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Abstract(13) HTML(3) PDF (3138KB)(20)
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Groundwater numerical model is not only an effective tool for understanding the formation and evolution mechanism of deep groundwater dynamic field, but also the basis for establishing numerical model of nuclide migration. Therefore, it is an important technical means in the site selection and safety assessment of HLW disposal repository. There are many numerical simulation methods for groundwater flow in deep geological disposal of high-level radioactive waste (HLW), and how to choose the suitable method is also a problem worth paying attention to. This article focuses on the research of groundwater numerical simulation technology for deep geological disposal of HLW. Through reviewing a lot of relevant papers, systematically expounds the research progress, applicable conditions and practical applications of four kinds of commonly used groundwater numerical simulation methods. In addition, summarizes the model uncertainty analysis methods and research results commonly used in deep geological disposal, and lists the numerical simulation software of groundwater flow suitable for geological disposal of HLW and its application in waste disposal selection and safety assessment. The results show that the equivalent continuum model is suitable for large, long sequence and high fracture development or uniform areas, with the advantages of mature method and easy to obtain the required data and parameters, but the flow characteristics of groundwater in fractured media cannot be described accurately. The discrete fracture network model is suitable for solving the groundwater flow problems that need to be finely described, such as disposal site and repository canister. However, due to the need for a large number of fracture characteristics, connectivity and related parameters data, this method has the disadvantages of heavy workload and time-consuming. The dual medium model is mainly used to solve the problem of regional-scale fractured groundwater flow, but it cannot show the characteristics of anisotropy and discontinuity of fractured media, so the scope of application has certain limitations. The equivalent discrete coupling model can adopt the equivalent continuum model for the area with high fracture density and the discrete fracture network model for the area with low fracture density through the domain decomposition method, which is more in line with the characteristics of fracture seepage under general geological conditions, but there is also the problems that the exchange capacity is difficult to determine and the coupling technology of two models. Sensitivity analysis sorts the influence degree of different sensitive factors on the model sensitive indexes, so as to improve the model accuracy and reduce the workload of parameter uncertainty analysis. Monte Carlo method is a commonly used method for model uncertainty analysis, which is simple in principle and beneficial to implementation. Finally, the author points out that numerical model simulation ability, uncertainty analysis, prediction simulation and multi-medium coupling model research should be strengthen in the future.
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In order to examine the dynamic characteristics of expansive soil in natural environment, the maximum shear modulus of undisturbed and remoulded Nanyang expansive soil specimens were tested by using a triaxial apparatus equipping with a pair of bender element. The saturated undisturbed Nanyang expansive soil specimen was tested using the bender element to measure the maximum shear modulus under different confining pressures. The maximum shear modulus of the undisturbed and remoulded specimens with the same dry density were measured in wetting-drying processes and analyzed in combination with the void ratio. The test results indicate that the maximum shear modulus of the saturated Nanyang expansive soil increases with the increasing confining pressure. In the relationship between the maximum shear modulus and water content, the drying curve is higher than the wetting one. It is also found that there is hysteretic characteristics in the maximum shear modulus and water content relationship, which is mainly due to the suction effect. Under similar dry density the maximum shear modulus of undisturbed specimen is smaller than the remoulded one. The reason is that there are more large pores in the undisturbed soil. Finally, an existing formula for the saturated soils is improved for predicting the maximum shear modulus of the unsaturated and undisturbed Nanyang expansive soil.
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Sand-gravel mixture is composed of materials with very different mechanical properties and structures, and the remolded strata composed of the sand-gravel mixture are prone to collapse and other problems. Therefore, the research on the mechanical properties of sand-gravel mixture is an urgent problem to be solved. The shape of gravel is an important attribute parameter in the study of the mechanical properties of sand and gravel. Description of gravel with regular graphics cannot reflect its real mechanical properties. In this paper, the gravel database constructed by digital image processing technology can reflect the true shape of gravel and analyse the specific shape parameters. The particle size distribution of the sand-gravel mixture is wide, and the characteristic particle size cannot be used to describe the overall particle size distribution. In this study, combined with the fractal theory, a double fractal model of the sand-gravel mixture is constructed, and the gradation distribution curve is inversed by the particle size fractal dimension value. Taking into account the discrete characteristics of the sand-gravel mixture, the discrete element software is used to carry out the numerical simulation of the direct shear test and analyse the mesostructure. The results indicate that the sand-
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The Lannigou rockslide is one of the most well-known giant and rapid rockslides with long runout in China. The 1965 Lannigou rockslide caused the most catastrophic consequence in China since 1920’s and followed by two more rockslides in 1991 and 2007, respectively. However, it remains unclear that how precursors of the 1965 rockslides were and relationship between the two movement sequences was, so do the following activities in 1991 and 2007. Those unclear questions were explored in this paper based on 23 remote sensing satellite images taken during the period between 1965 and 2020 and the UAV image taken in 2019 as well as field survey then. It is found that: 1) tension cracks could be seen in the northern slope of the source area before the 1965 rockslides, evidencing occurrence of precursors there, 2) 1965 rockslide first occurred on the northern slope, and subsequently induced a rockslide on the southern slope on next day as a result of impact by the failed northern slope, 3) rapid granular flow jumped and flew over the northern slope of the transition zone, and scrapped, entrained surficial layer there, 4) the granular flow did not reach the Jingsha River, but ended ca. 2.8 km east of the intersection between the Lannigou and the Pufu river; 5) the source area of the 1991 rockslide just neighbored the northwestern boundary of the 1965 rockslide on the northern slope, while the 2007 rockslide neighbored the upper boundary of the 1991 rockslide, and 6) the detached volumes and runouts of the 1965, 1991 and 2007 rockslides showed a decrease order. Recently, tension cracks can be clearly seen on both the northwestern and southwestern slopes. One of the tension cracks on the northwestern slope is extending with a rate of 16.7 m/a, while those on the southwestern slope has shown no sign of extension since 2014, indicating that the northwestern slope may fail again. It is thus that an attention should be paid to the northwestern slope via monitoring its deformation and keeping local people away from the area likely affected.
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Flow-like motion is the main forms of rock avalanche emplacement, which is the foundation to reveal the dynamic mechanisms of rock avalanches. In this paper, a series of physical modeling experiments based on the Particle Image Velocimetry（PIV）analysis method are conducted to research the internal velocity distribution, internal shear behavior and flow regimes of the granular flow under different grain size conditions. The flow-like motion of rock avalanches and the corresponding deposit features are further discussed and analyzed based on the experimental results. The research results show that the flow-like motion of the granular flow is significantly correlated with the grain size. With the decreasing grain size or the increasing fine particles content, the slip velocity at the bottom of the granular flow and the bulk velocity decrease gradually, the degree of internal shear of the granular flow increases, and the motion form of the granular materials changes from "sliding" to "flowing". When the grain size is smaller or the content of fine particles is higher, the increasing trend of the internal shear rate is more prominent at the bottom of the granular flow, which indicates that the reduction in grain size promotes shear localization at the bottom of the granular flow. The granular flow regime is different at different locations of the granular flow. The leading and trailing edges of the granular flow are mainly inertial regime, and the interaction between particles is dominated by collisions, while the particle interactions in the main body is dominated by frictional contact. On the surface and bottom of the granular flow, the interaction between particles is mainly collision, while particle interaction in the middle part is mainly frictional contact. For the granular flow with different grain sizes, with the increasing grain size and coarse particles content, the particle collisions in the granular flow are enhanced, and the flow regimes tend to be more inertial.
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How to identify deformed landslides in advance and conduct early risk assessments on them has become a research hotspot in the field of geological disaster prevention and control. In response to the above problems, the Jiangdingya landslide in the Bailong River Basin in Zhouqu is taken as a back analysis case, and a comprehensive study of the early identification and risk assessment of the landslide is carried out. In this paper, a full-process analysis method is proposed, which combine the small baseline subset interferometric synthetic aperture radar (SBAS-InSAR) technology interpretation, geo-mechanical analysis and dynamic process simulation. The research results show that the SABS-InSAR technology interpretation can effectively identify the range of the Jiangdingya landslide and its early deformation. It may be preliminarily determined that the failure mode of the Jiangdingya landslide is trailed and the plane characteristics of the landslide body is generally about 680 m in length and 210 m in width. Based on the early identification information and through geo-mechanical analysis, it is finally identified that the instability problem of the Jiangdingya landslide is a typical deformation problem of the front edge of the old accumulation layer landslide. The failure mode is the traction slip failure, the average thickness of the landslide body is in about 35 m, the overall slope of the sliding bed is relatively slow, and the moving speed is not large after instability. On the basis of the above analyses, a Coulomb friction model that conformed to the sliding friction characteristics of the Jiangdingya landslide body is selected. Based on the depth integral continuum equation, the dynamic process of the Jiangdingya landslide body is calculated and the speed of the landslide body is monitored. In terms of velocity monitoring curves and accumulation pattern, the sliding velocity of the landslide body is not large, the maximum value is about 2.2 m/s, the overall performance is pushing the Bailong River channel, and the possibility of blocking the river is relatively small. In addition, when the displacement of the front edge of the Jiangdingya landslide body is completed, the speed of the landslide body from the front edge to the rear edge quickly drope to zero, and the movement process is characterized by the traction movement. The analysis results of the Jiangdingya landslide in this paper are consistent with the actual event of the Jiangdingya landslide. The comprehensive analysis method and research model can provide a good reference for the early identification and risk assessment of similar landslides in the Bailong River Basin in Zhouqu county.
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Analysis of the coseismic differential response of adjacent monitoring wells is an important way to study the coseismic response mechanism of groundwater. On February 3, 2020, the Qingbaijiang earthquake caused the abnormal changes of groundwater levels and water quality in the monitoring wells of Longquanshan. In this paper, the coseismic differential response characteristics of two adjacent monitoring wells are analyzed by using the automatic monitoring data of various hydrochemical components and water levels. Based on the coupling response characteristics of hydrochemical components and water levels, the mechanism of differential response of hydrochemical components and water levels is discussed. In the case of the same energy density, the water level variation amplitude of well ZK1 is larger than that of well ZK6, which indicates that ZK1 is more sensitive to the earthquake response than ZK6. The earthquake mainly caused the discharge of the groundwater (Eh<0) from the second aquifer (${\rm{NH}}_4^+$ and ${\rm{NO}}_3^-$) to ZK1, while the groundwater (Eh>0) from the first aquifer (high concentration of Cl, TDS, and pH) to ZK6. The discharge and mixing of water from different aquifers into the wells are the reason for the different response of chemical components of groundwater in these two wells. According to the trends of chemical components and water levels after the earthquake, rock mass under seismic action of undrained volume change is the main cause of groundwater water status step change, that is, plastic deformation and permanent change in permeability occurred in the second aquifer around well ZK1, and no permanent change in permeability but elastic deformation occurred in rock mass around well ZK6.
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Fracturing flowback fluid poses serious challenges to environmental protection and human health, but also provides valuable information for geological and engineering applications. There is massive overdrainage in the fracturing flowback fluid from the Lucaogou formation in the Jimsar Sag in Xinjiang. In order to reveal the source and compositions of the excess fracturing flowback fluid and investigates the geochemical information of the original groundwater, in the absence of original groundwater samples, this research collects surface water, fracturing fluid and fracturing flowback fluid samples systematically from two horizontal wells in the study area to analyze the hydrogen and oxygen isotopic compositions and the dynamic change characteristics with the flowback time. The results indicate that, compared with the surface water and fracturing fluid rich in D and poor in 18O, the δ18O of fracturing flowback fluid has a positive shift, while the δ2D has a negative shift, distribution of the data points of δ2H and δ18O deviate from the local meteoric water line, and the water source has changed. With the continuous injection of fracturing fluid and connection of isolated reservoir space, the groundwater continues to mix into the fracturing fluid, the flowback fluid gradually turns from fracturing fluid into groundwater, and δ18O tends to be stable. Through the convergence model of δ18O with the flowback time established by the nonlinear fitting of the measured data of the flowback fluid, δ18O of groundwater is calculated to be −6.902‰. Based on the mass conservation law of isotopes, a formula for calculating groundwater content is established. On the 60th day of flowback, the groundwater content of the flowback fluid in the two wells is 84% and 81%, respectively, and the amount of the fracturing fluid remaining in the formation is 43 283.4 m3 and 39 150.3 m3, respectively. The majority of the fracturing fluid injected in the earlier stage is still retained in the formation, and the source of the overdrainage is the continuously mixed groundwater.
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In recent years, many linear loess fill slopes have appeared with the continuous development of “Governing valleys” and “Retaining plateau” projects in the Loess Plateau. Slope instability is induced by rainfall, which is an important factor. However, there are few studies on the deformation evolution characteristics and failure modes of rainfall-induced linear loess fill slopes. In this paper, the linear loess fill slope is taken as the research object, and the indoor rainfall model test is carried out through sensor monitoring, three-dimensional laser scanning technology and artificial rainfall system. The hydrological response characteristics and failure process of slope under rainfall infiltration are recorded, and the wetting front, soil particle migration, internal deformation response, fracture evolution characteristics and failure mode are analyzed. The test results show that with the infiltration of rainfall, when the wetting front is reached, the volumetric moisture content increases and remains stable at the maximum, while the matric suction decreases and remains stable at the minimum. The gully has a greater impact on the fill slope. The development of slope changes the characteristics of the water content in the slope, and at the same time it is the boundary that controls the overall sliding of the slope. The deformation response area of the slope is mainly the front accumulation area and the back slide area of the filling slope. The cracks evolve from the leading to the trailing edge, and its development offers preferential seepage channels for the infiltration of rainwater. At the same time, the cracks also intensifies the deformation and failure of the slope. The hydrodynamic force formed by rainfall drives the loss of fine particles in the slope from the rear edge of the fill slope to the front edge, weakens the cementation among the soil particles, reduces the shear strength, and causes the slope instability and failure. Therefore, under the rainfall infiltration, the deformation and failure modes of the linear loess fill slope are: gully failure at the top of slope and toe softening →local traction collapse and overall instability → block segmentation and at last the flow slip failure. The research results can provide a theoretical reference for the engineering construction of linear loess fill slope and the prevention and control of landslide disaster.
Abstract(10) HTML(4) PDF (4122KB)(5)
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Rapidly and accurately quantitative investigation and evaluation of landslides can provide scientific basis for the emergency treatment of landslide, and the unmanned aerial vehicle (UAV) aerial photography system has become a reliable means for geological disaster investigation due to its flexibility and rapid response. In this paper, the Pingqing landslide in Ceheng is taken as an example, and a set of processes of rapid slope investigation and quantitative evaluation based on the light UAV aerial photography technology are summarized. The path of establishing high-precision 3D geological model using various software is expounded, and the finite difference method (FDM) is applied to analyze the deformation mechanism and evaluate the stability of the landslide. The results show that (1) the Global mapper, Pix4Dmapper, Rhinoceros and other software are used to manage the data acquired by UAV and to establish a 3D model, which is convenient, rapid and reliable. (2) In the procedure, landslide investigation and evaluation based on UAV, the traditional qualitative analysis is combined with the quantitative analysis by means of numerical simulation, which can provide convincing basis and supporting data for emergency after. (3) The Pingqing landslide in Ceheng is a creepage-pull crack landslide caused by gravity stress of slope body under rainfall condition. At the period of investigation, the landslide had activated and the surface cracks had tended to expand rapidly.
Abstract(6) HTML(3) PDF (0KB)(2)
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Gaussian Process Regression (GPR) is a supervised learning algorithm based on Bayesian theory, which is widely used in model structural uncertainty analysis based on data-driven method (DDM). In this study, it is usually assumed that the physical parameters and hyperparameters are independent and identified jointly, which will lead to parameter compensation. In this paper, a two-stage based DDM method is proposed to quantify the model structural errors, and two case studies are used to compare and analyze the results of parameter identification and model prediction with considering the model structural errors (joint calibration based DDM and two-stage based DDM) and without considering the model structural errors. The results show that when the parameters are identified directly without considering the model structural errors, the parameters will be overfitted and compensate the model structural errors, thereby affecting the model prediction performance. When considering the model structure deviation based on DDM, the independence assumption of physical parameters and hyperparameters will affect the parameter estimation results. The proposed two-stage based DDM method does not assume that the physical parameters and hyperparameters are independent, and can reduce parameter overfitting caused by the independence assumption of physical parameters and hyperparameters, portraying more accurate structural errors and effectively improving the model prediction performance.
Abstract(7) HTML(5) PDF (3311KB)(13)
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A series of column tests of chromium-contaminated soft soil were performed in lab using self-designed electrokinetic soil flushing apparatus considering temperature. The changes of the current and electrolyte solution pH, and the effects of the type of leaching agent (i.e. sodium dodecylbenzene sulfonate, citric acid and oxalic acid), applied voltage and temperature on the removal behavior of chromium were analyzed. The results show that chromium in soil can be removed effectively with the electrokinetic soil flushing method. Compared with the single soil flushing method using sodium dodecylbenzene sulfonate (SDS), the removal ratio of Cr(VI) and Cr(total) can increase to 2.79 and 3.12 times when the voltage of 10 V is applied. When the raising temperature increases to 45 ℃, the removal ratio of Cr(VI) and Cr(total) both are greatly improved as citric acid (CA) and oxalic acid (OA) are leaching agents, while the removal ratio of Cr(total) decreases by 4.25% when using SDS as leaching agent. The group using oxalic acid as leaching agent shows the best removal efficiency, and the removal ratio of Cr(VI) and Cr(total) reach 82.08% and 77.57%, respectively. After remediation, the soil structure has changed, and pores between soil particles become smaller and the soils are more compacted.
Abstract(18) HTML(14) PDF (3824KB)(18)
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The rough back of a wall causes the deflection of the soil stress direction behind the wall. At present, there are few studies on the influence of the deflection of the soil stress direction on the earth pressure in cohesive soils. For this reason, this paper firstly discusses the deflection law of the principal stress of the soil behind the wall, and adopts a layered formation of curved thin-layer elements along the principal stress trace. By analyzing the force of the curved thin-layer element, the static balance equation of the curved thin-layer element is established, and the formula for the distribution of the earth pressure of the cohesive soil along the wall height in the translational mode is derived, and the new analysis method of the cohesive earth pressure is obtained. Finally, the method in this paper is compared with the actual measurement results and the existing theory and the parameters are analyzed to verify the reliability and rationality of the method in this paper. The research results show that the calculation results considering the effect of wall-soil friction can more accurately reflect the distribution law of cohesive soil along the wall height; the magnitude of earth pressure decreases with the increasing cohesion. With the increase of wall-soil friction angle soil, the pressure resultant force gradually decreases, and the height of the point of application increases slowly.
Abstract(9) HTML(8) PDF (11581KB)(18)
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Composite soil with deep mixed column is widely used in strengthening soft soil subgrade. However, there is still a lack of understanding the dynamic characteristics of composite soil with deep mixed column and evaluating unreasonably the long-term performance of composite soil with deep mixed column. Based on above, this study conducted a series of large-scale triaxial test to investigate the influence factors of static deviator stress, replacement ratio and incremental loading/unloading on the dynamic parameters of unit cell of deep mixed column-reinforced soft soil. The results show that with the increase of the static deviator stress, the dynamic elastic modulus increases, the damping ratio decreases, and the critical dynamic stress ratio decreases. With the increase of the area replacement ratio, the dynamic elastic modulus increases slightly and the damping ratio decreases slightly. The staged unloading can deteriorate the dynamic properties of the unit cell. The damping ratio is of strong volatility, and the variation coefficient of damping ratio is 2.8 to 7.0 times that of the dynamic elastic modulus. The dynamic elastic modulus of the unit cell of the composite soil is 2 to 6 times that of the soft soil, and the improvement factor increases with the increase of the static deviator stress.
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The thickness of hydration film of clay particles is the theoretical basis of swelling mechanism of argillaceous expansive rock and soil. There are abundant data on the measurement of clay particle hydration film thickness, but the study of the measurement of clay particle hydration film thickness by atomic force microscopy is relatively rare, and the test method is not perfect. Based on the three-layer hydration membrane structure model and atomic force microscope test technology, through the test and research on montmorillonite powder, mudstone powder and mudstone rock slice, this paper puts forward the measurement method of the thickness of the hydration film, the preparation method of powder sample and rock sample, and the statistical processing method of the test data. The variation rules of the free water section, weakly bound water section, strong bound water section and clay particle section of the hydration film thickness test curve are summarized. Through comparative analyses with the existing research results, the rationality and feasibility of the testing the thickness of the hydration film of clay particles by the atomic force microscope is demonstrated. Combined with engineering practice, the engineering significance and theoretical value of the quantitatively obtaining the hydration film thickness in understanding the swelling mechanism of the argillaceous expansive rock and soil are discussed.
Abstract(18) HTML(5) PDF (4010KB)(19)
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The quantitative relationship among the weathering, microscale structure, and microscale flow properties is a fundamental issue for the efficient preservation of the cultural relics in the grottoes. Sandstone weathering may affect the efficient preservation of the cultural relics in the grotto rocks. In this study, the microscopic images of the sandstones of various grottoes in the Yungang Grottoes are obtained by SEM (Scanning Electronic Microscopy), and the digital characteristic parameters of the particles and pores in the rock are obtained by using the image enhancement and image segmentations. A flow model reflecting the characteristics of the pore-throat connection is also established in the microscopic scale. The local hydraulic conductivity coefficients of the rocks at various grottoes are then obtained. The relationship among the hydraulic conductivity coefficients, digital characteristic parameters, and weathering levels is further explored. The results show that the weathering much affects the microstructure of the grotto sandstones; the corresponding great-small order of the weathering for the average long axeses of pores are the complete or high weathering, the moderate weathering, and the slight weathering or fresh sandstones, respectively, with the axeses of greater than 40 μm, 25 to 35 μm, and 15 to 25 μm. The higher levels of weathering will result in the greater hydraulic conductivities ranging from 1×10−9 to 1×10−4 cm/s; the hydraulic conductivity is closely related to the size and connectivity of the pore-throats; and the increases in the pore-throat radius ratios will result in the increase in the hydraulic conductivities.
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Based on a large number of measured data of surface settlement of open cut foundation pit engineering in different areas of Beijing in recent years, the typical curve "Four Point Broken Line Method" and its model parameters (slope K and intercept b) for predicting surface settlement are inversely analyzed by using theoretical calculation and regression analysis methods, and the empirical parameters for predicting surface settlement of open cut foundation pit under different regional geological conditions are obtained. Based on the statistical analyses of data and empirical parameters, the regional variation law of surface subsidence is summarized, and the range of parameters is defined. The prediction accuracy of empirical parameters is verified by using the measured data. The results show that the horizontal distance between the maximum settlement point and the retaining structure in the west of Beijing is larger than those in the middle and east of Beijing, which is about 30% of the depth of the foundation pit, while those in the middle and east of Beijing is relatively small, which are about 26% of the depth of the foundation pit. The surface settlement curve shape varies with the regional geological conditions, and the absolute value of the slope K of the first line AB of the four point broken line graph increases from west to east, showing the settlement slope of the east silty fine sand is more obvious than that of the west sandy cobble, and the absolute value of the slope K of the second straight line BC in the east is smaller than that in the west, indicating that the settlement influence range of the east is larger, the absolute value of the parameter bAB increases from west to east, indicating that the settlement value of the pile side soil of the silty clay and fine sand in the east is larger than that of the sandy pebble in the west. It is about 31% of the maximum settlement, 21% in the central region and only 16% in the western region. The research results will provide an important reference for surface deformation prediction and safety risk control of open cut foundation pit engineering in this region.
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CO2geological storage combined with saline recovery (CO2-EWR) is considered to be one of the effective storage methods. Taking the lead in carrying out CO2-EWR technology in the eastern Junggar of Xinjiang can achieve CO2 emission reduction and meanwhileproduce saline water, which can alleviate the local water resources shortage problem to a certain extent, and obtain dual benefits of environment and economy. Previous research mainly focused on generalized models, and the support of engineering practicesis lacking.Based on the evaluation results of the suitability of CO2 source - sink matching in the eastern Junggar Basin and the geologicaldata of the first CO2-EWR field pilot test site in China,a 3D heterogeneous model of the Xishanyao Formation of the CO2-EWR test site in the eastern Junggar Basin is constructed to studythe potential of the CO2-EWR technology. The results show that the theoretical storage capacity of CO2 at the test site is 1.72 × 106 (P50) tons,and the dynamic storage capacity is 2.14 × 106 tons. When the CO2-EWR technology is adopted, the CO2 dynamic storage capacity can reach 11.18 × 106 tons, which is 5.22 times the CO2geological storage only, and may increase the production of the saline water resources by 10.17 × 106 tons with a mass ratio of 1 to 0.91 of CO2 sweeping out saline water. Meanwhile, the CO2-EWR technology can effectively slow down the accumulation of reservoir pressure caused by the massive injection of CO2, improve the efficiency of CO2 storage, and increase the saline water production potential. This study can provide theoretical basis and technical support for the implementation of large-scale CO2 geological storage combined with deep saline water production project in the eastern Junggar of Xinjiang.
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2021, (5): 1-2.
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2021, 48(5): 1-12.   doi: 10.16030/j.cnki.issn.1000-3665.202104001
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The Sichuan-Tibet Railway is a century project under construction. The complex geological evolution history has led to large differences in geo-environmental conditions along the railway. Hydrogeological, engineering geological, and environmental geological problems are complex and changeable, which deserves great attention in engineering construction and future operations. Based on a brief review of the past geological work on the Sichuan-Tibet Railway corridor, the hydro-engineering-environmental geological problems that may be faced during the railway construction have been described. The hydrogeological problems include 1) high-pressure water inrush from plateau tectonic karst, 2) high-pressure water inrush and mud outburst from faulted bedrock fissures, 3) high-temperature hot water thermal damage. The engineering geological problems include 1) active faults and strong earthquake disasters, 2) high in-situ stress and rock burst or large deformation in deep tunnel, 3) problem rocks or soils and their disaster effects, 4) high-position landslide disaster chain. The environmental geological problems include 1) acidic water corrosiveness from coal-bearing strata and hydrothermal deposits, 2) wetland ecological degradation, 3) interaction effects between the railway construction and the sensitive ecological environment. In the meanwhile, key scientific and technological issues, which should be deeply studied in the future, are put forward. In terms of hydrogeology, such as 1) sequence law of plateau karst development and types of tectonic karst water storage structures, 2) disaster-generating models and prediction methods of water and mud bursts in deep-buried tunnels, 3) active fault control mechanisms and geothermal water circulation models, 4) identification of high-temperature heat hazard risk and geothermal resources utilization technology. In terms of engineering geology and geohazard, such as 1) investigation of fine features of active faults and related engineering fault effects, 2) development features of deep tectonic stress fields in complex geological structures, 3) engineering geological properties of tectonic mélange belts and related disaster effects, 4) surrounding rock stability and disaster effects of deep-buried tunnel under water-mechanical-thermal multi-field coupling condition, 5) mechanisms of high-position run-out landslide and risk control technology under internal and external dynamic coupling. In terms of environmental geology, such as 1) mechanisms of plateau multi-source water conversion cycle and the technology of ecological water demand control in the ecologically fragile area, 2) hydro-ecological environmental effect of tunnel construction, 3) key technology of ecological geological environment monitoring, evaluation and protection, 4) geo-ecological environmental effect of global climate warming, etc. From the view of combining non-profit geological surveys and commercial engineering surveys, a response strategy has been proposed that geological surveys are the foundation, scientific and technological research is the key, and the monitoring of potential hazards and engineering control should be promoted, which provides suggestions on developing direction for hydro-engineering-environmental geology work on major project planning areas.
2021, 48(5): 13-22.   doi: 10.16030/j.cnki.issn.1000-3665.202103101
Abstract(39) HTML(8) PDF (6324KB)(57)
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The Sichuan-Tibet Railway is located in the continental collision orogenic belt. Under the special geological structure background, the hydrogeological conditions along the railway are extremely complicated, which seriously restricts the planning and construction and safe operation of the Sichuan-Tibet Railway. To reduce the risk of major engineering hydrogeological disaster, and from the perspective of engineering hydrogeology, by combining the research results of basic geology and engineering geology, this paper expounds the major engineering hydrogeological problems along the Ya’an-Lingchi Section and puts forward suggestions for further research. The results show that the Ya’an-Lingchi section of the Sichuan-Tibet Railway may encounter three major engineering hydrogeological problems, namely, high water pressure and water inrush, high-temperature heat-damage of the tunnel, and the impact of tunnel drainage on ecological environment. Several regional fault zones developed along the railway may control the distribution of strata, hydrothermal activities and mineral resources and the circulation and evolution of groundwater, leading to prominent problems such as high-pressure water inrush, high-temperature heat-damage and groundwater drainage with high TDS in deep and long tunnels through the fault zone. The next step of the research on major engineering hydrogeological problems along the Sichuan-Tibet Railway is mainly to carry out high-precision and multi-scale hydrogeological survey, grasp the development rules and disaster-causing mechanisms of the major problems, and build a fine prediction and evaluation system and an active and passive disaster prevention and control system.
2021, 48(5): 23-33.   doi: 10.16030/j.cnki.issn.1000-3665.202104013
Abstract(20) HTML(6) PDF (3903KB)(38)
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The Bomi section of the Sichuan-Tibet Railway passes through the glacier-covered area where multiple large-scale river compounded with faults occur. The river water is abundant, leading to a tectonic high-pressure water inrush and mud outburst disaster risk source. This paper studies the flow characteristics of large-scale river and the transformation relationship between surface water and tectonic fissure water through flow measurement and analysis of precipitation, glacier melting water, river water and groundwater hydrochemistry, isotopic characteristics, and hydrogeochemical processes. The results show that the river water in Bomi glacier covered area in Tibet is mainly supplied by glacier melting water and precipitation. In rainy season, the values of δ 18O and δ D are less than those in dry season, indicating that the structure of water-supply source is different. During the dry season, the main source of replenishment is precipitation due to the low temperature, and in the rainy season the amount of glacier melting increases sharply, which becomes the main source of recharge. The discharge of rivers Guxianggou, Bitongqu and Longchongqu, which are compounded with the fault, is larger than 4×104 m3/d. However, the annual flow fluctuation is less than that of the rivers in the non-fault zone. The river water could supply the fault zone water, forming shallow circulation groundwater of 5−10 a and medium and deep circulation groundwater of more than 4000 a. There is a close hydraulic connection and frequent mutual transformation between the river and bedrock weathering fissure water in the non-fault zone. The research results can provide references for the early identification of high-pressure water and mud inrush disasters in tunnels and the formulation of disaster prevention measures in the glacier-covered area of the eastern Qinghai-Tibet Plateau.
2021, 48(5): 34-45.   doi: 10.16030/j.cnki.issn.1000-3665.202104005
Abstract(43) HTML(16) PDF (18911KB)(40)
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Construction of the Sichuan-Tibet Railway may face significant geological safety risks of water inrush and mud inrush in the plateau tectonic karst region. It is of great scientific and practical significance to carry out research on the evolution regularity of the plateau tectonic karst and the relevant karst groundwater circulation mode for the early prediction and identification of the water inrush and mud inrush disaster in the railway tunnel to be built. Based on the field survey and published literatures, this paper makes an in-depth analysis and draws some conclusions. The tectonic karst development shows obvious sequence characteristics and elevation zonation. The first level to fourth level karst development areas were formed before Miocene, late Miocene to Pliocene, Pliocene and Pliocene to Pleistocene, and occur in the elevation range of 4900−5300 m, 4000−4300 m, 3700−3800 m and 2900−3200 m, respectively. Active faults obviously control the distribution and enrichment of karst groundwater. Since the late Pleistocene, active faults have connected different karst areas and formed unique storage conditions for the tectonic karst groundwater in the plateau region. Karst groundwater system can be divided into high recharge area, remote pipeline flow area and concentrated discharge area. The high recharge area occurs in the first-level karst evaluation area, and the third-level and fourth-level are the concentrated discharge area which generally contain the outcropping springs with a discharge of more than 100 L/s. The groundwater system is appropriately divided into shallow and deep groundwater flow system. Karst springs are mainly supplied by ice and snow melting water, and exhibits the dynamic characteristics of the high water pressure, long flow path and deep water groundwater circulation. High CO2 saturation concentration of the melting water and the salt effect of sulfate promote the formation of high TDS sulfuric acid karst groundwater of low temperature.
2021, 48(5): 46-53.   doi: 10.16030/j.cnki.issn.1000-3665.202104007
Abstract(40) HTML(17) PDF (3821KB)(44)
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The Kangding tunnel of the Sichuan-Tibet Railway crosses the Xianshuihe Fault Zone where geothermal abnormity occurs and is harmful for railway construction. This paper analyzes the genetic mechanism of geothermal waters through the integration of field survey, hydrochemical analysis and D-O isotopic experiments. The results show that HCO3·Cl—Na and HCO3—Na types are the main hydrochemical types of hot springs in the Kangding tunnel area, which exists in the Zheduotang, Kangding and Zhonggu geothermal areas. Geothermal waters are immature and the reservoir temperature ranges from 104 ℃ to 172 ℃. Deep initial geothermal waters display the reservoir temperature of 186−250 ℃ and are mixed by 56%−81% of cold water. Hydrogen and oxygen isotopes show that the recharge elevation of the geothermal water ranges from 3768 m to 4926 m. In the study area, geothermal waters are recharged by water source at high elevation. The main fault is the structure of thermal conductivity, and secondary faults and fracture zones are the channel of water migration. Geothermal waters arise and expose as hot springs on the land surface. Simulated geothermal field of 100 m has the temperatures of 35.4−95.1 ℃. Relatively low-temperature channel may be existed among three geothermal areas. High-temperature geohazard induced by geothermal water should be focused in the Kangding area during tunnel construction.
2021, 48(5): 54-64.   doi: 10.16030/j.cnki.issn.1000-3665.202107012
Abstract(16) HTML(6) PDF (18819KB)(33)
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The Triassic silty mudstone is encountered in the Sichuan-Tibet Railway, when it passes through Gongjue County in Tibet of Chian, and the rock is prone to cause large deformation under the condition of high geo-stress. In this study, we carried out the triaxial rock compression and triaxial creep tests under different confining pressures. Combined with the PFC numerical simulation, we have also studied the creeping characteristics and long-term strength of the silty mudstone under different confining pressures. The results show that the rheology of the Gongjue silty mudstone is characterized by the Nishihara creep model. With the continuous increase of the confining pressure, under the conditions of the creep and conventional triaxial tests, the silty mudstone specimens all undergo transition from tensile-shear failure to single-shear failure. The angle between the shear fracture surface and the horizontal line gradually decreases, and the number of microcracks decreases. Compared with the conventional triaxial test, the creep test has a wider range of influence on the crush zone caused by tensile stress. Under the conditions of high confining pressure, the silty mudstone is more prone to rheology. The numerical simulation results show that when the confining pressure increases, the axial strain, lateral strain and volumetric strain will increase, while the number of microcracks decrease. There is a linear increasing relationship between the instantaneous elastic modulus and the viscoelastic coefficient with the confining pressure, the viscoelastic modulus has a logarithmic growth relationship with the confining pressure, and the viscoplastic coefficient has an exponential growth relationship with the confining pressure. Under long-term loading, the long-term strength phase of the rock is lower than the instantaneous strength.
2021, 48(5): 65-73.   doi: 10.16030/j.cnki.issn.1000-3665.202103073
Abstract(25) HTML(6) PDF (4432KB)(37)
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Freezing-thawing damage to rocks is one of the natural disasters that cannot be ignored in engineering construction in plateau regions. Under the action of freezing and thawing, uneven shrinkage of rock minerals and freezing of pore water lead to rock damage caused by pore expansion in rocks, which poses a great threat to engineering stability. In recent years, many researchers have conducted a lot of researches on rock properties under freezing-thawing conditions through theoretical and experimental methods. However, most of the previous studies focused mainly on sedimentary rocks such as sandstones, and very few studies were involved in freezing-thawing of granites in highland alpine regions. In this study, the granite on the landslide area was subjected to uniaxial compression, resistivity and electron microscope scanning (SEM) tests to discuss the damage of granite after multiple freezing-thawing cycles by simulating the cold climate changes on the plateau under freezing-thawing cycles. From the macro and micro multi-scale studies it can be found that: (1) the change of granite quality during freezing-thawing cycles tends to decrease, then increase and finally decrease, which is related to the dual effect of particle drop on the surface of the specimen and the expansion of internal fissures caused by freezing-thawing cycles. (2) As the freezing-thawing cycles increase, the uniaxial compressive strength, elastic modulus and cohesion of granite all show a non-linear decay, while the internal friction angle only fluctuates slightly around the mean value. (3) When the number of freezing-thawing cycles increases, both the freezing-thawing damage factor and the total damage factor under the coupling of freezing-thawing and load increase, which indicates that the number of freezing-thawing cycles has a greater influence on the strength of granite. The results of the study can provide a reference basis for measuring the freezing-thawing strength characteristics of granite in engineering construction in the plateau region.
2021, 48(5): 74-80.   doi: 10.16030/j.cnki.issn.1000-3665.202102035
Abstract(21) HTML(8) PDF (3797KB)(29)
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There are a lot of weak intercalations in the surrounding rock of tunnels along Sichuan Tibet railway, and they are greatly affected by the cold climate. To understand the influence of dip angle of interlayer and freezing thawing cycles on the mechanical properties of tunnel surrounding rock, the interlayered rock mass with different dip angle of weak interlayer and different freezing thawing cycles was prepared in laboratory, and the uniaxial compression test of rock mass with weak interlayer was carried out. The results show that: (1) the deformation of hard rock part with weak interlayer is smaller, while the failure of soft rock interlayer is more severe. When the dip angle of the interlayer is small (β=0° and 30°), the fracture crack is nearly parallel to the dip angle of the interlayer after rock failure. When the dip angle of the interlayer is large, the fracture surface of the rock mass and the interlayer present an X-shaped intersection. The more freezing thawing cycles, the stronger the damage degree of rock mass (2) Uniaxial compressive strength and elastic modulus of rock mass decrease first and then increase with the increase of dip angle of interlayer, and the compressive strength and elastic modulus are the minimum when the dip angle of interlayer β=45°. Compared with the rock mass with horizontal weak interlayer, the compressive strength is reduced by 35.27%, and the elastic modulus is reduced by 34.84%. (3) Freezing thawingw cycles have a significant deterioration effect on the mechanical properties of rock mass. The bearing capacity of rock mass decreases with the increase of freezing thawing cycles, but the plastic deformation capacity increases. There is a negative exponential correlation between uniaxial compressive strength, elastic modulus and freezing thawing cycles, and a positive linear correlation between peak strain and freezing thawing cycles.
2021, 48(5): 81-90.   doi: 10.16030/j.cnki.issn.1000-3665.202103099
Abstract(21) HTML(8) PDF (3820KB)(16)
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The large terrain undulations and strong regional geological structures are the typical characteristics along the Sichuan-Tibet Railway. The high ground stress problem in tunnel construction is extremely complex, especially the rockburst problem in deep-lying and hard rock tunnels, which restricts route selection schemes and becomes a major difficult problem of construction. Because of the complex geological conditions of the tunnel engineering, the evaluation results often deviate from the actual situation if the rockburst evaluation index is not pertinent. The key factors of rockburst is considering comprehensively, and five factors are selected as the evaluation indexes, including the ratio of the uniaxial compressive strength of rock to the maximum main stress of the surrounding cave wall, the ratio of the maximum tangential stress of the surrounding cave wall to the uniaxial compressive strength of rock, the ratio of compressive to the tensile strength of rock, the elastic strain energy index, and the intactness index of rock mass. The entropy weight method is used to determine the weight of each index, and a rock burst risk assessment model is constructed based on the basic theory and calculation rules of the ideal point method. By calculating the distance between each mileage section and the ideal point, a comprehensive comparison of rock burst risk assessment is carried out on three route plans of a tunnel on the Sichuan-Tibet Railway. The results show that the total rock burst sections of route B is 24.9%, and the uncontrollable rock burst sections account for 13.4%. The route B is about 4% lower than the other two alternative schemes. The route B is determined as the optimal plan according to the impact of rock burst disasters. This method can provide a new scientific basis and technical support for the comprehensive geological selection of deep-lying and hard rock tunnels.
2021, 48(5): 91-101.   doi: 10.16030/j.cnki.issn.1000-3665.202009024
Abstract(26) HTML(3) PDF (6112KB)(40)
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The Batang fault on the eastern Qinghai-Tibet Plateau has strong activity since the Holocene, where the geomorphology and geological structure is complex, and the historical earthquakes occurred frequently, which induced abundant landslides. For the long-term prevention of regional earthquake landslides in the Batang fault zone, based on analyzing the geological background and development characteristics of regional landslides, the Newmark model was used to complete the seismic landslide hazard assessment with exceeding probability 10% of 50 years in the Batang fault zone. The results show that the Batang fault zone and its adjacent Jinshajiang fault zone, the Jinsha River and its tributaries coast have the high seismic landslide hazard. The potential seismic landslide hazard zone has a general distribution trend of along the fault zone and the river canyons, which is significantly affected by the active faults and topography. The closer the slope to the fault is and the greater the slope angle is, the higher the seismic landslide hazard is. The Sichuan-Tibet Railway line under planning and construction extends from the Deda Town and Shama Town to the northwest and crosses the Jinsha River, and can traverse fewer zones with potential seismic landslide hazard. The planning and construction of Jinsha River hydropower project needs to strengthen the assessment and prevention of potential seismic landslide hazard. The potential seismic landslide hazard assessment results in the Batang fault zone can provide a scientific reference for the long-term prevention and control of earthquake landslides in the regional urban development and major engineering planning and construction.
2021, 48(5): 102-111.   doi: 10.16030/j.cnki.issn.1000-3665.202104009
Abstract(32) HTML(15) PDF (4155KB)(19)
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Located in east-central Qinghai-Tibet Plateau, the Sichuan-Tibet traffic corridor is one of fastest uplifting and geomorphic evolution regions on the earth. Under the coupling of internal and external dynamics, the landslide in this region is extremely developed, which seriously restricts the planning and construction of highways, railways and hydropower projects. Based on the data collection and analysis of regional geological data, this paper selects lithology, slope gradient, aspect, slope shape, topographic relief, terrain roughness, fault density and distance to rivers as contributing factors. Combined the advantages of traditional information value method and logistic regression, this paper uses the logistic regression-information value method to evaluate the landslide susceptibility of the study area. Through the multi-collinearity test and significance test of the contributing factors, it is found that the selected contributing factors have no multi-collinearity and have a significant impact on the occurrence of landslides. ROC curve is used to test the results of landslide susceptibility, and the AUC value is 0.81, which shows that the model can well predict the occurrence of landslides. The results show that the high risk areas in the study area mainly occur in the regions of the Longmenshan fault zone, Jinshajiang fault zone, Lancangjiang fault zone, Nujiang fault zone and Bianba-Luolong fault zone, as well as on the sides of deep valleys of large rivers with steep slope and large topographic relief. The middle risk areas widely exist on both sides of the tributaries of large rivers. The results are helpful in understanding the development and distribution of landslides in the Sichuan-Tibet traffic corridor, and also provide a scientific basis for the project planning and construction, disaster prevention and mitigation in the study area.
2021, 48(5): 112-119.   doi: 10.16030/j.cnki.issn.1000-3665.202103076
Abstract(17) HTML(4) PDF (4590KB)(35)
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The planned grand bridge is an important control bridge along the Sichuan-Tibet Railway. A large- scale bedding rock collapse occurred on the slope of the Baqu river side of Chengdu bank, with the protruding ridge, high elevation difference, complex and changeable lithology, poor rock mass structure and integrity, highly weathering and unloading and potential unstable rock mass on the surface of the slope. This paper investigates the topography and geomorphology, stratum lithology, discontinuities development and the characteristics of deformation and failure of the bank slope to Chengdu by remote sensing interpretation, profile measurement and stability calculation. The stability of bedding rock slope of the Baqu river side of Chengdu bank under natural and rainstorm conditions are analyzed and evaluated. The results show that the safety factor of slope stability is greater than 1.1; under the strong earthquake (PGA>0.3 g) conditions, the safety factor of slope stability is less than 1.0, and local or overall instability may occur. Based on removing the dangerous rock mass on the surface of the slope, it is suggested that the possible failure range and degree of the bedding rock slope on the Baqu river side should be further studied and the engineering prevention measures should be put forward.
2021, 48(5): 120-128.   doi: 10.16030/j.cnki.issn.1000-3665.202104036
Abstract(22) HTML(7) PDF (7885KB)(21)
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The Woda landslide in the upper reaches of the Jinshajiang River, has been deformed since 1985, whose surface deformation characteristics are obvious now. There is a potential risk that the landslide will slide further and block the Jinshajiang River. Based on the remote sensing interpretation, field investigation, engineering geological drilling and comprehensive monitoring, the spatial structure and deformation characteristics of the landslide are analyzed, the potential reactivation instability pattern of the landslide is clarified, and the risk of landslide blocking river is discussed by empirical formula calculation. The results show that the Woda landslide is a huge landslide with a volume of about 28.81×106 m3. It is speculated that the landslide had undergone massive sliding before the late Pleistocene. The whole landslide is currently creeping, and the local part of the landslide is in the accelerated deformation stage. The deformation range of reactivation zone is mainly concentrated in the middle and front parts, and the failure characteristics are progressive backward. The deformation on the right side of the reactivation zone is stronger than that on the left side. There are two sliding zones developing in the landslide, namely the shallow zone and deep sliding zone, whose average depth is about 15 m and 25.5 m, respectively. Accordingly, the landslide can be reactivated with two potential failure modes: the shallow slip and deep slip with progressive failure mode. When the sliding mass in the strong deformation area of the Woda landslide slides along the shallow sliding zone, the height of the landslide dam formed is about 87.2 m. If the whole sliding mass slides along the deep sliding zone, the height of the landslide dam formed is about 129.2 m. The Woda landslide has the risk of landslide-damming-outburst-flood chain disaster. It is suggested to further strengthen landslide monitoring and carry out drainage, reinforcement and other prevention works. This study can offer certain reference for preventing and controlling large geological disaster chain in the upper reaches of the Jinshajiang River.
2021, 48(5): 129-136.   doi: 10.16030/j.cnki.issn.1000-3665.202103097
Abstract(28) HTML(9) PDF (5152KB)(20)
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In order to examine the characteristics of geological hazards in the entrance planning area of the Kazila mountain tunnel on the Sichuan-Tibet Railway, and to evaluate the geological hazard risks that may be endangered during the planning, construction and operation of the Sichuan-Tibet Railway, the “air-space-ground” integrated technologies such as high-precision remote sensing, airborne Lidar and engineering geological survey are used in the study area, and two landslides and a potential unstable slope of Eluodui in the entrance area of the Kazila mountain tunnel are identified. The Eluodui unstable slope is located in the middle of the two landslides, the volume of 1# landslide and 2# landslide are about 32.48×106 m3 and 10.15×106 m3, respectively, and both of the landslides are large-scale rock ones that have occurred. The volume of the Eluodui unstable slope is about 35.80×104 m3, the lower part is strongly weathered rock mass, and the upper part is gravelly soil structure. It is a medium-sized composite structure slope. The evaluation results show that the route selection at the entrance of the Kazila mountain tunnel of the Sichuan-Tibet Railway passes through the middle ridge of two landslide masses, and the two landslides do not pose a geological safety risk to the railway route selection, but there are potential geological safety hazards on the unstable slope of Eluodui at the entrance of the tunnel, and the slided mass is stable under the natural conditions. The unstable slope of Eluodui is stable under the natural and seismic conditions, and is unstable under the rainstorm conditions. In order to avoid potential geological hazards caused by engineering construction disturbance, it is suggested to shift the route selection entrance of the Kazila mountain tunnel to the southeast, and prevent and control the potential landslide risk from the source through reasonable design of slope excavation and real-time monitoring during construction and engineering control during operation. The study may provide a scientific geological basis for scientific route selection of the Sichuan-Tibet Railway.
2021, 48(5): 137-149.   doi: 10.16030/j.cnki.issn.1000-3665.202103093
Abstract(20) HTML(8) PDF (5377KB)(32)
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One station of the Sichuan-Tibet Railway is located in the Dongcuoqu valley in southeast Tibet of China, and also lies in the debris-flow-prone area. Based on field investigations and remote sensing interpretation, we revealed the predisposing conditions and characteristics of the debris flow group, which have significant influence on the station safety. The results suggest that this region is characterized by ten rainstorm-induced debris flows and two glacier lake outburst-induced debris flows. Geomorphology, water sources and material sources exert dramatical controls on the characteristic of debris flows. Complex geological and environment background provides adequate material sources and potential energy conditions prone to the formation of catastrophic debris flows. The integrity coefficient of the debris flow gullies ranges between 0.15 and 0.55, with the morphology of long strip and oak leaf shape. The longitudinal slope of the main channel is relatively large, which is conducive to the water catchment and occurrence of debris flow. The slope of the channel bank slope in the debris flow basin is mostly 20°−40°, which provides appropriate supply to the material sources. We also calculated the kinetic parameters of 12 debris flows, and analyzed their dynamic characteristics and development tendency. The deposition fans of the debris flow group are ubiquitous without mitigation measures. Large-scale debris flows are prone to occur under the extreme rainstorms. Finally, we evaluated the potential engineering perniciousness of debris flow on railway in single debris flow-occurring circumstance and in debris flow-occurring in the both banks of the Dongcuoqu circumstance. It is suggested that drainage channels should be built for the railway at the deposition fan of gully for return flow, and safety measures should be taken to prevent boulders impact on the proposed bridge piers. Results in this study are expected to guide the design of the debris flow mitigation project in Sichuan-Tibet Railway, and also provide scientific basis for the reasonable selection of the vital traffic line in the mountainous areas.
2021, 48(5): 150-160.   doi: 10.16030/j.cnki.issn.1000-3665.202103104
Abstract(17) HTML(7) PDF (4789KB)(30)
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The Baqu glacial lakes outburst debris flow is close to a station of the Sichuan-Tibet Railway, which may threaten the construction and running of the railway. In this paper, the methods of in-site investigation and remote sensing were used to identify the basic geological characteristics of the Baqu gully. The kinetics parameters of debris flow were calculated by using the code-design-formulae method. Meanwhile, the stability of barrier dams of 7 glacial lakes in Baqu was evaluated based on the dimensionless blockage index (DBI). The results show that the DBI value of the 1# barrier dam was in the unstable region, and the DBI value of the 3#, 4# and 6# barrier dams were between the unstable region and the stable region, and there was a possibility of outburst. In this paper, we used RAMMS, a single-phase flow numerical method, to simulate and analyse the evolution process of glacial lakes outburst in the Baqu gully under 4 scenarios. The simulation results show that the evolution process is divided into 4 stages: initiation, confluence, runout and deposition, which lasted for 4.5 hours. The results also show that the maximum velocity, depth and discharge of the debris flow at the mouth of the channel were 5.92 m/s, 4.35 m and 1 954.42 m3/s (5.1 times of that of the rainstorm debris flow), respectively, under the condition of glacial lake 1#—4# and 6# outburst. In addition, the influence area of outburst flood in 4 scenarios affected the proposed station, and the maximum depth was 1.91 m, 3.36 m, 1.53 m and 4.35 m, respectively. Therefore, in the design of the station, it is necessary to take engineering measures such as drainage canal or diversion dike for protection and treatment, so as to ensure the safe running of the station. The above results can provide reference for the line selection of the Sichuan-Tibet Railway and the prevention and control of glacial lakes outburst debris flow in the Eastern part of the Qinghai-Tibet Plateau.
2021, 48(5): 161-167.   doi: 10.16030/j.cnki.issn.1000-3665.202009041
Abstract(19) HTML(7) PDF (3705KB)(30)
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In the present investigation, laboratorial test is conducted to examine the evolution law of fissures of the Wuxiang clay complexs under wetting and drying cycles. The oven drying method and the water film transfer method are employed to simulate the drying and wetting process, respectively. Digital photography and weighing are used to record the changes of fissures in each drying and wetting process, so as to conduct qualitative analyses. Matlab is applied to image processing to obtain the geometric feature values in the evolution process of fissures. The evolution rules of fissures are obtained by combining qualitative analyses and quantitative analyses, including: (1) in the drying process, the fissure rate of the clay complexs increases continuously and finally tends to be stable, and the first and second drying have the greatest influence on the fissure rate. In terms of the geometric characteristics, the fissures first grow and develop in all directions along the middle large fissure, and then turn to form a new large fissure with the increase number of cycles. (2) In the wetting process, the clay complexs expands when it absorbs water, and the fissures gradually tend to close, but the plastic deformation occurs. With the increasing wetting times, the accumulated deformation gradually decreases. After the fifth drying and wetting cycle, the accumulated deformation basically disappears, and the soil structure returns to a relatively uniform loose structure.
2021, 48(5): 168-175.   doi: 10.16030/j.cnki.issn.1000-3665.202012039
Abstract(17) HTML(5) PDF (4022KB)(25)
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The in-situ shear test has been justified as one of the most reliable and common method used to test shear strength of soil-rock mixture. However, the existing in-situ shear test apparatuses show some shortcomings in practice that will influence the accuracy of the test results, including the unreasonable normal pressure system and unable to reserve shear opening, etc. A new self-reacting direct shear apparatus owning two shear interfaces is introduced. The apparatus is characterized by the followings: (1) it provides horizontal reaction force by itself; (2) the vertical pressure system is fixed during shearing without roller row; (3) the adjustable width of shear opening can be reserved between shear boxes; (4) it is of high modularity, and is easy to handle, assembly and disassembly. It is validated through comparison with the single-box direct shear test. Compared with the experimental results obtained by the single box shear apparatus, the shear stress-shear displacement curve obtained by the self-reacting direct shear apparatus is a standard hyperbolic curve, and the shear stress-displacement curve under large shear displacement can be obtained. The maximum shear stress read by shear stress-displacement curve under large shear displacement is more practical. Compared with the shear strength obtained by the single-ring shear apparatus, the internal friction angle is 4.6 degree lower and the cohesion is 41.14 kPa higher. At the same time, through the image comparison of the shear failure surface obtained by the two shear apparatuses, it can be obviously found that the shear failure interfaces obtained by self-reacting direct shear apparatus owning two shear interfaces is relatively flat, and there is no concave phenomenon of the shear failure surface on the single-ring shear instrument.
2021, 48(5): 176-183.   doi: 10.16030/j.cnki.issn.1000-3665.202011051
Abstract(21) HTML(9) PDF (3513KB)(25)
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To provide service of all-weather, full automation and high precision deformation monitoring and to furthest reduce the effects of space environment factors on the high precision real-time positioning, on the digital CDRadio edge of RTK GNSS core analytic computing technology fusion algorithm is used, and “the Beidou high-precision geological disaster monitoring system with edge calculation based on broadcasting RTK”is developed, which is characterized by the independent intellectual property rights and structure open. The system can run stably for a long time, and can satisfy the functional requirements and non-functional requirements of all users. Taking the unstable slope of block 8 in the Gemstone Garden in Changzhou District of Wuzhou as an example, the monitoring results from May to November 2020 are analyzed. The monitoring data show that the whole slope body is in the stage of slow development, and the front edge of the slope top has a tendency of peristatically moving and sinking. The whole slope body tends to develop towards the southeast direction. Through the establishment of a good system information interaction platform, the statistical analysis information formed by the system is transmitted to users in a high speed and convenient way, which effectively improves the users' system management, decision-making and application ability. It can fully mine the data resources of the system, provide real-time forecasting services, effectively improve the accuracy and reliability of information collection, transmission, processing, analysis and forecast, comprehensively improve the ability of geological disaster monitoring, early warning and forecast management, and better provide scientific basis for the decision-making and command of management departments at all levels in emergency rescue and disaster relief.
2021, 48(5): 184-192.   doi: 10.16030/j.cnki.issn.1000-3665.202007011
Abstract(44) HTML(19) PDF (4316KB)(19)
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Geological disasters in China are characterized by multi-point and wide-range distribution, while the manpower and ability of geological disaster risk management and control are relatively limited. Therefore, it is necessary to carry out the sequencing work of geological disaster risk, screen out the geological disaster points for priority control and control, and ensure the pertinency and efficiency of the implementation of geological disaster risk management and control countermeasures. The essence of geological hazard risk ranking is to use quantitative risk evaluation to calculate the risk value of each disaster point, and then carry out the ranking work according to the risk value. At present, the quantitative risk assessment model is mostly used in the risk assessment of a single geological disaster point, but is not applied in the risk ranking work of a wide range of geological disasters. Moreover, the model is relatively complex, so it is difficult to popularize and use it. Based on the analysis of the response relationship and law between the collapse-landslide geological disasters and its environmental factors, this paper extracts the main controlling environmental factors and inducing factors of the collapse landslide geological disasters, and establishes the risk evaluation index system of geological disasters together with the vulnerable factors such as population, material and resources. Based on the interaction matrix of rock engineering system (RES) and expert scoring method, the weight of each level of geological hazard risk evaluation index factor is determined, and the geological hazard risk scoring system is constructed. According to the definition of risk assessment, a simple geological hazard risk calculation model which can be quantified quickly is proposed. Taking 98 potential geological hazards in Guizhou province as an example, the model verification and application were carried out by taking 98 potential geological hazards in Guizhou province as examples. The risk ranking results are consistent with the actual risks recognized by the disaster body management agencies, which verify the rationality and effectiveness of the model and greatly improve the ability and efficiency of geological disaster risk management and control.
2021, 48(5): 193-204.   doi: 10.16030/j.cnki.issn.1000-3665.202103058
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Abstract:
The Xining Basin in Qinghai Province is rich in geothermal resources of low to medium temperature, but the geothermal reservoir is dominated by weakly consolidated sandstone containing clay minerals, and the geothermal water has high salinity, which causes a significant risk of scaling during reinjection. In this paper, based on the analysis of the geothermal genesis and resource distribution characteristics in the Xining Basin, different methods, such as the mineral solubility method and saturation index method, are used to assess the scaling tendency and risk in typical geothermal water during reinjection. The results show that the “convex in concave” structure of the Xining Basin is beneficial for the enrichment and warming of thermal groundwater in the deep geothermal reservoir, and at the same time, a large number of dissolved minerals are brought to the central bulge in the Xining Basin. The geothermal reservoir in the Xining Bain is mainly buried at a depth of 700−1600 m with water temperature of 30−70 ℃. The hydrochemical type is mainly of SO4·Cl—Na type, and the salinity range from 1.85×103 to 4.80×104 mg/L. The main scaling product during reinjection is CaCO3. When the characteristics of reinjection water and geothermal water are similar, the risk of scaling mainly occurs in the reinjection wellbore, and the risk of formation scaling is relatively small. When the characteristics of reinjection water and geothermal water are quite different, the incompatibility will greatly increase the risk of formation scaling. Among them, when the water from Yaowangquan is mixed with that from DR2005Y by 1∶1, the maximum scaling amount can reach 177.57 mg/L, while the scaling amount from other geothermal water is smaller. Based on the above characteristics, three sets of comprehensive measures are proposed as the follows: physical anti-scaling + pipe anti-corrosion, system pressurization anti-scaling + pipe anti-corrosion and ground pretreatment + pipe anti-corrosion, supplemented by measures such as cathodic protection anticorrosion, optimized displacement, and pickling the wellbore. The results of this study can provide theoretical basis and technical support for the formulation of measures to ensure the reinjection capacity of geothermal water in the future.

Supervisor: China Geological Survey

Sponsor: China Geological Environment Monitoring Institute

Chief Editor: Li WenPeng

Editor: Editorial Office of Hydrogeology & Engineering Geology

Publication: Science Press

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