled products which would bind the soil particles and fill the pores of the soft soil. While, the inert particles with the coarser size in the composite cement binder were only served to fill the pores of the soil. With the higher initial water content of soft soil, the more amount of meso-scale pores were observed in the stabilized soil, which might induce the lower early compressive strength of the stabilized soil. With the increase of curing stress, the compressive strength and the stiffness of the composite cement stabilized soft soil enhanced in the 7-days curing period. The compactness of the stabilized soil became denser due to the higher curing stress. The function of the curing stress was found to develop the pre-stress state in the gel skeleton of the stabilized soil, and hence increase the compressive strength of the stabilized soil. Based on the test results, the formula was established to predict the early strength of the composite cement stabilized soil. At the same time, the hydration model of the soft soil stabilized by the composite cement binder was proposed.
In order to investigate the effect of ultra-fine cement on the early compressive strength development of cement stabilized soil, the composite cement binder is proposed by adding different contents of ultrafine cement into ordinary cement binder. Factors influencing the early strength of the composite cement stabilized soft soil were investigated. They include the content of the ultra-fine cement, the water content of soft soil and the curing stress. The curing equipment was designed and fabricated to apply the curing stress on the composite cement stabilized soil sample. The mechanical and micro-structural properties of the composite cement stabilized soft soil were obtained and analyzed via the unconfined compressive strength(UCS)test, the X-ray diffractometer(XRD)test, electron microscopy scanner(SEM)test, and proton nuclear magnetic resonance(NMR)test. The experimental results showed that at the same curing stress, the early compressive strength and the stiffness of the composite cement stabilized soft soil increased with the higher replacement contents of ultra-fine cement, regardless of the initial water content in the soft soil. The active particles with the smaller size in the composite cement binder could hydrate with free water in the stabilized soil, and then form the gelled products which would bind the soil particles and fill the pores of the soft soil. While, the inert particles with the coarser size in the composite cement binder were only served to fill the pores of the soil. With the higher initial water content of soft soil, the more amount of meso-scale pores were observed in the stabilized soil, which might induce the lower early compressive strength of the stabilized soil. With the increase of curing stress, the compressive strength and the stiffness of the composite cement stabilized soft soil enhanced in the 7-days curing period. The compactness of the stabilized soil became denser due to the higher curing stress. The function of the curing stress was found to develop the pre-stress state in the gel skeleton of the stabilized soil, and hence increase the compressive strength of the stabilized soil. Based on the test results, the formula was established to predict the early strength of the composite cement stabilized soil. At the same time, the hydration model of the soft soil stabilized by the composite cement binder was proposed.
2020, 28(4): 697-706.
There are few studies about using non-destructive testing technology to evaluate the reinforcement effect of microbial cementation presently. This paper is based on the determination of best microbial grouting period and grouting rate, and uses a self-design multi-layer porous microbial grouting pipeline system to carry out indoor model test of microbial grouting in shale residual soil. Effectiveness of reinforcement is evaluated with ultrasonic testing technology. The results show that: (1)The ultrasonic velocity of residual soil fillings increases obviously after microbial grouting with multi-layer porous grouting pipeline system, which proves that multi-layer porous grouting pipeline system performs well during the grouting. (2)The wave velocities and wave velocities increments of the cements are symmetrical. The reinforcement effect of the soil in the middle of the fillings is remarkable, which provides preliminary law about the process of microbial grouting with multi-layer porous grouting pipeline system in shale residual. (3)The strategy that "the side wave velocity value determines the total value while the front wave velocity value determines the proportion of each measuring point" is taken to calculate the velocity of each measuring point, which further reveals the process of reinforcement insides the fillings through cloud chart of wave velocity value of fillings. The research conclusions can provide reference and basis for the effect analysis of microbial reinforcement.
There are few studies about using non-destructive testing technology to evaluate the reinforcement effect of microbial cementation presently. This paper is based on the determination of best microbial grouting period and grouting rate, and uses a self-design multi-layer porous microbial grouting pipeline system to carry out indoor model test of microbial grouting in shale residual soil. Effectiveness of reinforcement is evaluated with ultrasonic testing technology. The results show that: (1)The ultrasonic velocity of residual soil fillings increases obviously after microbial grouting with multi-layer porous grouting pipeline system, which proves that multi-layer porous grouting pipeline system performs well during the grouting. (2)The wave velocities and wave velocities increments of the cements are symmetrical. The reinforcement effect of the soil in the middle of the fillings is remarkable, which provides preliminary law about the process of microbial grouting with multi-layer porous grouting pipeline system in shale residual. (3)The strategy that "the side wave velocity value determines the total value while the front wave velocity value determines the proportion of each measuring point" is taken to calculate the velocity of each measuring point, which further reveals the process of reinforcement insides the fillings through cloud chart of wave velocity value of fillings. The research conclusions can provide reference and basis for the effect analysis of microbial reinforcement.
2020, 28(4): 707-715.
In this paper, the testing system of pressure plate instrument is modified using the principle of shaft translation technology. On the basis of the original testing instrument, we add an automatic data acquisition system, a water storage flushing system and a bubble volume measurement system. Data acquisition system consists of data acquisition software on computer, precision balance, water container and several pipelines. Its function is to automatically record the change data of overflow water quantity of soil sample with time. The function of the data automatic acquisition system is to record the change data of soil sample overflow water quantity with time automatically. The water storage flushing system consists of a water storage container, a switch and some pipelines. Its function is to flush and saturate the whole testing system. The bubble volume measurement system consists of switches, pipelines and glass tubes with scales. Its function is to measure the volume of bubbles overflowing from the bottom of the clay. According to the existing saturation time evolution equation in non-equilibrium state, we established a nonlinear fitting model on Origin software. The dynamic multi-step flow method is further used to test silt. We apply the next suction before this suction reaches without equilibrium. The measured data of overflow water volume changing with time is measured by the data automatic acquisition system. Then we turn on the bubble measuring system to measure the volume of bubbles at the bottom of the clay plate. After the bubble volume is measured, we convert the bubble volume into the weight of water. We use the weight of water got by bubble measuring device correct the data of water weight with time change, and then a more accurate change value of overflow quality with time can be obtained. According to the actual measured water weight change data with time, we obtain the saturation change curve with time. After non-linear fitting of saturation change curve data with the model previously established in Origin software, we can obtain the unknown parameter water holding rate C and characteristic time τ. Through the above steps, the soil-water characteristic curve under the equilibrium state is measured. We compare the soil-water characteristic curve measured by this method with the soil-water characteristic curve measured when the instrument is not modified. We find that the two curves can overlap to a large extent. It takes about 5 days to determine a SWCC curve under the dynamic multi-step flow method. However, the time for measuring a soil-water characteristic curve is generally three months to six months according to the different soil samples when the instrument is not modified. Compared with the two methods, the test method in this paper can save time to a great extent. Moreover, the test method is simple to operate, saving a lot of manpower and material resources, and is efficient and convenient.
In this paper, the testing system of pressure plate instrument is modified using the principle of shaft translation technology. On the basis of the original testing instrument, we add an automatic data acquisition system, a water storage flushing system and a bubble volume measurement system. Data acquisition system consists of data acquisition software on computer, precision balance, water container and several pipelines. Its function is to automatically record the change data of overflow water quantity of soil sample with time. The function of the data automatic acquisition system is to record the change data of soil sample overflow water quantity with time automatically. The water storage flushing system consists of a water storage container, a switch and some pipelines. Its function is to flush and saturate the whole testing system. The bubble volume measurement system consists of switches, pipelines and glass tubes with scales. Its function is to measure the volume of bubbles overflowing from the bottom of the clay. According to the existing saturation time evolution equation in non-equilibrium state, we established a nonlinear fitting model on Origin software. The dynamic multi-step flow method is further used to test silt. We apply the next suction before this suction reaches without equilibrium. The measured data of overflow water volume changing with time is measured by the data automatic acquisition system. Then we turn on the bubble measuring system to measure the volume of bubbles at the bottom of the clay plate. After the bubble volume is measured, we convert the bubble volume into the weight of water. We use the weight of water got by bubble measuring device correct the data of water weight with time change, and then a more accurate change value of overflow quality with time can be obtained. According to the actual measured water weight change data with time, we obtain the saturation change curve with time. After non-linear fitting of saturation change curve data with the model previously established in Origin software, we can obtain the unknown parameter water holding rate C and characteristic time τ. Through the above steps, the soil-water characteristic curve under the equilibrium state is measured. We compare the soil-water characteristic curve measured by this method with the soil-water characteristic curve measured when the instrument is not modified. We find that the two curves can overlap to a large extent. It takes about 5 days to determine a SWCC curve under the dynamic multi-step flow method. However, the time for measuring a soil-water characteristic curve is generally three months to six months according to the different soil samples when the instrument is not modified. Compared with the two methods, the test method in this paper can save time to a great extent. Moreover, the test method is simple to operate, saving a lot of manpower and material resources, and is efficient and convenient.
2020, 28(4): 716-724.
The shearing failure of rock and soil masses is reckoned as a common trigger for geohazards, and it is therefore a critical issue to monitor the shear displacements of rock and soil for disaster prevention and mitigation in geotechnical engineering. Fiber optics sensing technology can be potentially used for shear displacements monitoring owing to its high sensitivity and distributed strain sensing(DSS)features. In this paper, we carried out an experimental study to investigate the feasibility of soil shear displacements based on the fully distributed Optical Frequency Domain Reflection(OFDR) and Particle Image Velocimetry(PIV)technologies. Taking into account the deformation compatibility of directly embedded optical fiber cables and the surrounding soil, the relationship between the distributed strain measurements and real soil shear displacements is explored, and we proposed the strain integral method to realize the conversion. The test results show that while the optical fiber cables are well coupled with soil, there is a linear relationship between the calculated elongation and soil shear displacements, indicating that it is feasible to use the high-accuracy and high-spatial resolution OFDR technology to monitor soil shear displacements. Installing tube-type anchorages on optical fiber cables or increasing the confining pressure can effectively enhance the soil-cable coupling capability, and help to obtain more reliable shear displacement measurements.
The shearing failure of rock and soil masses is reckoned as a common trigger for geohazards, and it is therefore a critical issue to monitor the shear displacements of rock and soil for disaster prevention and mitigation in geotechnical engineering. Fiber optics sensing technology can be potentially used for shear displacements monitoring owing to its high sensitivity and distributed strain sensing(DSS)features. In this paper, we carried out an experimental study to investigate the feasibility of soil shear displacements based on the fully distributed Optical Frequency Domain Reflection(OFDR) and Particle Image Velocimetry(PIV)technologies. Taking into account the deformation compatibility of directly embedded optical fiber cables and the surrounding soil, the relationship between the distributed strain measurements and real soil shear displacements is explored, and we proposed the strain integral method to realize the conversion. The test results show that while the optical fiber cables are well coupled with soil, there is a linear relationship between the calculated elongation and soil shear displacements, indicating that it is feasible to use the high-accuracy and high-spatial resolution OFDR technology to monitor soil shear displacements. Installing tube-type anchorages on optical fiber cables or increasing the confining pressure can effectively enhance the soil-cable coupling capability, and help to obtain more reliable shear displacement measurements.
2020, 28(4): 725-733.
In order to grasp the compression characteristics and microscopic mechanism of calcareous sand in the South China Sea, we did compression tests on three different groups of calcareous sand(S1:1.43~2mm, S2:0.5~1mm, S3:0.5~2mm). We used a self-made sand microstructure extraction device to obtain the microstructure of calcareous during compression. The results indicate that:(1)The size, shape and grade of the calcareous sands significantly affect the fracture of the particles. When the pressure is lower than 800kPa, the S1 group with large particle size is mainly broken by the angular break of the sand particle; but the S2 group with smaller particle size does not have obvious cracks. That's means relatively regular particle morphology leads S2 group to compress mainly by rolling and redistribution of the particles. For the well-graded S3 group, particles have no obvious cracks except for some low-width broken limb-shaped ones. (2)When the pressure is larger than 800kPa, S1 group of calcareous sand turns to the broken form dominated by the overall destruction of the particles; S2, S3 with the increase of the compactness, the damage of the two groups of calcareous sand sample is dominated by the overall fragmentation of the particles. Based on the microstructure changes of these different groups of calcareous sands during the compression, we summarized four contact modes which control the crushing of calcareous sands: point-line contact, line-surface contact, surface-surface contact and composite contact. These contact models can be used to determine the form of particle breakage under different conditions. Finally, we discussed the effect of crushing process on the geometry parameters of calcareous sands.
In order to grasp the compression characteristics and microscopic mechanism of calcareous sand in the South China Sea, we did compression tests on three different groups of calcareous sand(S1:1.43~2mm, S2:0.5~1mm, S3:0.5~2mm). We used a self-made sand microstructure extraction device to obtain the microstructure of calcareous during compression. The results indicate that:(1)The size, shape and grade of the calcareous sands significantly affect the fracture of the particles. When the pressure is lower than 800kPa, the S1 group with large particle size is mainly broken by the angular break of the sand particle; but the S2 group with smaller particle size does not have obvious cracks. That's means relatively regular particle morphology leads S2 group to compress mainly by rolling and redistribution of the particles. For the well-graded S3 group, particles have no obvious cracks except for some low-width broken limb-shaped ones. (2)When the pressure is larger than 800kPa, S1 group of calcareous sand turns to the broken form dominated by the overall destruction of the particles; S2, S3 with the increase of the compactness, the damage of the two groups of calcareous sand sample is dominated by the overall fragmentation of the particles. Based on the microstructure changes of these different groups of calcareous sands during the compression, we summarized four contact modes which control the crushing of calcareous sands: point-line contact, line-surface contact, surface-surface contact and composite contact. These contact models can be used to determine the form of particle breakage under different conditions. Finally, we discussed the effect of crushing process on the geometry parameters of calcareous sands.
2020, 28(4): 734-739.
Carbonate sand usually refers to the sediment with calcium carbonate content more than 50%. It has special physical and mechanical properties compared with the terrestrial sand. The dynamic cone penetration test is widely used to evaluate the engineering properties of soils. At present, the study of relationship between dynamic cone penetration indexes and soil physical properties are focused on clay and siliceous sand while weather the existing evaluation method is suitable for carbonate sand is controversial. To address the problem, in this study, a serious of field light dynamic penetration test are conducted to investigate the relationships of the dynamic cone penetration index with respect to the physical indexes including mean particle size, various densities, and relative density of the carbonate sand. Based on results of in situ tests, the relationships between the dynamic cone penetration index and physical indexes are established for the carbonate sand. The residual analysis shows that these formulas achieve certain accuracy. It can be found that to establish the relationship between penetration index and various densities as well as relative density need to consider the influence of average particle size, which is related to the easy crushing of carbonate sand. These results can be useful for engineers to evaluate engineering properties of carbonate sand in practice.
Carbonate sand usually refers to the sediment with calcium carbonate content more than 50%. It has special physical and mechanical properties compared with the terrestrial sand. The dynamic cone penetration test is widely used to evaluate the engineering properties of soils. At present, the study of relationship between dynamic cone penetration indexes and soil physical properties are focused on clay and siliceous sand while weather the existing evaluation method is suitable for carbonate sand is controversial. To address the problem, in this study, a serious of field light dynamic penetration test are conducted to investigate the relationships of the dynamic cone penetration index with respect to the physical indexes including mean particle size, various densities, and relative density of the carbonate sand. Based on results of in situ tests, the relationships between the dynamic cone penetration index and physical indexes are established for the carbonate sand. The residual analysis shows that these formulas achieve certain accuracy. It can be found that to establish the relationship between penetration index and various densities as well as relative density need to consider the influence of average particle size, which is related to the easy crushing of carbonate sand. These results can be useful for engineers to evaluate engineering properties of carbonate sand in practice.
2020, 28(4): 740-747.
The basal friction characteristics of granular materials are quite different from those of common solid. We carried out a series of sliding friction tests to investigate the effect of grain size distribution(i.e. particle size and mass percentage) on the basal dynamic friction coefficient of granular materials. Based on the analysis of video images and curve fitting method, the fitting function of displacement and time was established, which was used to deduce the dynamic friction coefficient by the analysis of acceleration in the sliding process. Experimental results indicate the following characteristics. The basal dynamic friction coefficient of granular materials decreases linearly with time. For monodisperse granular materials, the basal dynamic friction coefficient of fine particles is higher than that of coarse particles. For bidisperse granular materials, the basal dynamic friction coefficient of granular materials decreases sharply until reaching a minimum value(content of fine particles, CFP≤40%), then increases sharply(CFP 40% ~60%), and increases slowly with further increasing content of fine particles(CFP≥60%).
The basal friction characteristics of granular materials are quite different from those of common solid. We carried out a series of sliding friction tests to investigate the effect of grain size distribution(i.e. particle size and mass percentage) on the basal dynamic friction coefficient of granular materials. Based on the analysis of video images and curve fitting method, the fitting function of displacement and time was established, which was used to deduce the dynamic friction coefficient by the analysis of acceleration in the sliding process. Experimental results indicate the following characteristics. The basal dynamic friction coefficient of granular materials decreases linearly with time. For monodisperse granular materials, the basal dynamic friction coefficient of fine particles is higher than that of coarse particles. For bidisperse granular materials, the basal dynamic friction coefficient of granular materials decreases sharply until reaching a minimum value(content of fine particles, CFP≤40%), then increases sharply(CFP 40% ~60%), and increases slowly with further increasing content of fine particles(CFP≥60%).
2020, 28(4): 748-761.
Due to weak purpose and insufficient predictability of slope geological hazard investigation and evaluation, The Slope-geohazard Prevention System of Slope-unit Administrant was introduced to achieve the goal of systematic prevention and control of slope geological hazard risks. Under the premise of fully understanding the disaster-causing conditions, disaster-pregnancy process, and risks of slope hazards, this system advocates that the investigation and prevention of slope geological hazard should be based on different slope units to formulate a warning system, management rules and control measures. In this study, based on the detailed investigation of geological disasters in the key areas of Mayang County, Hunan Province, the basic process, investigation and evaluation methods and index system for the establishment of slope chief system were systematically expounded. Furthermore, we did comprehensive analyses and put forward some recommendations for the following contents: the selection and determination method for key areas; the determination method for slope units and the content for investigation and evaluation; the selection method, standards and responsibility of slope administrant; control process and core content for slope unit, warning model, legal system. The Slope-geohazard Prevention System of Slope-unit Administrant was proposed for the first time. Its establishment and continuous improvement will play a positive role in promoting the improvement of the regional geological hazard prevention and control in China.
Due to weak purpose and insufficient predictability of slope geological hazard investigation and evaluation, The Slope-geohazard Prevention System of Slope-unit Administrant was introduced to achieve the goal of systematic prevention and control of slope geological hazard risks. Under the premise of fully understanding the disaster-causing conditions, disaster-pregnancy process, and risks of slope hazards, this system advocates that the investigation and prevention of slope geological hazard should be based on different slope units to formulate a warning system, management rules and control measures. In this study, based on the detailed investigation of geological disasters in the key areas of Mayang County, Hunan Province, the basic process, investigation and evaluation methods and index system for the establishment of slope chief system were systematically expounded. Furthermore, we did comprehensive analyses and put forward some recommendations for the following contents: the selection and determination method for key areas; the determination method for slope units and the content for investigation and evaluation; the selection method, standards and responsibility of slope administrant; control process and core content for slope unit, warning model, legal system. The Slope-geohazard Prevention System of Slope-unit Administrant was proposed for the first time. Its establishment and continuous improvement will play a positive role in promoting the improvement of the regional geological hazard prevention and control in China.
2020, 28(4): 762-771.
On March 30, 2020, a huge forest fire broke out in Jingjiu Township, Xichang City, Liangshan Yi Autonomous Prefecture, Sichuan Province. The fire lasted 3 days and the fire area exceeded 30 km2. After the mountain fire, an ash layer with a thickness of 1~5 cm was deposited on the slope. At the same time, the structure of the burned area was disturbed. Under heavy rainfall conditions, it is very easy to induce post-fire debris flow disasters, which poses a serious threat to nearby schools, residents' concentrated residential areas, especially Lushan-Qionghai Scenic Area and other important infrastructure and people's lives and property. Through remote sensing interpretation, field investigations and surveys, the characteristics of ash layers and structural disturbances in different fire intensity and corresponding burned areas were identified. The results suggest that the severe, moderate and low burned areas account for 46.8%, 37.9% and 15.3%, respectively, and the average thickness of the ash and soil structure disturbance layer in the burned area is proportional to the fire intensity, of which the low, moderate and severe burned areas are 1.20 cm, 3.23 cm and 5.04 cm respectively. Five influencing factors were proposed based on the proportion of moderate and severe fire intensity area, the thickness of ash and structural disturbance layer on the burned ground, the average slope of the sand-producing area, the average vertical ratio drop of the main ditch, and the channel drainage area, the expert experience method was used to assess the susceptibility of a total of 63 potential debris flow gullies in the fire zone. The results showed that of the total channels in the fire zone, 29 were of highly susceptible, accounting for 46.0% of the total. 23 were of medium susceptibility, accounting for 36.5% of the total. 8 were of low susceptibility, accounting for 12.7% of the total. Three were not easy to occur, accounting for 4.8% of the total. Considering that catchment area of more than 50% of the burned area is less than 0.2 km2, the average longitudinal slopes of these gullies are large, and the loose source materials such as ash and silt on the slope are thick, the number of medium and high-prone debris flow gullies is as high as 82.5%. In the event of concentrated rainfall, the probability of post-fire debris flow occurrence is extremely high.
On March 30, 2020, a huge forest fire broke out in Jingjiu Township, Xichang City, Liangshan Yi Autonomous Prefecture, Sichuan Province. The fire lasted 3 days and the fire area exceeded 30 km2. After the mountain fire, an ash layer with a thickness of 1~5 cm was deposited on the slope. At the same time, the structure of the burned area was disturbed. Under heavy rainfall conditions, it is very easy to induce post-fire debris flow disasters, which poses a serious threat to nearby schools, residents' concentrated residential areas, especially Lushan-Qionghai Scenic Area and other important infrastructure and people's lives and property. Through remote sensing interpretation, field investigations and surveys, the characteristics of ash layers and structural disturbances in different fire intensity and corresponding burned areas were identified. The results suggest that the severe, moderate and low burned areas account for 46.8%, 37.9% and 15.3%, respectively, and the average thickness of the ash and soil structure disturbance layer in the burned area is proportional to the fire intensity, of which the low, moderate and severe burned areas are 1.20 cm, 3.23 cm and 5.04 cm respectively. Five influencing factors were proposed based on the proportion of moderate and severe fire intensity area, the thickness of ash and structural disturbance layer on the burned ground, the average slope of the sand-producing area, the average vertical ratio drop of the main ditch, and the channel drainage area, the expert experience method was used to assess the susceptibility of a total of 63 potential debris flow gullies in the fire zone. The results showed that of the total channels in the fire zone, 29 were of highly susceptible, accounting for 46.0% of the total. 23 were of medium susceptibility, accounting for 36.5% of the total. 8 were of low susceptibility, accounting for 12.7% of the total. Three were not easy to occur, accounting for 4.8% of the total. Considering that catchment area of more than 50% of the burned area is less than 0.2 km2, the average longitudinal slopes of these gullies are large, and the loose source materials such as ash and silt on the slope are thick, the number of medium and high-prone debris flow gullies is as high as 82.5%. In the event of concentrated rainfall, the probability of post-fire debris flow occurrence is extremely high.
2020, 28(4): 772-783.
The Rizha potential giant rock landslide is located on the left bank of Jiangqu River, Sichuan Province, with many alpine canyons and large vertical river slopes. The eastern boundary fault of Jinsha River fault zone, which has been active since late Pleistocene, passes through the foot of the slope. Based on remote sensing interpretation, field investigation and geophysical test analysis, the development characteristics and formation mechanism of the Rizha giant rock landslide are analyzed in this paper. It is considered that the Rizha landslide is a large deep giant potential rock landslide, which was formed under the influence of fault activity, karst water, long-term unloading and gravity. The Rizha landslide could be divided into three sub-zones spatially, i.e., the rear tensile deformation zone(Ⅰ), middle compression deformation zone(Ⅱ) and slope foot stress concentration zone(Ⅲ). The Rizha potential giant landslide is currently dominated by creeping deformation. There are four large tensile cracks developed well at its rear edge, with the maximum crack width up to 20~35 m and the depth up to 190 m by the geophysical data interpretation. The study result revealed that there were two main instability types of the Rizha giant potential landslide, the first one is the high shear instability type, with potential instability volumes of 7.9~10.2×107 m3(H1), 2.3~2.9×108 m3(H2), 4.8~7.2×108 m3(H3) and 6~10×108 m3(H4), and the other is deep-buried creeping deformation type, with deep-buried creep sliding zone and locking section in the deepen part of the sliding body. The maximum deformation thickness of the creeping body is 300 m(H5). The locking section of the Rizha landslide is likely to fail under the long-term unloading and gravity, earthquake activity, karst water activity, and the geo-hazard chain of the high-level rock falling-sliding-blocking the river is likely to occur. The deep creeping sliding might have great influence on the stability of major projects built in the slope, such as deep-buried tunnels. This kind of potential giant rock landslides are typically developed on the Tibetan Plateau. It is recommended to make further investigation of the Rizha potential giant landslide, to find out the spatial structural characteristics and stability, as well as monitoring and early warning if necessary.
The Rizha potential giant rock landslide is located on the left bank of Jiangqu River, Sichuan Province, with many alpine canyons and large vertical river slopes. The eastern boundary fault of Jinsha River fault zone, which has been active since late Pleistocene, passes through the foot of the slope. Based on remote sensing interpretation, field investigation and geophysical test analysis, the development characteristics and formation mechanism of the Rizha giant rock landslide are analyzed in this paper. It is considered that the Rizha landslide is a large deep giant potential rock landslide, which was formed under the influence of fault activity, karst water, long-term unloading and gravity. The Rizha landslide could be divided into three sub-zones spatially, i.e., the rear tensile deformation zone(Ⅰ), middle compression deformation zone(Ⅱ) and slope foot stress concentration zone(Ⅲ). The Rizha potential giant landslide is currently dominated by creeping deformation. There are four large tensile cracks developed well at its rear edge, with the maximum crack width up to 20~35 m and the depth up to 190 m by the geophysical data interpretation. The study result revealed that there were two main instability types of the Rizha giant potential landslide, the first one is the high shear instability type, with potential instability volumes of 7.9~10.2×107 m3(H1), 2.3~2.9×108 m3(H2), 4.8~7.2×108 m3(H3) and 6~10×108 m3(H4), and the other is deep-buried creeping deformation type, with deep-buried creep sliding zone and locking section in the deepen part of the sliding body. The maximum deformation thickness of the creeping body is 300 m(H5). The locking section of the Rizha landslide is likely to fail under the long-term unloading and gravity, earthquake activity, karst water activity, and the geo-hazard chain of the high-level rock falling-sliding-blocking the river is likely to occur. The deep creeping sliding might have great influence on the stability of major projects built in the slope, such as deep-buried tunnels. This kind of potential giant rock landslides are typically developed on the Tibetan Plateau. It is recommended to make further investigation of the Rizha potential giant landslide, to find out the spatial structural characteristics and stability, as well as monitoring and early warning if necessary.
2020, 28(4): 784-792.
Three important traffic projects were built along Lhasa-Yangbajing section of Tibet. They include Qinghai-Tibet Railway, 109 national highway(G109) and the 6th national highway(G6), as well as a large number of transmission lines. However, the mountains in this area are high and steep, thus rockfalls frequently occur. The rockfall poses a great threat to the safe operation of transportation and transmission. At present, the analysis and prediction of rockfall hazards are mostly based on the two-dimensional method of topographic profiles, which limits the movement direction of rockfall and makes it difficult to effectively assess their impact range. To solve these problems, the authors take the rockfall along Shexing village section of Qinghai-Tibet Railway as an example. They analyze the distribution of fallen rocks, the occurrences of rock mass structural planes, the characteristics of dangerous rock areas, and the kinematic simulation of rockfall. They use the methods of field investigation, high-precision three-dimensional surface topography modeling based on UAV aerial photography, and three-dimensional numerical simulation of rockfall. Through the simulation, the influence range, the arrival probability, the dominant motion paths, the height and kinetic energy of the fallen rocks are obtained. The results show that the rockfall mainly threatens the transmission lines and 109 national highway, and have rarely effects on Qinghai-Tibet Railway and the 6th national highway. The relevant simulation results are also instructive for the determination of the extent, height and mechanical strength of the protection facilities for rockfall.
Three important traffic projects were built along Lhasa-Yangbajing section of Tibet. They include Qinghai-Tibet Railway, 109 national highway(G109) and the 6th national highway(G6), as well as a large number of transmission lines. However, the mountains in this area are high and steep, thus rockfalls frequently occur. The rockfall poses a great threat to the safe operation of transportation and transmission. At present, the analysis and prediction of rockfall hazards are mostly based on the two-dimensional method of topographic profiles, which limits the movement direction of rockfall and makes it difficult to effectively assess their impact range. To solve these problems, the authors take the rockfall along Shexing village section of Qinghai-Tibet Railway as an example. They analyze the distribution of fallen rocks, the occurrences of rock mass structural planes, the characteristics of dangerous rock areas, and the kinematic simulation of rockfall. They use the methods of field investigation, high-precision three-dimensional surface topography modeling based on UAV aerial photography, and three-dimensional numerical simulation of rockfall. Through the simulation, the influence range, the arrival probability, the dominant motion paths, the height and kinetic energy of the fallen rocks are obtained. The results show that the rockfall mainly threatens the transmission lines and 109 national highway, and have rarely effects on Qinghai-Tibet Railway and the 6th national highway. The relevant simulation results are also instructive for the determination of the extent, height and mechanical strength of the protection facilities for rockfall.
2020, 28(4): 793-802.
The weakness of 3DEC software in the pre-processing of building the landslide model limits its application. As for this, this paper proposes a new modeling method for complex landslide with MATLAB. Firstly, the terrain maps before and after landslide are used as data sources. Using Distmesh toolbox to triangulate the landslide area, the triangular prisms are generated through an elevation-based interpolation algorithm and to reconstruct the sliding bed and the sliding mass. At the same time, the base material on the sliding path is modeled with Voronoi polyhedrons generated with Multi-Parametric Toolbox. Then, some functions are written to obtain the topology information of these blocks. According to the syntax rules of 3DEC, it is transformed into a command text file that can be received by 3DEC. By this way, the complex landslide model can be established quickly. Finally, taking the Xinmo Landslide in Maoxian County of Sichuan Province as an example, the modeling steps are described in detail. The result of numerical simulation shows that the model established by this method can well reproduce the sliding process, the entrainment of substrate material and the final deposition. The feasibility and practicability of this approach is verified.
The weakness of 3DEC software in the pre-processing of building the landslide model limits its application. As for this, this paper proposes a new modeling method for complex landslide with MATLAB. Firstly, the terrain maps before and after landslide are used as data sources. Using Distmesh toolbox to triangulate the landslide area, the triangular prisms are generated through an elevation-based interpolation algorithm and to reconstruct the sliding bed and the sliding mass. At the same time, the base material on the sliding path is modeled with Voronoi polyhedrons generated with Multi-Parametric Toolbox. Then, some functions are written to obtain the topology information of these blocks. According to the syntax rules of 3DEC, it is transformed into a command text file that can be received by 3DEC. By this way, the complex landslide model can be established quickly. Finally, taking the Xinmo Landslide in Maoxian County of Sichuan Province as an example, the modeling steps are described in detail. The result of numerical simulation shows that the model established by this method can well reproduce the sliding process, the entrainment of substrate material and the final deposition. The feasibility and practicability of this approach is verified.
2020, 28(4): 803-812.
Collapse is the most devastating disaster in natural landscape scenic spot. There are 34 potential rockfalls distributed in different positions of Helankou. All potential rockfalls pose a serious threat to rock paintings and tourists. Firstly, we comprehensively investigated the genesis, distribution, lithology and geometric characteristics of the 34 potential rockfalls. Secondly, we used the rockfall to analyze the movement process and energy change of the rockfalls. And then we found that there was a high probability that the falling points of the rockfalls can be the rock painting area and the tourist boardwalk. So we decided to use manual cleaning methods to clean up the potential rockfall, because mechanical and blast cleaning could cause irreparable damage to rock paintings. For the large-volume rock, it was better to crush by static crushing agent first. Finally, we did the rock crushing experiment to select the optimal arrangement of static crushing agent. We had the following conclusions. (1)The reasons for the formation of the potential rockfall are the concave of thin-layer, the rock layer level, and the two sets of joints to cut the thick-layer metasandstone. (2)The rockfalls can be divided into three different types: bedrock exposed, solitary belt, and debris flow gully. (3)It is very likely that the falling rocks can fall in the rock paintings area and destroy the rock paintings. (2)The best solution for the control of rockfall is static crushing combined with manual handling. And there is an optimal arrangement of static crushing agent. In short, our study can provide a new way and reference for the prevention of the rockfall disaster in Helankou Rock Painting.
Collapse is the most devastating disaster in natural landscape scenic spot. There are 34 potential rockfalls distributed in different positions of Helankou. All potential rockfalls pose a serious threat to rock paintings and tourists. Firstly, we comprehensively investigated the genesis, distribution, lithology and geometric characteristics of the 34 potential rockfalls. Secondly, we used the rockfall to analyze the movement process and energy change of the rockfalls. And then we found that there was a high probability that the falling points of the rockfalls can be the rock painting area and the tourist boardwalk. So we decided to use manual cleaning methods to clean up the potential rockfall, because mechanical and blast cleaning could cause irreparable damage to rock paintings. For the large-volume rock, it was better to crush by static crushing agent first. Finally, we did the rock crushing experiment to select the optimal arrangement of static crushing agent. We had the following conclusions. (1)The reasons for the formation of the potential rockfall are the concave of thin-layer, the rock layer level, and the two sets of joints to cut the thick-layer metasandstone. (2)The rockfalls can be divided into three different types: bedrock exposed, solitary belt, and debris flow gully. (3)It is very likely that the falling rocks can fall in the rock paintings area and destroy the rock paintings. (2)The best solution for the control of rockfall is static crushing combined with manual handling. And there is an optimal arrangement of static crushing agent. In short, our study can provide a new way and reference for the prevention of the rockfall disaster in Helankou Rock Painting.
2020, 28(4): 813-821.
As the mechanical properties of soil-rock mixture are complicated, the sliding surface of soil-rock mixture slope is affected by its microstructure characteristics. We established a typical soil-rock mixture slope model with particle discrete element method. The servo mechanism was applied to construct a numerical model with homogeneous stress. Then we calibrated the microparameters of contact model based on the laboratory test data. Combining the strength reduction method, we analysed the difference of the sliding surface morphology between the soil slope and soil-rock mixture slope. The results show that the existence of the block stone causes the nonuniform distribution of the contact force chain, and the block stone increases the slope stability. The development of the sliding surface tends to pass through the gaps between the blocks and is related to the location of block stone. Slope stability is closely related to rock content. As the content of rock reaches 30% ~50%, the landslide is dominated by the movement of local block and cannot form a continuous sliding surface. The study provides the reference for the analysis of failure mechanism of soil-rock mixture slope.
As the mechanical properties of soil-rock mixture are complicated, the sliding surface of soil-rock mixture slope is affected by its microstructure characteristics. We established a typical soil-rock mixture slope model with particle discrete element method. The servo mechanism was applied to construct a numerical model with homogeneous stress. Then we calibrated the microparameters of contact model based on the laboratory test data. Combining the strength reduction method, we analysed the difference of the sliding surface morphology between the soil slope and soil-rock mixture slope. The results show that the existence of the block stone causes the nonuniform distribution of the contact force chain, and the block stone increases the slope stability. The development of the sliding surface tends to pass through the gaps between the blocks and is related to the location of block stone. Slope stability is closely related to rock content. As the content of rock reaches 30% ~50%, the landslide is dominated by the movement of local block and cannot form a continuous sliding surface. The study provides the reference for the analysis of failure mechanism of soil-rock mixture slope.
2020, 28(4): 822-831.
Rock fall frequently happens in natural landscape scenic spot and imperils tourists. So it is of social and scientific significance to study the rock fall and collapse. RHRS risk evaluation system is used to analyze the various factors that can cause the rockfalls in scenic spots. They include slope height, geological characteristics, rockfall volume/block size, annual average rainfall, and historical rockfall frequency. In order to represent the extent of rockfall risk, the scores for rockfall risk are calculated with the original scoring formula to be 142 and 117.2 for the King of Medicine Mountain and Jianglang Mountain in Quzhou province, respectively. In this process, the abstract qualitative evaluation is converted into a specific quantitative evaluation. The FN curves and ALARP principle are combined to determine the allowable risk criteria, as well as clearly divide the high, medium and low risk areas. The average acceptable risk calculated is 1.62×10-5 per year. The upper and lower limits of the acceptable risk level on the FN curves are calculated as 10×10-4 per year and 10×10-5 per year respectively. The findings of this study can be used as a significant reference for rockfall risk evaluation and decision making in scenic spots.
Rock fall frequently happens in natural landscape scenic spot and imperils tourists. So it is of social and scientific significance to study the rock fall and collapse. RHRS risk evaluation system is used to analyze the various factors that can cause the rockfalls in scenic spots. They include slope height, geological characteristics, rockfall volume/block size, annual average rainfall, and historical rockfall frequency. In order to represent the extent of rockfall risk, the scores for rockfall risk are calculated with the original scoring formula to be 142 and 117.2 for the King of Medicine Mountain and Jianglang Mountain in Quzhou province, respectively. In this process, the abstract qualitative evaluation is converted into a specific quantitative evaluation. The FN curves and ALARP principle are combined to determine the allowable risk criteria, as well as clearly divide the high, medium and low risk areas. The average acceptable risk calculated is 1.62×10-5 per year. The upper and lower limits of the acceptable risk level on the FN curves are calculated as 10×10-4 per year and 10×10-5 per year respectively. The findings of this study can be used as a significant reference for rockfall risk evaluation and decision making in scenic spots.
2020, 28(4): 832-839.
The prediction of landslide imminent sliding time can be established according to the time curve of landslide deformation. But the existing prediction models of landslide imminent sliding time have not unified the calculation interval. So the time prediction value obtained by the same model in different calculation intervals may be quite different. Taking Longjingcun Landslide in Guizhou Province as an example, this paper analyzes the fine deformation data of the landslide with the Saito time prediction model. The calculation range of the deformation for the prediction of the time of imminent sliding is determined to be between 70 and 75 degrees of tangent angle. According to the deformation curve, the landslide has obvious upward warping characteristics when it is imminent sliding, which leads to the occurrence time of the landslide ahead of time. By analyzing the ratio between the tangential gradient and the segment gradient of the curve, a correction coefficient of 0.5 is introduced to correct the time prediction value of landslide. The results show that the improved prediction method of landslide deformation imminent sliding time has good accuracy and applicability.
The prediction of landslide imminent sliding time can be established according to the time curve of landslide deformation. But the existing prediction models of landslide imminent sliding time have not unified the calculation interval. So the time prediction value obtained by the same model in different calculation intervals may be quite different. Taking Longjingcun Landslide in Guizhou Province as an example, this paper analyzes the fine deformation data of the landslide with the Saito time prediction model. The calculation range of the deformation for the prediction of the time of imminent sliding is determined to be between 70 and 75 degrees of tangent angle. According to the deformation curve, the landslide has obvious upward warping characteristics when it is imminent sliding, which leads to the occurrence time of the landslide ahead of time. By analyzing the ratio between the tangential gradient and the segment gradient of the curve, a correction coefficient of 0.5 is introduced to correct the time prediction value of landslide. The results show that the improved prediction method of landslide deformation imminent sliding time has good accuracy and applicability.
2020, 28(4): 840-851.
High and steep loess slopes are formed due to the uplift of the Tibetan Plateau and the erosion of the Yellow River in the Loess Plateau. Under the influence of precipitation and agriculture irrigation, a large number of loess landslides occur every year due to the increased underground water table. Therefore, to reveal the spatial distribution and migration of water within the loess slope is key for the understanding of loess landslide mechanism and for the purpose of landslide early-warning. In this paper, electrical tomography(ERT) and model simulation methods are used to quantify the relationship between internal resistivity and water content of the slope. The two-dimensional imaging of the internal moisture of the slope is combined with the surfer software. The correlation analysis between loess resistivity and formation physicochemical parameters shows that the formation water content in the loess slope is the dominant factor in the formation resistivity change. The model fitting result based on the Archie formula can accurately quantify the relationship between resistivity and water content. The two-dimensional imaging results of formation water can visually show the temporal and spatial evolution of water inside the slope. This study quantifies and intuitively describes the water distribution characteristics inside the loess slope, which can provide the most direct and effective data for the prediction and warning of loess landslide.
High and steep loess slopes are formed due to the uplift of the Tibetan Plateau and the erosion of the Yellow River in the Loess Plateau. Under the influence of precipitation and agriculture irrigation, a large number of loess landslides occur every year due to the increased underground water table. Therefore, to reveal the spatial distribution and migration of water within the loess slope is key for the understanding of loess landslide mechanism and for the purpose of landslide early-warning. In this paper, electrical tomography(ERT) and model simulation methods are used to quantify the relationship between internal resistivity and water content of the slope. The two-dimensional imaging of the internal moisture of the slope is combined with the surfer software. The correlation analysis between loess resistivity and formation physicochemical parameters shows that the formation water content in the loess slope is the dominant factor in the formation resistivity change. The model fitting result based on the Archie formula can accurately quantify the relationship between resistivity and water content. The two-dimensional imaging results of formation water can visually show the temporal and spatial evolution of water inside the slope. This study quantifies and intuitively describes the water distribution characteristics inside the loess slope, which can provide the most direct and effective data for the prediction and warning of loess landslide.
2020, 28(4): 852-866.
Coal mined-out area, formed in mine production, usually induces a certain degree of ground subsidence and collapse. In many areas, the background information of coal seam mining is unclear, which brings trouble to the ecological restoration of the mining area and the reuse of land resources. Therefore, the calculation of the underground mining range is particularly important and can play a monitoring role in the cross-border mining of coal mines. This paper uses Japan's PALSAR-2 satellite data with a data resolution of about 3 m, and a total of 16 scenes in two observation directions of ascending and descending. Using InSAR technology, the multi-phase surface deformation monitoring is carried out in the mine goaf of Zhenfeng County, Guizhou Province. Based on the geological conditions, underground mining conditions, and field investigations in the study area, this paper calculates the relationship between mining subsidence parameters and time lags in the study area. The calculation combines the surface deformation of the known coal mines and the underground mining information. Then using the above-mentioned parameters and surface deformation information, this paper inverts an abandoned coal mine near the area and calculates the underground goaf range and mining time. The results are as follows. The study area is dominated by slow-sloping sandstone and mudstone. The coal mining strike influence angle is 83°, the uphill influence angle is 75°and the downhill influence angle is 80°. Inversion calculation gives the mining range of 380 m×150 m underground and the mining time of each area. FLAC3D numerical simulation calculation of the mined area of the abandoned coal mine is used to verify the accuracy of the range of the mined area. Compared with the calculation results of InSAR, the surface deformation trend of the mining area obtained by FLAC3D is more consistent, and the root meant square error of the trend and tendency is about 6 cm.
Coal mined-out area, formed in mine production, usually induces a certain degree of ground subsidence and collapse. In many areas, the background information of coal seam mining is unclear, which brings trouble to the ecological restoration of the mining area and the reuse of land resources. Therefore, the calculation of the underground mining range is particularly important and can play a monitoring role in the cross-border mining of coal mines. This paper uses Japan's PALSAR-2 satellite data with a data resolution of about 3 m, and a total of 16 scenes in two observation directions of ascending and descending. Using InSAR technology, the multi-phase surface deformation monitoring is carried out in the mine goaf of Zhenfeng County, Guizhou Province. Based on the geological conditions, underground mining conditions, and field investigations in the study area, this paper calculates the relationship between mining subsidence parameters and time lags in the study area. The calculation combines the surface deformation of the known coal mines and the underground mining information. Then using the above-mentioned parameters and surface deformation information, this paper inverts an abandoned coal mine near the area and calculates the underground goaf range and mining time. The results are as follows. The study area is dominated by slow-sloping sandstone and mudstone. The coal mining strike influence angle is 83°, the uphill influence angle is 75°and the downhill influence angle is 80°. Inversion calculation gives the mining range of 380 m×150 m underground and the mining time of each area. FLAC3D numerical simulation calculation of the mined area of the abandoned coal mine is used to verify the accuracy of the range of the mined area. Compared with the calculation results of InSAR, the surface deformation trend of the mining area obtained by FLAC3D is more consistent, and the root meant square error of the trend and tendency is about 6 cm.
2020, 28(4): 867-876.
The Nairobi-Malabar railway runs through the great rift valley, and has tunnels running through many active faults. In the design of tunnel structure, both earthquake and dislocation of fault are considered. In the seismic and seismic design of the tunnel, the tunnel structure is designed as the chain. So the tunnel structure can automatically adjust its deformation with the action of the earthquake and fault dislocation, without causing the overall failure. In order to analyze the seismic response of tunnel structure, a numerical model of dynamic analysis is established. The synthetic time history of acceleration with a probability of over 2%in 100 years is considered as a horizontal seismic action input at the bottom of the numerical model. The response law and chain characteristics of tunnel structure under earthquake are calculated and analyzed. The calculation shows that the chain-like tunnel structure can play a good role in seismic energy dissipation. In addition, due to the dislocation of the fault, the inner limit of the tunnel is reduced, which makes the tunnel loses its normal traffic function. Therefore, in the fault dislocation design, according to the characteristics of the fault and the type of catenary, the tunnel section expansion size is determined comprehensively. When the fault dislocation affects the normal traffic operation, the footwall tunnel can be expanded and backfilled according to the characteristics of the normal fault. Adjusting the slope of the line, the insulation distance of the catenary and the suspension mode can eliminate the dislocation amount of the fault. So the normal passage condition of the line in the tunnel can be achieved, without rebuilding the second lining structure of the tunnel.
The Nairobi-Malabar railway runs through the great rift valley, and has tunnels running through many active faults. In the design of tunnel structure, both earthquake and dislocation of fault are considered. In the seismic and seismic design of the tunnel, the tunnel structure is designed as the chain. So the tunnel structure can automatically adjust its deformation with the action of the earthquake and fault dislocation, without causing the overall failure. In order to analyze the seismic response of tunnel structure, a numerical model of dynamic analysis is established. The synthetic time history of acceleration with a probability of over 2%in 100 years is considered as a horizontal seismic action input at the bottom of the numerical model. The response law and chain characteristics of tunnel structure under earthquake are calculated and analyzed. The calculation shows that the chain-like tunnel structure can play a good role in seismic energy dissipation. In addition, due to the dislocation of the fault, the inner limit of the tunnel is reduced, which makes the tunnel loses its normal traffic function. Therefore, in the fault dislocation design, according to the characteristics of the fault and the type of catenary, the tunnel section expansion size is determined comprehensively. When the fault dislocation affects the normal traffic operation, the footwall tunnel can be expanded and backfilled according to the characteristics of the normal fault. Adjusting the slope of the line, the insulation distance of the catenary and the suspension mode can eliminate the dislocation amount of the fault. So the normal passage condition of the line in the tunnel can be achieved, without rebuilding the second lining structure of the tunnel.
2020, 28(4): 877-886.
As for the fact that the frequent and serious water damage disasters in the Gaizi River section of Sino-Pakistan Highway, we performed analysis and optimization design research for the actual road waterlogging disasters. In investigation, we found there was a total number of 18 water damaged work sites in the Gaizi river section. The work sites had various types and they were segmental distributed. The result shows that the hydrology and topographic conditions of the Gaizi River control the occurrence and development of water damage at the worksite. The hydrodynamic conditions are the most important control elements of water damage on roads. The valley terrain controls the distribution characteristics and the destructive form of water damage. The combined effect of hydrology and topographic conditions contributed to the current distribution of water destroyed worksites in the Gaizi river section. After verifying the current water damage characteristics and the water damage problems by hydraulic model test, we analysed the characteristics in real water damage disasters and the problems existing in the prevention and control project in paper. We proposed the optimal design scheme of typical water damage prevention and control project from the perspective of technical scheme adjustment and economic rationality. Finally, it was found that the protection effect was better in the later operation.
As for the fact that the frequent and serious water damage disasters in the Gaizi River section of Sino-Pakistan Highway, we performed analysis and optimization design research for the actual road waterlogging disasters. In investigation, we found there was a total number of 18 water damaged work sites in the Gaizi river section. The work sites had various types and they were segmental distributed. The result shows that the hydrology and topographic conditions of the Gaizi River control the occurrence and development of water damage at the worksite. The hydrodynamic conditions are the most important control elements of water damage on roads. The valley terrain controls the distribution characteristics and the destructive form of water damage. The combined effect of hydrology and topographic conditions contributed to the current distribution of water destroyed worksites in the Gaizi river section. After verifying the current water damage characteristics and the water damage problems by hydraulic model test, we analysed the characteristics in real water damage disasters and the problems existing in the prevention and control project in paper. We proposed the optimal design scheme of typical water damage prevention and control project from the perspective of technical scheme adjustment and economic rationality. Finally, it was found that the protection effect was better in the later operation.
2020, 28(4): 887-895.
Geologic body usually presents complex three-dimensional spatial distribution in actual engineering. Traditional high-density resistivity method based on the assumption of two-dimensional medium may not be able to accurately reflect its spatial position and trend, while three-dimensional high-density resistivity method can handle such problems perfectly. But it is restricted in application due to the difficulty in data acquisition and processing. This paper attempts to study the effect of three dimensional high-density resistivity method in the exploration of unfavorable geologic bodies with complex spatial form and compare the difference from two-dimensional resistivity method. This paper firstly studies the principle and data processing method of three-dimensional high-density resistivity method, and then carries out the application research through the field test which is based on the goaf in Fujian Shouning. Both two-dimensional and three-dimensional high-density resistivity methods are used in the exploration. The results are verified by three-dimensional laser scanning. It successfully realizes the three-dimensional resistivity data acquisition of 240 electrodes in complex terrain, introduces the least square method based on the smooth constraint technique and finished the inversion of three-dimensional resistivity data. The research results show that three-dimensional laser scanning can accurately acquire goaf form and trend, which verifies the results of the resistivity method reliably. The three-dimensional high-density resistivity method can accurately reflect the location and trend of abnormal resistance. Compared with the two-dimensional high-density resistivity method, its inversion converges, which eliminates the deep interference information and reduces multiplicity of solution.
Geologic body usually presents complex three-dimensional spatial distribution in actual engineering. Traditional high-density resistivity method based on the assumption of two-dimensional medium may not be able to accurately reflect its spatial position and trend, while three-dimensional high-density resistivity method can handle such problems perfectly. But it is restricted in application due to the difficulty in data acquisition and processing. This paper attempts to study the effect of three dimensional high-density resistivity method in the exploration of unfavorable geologic bodies with complex spatial form and compare the difference from two-dimensional resistivity method. This paper firstly studies the principle and data processing method of three-dimensional high-density resistivity method, and then carries out the application research through the field test which is based on the goaf in Fujian Shouning. Both two-dimensional and three-dimensional high-density resistivity methods are used in the exploration. The results are verified by three-dimensional laser scanning. It successfully realizes the three-dimensional resistivity data acquisition of 240 electrodes in complex terrain, introduces the least square method based on the smooth constraint technique and finished the inversion of three-dimensional resistivity data. The research results show that three-dimensional laser scanning can accurately acquire goaf form and trend, which verifies the results of the resistivity method reliably. The three-dimensional high-density resistivity method can accurately reflect the location and trend of abnormal resistance. Compared with the two-dimensional high-density resistivity method, its inversion converges, which eliminates the deep interference information and reduces multiplicity of solution.
2020, 28(4): 896-906.
There are many difficulties in testing the mechanical properties of prestressed high strength(PHC)pipe pile, because of the complicated production process, unique pile structure and large pile resistance. At present, the test techniques for testing the mechanical properties of PHC pipe pile can be divided into four categories: point monitoring, linear monitoring, distributed optical fiber monitoring, and quasi-distributed fiber bragg grating monitoring. This paper summarizes the principle, advantages and disadvantages, application status of the test technology for PHC pipe pile, as well as the installation method of related sensors. It further discusses the problems existing in the test technology and installation method. The analysis indicates that distributed optical fiber monitoring and quasi-distributed fiber bragg grating monitoring have higher test accuracy, wider monitoring range and better monitoring results. The coordination of deformation between optical fiber and pile body, survival rate of the installed fiber and impact of installation on PHC pipe pile are the hot research topics in the future.
There are many difficulties in testing the mechanical properties of prestressed high strength(PHC)pipe pile, because of the complicated production process, unique pile structure and large pile resistance. At present, the test techniques for testing the mechanical properties of PHC pipe pile can be divided into four categories: point monitoring, linear monitoring, distributed optical fiber monitoring, and quasi-distributed fiber bragg grating monitoring. This paper summarizes the principle, advantages and disadvantages, application status of the test technology for PHC pipe pile, as well as the installation method of related sensors. It further discusses the problems existing in the test technology and installation method. The analysis indicates that distributed optical fiber monitoring and quasi-distributed fiber bragg grating monitoring have higher test accuracy, wider monitoring range and better monitoring results. The coordination of deformation between optical fiber and pile body, survival rate of the installed fiber and impact of installation on PHC pipe pile are the hot research topics in the future.
2020, 28(4): 907-915.
Based on the ground vibration and settlement of track-bridge-pier-seasonal frozen soil site caused by high-speed train operation, we selected a pier and surrounding foundation site of Tieling-Siping section of Harbin-Dalian high-speed railway as the test site. The measured data are analyzed in time domain and frequency domain. And we studied the vibration characteristics of piers and surrounding sites. The results show that the vibration characteristics of bridge pier and foundation site are quite different, and the vibration amplification effect of different foundation site is also significantly different. Combining with the survey, we established the finite element numerical model of pier-foundation site. We analyzed the vibration propagation characteristics of pier and foundation site in different seasons and the stress distribution in the soil of foundation site. We used the accumulated plastic strain model to analyze the settlement and deformation of the foundation site in seasonal frozen soil region under repeated train loads. It is found that the peak vibration acceleration of site decreases with the increase of the distance R from the pier, and the vibration attenuation rate of freezing season is obviously lower than vibration attenuation rate of non-freezing season. The cumulative settlement of the ground surface of the foundation site is the largest where the distance from the bottom of the pier is 0.5 m. The permanent deformation of foundation site caused by train loading increases with the increase of the times of train load, and the deformation tends to be stable with the increase of time as well.
Based on the ground vibration and settlement of track-bridge-pier-seasonal frozen soil site caused by high-speed train operation, we selected a pier and surrounding foundation site of Tieling-Siping section of Harbin-Dalian high-speed railway as the test site. The measured data are analyzed in time domain and frequency domain. And we studied the vibration characteristics of piers and surrounding sites. The results show that the vibration characteristics of bridge pier and foundation site are quite different, and the vibration amplification effect of different foundation site is also significantly different. Combining with the survey, we established the finite element numerical model of pier-foundation site. We analyzed the vibration propagation characteristics of pier and foundation site in different seasons and the stress distribution in the soil of foundation site. We used the accumulated plastic strain model to analyze the settlement and deformation of the foundation site in seasonal frozen soil region under repeated train loads. It is found that the peak vibration acceleration of site decreases with the increase of the distance R from the pier, and the vibration attenuation rate of freezing season is obviously lower than vibration attenuation rate of non-freezing season. The cumulative settlement of the ground surface of the foundation site is the largest where the distance from the bottom of the pier is 0.5 m. The permanent deformation of foundation site caused by train loading increases with the increase of the times of train load, and the deformation tends to be stable with the increase of time as well.
2020, 28(4): 916-924.
Based on the geothermal setting of the Awang Township of Tibet, we analyzed the characteristics and genetic mechanism of geothermal water with the aid of field investigation, hydrogeochemistry, and environmental isotopes. The hydrochemical types of geothermal water belong to HCO3-Na type, resulting from leaching and cation interaction between geothermal water and surrounding rocks. The composition of hydrogen and oxygen isotope indicates an origin of meteoric water. The slight oxygen drift is produced by water-rock interaction and high temperature of geothermal reservoir. The recharge area with estimated altitude of 4600~4800 m is located in northwest mountain areas. The analyses of Na-K-Mg triangle graph and saturation index collectively show the geothermal water is mixed by shallow cold water with the proportion of 60% to 70%. The temperatures of deep geothermal reservoirs are 170~200 ℃ suggesting by quartz and Na-K geothermometers. The circulation depth of geothermal water is 4500~5300 m. The genetic mechanism of geothermal water in Awang Township can be concluded as follows: the thermal water recharged from precipitation is heated by terrestrial heat flow, arises and exposes as geothermal springs along the fault zone.
Based on the geothermal setting of the Awang Township of Tibet, we analyzed the characteristics and genetic mechanism of geothermal water with the aid of field investigation, hydrogeochemistry, and environmental isotopes. The hydrochemical types of geothermal water belong to HCO3-Na type, resulting from leaching and cation interaction between geothermal water and surrounding rocks. The composition of hydrogen and oxygen isotope indicates an origin of meteoric water. The slight oxygen drift is produced by water-rock interaction and high temperature of geothermal reservoir. The recharge area with estimated altitude of 4600~4800 m is located in northwest mountain areas. The analyses of Na-K-Mg triangle graph and saturation index collectively show the geothermal water is mixed by shallow cold water with the proportion of 60% to 70%. The temperatures of deep geothermal reservoirs are 170~200 ℃ suggesting by quartz and Na-K geothermometers. The circulation depth of geothermal water is 4500~5300 m. The genetic mechanism of geothermal water in Awang Township can be concluded as follows: the thermal water recharged from precipitation is heated by terrestrial heat flow, arises and exposes as geothermal springs along the fault zone.
2020, 28(4): 925-934.
Taiyuan Basin is a Cenozoic fault basin. The formation of faults block and horst in the basin is controlled by the north-south and east-west faults. The karst thermal mineral water is mainly distributed in the area between the Sanji horst and the Tianzhuang fault. The main aquifers of karst thermal water are the carbonate of the Ordovician Fengfeng group, the upper and lower Majiagou groups. We took 18 geothermal water samples in the field, and collected the hydrochemical data of 9 geothermal water and 3 geothermal water in the existing literature. According to the analysis and test results, the hydrochemical type of karst thermal water is SO4-Ca ·Mg type. According to the ion concentration relationship and the saturation index of the main mineral in the thermal mineral water, it can be inferred that the hydrochemical type is mainly affected by the gypsum layer. In addition to the dissolution of calcite and dolomite, the dissolution of gypsum plays a leading role in the process of groundwater dissolution and filtration. According to the mineral saturation index, Ca2+ produced by gypsum dissolution and the increase of geothermal mineral water temperature also lead to the saturation of calcite or dolomite, which may lead to precipitation. The effect of the dissolution of gypsum on the dissolution of calcite and dolomite has an inhibitory effect. The age of karst thermal mineral water in the Xiwenzhuang uplift is more than 20, 000 a, which is mixed with ancient water. The temperature of karst thermal reservoir is 72.6~91.1 ℃, and the depth of circulation is 2123~2663 m. Long-term water-rock interactions provide the time of conduction heating and enriched mineral components for the thermal mineral water. As the high value area of the temperature, TDS and Sr concentration in karst thermal mineral water, Xiwenzhuang uplift is the catchment area of thermal mineral water in the basin, and also the best area of regional thermal mineral water. The increasing trend of TDS and Sr concentration reflects the obvious dissolution and filtration of groundwater from recharge area to drainage area in the basin. There are occurred such a trend: cold underground water with low TDS and hydrochemical type of HCO3-Ca ·Mg to karst thermal mineral water with high TDS and hydrochemical type of SO4-Ca ·Mg.
Taiyuan Basin is a Cenozoic fault basin. The formation of faults block and horst in the basin is controlled by the north-south and east-west faults. The karst thermal mineral water is mainly distributed in the area between the Sanji horst and the Tianzhuang fault. The main aquifers of karst thermal water are the carbonate of the Ordovician Fengfeng group, the upper and lower Majiagou groups. We took 18 geothermal water samples in the field, and collected the hydrochemical data of 9 geothermal water and 3 geothermal water in the existing literature. According to the analysis and test results, the hydrochemical type of karst thermal water is SO4-Ca ·Mg type. According to the ion concentration relationship and the saturation index of the main mineral in the thermal mineral water, it can be inferred that the hydrochemical type is mainly affected by the gypsum layer. In addition to the dissolution of calcite and dolomite, the dissolution of gypsum plays a leading role in the process of groundwater dissolution and filtration. According to the mineral saturation index, Ca2+ produced by gypsum dissolution and the increase of geothermal mineral water temperature also lead to the saturation of calcite or dolomite, which may lead to precipitation. The effect of the dissolution of gypsum on the dissolution of calcite and dolomite has an inhibitory effect. The age of karst thermal mineral water in the Xiwenzhuang uplift is more than 20, 000 a, which is mixed with ancient water. The temperature of karst thermal reservoir is 72.6~91.1 ℃, and the depth of circulation is 2123~2663 m. Long-term water-rock interactions provide the time of conduction heating and enriched mineral components for the thermal mineral water. As the high value area of the temperature, TDS and Sr concentration in karst thermal mineral water, Xiwenzhuang uplift is the catchment area of thermal mineral water in the basin, and also the best area of regional thermal mineral water. The increasing trend of TDS and Sr concentration reflects the obvious dissolution and filtration of groundwater from recharge area to drainage area in the basin. There are occurred such a trend: cold underground water with low TDS and hydrochemical type of HCO3-Ca ·Mg to karst thermal mineral water with high TDS and hydrochemical type of SO4-Ca ·Mg.
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