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Editor Work2018 Vol. 26, No. 3
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2018, 26(3): 561-571.
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Stress-release zone always connects with alpine valleys or a certain scale of underground engineering, which is generally thought to be caused by stream trenching or large scale engineering excavation. However there are few research in stress-release under the ridge's sharp turn. During the engineering geological investigation in the CSNS site which located in southern Guangdong Province, leakage occurred in drilling process of four adjacent boreholes and found locally broken argillization zone in the intact rock. To study and explain this phenomenon, we first arranged some geophysical lines across the engineering site to probe the underground. And the electrical geophysical profile indicates there is a local low resistivity zone exists under the ridge sharp turn. Then, during the geologic mapping work, we found that the argillization zone just located in the contacting zone between northern granite belt and southern granulite belt. Third, by analysis the engineering geological investigation report, we circled the muddy zone in borehole profiles and contour maps, which tallies with geophysical results. After all these outdoor and indoor works, we used computer building an authentic surface model to simulate the influence of weathering and unloading on the mountain from earliest times. The numerical results show that stress unloading happened in a certain depth under the ridge's sharp turn because of the erosion unloading. It also made partial rock quality worse which approached to the contacting zone of dike and granulite, and formed crushing zone and control the local enrichment of groundwater and the generate of fountain. We analyzed the geological prospecting and geophysical data to conjecture what caused muddy zone in borehole ZK94 and neighboring areas' low RQD, and verified it by numerical simulation. We found that the muddy zone was caused by multiple factors. First and the most important factor, the metamorphic sandstone developed in the contacting zone of granite and granulite was harder and brittler than the other two rocks, which become the internal cause of muddy zone. Second, by analyzing substantial drilling information, there is a low RQD zone at a certain depth, which located in contact zones between granite and granulite. The contact zone was affected by the later southern granite intrusion, and presented as saddle and gully on surface, even made the rock broken near the contact zone. At last, the numerical simulation indicates borehole ZK94 which located at the ridge's sharp turn was a low stress zone, and the original compressional stress changed in this area. With the surface weathering and tectonic uplift, the exposed rock masses unloaded and produced a weak area under the ridge, so that make rock fracture developed further and the rock masses became more broken. Besides, the sudden water inflow happened in borehole ZK99 and ZK101 indicates that headwaters exist nearby. Thus the broken rock masses in the lithologic boundary formed water conducting fracture, and the groundwater via the fracture soften the rock in return. In this circle, it finally formed muddy zone near ZK94. This study reveals the influence of a ridge's sudden change on in-situ stress and rock structure, and it is expected to provide reference to similar geological anomaly analyses.
Stress-release zone always connects with alpine valleys or a certain scale of underground engineering, which is generally thought to be caused by stream trenching or large scale engineering excavation. However there are few research in stress-release under the ridge's sharp turn. During the engineering geological investigation in the CSNS site which located in southern Guangdong Province, leakage occurred in drilling process of four adjacent boreholes and found locally broken argillization zone in the intact rock. To study and explain this phenomenon, we first arranged some geophysical lines across the engineering site to probe the underground. And the electrical geophysical profile indicates there is a local low resistivity zone exists under the ridge sharp turn. Then, during the geologic mapping work, we found that the argillization zone just located in the contacting zone between northern granite belt and southern granulite belt. Third, by analysis the engineering geological investigation report, we circled the muddy zone in borehole profiles and contour maps, which tallies with geophysical results. After all these outdoor and indoor works, we used computer building an authentic surface model to simulate the influence of weathering and unloading on the mountain from earliest times. The numerical results show that stress unloading happened in a certain depth under the ridge's sharp turn because of the erosion unloading. It also made partial rock quality worse which approached to the contacting zone of dike and granulite, and formed crushing zone and control the local enrichment of groundwater and the generate of fountain. We analyzed the geological prospecting and geophysical data to conjecture what caused muddy zone in borehole ZK94 and neighboring areas' low RQD, and verified it by numerical simulation. We found that the muddy zone was caused by multiple factors. First and the most important factor, the metamorphic sandstone developed in the contacting zone of granite and granulite was harder and brittler than the other two rocks, which become the internal cause of muddy zone. Second, by analyzing substantial drilling information, there is a low RQD zone at a certain depth, which located in contact zones between granite and granulite. The contact zone was affected by the later southern granite intrusion, and presented as saddle and gully on surface, even made the rock broken near the contact zone. At last, the numerical simulation indicates borehole ZK94 which located at the ridge's sharp turn was a low stress zone, and the original compressional stress changed in this area. With the surface weathering and tectonic uplift, the exposed rock masses unloaded and produced a weak area under the ridge, so that make rock fracture developed further and the rock masses became more broken. Besides, the sudden water inflow happened in borehole ZK99 and ZK101 indicates that headwaters exist nearby. Thus the broken rock masses in the lithologic boundary formed water conducting fracture, and the groundwater via the fracture soften the rock in return. In this circle, it finally formed muddy zone near ZK94. This study reveals the influence of a ridge's sudden change on in-situ stress and rock structure, and it is expected to provide reference to similar geological anomaly analyses.
2018, 26(3): 572-582.
Granite is a kind of surrounding rock in high-level radioactive waste geological repository. Hydraulic characteristics of the surrounding rock directly determine whether or not it can effectively block the groundwater to the direction of nuclear waste repository. The micro cracks structure and chemical weathering is the performance of hydraulic characteristics in surrounding rock. So a quantitative analysis of granite micro cracks and chemical weathering analysis has the certain scientific significance for comparison of the buried depth of high-level radioactive waste geological repository. In this study, seven core samples in different depth of the granite drilling within 600 meters were taken as the research object. The borehole is located in Alxa, Inner Mongolia, China. Using survey grid method and image processing technology, micrographs were translated into binaryzation image of micro cracks. Then, geometric parameters of the micro cracks(such as quantity, width, cranny ratio, etc) were analyzed to describe the spatial distribution the micro cracks characteristics. The morphology characteristics and element content of micro cracks were analyzed by scanning electron microscopy energy dispersive X ray analysis(SEM-EDS).The natural moisture content and CIA are two important parameters of chemical weathering in this study. Finally, Comprehensive evaluation was used to analyze granite integrity. The results show: (1)The complete granite samples' micro cracks development have a general trend from high to low as the sampling depth from shallow to deep in this study area.(2)Fissures are inclined to develop among feldspar and biotite. On the contrary, fissures are more commonly developed in quartz grains.(3)Cranny ratio, average gap width, fracture number and CIA become larger near broken zones.(4)The distance of fracture zone influence on the complete granite can be more than 10.6 m. And the late hydrothermal seepage distance can be more than 50.27 m.(5)Through comprehensive evaluation, 598.8 m underground was the optimum buried depth of nuclear waste disposal repository.
Granite is a kind of surrounding rock in high-level radioactive waste geological repository. Hydraulic characteristics of the surrounding rock directly determine whether or not it can effectively block the groundwater to the direction of nuclear waste repository. The micro cracks structure and chemical weathering is the performance of hydraulic characteristics in surrounding rock. So a quantitative analysis of granite micro cracks and chemical weathering analysis has the certain scientific significance for comparison of the buried depth of high-level radioactive waste geological repository. In this study, seven core samples in different depth of the granite drilling within 600 meters were taken as the research object. The borehole is located in Alxa, Inner Mongolia, China. Using survey grid method and image processing technology, micrographs were translated into binaryzation image of micro cracks. Then, geometric parameters of the micro cracks(such as quantity, width, cranny ratio, etc) were analyzed to describe the spatial distribution the micro cracks characteristics. The morphology characteristics and element content of micro cracks were analyzed by scanning electron microscopy energy dispersive X ray analysis(SEM-EDS).The natural moisture content and CIA are two important parameters of chemical weathering in this study. Finally, Comprehensive evaluation was used to analyze granite integrity. The results show: (1)The complete granite samples' micro cracks development have a general trend from high to low as the sampling depth from shallow to deep in this study area.(2)Fissures are inclined to develop among feldspar and biotite. On the contrary, fissures are more commonly developed in quartz grains.(3)Cranny ratio, average gap width, fracture number and CIA become larger near broken zones.(4)The distance of fracture zone influence on the complete granite can be more than 10.6 m. And the late hydrothermal seepage distance can be more than 50.27 m.(5)Through comprehensive evaluation, 598.8 m underground was the optimum buried depth of nuclear waste disposal repository.
2018, 26(3): 583-591.
The leakage of diesel oil in the distribution area of red clay in Guangxi has caused a certain degree of pollution to the soil. This paper studied the effect of the pore fluid of the light non-aqueous phase non-polar diesel on mechanical properties of red clay. It used 0# diesel as additives and undrained quick direct shear test method to explore the strength characteristics of red clay. It measured the variations of shear strength parameters under different moisture contents, oil contents and normal pressures. The results show that the pore fluid of the non-polar diesel has relatively small influence on the strength of red clay in the soil-water-oil system. It is affected by the water content. The shear strength, internal friction angle and cohesion of red clay decrease with the increase of water content in the same oil content. In the same water content, normal pressure influences the mode of diesel oil effect and the variation of shear strength parameters is more complicated with the increase of oil content. When the water content is 20%, as the increase of oil content, the internal friction angle and cohesion fluctuate in the opposite direction. With the same moisture content, the increase of the proportion of diesel oil leads to the increase of the shear strength parameters of red clay. SEM shows that the intervention of the pore fluid of the non-polar diesel changes the electrostatic and structural mode of the water-soil system and leads to changes in the strength of red clay. The paper established "multiscale and multistage diesel oil effect microstructure model" and clarified the microscopic mechanism of the influence of diesel pore fluid on the strength characteristics of red clay.
The leakage of diesel oil in the distribution area of red clay in Guangxi has caused a certain degree of pollution to the soil. This paper studied the effect of the pore fluid of the light non-aqueous phase non-polar diesel on mechanical properties of red clay. It used 0# diesel as additives and undrained quick direct shear test method to explore the strength characteristics of red clay. It measured the variations of shear strength parameters under different moisture contents, oil contents and normal pressures. The results show that the pore fluid of the non-polar diesel has relatively small influence on the strength of red clay in the soil-water-oil system. It is affected by the water content. The shear strength, internal friction angle and cohesion of red clay decrease with the increase of water content in the same oil content. In the same water content, normal pressure influences the mode of diesel oil effect and the variation of shear strength parameters is more complicated with the increase of oil content. When the water content is 20%, as the increase of oil content, the internal friction angle and cohesion fluctuate in the opposite direction. With the same moisture content, the increase of the proportion of diesel oil leads to the increase of the shear strength parameters of red clay. SEM shows that the intervention of the pore fluid of the non-polar diesel changes the electrostatic and structural mode of the water-soil system and leads to changes in the strength of red clay. The paper established "multiscale and multistage diesel oil effect microstructure model" and clarified the microscopic mechanism of the influence of diesel pore fluid on the strength characteristics of red clay.
2018, 26(3): 592-601.
Uncertainty characteristic of geotechnical parameters summarized from large sample data can provide an objective basis for calculating indexes in reliability analysis of geotechnical engineering and improving the precision of calculation results. Test data from nearly one thousand geotechnical specimens were collected from six railways in China. According to the cluster analysis of engineering geological units, 13 groups of large samples of soil samples were established, and the probability distribution of soil strength parameters(c, φ) and their coefficients of variation (δc, δφ) were analyzed using probability and statistics method. The ranking of soil physical-mechanical indexes affecting the variation of strength parameters was discussed using Gray Relational method. The results show that: δc and δφ generally present large variation level, and the value of δc and δφ are positive correlated. The state indices of soil such as liquidity index IL, water content ratio w, coefficient of compressibility a1-2 and natural porosity index e present more relatively influence to δc and δφ than the plasticity index IP, which reflects the soil property. The index of IL is the most important correlation factor affecting δc and δφ, and then followed by a1-2 and w respectively. The correlation between variation level and impact factors can provide prior information for judgement of geotechnical uncertainty in a limited sample case.
Uncertainty characteristic of geotechnical parameters summarized from large sample data can provide an objective basis for calculating indexes in reliability analysis of geotechnical engineering and improving the precision of calculation results. Test data from nearly one thousand geotechnical specimens were collected from six railways in China. According to the cluster analysis of engineering geological units, 13 groups of large samples of soil samples were established, and the probability distribution of soil strength parameters(c, φ) and their coefficients of variation (δc, δφ) were analyzed using probability and statistics method. The ranking of soil physical-mechanical indexes affecting the variation of strength parameters was discussed using Gray Relational method. The results show that: δc and δφ generally present large variation level, and the value of δc and δφ are positive correlated. The state indices of soil such as liquidity index IL, water content ratio w, coefficient of compressibility a1-2 and natural porosity index e present more relatively influence to δc and δφ than the plasticity index IP, which reflects the soil property. The index of IL is the most important correlation factor affecting δc and δφ, and then followed by a1-2 and w respectively. The correlation between variation level and impact factors can provide prior information for judgement of geotechnical uncertainty in a limited sample case.
2018, 26(3): 602-610.
The failure of locking section of rock bridge is closely related to the cumulative and release of energy. The conventional triaxial loading test and triaxial loading and unloading test were carried out for granite rock bridge sample using the MTS815 servo control rigid mechanical testing machine. The variation trend of energy in various stages before the loading peak can be effectively compared and analyzed under different loading conditions using the energy analysis method on the basis of the axial stress ratio. The result shows that the variation of energy characteristics before stress peak is mainly divided into compaction stage and elastic stage. When the specimen is in the compaction stage, the energy dissipation ratio increases with the initial crack closure and friction. During the elastic stage, most of the work done by the load is converted to elastic energy and stored in the specimen, and the elastic energy ratio increases substantially. As the existence of prefabricated crack, the yield stage does not appear obviously before the destruction, and the "burst type" brittle failure of rock bridge sample is presented. The total energy and elastic energy at point of stress peak will have a significant increase with the increasing of initial confining pressure. With the growth of the rock bridge's length, the absorption of total energy and limit elastic energy storage are increased gradually, the ratio of elastic energy to total energy is also increased at the point of stress peak, while the length of the rock bridge has little influence on the dissipated energy.
The failure of locking section of rock bridge is closely related to the cumulative and release of energy. The conventional triaxial loading test and triaxial loading and unloading test were carried out for granite rock bridge sample using the MTS815 servo control rigid mechanical testing machine. The variation trend of energy in various stages before the loading peak can be effectively compared and analyzed under different loading conditions using the energy analysis method on the basis of the axial stress ratio. The result shows that the variation of energy characteristics before stress peak is mainly divided into compaction stage and elastic stage. When the specimen is in the compaction stage, the energy dissipation ratio increases with the initial crack closure and friction. During the elastic stage, most of the work done by the load is converted to elastic energy and stored in the specimen, and the elastic energy ratio increases substantially. As the existence of prefabricated crack, the yield stage does not appear obviously before the destruction, and the "burst type" brittle failure of rock bridge sample is presented. The total energy and elastic energy at point of stress peak will have a significant increase with the increasing of initial confining pressure. With the growth of the rock bridge's length, the absorption of total energy and limit elastic energy storage are increased gradually, the ratio of elastic energy to total energy is also increased at the point of stress peak, while the length of the rock bridge has little influence on the dissipated energy.
2018, 26(3): 611-619.
In order to study the formation mechanism of sandstone pore weathering in Yungang Grottoes, three kinds of typical regions of sandstone concretion, sandstone matrix and sandstone matrix interface were observed by laser confocal microscopy. The crack propagation law of the concretion sandstone is analyzed, and the freezing and thawing failure model of the concretion sandstone is established. The results show that with the increase of freeze-thaw cycle, the cracks at the interface between concretion and rock matrix, at the concretion center and at the sandstone matrix appeared successively. The crack width of each region increases with the increase of freeze-thaw cycle, but there are differences in the development process of the three positions, and the cracks at the interface extend along the interface. The new cracks are produced in the concretion center, and the early cracks are extended, producing crack network. Sandstone matrix crack was developed slowly. Concretion changed the physical and mechanical properties, and significantly enhanced the heterogeneity of sandstone. The model of freeze-thaw damage of concretion sandstone revealed that the crack was generally developed at the interface. The heterogeneity of sandstone is the internal reason for the formation of pore weathering in Yungang Grottoes.
In order to study the formation mechanism of sandstone pore weathering in Yungang Grottoes, three kinds of typical regions of sandstone concretion, sandstone matrix and sandstone matrix interface were observed by laser confocal microscopy. The crack propagation law of the concretion sandstone is analyzed, and the freezing and thawing failure model of the concretion sandstone is established. The results show that with the increase of freeze-thaw cycle, the cracks at the interface between concretion and rock matrix, at the concretion center and at the sandstone matrix appeared successively. The crack width of each region increases with the increase of freeze-thaw cycle, but there are differences in the development process of the three positions, and the cracks at the interface extend along the interface. The new cracks are produced in the concretion center, and the early cracks are extended, producing crack network. Sandstone matrix crack was developed slowly. Concretion changed the physical and mechanical properties, and significantly enhanced the heterogeneity of sandstone. The model of freeze-thaw damage of concretion sandstone revealed that the crack was generally developed at the interface. The heterogeneity of sandstone is the internal reason for the formation of pore weathering in Yungang Grottoes.
2018, 26(3): 620-625.
Unsaturated hydraulic conductivity is the foundation of seepage analysis in soil. The theory system of unsaturated seepage is not mature enough, so the best method to obtain unsaturated hydraulic conductivity is measurement directly. There is not a few measurement technology of unsaturated hydraulic conductivity with long cycles and higher requirements on the environment. Chengdu clay is a kind of typical unsaturated expansive soil and has the characteristics of swelling and shrinkage. In the process of infiltration under confined condition, the expansion of the clay particles causes pore volume decrease, and lower permeability. Unsaturated infiltration experiments of Chengdu clay are quite difficult to be carried out. According to the instantaneous profile method, infiltration experiments were conducted to study the unsaturated permeability of Chengdu clay under confined condition. To do so, water contents and matric suctions were respectively monitored by EC-5 soil moisture sensors and MPS-2 dielectric water potential sensors. Synchronous measurements of moisture content and matrix suction, ensured the consistency of test conditions and avoided the influence of using other soil water characteristic curve. Considering the ceramic plate probe of MPS-2 is fragile and convenient components installed, a removable cuboid permeameter(50 cm long, 10 cm wide and 10 cm high) was custom-made. The dry density of the soil sample is 1.7 g·cm-3 and initial water content is 27%.The result shows that, during water infiltration, the unsaturated hydraulic conductivity of the sample is between 1.33×10-11 and 3.14×10-9 m·s-1, and it does not change linearly with matric suction. At the beginning of infiltration, i.e.when the matric suction is high, the hydraulic conductivity does not change significantly with the influence of expansion of clay particles. When the matric suction reduces to a certain value, the hydraulic conductivity increases rapidly. At the end of the experiment, the sample was near saturation, and presented an increasing trend of hydraulic conductivity because the discharge of gas in the sample is very slow and effective flow cross sectional area increases slowly. Derived from fitting the VG model to the experimental data, the α value was 0.048 kPa-1, the n value was 1.79 and the m value was 0.48. The conclusion can be utilized for seepage analysis of Chengdu clay area.
Unsaturated hydraulic conductivity is the foundation of seepage analysis in soil. The theory system of unsaturated seepage is not mature enough, so the best method to obtain unsaturated hydraulic conductivity is measurement directly. There is not a few measurement technology of unsaturated hydraulic conductivity with long cycles and higher requirements on the environment. Chengdu clay is a kind of typical unsaturated expansive soil and has the characteristics of swelling and shrinkage. In the process of infiltration under confined condition, the expansion of the clay particles causes pore volume decrease, and lower permeability. Unsaturated infiltration experiments of Chengdu clay are quite difficult to be carried out. According to the instantaneous profile method, infiltration experiments were conducted to study the unsaturated permeability of Chengdu clay under confined condition. To do so, water contents and matric suctions were respectively monitored by EC-5 soil moisture sensors and MPS-2 dielectric water potential sensors. Synchronous measurements of moisture content and matrix suction, ensured the consistency of test conditions and avoided the influence of using other soil water characteristic curve. Considering the ceramic plate probe of MPS-2 is fragile and convenient components installed, a removable cuboid permeameter(50 cm long, 10 cm wide and 10 cm high) was custom-made. The dry density of the soil sample is 1.7 g·cm-3 and initial water content is 27%.The result shows that, during water infiltration, the unsaturated hydraulic conductivity of the sample is between 1.33×10-11 and 3.14×10-9 m·s-1, and it does not change linearly with matric suction. At the beginning of infiltration, i.e.when the matric suction is high, the hydraulic conductivity does not change significantly with the influence of expansion of clay particles. When the matric suction reduces to a certain value, the hydraulic conductivity increases rapidly. At the end of the experiment, the sample was near saturation, and presented an increasing trend of hydraulic conductivity because the discharge of gas in the sample is very slow and effective flow cross sectional area increases slowly. Derived from fitting the VG model to the experimental data, the α value was 0.048 kPa-1, the n value was 1.79 and the m value was 0.48. The conclusion can be utilized for seepage analysis of Chengdu clay area.
2018, 26(3): 626-632.
The saturated liquefaction failure of loess occurs frequently in the loess area due to heavy rainfall and irrigation, and induces loess landslide and brings huge economic loss to the local people. The shear strength of saturated loess is influenced by many factors. So saturation experiments of remolded loess of Malan loess in Dangchuan district are carried on the modified TFB-1 type triaxial apparatus of stress and strain controlled for unsaturated soil through the combination of hydraulic saturation and back pressure saturation. The saturated remolded soil samples are conducted on consolidated undrained test under the conditions of the confining pressure of 50 kPa, 100 kPa, 200 kPa and 400 kPa respectively, and the shear rate of 0.02 mm·min-1, 0.06 mm·min-1, 0.2 mm·min-1 and 0.4 mm·min-1 respectively. The influence of confining pressure and shear rate on the shear strength of saturated loess is discussed. The results show that the shear strength of the saturated remolded loess increases first and then decreases with the increase of shear rate under the same confining pressure. The shear strength of the saturated remolded loess is higher with the increase of confining pressure under the same shear rate. The total cohesion and the effective cohesion of the remolded loess increase first and then decrease with the shear rate under the same dry density. The total internal friction angle and the effective internal friction angle increase first and then decrease with the increase of shear rate. The study can provide a basis for loess landslide prediction and scope.
The saturated liquefaction failure of loess occurs frequently in the loess area due to heavy rainfall and irrigation, and induces loess landslide and brings huge economic loss to the local people. The shear strength of saturated loess is influenced by many factors. So saturation experiments of remolded loess of Malan loess in Dangchuan district are carried on the modified TFB-1 type triaxial apparatus of stress and strain controlled for unsaturated soil through the combination of hydraulic saturation and back pressure saturation. The saturated remolded soil samples are conducted on consolidated undrained test under the conditions of the confining pressure of 50 kPa, 100 kPa, 200 kPa and 400 kPa respectively, and the shear rate of 0.02 mm·min-1, 0.06 mm·min-1, 0.2 mm·min-1 and 0.4 mm·min-1 respectively. The influence of confining pressure and shear rate on the shear strength of saturated loess is discussed. The results show that the shear strength of the saturated remolded loess increases first and then decreases with the increase of shear rate under the same confining pressure. The shear strength of the saturated remolded loess is higher with the increase of confining pressure under the same shear rate. The total cohesion and the effective cohesion of the remolded loess increase first and then decrease with the shear rate under the same dry density. The total internal friction angle and the effective internal friction angle increase first and then decrease with the increase of shear rate. The study can provide a basis for loess landslide prediction and scope.
2018, 26(3): 633-638.
The soil water characteristic curve(SWCC) is an important engineering characteristic. This paper uses the SDSWCC pressure plate apparatus and GDS saturated-unsaturated stress path triaxial testing system to test the SWCC of arolian soil in western Liaoning Province. Also, detailed studies are carried out on the different dry density, dry-wet cycle and net mean stress for their influence on the SWCC of the aeolian soil. The usual three models use a mathematical method for fitting the measured data. The test results show that at the low matrix suction stage, the three factors of dry density, dry-wet cycle and stress have significant effects on the SWCC of aeolian soil. When the soil dry density is larger, the porosity in soil is lower, the saturated water content is lower, the air-entry value is bigger, water capacity is better. Under the action of dry and wet cycle, with the increase of the cycle times, the saturated water content is increased, the water loss rate becomes larger, the intake value is reduced, and the water holding performance is weakened. But after 3 times of the dry-wet cycle, it tends to be stable. Under the action of stress, there is shrinkage deformation of the soil. The density of soil becomes greater. The impact law is similar to that of the dry density. In the high matrix suction stage, the influences of the three factors are small. Curve fitting analysis shows that Van Genuchten model has the highest fitting precision. It is better to describe and forecast SWCC of the aeolian soil in western Liaoning. The results reveal engineering and mechanical properties of the aeolian soil in western Liaoning have the same laws with soils in other regions. The results also reveal the unique features of aeolian soil. It can offer some reference and evidence to determine the aeolian soil properties. It is good for wide development of aeolian soil subgrade, bridge foundation engineering, and other projects.
The soil water characteristic curve(SWCC) is an important engineering characteristic. This paper uses the SDSWCC pressure plate apparatus and GDS saturated-unsaturated stress path triaxial testing system to test the SWCC of arolian soil in western Liaoning Province. Also, detailed studies are carried out on the different dry density, dry-wet cycle and net mean stress for their influence on the SWCC of the aeolian soil. The usual three models use a mathematical method for fitting the measured data. The test results show that at the low matrix suction stage, the three factors of dry density, dry-wet cycle and stress have significant effects on the SWCC of aeolian soil. When the soil dry density is larger, the porosity in soil is lower, the saturated water content is lower, the air-entry value is bigger, water capacity is better. Under the action of dry and wet cycle, with the increase of the cycle times, the saturated water content is increased, the water loss rate becomes larger, the intake value is reduced, and the water holding performance is weakened. But after 3 times of the dry-wet cycle, it tends to be stable. Under the action of stress, there is shrinkage deformation of the soil. The density of soil becomes greater. The impact law is similar to that of the dry density. In the high matrix suction stage, the influences of the three factors are small. Curve fitting analysis shows that Van Genuchten model has the highest fitting precision. It is better to describe and forecast SWCC of the aeolian soil in western Liaoning. The results reveal engineering and mechanical properties of the aeolian soil in western Liaoning have the same laws with soils in other regions. The results also reveal the unique features of aeolian soil. It can offer some reference and evidence to determine the aeolian soil properties. It is good for wide development of aeolian soil subgrade, bridge foundation engineering, and other projects.
2018, 26(3): 639-646.
It is well recognized that the characteristic of slow-moving landslides is controlled by creep shear behavior of its slip zone's materials. However, it is obvious that creep behavior of the slip zone's materials of the new-born and reactivated slow-moving landslides belongs to creep shear behavior under pre-peak state and at residual state, respectively. Up to now, neither certain answer has been given nor insight has been disclosed yet by professionals about the differences when the slip zone's materials experience creep shear under different states. To investigate this issue, creep behavior of the slip zones' materials of two giant slow-moving landslides in Zhouqu county of Gansu province, called the Suoertou landslide and the Xieliupo landslide respectively, were studied experimentally. Slip zones of the two landslides are composed of cohesive soil with various amount of gravel. The soils were sheared under the pre-peak state and at residual state respectively with direct shear creep test and that following reversed direct shear. It was found that the soils experienced various stages of creep under both states, and that the critical shear stresses at each creep stage linearly increased with both normal and shear stresses, and gravel content as well. However, there was no second creep stage when the soil was re-sheared at the residual state, while the soil experienced a significant second creep stage under the pre-peak state. Moreover, it was observed that for the soil experienced creep shear under pre-peak state its critical shear stress at the tertiary creep was greater than that at the residual state. Significantly, under pre-peak state, the soils' critical shear stress at the tertiary creep was much less than its peak strength and greater than its residual strength, whereas at the residual state, its critical shear stress at the tertiary creep was very slightly greater than the residual strength. It was further discussed that for the cohesive soil mechanism behind the different creep behavior of the cohesive soil under different state should be largely attributed to its structures, specifically no structural defect under pre-peak state versus occurrence of well-defined structural defect at the residual state. These findings give an important implication that the slopes composed of cohesive soils may be more prone to occur the reactivated slow-moving landslides than the new-born slow-moving landslides.
It is well recognized that the characteristic of slow-moving landslides is controlled by creep shear behavior of its slip zone's materials. However, it is obvious that creep behavior of the slip zone's materials of the new-born and reactivated slow-moving landslides belongs to creep shear behavior under pre-peak state and at residual state, respectively. Up to now, neither certain answer has been given nor insight has been disclosed yet by professionals about the differences when the slip zone's materials experience creep shear under different states. To investigate this issue, creep behavior of the slip zones' materials of two giant slow-moving landslides in Zhouqu county of Gansu province, called the Suoertou landslide and the Xieliupo landslide respectively, were studied experimentally. Slip zones of the two landslides are composed of cohesive soil with various amount of gravel. The soils were sheared under the pre-peak state and at residual state respectively with direct shear creep test and that following reversed direct shear. It was found that the soils experienced various stages of creep under both states, and that the critical shear stresses at each creep stage linearly increased with both normal and shear stresses, and gravel content as well. However, there was no second creep stage when the soil was re-sheared at the residual state, while the soil experienced a significant second creep stage under the pre-peak state. Moreover, it was observed that for the soil experienced creep shear under pre-peak state its critical shear stress at the tertiary creep was greater than that at the residual state. Significantly, under pre-peak state, the soils' critical shear stress at the tertiary creep was much less than its peak strength and greater than its residual strength, whereas at the residual state, its critical shear stress at the tertiary creep was very slightly greater than the residual strength. It was further discussed that for the cohesive soil mechanism behind the different creep behavior of the cohesive soil under different state should be largely attributed to its structures, specifically no structural defect under pre-peak state versus occurrence of well-defined structural defect at the residual state. These findings give an important implication that the slopes composed of cohesive soils may be more prone to occur the reactivated slow-moving landslides than the new-born slow-moving landslides.
2018, 26(3): 647-654.
Daguangbao landslide is the largest landslide triggered by the 2008 Wenchuan earthquake.The sliding zone formed in a bedding fault which was composed of the material of mylonite and mud.The groundwater could be found flowing out.To analyze the process of earthquake dynamic characteristics of the saturated fault material, a series of dynamic triaxial tests were conducted on the three samples C1, C2 and C3 which were taken from an exploratory tunnel in the fault.The results show that:(1)Under dynamic load(40 kPa, 60 kPa, and 80 kPa), C1 and C2 pore pressure shows slow growth, dynamic pore pressure is still far less than the confining pressure when achieving strain 5%, and the samples have no liquefactive.C3 dynamic pore pressure is growing rapidly.When strain achieves 5%, dynamic pore pressure is equal to the confining pressure, and the sample is liquefied.(2)The dynamic strength and strain relations of sample are close.With the increase of strain, under the same cycles C3 dynamic shear stress decreases obviously, while C1 and C2 have modest increase.(3)When the dynamic strain is certain, C3 dynamic stress and the elastic modulus are the biggest, and its dynamic damping ratio is the least.C2 dynamic stress and the elastic modulus are the least, and its dynamic damping ratio is the largest.It can be concluded that the fault material might be liquefied during the 2008 Wenchuan earthquake resulted in rapidly decreasing of the shear strength of the bedding fault.The Daguangbao landslide might be initiated suddenly.
Daguangbao landslide is the largest landslide triggered by the 2008 Wenchuan earthquake.The sliding zone formed in a bedding fault which was composed of the material of mylonite and mud.The groundwater could be found flowing out.To analyze the process of earthquake dynamic characteristics of the saturated fault material, a series of dynamic triaxial tests were conducted on the three samples C1, C2 and C3 which were taken from an exploratory tunnel in the fault.The results show that:(1)Under dynamic load(40 kPa, 60 kPa, and 80 kPa), C1 and C2 pore pressure shows slow growth, dynamic pore pressure is still far less than the confining pressure when achieving strain 5%, and the samples have no liquefactive.C3 dynamic pore pressure is growing rapidly.When strain achieves 5%, dynamic pore pressure is equal to the confining pressure, and the sample is liquefied.(2)The dynamic strength and strain relations of sample are close.With the increase of strain, under the same cycles C3 dynamic shear stress decreases obviously, while C1 and C2 have modest increase.(3)When the dynamic strain is certain, C3 dynamic stress and the elastic modulus are the biggest, and its dynamic damping ratio is the least.C2 dynamic stress and the elastic modulus are the least, and its dynamic damping ratio is the largest.It can be concluded that the fault material might be liquefied during the 2008 Wenchuan earthquake resulted in rapidly decreasing of the shear strength of the bedding fault.The Daguangbao landslide might be initiated suddenly.
2018, 26(3): 655-662.
This paper studies the influence of rainfall on the slope stability of the ice accumulation in the upper reaches of Minjiang River.It takes the Huanxipo as an example.Based on the field rainfall simulation tests, a series of tests including permeability, water content and shear strength are carried out.The coupling of SEEP/W module and SLOPE/W module are used to analyze the influence of rainfall intensity and rainfall duration on the slope stability of this type of ice water accumulation.Research results show the follows.(1)The content of clay minerals in the ice accumulation body is up to 50%, and the content can reach more than 85% after saturation.The breccia soil has the characteristics of porosity development and poor gradation.The double loop permeability test is in good agreement with the experimental results.The permeability coefficient of the breccia is determined comprehensively as 1.315×10-3cm·s-1, belongs to medium to weak permeable matrix.(2)In the natural state, the shear strength of the breccia soil is higher.Water content has obvious effect on shear strength.From natural to saturation, the decay rate of cohesion c is obviously higher than that of internal friction angle φ.The cohesion c can be reduced 64.4%, while the internal friction angle is only decreased by 22.5%.(3)Under certain rainfall intensity, the slope stability coefficient decreases with the increase of rainfall duration.When the duration of rainfall is the same, the greater the rainfall intensity, the greater the slope stability decreases, but the stability of the steep declines in the timing of the inflection point in advance.
This paper studies the influence of rainfall on the slope stability of the ice accumulation in the upper reaches of Minjiang River.It takes the Huanxipo as an example.Based on the field rainfall simulation tests, a series of tests including permeability, water content and shear strength are carried out.The coupling of SEEP/W module and SLOPE/W module are used to analyze the influence of rainfall intensity and rainfall duration on the slope stability of this type of ice water accumulation.Research results show the follows.(1)The content of clay minerals in the ice accumulation body is up to 50%, and the content can reach more than 85% after saturation.The breccia soil has the characteristics of porosity development and poor gradation.The double loop permeability test is in good agreement with the experimental results.The permeability coefficient of the breccia is determined comprehensively as 1.315×10-3cm·s-1, belongs to medium to weak permeable matrix.(2)In the natural state, the shear strength of the breccia soil is higher.Water content has obvious effect on shear strength.From natural to saturation, the decay rate of cohesion c is obviously higher than that of internal friction angle φ.The cohesion c can be reduced 64.4%, while the internal friction angle is only decreased by 22.5%.(3)Under certain rainfall intensity, the slope stability coefficient decreases with the increase of rainfall duration.When the duration of rainfall is the same, the greater the rainfall intensity, the greater the slope stability decreases, but the stability of the steep declines in the timing of the inflection point in advance.
2018, 26(3): 673-683.
In the eastern margin of Tibetan Plateau, the complicated geomorphology and strong tectonic activities bring frequent and destructive geohazards.Especially in recent years, earthquakes and human engineering activities have seriously increased geohazard intensity.So far, these unwelcome geohazards have caused great harms to national major projects, regional development, life and property and public safety.This paper firstly presents a general overview of the forming background and development characteristics of geohazards in the Eastern Margin of Tibetan Plateau.Then, the relationship between the geohazard distribution and causative factors was analyzed.Especially the control effect of causative factors on geohazard distribution was discussed through comparatively analyzing the differences of geohazard density of different regions.Finally, sensitivity of the causative factors of geohazards in the eastern margin of Tibetan Plateau was examined in depth.The study results show that nine factors have higher geohazard sensitivity.They are terrain slope, terrain relief, slope shape, annual 24 h maximum precipitation, river density, distance to fault, ground peak acceleration, engineering geological group and human activity intensity.That is to say, they are more prone to geohazard occurrence.However, the slope aspect and annual precipitation have lower geohazard sensitivity and fewer control effect to geohazard occurrence.Moreover, the terrain slope of 25°~40° and terrain relief of 120~160 m·km-2 have the highest geohazard sensitivity.The geohazard sensitivity of convex slope is higher than that of concave slope.The heavy rainfall with short duration(24 h maximum rainfall) has a higher control effect to geohazard occurrence.With the increase of river density, the geohazard intensity and density shows a corresponding increasing trend.With the decrease of distance to fault or the increase of ground peak acceleration, the geohazard intensity and density all shows an accompanying increasing trend.The study results can deepen the understanding of forming background of geohazards and also provide significant reference for establishing geohazard evaluation index system in the eastern margin of Tibetan Plateau.
In the eastern margin of Tibetan Plateau, the complicated geomorphology and strong tectonic activities bring frequent and destructive geohazards.Especially in recent years, earthquakes and human engineering activities have seriously increased geohazard intensity.So far, these unwelcome geohazards have caused great harms to national major projects, regional development, life and property and public safety.This paper firstly presents a general overview of the forming background and development characteristics of geohazards in the Eastern Margin of Tibetan Plateau.Then, the relationship between the geohazard distribution and causative factors was analyzed.Especially the control effect of causative factors on geohazard distribution was discussed through comparatively analyzing the differences of geohazard density of different regions.Finally, sensitivity of the causative factors of geohazards in the eastern margin of Tibetan Plateau was examined in depth.The study results show that nine factors have higher geohazard sensitivity.They are terrain slope, terrain relief, slope shape, annual 24 h maximum precipitation, river density, distance to fault, ground peak acceleration, engineering geological group and human activity intensity.That is to say, they are more prone to geohazard occurrence.However, the slope aspect and annual precipitation have lower geohazard sensitivity and fewer control effect to geohazard occurrence.Moreover, the terrain slope of 25°~40° and terrain relief of 120~160 m·km-2 have the highest geohazard sensitivity.The geohazard sensitivity of convex slope is higher than that of concave slope.The heavy rainfall with short duration(24 h maximum rainfall) has a higher control effect to geohazard occurrence.With the increase of river density, the geohazard intensity and density shows a corresponding increasing trend.With the decrease of distance to fault or the increase of ground peak acceleration, the geohazard intensity and density all shows an accompanying increasing trend.The study results can deepen the understanding of forming background of geohazards and also provide significant reference for establishing geohazard evaluation index system in the eastern margin of Tibetan Plateau.
2018, 26(3): 684-693.
Loess landslides induced by excavation occur frequently.The loess area of the construction project had a great threat by such landslides.They seriously hindered the construction of various infrastructures.To promote and understand the mechanical response, the mechanism and deformation and failure process of loess slope during excavation unloading process is a prerequisite and important basis to this type of landslide prevention.On this basis, this paper carries out the conventional triaxial test and the triaxial shear test of saturated loess under unloading path to emphatically analyze the mechanical response and deformation characteristics of saturated loess under two kinds of stress paths, and studies the formation mechanism of Shangwazi landslide in Lanzhou.The results show the following.(1)Compared to the general conditions, under lateral unloading, pore pressure increase is low.But unloading caused lateral pressure is greatly reduced.So pore pressure then rapidly grows and effective stress decreases, which is more unfavourable to slope stability.(2)Under the conditions of lateral unloading, the strain required to reach the peak intensity is smaller(1% ~2%), which indicates that the slope is more destructible under unloading conditions.(3)Two saturated soils under different stress paths on shear strength parameters are significantly different, compared with standard triaxial shear test, vacuum under triaxial shear, c' decreased 62.32% ~76.92%and close to zero, effective friction angle φ' value 26.92% ~29.77%.(4)Using FLAC-3D to simulate the upper embankment landslide, the results of lateral unloading triaxial shear test are more in line with the real stress path of soil, which proves that the failure mode of Shangwazi landslide is a type of "backward progressive".
Loess landslides induced by excavation occur frequently.The loess area of the construction project had a great threat by such landslides.They seriously hindered the construction of various infrastructures.To promote and understand the mechanical response, the mechanism and deformation and failure process of loess slope during excavation unloading process is a prerequisite and important basis to this type of landslide prevention.On this basis, this paper carries out the conventional triaxial test and the triaxial shear test of saturated loess under unloading path to emphatically analyze the mechanical response and deformation characteristics of saturated loess under two kinds of stress paths, and studies the formation mechanism of Shangwazi landslide in Lanzhou.The results show the following.(1)Compared to the general conditions, under lateral unloading, pore pressure increase is low.But unloading caused lateral pressure is greatly reduced.So pore pressure then rapidly grows and effective stress decreases, which is more unfavourable to slope stability.(2)Under the conditions of lateral unloading, the strain required to reach the peak intensity is smaller(1% ~2%), which indicates that the slope is more destructible under unloading conditions.(3)Two saturated soils under different stress paths on shear strength parameters are significantly different, compared with standard triaxial shear test, vacuum under triaxial shear, c' decreased 62.32% ~76.92%and close to zero, effective friction angle φ' value 26.92% ~29.77%.(4)Using FLAC-3D to simulate the upper embankment landslide, the results of lateral unloading triaxial shear test are more in line with the real stress path of soil, which proves that the failure mode of Shangwazi landslide is a type of "backward progressive".
2018, 26(3): 694-702.
The study of deformation law, influence factors and failure conditions of reservoir landslide in gently under-dip slopes is carried out by physical modeling.The Xiang Jiaping landslide in the Three Gorges Reservoir region is used as a case example.Based on the similarity model, considering the factors such as water level fluctuation and rainfall(including flood season), this paper analyzes the deformation characteristics and laws of landslide with monitoring the spatiotemporal evolution of displacement, soil pressure and pore water pressure.The results show that the reservoir level rises and the front edge of the slope is continuously submerged, resulting in loosening of the soil structure and slipping in the leading edge.With decreases of reservoir water, change of displacement, soil pressure and pore water pressure were not monitored in the middle and trailing edge of the slope, but the failure of the leading edge extended backward to the middle of the slope.The independent change of reservoir water level only affects the water level of the slide bed, but when it is coupled with the bedrock fissure water of the trailing edge, the pressure of the bed can be changed.During flooding season, the soil pressure and the pore water pressure have little change, and there is no displacement deformation, because of low rainfall intensity.Under the heavy rain, the soil pressure accumulates and releases, which leads to the deformation of the middle and trailing edge of the slope.When the reservoir water level drops, the heavy rainfall would change the original stress state of the slope, and the slope would produce small deformation.Under extreme conditions, the coupling of decline of reservoir water, rainfall and the trailing edge water level can result in deformation of the slope, which makes the failure possibility of Xiang Jiaping landslide larger.The results can provide scientific basis for geological disaster prevention and mitigation in reservoir area.
The study of deformation law, influence factors and failure conditions of reservoir landslide in gently under-dip slopes is carried out by physical modeling.The Xiang Jiaping landslide in the Three Gorges Reservoir region is used as a case example.Based on the similarity model, considering the factors such as water level fluctuation and rainfall(including flood season), this paper analyzes the deformation characteristics and laws of landslide with monitoring the spatiotemporal evolution of displacement, soil pressure and pore water pressure.The results show that the reservoir level rises and the front edge of the slope is continuously submerged, resulting in loosening of the soil structure and slipping in the leading edge.With decreases of reservoir water, change of displacement, soil pressure and pore water pressure were not monitored in the middle and trailing edge of the slope, but the failure of the leading edge extended backward to the middle of the slope.The independent change of reservoir water level only affects the water level of the slide bed, but when it is coupled with the bedrock fissure water of the trailing edge, the pressure of the bed can be changed.During flooding season, the soil pressure and the pore water pressure have little change, and there is no displacement deformation, because of low rainfall intensity.Under the heavy rain, the soil pressure accumulates and releases, which leads to the deformation of the middle and trailing edge of the slope.When the reservoir water level drops, the heavy rainfall would change the original stress state of the slope, and the slope would produce small deformation.Under extreme conditions, the coupling of decline of reservoir water, rainfall and the trailing edge water level can result in deformation of the slope, which makes the failure possibility of Xiang Jiaping landslide larger.The results can provide scientific basis for geological disaster prevention and mitigation in reservoir area.
2018, 26(3): 703-710.
Based on the analysis of rainfall data, this paper summarizes some key technologies of debris flow automatic real-time monitoring and early warning, and presents a solution and a system for real-time monitoring and early warning of debris flow based on rainfall process.Rainfall intensity and cumulative rainfall are the main parameters for the early warning of debris flow.Methods to correctly identify a rainfall process are of great significance for improving the accuracy of debris flow monitoring and early warning.Combined with the characteristics of the rainfall data, and the criterion of the classification of a rainfall process presented by Jan, the automatic recognition of the rainfall process is realized with the database technique.Due to the influence of the rain gauge operating mode, the time interval of the original data is random.It cannot be directly used for the calculation of the early warning model.Therefore, the rainfall data need to be treated at equal intervals.In the process of early warning, the task to achieve early warning process without manual intervention completely automatic, real-time and stable operation has been a difficult problem of early warning work.This solution introduces the "system services" technology.The entire early warning system is as a system-level background service running on the server to ensure the stable operation of the whole process of early warning and to achieve a true sense of the automatic real-time process of monitoring and early warning of debris flow.The results of this study are applied to the monitoring and early warning of debris flow in Zoumaling gully, which successfully predicted the debris flow events in July 8, 2013.
Based on the analysis of rainfall data, this paper summarizes some key technologies of debris flow automatic real-time monitoring and early warning, and presents a solution and a system for real-time monitoring and early warning of debris flow based on rainfall process.Rainfall intensity and cumulative rainfall are the main parameters for the early warning of debris flow.Methods to correctly identify a rainfall process are of great significance for improving the accuracy of debris flow monitoring and early warning.Combined with the characteristics of the rainfall data, and the criterion of the classification of a rainfall process presented by Jan, the automatic recognition of the rainfall process is realized with the database technique.Due to the influence of the rain gauge operating mode, the time interval of the original data is random.It cannot be directly used for the calculation of the early warning model.Therefore, the rainfall data need to be treated at equal intervals.In the process of early warning, the task to achieve early warning process without manual intervention completely automatic, real-time and stable operation has been a difficult problem of early warning work.This solution introduces the "system services" technology.The entire early warning system is as a system-level background service running on the server to ensure the stable operation of the whole process of early warning and to achieve a true sense of the automatic real-time process of monitoring and early warning of debris flow.The results of this study are applied to the monitoring and early warning of debris flow in Zoumaling gully, which successfully predicted the debris flow events in July 8, 2013.
2018, 26(3): 711-719.
Risk assessment of geo-hazards has important significance for geo-hazards prevention and management.Suide city is located in the hinterland of North Shaanxi Loess Plateau.In this field, crisscross gulleys, steep topography, fierce landform incision, and rainfall caused many geological hazards.This paper tries to assess the risk of geo-hazards in Suide city.The urban slope area is divided into 1050 slope units.The stability of each slope unit under different water content conditions is calculated.The hazard of the slope units are assessed by combining the soil moisture content monitoring data.On this basis, the elements at risk in the slope units are identified using 1:10000 remote sensing data, and it's vulnerability is analyzed and it's consequence is assessed.Risk assessment of geo-hazards is completed on the basis of slope unit according to the results of the assessment of hazards and consequences in Suide city and the surrounding area.The assessment results show that the very high risk area is 2.27 km2, including 106 slope units.The high risk area is 3.03 km2, including 114 slope units.The medium risk area is 10.40 km2, including 362 slope units.The low risk area is 12.81 km2, including 468 slope units
Risk assessment of geo-hazards has important significance for geo-hazards prevention and management.Suide city is located in the hinterland of North Shaanxi Loess Plateau.In this field, crisscross gulleys, steep topography, fierce landform incision, and rainfall caused many geological hazards.This paper tries to assess the risk of geo-hazards in Suide city.The urban slope area is divided into 1050 slope units.The stability of each slope unit under different water content conditions is calculated.The hazard of the slope units are assessed by combining the soil moisture content monitoring data.On this basis, the elements at risk in the slope units are identified using 1:10000 remote sensing data, and it's vulnerability is analyzed and it's consequence is assessed.Risk assessment of geo-hazards is completed on the basis of slope unit according to the results of the assessment of hazards and consequences in Suide city and the surrounding area.The assessment results show that the very high risk area is 2.27 km2, including 106 slope units.The high risk area is 3.03 km2, including 114 slope units.The medium risk area is 10.40 km2, including 362 slope units.The low risk area is 12.81 km2, including 468 slope units
2018, 26(3): 720-731.
Yuanjiang County is located in the middle of the Ailaoshan fold belt and Red River fault, The geological structure is complex and the engineering geological conditions are fragile.It is one of the most developed areas of geological disasters in Yunnan Province.The authors elaborate the distribution law of geological disasters from the space side.(1)The difference is obviously of spatial distribution of geological disasters in the study area.The characteristics of spatial distribution are not uniform.The concentrated distribution areas are on both sides of the Red River.(2)The geological disasters are mostly developed in the terrains of linear and stepped slope types, slope dip directions of 45°~135°, slope dip angles of 20°~50°, and elevation of l500 to 2000 m.(3)The number of geological disasters is the largest in the Ailao Mountain area of the western part to study area.The density of geological disasters is the largest in the south of the Red River.(4)The control effect of geological disasters is obvious the main control structure in the study area.The geological disasters are very developed in the Yuanjiang county.The findings can provide geological basis and reference for disaster in the junction of the fault zone or at the change of main rupture.The study on the spatial distribution of prevention and mitigation can guide the local geological disaster management and relocation site effectively.
Yuanjiang County is located in the middle of the Ailaoshan fold belt and Red River fault, The geological structure is complex and the engineering geological conditions are fragile.It is one of the most developed areas of geological disasters in Yunnan Province.The authors elaborate the distribution law of geological disasters from the space side.(1)The difference is obviously of spatial distribution of geological disasters in the study area.The characteristics of spatial distribution are not uniform.The concentrated distribution areas are on both sides of the Red River.(2)The geological disasters are mostly developed in the terrains of linear and stepped slope types, slope dip directions of 45°~135°, slope dip angles of 20°~50°, and elevation of l500 to 2000 m.(3)The number of geological disasters is the largest in the Ailao Mountain area of the western part to study area.The density of geological disasters is the largest in the south of the Red River.(4)The control effect of geological disasters is obvious the main control structure in the study area.The geological disasters are very developed in the Yuanjiang county.The findings can provide geological basis and reference for disaster in the junction of the fault zone or at the change of main rupture.The study on the spatial distribution of prevention and mitigation can guide the local geological disaster management and relocation site effectively.
2018, 26(3): 732-740.
Slope surface erosion due to rainfall is liable to cause soil erosion and landslide hazard, which is a difficult problem.This paper takes a loess slope as an example and puts forward a comprehensive protection method of ecological slope based on the concept of water reducing and drainage.In order to study on soil erosion law and evolution mechanism of slope under different factors, the simulation experiments were carried out with the self-developed slope rainfall simulator.It considers modifier content, lattice protective form, intensity, duration, aspect ratio on the effect of protection.Test results show that the loess slope surface erosion can be summarized as splash erosion, sheet erosion, gully erosion and landslides.With the increase of the modifier content, the corrosion resistance of the improved slope is enhanced, and the optimal dosage of the modifier is 3‰.Compared with the plain loess slope, rainfall intensity has little influence on improved slope with 3‰modifier.With the increase of rainfall duration, the improvement effect of the modifier is more obvious.Modifier and frame as well as their comprehensive utilization can effectively improve the slope resistance to rainfall erosion.When the slope gradient increases to a certain extent, the slope is prone to collapse suddenly due to the rainfall erosion, which needs to be emphasized.The modifier mainly makes the soil particles more compacted by flocculation, so as to improve the water holding capacity and corrosion resistance of loess.
Slope surface erosion due to rainfall is liable to cause soil erosion and landslide hazard, which is a difficult problem.This paper takes a loess slope as an example and puts forward a comprehensive protection method of ecological slope based on the concept of water reducing and drainage.In order to study on soil erosion law and evolution mechanism of slope under different factors, the simulation experiments were carried out with the self-developed slope rainfall simulator.It considers modifier content, lattice protective form, intensity, duration, aspect ratio on the effect of protection.Test results show that the loess slope surface erosion can be summarized as splash erosion, sheet erosion, gully erosion and landslides.With the increase of the modifier content, the corrosion resistance of the improved slope is enhanced, and the optimal dosage of the modifier is 3‰.Compared with the plain loess slope, rainfall intensity has little influence on improved slope with 3‰modifier.With the increase of rainfall duration, the improvement effect of the modifier is more obvious.Modifier and frame as well as their comprehensive utilization can effectively improve the slope resistance to rainfall erosion.When the slope gradient increases to a certain extent, the slope is prone to collapse suddenly due to the rainfall erosion, which needs to be emphasized.The modifier mainly makes the soil particles more compacted by flocculation, so as to improve the water holding capacity and corrosion resistance of loess.
2018, 26(3): 741-748.
The paper studies characteristic of spalling disease of loess slope caused by salification erosion through field investigation and indoor water content and soluble salt tests. The results show that the salification erosion spalling disease can be divided into strip-shape, sheet-shape and cavity-shape spalling on the basis of spalling shape. Furthermore, the salification erosion spalling disease can further be divided into Q3 loess, Q2 loess, paleosol layer and artificial compacted loess spalling according to the geological conditions. The water content of loess sample increases with the increment of vertical depth from slope surface. With the increase of vertical depth from slope surface, the total salt content decreases greatly and reaches a stable value soon. The CO32- and HCO3- ion contents have no obvious change rule with increasing vertical depth. With the increase of vertical depth, the Cl- and SO42- ion contents decrease greatly and reaches a stable value soon. The K+, Mg2+ and Ca2+ ion contents have no obvious change rule with increasing vertical depth. With the increase of vertical depth, the Na+ion content decreases greatly and reaches a stable value eventually. The SO42- and Cl- ion contents are higher in the anions with the Na+ ion content highest in the cations. Therefore, Na2SO4 and NaCl are the main components of soluble salt in soil on the surface of loess slope. Furthermore, Na2SO4 and NaCl repeatedly dissolve and crystallize under condition of climate change, which causes the spalling disease of loess slope.
The paper studies characteristic of spalling disease of loess slope caused by salification erosion through field investigation and indoor water content and soluble salt tests. The results show that the salification erosion spalling disease can be divided into strip-shape, sheet-shape and cavity-shape spalling on the basis of spalling shape. Furthermore, the salification erosion spalling disease can further be divided into Q3 loess, Q2 loess, paleosol layer and artificial compacted loess spalling according to the geological conditions. The water content of loess sample increases with the increment of vertical depth from slope surface. With the increase of vertical depth from slope surface, the total salt content decreases greatly and reaches a stable value soon. The CO32- and HCO3- ion contents have no obvious change rule with increasing vertical depth. With the increase of vertical depth, the Cl- and SO42- ion contents decrease greatly and reaches a stable value soon. The K+, Mg2+ and Ca2+ ion contents have no obvious change rule with increasing vertical depth. With the increase of vertical depth, the Na+ion content decreases greatly and reaches a stable value eventually. The SO42- and Cl- ion contents are higher in the anions with the Na+ ion content highest in the cations. Therefore, Na2SO4 and NaCl are the main components of soluble salt in soil on the surface of loess slope. Furthermore, Na2SO4 and NaCl repeatedly dissolve and crystallize under condition of climate change, which causes the spalling disease of loess slope.
2018, 26(3): 749-757.
Relying on the counter-tilt slope of the right bank of dam site of Zha La hydropower station in Tibet, a slope physical model is established based on geological knowledge and similarity theory. A method of staged excavation is adopted to simulate the incised action of a valley, and the evolution process of toppling deformation of a toppling rock slope is studied. The development process of deformation and fracture after excavation shows that: The toppling deformation modes of counter-tilt slope are initial unloading rebound deformation, long-term gravity bending(fracture) deformation and creep deformation in the later stage. Through the analysis of the law of displacement, deformation rate and deformation acceleration: The toppling deformation process of counter-tilt slope can be divided into 3 evolution stages(the stage of toppling initiation, the stage of steady deformation and the stage of rapid destabilization) according to the deformation acceleration a. Each stage corresponds to the deformation characteristics of attenuation creep, steady creep and accelerated creep respectively. On this basis, the deformation acceleration a is used as the criterion of slope stability, and try to use a(deformation acceleration)≥a2(upper limit of steady-state creep) as a slope instability prediction criterion.
Relying on the counter-tilt slope of the right bank of dam site of Zha La hydropower station in Tibet, a slope physical model is established based on geological knowledge and similarity theory. A method of staged excavation is adopted to simulate the incised action of a valley, and the evolution process of toppling deformation of a toppling rock slope is studied. The development process of deformation and fracture after excavation shows that: The toppling deformation modes of counter-tilt slope are initial unloading rebound deformation, long-term gravity bending(fracture) deformation and creep deformation in the later stage. Through the analysis of the law of displacement, deformation rate and deformation acceleration: The toppling deformation process of counter-tilt slope can be divided into 3 evolution stages(the stage of toppling initiation, the stage of steady deformation and the stage of rapid destabilization) according to the deformation acceleration a. Each stage corresponds to the deformation characteristics of attenuation creep, steady creep and accelerated creep respectively. On this basis, the deformation acceleration a is used as the criterion of slope stability, and try to use a(deformation acceleration)≥a2(upper limit of steady-state creep) as a slope instability prediction criterion.
2018, 26(3): 758-766.
Based on the differences in pore structure characteristics between marine and continental shale in China, Weiyuan marine shale(1#), Jiao Shiba marine shale(2#), Yaoqu tuff(4#) and Yaoqu continental shale(5# and 6#)were selected to study the pore structure characteristics using cold field emission scanning microscopy(FE-SEM) and nuclear magnetic resonance(NMR). Nuclear magnetic resonance cryoporometry(NMRC)was employed to represent nano-scale pore structure. This method can be extended to microns measurement combining nuclear magnetic resonance relaxation analysis to detect in detail the pore structure of shales under the different aperture scales. The smaller the test temperature gradient is, the finer the result of pore distribution is. Test results show decreasing porosity from sample 5#, 2#, 6#, and 1# to sample 4#. NMRC, low field nuclear magnetic resonance(LFNMR), mercury intrusion porosimetry(MIP) and gas adsorption(GA)methods show good agreement of pore size distribution in their respective scope of application. Hence, the pore structure of the reservoir shale can be evaluated more accurately by combining NMRC, LFNMR with GA and MIP. Thus the nano-pores of continental shale(5# Yaoqu shale) are clearly better developed and will more likely have a higher commercial exploitation value than those of marine shale.
Based on the differences in pore structure characteristics between marine and continental shale in China, Weiyuan marine shale(1#), Jiao Shiba marine shale(2#), Yaoqu tuff(4#) and Yaoqu continental shale(5# and 6#)were selected to study the pore structure characteristics using cold field emission scanning microscopy(FE-SEM) and nuclear magnetic resonance(NMR). Nuclear magnetic resonance cryoporometry(NMRC)was employed to represent nano-scale pore structure. This method can be extended to microns measurement combining nuclear magnetic resonance relaxation analysis to detect in detail the pore structure of shales under the different aperture scales. The smaller the test temperature gradient is, the finer the result of pore distribution is. Test results show decreasing porosity from sample 5#, 2#, 6#, and 1# to sample 4#. NMRC, low field nuclear magnetic resonance(LFNMR), mercury intrusion porosimetry(MIP) and gas adsorption(GA)methods show good agreement of pore size distribution in their respective scope of application. Hence, the pore structure of the reservoir shale can be evaluated more accurately by combining NMRC, LFNMR with GA and MIP. Thus the nano-pores of continental shale(5# Yaoqu shale) are clearly better developed and will more likely have a higher commercial exploitation value than those of marine shale.
2018, 26(3): 767-775.
Based on the A. Nermoen's physics experiment, this article simulates the formation of shallow gas spilling. Different from the Euler-Euler method, this article uses a new discrete particle simulation method MP-PIC model that is based on Euler-Lagrange method. This article revealed the mechanism of overpressure gas release and the change and regular of velocity and pressure in the formation process of the shallow gas. The simulation results show that the fluidization of particles and the formation, movement and spray of bubbles are consistent with the experimental phenomenon. The correlation coefficient between the calculated results and the experimental data is 0.94, which is a good correlation. The critical fluidization velocity and pressure are positively correlated with the height of soil. The critical fluidization pressure is close to the experimental results. However, because of some other external forces which are not considered, such as the force of Magnus force, the critical fluidization velocity is lower than that of the experiment. The model can deal with particles of arbitrary size, which is suitable for enormous particle quantity and tightly coupling the interaction between liquid and solid. Good applicability and High accuracy of this model provide convenience for numerical simulation.
Based on the A. Nermoen's physics experiment, this article simulates the formation of shallow gas spilling. Different from the Euler-Euler method, this article uses a new discrete particle simulation method MP-PIC model that is based on Euler-Lagrange method. This article revealed the mechanism of overpressure gas release and the change and regular of velocity and pressure in the formation process of the shallow gas. The simulation results show that the fluidization of particles and the formation, movement and spray of bubbles are consistent with the experimental phenomenon. The correlation coefficient between the calculated results and the experimental data is 0.94, which is a good correlation. The critical fluidization velocity and pressure are positively correlated with the height of soil. The critical fluidization pressure is close to the experimental results. However, because of some other external forces which are not considered, such as the force of Magnus force, the critical fluidization velocity is lower than that of the experiment. The model can deal with particles of arbitrary size, which is suitable for enormous particle quantity and tightly coupling the interaction between liquid and solid. Good applicability and High accuracy of this model provide convenience for numerical simulation.
2018, 26(3): 776-784.
Recently, fibre reinforced polymer(FRP)materials are gaining increasing popularity in the field of geotechnical anchoring owing to their superior characteristics such as the resistance to corrosion, high strength-to-weight ratio to conventional steel materials. FRP represents the future development direction of geotechnical anchorage material, but now its research results are relatively scattered. Based on the mechanical properties of the material, FRP has many advantages such as high tensile strength, long-term performance and good fatigue properties. However, there are several drawbacks for FRP to be considered in the anchorage design of rock and soil. They include poor bending and shear strength, as well as brittle failure. The failure modes of FRP anchorage system are summarized, which shows that the failure of anchorage system is usually caused by coupling effect of multiple failure modes. The key issues for the study of grouted FRP anchoring are summarized and include the influence factors of bond behavior between bolt and anchorage medium, calculation model for bond stresses, the bond-slip relationship and description of the stress distribution of the anchoring interface. Finally, this paper gives some examples in engineering application of FRP bolt at home and abroad, and also points out its further research direction.
Recently, fibre reinforced polymer(FRP)materials are gaining increasing popularity in the field of geotechnical anchoring owing to their superior characteristics such as the resistance to corrosion, high strength-to-weight ratio to conventional steel materials. FRP represents the future development direction of geotechnical anchorage material, but now its research results are relatively scattered. Based on the mechanical properties of the material, FRP has many advantages such as high tensile strength, long-term performance and good fatigue properties. However, there are several drawbacks for FRP to be considered in the anchorage design of rock and soil. They include poor bending and shear strength, as well as brittle failure. The failure modes of FRP anchorage system are summarized, which shows that the failure of anchorage system is usually caused by coupling effect of multiple failure modes. The key issues for the study of grouted FRP anchoring are summarized and include the influence factors of bond behavior between bolt and anchorage medium, calculation model for bond stresses, the bond-slip relationship and description of the stress distribution of the anchoring interface. Finally, this paper gives some examples in engineering application of FRP bolt at home and abroad, and also points out its further research direction.
2018, 26(3): 785-793.
As underground utility tunnels are buried at shallow depths, the effects of Rayleigh waves should be considered in relevant seismic analysis. To investigate the dynamic response characteristics of utility tunnels subjected to Rayleigh waves and bottom earthquake acceleration, a three dimensional(3D) finite element(FE)numerical model for double-cabin utility tunnels was built. An advanced constitutive model characterized by hysteresis loops(HSS model) was used to simulate the soil mass. Rayleigh waves were generated by multiple pulse loads at the boundary. Upland waves, Kobe waves and Taft waves were applied horizontally at the bottom of the model. The results were compared with those derived from the conventional time-history analysis where only transverse force was taken into account. The research results showed that the transverse dynamic response of utility tunnels was mainly influenced by transverse seismic waves, while the longitudinal dynamic response was affected by Rayleigh waves that were incident along the axial direction of the structure. The dynamic response to the input of Rayleigh waves plus bottom seismic waves was more significant than that to the input of bottom seismic waves alone. When different earthquake acceleration time histories were input, the dynamic response rules of tunnels were similar but the impacts on them varied, which implied that the compatibility between bottom seismic waves and Rayleigh waves exerted a certain influence on the dynamic response of the structure. The research findings are expected to provide a reference for the fine numerical analysis of the dynamic response of earthquake-excited underground utility tunnels as well as their seismic design.
As underground utility tunnels are buried at shallow depths, the effects of Rayleigh waves should be considered in relevant seismic analysis. To investigate the dynamic response characteristics of utility tunnels subjected to Rayleigh waves and bottom earthquake acceleration, a three dimensional(3D) finite element(FE)numerical model for double-cabin utility tunnels was built. An advanced constitutive model characterized by hysteresis loops(HSS model) was used to simulate the soil mass. Rayleigh waves were generated by multiple pulse loads at the boundary. Upland waves, Kobe waves and Taft waves were applied horizontally at the bottom of the model. The results were compared with those derived from the conventional time-history analysis where only transverse force was taken into account. The research results showed that the transverse dynamic response of utility tunnels was mainly influenced by transverse seismic waves, while the longitudinal dynamic response was affected by Rayleigh waves that were incident along the axial direction of the structure. The dynamic response to the input of Rayleigh waves plus bottom seismic waves was more significant than that to the input of bottom seismic waves alone. When different earthquake acceleration time histories were input, the dynamic response rules of tunnels were similar but the impacts on them varied, which implied that the compatibility between bottom seismic waves and Rayleigh waves exerted a certain influence on the dynamic response of the structure. The research findings are expected to provide a reference for the fine numerical analysis of the dynamic response of earthquake-excited underground utility tunnels as well as their seismic design.
2018, 26(3): 794-801.
Contour map is the most important method to study the spatial distribution of foundation soil. Nevertheless, the interpolation accuracy of foundation soil was seldom examined by geological investigation drillings. This paper takes the Holocene first marine facies drilling data in Binhai New Area of Tianjin as example and carries on the comparative study on the spatial interpolation of the buried depth and thickness of foundation soil. Such cross validation evaluates the interpolation accuracy and interpolation effect of ordinary Kriging, inverse distance weighted and thin-plate splines with tension. In addition, it focuses on the influence of spatial scale and the number of geotechnical investigation drillings on interpolation effect, and gives the optima spatial scale and drilling quantity. Under the 2000 m×2000 m and the original scale, we compared the statistics of the engineering geological zoning of foundation soils in different buried depth and thickness of each level distribution area. On this foundation, this paper analyses the change of the spatial interpolation, which is about of buried depth and thickness of standard foundation soil. The results show that with the method of ordinary Kriging interpolation and under the 2000 m×2000 m scale, the spatial interpolation of foundation soil in the Binhai New Area of Tianjin is the best. It can accurately explore the spatial distribution of foundation soil.
Contour map is the most important method to study the spatial distribution of foundation soil. Nevertheless, the interpolation accuracy of foundation soil was seldom examined by geological investigation drillings. This paper takes the Holocene first marine facies drilling data in Binhai New Area of Tianjin as example and carries on the comparative study on the spatial interpolation of the buried depth and thickness of foundation soil. Such cross validation evaluates the interpolation accuracy and interpolation effect of ordinary Kriging, inverse distance weighted and thin-plate splines with tension. In addition, it focuses on the influence of spatial scale and the number of geotechnical investigation drillings on interpolation effect, and gives the optima spatial scale and drilling quantity. Under the 2000 m×2000 m and the original scale, we compared the statistics of the engineering geological zoning of foundation soils in different buried depth and thickness of each level distribution area. On this foundation, this paper analyses the change of the spatial interpolation, which is about of buried depth and thickness of standard foundation soil. The results show that with the method of ordinary Kriging interpolation and under the 2000 m×2000 m scale, the spatial interpolation of foundation soil in the Binhai New Area of Tianjin is the best. It can accurately explore the spatial distribution of foundation soil.
2018, 26(3): 802-809.
This paper attempts to determine the underground thermal properties of a region in Heze, Shandong Province. On the basis of the theory of line source, a field thermal response test was carried out using distributed temperature sensing technology(DTS). Temperature measurement cables were used to capture distributed temperatures of the borehole during heating or cooling process, under single and double U buried pipe conditions respectively. The thermal conductivities of each layer were subsequently calculated. The experimental results show that the thermal conductivity of different strata can be accurately and reliably obtained with DTS technology in the field thermal response test, and the heat exchange capacity of each stratum can be evaluated. There is a significant improving effect of seepage on the thermal conductivity. It is also found that the results obtained by the double U-tube test are more accurate than that obtained by single U-tube test. Because of the heat accumulation effect, the longer the test time is, the smaller the thermal conductivity is. If the test time is long enough, the thermal conductivity would become a stable value. The results of this study can provide the basic basis for ground source heat pump design.
This paper attempts to determine the underground thermal properties of a region in Heze, Shandong Province. On the basis of the theory of line source, a field thermal response test was carried out using distributed temperature sensing technology(DTS). Temperature measurement cables were used to capture distributed temperatures of the borehole during heating or cooling process, under single and double U buried pipe conditions respectively. The thermal conductivities of each layer were subsequently calculated. The experimental results show that the thermal conductivity of different strata can be accurately and reliably obtained with DTS technology in the field thermal response test, and the heat exchange capacity of each stratum can be evaluated. There is a significant improving effect of seepage on the thermal conductivity. It is also found that the results obtained by the double U-tube test are more accurate than that obtained by single U-tube test. Because of the heat accumulation effect, the longer the test time is, the smaller the thermal conductivity is. If the test time is long enough, the thermal conductivity would become a stable value. The results of this study can provide the basic basis for ground source heat pump design.
2018, 26(3): 810-816.
The old clay in the karst area can change its dynamic deformation characteristics and weak the intensity parameters correspondingly under the dynamic load caused by human engineering activities, which may leading to the structural damage on soil cave eventually. The old clay in Penghu Bay of Wuhan City was taken as the study object. Combined with the engineering geological conditions of the karst collapse site, the indoor dynamic triaxial test of the old clay was carried out to study the dynamic deformation characteristics and the strength weakening law under the influence of the factors such as dynamic stress ratio, confining pressure and cycle times, then the strength weakening model under cyclic loading was proposed. The results show that the pore water pressure of the old clay increases with the increase of the confining pressure and the dynamic stress ratio and the number of cycles. When the dynamic stress ratio and the cycling numbers do not exceed a certain critical value, the strength of the soil increases with the enhancing of dynamic stress ratio and the number of cycles, that is to say the increase in pore pressure triggers the attenuation of soil strength. In the early raising period of confining pressure, the strength of soil increases with the addition of confining pressure. When the confining pressure increases until the soil structural damaged, the shear strength of the old clay is greatly reduced. The strength reduction rate decreases correspondingly with the increase of the confining pressure, dynamic stress ratio and the number of cycles. The correlation of the old clay strength weakening model obtained with empirical formula is fairly high. The weakening mechanism of the strength of the old clay is further obtained.
The old clay in the karst area can change its dynamic deformation characteristics and weak the intensity parameters correspondingly under the dynamic load caused by human engineering activities, which may leading to the structural damage on soil cave eventually. The old clay in Penghu Bay of Wuhan City was taken as the study object. Combined with the engineering geological conditions of the karst collapse site, the indoor dynamic triaxial test of the old clay was carried out to study the dynamic deformation characteristics and the strength weakening law under the influence of the factors such as dynamic stress ratio, confining pressure and cycle times, then the strength weakening model under cyclic loading was proposed. The results show that the pore water pressure of the old clay increases with the increase of the confining pressure and the dynamic stress ratio and the number of cycles. When the dynamic stress ratio and the cycling numbers do not exceed a certain critical value, the strength of the soil increases with the enhancing of dynamic stress ratio and the number of cycles, that is to say the increase in pore pressure triggers the attenuation of soil strength. In the early raising period of confining pressure, the strength of soil increases with the addition of confining pressure. When the confining pressure increases until the soil structural damaged, the shear strength of the old clay is greatly reduced. The strength reduction rate decreases correspondingly with the increase of the confining pressure, dynamic stress ratio and the number of cycles. The correlation of the old clay strength weakening model obtained with empirical formula is fairly high. The weakening mechanism of the strength of the old clay is further obtained.
2018, 26(3): 817-824.
The underground water-sealed caverns are mainly built in the crystalline rock mass in China, where water-sealing condition is very complicated considering the heterogeneous anisotropic spatial distribution of fractures in the rock mass. As the core constitution of underground water-sealed cavern, water curtain system directly concerns the water-sealed tightness. Considering the influence of geologic body anisotropy, it is necessary to evaluate hydraulic transmission efficiency between water curtain network and surrounding rock, namely, test water curtain boreholes efficiency. In the previous studies, the geological conditions are usually simplified as isotropic mediums, while geological body anisotropy are discussed in the laboratory scale in some references, which engineering applicability is general. This paper analyzes the influence of the rock mass anisotropy on hydraulic transmission efficiency in the site scale and proposes the optimization method of water curtain system considering this effect. It introduces the concept of water curtain efficiency with the lights of engineering experience. The multi-joint water curtain borehole test method is used for water curtain borehole efficiency testing in an underground water-sealed storage cavern project in Yantai. Then the water curtain system network is optimized with adding another boreholes according to experimental results. The results are obtained with threshold method which satisfies the air-tightness require under the condition of geological anisotropy. Practice proves that this method is more suitable for practical engineering and it can enhance the hydraulic transmission capacity of water curtain system significantly in the anisotropic field.
The underground water-sealed caverns are mainly built in the crystalline rock mass in China, where water-sealing condition is very complicated considering the heterogeneous anisotropic spatial distribution of fractures in the rock mass. As the core constitution of underground water-sealed cavern, water curtain system directly concerns the water-sealed tightness. Considering the influence of geologic body anisotropy, it is necessary to evaluate hydraulic transmission efficiency between water curtain network and surrounding rock, namely, test water curtain boreholes efficiency. In the previous studies, the geological conditions are usually simplified as isotropic mediums, while geological body anisotropy are discussed in the laboratory scale in some references, which engineering applicability is general. This paper analyzes the influence of the rock mass anisotropy on hydraulic transmission efficiency in the site scale and proposes the optimization method of water curtain system considering this effect. It introduces the concept of water curtain efficiency with the lights of engineering experience. The multi-joint water curtain borehole test method is used for water curtain borehole efficiency testing in an underground water-sealed storage cavern project in Yantai. Then the water curtain system network is optimized with adding another boreholes according to experimental results. The results are obtained with threshold method which satisfies the air-tightness require under the condition of geological anisotropy. Practice proves that this method is more suitable for practical engineering and it can enhance the hydraulic transmission capacity of water curtain system significantly in the anisotropic field.
2018, 26(3): 663-672.
In the morning of 9 March 2016, a landslide-mudflow occurred in South Jiangyang Platform near Jiangliu Village. After that we conducted a field investigation. It is found that the groundwater level had reached the foot of slope, and there were many water spray places. Shallow cracks were widely distributed in the surface, and deep cracks were also visible. It is obvious that the cracks provided advantage paths and promoted the infiltration of water. By testing the water content of the soil in the sliding area, it is found that the hydraulic conductivity of paleosol was very low, and it resulted in the formation of the aquifer in the paleosol. It is estimated that the loess layer collected water and formed a zone with a high water content, and then resulted in the "3.8" Jiangliu loess landslide. Utilizing LS_RAPID, the motion of the landslide was simulated. It showed that the whole motion process can be divided into four stages: 0-4.0 s, which was the first stage of the landslide. The slope collapsed rapidly and the maximum speed reached 10.3 m·s-1; 4.0-4.9 s, which was the collision stage between the sliding mass with the ground. Then, the speed slowed down, and reduced to 7.3 m·s-1 at 4.9 s; 4.9-6.7 s, which was called the second acceleration stage. The landslide formed a landslide-mudflow on the flat terraces, and the maximum speed reached 18.4 m·s-1; 6.7-29.5 s, which was the deceleration stage, and the kinetic energy of the landslide gradually exhausted and landslide stopped. The final sliding distance of the landslide reached 275 m and the time of motion was 29.5 s. The sliding distance and the accumulation range were consistent with the field situation.
In the morning of 9 March 2016, a landslide-mudflow occurred in South Jiangyang Platform near Jiangliu Village. After that we conducted a field investigation. It is found that the groundwater level had reached the foot of slope, and there were many water spray places. Shallow cracks were widely distributed in the surface, and deep cracks were also visible. It is obvious that the cracks provided advantage paths and promoted the infiltration of water. By testing the water content of the soil in the sliding area, it is found that the hydraulic conductivity of paleosol was very low, and it resulted in the formation of the aquifer in the paleosol. It is estimated that the loess layer collected water and formed a zone with a high water content, and then resulted in the "3.8" Jiangliu loess landslide. Utilizing LS_RAPID, the motion of the landslide was simulated. It showed that the whole motion process can be divided into four stages: 0-4.0 s, which was the first stage of the landslide. The slope collapsed rapidly and the maximum speed reached 10.3 m·s-1; 4.0-4.9 s, which was the collision stage between the sliding mass with the ground. Then, the speed slowed down, and reduced to 7.3 m·s-1 at 4.9 s; 4.9-6.7 s, which was called the second acceleration stage. The landslide formed a landslide-mudflow on the flat terraces, and the maximum speed reached 18.4 m·s-1; 6.7-29.5 s, which was the deceleration stage, and the kinetic energy of the landslide gradually exhausted and landslide stopped. The final sliding distance of the landslide reached 275 m and the time of motion was 29.5 s. The sliding distance and the accumulation range were consistent with the field situation.
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