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Editor Work2022 Vol. 30, No. 2
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2022, 30(2): 281-292.
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This paper aims to deeply investigate the role of vegetation roots in faxing soil and increasing soil strength and probe into the influence of soil moisture content on soil strength. It selects Changlinggou catchment in Xining Basin as the tested site. Four types of local vegetation were chosen as the tested species. They are Caragana korshinskii Kom., Nitraria sphaerocarpa Maxim., Achnatherum splendens(Trin.)Nevski, and Agropyron trachycaulum Linn. Gaertn. Five sets of undisturbed and remolded rooted soil with soil moisture contents increasing from 6% to 22% were prepared for indoor direct shear tests. The results show that all of the vegetation roots possess a capacity of significantly resisting deformation of rooted soil, but as moisture contents increase, the root role in resisting soil deformation is reduced. At the same moisture content, the cohesion of rooted soil is generally larger than that of non-rooted soil. The growth rate of cohesion is 1.94~12.17 kPa and the growth amplitude is 34.50% ~360.69% in comparison to the non-rooted soil. However, the same trend did not occur in the internal friction angle. A binomial function can describe the relation of soil moisture content with its cohesion for all of the soil. Moreover, as the moisture content increases from 6% to 22%, the cohesion declines from 28.50% to 61.78% and the internal friction angle declines by 38.73%. The works possess theoretical and practical significance on further exploring the factors influencing the shear strength of herb and shrub root-soil composite systems, adopting dominant local plants to carry out slope protection, and effectively preventing and controlling regional soil erosion, shallow landslide and other geological disasters.
This paper aims to deeply investigate the role of vegetation roots in faxing soil and increasing soil strength and probe into the influence of soil moisture content on soil strength. It selects Changlinggou catchment in Xining Basin as the tested site. Four types of local vegetation were chosen as the tested species. They are Caragana korshinskii Kom., Nitraria sphaerocarpa Maxim., Achnatherum splendens(Trin.)Nevski, and Agropyron trachycaulum Linn. Gaertn. Five sets of undisturbed and remolded rooted soil with soil moisture contents increasing from 6% to 22% were prepared for indoor direct shear tests. The results show that all of the vegetation roots possess a capacity of significantly resisting deformation of rooted soil, but as moisture contents increase, the root role in resisting soil deformation is reduced. At the same moisture content, the cohesion of rooted soil is generally larger than that of non-rooted soil. The growth rate of cohesion is 1.94~12.17 kPa and the growth amplitude is 34.50% ~360.69% in comparison to the non-rooted soil. However, the same trend did not occur in the internal friction angle. A binomial function can describe the relation of soil moisture content with its cohesion for all of the soil. Moreover, as the moisture content increases from 6% to 22%, the cohesion declines from 28.50% to 61.78% and the internal friction angle declines by 38.73%. The works possess theoretical and practical significance on further exploring the factors influencing the shear strength of herb and shrub root-soil composite systems, adopting dominant local plants to carry out slope protection, and effectively preventing and controlling regional soil erosion, shallow landslide and other geological disasters.
2022, 30(2): 293-300.
This paper investigates the accuracy and applicability of axial strain obtained by axial extensometer, LVDT and press-plate displacement. We carried out the uniaxial and triaxial compression tests of rock with MTS testing machine, and compared the stress-strain curves obtained with the axial extensometer, press-plate displacement and LVDT. Furthermore, we analyzed the effects of the results under three different measurement methods on the shape, strength and deformation parameters of the stress-strain curves of rock samples. The results show that in the pre-peak strength stage, the deformation data measured by the plate displacement and LVDT, the stress threshold value and deformation parameters have large differences. So axial strain should adopt the axial extensometer to obtain the deformation data. In addition, when the deformation data measured by the axial extensometer reaches the peak strength, the axial strain can decrease, and this curve can be easily mistaken as a class Ⅱ curve. It is recommended to install a LVDT sensor at the fixed head of the MTS testing machine, and calculate the axial strain after peak strength with the axial deformation measured by LVDT. When the LVDT sensor is not allowed to be installed, we should adopt the pressure plate displacement measurement to represent the deformation of the sample after the peak strength.
This paper investigates the accuracy and applicability of axial strain obtained by axial extensometer, LVDT and press-plate displacement. We carried out the uniaxial and triaxial compression tests of rock with MTS testing machine, and compared the stress-strain curves obtained with the axial extensometer, press-plate displacement and LVDT. Furthermore, we analyzed the effects of the results under three different measurement methods on the shape, strength and deformation parameters of the stress-strain curves of rock samples. The results show that in the pre-peak strength stage, the deformation data measured by the plate displacement and LVDT, the stress threshold value and deformation parameters have large differences. So axial strain should adopt the axial extensometer to obtain the deformation data. In addition, when the deformation data measured by the axial extensometer reaches the peak strength, the axial strain can decrease, and this curve can be easily mistaken as a class Ⅱ curve. It is recommended to install a LVDT sensor at the fixed head of the MTS testing machine, and calculate the axial strain after peak strength with the axial deformation measured by LVDT. When the LVDT sensor is not allowed to be installed, we should adopt the pressure plate displacement measurement to represent the deformation of the sample after the peak strength.
2022, 30(2): 301-308.
The soil water characteristic curve(SWCC) of an unsaturated soil defines the relationship between the matrix suction and the water content. It is closely related to the permeability and shear strength of unsaturated soils. In this paper, based on statistical analyses of the soil water characteristic curves(SWCCs) and particle size distributions(PSDs) of 100 sand samples, a probabilistic method is suggested to predict the SWCC based on PSD through the commonly used VG model. The validity of the developed model is then assessed through 30 sets of independent data. Results from this study show that SWCC cannot be uniquely determined based on PSD. Compared with the existing methods, the proposed method can not only predict the most probable SWCC, but also the variability of the SWCC such that the error associated with the prediction model can be explicitly considered.
The soil water characteristic curve(SWCC) of an unsaturated soil defines the relationship between the matrix suction and the water content. It is closely related to the permeability and shear strength of unsaturated soils. In this paper, based on statistical analyses of the soil water characteristic curves(SWCCs) and particle size distributions(PSDs) of 100 sand samples, a probabilistic method is suggested to predict the SWCC based on PSD through the commonly used VG model. The validity of the developed model is then assessed through 30 sets of independent data. Results from this study show that SWCC cannot be uniquely determined based on PSD. Compared with the existing methods, the proposed method can not only predict the most probable SWCC, but also the variability of the SWCC such that the error associated with the prediction model can be explicitly considered.
2022, 30(2): 309-316.
This paper uses the mixed solution of Na2CO3 and Na3PO4 to percolate the silty clay in Xuzhou of China. It completes 10 times dry-wet cycles. The solution is a terminal product of degradation of municipal waste. The evolution characteristics of the properties of silty clay under the dry-wet cycles are analyzed, and the evolution mechanism is revealed. The results show that the permeability of silty clay increases, the resistivity decreases, the density first decreases and then rises, the cohesion and the angle of internal friction decrease, and the change of soil properties with a long seepage path has a certain lag, the dry shrinkage cracks on the surface of the soil develop and expand gradually, and the seepage path of the soil develops gradually during the dry and wet cycles. The shorter the seepage path of the soil samples, the greater the density variation of elements. The main reasons for the change of soil properties under the dry-wet cycles are the combination of seepage erosion, chemical reaction, Na+ion adsorption, wet expansion, dry shrinkage, and gravity infiltration.
This paper uses the mixed solution of Na2CO3 and Na3PO4 to percolate the silty clay in Xuzhou of China. It completes 10 times dry-wet cycles. The solution is a terminal product of degradation of municipal waste. The evolution characteristics of the properties of silty clay under the dry-wet cycles are analyzed, and the evolution mechanism is revealed. The results show that the permeability of silty clay increases, the resistivity decreases, the density first decreases and then rises, the cohesion and the angle of internal friction decrease, and the change of soil properties with a long seepage path has a certain lag, the dry shrinkage cracks on the surface of the soil develop and expand gradually, and the seepage path of the soil develops gradually during the dry and wet cycles. The shorter the seepage path of the soil samples, the greater the density variation of elements. The main reasons for the change of soil properties under the dry-wet cycles are the combination of seepage erosion, chemical reaction, Na+ion adsorption, wet expansion, dry shrinkage, and gravity infiltration.
2022, 30(2): 317-326.
Diatomite often appears white, yellow, black or other colors. The white diatomite is more special, and its strength decreases significantly when it meets water. In order to accurately grasp the engineering characteristics of white diatomite, it is necessary to master the microstructure of white diatomite. This paper takes the white diatomite as the research object. We use the SEM test and display the pore characteristics of the white diatomite by numerical method. The overall morphology of the white diatomite is analyzed from the microscopic point of view. At the same time, we quantitatively analyzes the microstructure of the white diatomite, and studies the micro characteristics of the pores of the white diatomite through the binarization analysis and fractal dimension analysis. The results show the following findings. (1)The white diatomite has a unique disordered porous structure. The aggregation of particles is mainly in the form of accumulation polymerization. Its overall structure is mainly in the form of dispersion structure. The contact form is mainly face-to-face. (2)The micro pore size of white diatomite is generally small. The pore size presents an irregular distribution with strong randomness. The pore structure has irregular shape, showing a small pore shape. (3)White diatomite has relatively high surface porosity. It is manifested as small pore size, large quantity and complex structure on the microscopic level. (4)White diatomite has good fractal characteristics. The fractal dimension of diatomite shows a nonlinear decreasing trend under different thresholds. The larger the threshold is, the larger the fractal dimension decreases. At the same time, the fractal dimension value of white diatomite is large. This result indicates that there are more pore structure units on the micro surface of white diatomite, which shows the characteristics of small pores and large number of pores on the macro level.
Diatomite often appears white, yellow, black or other colors. The white diatomite is more special, and its strength decreases significantly when it meets water. In order to accurately grasp the engineering characteristics of white diatomite, it is necessary to master the microstructure of white diatomite. This paper takes the white diatomite as the research object. We use the SEM test and display the pore characteristics of the white diatomite by numerical method. The overall morphology of the white diatomite is analyzed from the microscopic point of view. At the same time, we quantitatively analyzes the microstructure of the white diatomite, and studies the micro characteristics of the pores of the white diatomite through the binarization analysis and fractal dimension analysis. The results show the following findings. (1)The white diatomite has a unique disordered porous structure. The aggregation of particles is mainly in the form of accumulation polymerization. Its overall structure is mainly in the form of dispersion structure. The contact form is mainly face-to-face. (2)The micro pore size of white diatomite is generally small. The pore size presents an irregular distribution with strong randomness. The pore structure has irregular shape, showing a small pore shape. (3)White diatomite has relatively high surface porosity. It is manifested as small pore size, large quantity and complex structure on the microscopic level. (4)White diatomite has good fractal characteristics. The fractal dimension of diatomite shows a nonlinear decreasing trend under different thresholds. The larger the threshold is, the larger the fractal dimension decreases. At the same time, the fractal dimension value of white diatomite is large. This result indicates that there are more pore structure units on the micro surface of white diatomite, which shows the characteristics of small pores and large number of pores on the macro level.
2022, 30(2): 327-337.
The current study investigates the use of Alkali-Activated Material (AAM) to stabilize a silty clay with low liquid limit, collected from a construction site between Fengchang to Ni Leke section of line S315 in Yili Area. The experimental program includes road performance index tests and freeze-thaw cycling tests. They are performed on the silty clay and the stabilized soil to study the effect of AAM on the road performance index and freeze-thaw resistance. Micro characterization using scanning electron microscope(SEM) and X-Ray diffraction(XRD) is also carried out to study the underlying stabilizing mechanisms. The results show that the unconfined compressive strength and shear strength of solidified soil increase with the content of AAM and the curing age. The CBR value and resilient modulus of solidified soil increase with the content of AAM. The road performance indices of AAM stabilized soils satisfy the regulation requirements. The frozen heave and thawed settlement rates of silty clay are related to temperature gradient and water content. At the same temperature dropping range, the freeze-thaw effect is more evident on the silty clay at smaller temperature gradient. At the same temperature gradient, the freeze-thaw effect is more evident at higher water content. The frost heave rate of silty clay treated with different content of AAM under water supply condition is less than 1%, showing no frozen heave tendency. The results of micro characterization show that the C(-A)-S-H gel is the major cementing agents formed after AAM stabilization and its content increases with curing age. This cementing agent fills the pores between the soil particles and cements the soil particles together leading to a dense micro structure, which increases the strength and freeze-thaw resistance of stabilized soil.
The current study investigates the use of Alkali-Activated Material (AAM) to stabilize a silty clay with low liquid limit, collected from a construction site between Fengchang to Ni Leke section of line S315 in Yili Area. The experimental program includes road performance index tests and freeze-thaw cycling tests. They are performed on the silty clay and the stabilized soil to study the effect of AAM on the road performance index and freeze-thaw resistance. Micro characterization using scanning electron microscope(SEM) and X-Ray diffraction(XRD) is also carried out to study the underlying stabilizing mechanisms. The results show that the unconfined compressive strength and shear strength of solidified soil increase with the content of AAM and the curing age. The CBR value and resilient modulus of solidified soil increase with the content of AAM. The road performance indices of AAM stabilized soils satisfy the regulation requirements. The frozen heave and thawed settlement rates of silty clay are related to temperature gradient and water content. At the same temperature dropping range, the freeze-thaw effect is more evident on the silty clay at smaller temperature gradient. At the same temperature gradient, the freeze-thaw effect is more evident at higher water content. The frost heave rate of silty clay treated with different content of AAM under water supply condition is less than 1%, showing no frozen heave tendency. The results of micro characterization show that the C(-A)-S-H gel is the major cementing agents formed after AAM stabilization and its content increases with curing age. This cementing agent fills the pores between the soil particles and cements the soil particles together leading to a dense micro structure, which increases the strength and freeze-thaw resistance of stabilized soil.
2022, 30(2): 338-346.
During the long-term operation of deep geological repository of high-level radiational waste, the chemical environment causes changes to the pore structure of the buffer/backfill material, which can affect the material's hydro-mechanical properties. Under the foundation of fractal theory and dual-porosity theory, we establish two pore structure based SWRC predicting models to study the feasibility of the two theories to connect the microstructure with hydraulic properties of compacted betonite considering chemical effects. The pore size distribution data of compacted GMZ bentonite treated with different concentrations of NaCl solution is obtained by mercury intrusion method. The SWRCs of the samples are predicted through the established models and compared with the measured curves. Results show that the predicted SWRCs tend to be the same as the measured SWRCs in the higher range of matric suction. However, compared with the dual-porosity of the SWRC testing specimen, only the intra-aggregate pores control the water retention capacity of the compacted bentonite after the wetting and drying process. Therefore, the predicted SWRCs show single peak and the established models don't perform well in the lower suction range. Compared with the distilled water treatment, the salt solution leads to the decrease of inter-aggregate porosity and the decrease of water content under the same matric suction. However, with the treatment of more concentrated salt solution, the water retention capacity of the specimen increases slightly in the range of high suction due to the increase of pore fluid channels and the formation of micro-cracks in the compacted bentonite.
During the long-term operation of deep geological repository of high-level radiational waste, the chemical environment causes changes to the pore structure of the buffer/backfill material, which can affect the material's hydro-mechanical properties. Under the foundation of fractal theory and dual-porosity theory, we establish two pore structure based SWRC predicting models to study the feasibility of the two theories to connect the microstructure with hydraulic properties of compacted betonite considering chemical effects. The pore size distribution data of compacted GMZ bentonite treated with different concentrations of NaCl solution is obtained by mercury intrusion method. The SWRCs of the samples are predicted through the established models and compared with the measured curves. Results show that the predicted SWRCs tend to be the same as the measured SWRCs in the higher range of matric suction. However, compared with the dual-porosity of the SWRC testing specimen, only the intra-aggregate pores control the water retention capacity of the compacted bentonite after the wetting and drying process. Therefore, the predicted SWRCs show single peak and the established models don't perform well in the lower suction range. Compared with the distilled water treatment, the salt solution leads to the decrease of inter-aggregate porosity and the decrease of water content under the same matric suction. However, with the treatment of more concentrated salt solution, the water retention capacity of the specimen increases slightly in the range of high suction due to the increase of pore fluid channels and the formation of micro-cracks in the compacted bentonite.
2022, 30(2): 347-356.
The permeability coefficient is an important parameter in the study of loess seepage deformation and loess hydraulic properties. However,the gas permeability coefficient has a good correlation with the permeability coefficient,and water sensitivity of loess can not affect its testing process. At the same time,it is more convenient and faster than the determination of permeability coefficient. So it has a good prospect of popularization and application. This paper introduces the principle of loess in-situ gas permeability test method. On this basis,we carry a series of in-situ gas permeability tests in different loess areas by contact type and plug-in type. The test results show that the two methods have different application scopes for loess stratum. The plug-in method is more suitable when the clay content of loess is greater than 12.44%(the plasticity index is greater than 11.2). On the contrary,when the clay content is less than 12.44%(the plasticity index is less than 11.2),the plug-in method can cause larger errors. The comprehensive comparison shows the contact method is generally applicable to loess strata because of its less human error. But this method needs a larger working face and is more suitable for horizontal working face,which affects the test speed and convenience. The plug-in method needs a smaller working face,and is suitable for both horizontal and vertical working face. So it is more convenient and faster. However,the process of probe inserting into loess can cause disturbance,so this method is more suitable for loess layer with higher clay content. When the clay content of loess is greater than 12.44%(the plasticity index is greater than 11.2),we suggest to give priority to the plug-in method. If the site does not meet these conditions,we suggest to choose the contact method. The two determination methods of in-situ gas permeability coefficient of loess and their application scope provide a theoretical basis for further application in practice.
The permeability coefficient is an important parameter in the study of loess seepage deformation and loess hydraulic properties. However,the gas permeability coefficient has a good correlation with the permeability coefficient,and water sensitivity of loess can not affect its testing process. At the same time,it is more convenient and faster than the determination of permeability coefficient. So it has a good prospect of popularization and application. This paper introduces the principle of loess in-situ gas permeability test method. On this basis,we carry a series of in-situ gas permeability tests in different loess areas by contact type and plug-in type. The test results show that the two methods have different application scopes for loess stratum. The plug-in method is more suitable when the clay content of loess is greater than 12.44%(the plasticity index is greater than 11.2). On the contrary,when the clay content is less than 12.44%(the plasticity index is less than 11.2),the plug-in method can cause larger errors. The comprehensive comparison shows the contact method is generally applicable to loess strata because of its less human error. But this method needs a larger working face and is more suitable for horizontal working face,which affects the test speed and convenience. The plug-in method needs a smaller working face,and is suitable for both horizontal and vertical working face. So it is more convenient and faster. However,the process of probe inserting into loess can cause disturbance,so this method is more suitable for loess layer with higher clay content. When the clay content of loess is greater than 12.44%(the plasticity index is greater than 11.2),we suggest to give priority to the plug-in method. If the site does not meet these conditions,we suggest to choose the contact method. The two determination methods of in-situ gas permeability coefficient of loess and their application scope provide a theoretical basis for further application in practice.
2022, 30(2): 357-365.
The present-day loess structure is gradually formed with the process of initial accumulation of loess particles and the later lossification. The climate is typically dry in the period of loess accumulation and the initial loess deposit(ILD)suffers from daily and seasonal temperature fluctuations,which evidently leads to structural evolution of ILD. However,the mechanism behind is still unclear. In this study,ILD is reconstructed in the laboratory and physical simulation with temperature fluctuation is carried out. Ambient temperature,soil temperature,vertical deformation and structure of top surface of soil sample are monitored with thermocouple temperature sensors,laser displacement sensors and an industrial camera of high-resolution. The results show that both soil temperature and vertical deformation of soil sample fluctuate with the ambient temperature,but lag behind. The vertical deformation exhibits a synchronous fluctuation with the soil temperature. With temperature cycles,the soil sample keeps contraction,and the soil sample experiences elastic-plastic deformation and then elastic deformation. Compared with the effects of water and overlying load,the deformation and structure disturbance of ILD due to temperature fluctuation are minimum(about 0.25%). This indicates that temperature fluctuation plays a noncrucial role in the formation of present-day loess structure.
The present-day loess structure is gradually formed with the process of initial accumulation of loess particles and the later lossification. The climate is typically dry in the period of loess accumulation and the initial loess deposit(ILD)suffers from daily and seasonal temperature fluctuations,which evidently leads to structural evolution of ILD. However,the mechanism behind is still unclear. In this study,ILD is reconstructed in the laboratory and physical simulation with temperature fluctuation is carried out. Ambient temperature,soil temperature,vertical deformation and structure of top surface of soil sample are monitored with thermocouple temperature sensors,laser displacement sensors and an industrial camera of high-resolution. The results show that both soil temperature and vertical deformation of soil sample fluctuate with the ambient temperature,but lag behind. The vertical deformation exhibits a synchronous fluctuation with the soil temperature. With temperature cycles,the soil sample keeps contraction,and the soil sample experiences elastic-plastic deformation and then elastic deformation. Compared with the effects of water and overlying load,the deformation and structure disturbance of ILD due to temperature fluctuation are minimum(about 0.25%). This indicates that temperature fluctuation plays a noncrucial role in the formation of present-day loess structure.
2022, 30(2): 366-373.
This paper uses Dongting Lake soft soil and high organic matter content peat soil to reshape samples with different organic matter content. It conducts one-dimensional consolidation creep tests to detected the content of adsorbed bound water and organic matter. It then determines the relationship between adsorbed bound water and organic matter content. It analyzes the effect of organic matter content on the secondary consolidation characteristics of soft soil. The research results show that the organic matter in the soil and the adsorbed bound water are linearly increasing: the higher content of organic matter,the greater the content of adsorbed bound water. In view of this,we put forward the corresponding calculation formula. Moreover,the relationship curve between secondary consolidation coefficient and consolidation pressure has a peak point near the structural strength. The secondary consolidation coefficient can be approximately regarded as a constant under the action of large consolidation pressure. In addition,with the increase of organic matter content in soil,the secondary consolidation coefficient increases obviously,especially at high stress level. We discuss its causes in this paper. The research has certain guiding significance for controlling post construction settlement in soft soil area.
This paper uses Dongting Lake soft soil and high organic matter content peat soil to reshape samples with different organic matter content. It conducts one-dimensional consolidation creep tests to detected the content of adsorbed bound water and organic matter. It then determines the relationship between adsorbed bound water and organic matter content. It analyzes the effect of organic matter content on the secondary consolidation characteristics of soft soil. The research results show that the organic matter in the soil and the adsorbed bound water are linearly increasing: the higher content of organic matter,the greater the content of adsorbed bound water. In view of this,we put forward the corresponding calculation formula. Moreover,the relationship curve between secondary consolidation coefficient and consolidation pressure has a peak point near the structural strength. The secondary consolidation coefficient can be approximately regarded as a constant under the action of large consolidation pressure. In addition,with the increase of organic matter content in soil,the secondary consolidation coefficient increases obviously,especially at high stress level. We discuss its causes in this paper. The research has certain guiding significance for controlling post construction settlement in soft soil area.
2022, 30(2): 374-382.
The mechanical properties of the structural surface affect the stability of the engineering rock mass directly. The filling has a greater impact on the mechanical properties of the structural surface. In order to accurately analyze the effect of filling on the shear performance of structural surface,we prepared the artificial joint samples. We take the joint rock mass of the typical reservoir bank slope in the Three Gorges Reservoir area as the research object. We operate repeated shear tests on structural surfaces before and after filling,according to the filling degree 100%.The results show the following findings. (1)Based on the law of change in the shear resistance of the structural surface during the repeated shearing process,we proposes a method for repeated shearing of single specimen before and after filling. We proposes the experimental procedure and data processing method for analyze the influence of the filling on the structural surface. It can accurately analyze the influence of fillings on the shear resistance of structural surfaces. (2)The shear resistance of the structural surface deteriorates obviously after filling. The drop rate in different normal stresses is between 38.51% ~54.82%. The greater the normal stress,the greater the reduction. (3)During repeated shear,the shear strength of the filling structure surface shows a law of increasing,then decreasing,and stabilizing. It is related to the reduction of the filling material,the expose of the structural surface and the filling of the mud. The related test methods can provide a good reference for the analysis of the shear performance on the filling structure surface
The mechanical properties of the structural surface affect the stability of the engineering rock mass directly. The filling has a greater impact on the mechanical properties of the structural surface. In order to accurately analyze the effect of filling on the shear performance of structural surface,we prepared the artificial joint samples. We take the joint rock mass of the typical reservoir bank slope in the Three Gorges Reservoir area as the research object. We operate repeated shear tests on structural surfaces before and after filling,according to the filling degree 100%.The results show the following findings. (1)Based on the law of change in the shear resistance of the structural surface during the repeated shearing process,we proposes a method for repeated shearing of single specimen before and after filling. We proposes the experimental procedure and data processing method for analyze the influence of the filling on the structural surface. It can accurately analyze the influence of fillings on the shear resistance of structural surfaces. (2)The shear resistance of the structural surface deteriorates obviously after filling. The drop rate in different normal stresses is between 38.51% ~54.82%. The greater the normal stress,the greater the reduction. (3)During repeated shear,the shear strength of the filling structure surface shows a law of increasing,then decreasing,and stabilizing. It is related to the reduction of the filling material,the expose of the structural surface and the filling of the mud. The related test methods can provide a good reference for the analysis of the shear performance on the filling structure surface
2022, 30(2): 383-393.
This paper aims to assess the contribution of roots of inter-planted herbaceous in reinforcing dump-slope soil in alpine mining areas and improving slope stability. It selects Jiangcang mining sites in Muli mining area as the testing area,where herbs of Elymus nutans Griseb. and Poa crymophila Keng are inter-planted. It uses a series of mechanical experiments to rooted soil as well as soil without root and determines,the physical and mechanical indices of the rooted soil as well as soil without root. It further conducts the Pearson correlation analysis to identify the correlation among cohesion of soil samples(rooted soil and soil without root),soil density,soil moisture content and root content. Results shows that the soil density of rooted soil,can decline from 0.13 to 0.21g ·cm-3 with the corresponding declining percent of 6.31%~11.05%,while moisture content and cohesion can increase from 0.40% to 2.91%(with the increase percent of 4.47%~26.11%) and from 1.18 to 10.58 kPa(with the increase percent of 5.77%~62.11%),respectively. In contrast to the soil without root,indicating inter-planted herbs roots are more capable in reinforcing loose soil and improving slope stability. Pearson correlation analysis shows cohesion in vegetated slopes is positively correlated with its root content(P<0.05). Its correlation coefficient value is absolutely higher than the counterparts of soil density,and moisture content,which suggests a closer relationship between root content and soil cohesion. This conclusion can be used as a reference in the projects of alpine mining area ecological restoration and has a theoretical and practical values in geo-hazards prevention and control.
This paper aims to assess the contribution of roots of inter-planted herbaceous in reinforcing dump-slope soil in alpine mining areas and improving slope stability. It selects Jiangcang mining sites in Muli mining area as the testing area,where herbs of Elymus nutans Griseb. and Poa crymophila Keng are inter-planted. It uses a series of mechanical experiments to rooted soil as well as soil without root and determines,the physical and mechanical indices of the rooted soil as well as soil without root. It further conducts the Pearson correlation analysis to identify the correlation among cohesion of soil samples(rooted soil and soil without root),soil density,soil moisture content and root content. Results shows that the soil density of rooted soil,can decline from 0.13 to 0.21g ·cm-3 with the corresponding declining percent of 6.31%~11.05%,while moisture content and cohesion can increase from 0.40% to 2.91%(with the increase percent of 4.47%~26.11%) and from 1.18 to 10.58 kPa(with the increase percent of 5.77%~62.11%),respectively. In contrast to the soil without root,indicating inter-planted herbs roots are more capable in reinforcing loose soil and improving slope stability. Pearson correlation analysis shows cohesion in vegetated slopes is positively correlated with its root content(P<0.05). Its correlation coefficient value is absolutely higher than the counterparts of soil density,and moisture content,which suggests a closer relationship between root content and soil cohesion. This conclusion can be used as a reference in the projects of alpine mining area ecological restoration and has a theoretical and practical values in geo-hazards prevention and control.
2022, 30(2): 394-406.
The geological environment of China's southeast coast is complex and fragile,with frequent landslides triggered by typhoons and rainstorms. The key factor that leads to the deformation of the slope body,then landslide and mudslide is the rainwater infiltration into the soil. This paper studies the landslide in Yandou Village. It is located in the east of Fujian Province. The study uses a self-developed artificial rainfall soil columns infiltration experiment device. It considers different rainfall,rainfall duration,rainfall interval time,and other working conditions. It conducts different cumulative cyclic rainfall experiments on the slope residual soil of landslides at different rainfall intensities(20 and 60 mm·h-1). The experiments give the rainfall infiltration data,including changes in water content,resistivity,and matric suction of soil under drying and wetting circles. The analysis of the test results show the following findings. (1) Under cumulative rainfall circumstances,the peak water content of the upper soil slowly decreases with the increase of wet and dry cycles times,while the deeper soil gradually accumulates water content and the peak water content slowly increases. (2) The soil columns feature heterogeneity. Different depths of soil show various resistivity. There is a highly correlation between the resistivity response time and the water content response time. The resistivity changes almost simultaneously when the water content changes,but these changing indicators are on the contrary. (3) The matric suction represents a very limited recovery during the rain-stopping phase of the cumulative rainfall. From the second rainfall,due to the water of the last rainfall still remaining in the soil,the matric suction drops to 0 kPa after cumulative rainfall. (4) The errors can be smaller using the expansion Archie model modified by Keller to conduct resistivity and water content fitting in the research area. This paper combined the expansion Archie model,the Green-Ampt model,and the Philip infiltration model to obtain the Green-Ampt and Philip infiltration model based on resistivity. This provides a new measurement perspective for soil infiltration with practical value. The results of this study contribute to exploring further the resistivity evolution of slope residual soils under the action of typhoons and rainstorms in the research area. In addition,the achievements reveal rainfall infiltration mechanisms of slope residual soil under cumulative rainfall circumstances that are of important theoretical and practical significance to analyze the stability of typhoon and rainstorm type landslides and to monitor and early warning activities.
The geological environment of China's southeast coast is complex and fragile,with frequent landslides triggered by typhoons and rainstorms. The key factor that leads to the deformation of the slope body,then landslide and mudslide is the rainwater infiltration into the soil. This paper studies the landslide in Yandou Village. It is located in the east of Fujian Province. The study uses a self-developed artificial rainfall soil columns infiltration experiment device. It considers different rainfall,rainfall duration,rainfall interval time,and other working conditions. It conducts different cumulative cyclic rainfall experiments on the slope residual soil of landslides at different rainfall intensities(20 and 60 mm·h-1). The experiments give the rainfall infiltration data,including changes in water content,resistivity,and matric suction of soil under drying and wetting circles. The analysis of the test results show the following findings. (1) Under cumulative rainfall circumstances,the peak water content of the upper soil slowly decreases with the increase of wet and dry cycles times,while the deeper soil gradually accumulates water content and the peak water content slowly increases. (2) The soil columns feature heterogeneity. Different depths of soil show various resistivity. There is a highly correlation between the resistivity response time and the water content response time. The resistivity changes almost simultaneously when the water content changes,but these changing indicators are on the contrary. (3) The matric suction represents a very limited recovery during the rain-stopping phase of the cumulative rainfall. From the second rainfall,due to the water of the last rainfall still remaining in the soil,the matric suction drops to 0 kPa after cumulative rainfall. (4) The errors can be smaller using the expansion Archie model modified by Keller to conduct resistivity and water content fitting in the research area. This paper combined the expansion Archie model,the Green-Ampt model,and the Philip infiltration model to obtain the Green-Ampt and Philip infiltration model based on resistivity. This provides a new measurement perspective for soil infiltration with practical value. The results of this study contribute to exploring further the resistivity evolution of slope residual soils under the action of typhoons and rainstorms in the research area. In addition,the achievements reveal rainfall infiltration mechanisms of slope residual soil under cumulative rainfall circumstances that are of important theoretical and practical significance to analyze the stability of typhoon and rainstorm type landslides and to monitor and early warning activities.
2022, 30(2): 407-416.
Wuzhou City is the distribution area of the granite weathering crust with huge thickness in South China. It is selected as the study area. The study aims to establish a systematic,scientific,and operable standard for the vertical division of granite weathering crust. On the basis of field investigation,drilling,in-situ test,laboratory test,and comprehensive research,an index system of qualitative and quantitative composite judgment is established. The vertical zoning and engineering geological characteristics of granite weathering crust in Wuzhou City are studied. The studies show that: (1) Granularity analysis can be used as one of the methods of vertical zoning of granite weathering crust. The division results are in good agreement with the results of the in-situ test division. (2) Clay,silt and sand soil account for the largest proportion in residual soil zone,completely weathered zone and strongly weathered zone,respectively. The size of soil particles increases with increasing depth. The proportion of gravel and sand particles with relatively large particle sizes gradually increases. The proportion of powder and clay particles with relatively small particle sizes gradually decreases. Particle size 0.05mm is the boundary of curve intersection of residual soil,fully weathering zone and strongly weathering zone. The percentage of soil content at this place is approximately equal,revealing that the value of 0.05mm particle size is one of the important indicators for the vertical division of granite weathering crust. (3) With the increase of the drilling depth,the number of cone dynamic penetration test hits and the number of standard penetration tests increase simultaneously. The corrected standard penetration number N and cone dynamic penetration penetration number N63.5 show a polynomial correlation. In this paper,the standard of vertical zoning of granite weathering crust was established,and the recommended value of the bearing capacity of the granite weathering crust soil is given,which had certain guiding and reference significance for major project construction and selection of engineering geological characteristic parameters in granite distribution area.
Wuzhou City is the distribution area of the granite weathering crust with huge thickness in South China. It is selected as the study area. The study aims to establish a systematic,scientific,and operable standard for the vertical division of granite weathering crust. On the basis of field investigation,drilling,in-situ test,laboratory test,and comprehensive research,an index system of qualitative and quantitative composite judgment is established. The vertical zoning and engineering geological characteristics of granite weathering crust in Wuzhou City are studied. The studies show that: (1) Granularity analysis can be used as one of the methods of vertical zoning of granite weathering crust. The division results are in good agreement with the results of the in-situ test division. (2) Clay,silt and sand soil account for the largest proportion in residual soil zone,completely weathered zone and strongly weathered zone,respectively. The size of soil particles increases with increasing depth. The proportion of gravel and sand particles with relatively large particle sizes gradually increases. The proportion of powder and clay particles with relatively small particle sizes gradually decreases. Particle size 0.05mm is the boundary of curve intersection of residual soil,fully weathering zone and strongly weathering zone. The percentage of soil content at this place is approximately equal,revealing that the value of 0.05mm particle size is one of the important indicators for the vertical division of granite weathering crust. (3) With the increase of the drilling depth,the number of cone dynamic penetration test hits and the number of standard penetration tests increase simultaneously. The corrected standard penetration number N and cone dynamic penetration penetration number N63.5 show a polynomial correlation. In this paper,the standard of vertical zoning of granite weathering crust was established,and the recommended value of the bearing capacity of the granite weathering crust soil is given,which had certain guiding and reference significance for major project construction and selection of engineering geological characteristic parameters in granite distribution area.
2022, 30(2): 417-431.
This paper uses the time series InSAR and GPS technologies to obtain the three-dimensional surface deformation in Beijing Plain. It analyze its spatial distribution and evolution characteristics. The results show the following findings. (1)Under the Quaternary additional stress field caused by pumping,the three-dimensional surface deformation characteristics are significant in Beijing Plain. The vertical deformation is the main component and horizontal displacement is a supplement. (2)Land subsidence are mainly located in the east,north and south part of Beijing plain. There are multiple subsidence centers,and the overall trend is slowing down. The most serious subsidence areas are distributed in east part of Chaoyang District and parts of Tongzhou District. The subsidence rate has exceeded 100 mm·a-1 for many years. The maximum subsidence rate is 143.20 mm·a-1,the maximum accumulated subsidence is 816.77 mm,and the uneven subsidence is obvious. (3)Under the ITRF2005 reference frame,the horizontal direction of GPS points in the plain are consistent,mainly in the SE direction. The dominant movement direction is NE112.5°~NE113.8°. The movement rate of E direction is 27.12~36.19 mm·a-1,and the average rate is 30.78 mm·a-1. The movement rate of N direction is -10.90~-19.73 mm·a-1,and the average rate is -13.57 mm·a-1. They reflect that the continuous deformation in Beijing plain is under the situation of a unified continental dynamic environment. (4)Under the Eurasian reference frame,the horizontal movement rate of GPS points are significantly reduced. The deformation between GPS points is varies with no consistent change trend. In particular,in joint area of several major active faults,where both of the InSAR derived vertical subsidence rate and the GPS horizontal movement rate are large. The horizontal movement direction of the GPS points generally direct to the center of subsidence or the funnel of the groundwater level,or from the high water level to the low water level area. This is mainly caused by the horizontal deformation of the Quaternary aquifer system caused by the extraction of groundwater.
This paper uses the time series InSAR and GPS technologies to obtain the three-dimensional surface deformation in Beijing Plain. It analyze its spatial distribution and evolution characteristics. The results show the following findings. (1)Under the Quaternary additional stress field caused by pumping,the three-dimensional surface deformation characteristics are significant in Beijing Plain. The vertical deformation is the main component and horizontal displacement is a supplement. (2)Land subsidence are mainly located in the east,north and south part of Beijing plain. There are multiple subsidence centers,and the overall trend is slowing down. The most serious subsidence areas are distributed in east part of Chaoyang District and parts of Tongzhou District. The subsidence rate has exceeded 100 mm·a-1 for many years. The maximum subsidence rate is 143.20 mm·a-1,the maximum accumulated subsidence is 816.77 mm,and the uneven subsidence is obvious. (3)Under the ITRF2005 reference frame,the horizontal direction of GPS points in the plain are consistent,mainly in the SE direction. The dominant movement direction is NE112.5°~NE113.8°. The movement rate of E direction is 27.12~36.19 mm·a-1,and the average rate is 30.78 mm·a-1. The movement rate of N direction is -10.90~-19.73 mm·a-1,and the average rate is -13.57 mm·a-1. They reflect that the continuous deformation in Beijing plain is under the situation of a unified continental dynamic environment. (4)Under the Eurasian reference frame,the horizontal movement rate of GPS points are significantly reduced. The deformation between GPS points is varies with no consistent change trend. In particular,in joint area of several major active faults,where both of the InSAR derived vertical subsidence rate and the GPS horizontal movement rate are large. The horizontal movement direction of the GPS points generally direct to the center of subsidence or the funnel of the groundwater level,or from the high water level to the low water level area. This is mainly caused by the horizontal deformation of the Quaternary aquifer system caused by the extraction of groundwater.
2022, 30(2): 432-441.
The Jigongshan Mountain tunnel,part of the Banyin Expressway in Shenzhen,is designed to cross underneath the Xiaping Municipal Solid Waste Landfill. Due to the prohibition of preliminary geological surveys in the landfill region,the geological conditions and the distribution of leachate and landfill gas remain unknown in the tunnel section under the landfill. Moreover,considering the risk of environmental disaster,the traditional geological prediction methodology is no longer suitable for the project of tunneling under a landfill. This study develops an innovative strategy of geological prediction for tunneling under a landfill. It is based on multiple geological and geophysical methods. It includes tunnel geological prediction(TGP),transient electromagnetic method(TEM),geological drilling,and chemical analysis. We also performed comprehensive detection and analysis on the quality of surround rock and the distribution of leachate and landfill gas under the landfill. The results show the following findings:(1)The comprehensive prediction method can improve the accuracy of the determination of surround rock quality ahead of the tunnel. (2)Potential leachate pathways connecting the landfill bottom and the tunnel are detected,however,no leachate and landfill gas leakage occur yet. (3)In the tunnel sections with high leakage risk,enhancement of the lining material and waterproof layer is put into practice during tunnel construction. This study offers a valuable reference for similar investigative projects concerning tunnel construction in regions with potential environmental risk.
The Jigongshan Mountain tunnel,part of the Banyin Expressway in Shenzhen,is designed to cross underneath the Xiaping Municipal Solid Waste Landfill. Due to the prohibition of preliminary geological surveys in the landfill region,the geological conditions and the distribution of leachate and landfill gas remain unknown in the tunnel section under the landfill. Moreover,considering the risk of environmental disaster,the traditional geological prediction methodology is no longer suitable for the project of tunneling under a landfill. This study develops an innovative strategy of geological prediction for tunneling under a landfill. It is based on multiple geological and geophysical methods. It includes tunnel geological prediction(TGP),transient electromagnetic method(TEM),geological drilling,and chemical analysis. We also performed comprehensive detection and analysis on the quality of surround rock and the distribution of leachate and landfill gas under the landfill. The results show the following findings:(1)The comprehensive prediction method can improve the accuracy of the determination of surround rock quality ahead of the tunnel. (2)Potential leachate pathways connecting the landfill bottom and the tunnel are detected,however,no leachate and landfill gas leakage occur yet. (3)In the tunnel sections with high leakage risk,enhancement of the lining material and waterproof layer is put into practice during tunnel construction. This study offers a valuable reference for similar investigative projects concerning tunnel construction in regions with potential environmental risk.
2022, 30(2): 442-458.
Land subsidence caused by over-exploitation of groundwater has become one of the most important geological disasters in the Beijing Plain. The important tasks are to accurately identify the main contributing layers of land subsidence and to analyze the characteristics of soil deformation under different water level change modes. They are of great significance for establishing a suitable groundwater-land subsidence model and achieving precise prevention and control of land subsidence. This paper uses the extensometer and corresponding groundwater level observation data at land subsidence monitoring stations in Beijing for the past ten years. It accurately identifies the main deformation layers and reveals the deformation characteristics at different depths of soil layers. It then analyzes the deformation characteristics of different compression layer groups and sand layers under different water level change modes. It discusses the reasons for the large residual deformation and the deformation lag of the clayey soil layers. The results show the following findings. (1)The main subsidence layers are the second compression layer group(middle-deep strata) and the third compression layer group(deep strata) in the Beijing land subsidence area. The average subsidence ratio is 31.01% and 60.73%. The proportion of subsidence is gradually increased. (2)The amount of soil deformation at different depths and its proportion in the total subsidence are not only closely related to variation of groundwater level, but also related to the lithology and thickness of the soil layer. When the thickness of the compressible soil layer is large, even if the groundwater level drops small, it can produce a large amount of deformation. (3)The deformation characteristics of different lithological soil layers under different water level change modes can be summarized into 5 categories. The sand layer is mainly characterized by elastic deformation. The cohesive soil layers of different depths have elastic, plastic and creep deformation. The soil layers have obvious characteristics of viscoelastic-plastic deformation. (4)The groundwater level in the plain has changed from falling to rising in 2017. The deformation characteristics of the soil layers are quite different. The first compression layer group is transformed from elastoplastic deformation to elastic deformation. When the second and third compression layer groups are mainly cohesive soil, the soil layer always exhibits plastic and creep deformation. If it is mainly sand layer, it can show the plastic and creep deformation before 2017, and the plasticity, creep and elastic deformation after 2017, with obvious viscoelastic-plastic features. (5)The large residual deformation and deformation lagging of the cohesive soil layer are mainly caused by two factors. First, the inelastic water storage rate is greater than the elastic water storage rate. Second, the excess pore water pressure in the cohesive soil layer dissipates slowly, and the soil layer exhibits delayed water release, which results in delayed soil deformation.
Land subsidence caused by over-exploitation of groundwater has become one of the most important geological disasters in the Beijing Plain. The important tasks are to accurately identify the main contributing layers of land subsidence and to analyze the characteristics of soil deformation under different water level change modes. They are of great significance for establishing a suitable groundwater-land subsidence model and achieving precise prevention and control of land subsidence. This paper uses the extensometer and corresponding groundwater level observation data at land subsidence monitoring stations in Beijing for the past ten years. It accurately identifies the main deformation layers and reveals the deformation characteristics at different depths of soil layers. It then analyzes the deformation characteristics of different compression layer groups and sand layers under different water level change modes. It discusses the reasons for the large residual deformation and the deformation lag of the clayey soil layers. The results show the following findings. (1)The main subsidence layers are the second compression layer group(middle-deep strata) and the third compression layer group(deep strata) in the Beijing land subsidence area. The average subsidence ratio is 31.01% and 60.73%. The proportion of subsidence is gradually increased. (2)The amount of soil deformation at different depths and its proportion in the total subsidence are not only closely related to variation of groundwater level, but also related to the lithology and thickness of the soil layer. When the thickness of the compressible soil layer is large, even if the groundwater level drops small, it can produce a large amount of deformation. (3)The deformation characteristics of different lithological soil layers under different water level change modes can be summarized into 5 categories. The sand layer is mainly characterized by elastic deformation. The cohesive soil layers of different depths have elastic, plastic and creep deformation. The soil layers have obvious characteristics of viscoelastic-plastic deformation. (4)The groundwater level in the plain has changed from falling to rising in 2017. The deformation characteristics of the soil layers are quite different. The first compression layer group is transformed from elastoplastic deformation to elastic deformation. When the second and third compression layer groups are mainly cohesive soil, the soil layer always exhibits plastic and creep deformation. If it is mainly sand layer, it can show the plastic and creep deformation before 2017, and the plasticity, creep and elastic deformation after 2017, with obvious viscoelastic-plastic features. (5)The large residual deformation and deformation lagging of the cohesive soil layer are mainly caused by two factors. First, the inelastic water storage rate is greater than the elastic water storage rate. Second, the excess pore water pressure in the cohesive soil layer dissipates slowly, and the soil layer exhibits delayed water release, which results in delayed soil deformation.
2022, 30(2): 459-474.
The thickness of rock mass for prevention of water inrush between tunnel and karst cave is one of the important factors in selecting a tunnel site in karst mountain area. In the process of karst tunnel construction,karst water gushing often leads to some accidents,economic losses or construction delay if the wall thickness is too thin. The classification of water inrush failure types is simple. Most classification studies ignore that the structure of tunnel surrounding rock can affect the thickness of rock mass for prevention of water bursting. This paper studies the inrush model in rock mass failure from three aspects: the structure type of surrounding rock of karst tunnel,the relative size and relative position between karst cave and tunnel. Then the failure modes can be subdivided into many mechanical models including beam model,rectangular or circular thin plate model,punching shear column model,wing crack tension through model,tension shear composite fracture model,bedding slip model. Finally,the different failure models are used to summarize the calculation formulas of the thickness of rock mass for prevention of water inrush. The findings can provide suggestions for tunnel route selection in karst area,and provide reference for predicting water inrush geological disasters during tunnel construction.
The thickness of rock mass for prevention of water inrush between tunnel and karst cave is one of the important factors in selecting a tunnel site in karst mountain area. In the process of karst tunnel construction,karst water gushing often leads to some accidents,economic losses or construction delay if the wall thickness is too thin. The classification of water inrush failure types is simple. Most classification studies ignore that the structure of tunnel surrounding rock can affect the thickness of rock mass for prevention of water bursting. This paper studies the inrush model in rock mass failure from three aspects: the structure type of surrounding rock of karst tunnel,the relative size and relative position between karst cave and tunnel. Then the failure modes can be subdivided into many mechanical models including beam model,rectangular or circular thin plate model,punching shear column model,wing crack tension through model,tension shear composite fracture model,bedding slip model. Finally,the different failure models are used to summarize the calculation formulas of the thickness of rock mass for prevention of water inrush. The findings can provide suggestions for tunnel route selection in karst area,and provide reference for predicting water inrush geological disasters during tunnel construction.
2022, 30(2): 475-483.
The triaxial test was utilized to evaluate the stress-strain characteristics of remould loess with different water contents,and the strain variation of support structure and the excavation influence range of crossing tunnel in loess were revealed by the model test. The investigation shows that the deformation of the support structure is related to the position of the tunnel face,and the deformation of the steel arch was observed when the distance between tunnel face and monitoring section was within 1.5 D(D is the diameter of the tunnel),and when the distance exceeded 1.5 D from the monitoring section,the deformation was stabilized,which indicates that the horizontal influence range of excavation was about 1.5 D before and after the tunnel face. Besides,the deformation of the support structure is most obvious in the range of 0.5 D before and after the monitoring section,which accounts for more than 70% of the total strain release. It indicates that the deformation can be controlled by the support structure well,and also large deformation of surrounding rock occurs immediately after excavation,hence timely support should be provided to ensure the stability of the tunnel after excavation is completed. The largest deformation of the tunnel in the vault of the intersection was observed,which was the result of the different stress conditions between vault,hance and vertical wall,and the vault is subject to the vertical load,the hance and vertical wall is subjected to the lateral load. After the excavation of the main tunnel is completed and the deformation of the support structure being stabilized,the secondary deformation of the support structure in the intersection can be influenced by the excavation of the bifurcation tunnel. The deformation of the vault accounts for about 2/5 of the total deformation,and the further the monitoring section is away from the intersection,the deformation of the monitoring section was already very small. These results show that the closer the distance to the intersection,the greater the deformation is. So,the stability of the intersection is the key to the stability of the tunnel.
The triaxial test was utilized to evaluate the stress-strain characteristics of remould loess with different water contents,and the strain variation of support structure and the excavation influence range of crossing tunnel in loess were revealed by the model test. The investigation shows that the deformation of the support structure is related to the position of the tunnel face,and the deformation of the steel arch was observed when the distance between tunnel face and monitoring section was within 1.5 D(D is the diameter of the tunnel),and when the distance exceeded 1.5 D from the monitoring section,the deformation was stabilized,which indicates that the horizontal influence range of excavation was about 1.5 D before and after the tunnel face. Besides,the deformation of the support structure is most obvious in the range of 0.5 D before and after the monitoring section,which accounts for more than 70% of the total strain release. It indicates that the deformation can be controlled by the support structure well,and also large deformation of surrounding rock occurs immediately after excavation,hence timely support should be provided to ensure the stability of the tunnel after excavation is completed. The largest deformation of the tunnel in the vault of the intersection was observed,which was the result of the different stress conditions between vault,hance and vertical wall,and the vault is subject to the vertical load,the hance and vertical wall is subjected to the lateral load. After the excavation of the main tunnel is completed and the deformation of the support structure being stabilized,the secondary deformation of the support structure in the intersection can be influenced by the excavation of the bifurcation tunnel. The deformation of the vault accounts for about 2/5 of the total deformation,and the further the monitoring section is away from the intersection,the deformation of the monitoring section was already very small. These results show that the closer the distance to the intersection,the greater the deformation is. So,the stability of the intersection is the key to the stability of the tunnel.
2022, 30(2): 484-495.
In the theoretical research of jacked pile,the first problem to analyze the penetration characteristics of jacked pile in the process of pile jacking is to clarify the penetration mechanism of jacked pile. Based on the analysis of penetration mechanism in the process of pile jacking,this paper summarizes and analyzes three theoretical analysis methods of pile jacking. They are circular hole expansion theory,strain path method and finite element analysis. This paper points out the shortcomings of the current research on the penetration mechanism of jacked pile and puts forward some suggestions and understandings on the penetration mechanism. Based on the traditional theory of hole expansion and the strain path method,it is suggested to analyze the nature of pile sinking mechanism of static pile based on the nonlinearity of soil,the interaction between pile and soil and the spatial characteristics. The summary of the theoretical research on the penetration mechanism of jacked pile can be helpful to estimate the construction impact range of jacked pile,so as to provide better reference for the design and construction of jacked pile and bring good economic benefits.
In the theoretical research of jacked pile,the first problem to analyze the penetration characteristics of jacked pile in the process of pile jacking is to clarify the penetration mechanism of jacked pile. Based on the analysis of penetration mechanism in the process of pile jacking,this paper summarizes and analyzes three theoretical analysis methods of pile jacking. They are circular hole expansion theory,strain path method and finite element analysis. This paper points out the shortcomings of the current research on the penetration mechanism of jacked pile and puts forward some suggestions and understandings on the penetration mechanism. Based on the traditional theory of hole expansion and the strain path method,it is suggested to analyze the nature of pile sinking mechanism of static pile based on the nonlinearity of soil,the interaction between pile and soil and the spatial characteristics. The summary of the theoretical research on the penetration mechanism of jacked pile can be helpful to estimate the construction impact range of jacked pile,so as to provide better reference for the design and construction of jacked pile and bring good economic benefits.
2022, 30(2): 496-506.
This paper aims to study the influence of geometric parameters of rectangular trench on the vibration isolation effect of the area behind the trench. The amplitude of acceleration at the corresponding control point when the free foundation and rectangular trench are measured respectively through field tests. The two-dimensional plane contour map about the ratio of the two are drawn. The area with a ratio less than 0.4 is taken as the vibration shielding area. The vibration shielding area is taken as the evaluation index of vibration isolation effect. The following conclusions are drawn through the research. Energy redistribution can occur when Rayleigh waves meet rectangular trench in the process of propagation. Part of Rayleigh waves can break through the barrier of trench and continue to propagate forward,while the other part can be bounced back by rectangular trench and propagate backward. When the ratio of rectangular groove depth to Rayleigh wave length is 0.08~0.53,increasing the ratio can significantly increase the vibration shielding area. But when the ratio is 0.53~0.75,it has little influence on the vibration shielding area. The ratio of rectangular trench width to Rayleigh wave length has little influence on the vibration shielding area. When the ratio of rectangular trench length to Rayleigh wave length varies within the range of 1.11~1.52,the vibration shielding area does not change significantly. When the ratio of the rectangular trench source distance to the Rayleigh wave length is 0.78~1.13,the change of the ratio has little influence on the vibration shielding area. When the normalized cross-sectional area of the trench varies from 0.02 to 0.78,it has a significant effect on the area of the vibration shielding area.
This paper aims to study the influence of geometric parameters of rectangular trench on the vibration isolation effect of the area behind the trench. The amplitude of acceleration at the corresponding control point when the free foundation and rectangular trench are measured respectively through field tests. The two-dimensional plane contour map about the ratio of the two are drawn. The area with a ratio less than 0.4 is taken as the vibration shielding area. The vibration shielding area is taken as the evaluation index of vibration isolation effect. The following conclusions are drawn through the research. Energy redistribution can occur when Rayleigh waves meet rectangular trench in the process of propagation. Part of Rayleigh waves can break through the barrier of trench and continue to propagate forward,while the other part can be bounced back by rectangular trench and propagate backward. When the ratio of rectangular groove depth to Rayleigh wave length is 0.08~0.53,increasing the ratio can significantly increase the vibration shielding area. But when the ratio is 0.53~0.75,it has little influence on the vibration shielding area. The ratio of rectangular trench width to Rayleigh wave length has little influence on the vibration shielding area. When the ratio of rectangular trench length to Rayleigh wave length varies within the range of 1.11~1.52,the vibration shielding area does not change significantly. When the ratio of the rectangular trench source distance to the Rayleigh wave length is 0.78~1.13,the change of the ratio has little influence on the vibration shielding area. When the normalized cross-sectional area of the trench varies from 0.02 to 0.78,it has a significant effect on the area of the vibration shielding area.
2022, 30(2): 507-519.
This paper examines the Standard Penetration Tests(SPTs) according to Standard Test Method for Standard Penetration Test(SPT) and Split-Barrel Sampling of Soils(ASTM D1586-11) and Chinese Code for Investigation of Geotechnical Engineering(GB 50021-2001). It conducts the SPT at a sand site in Guangdong province,China. It is found that tests conducted according to ASTM D1586-11 have higher penetration energy than those conducted according to GB 50021-2001. To consider the spatial variability of the blow counts,an empirical Bayesian Kriging method is used to interpolate the blow counts measured through tests conducted according to GB 50021-2001 at the locations where tests according to ASTM D1586-11 are conducted. The maximum likelihood method is used to calibrate the relationship between the blow counts measured from the two types of tests with and without consideration of the interpolation error. After the interpolation error is considered,the model uncertainty of the relationship between blow counts measured through the two types of tests is significantly reduced. Through the conversion relationship suggested in this paper,the liquefaction phenomena observed in a liquefaction database with case histories collected outside mainland China become more consistent with the liquefaction potential assessment model specified in the Chinese Code for Seismic Design of Buildings Code(GB 50011-2010).
This paper examines the Standard Penetration Tests(SPTs) according to Standard Test Method for Standard Penetration Test(SPT) and Split-Barrel Sampling of Soils(ASTM D1586-11) and Chinese Code for Investigation of Geotechnical Engineering(GB 50021-2001). It conducts the SPT at a sand site in Guangdong province,China. It is found that tests conducted according to ASTM D1586-11 have higher penetration energy than those conducted according to GB 50021-2001. To consider the spatial variability of the blow counts,an empirical Bayesian Kriging method is used to interpolate the blow counts measured through tests conducted according to GB 50021-2001 at the locations where tests according to ASTM D1586-11 are conducted. The maximum likelihood method is used to calibrate the relationship between the blow counts measured from the two types of tests with and without consideration of the interpolation error. After the interpolation error is considered,the model uncertainty of the relationship between blow counts measured through the two types of tests is significantly reduced. Through the conversion relationship suggested in this paper,the liquefaction phenomena observed in a liquefaction database with case histories collected outside mainland China become more consistent with the liquefaction potential assessment model specified in the Chinese Code for Seismic Design of Buildings Code(GB 50011-2010).
2022, 30(2): 520-532.
In order to ensure the safety of foundation pit construction,numerical simulation is used to predict the displacement of support structure. The selection of geotechnical parameters has the greatest influence on the numerical simulation results. A back analysis method based on multioutput least-squares support vector regression machine(MLSSVR) and particle swarm(PSO) is proposed to estimate multiple geotechnical parameters. This paper uses PSO-MLSSVR method to invert geotechnical parameters based on horizontal displacement monitoring data from the top of the supporting piles in a deep foundation pit in Shenzhen. Based on the orthogonal design method,representative combinations of geotechnical parameters are generated. Using these combinations,finite element method(FEM) is used to calculate the displacement of the measured points. PSO algorithm is used to optimize the parameters of MLSSVR model. Using MLSSVR to construct mapping relationships between inversion parameters and displacements to invert soil parameters in rock-fill,silt and sandy clay layers. The inverse parameters are substituted into the finite element model to calculate the measured point displacements. The results show that the MLSSVR model takes less time than the single output least squares support vector regressor(LSSVR) in inverting the parameters. When the inversion parameters of both models are substituted into the finite element model for calculation,the results of MLSSVR are closer to the actual monitoring values than LSSVR. The comparative results validate the superiority of the study methodology. In different stages of construction,the inversion parameters obtained by MLSSVR are used for numerical simulation. The simulation results are in good agreement with the monitoring data,which verified the accuracy and practicability of this method. The results show that the method in this paper is helpful to the selection of soil parameters and improve the accuracy of numerical simulation results.
In order to ensure the safety of foundation pit construction,numerical simulation is used to predict the displacement of support structure. The selection of geotechnical parameters has the greatest influence on the numerical simulation results. A back analysis method based on multioutput least-squares support vector regression machine(MLSSVR) and particle swarm(PSO) is proposed to estimate multiple geotechnical parameters. This paper uses PSO-MLSSVR method to invert geotechnical parameters based on horizontal displacement monitoring data from the top of the supporting piles in a deep foundation pit in Shenzhen. Based on the orthogonal design method,representative combinations of geotechnical parameters are generated. Using these combinations,finite element method(FEM) is used to calculate the displacement of the measured points. PSO algorithm is used to optimize the parameters of MLSSVR model. Using MLSSVR to construct mapping relationships between inversion parameters and displacements to invert soil parameters in rock-fill,silt and sandy clay layers. The inverse parameters are substituted into the finite element model to calculate the measured point displacements. The results show that the MLSSVR model takes less time than the single output least squares support vector regressor(LSSVR) in inverting the parameters. When the inversion parameters of both models are substituted into the finite element model for calculation,the results of MLSSVR are closer to the actual monitoring values than LSSVR. The comparative results validate the superiority of the study methodology. In different stages of construction,the inversion parameters obtained by MLSSVR are used for numerical simulation. The simulation results are in good agreement with the monitoring data,which verified the accuracy and practicability of this method. The results show that the method in this paper is helpful to the selection of soil parameters and improve the accuracy of numerical simulation results.
2022, 30(2): 533-541.
It is of great significance to analyze the seismic shaking conditions of coseismic rock avalanches in Gong County area. The area is just located in gentle stepped rock slope of hilly area of south Sichuan Province. A set of seismic stations,located into Wutong village of Gong County,captured a MS3.1 earthquake. Based on the captured seismic data,a series of analysis are carried out. The results show the upper stepped rock mass can produce larger site amplification and resonance amplification than the lower stepped rock. Due to the development of fissures and joints in cliff,the PGA and Arias of inner section of the upper stepped rock reduced 1.73 and 2.20 compared to the cliff section. This indicates that cliff exists site amplification effect. The seismic duration of the inner section of the upper stepped rock(convex terrain) is 1.25 times of the referred point(the lower stepped rock and the concave terrain). This indicates that micro topography has seismic duration amplification.
It is of great significance to analyze the seismic shaking conditions of coseismic rock avalanches in Gong County area. The area is just located in gentle stepped rock slope of hilly area of south Sichuan Province. A set of seismic stations,located into Wutong village of Gong County,captured a MS3.1 earthquake. Based on the captured seismic data,a series of analysis are carried out. The results show the upper stepped rock mass can produce larger site amplification and resonance amplification than the lower stepped rock. Due to the development of fissures and joints in cliff,the PGA and Arias of inner section of the upper stepped rock reduced 1.73 and 2.20 compared to the cliff section. This indicates that cliff exists site amplification effect. The seismic duration of the inner section of the upper stepped rock(convex terrain) is 1.25 times of the referred point(the lower stepped rock and the concave terrain). This indicates that micro topography has seismic duration amplification.
2022, 30(2): 542-552.
Sanguanmiao shattered mountain is located in Wenchuan earthquake area,where two post-earthquake rockfalls had occurred on July 20,2018 and August 22,2019,respectively. They caused considerable economic losses and threatened the safety of residents. Therefore,this paper performs a detailed analysis on study area by using field investigation of dangerous rocks in shattered mountains,unmanned aerial vehicle survey and three-dimensional numerical simulation,clarifying the mechanisms and kinematic processes of the rockfall evolved from shattered mountain. Meanwhile,the risk of potentially dangerous rock area has been assessed. The results suggest the following findings. The formation process of this type of rockfall could be divided into three stages,including early structure and unloading crack development of potentially dangerous rock slope,formation of shattered mountains(dangerous rock mass) and occurrence of post-earthquake rockfalls. Firstly,the rock masses in the source area formed unloading fissures during the incision of the Minjiang River,and then under the role of the "5.12" strong earthquake and aftershocks,tensile fissures formed and the ridge top deformed and shattered,forming shattered mountains. Eventually,heavy rainfall in the rainy season directly triggered the rockfalls. The three-dimensional simulation software RocPro3D is used to simulate the accumulation range and the dominant moving trajectory,which are compared and verified with the existing accumulation area,comprehensively obtain the rock and soil characteristic parameters,and further simulated and predicted the possibility of the dangerous rock area based on the validated parameters. The movement characteristics,dominant moving trajectory,moving velocity,energy and bounce height are analyzed to obtain the impact extent of the rockfall. The results can provide an insight into potential disasters reduction and prevention of shattered mountain failure in the strong earthquake area.
Sanguanmiao shattered mountain is located in Wenchuan earthquake area,where two post-earthquake rockfalls had occurred on July 20,2018 and August 22,2019,respectively. They caused considerable economic losses and threatened the safety of residents. Therefore,this paper performs a detailed analysis on study area by using field investigation of dangerous rocks in shattered mountains,unmanned aerial vehicle survey and three-dimensional numerical simulation,clarifying the mechanisms and kinematic processes of the rockfall evolved from shattered mountain. Meanwhile,the risk of potentially dangerous rock area has been assessed. The results suggest the following findings. The formation process of this type of rockfall could be divided into three stages,including early structure and unloading crack development of potentially dangerous rock slope,formation of shattered mountains(dangerous rock mass) and occurrence of post-earthquake rockfalls. Firstly,the rock masses in the source area formed unloading fissures during the incision of the Minjiang River,and then under the role of the "5.12" strong earthquake and aftershocks,tensile fissures formed and the ridge top deformed and shattered,forming shattered mountains. Eventually,heavy rainfall in the rainy season directly triggered the rockfalls. The three-dimensional simulation software RocPro3D is used to simulate the accumulation range and the dominant moving trajectory,which are compared and verified with the existing accumulation area,comprehensively obtain the rock and soil characteristic parameters,and further simulated and predicted the possibility of the dangerous rock area based on the validated parameters. The movement characteristics,dominant moving trajectory,moving velocity,energy and bounce height are analyzed to obtain the impact extent of the rockfall. The results can provide an insight into potential disasters reduction and prevention of shattered mountain failure in the strong earthquake area.
2022, 30(2): 553-564.
Since the late 1950s,Xi'an City has suffered from serious land subsidence and ground fissure,which seriously restricted the urban construction and development planning of Xi'an City. In this study,Yuhua Village,one of the typical land subsidence areas in Xi'an City,was taken as the research area. Based on the SBAS-InSAR technique,ERS(1992-1993),Envisat(2003-2010) and Sentinel-1A(2015-2020)satellite datas covering the study area are used to analyze the temporal and spatial evolution characteristics of land subsidence and ground fissures in the surrounding area of Yuhua Village. The drilling data and the history and current situation of groundwater exploitation and urban development are used in this paper. The genetic mechanism of land subsidence and ground fissures in the study area is also discussed. The main conclusions of this study are as follows. (1)The annual average subsidence rate of three stages in the surrounding area of Yuhua Village from 1992 to 2020 is obtained,which reveals that the subsidence center changes from the Electronic City(90mm ·a-1)in the 1990s to the present Yuhua Village(50mm ·a-1). (2)It is confirmed that there is a correlation between the land subsidence and the ground fissure in the temporal and spatial distribution. The ground fissures develop in the north edge of the land subsidence trough,which limit the northward development of land subsidence trough. And the ground fissures extend with the development of the land subsidence trough. (3)It is revealed that the Yuhua Village subsidence center is still expanding,and the f4 ground fissure may extend westward. (4)The development of land subsidence and ground fissure around Yuhua Village is affected by the exploitation of underground confined aquifer and human construction activities. The above understanding can provide certain reference and support for urban land development and disaster prevention affected by land subsidence and ground fissures.
Since the late 1950s,Xi'an City has suffered from serious land subsidence and ground fissure,which seriously restricted the urban construction and development planning of Xi'an City. In this study,Yuhua Village,one of the typical land subsidence areas in Xi'an City,was taken as the research area. Based on the SBAS-InSAR technique,ERS(1992-1993),Envisat(2003-2010) and Sentinel-1A(2015-2020)satellite datas covering the study area are used to analyze the temporal and spatial evolution characteristics of land subsidence and ground fissures in the surrounding area of Yuhua Village. The drilling data and the history and current situation of groundwater exploitation and urban development are used in this paper. The genetic mechanism of land subsidence and ground fissures in the study area is also discussed. The main conclusions of this study are as follows. (1)The annual average subsidence rate of three stages in the surrounding area of Yuhua Village from 1992 to 2020 is obtained,which reveals that the subsidence center changes from the Electronic City(90mm ·a-1)in the 1990s to the present Yuhua Village(50mm ·a-1). (2)It is confirmed that there is a correlation between the land subsidence and the ground fissure in the temporal and spatial distribution. The ground fissures develop in the north edge of the land subsidence trough,which limit the northward development of land subsidence trough. And the ground fissures extend with the development of the land subsidence trough. (3)It is revealed that the Yuhua Village subsidence center is still expanding,and the f4 ground fissure may extend westward. (4)The development of land subsidence and ground fissure around Yuhua Village is affected by the exploitation of underground confined aquifer and human construction activities. The above understanding can provide certain reference and support for urban land development and disaster prevention affected by land subsidence and ground fissures.
2022, 30(2): 565-574.
The disaster-causing range formed by the earthquake landslide is an important basis for judging whether the landslide can cause losses to existing structures and determining the early warning evacuation range. Therefore,it is necessary to study the sliding body size and disaster-causing range after the post sliding of soil slopes triggered by the earthquake. Based on the dynamic SPH analysis method,combined with the elastoplastic constitutive model and the governing equation of solid mechanics,we establish a dynamic analysis model for the seismic soil slope failure. By setting the vibration boundary particles and the free field boundary particles,we realize the application of ground motion acceleration and the simulation of the free field boundary. We use the dynamic SPH analysis method to simulate an existing shaking table test for soil slope. And we obtain a sliding form similar to the shaking table test slope from the SPH simulation. This result verifies the accuracy and precision of the dynamic SPH analysis method. Afterwards,we design calculation cases of soil slopes with different slope angles. And we carriy out SPH analysis considering the influence of ground motion acceleration amplitude. Finally we obtain the sliding body size and the disaster-causing range of landslide after instability of seismic soil slopes under various working conditions. The simulation results show that the soil slope has a similar sliding surface under the action of different ground motion amplitudes. And the potential sliding area increases with the increase of the ground motion amplitude. Meanwhile,the stability of the soil slope under different ground motion acceleration amplitudes shows a downward trend. And the disaster-causing range becomes larger,while the sliding body size is decreasing.
The disaster-causing range formed by the earthquake landslide is an important basis for judging whether the landslide can cause losses to existing structures and determining the early warning evacuation range. Therefore,it is necessary to study the sliding body size and disaster-causing range after the post sliding of soil slopes triggered by the earthquake. Based on the dynamic SPH analysis method,combined with the elastoplastic constitutive model and the governing equation of solid mechanics,we establish a dynamic analysis model for the seismic soil slope failure. By setting the vibration boundary particles and the free field boundary particles,we realize the application of ground motion acceleration and the simulation of the free field boundary. We use the dynamic SPH analysis method to simulate an existing shaking table test for soil slope. And we obtain a sliding form similar to the shaking table test slope from the SPH simulation. This result verifies the accuracy and precision of the dynamic SPH analysis method. Afterwards,we design calculation cases of soil slopes with different slope angles. And we carriy out SPH analysis considering the influence of ground motion acceleration amplitude. Finally we obtain the sliding body size and the disaster-causing range of landslide after instability of seismic soil slopes under various working conditions. The simulation results show that the soil slope has a similar sliding surface under the action of different ground motion amplitudes. And the potential sliding area increases with the increase of the ground motion amplitude. Meanwhile,the stability of the soil slope under different ground motion acceleration amplitudes shows a downward trend. And the disaster-causing range becomes larger,while the sliding body size is decreasing.
2022, 30(2): 575-588.
This paper puts forward a landslide displacement prediction model. The model is based on time series decomposition and hybrid kernel function SA-SVR. It makes progresses on solving problems of being difficult to quantitatively predict step-type landslide deformation. Firstly,based on the principle of time series decomposition,exponential smoothing is used repeatedly to decompose the cumulative displacement of the landslide into trend displacement and periodic displacement to make the decomposed trend displacement smoother and keep the accuracy of periodic displacement forecast. At the same time,the third-order polynomial of K-flod cross-validation is used to predict the trend displacement avoiding the problems in polynomial prediction. The prediction is easy to overfit and the predicted value deviates from the true value. Based on the properties of SVR kernel function,the mixed kernel function with strong generalization ability and learning ability was constructed as the kernel method of SVR model. The landslide inducing factor is taken as the input vector of SVR model. The simulated annealing(SA)is used to optimize the parameters of SVR model using the mixed kernel function. Thus the SA-SVR model with mixed kernel function is established to predict the periodic displacement. Finally,the trend displacement and periodic displacement are combined to get the predicted total displacement. The paper takes the Baijiabao landslide in the Three Gorges reservoir area as an example,selects the data of ZG325 monitoring point from January 2012 to September 2020,and uses the ZG324 monitoring point as auxiliary verification. The results show that compared with the conventional SVR prediction model,the simulated annealing(SA)performs well in parameter optimization,and the hybrid kernel function is more sensitive to the SVR model,which can greatly improve the prediction accuracy and has high application and promotion value.
This paper puts forward a landslide displacement prediction model. The model is based on time series decomposition and hybrid kernel function SA-SVR. It makes progresses on solving problems of being difficult to quantitatively predict step-type landslide deformation. Firstly,based on the principle of time series decomposition,exponential smoothing is used repeatedly to decompose the cumulative displacement of the landslide into trend displacement and periodic displacement to make the decomposed trend displacement smoother and keep the accuracy of periodic displacement forecast. At the same time,the third-order polynomial of K-flod cross-validation is used to predict the trend displacement avoiding the problems in polynomial prediction. The prediction is easy to overfit and the predicted value deviates from the true value. Based on the properties of SVR kernel function,the mixed kernel function with strong generalization ability and learning ability was constructed as the kernel method of SVR model. The landslide inducing factor is taken as the input vector of SVR model. The simulated annealing(SA)is used to optimize the parameters of SVR model using the mixed kernel function. Thus the SA-SVR model with mixed kernel function is established to predict the periodic displacement. Finally,the trend displacement and periodic displacement are combined to get the predicted total displacement. The paper takes the Baijiabao landslide in the Three Gorges reservoir area as an example,selects the data of ZG325 monitoring point from January 2012 to September 2020,and uses the ZG324 monitoring point as auxiliary verification. The results show that compared with the conventional SVR prediction model,the simulated annealing(SA)performs well in parameter optimization,and the hybrid kernel function is more sensitive to the SVR model,which can greatly improve the prediction accuracy and has high application and promotion value.
2022, 30(2): 589-598.
High level rockfall is one of the main geological disasters causing the damage of long-distance buried oil and gas pipelines. Based on the analysis of 111 mountain pipeline collapse cases,this paper summarizes three modes of interaction between collapse and buried pipeline,Smashing pipeline,traction pipeline and buried pipeline. Among them,smashing the pipeline is the most harmful. And the geomechanical model of the interaction between collapse and pipeline is established. The response process and influencing factors of rockfall impact,soil and pipeline deformation are simulated by the finite element simulation software. It is found that the rockfall impact process is a transient process with a duration of about 0.1 s,which reveals the dynamic response law of soil and pipeline and the pipe-soil interaction mechanism. The pipe-soil deformation can experience the development and evolution process from coordinated deformation to uncoordinated deformation. On this basis,through the analysis of influencing factors such as different rockfall velocity,pipeline buried depth,internal pressure,rockfall shape and protection engineering,some suggestions on pipeline protection design in collapse area are put forward. The buried depth of the pipeline is designed to be more than 2.0 m and the thickness of the cover plate is not less than 0.2 m,which can effectively reduce the risk of rockfall impact damage to the pipeline.
High level rockfall is one of the main geological disasters causing the damage of long-distance buried oil and gas pipelines. Based on the analysis of 111 mountain pipeline collapse cases,this paper summarizes three modes of interaction between collapse and buried pipeline,Smashing pipeline,traction pipeline and buried pipeline. Among them,smashing the pipeline is the most harmful. And the geomechanical model of the interaction between collapse and pipeline is established. The response process and influencing factors of rockfall impact,soil and pipeline deformation are simulated by the finite element simulation software. It is found that the rockfall impact process is a transient process with a duration of about 0.1 s,which reveals the dynamic response law of soil and pipeline and the pipe-soil interaction mechanism. The pipe-soil deformation can experience the development and evolution process from coordinated deformation to uncoordinated deformation. On this basis,through the analysis of influencing factors such as different rockfall velocity,pipeline buried depth,internal pressure,rockfall shape and protection engineering,some suggestions on pipeline protection design in collapse area are put forward. The buried depth of the pipeline is designed to be more than 2.0 m and the thickness of the cover plate is not less than 0.2 m,which can effectively reduce the risk of rockfall impact damage to the pipeline.
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