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The coefficient of lateral earth pressure(K0) is a key parameter for calculating lateral earth pressure in geotechnical engineering. The development trend of K0 value of intact and remolded loess during consolidation is obviously different from that of clay or sand. In order to study the influence of confining pressure and initial void ratio on K0 value of intact and remolded loess, K0 consolidation tests were carried out by using the stress path triaxial apparatus, that is also equipped with a high precise internal radial LVDT. The results reveal that: (1)the K0 value of remolded loess samples is strongly affected by the initial void ratio(e0), when the initial void ratio decreases from 0.775 to 0.503, the maximum reduction of K0 value is about 55%. For the intact loess samples it is strongly affected by the effective confining pressure(σ3), the K0 value is 0.77~0.85 when σ3 < 350kPa and 0.46~0.51 when σ3>350kPa; (2)in the consolidation stage, a sudden drop of K0 value is found in intact and remolded loess samples. In brief, in dense sample of remolded loess(e0 < 0.6)the drop takes place at the initial stage of consolidation. In loose sample of remolded loess(e0 ≈ 0.77)the drop is near the effective confining pressure of 100kPa. For intact loess samples the drop is observed at the effective confining pressure of 350kPa; (3)under otherwise similar conditions in terms of stress level and density, the K0 value of intact loess is higher than that of remolded loess. By using the nuclear magnetic resonance(NMR)technique, the pore size distributions of remolded and intact loess are obtained. In conjunction with the experimental results in excess pore water pressure and changes of sample volume, etc. The observed discrepancies in the K0 value is mainly attributed to the characteristics of soil fabric. The coefficient of lateral earth pressure(K0) is a key parameter for calculating lateral earth pressure in geotechnical engineering. The development trend of K0 value of intact and remolded loess during consolidation is obviously different from that of clay or sand. In order to study the influence of confining pressure and initial void ratio on K0 value of intact and remolded loess, K0 consolidation tests were carried out by using the stress path triaxial apparatus, that is also equipped with a high precise internal radial LVDT. The results reveal that: (1)the K0 value of remolded loess samples is strongly affected by the initial void ratio(e0), when the initial void ratio decreases from 0.775 to 0.503, the maximum reduction of K0 value is about 55%. For the intact loess samples it is strongly affected by the effective confining pressure(σ3), the K0 value is 0.77~0.85 when σ3 < 350kPa and 0.46~0.51 when σ3>350kPa; (2)in the consolidation stage, a sudden drop of K0 value is found in intact and remolded loess samples. In brief, in dense sample of remolded loess(e0 < 0.6)the drop takes place at the initial stage of consolidation. In loose sample of remolded loess(e0 ≈ 0.77)the drop is near the effective confining pressure of 100kPa. For intact loess samples the drop is observed at the effective confining pressure of 350kPa; (3)under otherwise similar conditions in terms of stress level and density, the K0 value of intact loess is higher than that of remolded loess. By using the nuclear magnetic resonance(NMR)technique, the pore size distributions of remolded and intact loess are obtained. In conjunction with the experimental results in excess pore water pressure and changes of sample volume, etc. The observed discrepancies in the K0 value is mainly attributed to the characteristics of soil fabric.
This paper explores the complex relationship between the surface moisture of the loess high-filling body and provides the basis for preventing and controlling the shallow water-soil disasters of the slope. It takes a loess high-filling body in Ansai of Yan'an as the object, and carries out the in-situ long time series monitoring. The correlationship between the surface moisture of the loess high-filling slope under the influence of slope effect is studied by cross wavelet and wavelet coherence analysis method. The results show that the wavelet analysis method can be used to semi-quantitatively study the relationship between internal and external soil moisture in loess high-filling slope, can clearly show the relationship and variation details of two time series in time domain and frequency domain. There are two main resonance time scales of 0.06~1.78d and 3.56~28.47d between rainfall and shallow soil moisture of slope. The correlation shows an increasing trend in this two time scales. The correlation between rainfall and shallow soil moisture has obvious time scale dependence. The correlation between the soil moisture and the intensity of exchange and transformation can be expressed by the percent area of significant coherence(PASC). The average values of PASC at different positions of the slope as ranked as follows: the top of the slope(36.39%) < the upper slope(37.6%) < the middle slope(39.17%). The slope improves the exchange and transformation of vertical soil moisture. The existence of slope effect is not conducive to the transformation from rainfall to soil moisture, but enhances the exchange and transformation of surface vertical soil moisture. This paper explores the complex relationship between the surface moisture of the loess high-filling body and provides the basis for preventing and controlling the shallow water-soil disasters of the slope. It takes a loess high-filling body in Ansai of Yan'an as the object, and carries out the in-situ long time series monitoring. The correlationship between the surface moisture of the loess high-filling slope under the influence of slope effect is studied by cross wavelet and wavelet coherence analysis method. The results show that the wavelet analysis method can be used to semi-quantitatively study the relationship between internal and external soil moisture in loess high-filling slope, can clearly show the relationship and variation details of two time series in time domain and frequency domain. There are two main resonance time scales of 0.06~1.78d and 3.56~28.47d between rainfall and shallow soil moisture of slope. The correlation shows an increasing trend in this two time scales. The correlation between rainfall and shallow soil moisture has obvious time scale dependence. The correlation between the soil moisture and the intensity of exchange and transformation can be expressed by the percent area of significant coherence(PASC). The average values of PASC at different positions of the slope as ranked as follows: the top of the slope(36.39%) < the upper slope(37.6%) < the middle slope(39.17%). The slope improves the exchange and transformation of vertical soil moisture. The existence of slope effect is not conducive to the transformation from rainfall to soil moisture, but enhances the exchange and transformation of surface vertical soil moisture.
Moisture in the air can be absorped by bentonite readily. This paper studies the hygroscopicity of Gaomiaozi Na-bentonite under different conditions including drying temperatures, drying time, environmental relative humidites, thickness, and surface area. The results show that the mass of bentonite is stable after it has been dried at 110℃for 8hours. The final absorped moisture content does not increase with the surface area. There is depth effect in bentonite that the absorped moisture content decreases as the depth increases. The relationship of the absorped moisture content with time is fitted well by Peleg model. First, 20g bentonite is dried at 110℃. Then the dried bentonite is exposed in air with 55% and 82% relative humidity, respectively. The strongly bound water is absorped in 2 minutes, which indicates that the adsorption of bound water is less affected by relative humidity. The contents of free water, weakly bound water and strongly bound water are 7.873%, 0.749% and 1.316%, and 9.408%, 1.128%, 1.412%, respectively. And their water film thickness is 5.56Å and 7.71Å, respectively. Moisture in the air can be absorped by bentonite readily. This paper studies the hygroscopicity of Gaomiaozi Na-bentonite under different conditions including drying temperatures, drying time, environmental relative humidites, thickness, and surface area. The results show that the mass of bentonite is stable after it has been dried at 110℃for 8hours. The final absorped moisture content does not increase with the surface area. There is depth effect in bentonite that the absorped moisture content decreases as the depth increases. The relationship of the absorped moisture content with time is fitted well by Peleg model. First, 20g bentonite is dried at 110℃. Then the dried bentonite is exposed in air with 55% and 82% relative humidity, respectively. The strongly bound water is absorped in 2 minutes, which indicates that the adsorption of bound water is less affected by relative humidity. The contents of free water, weakly bound water and strongly bound water are 7.873%, 0.749% and 1.316%, and 9.408%, 1.128%, 1.412%, respectively. And their water film thickness is 5.56Å and 7.71Å, respectively.
Under the carbon peaking and carbon neutrality goals,seeking green cementitious materials from natural geomaterials is widely focused. The fine tuff powder is a solid waste produced in the process of manufactured sand production,and is a natural silica-aluminum geopolymer. There are few studies on the strength and shrinkage properties of tuff powder and aggregate composite. We select quartz tuff powder,blast furnace slag,sand,gravel and hydrophobic agent as raw materials to prepare alkali activated tuff powder slurry,tuff powder mortar and tuff-based concrete. After 60℃curing,the compressive strength,splitting tensile strength and shrinkage of the composites are investigated. The influences of each component on their physical and mechanical properties are analyzed. The results showed that the compressive strength of alkali activated tuff powder without additive is 12.7MPa and is higher than that of tuff powder and aggregate composite (of 4.4~7.0MPa). The results are attributed to the weak interfaces formed by the aggregate adding and different thermal expansion rates of aggregate and paste. The compression modulus of samples also is reduced when the sand and crushed stone are added in the composite. The mineral composition of tuff powder is similar to that of tuff aggregate. Due to the depolymerization and polymerization reaction under the action of alkali activator,the hydrated calcium aluminosilicate and hydrated sodium aluminosilicate are formed on particle surface. Then,the strengths of tuff powder and tuff aggregate composite are higher. With the addition of sand and gravel,the shrinkage of the sample decreases. The minimum shrinkage is 0.4% for the tuff powder,quartz sand and tuff gravel composite. For the hydrophobicity,bonding strength weakening and surface reaction preventing,the Lotus leaf hydrophobic agent(LHG) and Boiled wood oil(BWO)reduce the strength of tuff based geopolymer and tuff powder-sand-gravel composite. The strength of samples with shrinkage reducing agent(SRA)is higher than that of LHG and BWO groups,which is attributed to the water retention capacity of SRA. The shrinkage migration effects of LHG,BWO and SRA on tuff powder geopolymer are not significant. For the tuff powder and sand composite,the shrinkage ratio of samples with SRA is 0.9% and lower than that of LHG and BWO groups. For the tuff powder,sand and gravel composite,the shrinkage rate of samples without additives is lower,indicating that the volume shrinkage of the powder-sand-gravel composite is mainly influenced by the skeleton supporting. Based on the above analysis,the optimum proportions of each groups are suggested. Under the carbon peaking and carbon neutrality goals,seeking green cementitious materials from natural geomaterials is widely focused. The fine tuff powder is a solid waste produced in the process of manufactured sand production,and is a natural silica-aluminum geopolymer. There are few studies on the strength and shrinkage properties of tuff powder and aggregate composite. We select quartz tuff powder,blast furnace slag,sand,gravel and hydrophobic agent as raw materials to prepare alkali activated tuff powder slurry,tuff powder mortar and tuff-based concrete. After 60℃curing,the compressive strength,splitting tensile strength and shrinkage of the composites are investigated. The influences of each component on their physical and mechanical properties are analyzed. The results showed that the compressive strength of alkali activated tuff powder without additive is 12.7MPa and is higher than that of tuff powder and aggregate composite (of 4.4~7.0MPa). The results are attributed to the weak interfaces formed by the aggregate adding and different thermal expansion rates of aggregate and paste. The compression modulus of samples also is reduced when the sand and crushed stone are added in the composite. The mineral composition of tuff powder is similar to that of tuff aggregate. Due to the depolymerization and polymerization reaction under the action of alkali activator,the hydrated calcium aluminosilicate and hydrated sodium aluminosilicate are formed on particle surface. Then,the strengths of tuff powder and tuff aggregate composite are higher. With the addition of sand and gravel,the shrinkage of the sample decreases. The minimum shrinkage is 0.4% for the tuff powder,quartz sand and tuff gravel composite. For the hydrophobicity,bonding strength weakening and surface reaction preventing,the Lotus leaf hydrophobic agent(LHG) and Boiled wood oil(BWO)reduce the strength of tuff based geopolymer and tuff powder-sand-gravel composite. The strength of samples with shrinkage reducing agent(SRA)is higher than that of LHG and BWO groups,which is attributed to the water retention capacity of SRA. The shrinkage migration effects of LHG,BWO and SRA on tuff powder geopolymer are not significant. For the tuff powder and sand composite,the shrinkage ratio of samples with SRA is 0.9% and lower than that of LHG and BWO groups. For the tuff powder,sand and gravel composite,the shrinkage rate of samples without additives is lower,indicating that the volume shrinkage of the powder-sand-gravel composite is mainly influenced by the skeleton supporting. Based on the above analysis,the optimum proportions of each groups are suggested.
Advancing gas hydrate exploitation is one of the most important tasks for China's future energy strategy. The interbedded formation of hydrate-bearing sediments is a common feature in many target production regions. However,the hydrate gas production process disturbs the hydrate-bearing sediment,which induces shear strain to mobilise the reservoir stability and severely restrain the safe exploitation of hydrate resources. The existing constitutive characterization of hydrate-bearing sediments is mainly based on the assumption of homogeneous and isotropic material properties,and without a proper constitutive characterization method to consider the strong non-linear mechanical properties of hydrate-bearing sediments affected by the interbedded formation,that leads to inaccurate estimation of the stress and strain responses of the target production region. This study uses the homogenization theory to construct the macro and mesoscopic control equations of interbedded sediments. Based on the elastic-plastic stiffness matrix of each layer of sediments,a constitutive model for interbedded hydrate-bearing sediments was established. Sediment model parameters representing each layer within a representative volume element can be obtained based on triaxial test results of homogeneous hydrate-bearing sediment samples. By comparing the prediction results of the proposed constitutive model with the stress-strain results of the interbedded sediment triaxial test and numerical simulation,the proposed constitutive model can accurately describe the mechanical behavior of interbedded hydrate-bearing sediments in the in-situ reservoirs. Advancing gas hydrate exploitation is one of the most important tasks for China's future energy strategy. The interbedded formation of hydrate-bearing sediments is a common feature in many target production regions. However,the hydrate gas production process disturbs the hydrate-bearing sediment,which induces shear strain to mobilise the reservoir stability and severely restrain the safe exploitation of hydrate resources. The existing constitutive characterization of hydrate-bearing sediments is mainly based on the assumption of homogeneous and isotropic material properties,and without a proper constitutive characterization method to consider the strong non-linear mechanical properties of hydrate-bearing sediments affected by the interbedded formation,that leads to inaccurate estimation of the stress and strain responses of the target production region. This study uses the homogenization theory to construct the macro and mesoscopic control equations of interbedded sediments. Based on the elastic-plastic stiffness matrix of each layer of sediments,a constitutive model for interbedded hydrate-bearing sediments was established. Sediment model parameters representing each layer within a representative volume element can be obtained based on triaxial test results of homogeneous hydrate-bearing sediment samples. By comparing the prediction results of the proposed constitutive model with the stress-strain results of the interbedded sediment triaxial test and numerical simulation,the proposed constitutive model can accurately describe the mechanical behavior of interbedded hydrate-bearing sediments in the in-situ reservoirs.
The natural damage such as cracks and holes in rock can have important impact on the mechanical properties and failure process of rock. Using the cellular automata theory and CT nondestructive identification technology,we study the whole process of crack propagation and coalescence and the change law of mechanical properties of rock containing natural cracks under splitting conditions. Based on the real micro-structure of fractured sandstone,we construct the numerical calculation model of natural fractured rock,complete the numerical test of sandstone splitting failure with different fracture dip angles,and analyze the influence of fracture dip angle on the mechanical properties,crack propagation process and energy evolution of sandstone. The results show that:(1)The tensile strength of fractured sandstone is closely related to the fracture dip angle. With the increase of fracture dip angle,the tensile strength decreases first and then increases. (2)The fracture starts at the tip of the initial fracture. When the dip angle is greater than 0° and less than 48°,the staggered crack causes the failure of the rock sample,and the main crack propagates along the vertical direction near the initial fracture; When the dip angle is greater than 48° and less than 94°,open crack causes the failure of rock sample,and the main crack propagates along the parallel direction with the initial crack. (3)There are tensile stress zone and compressive stress zone at the crack tip during the splitting process. The tensile stress causes the wing crack to initiate and propagate along the natural crack tip,while the compressive stress causes the secondary crack to propagate along the original crack direction. (4)We divide the energy evolution of the splitting failure process of sandstone with natural fractures into four stages. With the increase of fracture dip angle,the total energy density and elastic energy density at the peak point decrease slowly and then increase rapidly,but have little effect on the dissipation energy of rock samples. The natural damage such as cracks and holes in rock can have important impact on the mechanical properties and failure process of rock. Using the cellular automata theory and CT nondestructive identification technology,we study the whole process of crack propagation and coalescence and the change law of mechanical properties of rock containing natural cracks under splitting conditions. Based on the real micro-structure of fractured sandstone,we construct the numerical calculation model of natural fractured rock,complete the numerical test of sandstone splitting failure with different fracture dip angles,and analyze the influence of fracture dip angle on the mechanical properties,crack propagation process and energy evolution of sandstone. The results show that:(1)The tensile strength of fractured sandstone is closely related to the fracture dip angle. With the increase of fracture dip angle,the tensile strength decreases first and then increases. (2)The fracture starts at the tip of the initial fracture. When the dip angle is greater than 0° and less than 48°,the staggered crack causes the failure of the rock sample,and the main crack propagates along the vertical direction near the initial fracture; When the dip angle is greater than 48° and less than 94°,open crack causes the failure of rock sample,and the main crack propagates along the parallel direction with the initial crack. (3)There are tensile stress zone and compressive stress zone at the crack tip during the splitting process. The tensile stress causes the wing crack to initiate and propagate along the natural crack tip,while the compressive stress causes the secondary crack to propagate along the original crack direction. (4)We divide the energy evolution of the splitting failure process of sandstone with natural fractures into four stages. With the increase of fracture dip angle,the total energy density and elastic energy density at the peak point decrease slowly and then increase rapidly,but have little effect on the dissipation energy of rock samples.
A large number of moraine soil accumulation slopes are widely developed in alpine mountainous areas of China. The slopes are generally characterized by wide gradation,poor sorting and large porosity. Under the influence of complex tectonic geomorphic conditions and freeze-thaw conditions,violent water-heat-mass exchange often occurs and produces ice-rich stagnant water lubrication effect,thus inducing moraine soil interface landslide disaster. The moraine soil interface landslide has great potential risks to the engineering construction in this region. It is the basic work to realize the scientific prevention and control of this kind of geological disasters to systematically grasp the mechanism of hydrothermal migration and frost swelling of moraine soil in alpine mountainous areas. Accordingly,the particle size composition and structural characteristics of moraine soils are studied. The typical "two-grain group" constitutive characteristics of moraine soils are clarified. Then,the current situation of research on hydrothermal migration and frost swelling of moraine soils under freeze-thaw is analysed. The multi-phase multi-field migration mechanism and frost swelling characteristics of moraine soils are clarified. Finally,the study focuses on the evolutionary process of moraine soil slope,and elucidates the causes of the internal ice-rich belt and the mechanism of stagnant water-promoted sliding instability. The study shows that:(1)the typical constitutive characteristics of moraine soils provide the preconditions for the multiphase and multifield migration of water-thermal-mass,and are also the important factors inducing localized freezing and swelling; (2)The oriented interfacial poly-icing phenomenon is produced by the intense hydrothermal migration of moraine soil. The interfacial effect is the source of induced slope instability. To explore the slope instability of the moraine soil,we should focus on the characteristics of the development of ice-rich belt and its pro-slip instability mechanism. (3)The mechanism of disaster generation on moraine soil slopes in alpine mountainous areas is mainly controlled by the following two modes: ① Ice accumulation effect of mixed-state water-thermal migration; ②Stagnant water lubrication effect at the interface of the ice-rich belt. This paper is intended to provide a basic reference for the multi-phase multi-field disaster mechanism of moraine soil slopes in alpine mountain areas. A large number of moraine soil accumulation slopes are widely developed in alpine mountainous areas of China. The slopes are generally characterized by wide gradation,poor sorting and large porosity. Under the influence of complex tectonic geomorphic conditions and freeze-thaw conditions,violent water-heat-mass exchange often occurs and produces ice-rich stagnant water lubrication effect,thus inducing moraine soil interface landslide disaster. The moraine soil interface landslide has great potential risks to the engineering construction in this region. It is the basic work to realize the scientific prevention and control of this kind of geological disasters to systematically grasp the mechanism of hydrothermal migration and frost swelling of moraine soil in alpine mountainous areas. Accordingly,the particle size composition and structural characteristics of moraine soils are studied. The typical "two-grain group" constitutive characteristics of moraine soils are clarified. Then,the current situation of research on hydrothermal migration and frost swelling of moraine soils under freeze-thaw is analysed. The multi-phase multi-field migration mechanism and frost swelling characteristics of moraine soils are clarified. Finally,the study focuses on the evolutionary process of moraine soil slope,and elucidates the causes of the internal ice-rich belt and the mechanism of stagnant water-promoted sliding instability. The study shows that:(1)the typical constitutive characteristics of moraine soils provide the preconditions for the multiphase and multifield migration of water-thermal-mass,and are also the important factors inducing localized freezing and swelling; (2)The oriented interfacial poly-icing phenomenon is produced by the intense hydrothermal migration of moraine soil. The interfacial effect is the source of induced slope instability. To explore the slope instability of the moraine soil,we should focus on the characteristics of the development of ice-rich belt and its pro-slip instability mechanism. (3)The mechanism of disaster generation on moraine soil slopes in alpine mountainous areas is mainly controlled by the following two modes: ① Ice accumulation effect of mixed-state water-thermal migration; ②Stagnant water lubrication effect at the interface of the ice-rich belt. This paper is intended to provide a basic reference for the multi-phase multi-field disaster mechanism of moraine soil slopes in alpine mountain areas.
This paper studies the damage characteristics of Guiyang red clay under cyclic loading and reveals the evolution of shear strength parameters with the loading and unloading process. Using the stress path test module in the stress-strain controlled triaxial shear penetrometer,we conducted consolidation undrained shear cyclic loading and unloading tests on Guiyang red clay with four water contents of ω=29%,32%,35% and 38% at σ3=100 kPa,200 kPa and 300 kPa surrounding pressure,respectively. This study shows the follows. The soil samples exhibit deformation enhancement during unloading,the larger the axial strain increment after unloading,the longer the relaxation time,and the larger the rebound deformation. Taking into account the effects of water content and surrounding pressure conditions,we established the mathematical relational equation for the evolution of elastic deformation during shearing of Guiyang red clay. We compared the mathematical relational equation with the experimental results to verify that the fit was more than 95%. We adopted the equivalent plastic shear strain as the plastic internal variable to study the strength damage characteristics of Guiyang red clay during the whole shear process. The results found that its cementation strength kept losing while the friction strength kept increasing. With the increase of water content,the internal friction angle and cohesiveness range from 21.8°to 16.1°and 83.7 kPa to 57.5 kPa,respectively. The research is expected to provide theoretical guidance for the compaction of road base and the evaluation of soil slope stability considering the loading and unloading conditions. This paper studies the damage characteristics of Guiyang red clay under cyclic loading and reveals the evolution of shear strength parameters with the loading and unloading process. Using the stress path test module in the stress-strain controlled triaxial shear penetrometer,we conducted consolidation undrained shear cyclic loading and unloading tests on Guiyang red clay with four water contents of ω=29%,32%,35% and 38% at σ3=100 kPa,200 kPa and 300 kPa surrounding pressure,respectively. This study shows the follows. The soil samples exhibit deformation enhancement during unloading,the larger the axial strain increment after unloading,the longer the relaxation time,and the larger the rebound deformation. Taking into account the effects of water content and surrounding pressure conditions,we established the mathematical relational equation for the evolution of elastic deformation during shearing of Guiyang red clay. We compared the mathematical relational equation with the experimental results to verify that the fit was more than 95%. We adopted the equivalent plastic shear strain as the plastic internal variable to study the strength damage characteristics of Guiyang red clay during the whole shear process. The results found that its cementation strength kept losing while the friction strength kept increasing. With the increase of water content,the internal friction angle and cohesiveness range from 21.8°to 16.1°and 83.7 kPa to 57.5 kPa,respectively. The research is expected to provide theoretical guidance for the compaction of road base and the evaluation of soil slope stability considering the loading and unloading conditions.
In the spring-thawing season,the reduction in shear strength at the freeze-thaw interface affects the stability of the slope. This paper studies the strength variation of fine-grained soil freezing-thawing interface. It carries out low-temperature direct shear tests at different freezing temperatures(-12 ℃,-7 ℃,-2 ℃),shear temperatures(-5 ℃,-2 ℃,1 ℃),and moisture contents(9%,16%,23%)respectively. In addition,according to the grey correlation analysis method,the paper determines and analyses the grey correlation of the factors. The test results show that the shear strength at the freeze-thaw surface decreases as the shear temperature and freezing temperature increase. The change of specimen strength is mainly related to the change of cohesion,and the change of internal friction angle is small. The order of the gray relational grade of the factors is water content>freezing temperature>shear temperature. The effect of ground temperature(freezing temperature) cannot be ignored when considering the effect of temperature on strength. In the spring-thawing season,the reduction in shear strength at the freeze-thaw interface affects the stability of the slope. This paper studies the strength variation of fine-grained soil freezing-thawing interface. It carries out low-temperature direct shear tests at different freezing temperatures(-12 ℃,-7 ℃,-2 ℃),shear temperatures(-5 ℃,-2 ℃,1 ℃),and moisture contents(9%,16%,23%)respectively. In addition,according to the grey correlation analysis method,the paper determines and analyses the grey correlation of the factors. The test results show that the shear strength at the freeze-thaw surface decreases as the shear temperature and freezing temperature increase. The change of specimen strength is mainly related to the change of cohesion,and the change of internal friction angle is small. The order of the gray relational grade of the factors is water content>freezing temperature>shear temperature. The effect of ground temperature(freezing temperature) cannot be ignored when considering the effect of temperature on strength.
Granular materials exhibit cyclic hardening behavior under cyclic loading. However,there are few studies on the mechanistic explanation of cyclic hardening behavior at the macro-micro scale. In this paper,the cyclic triaxial test DEM simulation is carried out to study the cyclic hardening behavior of granular materials with different particle size distribution under cyclic loading. The evolution of (axial) average deformation modulus and energy dissipation due to sliding contact is analyzed. The results show that the average modulus increases gradually and tends to asymptotic values as the cyclic loading progresses. The energy dissipation of each cycle does not always decay with the increase of cycles,but has a threshold. The increase index of the average modulus and the decay index of energy dissipation are similar in magnitude(about 0.6)for all the specimens with different particle size distribution,indicating that whether the deformation modulus or the normalized energy dissipation are used,the results are consistent when describing the cyclic hardening behavior. The energy dissipation caused by sliding contact at the microscale is mapped to the average modulus at the macroscale. The larger the average particle size of the granular assembly,the larger the average modulus,and the earlier the completion of the energy dissipation process. However,the corresponding energy dissipation threshold difference under different particle size distributions is small,basically maintained at a constant of 0.15. Granular materials exhibit cyclic hardening behavior under cyclic loading. However,there are few studies on the mechanistic explanation of cyclic hardening behavior at the macro-micro scale. In this paper,the cyclic triaxial test DEM simulation is carried out to study the cyclic hardening behavior of granular materials with different particle size distribution under cyclic loading. The evolution of (axial) average deformation modulus and energy dissipation due to sliding contact is analyzed. The results show that the average modulus increases gradually and tends to asymptotic values as the cyclic loading progresses. The energy dissipation of each cycle does not always decay with the increase of cycles,but has a threshold. The increase index of the average modulus and the decay index of energy dissipation are similar in magnitude(about 0.6)for all the specimens with different particle size distribution,indicating that whether the deformation modulus or the normalized energy dissipation are used,the results are consistent when describing the cyclic hardening behavior. The energy dissipation caused by sliding contact at the microscale is mapped to the average modulus at the macroscale. The larger the average particle size of the granular assembly,the larger the average modulus,and the earlier the completion of the energy dissipation process. However,the corresponding energy dissipation threshold difference under different particle size distributions is small,basically maintained at a constant of 0.15.
In this study,5 different types of capillary water-conducting materials(i.e.,COOLPASS,COOLPLUS,COOLMAX,SHCOOL,and Ordinary Mesh Fabrics) are selected for water absorption and drainage test,NMR test,and capillary rising test to investigate their drainage performance and pore structures. The purpose is to reveal the mechanism of capillary water absorption and drainage performance,and as a reference for finding or producing a geotextile that can be applied to some unsaturated soil with high moisture content in the country. Results show that these capillary water-conducting materials have good water absorption and drainage effect in both soil and water. Through the drainage test of capillary water-conducting materials in water,it is found that capillary rising distance and air relative humidity affect the water removal effect. Generally,we divide these five kinds of fabrics into two levels by their performance: the COOLPASS,COOLMAX and Ordinary Mesh Fabrics have the best drainage performance,while the performance of SHCOOL and COOLPLUS are slightly weaker. The pore sizes of COOLPASS,COOLMAX and Ordinary Mesh Fabric are about 53.4 μm and the pore size of SHCOOL and COOLPLUS are 37.8 μm through the NMR test. According to the NMR test of these materials,it is found that the ability of drainage is related to their pore diameters and distribution characteristics. Considering the two processes of capillary absorption and evaporation drainage of the water-conducting capillary materials,the drainage effect of the material with a large pore diameter and sparse distribution is better in unsaturated soil,the moisture content of the soil sample decreases by 2.19% more than the soil sample without capillary drainage material under the same condition. In the capillary rising test,the capillary rise height of COOLMAX is the highest. Therefore,the water absorption capacity of capillary water-conducting material is related to its pore distribution characteristics,the denser the pore distribution is,the stronger the water absorption capacity is. In this study,5 different types of capillary water-conducting materials(i.e.,COOLPASS,COOLPLUS,COOLMAX,SHCOOL,and Ordinary Mesh Fabrics) are selected for water absorption and drainage test,NMR test,and capillary rising test to investigate their drainage performance and pore structures. The purpose is to reveal the mechanism of capillary water absorption and drainage performance,and as a reference for finding or producing a geotextile that can be applied to some unsaturated soil with high moisture content in the country. Results show that these capillary water-conducting materials have good water absorption and drainage effect in both soil and water. Through the drainage test of capillary water-conducting materials in water,it is found that capillary rising distance and air relative humidity affect the water removal effect. Generally,we divide these five kinds of fabrics into two levels by their performance: the COOLPASS,COOLMAX and Ordinary Mesh Fabrics have the best drainage performance,while the performance of SHCOOL and COOLPLUS are slightly weaker. The pore sizes of COOLPASS,COOLMAX and Ordinary Mesh Fabric are about 53.4 μm and the pore size of SHCOOL and COOLPLUS are 37.8 μm through the NMR test. According to the NMR test of these materials,it is found that the ability of drainage is related to their pore diameters and distribution characteristics. Considering the two processes of capillary absorption and evaporation drainage of the water-conducting capillary materials,the drainage effect of the material with a large pore diameter and sparse distribution is better in unsaturated soil,the moisture content of the soil sample decreases by 2.19% more than the soil sample without capillary drainage material under the same condition. In the capillary rising test,the capillary rise height of COOLMAX is the highest. Therefore,the water absorption capacity of capillary water-conducting material is related to its pore distribution characteristics,the denser the pore distribution is,the stronger the water absorption capacity is.
A MS6.8 earthquake struck Luding County,Ganzi Tibetan Autonomous Prefecture,Sichuan Province,China on September 5,2022. The earthquake triggered large amounts of geological hazards,such as landslides,rockfalls,and debris flows,and caused severe fatalities and infrastructure damages. Utilizing the recently developed near real-time prediction model,we rapidly predicted the spatial distribution probability of the coseismic landslides in the region within two hours after the earthquake. Meanwhile,based on the high-resolution imagery from the Unmanned Aerial Vehicles(UAVs) and the Gaofen-6 Satellite,we interpreted a total of 3,633 coseismic landslides in the region with an area of 13.78 km2. We then validated the results based on the field investigation. The results indicate that the coseismic landslides induced by the Luding earthquake are smaller than those triggered by the 2008 Wenchuan earthquake and the 2017 Jiuzhaigou earthquake. The coseismic landslides,which show a banded distribution pattern,mainly located on the sides of the Xianshuihe fault zone and the Dadu River and concentrate in the areas with a shaking intensity of Ⅸ degrees,such as Moxi Town,Detuo Town,and Wanggangping Town. We further analyzed nine controlling factors of the coseismic landslides,such as topography,lithology,ground motion parameters,et al. We find that landslides mainly occurred in the regions with an elevation range of 1000~1800 m and a slope range of 35°~55°. Most coseismic landslides are distributed within 1 km of the fault zone and in the granite formation,which highlights the strong impact of the fault zone. This study's results provide essential support to emergency response and risk mitigation. A MS6.8 earthquake struck Luding County,Ganzi Tibetan Autonomous Prefecture,Sichuan Province,China on September 5,2022. The earthquake triggered large amounts of geological hazards,such as landslides,rockfalls,and debris flows,and caused severe fatalities and infrastructure damages. Utilizing the recently developed near real-time prediction model,we rapidly predicted the spatial distribution probability of the coseismic landslides in the region within two hours after the earthquake. Meanwhile,based on the high-resolution imagery from the Unmanned Aerial Vehicles(UAVs) and the Gaofen-6 Satellite,we interpreted a total of 3,633 coseismic landslides in the region with an area of 13.78 km2. We then validated the results based on the field investigation. The results indicate that the coseismic landslides induced by the Luding earthquake are smaller than those triggered by the 2008 Wenchuan earthquake and the 2017 Jiuzhaigou earthquake. The coseismic landslides,which show a banded distribution pattern,mainly located on the sides of the Xianshuihe fault zone and the Dadu River and concentrate in the areas with a shaking intensity of Ⅸ degrees,such as Moxi Town,Detuo Town,and Wanggangping Town. We further analyzed nine controlling factors of the coseismic landslides,such as topography,lithology,ground motion parameters,et al. We find that landslides mainly occurred in the regions with an elevation range of 1000~1800 m and a slope range of 35°~55°. Most coseismic landslides are distributed within 1 km of the fault zone and in the granite formation,which highlights the strong impact of the fault zone. This study's results provide essential support to emergency response and risk mitigation.
Understanding the causes of landslides from real-time monitoring data is important for identifying triggering mechanisms and potential hazard areas and formulating mitigation measures in a timely manner. However, due to the large amount and diverse sources of monitoring data, the conventional data processing methods can hardly extract useful information from huge monitoring data so as to make a correct evaluation of landslide deformation behaviors and evolution trends. This paper introduces the two-step clustering and association rule analysis methods in the classical data mining methods, proposes the data mining process of association analysis of slope deformation behavior, takes the Xinpu landslide in the Three Gorges reservoir region of Yangtze River as an example, and carries out the association analysis of slope displacement velocity under the influence of reservoir water level and rainfall. The results show that the landslide deformation in the reservoir area is influenced by multiple factors such as the elevation of reservoir water level, reservoir water level fluctuation velocity and rainfall intensity. Water level decline and strong rainfall are closely related to landslide deformation. There are differences in deformation influencing factors at different spatial locations of the landslide. The influence level of reservoir water level fluctuation decreases and the influence level of rainfall intensity increases from front part to rear part. The data mining method can be used to analyze the influencing factors of landslide deformation. It can be used to analyze the influencing factors of landslide deformation, and the comparison with the measured data verifies the reliability of the rules. These results are important for the analysis of the causes of landslide disasters under the massive monitoring data. Understanding the causes of landslides from real-time monitoring data is important for identifying triggering mechanisms and potential hazard areas and formulating mitigation measures in a timely manner. However, due to the large amount and diverse sources of monitoring data, the conventional data processing methods can hardly extract useful information from huge monitoring data so as to make a correct evaluation of landslide deformation behaviors and evolution trends. This paper introduces the two-step clustering and association rule analysis methods in the classical data mining methods, proposes the data mining process of association analysis of slope deformation behavior, takes the Xinpu landslide in the Three Gorges reservoir region of Yangtze River as an example, and carries out the association analysis of slope displacement velocity under the influence of reservoir water level and rainfall. The results show that the landslide deformation in the reservoir area is influenced by multiple factors such as the elevation of reservoir water level, reservoir water level fluctuation velocity and rainfall intensity. Water level decline and strong rainfall are closely related to landslide deformation. There are differences in deformation influencing factors at different spatial locations of the landslide. The influence level of reservoir water level fluctuation decreases and the influence level of rainfall intensity increases from front part to rear part. The data mining method can be used to analyze the influencing factors of landslide deformation. It can be used to analyze the influencing factors of landslide deformation, and the comparison with the measured data verifies the reliability of the rules. These results are important for the analysis of the causes of landslide disasters under the massive monitoring data.
Landslide disasters occur frequently in China's loess plateau. Most of landslides are related to rainfall. The joint is also one of the important factors leading to the occurrence of loess landslides. In order to further reveal the influence of joints on loess landslides, this paper takes loess joints as the starting point of research. It is based on fieldwork and carries out a large-scale physical model test of artificial rainfall-induced landslides with preset joints. It carries out the real-time monitoring of the stage changes of soil water content and pore water pressure with the rainfall process. It analyses the expansion and evolution law of joints and fissures in the slope, as well as the trend of slope displacement and deformation. It reveals the potential mechanism of the existence of joints for inducing landslides and the law of slope response. The test results show the follows. The joints have obvious accelerating and promoting effects on the infiltration of rainwater inside the slope. The model slopes on the preset joint side have a faster and larger increase in the water content of the soil, comparing to the side without joints and have a wider range of influence. The opening degree of the joints crack in the middle of the model slope is the largest. The opening degree of the crack of the side slope with joints is about twice as large as that of the side without joints. The increase in pore water pressure on the side with joints is relatively large when the landslide occurs. The sensitivity and variation range of soil moisture content to rainfall is inversely proportional to the depth of burial. The response of moisture content in the superficial part of the slope body is quickly and fluctuates greatly while in the deep part it is opposite. The research results can provide experimental basis and theoretical reference for further clarifying the cause and failure mechanism of loess landslides. Landslide disasters occur frequently in China's loess plateau. Most of landslides are related to rainfall. The joint is also one of the important factors leading to the occurrence of loess landslides. In order to further reveal the influence of joints on loess landslides, this paper takes loess joints as the starting point of research. It is based on fieldwork and carries out a large-scale physical model test of artificial rainfall-induced landslides with preset joints. It carries out the real-time monitoring of the stage changes of soil water content and pore water pressure with the rainfall process. It analyses the expansion and evolution law of joints and fissures in the slope, as well as the trend of slope displacement and deformation. It reveals the potential mechanism of the existence of joints for inducing landslides and the law of slope response. The test results show the follows. The joints have obvious accelerating and promoting effects on the infiltration of rainwater inside the slope. The model slopes on the preset joint side have a faster and larger increase in the water content of the soil, comparing to the side without joints and have a wider range of influence. The opening degree of the joints crack in the middle of the model slope is the largest. The opening degree of the crack of the side slope with joints is about twice as large as that of the side without joints. The increase in pore water pressure on the side with joints is relatively large when the landslide occurs. The sensitivity and variation range of soil moisture content to rainfall is inversely proportional to the depth of burial. The response of moisture content in the superficial part of the slope body is quickly and fluctuates greatly while in the deep part it is opposite. The research results can provide experimental basis and theoretical reference for further clarifying the cause and failure mechanism of loess landslides.
Soil-rock mixture is a geological material with complex physical and mechanical properties. The stability evaluation of soil-rock mixture slope is very important in the field of engineering geology. In order to improve the ability of slope stability prediction, this paper presents a fusion algorithm by combining the particle swarm optimization swith the fruit fly optimization algorithm. Then based on the fusion algorithm, the paper constracts the machine learning prediction models for slope stability of soil-rock mixture. It uses three evaluation indexes to evaluate the accuracy of the models. Finally, the important analysis of input parameters is carried out using the gradient boosting decision tree model based on fusion algorithm. The results of this paper show the following. (1)Compared with the particle swarm and the fruit fly optimization algorithm, the fusion algorithm can effectively optimize the parameters of the machine learning model to significantly improve the prediction accuracy of the prediction model. (2)The prediction model of the gradient boosting decision tree model based on the fusion algorithm has the highest accuracy up to 93.33%, which is obviously better than the decision tree model and the stacking model with the fusion algorithm. (3)The structural factors that influence the stability of the soil-rock mixture slope are, from high to low, the inclination angle of the bedrock surface, the stone content, the overall slope angle, and the slope height. Soil-rock mixture is a geological material with complex physical and mechanical properties. The stability evaluation of soil-rock mixture slope is very important in the field of engineering geology. In order to improve the ability of slope stability prediction, this paper presents a fusion algorithm by combining the particle swarm optimization swith the fruit fly optimization algorithm. Then based on the fusion algorithm, the paper constracts the machine learning prediction models for slope stability of soil-rock mixture. It uses three evaluation indexes to evaluate the accuracy of the models. Finally, the important analysis of input parameters is carried out using the gradient boosting decision tree model based on fusion algorithm. The results of this paper show the following. (1)Compared with the particle swarm and the fruit fly optimization algorithm, the fusion algorithm can effectively optimize the parameters of the machine learning model to significantly improve the prediction accuracy of the prediction model. (2)The prediction model of the gradient boosting decision tree model based on the fusion algorithm has the highest accuracy up to 93.33%, which is obviously better than the decision tree model and the stacking model with the fusion algorithm. (3)The structural factors that influence the stability of the soil-rock mixture slope are, from high to low, the inclination angle of the bedrock surface, the stone content, the overall slope angle, and the slope height.
The Manas River Basin in Xinjiang have many geological disasters. This paper takes this area as the study area. It analyze the respective advantages and limitations of the information model and logistic regression model in the evaluation of the susceptibility to geological disasters. It explores and proposes the information-logistics model. Evaluation influencing factors include elevation, terrain relief, slope, slope aspect, terrain wetness index(TWI), lithology, water system, fault, and land use type. This study takes 355 geological disaster points in the whole region as sample data and analyses the characteristics of evaluation factors. Finally, the susceptibility of geological disasters is evaluated in the Manas River Basin through the ArcGIS platform. The evaluation results show that the high-risk area and the high-risk area are concentrated in the low-mountain and hilly areas in the southern part of the basin. The high-prone zone covers an area of 1, 760 square kilometers, 7.98% of the total area of the study area. The low-risk area covers an area of 2, 200 square kilometers, 9.97% of the total area of the study area. The evaluation accuracy is as high as 91.3%. These results can provide important reference for local geological disaster prevention and national land space planning. The Manas River Basin in Xinjiang have many geological disasters. This paper takes this area as the study area. It analyze the respective advantages and limitations of the information model and logistic regression model in the evaluation of the susceptibility to geological disasters. It explores and proposes the information-logistics model. Evaluation influencing factors include elevation, terrain relief, slope, slope aspect, terrain wetness index(TWI), lithology, water system, fault, and land use type. This study takes 355 geological disaster points in the whole region as sample data and analyses the characteristics of evaluation factors. Finally, the susceptibility of geological disasters is evaluated in the Manas River Basin through the ArcGIS platform. The evaluation results show that the high-risk area and the high-risk area are concentrated in the low-mountain and hilly areas in the southern part of the basin. The high-prone zone covers an area of 1, 760 square kilometers, 7.98% of the total area of the study area. The low-risk area covers an area of 2, 200 square kilometers, 9.97% of the total area of the study area. The evaluation accuracy is as high as 91.3%. These results can provide important reference for local geological disaster prevention and national land space planning.
The displacement of colluvial landslide in reservoir area is affected by the compound dynamics of the circulating fluctuation reservoir water level and rainfall. This paper is based on the systematic analysis of the change law of reservoir water level, rainfall and displacements of reservoir landslide. It proposes and determines the calculation method for the conversion coefficient k of rainfall and reservoir water dynamics. Through the conversion coefficient(k), the paper organically couples and superimposes the two different hydrodynamic loading effects of rainfall dynamics and reservoir water dynamics, and establishes the calculation method of compound hydrodynamic loading parameters. Then, the paper takes the compound hydrodynamic change and its displacement change as the dynamic loading parameters and its response parameters respectively, and establishes the physical prediction parameter and model of the displacement response ratio with dynamics increment for the reservoir landslide. At the same time, the paper studies the model to the systematic analysis and evaluation of the stability evolution of Baishuihe landslide under the compound hydrodynamic action. The results show that the change law of the compound hydrodynamic displacement response ratio with dynamics increment for the landslide is consistent with the dynamic evolution law of the stability. It is shown that the compound hydrodynamic displacement response ratio with dynamics increment is an effective physical evaluation parameter of reservoir landslide. The stability of this kind of landslide can be analyzed and evaluated by using this physical evaluation parameter and prediction model. The displacement of colluvial landslide in reservoir area is affected by the compound dynamics of the circulating fluctuation reservoir water level and rainfall. This paper is based on the systematic analysis of the change law of reservoir water level, rainfall and displacements of reservoir landslide. It proposes and determines the calculation method for the conversion coefficient k of rainfall and reservoir water dynamics. Through the conversion coefficient(k), the paper organically couples and superimposes the two different hydrodynamic loading effects of rainfall dynamics and reservoir water dynamics, and establishes the calculation method of compound hydrodynamic loading parameters. Then, the paper takes the compound hydrodynamic change and its displacement change as the dynamic loading parameters and its response parameters respectively, and establishes the physical prediction parameter and model of the displacement response ratio with dynamics increment for the reservoir landslide. At the same time, the paper studies the model to the systematic analysis and evaluation of the stability evolution of Baishuihe landslide under the compound hydrodynamic action. The results show that the change law of the compound hydrodynamic displacement response ratio with dynamics increment for the landslide is consistent with the dynamic evolution law of the stability. It is shown that the compound hydrodynamic displacement response ratio with dynamics increment is an effective physical evaluation parameter of reservoir landslide. The stability of this kind of landslide can be analyzed and evaluated by using this physical evaluation parameter and prediction model.
The morphological elements and development characteristics of landslides are important contents of the field investigation and remote sensing image identification of ancient landslides, and the engineering geology analysis of infrastructure route/site selection in mountainous areas. Due to the complex geological environment, there are a lot of ancient landslides in the eastern margin of the Tibetan Plateau under the internal and external dynamic geological actions. This paper takes Luanshibao Landslide, a large ancient landslide in Maoyaba Basin in the eastern margin of Tibetan Plateau, as an example to study the morphological elements of landslide ponds. It uses the UAV photogrammetry technology, hydrogeological survey, spontaneous potential geophysical exploration and seepage numerical simulation. It explores the geometric characteristics and seepage development characteristics of the Luanshibao Landslide ponds. It further reveals the development characteristics and formation mechanism of the Luanshibao Landslide pords. The results show that low-lying terrain is formed on the platform and main scarp of the landslide after the occurrence of Luanshibao Landslide. The groundwater along the Litang-Dewu fault produces spring water and surface runoff. The continuous recharge of groundwater eventually forms a large landslide pond with a volume of 5505 m3. The maximum water depth is 2 m on the west side of the landslide pond. In the process of landslide movement, the secondary scarp is formed under the platform at the back edge of landslide. The long-term action of the high waterhead of the upper landslide pond leads to the internal seepage in the loose and broken material structure of the slope body on the west side of the back edge of the landslide. A spring appears in the middle of the steep secondary scarp, and then forms a small landslide pond with the volume of 35 m3 at the low-lying terrain. Under the action of long-term seepage, there is a potential seepage erosion risk in the accumulation body. It is suggested to carry out a long-term observation research on seepage potential erosion rate of spring point at secondary sliding wall in the later stage, which provides an important basis for the evolution of Luanshibao Landslide ponds. The morphological elements and development characteristics of landslides are important contents of the field investigation and remote sensing image identification of ancient landslides, and the engineering geology analysis of infrastructure route/site selection in mountainous areas. Due to the complex geological environment, there are a lot of ancient landslides in the eastern margin of the Tibetan Plateau under the internal and external dynamic geological actions. This paper takes Luanshibao Landslide, a large ancient landslide in Maoyaba Basin in the eastern margin of Tibetan Plateau, as an example to study the morphological elements of landslide ponds. It uses the UAV photogrammetry technology, hydrogeological survey, spontaneous potential geophysical exploration and seepage numerical simulation. It explores the geometric characteristics and seepage development characteristics of the Luanshibao Landslide ponds. It further reveals the development characteristics and formation mechanism of the Luanshibao Landslide pords. The results show that low-lying terrain is formed on the platform and main scarp of the landslide after the occurrence of Luanshibao Landslide. The groundwater along the Litang-Dewu fault produces spring water and surface runoff. The continuous recharge of groundwater eventually forms a large landslide pond with a volume of 5505 m3. The maximum water depth is 2 m on the west side of the landslide pond. In the process of landslide movement, the secondary scarp is formed under the platform at the back edge of landslide. The long-term action of the high waterhead of the upper landslide pond leads to the internal seepage in the loose and broken material structure of the slope body on the west side of the back edge of the landslide. A spring appears in the middle of the steep secondary scarp, and then forms a small landslide pond with the volume of 35 m3 at the low-lying terrain. Under the action of long-term seepage, there is a potential seepage erosion risk in the accumulation body. It is suggested to carry out a long-term observation research on seepage potential erosion rate of spring point at secondary sliding wall in the later stage, which provides an important basis for the evolution of Luanshibao Landslide ponds.
The Taihang Grand Canyon Scenic Area in Huguan County, Shanxi Province is one of the ten most beautiful canyons in China, but frequent rockfall events seriously threaten the safe operation of the scenic spot. By incorporating high-precision topographic information and geotechnical properties, the slope angle distribution method was used for identification of potential rockfall sources at regional scale. Moreover, the failure sensitivity index of rock masses was introduced to quantitatively describe the instability probability of potential rockfall source areas. Then, the empirical model Flow-R was used to simulate the diffusion range of rockfall movements to obtain the propagation probability and energy distribution of rockfalls. Finally, a two-factor evaluation model was constructed to realize the quantitative evaluation of rockfall hazards in the study area. The main conclusions are as follows: (1)The area of potential rockfall sources in the study area is 25.7 km2(35.7%) and is mainly distributed in strips on the steep walls of the canyon. Among them, the area of high sensitivity to rock mass failure is 3.3 km2. (2)The high-hazard area of rockfalls in the study area is 3.22 km2, which mainly threatens the tourist distribution area and traffic routes in the scenic area, especially the provincial highway S327 near the entrance of Hongdou Gorge. (3)The field survey validation results show that the application of the slope angle distribution method is efficient and accurate in identifying rockfall source areas, and the proposed two-factor evaluation model can provide a rapid solution for rockfall hazard assessment in canyon areas. The complete technical solutions of "regional potential rockfall sources identification-instability probability analysis-rockfall hazard assessment" proposed in this study can provide technical reference for the early identification and risk assessment of rockfall events in similar alpine valley areas. The Taihang Grand Canyon Scenic Area in Huguan County, Shanxi Province is one of the ten most beautiful canyons in China, but frequent rockfall events seriously threaten the safe operation of the scenic spot. By incorporating high-precision topographic information and geotechnical properties, the slope angle distribution method was used for identification of potential rockfall sources at regional scale. Moreover, the failure sensitivity index of rock masses was introduced to quantitatively describe the instability probability of potential rockfall source areas. Then, the empirical model Flow-R was used to simulate the diffusion range of rockfall movements to obtain the propagation probability and energy distribution of rockfalls. Finally, a two-factor evaluation model was constructed to realize the quantitative evaluation of rockfall hazards in the study area. The main conclusions are as follows: (1)The area of potential rockfall sources in the study area is 25.7 km2(35.7%) and is mainly distributed in strips on the steep walls of the canyon. Among them, the area of high sensitivity to rock mass failure is 3.3 km2. (2)The high-hazard area of rockfalls in the study area is 3.22 km2, which mainly threatens the tourist distribution area and traffic routes in the scenic area, especially the provincial highway S327 near the entrance of Hongdou Gorge. (3)The field survey validation results show that the application of the slope angle distribution method is efficient and accurate in identifying rockfall source areas, and the proposed two-factor evaluation model can provide a rapid solution for rockfall hazard assessment in canyon areas. The complete technical solutions of "regional potential rockfall sources identification-instability probability analysis-rockfall hazard assessment" proposed in this study can provide technical reference for the early identification and risk assessment of rockfall events in similar alpine valley areas.
The red-bed soft rock has weak water permeability and strong hydrophilicity, and is prone to softening and disintegration under the influence of water content and hydrothermal(temperature and rainfall) changes, which brings challenges to engineering construction and geological environment in red-bed soft rock areas. This paper studies the disintegration characteristics and microscopic mechanism of red-bed soft rock under different water contents and various hydrothermal test conditions. It uses samples from the red-bed soft rock excavations of the slopes of the Jintang and Zhongjiang sections in Western Sichuan. It uses a self-made rainfall device and temperature control equipement to carry out the cyclic disintegration tests on samples with different initial water contents under multi-hydrothermal test conditions. Red-bed soft rock disintegration is studied from five aspects including macro-morphological evolution, micro-structure and mineral difference, disintegration coefficient, R value(disintegration mass loss rate), and particle analysis after disintegration. The test results show a certain interaction between the macroscopic morphology evolution characteristics of the red-bed soft rock and the changes in micro-structure and mineral differences. The clay mineral content can be the main internal cause of disintegration of red-bed soft rock and is positively correlated with disintegration. The degree of disintegration is closely related to initial water content and hydrothermal effect. The R values of the two red-bed soft rock samples range from 0.22% to 1.63% and 0.05% to 2.17%. The particle size distribution is a good indicator for the degree of disintegration of a red-bed soft rock. Higher disintegration is characterized by fewer large and more small particles, and the small particles are mostly concentrated between 0.075 and 0.5 mm. A combined analysis of the disintegration coefficient, R value, and final particle size distribution curve can be effective for quantitatively assessing the disintegration and explaining the disintegration evolution characteristics of red-bed soft rock in conjunction with micro-structure and mineral differences. The research results can provide a certain reference for the engineering construction and geological evaluation of Jintang, Zhongjiang, and other red-bed soft rock areas in Sichuan. The red-bed soft rock has weak water permeability and strong hydrophilicity, and is prone to softening and disintegration under the influence of water content and hydrothermal(temperature and rainfall) changes, which brings challenges to engineering construction and geological environment in red-bed soft rock areas. This paper studies the disintegration characteristics and microscopic mechanism of red-bed soft rock under different water contents and various hydrothermal test conditions. It uses samples from the red-bed soft rock excavations of the slopes of the Jintang and Zhongjiang sections in Western Sichuan. It uses a self-made rainfall device and temperature control equipement to carry out the cyclic disintegration tests on samples with different initial water contents under multi-hydrothermal test conditions. Red-bed soft rock disintegration is studied from five aspects including macro-morphological evolution, micro-structure and mineral difference, disintegration coefficient, R value(disintegration mass loss rate), and particle analysis after disintegration. The test results show a certain interaction between the macroscopic morphology evolution characteristics of the red-bed soft rock and the changes in micro-structure and mineral differences. The clay mineral content can be the main internal cause of disintegration of red-bed soft rock and is positively correlated with disintegration. The degree of disintegration is closely related to initial water content and hydrothermal effect. The R values of the two red-bed soft rock samples range from 0.22% to 1.63% and 0.05% to 2.17%. The particle size distribution is a good indicator for the degree of disintegration of a red-bed soft rock. Higher disintegration is characterized by fewer large and more small particles, and the small particles are mostly concentrated between 0.075 and 0.5 mm. A combined analysis of the disintegration coefficient, R value, and final particle size distribution curve can be effective for quantitatively assessing the disintegration and explaining the disintegration evolution characteristics of red-bed soft rock in conjunction with micro-structure and mineral differences. The research results can provide a certain reference for the engineering construction and geological evaluation of Jintang, Zhongjiang, and other red-bed soft rock areas in Sichuan.
Landslide instability in the reservoir area usually disproportionately impacts on the safety of life and production. Reliable landslide displacement prediction is of great importance for risk warning and disaster prevention and mitigation. However, conventional displacement prediction models fail to consider the lag effect of landslide deformation induced by the controlling factors(rainfall and reservoir water level), and to determine the lag time and the degree of influence. This paper takes the Xinpu landslide in the Three Gorges reservoir area as an example. The lag effect of landslide deformation induced by rainfall and reservoir water level at the hillslope scale is quantitatively described using Pearson correlation coefficient method based on the displacement monitoring and hydro-meteorological dataset in 2021. A novel landslide displacement prediction method considering the lag effect is presented using BP neural network model. The results show that the time lag effect of surface deformation induced by reservoir water level changes is obvious on the hillside scale. The lag time shows a pattern of increasing from near shore to far shore. The time lag effect induced by rainfall on surface deformation is weaker, and shows a pattern of low correlation with shorter lag time. Compared with the prediction model without considering the time lag effect, the fit of the model accounting for time lag effect is improved by 55.77%, and the root mean square error is reduced by 31.5%. The research results reveal the deformation mechanism of large-scale reservoir landslides to a certain extent, which can provide a reference for displacement prediction of similar landslides. Landslide instability in the reservoir area usually disproportionately impacts on the safety of life and production. Reliable landslide displacement prediction is of great importance for risk warning and disaster prevention and mitigation. However, conventional displacement prediction models fail to consider the lag effect of landslide deformation induced by the controlling factors(rainfall and reservoir water level), and to determine the lag time and the degree of influence. This paper takes the Xinpu landslide in the Three Gorges reservoir area as an example. The lag effect of landslide deformation induced by rainfall and reservoir water level at the hillslope scale is quantitatively described using Pearson correlation coefficient method based on the displacement monitoring and hydro-meteorological dataset in 2021. A novel landslide displacement prediction method considering the lag effect is presented using BP neural network model. The results show that the time lag effect of surface deformation induced by reservoir water level changes is obvious on the hillside scale. The lag time shows a pattern of increasing from near shore to far shore. The time lag effect induced by rainfall on surface deformation is weaker, and shows a pattern of low correlation with shorter lag time. Compared with the prediction model without considering the time lag effect, the fit of the model accounting for time lag effect is improved by 55.77%, and the root mean square error is reduced by 31.5%. The research results reveal the deformation mechanism of large-scale reservoir landslides to a certain extent, which can provide a reference for displacement prediction of similar landslides.
The combined structure of anchor cables and stabilizing piles is the main measure for slope reinforcement. In reinforcement design, the traditional safety factor cannot reflect the influence of seismic wave types. This paper aims to accurately evaluate the stability of the slope and carries out the research on the performance design method. Based on the limit analysis method, the displacement formula of stabilizing pile is derived. The difference between far and near field seismic waves is compared under the framework of vulnerability. The results show that: (1)Introducing the nonlinear model into the Newmark method can realize the real-time update of the anti-sliding force. (2)Considering the randomness of seismic loads, the performance-based design method is more reasonable. The fragility curve can be used to quantitatively evaluate the failure probability of the slope. (3)The failure state of the slope is related to the earthquake intensity and the type of ground motion. When the earthquake intensity is low, the probability of minor damage and moderate damage is greater. With the increase of earthquake intensity, the slope is more prone to serious damage. Near-field earthquakes have the characteristics of high energy and strong impact, which are more likely to cause slope instability. The combined structure of anchor cables and stabilizing piles is the main measure for slope reinforcement. In reinforcement design, the traditional safety factor cannot reflect the influence of seismic wave types. This paper aims to accurately evaluate the stability of the slope and carries out the research on the performance design method. Based on the limit analysis method, the displacement formula of stabilizing pile is derived. The difference between far and near field seismic waves is compared under the framework of vulnerability. The results show that: (1)Introducing the nonlinear model into the Newmark method can realize the real-time update of the anti-sliding force. (2)Considering the randomness of seismic loads, the performance-based design method is more reasonable. The fragility curve can be used to quantitatively evaluate the failure probability of the slope. (3)The failure state of the slope is related to the earthquake intensity and the type of ground motion. When the earthquake intensity is low, the probability of minor damage and moderate damage is greater. With the increase of earthquake intensity, the slope is more prone to serious damage. Near-field earthquakes have the characteristics of high energy and strong impact, which are more likely to cause slope instability.
Urban geological environment, as an important carrier of urban sustainable development, can provide necessary land, mineral and other resources for human production and life. However, there are still a series of adverse geological phenomena, such as land subsidence and landslides, which seriously threaten the health and safety of the city. On this basis, a new evaluation method is needed for urban daily management to clarify the current specific status of each region of the city. Based on this, the basic concept of urban geological environment health is put forward. It is necessary to comprehensively apply the theory and practice of geology to its evaluation, give a quantitative evaluation, and determine the health level of different areas of the city, from the perspective of urban construction and management, residents' life and safety, and on the basis of comprehensive and systematic investigation and analysis of the geological environment. In this paper, the main work is to establish a complete theoretical system of urban geological environment health, define the concept of urban geological environment health, explain its connotation and extension, analyze its influencing factors, establish a corresponding evaluation system, and give the use method of the evaluation system. Specifically, taking Shanghai as an example, the established system is used to evaluate the geological environment health level of various regions in Shanghai. Urban geological environment, as an important carrier of urban sustainable development, can provide necessary land, mineral and other resources for human production and life. However, there are still a series of adverse geological phenomena, such as land subsidence and landslides, which seriously threaten the health and safety of the city. On this basis, a new evaluation method is needed for urban daily management to clarify the current specific status of each region of the city. Based on this, the basic concept of urban geological environment health is put forward. It is necessary to comprehensively apply the theory and practice of geology to its evaluation, give a quantitative evaluation, and determine the health level of different areas of the city, from the perspective of urban construction and management, residents' life and safety, and on the basis of comprehensive and systematic investigation and analysis of the geological environment. In this paper, the main work is to establish a complete theoretical system of urban geological environment health, define the concept of urban geological environment health, explain its connotation and extension, analyze its influencing factors, establish a corresponding evaluation system, and give the use method of the evaluation system. Specifically, taking Shanghai as an example, the established system is used to evaluate the geological environment health level of various regions in Shanghai.
The overburden layer with large thickness and strong-weak-strong permeability combination is widely distributed in valleys of southwestern China. This paper studies the characteristics and influencing factors of the dam foundation seepage field in the interbed type hydrogeological structure. It uses Visual MODFLOW to simulate the seepage field of 16 working conditions with two types of constant thickness and variable thickness. It analyzes the influence of permeability and thickness of the weak permeable layers to the seepage field morphology, by the change of head difference and hydraulic gradient of roof and floor of the weak permeable layer. The paper reaches the following conclusions. The plane seepage field of dam foundation is strongly influenced by the property of strong permeable cover in upper layer. In constant thickness condition, the head difference of weak permeable roof and floor is related to the permeability ratio of strong permeable layer to weak permeable layer. When the permeability ratio of strong and weak permeable layers is greater than 500, the head difference of weak permeable roof and floor changes slightly. In variable thickness condition, the head difference of weak permeable roof and floor increases with the thickness of weak permeable layer. When the thickness of weak permeable layer is greater than 20m, the head difference changes weakly. Hydraulic gradient decreases with increasing thickness of weak permeable layer. In conclusion, the thickness and permeability of the weak permeable layer play a controlling role in the seepage field in the interlayer hydrogeological structure. The research results can provide support for water prevention and control of dam foundation of water conservancy and hydropower projects in deep covered valley. The overburden layer with large thickness and strong-weak-strong permeability combination is widely distributed in valleys of southwestern China. This paper studies the characteristics and influencing factors of the dam foundation seepage field in the interbed type hydrogeological structure. It uses Visual MODFLOW to simulate the seepage field of 16 working conditions with two types of constant thickness and variable thickness. It analyzes the influence of permeability and thickness of the weak permeable layers to the seepage field morphology, by the change of head difference and hydraulic gradient of roof and floor of the weak permeable layer. The paper reaches the following conclusions. The plane seepage field of dam foundation is strongly influenced by the property of strong permeable cover in upper layer. In constant thickness condition, the head difference of weak permeable roof and floor is related to the permeability ratio of strong permeable layer to weak permeable layer. When the permeability ratio of strong and weak permeable layers is greater than 500, the head difference of weak permeable roof and floor changes slightly. In variable thickness condition, the head difference of weak permeable roof and floor increases with the thickness of weak permeable layer. When the thickness of weak permeable layer is greater than 20m, the head difference changes weakly. Hydraulic gradient decreases with increasing thickness of weak permeable layer. In conclusion, the thickness and permeability of the weak permeable layer play a controlling role in the seepage field in the interlayer hydrogeological structure. The research results can provide support for water prevention and control of dam foundation of water conservancy and hydropower projects in deep covered valley.
The overburden subsidence of coal seam mining is ahead of the surface subsidence and can be used as an early warning indicator of surface stability. This paper studies the problem of overburden subsidence prediction caused by coal seam mining, uses distributed optical fiber sensing technology, makes a similar material test model for mining overburden in Daliuta Coal Mine, and study the deformation characteristics of overburden caused by coal seam mining. Based on grey theory and Knothe time function, the paper further establishes a prediction model of mining overburden settlement based on measured strain, and discusses the accuracy of the prediction model. It achieves the following research results. Overburden strain distribution based on distributed optical fiber sensing technology accurately reflects development characteristics of falling zone and water-conducting fracture zone. The prediction accuracy of overburden settlement based on GM(1, 1)model and metabolic model is better but limited to short-term prediction. According to the calculation method of reverse parameters when the relative residual maximum value and the sum of relative residual take the minimum value, the settlement parameters c value and τ value are solved, which improves the accuracy of the Knothe time function prediction. The paper also establishes the expression of dynamic subsidence prediction model of overlying strata in Daliuta coal seam, which is suitable for the early stage and later stage prediction of overlying strata subsidence. The overburden subsidence of coal seam mining is ahead of the surface subsidence and can be used as an early warning indicator of surface stability. This paper studies the problem of overburden subsidence prediction caused by coal seam mining, uses distributed optical fiber sensing technology, makes a similar material test model for mining overburden in Daliuta Coal Mine, and study the deformation characteristics of overburden caused by coal seam mining. Based on grey theory and Knothe time function, the paper further establishes a prediction model of mining overburden settlement based on measured strain, and discusses the accuracy of the prediction model. It achieves the following research results. Overburden strain distribution based on distributed optical fiber sensing technology accurately reflects development characteristics of falling zone and water-conducting fracture zone. The prediction accuracy of overburden settlement based on GM(1, 1)model and metabolic model is better but limited to short-term prediction. According to the calculation method of reverse parameters when the relative residual maximum value and the sum of relative residual take the minimum value, the settlement parameters c value and τ value are solved, which improves the accuracy of the Knothe time function prediction. The paper also establishes the expression of dynamic subsidence prediction model of overlying strata in Daliuta coal seam, which is suitable for the early stage and later stage prediction of overlying strata subsidence.
Quantitative characterization of rockmass discontinuities has significant impact on the evaluation of slope stability. Considering the situation of the complex terrain and the difficulty of manual measurement at high and steep rock slope,unsatisfactory slope model construction affects the accuracy of slope stability analysis. This paper presents a field application on Yinshan open-pit copper mine in Dexing,Jiangxi Province. 3D point cloud model is first generated based on unmanned aerial vehicle(UAV)photogrammetry integrated with a structure from-motion(SfM)technique. An automatic procedure for discontinuity detection,digital trace mapping and discontinuity parameters is established. The parameters include the orientation,number of sets,trace length,and set spacing. The extracted values are compared with planned manual measurements through scanline method. The results show that the slope shape and the rockmass model obtained by the UAV photogrammetry are more in line with the actual rock slope. The discrete fracture network(DFN) is established based on the statistic model of rockmass. Then a 3D numerical model is quickly built using non-uniform rational B-spline(NURBS)surface reconstruction and a combined modeling method of "Rhino-Griddle-3DEC". And better numerical simulation results are obtained to meet the demands of open pit mine slope stability analysis. Quantitative characterization of rockmass discontinuities has significant impact on the evaluation of slope stability. Considering the situation of the complex terrain and the difficulty of manual measurement at high and steep rock slope,unsatisfactory slope model construction affects the accuracy of slope stability analysis. This paper presents a field application on Yinshan open-pit copper mine in Dexing,Jiangxi Province. 3D point cloud model is first generated based on unmanned aerial vehicle(UAV)photogrammetry integrated with a structure from-motion(SfM)technique. An automatic procedure for discontinuity detection,digital trace mapping and discontinuity parameters is established. The parameters include the orientation,number of sets,trace length,and set spacing. The extracted values are compared with planned manual measurements through scanline method. The results show that the slope shape and the rockmass model obtained by the UAV photogrammetry are more in line with the actual rock slope. The discrete fracture network(DFN) is established based on the statistic model of rockmass. Then a 3D numerical model is quickly built using non-uniform rational B-spline(NURBS)surface reconstruction and a combined modeling method of "Rhino-Griddle-3DEC". And better numerical simulation results are obtained to meet the demands of open pit mine slope stability analysis.
When the gravel layer is excavated,the main failure mode is not the general macro overall shear failure. Instead,it is a process that a cutting tool cuts into the gap between pebbles and gravels to peel the pebbles and gravels out of the original stratum. This process is more in line with the physical and mechanical hypothesis of particle discrete element. In order to determine the optimal meso parameters of granular materials under excavation conditions,the three-dimensional cutting simulation is carried out for granular materials with different combination of meso parameters. The parameters include particle contact normal stiffness,contact stiffness ratio,inter particle friction coefficient,particle shape,and particle size. The effects of different meso parameters on excavation are analyzed and studied. The calculation results show that a variety of combinations of meso parameters,such as the normal stiffness of particle contact and the contact stiffness ratio can correspond to the same macro elastic modulus value. The combination of meso parameters with large contact stiffness ratio has greater capability for resisting excavation. The combination of multiple meso parameters of particle shape and inter particle friction coefficient can correspond to the same internal friction angle value. The particle material with complex shape has greater capability for resisting digging. Under the same macro parameters,the larger the average particle size,the greater the resisting digging capability. Therefore,when using the particle discrete element to simulate the excavation of gravel stratum,it is also necessary to further calibrate the meso parameters according to the excavation resistance ability of the material and to obtain a simulation effect closer to the actual situation in addition to ensuring that the macroscopic overall shear failure response of the virtual particle material is basically consistent with the real material. The method proposed in this paper can provide a reference for the parameter calibration of other particle discrete element numerical simulation of excavation conditions. When the gravel layer is excavated,the main failure mode is not the general macro overall shear failure. Instead,it is a process that a cutting tool cuts into the gap between pebbles and gravels to peel the pebbles and gravels out of the original stratum. This process is more in line with the physical and mechanical hypothesis of particle discrete element. In order to determine the optimal meso parameters of granular materials under excavation conditions,the three-dimensional cutting simulation is carried out for granular materials with different combination of meso parameters. The parameters include particle contact normal stiffness,contact stiffness ratio,inter particle friction coefficient,particle shape,and particle size. The effects of different meso parameters on excavation are analyzed and studied. The calculation results show that a variety of combinations of meso parameters,such as the normal stiffness of particle contact and the contact stiffness ratio can correspond to the same macro elastic modulus value. The combination of meso parameters with large contact stiffness ratio has greater capability for resisting excavation. The combination of multiple meso parameters of particle shape and inter particle friction coefficient can correspond to the same internal friction angle value. The particle material with complex shape has greater capability for resisting digging. Under the same macro parameters,the larger the average particle size,the greater the resisting digging capability. Therefore,when using the particle discrete element to simulate the excavation of gravel stratum,it is also necessary to further calibrate the meso parameters according to the excavation resistance ability of the material and to obtain a simulation effect closer to the actual situation in addition to ensuring that the macroscopic overall shear failure response of the virtual particle material is basically consistent with the real material. The method proposed in this paper can provide a reference for the parameter calibration of other particle discrete element numerical simulation of excavation conditions.
The deformation of surrounding rock in deep depth caused by high in-situ stress is a key factor that restricts the safe and efficient construction of TBM tunnel. As a result of deep depth,high in-situ stress,and hard rock,there are different kinds of failures in the surrounding rock after the excavation unloading. The failure pattern varies with time and the degree of stress concentration. It may cause vault settlement and arch bottom uplift,which greatly threaten the safety of construction personnel and equipment. The failure pattern and deformation of surrounding rock of Yin-Han-Ji-Wei water conveyance tunnel(K45+534.70-K45+701.92) are monitored and examined in this present paper. The process of surrounding rock failure is analyzed. The law of deformation of arch shoulder and vault is revealed,and the support measures for deformation of hard rock with high in-situ stress are put forward. As a result of tangential stress of surrounding rock,tensile-shear failure is mainly caused by splitting. The failures of surrounding rock include rock burst and static brittle failure(rib spalling,exfoliation,slabbing failure). The deformation of surrounding rock can be divided into three stages: rapid deformation stage,transitional stage and slow deformation stage. The deformation at initial two stages is about 60% ~80% of ultimate deformation. Accelerated deformation may occur two or three times in some conditions. The first acceleration is mainly caused by the opening cracks,the dilatation of rock slab and the partial flexion,which occurs quickly and lasts for a short time. However,the second acceleration deformation is mainly caused by the deflection of rock slab and the expansion of rock block. Its deformation speed is small but the duration is long. The surrounding rock support measures including NPR bolt,steel arch and steel fiber reinforced concrete are put forward,which provides engineering experience and theoretical basis for the safe and efficient construction of similar TBM tunnels. The deformation of surrounding rock in deep depth caused by high in-situ stress is a key factor that restricts the safe and efficient construction of TBM tunnel. As a result of deep depth,high in-situ stress,and hard rock,there are different kinds of failures in the surrounding rock after the excavation unloading. The failure pattern varies with time and the degree of stress concentration. It may cause vault settlement and arch bottom uplift,which greatly threaten the safety of construction personnel and equipment. The failure pattern and deformation of surrounding rock of Yin-Han-Ji-Wei water conveyance tunnel(K45+534.70-K45+701.92) are monitored and examined in this present paper. The process of surrounding rock failure is analyzed. The law of deformation of arch shoulder and vault is revealed,and the support measures for deformation of hard rock with high in-situ stress are put forward. As a result of tangential stress of surrounding rock,tensile-shear failure is mainly caused by splitting. The failures of surrounding rock include rock burst and static brittle failure(rib spalling,exfoliation,slabbing failure). The deformation of surrounding rock can be divided into three stages: rapid deformation stage,transitional stage and slow deformation stage. The deformation at initial two stages is about 60% ~80% of ultimate deformation. Accelerated deformation may occur two or three times in some conditions. The first acceleration is mainly caused by the opening cracks,the dilatation of rock slab and the partial flexion,which occurs quickly and lasts for a short time. However,the second acceleration deformation is mainly caused by the deflection of rock slab and the expansion of rock block. Its deformation speed is small but the duration is long. The surrounding rock support measures including NPR bolt,steel arch and steel fiber reinforced concrete are put forward,which provides engineering experience and theoretical basis for the safe and efficient construction of similar TBM tunnels.
Evaluation of geological conditions and excavation risks is one of the important stages in the process of design and construction of underground engineering. It is very important to estimate and identify the potential trend of deformation of rock mass when selecting appropriate excavation methods and support systems. In the present study,we study the potential deformation trend of rock mass in Lianhua tunnel of Pinglian expressway. Firstly,we introduce the engineering geological environment,engineering characteristics of surrounding rock,rock mass quality evaluation and field measured deformation of Lianhua tunnel. Then,the deformation trend of Lianhua tunnel is predicted by empirical method and semi-empirical and semi-theoretical method. The predicted results are compared with the actual results of deformation monitoring. The results indicate that the large deformation of Lianhua tunnel is mainly affected by the loose and broken soft surrounding rock,abundant underground and surface water,fault fracture zone and tectonic activities. For Lianhua tunnel,there are problems in the current large deformation prediction methods: the empirical method mainly predicts the deformation trend based on the results of rock mass quality classification,which has certain subjectivity. A certain deviation exists between the prediction results and the actual deformation results. For semi-empirical semi-theoretical method,the prediction effect of based on the relationship between the strength and stress of surrounding rock is pretty good,but the results of Jethwa's method,Hoek's method and ISRM method based on the ratio of strength of surrounding rock and geo-stress are relatively conservative. To sum up,the surrounding rock quality classification,ground stress measurement,groundwater and geological structure exploration shall be carried out objectively and carefully in the stage of engineering investigation and design. The large deformation trend and value shall be predicted by combining the empirical method and semi-empirical and semi-theoretical method,so as to provide sufficient and reliable basis for the design and construction. Evaluation of geological conditions and excavation risks is one of the important stages in the process of design and construction of underground engineering. It is very important to estimate and identify the potential trend of deformation of rock mass when selecting appropriate excavation methods and support systems. In the present study,we study the potential deformation trend of rock mass in Lianhua tunnel of Pinglian expressway. Firstly,we introduce the engineering geological environment,engineering characteristics of surrounding rock,rock mass quality evaluation and field measured deformation of Lianhua tunnel. Then,the deformation trend of Lianhua tunnel is predicted by empirical method and semi-empirical and semi-theoretical method. The predicted results are compared with the actual results of deformation monitoring. The results indicate that the large deformation of Lianhua tunnel is mainly affected by the loose and broken soft surrounding rock,abundant underground and surface water,fault fracture zone and tectonic activities. For Lianhua tunnel,there are problems in the current large deformation prediction methods: the empirical method mainly predicts the deformation trend based on the results of rock mass quality classification,which has certain subjectivity. A certain deviation exists between the prediction results and the actual deformation results. For semi-empirical semi-theoretical method,the prediction effect of based on the relationship between the strength and stress of surrounding rock is pretty good,but the results of Jethwa's method,Hoek's method and ISRM method based on the ratio of strength of surrounding rock and geo-stress are relatively conservative. To sum up,the surrounding rock quality classification,ground stress measurement,groundwater and geological structure exploration shall be carried out objectively and carefully in the stage of engineering investigation and design. The large deformation trend and value shall be predicted by combining the empirical method and semi-empirical and semi-theoretical method,so as to provide sufficient and reliable basis for the design and construction.
During the construction of a large section rectangular pipe jacking over an existing subway tunnel,the unloading effect caused by the close excavation of the soil leads to the floating deformation of the existing subway tunnel,which can endanger the safety of subway operation. In order to study the influence of the large-section rectangular pipe jacking construction on the deformation of existing subway tunnels,this paper takes the rectangular pipe jacking project of the comprehensive pipe corridor in Changhe West Road(Zhaoshan Street~Luyang Street),Tongzhou District,Beijing as research project. This paper uses FLAC3D finite difference software,establishes a 3D numerical model of a large section rectangular pipe jacking over an existing subway tunnel and studies the floating deformation pattern of the subway tunnel caused by double-line rectangular pipe jacking construction and the influence of different anti-floating weights on the deformation of the existing subway tunnel. The simulation results are compared with on-site monitoring data to verify the accuracy of the numerical model. The results show that the floating deformation of the subway tunnel caused by the double-line pipe jacking construction is larger than that caused by the single-line pipe jacking. The maximum floating deformation is located at the axis of the pipe jacking tunnel. When a counterweight similar to the weight of the soil lost by excavation is applied,the original horizontal deformation pattern of the subway tunnel can be changed as follows. (1)The subway tunnel that has been traversed first moves to the direction of the originating shaft; (2)The subway tunnel that has been traversed later moves to the direction of the receiving shaft. Floating deformation and tensile stress of subway tunnel decrease with the increase of anti-floating weights. Applying anti-floating weight of 50% of the lost soil weight during excavation can control the floating deformation of the subway tunnel within 1.4 mm. The results provide a reference for the anti-floating design of the subway tunnel in this project. During the construction of a large section rectangular pipe jacking over an existing subway tunnel,the unloading effect caused by the close excavation of the soil leads to the floating deformation of the existing subway tunnel,which can endanger the safety of subway operation. In order to study the influence of the large-section rectangular pipe jacking construction on the deformation of existing subway tunnels,this paper takes the rectangular pipe jacking project of the comprehensive pipe corridor in Changhe West Road(Zhaoshan Street~Luyang Street),Tongzhou District,Beijing as research project. This paper uses FLAC3D finite difference software,establishes a 3D numerical model of a large section rectangular pipe jacking over an existing subway tunnel and studies the floating deformation pattern of the subway tunnel caused by double-line rectangular pipe jacking construction and the influence of different anti-floating weights on the deformation of the existing subway tunnel. The simulation results are compared with on-site monitoring data to verify the accuracy of the numerical model. The results show that the floating deformation of the subway tunnel caused by the double-line pipe jacking construction is larger than that caused by the single-line pipe jacking. The maximum floating deformation is located at the axis of the pipe jacking tunnel. When a counterweight similar to the weight of the soil lost by excavation is applied,the original horizontal deformation pattern of the subway tunnel can be changed as follows. (1)The subway tunnel that has been traversed first moves to the direction of the originating shaft; (2)The subway tunnel that has been traversed later moves to the direction of the receiving shaft. Floating deformation and tensile stress of subway tunnel decrease with the increase of anti-floating weights. Applying anti-floating weight of 50% of the lost soil weight during excavation can control the floating deformation of the subway tunnel within 1.4 mm. The results provide a reference for the anti-floating design of the subway tunnel in this project.
China has a complex water system with severe flood control and disaster reduction situations. There is an urgent need to continuously enhance the level of embankment safety monitoring. The seepage field in embankment is a crucial factor affecting the embankment safety,so the identification of the characteristics of the flow field is an essential prerequisite to ensure the embankment security. To make up for the insufficiency of conventional flow field monitoring technology,we carry out single-borehole thermal response tests based on the Actively Heated Fiber Optics Based Thermal Response Test(ATRT) and explores the advanced evaluation method of the seepage field in embankment by taking the collapse site in the Zhinan Village,Yangzhong city. The Zhinan Village collapse is known as the most significant collapse on the Yangtze River. The results show that: (1)ATRT can obtain temperature response data with a high temporal-spatial resolution(temporal sampling interval 30 s,spatial sampling interval 0.41 m),thereby identifying the differences in groundwater flow rate in different strata; (2)Groundwater flow rates in fine sand and gravel sand have different evolution law; (3)The groundwater flow field in the collapse site of Zhinan Village has a connection with the surface water,and groundwater rate is characterized by "The groundwater rate near the riverbank is high,while that far away from the riverbank is low",which may be an essential cause of the collapse. The research results verify the feasibility of ATRT in evaluating the seepage field in embankment characteristics. The method can obtain the vertical distribution characteristic of the flow field with a high spatial resolution based on a single borehole. The ATRT technology is simple and shows excellent application potential in evaluating the seepage field in embankment. China has a complex water system with severe flood control and disaster reduction situations. There is an urgent need to continuously enhance the level of embankment safety monitoring. The seepage field in embankment is a crucial factor affecting the embankment safety,so the identification of the characteristics of the flow field is an essential prerequisite to ensure the embankment security. To make up for the insufficiency of conventional flow field monitoring technology,we carry out single-borehole thermal response tests based on the Actively Heated Fiber Optics Based Thermal Response Test(ATRT) and explores the advanced evaluation method of the seepage field in embankment by taking the collapse site in the Zhinan Village,Yangzhong city. The Zhinan Village collapse is known as the most significant collapse on the Yangtze River. The results show that: (1)ATRT can obtain temperature response data with a high temporal-spatial resolution(temporal sampling interval 30 s,spatial sampling interval 0.41 m),thereby identifying the differences in groundwater flow rate in different strata; (2)Groundwater flow rates in fine sand and gravel sand have different evolution law; (3)The groundwater flow field in the collapse site of Zhinan Village has a connection with the surface water,and groundwater rate is characterized by "The groundwater rate near the riverbank is high,while that far away from the riverbank is low",which may be an essential cause of the collapse. The research results verify the feasibility of ATRT in evaluating the seepage field in embankment characteristics. The method can obtain the vertical distribution characteristic of the flow field with a high spatial resolution based on a single borehole. The ATRT technology is simple and shows excellent application potential in evaluating the seepage field in embankment.
Shield tunnel construction in the biogenic gas-rich ground is a dangerous procedure. Biogenic gas is prone to penetrate shield TBM and shield tunnel through excavation cabin, slurry pipeline, tail clearance and segment clearance. It will induce combustion and explosion accidents and threaten the construction safety of shield tunnels. To seal and block the leakage of biogenic gas, clay shock is utilized to fill the gap between the middle shield and tunnel wall. In this study, aiming at the sealing and blocking problem of biogenic gas in the process of shield tunneling, a test apparatus and test method for analyzing the sealing and blocking effect of clay shock on biogenic gas have been developed. The correlation between clay shock injection thickness and gas breakdown time has been studied. The permeation mechanism of biogenic gas has been revealed. The application effect of clay shock in Sutong GIL Yangtze River Crossing Cable Tunnel has been verified. The results indicate that the gas breakdown time increases linearly with the increase of clay shock thickness. When clay shock thickness is 30 mm, the average breakdown time is 51.5 min, which exceeds the longest time required for single-ring segment assembly by 50 min and meets the requirements of the Sutong GIL Yangtze River Crossing Cable Tunnel. Field gas monitoring results indicate that when the excavation gap is filled with clay shock during shield tunnel construction, the concentration of CH4 and CO are within the allowable range and clay shock achieves the sealing and blocking effect compared to the absence of biogenic gas prevention measures. The presented study provides a theoretical basis and technical support for the prevention and control of biogenic gas in similar engineering geological conditions. Shield tunnel construction in the biogenic gas-rich ground is a dangerous procedure. Biogenic gas is prone to penetrate shield TBM and shield tunnel through excavation cabin, slurry pipeline, tail clearance and segment clearance. It will induce combustion and explosion accidents and threaten the construction safety of shield tunnels. To seal and block the leakage of biogenic gas, clay shock is utilized to fill the gap between the middle shield and tunnel wall. In this study, aiming at the sealing and blocking problem of biogenic gas in the process of shield tunneling, a test apparatus and test method for analyzing the sealing and blocking effect of clay shock on biogenic gas have been developed. The correlation between clay shock injection thickness and gas breakdown time has been studied. The permeation mechanism of biogenic gas has been revealed. The application effect of clay shock in Sutong GIL Yangtze River Crossing Cable Tunnel has been verified. The results indicate that the gas breakdown time increases linearly with the increase of clay shock thickness. When clay shock thickness is 30 mm, the average breakdown time is 51.5 min, which exceeds the longest time required for single-ring segment assembly by 50 min and meets the requirements of the Sutong GIL Yangtze River Crossing Cable Tunnel. Field gas monitoring results indicate that when the excavation gap is filled with clay shock during shield tunnel construction, the concentration of CH4 and CO are within the allowable range and clay shock achieves the sealing and blocking effect compared to the absence of biogenic gas prevention measures. The presented study provides a theoretical basis and technical support for the prevention and control of biogenic gas in similar engineering geological conditions.
Plant has been widely recognized for improving the sustainable performance of geotechnical infrastructures. However, the influences of plant growth on water infiltration into layered landfill cover are still unclear. This study aims to quantify the effects of plant growth on the variations of soil hydraulic properties and water infiltration into a three-layer landfill cover using recycled concrete without geomembrane under humid climates. Full-scale field monitoring was carried out for two years at the Shenzhen Xiaping landfill. Numerical analyses and parametric study were also conducted. The field monitoring results show that saturated water permeability(ks) decreased linearly with the increase of root length density(RLD). Compared with bare soil, the reductions in ks and infiltration rate due to the rise of RLD were up to 55%, 18% and 35%,respectively. Consequently, higher matric suctions were preserved in the grassed three-layer landfill cover system compared to the bare one during the field monitoring, which are also support by the numerical results. However, no significant difference in matric suction was observed between the bare and grassed covers under the 100-year return period rainfall. During the two-year monitoring, the occurrence of grass roots resulted in a reduction in cumulative percolation by 21%. They all meet the USEPA recommended criterion of 30 mm ·a-1. The field monitoring results demonstrate the effectiveness of bare and grassed three-layer cover systems using construction waste without geomembrane in humid climate areas. Plant has been widely recognized for improving the sustainable performance of geotechnical infrastructures. However, the influences of plant growth on water infiltration into layered landfill cover are still unclear. This study aims to quantify the effects of plant growth on the variations of soil hydraulic properties and water infiltration into a three-layer landfill cover using recycled concrete without geomembrane under humid climates. Full-scale field monitoring was carried out for two years at the Shenzhen Xiaping landfill. Numerical analyses and parametric study were also conducted. The field monitoring results show that saturated water permeability(ks) decreased linearly with the increase of root length density(RLD). Compared with bare soil, the reductions in ks and infiltration rate due to the rise of RLD were up to 55%, 18% and 35%,respectively. Consequently, higher matric suctions were preserved in the grassed three-layer landfill cover system compared to the bare one during the field monitoring, which are also support by the numerical results. However, no significant difference in matric suction was observed between the bare and grassed covers under the 100-year return period rainfall. During the two-year monitoring, the occurrence of grass roots resulted in a reduction in cumulative percolation by 21%. They all meet the USEPA recommended criterion of 30 mm ·a-1. The field monitoring results demonstrate the effectiveness of bare and grassed three-layer cover systems using construction waste without geomembrane in humid climate areas.
Soil nailing is an economic and convenient method for slope stabilization and excavation support. In engineering practice,geotechnical practitioners only take tensile forces into consideration during design,regardless of shear forces. To investigate the contribution of the shear effect of soil nails to the stability of clay slopes,this paper draws attention to the effect of shear forces on the factor of safety and potential failure surface,using Geo-studio's slope/W mode,and concludes some suggestions to soil nailing designing. The result demonstrates that the increase of shear force can increase optimized nail inclination and makes potential failure surface move towards the back of slope. Also,the shear forces can generate approximately 30% to 50% improvement to factor of safety with the ratio of tensile capacity and shear capacity increasing from 0 to 0.5. Soil nailing is an economic and convenient method for slope stabilization and excavation support. In engineering practice,geotechnical practitioners only take tensile forces into consideration during design,regardless of shear forces. To investigate the contribution of the shear effect of soil nails to the stability of clay slopes,this paper draws attention to the effect of shear forces on the factor of safety and potential failure surface,using Geo-studio's slope/W mode,and concludes some suggestions to soil nailing designing. The result demonstrates that the increase of shear force can increase optimized nail inclination and makes potential failure surface move towards the back of slope. Also,the shear forces can generate approximately 30% to 50% improvement to factor of safety with the ratio of tensile capacity and shear capacity increasing from 0 to 0.5.
The suction bucket foundation has the advantages of bearing capacity,easy installation,reusability and low construction costs,and is gradually used in offshore wind turbine. At present,there is no unified standard for the calculation method of bearing capacity of the suction bucket foundation. This paper is based on API and the theory of foundation bearing capacity,summarizes three different bearing capacity modes of the suction bucket foundation,and proposes a calculation formula for the bearing mode of "lid+outer frictional resistance of bucket". According to the engineering case and the finite element software PLAXIS,this theory is verified,and the optimized design scheme is proposed. The calculation results of the "resistance of tips+the outer and inner frictional resistance of bucket" and the "lid+outer frictional resistance of bucket" proposed in this paper conform to the DNV-OS-J101 standard. The proposed design scheme can reduce the material costs of the bucket foundation by up to 13%,which is obtained for engineering practice. The suction bucket foundation has the advantages of bearing capacity,easy installation,reusability and low construction costs,and is gradually used in offshore wind turbine. At present,there is no unified standard for the calculation method of bearing capacity of the suction bucket foundation. This paper is based on API and the theory of foundation bearing capacity,summarizes three different bearing capacity modes of the suction bucket foundation,and proposes a calculation formula for the bearing mode of "lid+outer frictional resistance of bucket". According to the engineering case and the finite element software PLAXIS,this theory is verified,and the optimized design scheme is proposed. The calculation results of the "resistance of tips+the outer and inner frictional resistance of bucket" and the "lid+outer frictional resistance of bucket" proposed in this paper conform to the DNV-OS-J101 standard. The proposed design scheme can reduce the material costs of the bucket foundation by up to 13%,which is obtained for engineering practice.