ISSN 1000-3665 CN 11-2202/P
• Chinese Core Journals
• CSCD core journals
• Chinese science double effect journals
• The key magazine of China technology
• Caj-cd Standard Award winning journals
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Abstract(9) HTML(9) PDF (3342KB)(1)
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Considering the occurrence condition and water resources management, this paper studies the zoning of the groundwater heat pump system in the city of Anyang in Henan, makes the combination of technology and management and improves the evaluation standard, which is of good practicability. The evaluation of groundwater resources management and division is established by synthetically analyzing the hydrogeological, hydrodynamic and hydrochemical conditions of Anyang. The first-level evaluation is carried out by using the improved analytic hierarchy process of cloud model. The second-level evaluation is completed by using GIS spatial analysis function, dividing the groundwater heat pump system into three grades in the study area. The results show that the suitable development area for the groundwater heat pump system is 117.45 km2, which mainly distributes in the strong groundwater-abundant area in the center of the alluvial-proluvial fan of the Anyang River and partially distributes in the peripheral area at the fan edge. The restricted development area covers an area of 459.26 km2, which distributes in the hilly weak groundwater-abundant areas in southwest and north of the fan margin with the groundwater level drawdown funnel in the center of the fan body. The forbidden development area is of 24.02 km2 and distributes crossly, covering the water source area, the protected area of the South-to-North Water Transfer Project, along the railway and expressway. It is more comprehensive and reasonable to take the groundwater resources management and division into account on the basis of the suitability zoning, which may provide references for the scientific layout and rational development and utilization of the groundwater heat pump system.
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The studies of foundation treatment methods are carried out for the special and complex foundation in the fill, saturated silty fine sand and silt in the coastal backfill area of the coastal zone of the Shandong Peninsula. Based on the economical and efficient dynamic compaction method, the concept of integrated combined drainage is put forward. The relay drainage system of the shallow and deep vertical drainage channels and their relay horizontal drainage channels are designed, and field tests are undertaken. The monitoring data show that under the dynamic compaction load, the relay drainage system can coordinate drainage as a whole, which can quickly discharge the groundwater to dissipate the excess pore water pressure. The rise of groundwater level and dissipation of pore water pressure caused by dynamic compaction can be basically eliminated in about 7 hours. With continuous precipitation, the surface settlement is 0.7%~2.0% of the thickness of the upper soil mass. Under the dynamic load of dynamic compaction, the surface soil is compressed to 8.7%~10.9% of the thickness of the upper soil. The soil settlement is about 5 ‰ and 3 ‰ of the soil thickness at the buried depth of 3~7 m, and 2 ‰ of the soil thickness is at the buried depth of 7~10 m. The test data show that in the effective depth of dynamic compaction, the effect of foundation treatment is obvious, the engineering properties and the degree of consolidation of foundation are improved. The surface bearing capacity and deformation modulus meet the design requirements, the average bearing capacity of silt below 4 m is slightly lower than the design requirements, and the average degree of consolidation of mucky soil is 77%. The monitoring data of one month after tamping shows that the surface subsidence is within 25 mm, which tends to be stable, the layered settlement and pore water pressure are stable and slightly decreased.
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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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The influence of the shield tunnel construction on the adjacent grounds and buildings is a fundamental issue for the safe construction and regular service of the shield tunnel in the soft soil area. In order to investigate the influences of the double-track shield tunnel construction between the Tongde Road Station and the Shiqi Station of the Ningbo Metro Line 5 on the adjacent grounds and buildings, a dynamic 3D finite element model of shield tunneling is established. After comparing the simulated and monitered settlements of the ground surface and adjacent building, the influences of the tunnel construction on the adjacent ground surface and building are thereafter explored. The results show that when the excavation is completed, the subsidence tank deviates from the direction of the upward tunnel with an inverted trapezoidal shape, and the final cross-sectional influence area is less than 3 times the tunnel diameter from the center of the double-track tunnel axis. After the excavation of the ascending line, the surface settlement does not increase, but the width of the settlement groove increases. The settlement generated before the arrival of the downstream line accounts for 67% of the final cumulative settlement. The building inclines along the direction of shield tunneling as the shield reaches the building, while the building inclines along the opposite direction of shield tunneling as the shield leaves the building. The settlements at both sides of the building are reduced by 83%, compared with those at the middle part. After the two lines are connected, the settlements of the building shows a "U" shape distribution, and the maximum settlement occurring at the middle building is 0.5 m from the tunnel.
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In order to reflect the whole deformation process of unsaturated foundation soil, the consolidated drained triaxial compression test is carried out on the unsaturated soil of a foundation project. It is found that the partial stress-strain curve of unsaturated soil is similar to hyperbola, and the matrix suction has an obvious influence on the mechanical behavior of soil. The greater the matrix suction, the higher the partial stress of soil. According to the deformation characteristics and engineering characteristics of unsaturated soil, the Duncan-Chang hyperbolic model is selected as the basic model, and the statistical damage theory is introduced. Assuming that the micro element strength of unsaturated soil obeys the Weibull probability density distribution, the Duncan-Chang statistical damage model is established. By establishing the relationship between the initial tangent modulus and matrix suction, a new Duncan-Chang statistical damage model of the unsaturated soil considering matrix suction is established. The parameter analysis method is given, and the empirical expression of the Weibull distribution parameters is obtained, which is used to modify the model. The damage accumulation law of unsaturated soil under different matrix suction conditions is analyzed, and the partial stress-strain test curve of unsaturated soil is compared with the traditional Duncan-Chang model, which proves the feasibility and rationality of the model. The research results provide a certain reference for the study of mechanical properties and identification simulation of unsaturated soil.
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Freezing-thawing action will affect the mechanical and structural characteristics of sludge solidified light soil. In order to study the dynamic characteristics and structural evolution of sludge solidified light soil under different freezing-thawing cycles and freezing temperatures, dynamic triaxial tests and consolidation tests were carried out on the sludge solidified light soil after freezing-thawing cycles. The test results show that the dynamic stress-strain curve of light soil solidified by sludge is of weak strain hardening type under the action of freezing-thawing cycle. The dynamic strength and deformation of sludge solidified light soil decrease with the increase of freezing-thawing times （n） and the decrease of freezing temperature （T）. The first four freezing-thawing cycles have a great influence on the deformation and dynamic strength of solidified soil, and the dynamic characteristics of soil tend to be stable after eight freezing-thawing cycles. The influence of freezing-thawing cycle on is essentially the influence on soil structure. The variation law of freezing-thawing structural potential （mdσn） of solidified soil is similar to that of dynamic strength, showing the decrease with the increasing freezing and thawing times and the decrease with the decreasing freezing temperature. The number of freezing-thawing cycles is the main factor affecting the dynamic characteristics and structure of sludge solidified light soil, and the freezing temperature is the secondary factor.
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The traditional field contact measurement for obtaining parameters of the rock mass discontinuity is of low efficiency and big workload, and the accuracy of the results are affected by human factors. In this paper a method is presented to automatically recognize the discontinuity based on the three dimensional (3D) digital surface model (DSM) of rock mass obtained with the digital photogrammetry and structure from motion (SFM) algorithm. The steps of rock mass DSM reconstruction include collecting rock mass images, matching image features based on the Scale-Invariant Feature Transform (SIFT) algorithm, reconstructing sparse point cloud, encrypting point cloud, and reconstructing the rock mass surface model. The main flow of the discontinuity recognition method include smoothing the DSM of rock mass, changing the searching radius and the angle threshold to split model plane, searching the discontinuity based on the regional growth principle, and fitting the discontinuity based on random sampling consistency to get the orientation. The method is applied to the underground experimental roadway in the Beishan area of Gansu, and the reconstruction of 3D digital surface model of roadway and the orientation acquisition of discontinuities are realized. The discontinuities are also mapped on the roadway model by groups. A comparison the results with those of the manual field measurement method and the existing discontinuity recognition software shows that the method proposed in this paper is of good accuracy and can provide a certain reference for engineering applications.
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In order to reinforce the soft sludge and makes it meet the certain bearing capacity of the engineering construction, the consolidation and solidification composite technology is used to reinforce the sludge in the field site. During the test, a certain thickness of sludge is divided into a shallow solidification layer and a deep consolidation layer. The solidification technology is used to reinforce the shallow (≤1 m) sludge so as to form a high-strength overlying crust. For the deep (>1 m) sludge, the vacuum preloading technology is used to improve the bearing capacity of the deep sludge and control the later settlement of the reinforced soil. The experimental results show that the characteristic value of the shallow solidified soil bearing capacity ranges from 109 to 330 kPa when the dosage of solidified agent is 0.6%～5.0%. The consolidation and solidification composite technology has a prominent effect on the reinforcement of the sludge and the characteristic value of the overall bearing capacity of the layered reinforced soil varies between 89 and 230 kPa. After the solidification treatment of the shallow sludge, the soil strength is higher, which can generate an obvious diffusion effect on the surface load and effectively reduces the additional stress in the underlying layer caused by the surface load. The stress diffusion angle of shallow solidified soil in most test units varies between 19.474° and 26.303° in this experiment.
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As a new type of cantilever-type supporting structure, the double-row pile supporting combination system can improve the overall rigidity to maintain the safety and stability of the side of the foundation pit. The case of a double-row pile foundation pit support project in the Wanquan District of Zhangjiakou is taken as an example. Based on the existing double-row pile crown beam stiffness coefficient calculation method, the effect coefficient of the crown beam and the coupling beam is introduced to optimize and improve the effect of the coupling beam and the crown beam. The results show that (1) in the calculation of the double-row pile structure, the common lateral restraint effect of the crown beam and the connecting beam on the double-row supporting piles should be considered, and the rigid connection of the crown beam and the connecting beam should be taken as a whole to improve the rigidity coefficient of the double beam lateral support of a rectangular double-row pile. (2) The combined stiffness of the double-beam combined support system has a greater impact on the displacement of the pile top, and the displacement under a combined stiffness of 40~50 MN/m are close to the observed value. The calculated length of the crown beam and the introduced crown beam and connecting beam effect coefficient have a great influence on the combined stiffness of the double-beam composite support system. The combined stiffness decreases with the increase of the calculated length, and increases with the decrease of the effect coefficient. (3) The lateral support stiffness of the double-row piles under the double-beam composite support system is affected by the difference between the vertical and lateral displacements of the front and rear piles. The maximum lateral displacement of the front and rear piles is affected by the friction angle of the soil, the cohesion and the proportional coefficient of the horizontal resistance of the soil. Changing the tensile strength will not affect the displacement and deformation of the double-row piles. There is a displacement inflection point below the buried depth of the foundation pit and within the scope of the pile bottom. The displacement at the inflection point is equal under different friction angles and different cohesive forces.
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Investigation of groundwater variable-density flow and solute transport is usually limited in a 2D system. There are only a few studies performed in a 3D system. However, there are still studies showing differences in free convection between the 2D and 3D systems. This study systematically investigates the variable-density solute transport processes in the 2D and 3D systems and quantifies the system instability, solute spreading and dilution using the Sherwood number, spatial moments and dilution index. The results show that the separate fingers form in the 2D system while they are suppressed in the 3D system due to the enhanced diffusion. However, the instability is stronger and the convective infiltration is faster in the 3D system, which is not directly related to the fingering phenomenon. Furthermore, dilution is stronger in the 3D system, and it reaches to the maximum values at a faster rate in the 2D system. The traditional second central moment may lead to the wrong estimation of spreading and solute dilution in free convection and unstable solute transport.
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The Geo-hazards comprehensive evaluation index system was established in the early stage of the team, and the number, the number density, the volume and the volume density, which reflect the spatial dimension, are used to evaluate the development degree of geo-hazards, excluding the evaluation factors reflecting the time dimension. In this paper, disaster years reflecting the time dimension are introduced to enrich the development degree evaluation system of geo-hazards. The median logarithmic method and probability density distribution are respectively used to processing data of disaster years and volume, and the entropy weight is used to determine the weight of evaluation factors. The evaluation models are established and the evaluation results are divided into four levels by the slope method, reflecting the development status of disasters. The geo-hazards occurred in China (excluding Hong Kong, Macao and Taiwan) from 2011 to 2020 are taken as examples, the development degree of geo-hazards (landslide, collapse and debris flow) is evaluated and divided according to this method. The results show that the geo-hazards high development areas cover 323 counties in total, involving 19 provinces, mainly occurring in most of Hunan, western and eastern Hubei, southeastern Jiangxi, eastern Guangdong, central and western Fujian, eastern Sichuan, northern Chongqing and southern Gansu. The sub-high development areas occupy 566 counties in total, involving 25 provinces, mainly occurring in most of Sichuan, western and southern Yunnan, southeastern Hunan, northern Hubei, most of Jiangxi and Guangdong, Guangxi, Fujian and Zhejiang, southwestern Guizhou, southern Shaanxi and eastern Jilin. The moderately development areas cover 623 counties in total, involving 30 provinces, mainly occurring in most of Xinjiang, Tibet, Gansu, Hebei, Shanxi and Henan. The low development areas occupy 1336 counties in total, involving 30 provinces, mainly occurring in Qinghai, most of Tibet, northern Gansu, Inner Mongolia, Heilongjiang, western Jilin and Liaoning, eastern and southern Hebei, Shandong, eastern Henan, central and northern Anhui and Jiangsu. When compared with the national disaster prevention deployment situation or the Geo-hazards distribution, the evaluation results are in good agreement with the reality. In addition, through field investigation, the evaluation results are more scientific and reasonable than before.
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Identifying the permeability structure of the dam foundation rock mass is important for the formulation of seepage control schemes. For the horizontally-stratified red-bed rock mass of the Guxian Dam foundation, this paper adopted a "continuous, high-resolution" water pressure test data processing method to analyze the relationships between rock mass permeability and elevation, lithology and shear zones, clarifiy the permeability structure of the dam foundation rock mass, and propose seepage control advice. The results indicate that the Guxian Dam foundation rock mass is characterized by a structural and random permeability behavior. The structure shows that the permeability decreases with elevation. The randomness shows that the permeability randomly fluctuates due to lithology and shear zones. For the river-bed dam foundation rock mass, the bottom elevation of the weathering and unloading zone is 450 m or so, and the 1Lu bottom boundary is at the elevation of approximately 340 m. For the rock mass of the dam abutment, the 3Lu bottom boundary is located at the elevation of 560～580 m. The section of 350～360 m elevation has a certain thickness of soft rock, a poor development of shear structure, and a low permeability. It can be regarded as a confining layer and a potential target for the optimization of seepage control schemes. In view of the universal applicability, the method proposed in this paper can be used for reference in similar projects.
Abstract(32) HTML(18) PDF (11579KB)(24)
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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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Since 2002, the China Geological Survey has successively organized and implemented hydrogeological survey and groundwater exploration in water deficient areas, such as severe water shortage areas in west China, Wumeng Mountain area, Yimeng mountain area and red bed area in southern Jiangxi, obtained a large number of exploration data conducive to promoting discipline development, and summarized the law of water abundance. In recent decades, water prospecting and well drilling in bedrock mountainous areas serving poverty alleviation have not been systematically summarized based on water storage structures and their attributes. This paper takes the water storage structure as the theoretical guidance, considers geomorphic catchment, lithological water accumulation, structural water control and other control factors, and takes structure as the main control factor. The factors such as topography, formation lithology, vegetation development and actual value of development and utilization are systematically summarized and 8 types of 20 type 35 type water storage structures are divided, such as the horizontal rock stratum, monocline formation, fold, fault, contact zone, weathered crust, composite and cave reservoir. The common characteristics of different scales and types of water storage structures are analyzed and summarized with reference to and in combination with the neotectonic water control theory and groundwater system theory. From the aspects of spatial combination characteristics of water storage structure, boundary hydrogeological properties, hydrodynamic conditions, scale effect, symbiotic characteristics of water control and practical value of development and utilization, this paper puts forward the correlation between the lithology and geological structure, the relativity of permeability and water separation, the balance between catchment and water storage, the unity of scale and system, the inheritance of formation and transformation and the matching of scale and purpose. The research results refine and improve the classification of groundwater storage structure types in bedrock mountain areas with water shortage, summarize the attribute characteristics of water storage structure, deepen the understanding of the concept and connotation of water storage structure, not only further promote the research of hydrogeology in bedrock mountain areas, but also provide references for water prospecting and well locating in water shortage areas, and guide the sustainable utilization of water resources in water shortage areas.
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The migration and distribution of dense non-aqueous phase liquid (DNAPLs) in fractured media are affected by many factors, including the physical and chemical properties of DNAPLs, geometric and chemical properties of fractures and leakage conditions. Previous studies were mostly conducted in a single fracture, while the migration of DNAPLs in stochastic network fracture were seldom examined. In this paper, stochastic network fractures are generated using the Monte Carlo method. The coordinates and apertures of fractures are identified and output by pixel scanning. The migration of Perchloroethylene (PCE) in the stochastic network fractures is simulated by PetraSim. The effects of the geometric properties of the fractures and the leakage conditions (including the leakage rate and the leakage location) on the migration of DNAPLs are discussed. The numerical simulation results show that the spatial variability of fractures also affects the migration path and spatial distribution of DNAPLs. With the increase of spatial variability of fracture width in the network fractures, dominant channels appear, the migration rate of DNAPLs accelerates, and the location of DNAPLs centroid and the spatial distribution of saturation change significantly. The leakage rate affects the migration range and spatial distribution of DNAPLs. The higher the leakage rate is, the faster the migration rate of DNAPLs will be. The more saturated the accumulated DNAPLs at the bottom of the model, the greater the spatial distribution of DNAPLs is. In the same network fracture, different leakage locations will also lead to different migration paths and distribution ranges of DNAPLs. The spatial variability of fractures in the gravity direction at different leakage locations is different, leading to different migration paths and spatial distribution of DNAPLs.
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Groundwater level fluctuations in China are being monitored with unprecedented frequency and density, which drives the need for mining such types of data. In a typical aquifer analysis project, groundwater level data is generally applied after the completion of the aquifer conceptual framework. When the temporal and spatial density of groundwater level data gradually increases, the information gain needs to be effectively transformed into conceptual knowledge of the model. In this study, we propose a method to identify hydrological boundaries based on the groundwater level monitoring data. In this method we discretize space into a triangular mesh using monitoring wells as the initial nodes, and a transformation function gradF is defined to calculate the hydraulic gradient at any given location on the mesh. The hydraulic gradient field is subsequently use to drive an array of randomly scattered particles to obtain the streamline representation of the flow field, which will in turn serve as the basis for deducing and refining the recharge and discharge boundaries of a hydrogeological domain. This method is implemented into the geo-environmental scientific computation platform (EnviFusion-CGS), and a detailed work flow is developed to facilitate the development of the aquifer conceptual model. This method is applied to the hydrogeological investigation of the Dagu aquifer located in Qingdao of Shandong Province, where the spatial distributions and dynamic fluctuations of the hydrogeological boundaries are identified.
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The structural characteristics of karst conduit have an important influence on the rational use and protection of karst groundwater resources and the safe construction of underground engineering. At present, when using the tracer test curve to analyze the structural characteristics of karst conduit, there are some problems, including the curve superposition shape, blunt front shape, irregular rise and fall of curve, connection relationship between multiple karst conduit, location of underground lake and groundwater state. In this paper, the time concentration curve of the tracer test is used to explain the structural characteristics of karst conduit through the numerical simulation of the karst conduit flow tracer test and the change of water flow state. The results show that (1) the number of curve peaks corresponds to the number of karst conduit, and there are three models for the parallel curve of double pipelines due to the difference of the length and velocity of karst conduit runoff. (2) The number of the single karst conduit curve decline gradients corresponds to the number of blue hole, and the relationship between the decline gradients and the number of blue hole should be analyzed for multiple karst conduit in combination with the number of karst conduit and the location of blue hole. There are four types of parallel karst conduits. (3) The rapid change of curve shape indicates the mutual transformation of surface flow and pressure flow.
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Hydraulic fracturing is necessary to obtain geothermal energy from the hot dry rocks. The structure of the artificial fractures plays an important role in controlling the water and heat transport during the heat production. In this study, we analyzed the influence of the permeability and width of artificial fracture zone on the coupled heat and flow processes in the Gonghe Basin, China. The results showed that in the fractured reservoir with permeability lower than 5 D, the outflow temperature increases with the width of the fracture zones. This is because the injected cold water can sufficiently merge with the thermal water in the reservoir, and has a weak influence on the water temperature close to the extraction well. A special situation occurs in the horizontal reservoir with permeability higher than 10 D, where the outflow temperature decreases with the increase of fracture zone width, because the overall low temperature zone is increased due to the rapid diffusion of injected cold water. In the reservoir with horizontal fracture zone, outflow temperature decreases with the increase of the permeability, because the injected cold water easily arrives the production well. In contrast, in the vertical or tilted fracture reservoir, the outflow temperature increases with the permeability, because the free convection occurs strongly in the high-permeable reservoirs. A synthetic comparison suggested that under the same well distance, heat production is higher in the reservoirs with low-permeable horizontal fracture zone and with high-permeable vertical fracture zone, among other fracture zones.
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Due to the effect of climate changes and human activities, groundwater over-exploitation and aquifer depletion have become global issues of concern. Artificial recharge of groundwater through a river has been paid more attention among a variety of artificial intervention measures. It is found that not all rivers or river reaches are suitable for artificial recharge of groundwater owing to the limitations of recharge potential by infiltration and storage capacity of the vadose zone. At present, there is still a lack of widely accepted suitability assessment methods. In this study, the Yongding River in the Beijing Plain section and the underlying aquifer are taken as the study area and the case study is carried out. Moreover, the measured data are used to verify the results. The suitability assessment model (LMBGITSC model) constructed by the index system method includes eight indexes: land use types of riverbed, sediment types of riverbed, channel width, channel topographic slope, medium types of the vadose zone, thickness of the vadose zone, specific yield of the vadose zone and horizontal permeability of the vadose zone. The results show that the suitability of groundwater recharge in the Yongding River changes from good degree to medium degree along the river flow direction (except the reaches carried out anti-seepage engineering), presenting a "step-type" evolution law. The proposed method is of good applicability and can also provide reference for similar regions.
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Soil–water characteristic curves (SWCCs) are considered as a basis for analyzing fluid–solid coupling of unsaturated soil. How to estimate the SWCC over the whole region with matric suction based on the limited local datasets is challenging. Laboratory test is separately carried out on the ranges with low and high matric suctions of the undisturbed residual soil widely distributed in southeast China. With the test data, a model for SWCCs of soil in the whole range with matric suction is established by applying the reliability analysis method. Through analysis and verification based on the test data and data of 52 samples of three types of soil (sand, silt-loam and clay) obtained from UNSODA, it is found that the model parameters involved in the model show significant physics meaning. The model can be used to estimate the SWCC of soil within the whole range with matric suction according to part of the data (in the low or high matric suction part). Compared with the other models, the model is robust and is applicable for acquiring SWCCs of different types of soil within the whole range matric suction with R2>0.98. In addition, the model provides an important method to obtain SWCCs of soils with different texture, and is of the reference significance to the geotechnical AI analysis.
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Because river water in the Yangtze River watershed with a huge area is influenced by variable lithologies and large-scale water projects such as the Three Gorges Dam, the hydrochemical origins of the main stream are still controversial. Furthermore, previous estimations on the carbon sink in the watershed caused by mineral weathering are mostly based on the mass-balance calculations of cations, but this method generally involves the selection of parameters of various mineral end-members, which causes the uncertainty of results. In this study, the temporal and spatial evolutions of hydrochemistry of the main stream are determined, and a new method for the determination of CO2 consumption rates during mineral weathering processes are proposed based on the mass-balance calculations of $\rm{HCO}_3^{-}$ of the upper reaches. The results show that dissolution of evaporites, circulating salts, minerals weathering and sulfate dissolution are the main hydrogeochemical reactions controlling the ionic compositions of river water of the mainstream of the Yangtze River, while human activities mainly control the contents of $\rm{NO}_3^{-}$ in the river water within 3000 km from the estuary. The CO2 consumption rates of silicate weathering and carbonate weathering in the upper reaches of the Yangtze River are 1.16×105 mol/(km2·a) and 4.75×105 mol/(km2·a), respectively. This study may provide a better understanding of the major hydrochemical processes, enriches and promotes the theory of carbon cycle.
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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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2021, (6): 1-2.
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2021, 48(6): 1-12.   doi: 10.16030/j.cnki.issn.1000-3665.202104057
Abstract(45) HTML(6) PDF (4893KB)(23)
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The recharge and discharge of groundwater are mainly vertical surface infiltration recharge, evaporation discharge (evaporation can be shown as negative value of infiltration) and lateral surface water recharge and discharge. One of the most basic problems in hydrogeology is the evaluation criteria of sustainable exploitation of groundwater, which involves the increment of recharge and the decrease of discharge. Therefore, the prediction model of groundwater exploitation must include the above two kinds of recharge and discharge factors, otherwise the evaluation of groundwater cannot meet the requirements. However, the classic Theis unsteady well flow model (1935) only involves the recharge and discharge of the side boundary, and does not considers the surface infiltration recharge of the upper boundary, even when groundwater is pumped near the river. In this way, the analytical model cannot be basically used for prediction, and can only be used for well flow test to obtain the aquifer parameters in dry season. Therefore, the goal of this paper is to develop the Theis unsteady well flow model with surface infiltration recharge. For the problem of phreatic flow, the equation of groundwater flow cannot be established by using head as the dependent variable in a confined aquifer. We use the potential function of the second linearization method to establish groundwater flow equation in the phreatic aquifer. For the solution of the generalized mathematical model of the complex hydrogeological problem with rainfall infiltration and a pumping well, we adopt the method of decomposing it into several simple sub-models and synthesizing them into the solution of the original complex mathematical model. Based on the principle of mass conservation and assuming that the seepage obeys the Darcy’s law and satisfies the Dupuit's assumptions, the differential equation of groundwater flow is established. Then, for the well flow problem with uniform and stable infiltration recharge in two parallel rivers and two kinds of strip regions formed by a river parallel to an impermeable boundary, the general equation of groundwater flow and several kinds of water table equations under specific conditions and their flux equations are obtained. In addition, the “boundary to boundary reflection method” is proposed and applied to solve the same problem in a strip of region between a river boundary in parallel to an impermeable boundary, which reduces many derivation processes. Finally, as a preliminary application of the above theoretical results, it is also an important application, that is, there is a pumping well near the river whose water quality cannot meet the requirements, and the critical flux equation of the pumping well is calculated on the premise of not absorbing the river water. The important and concise relation equation is obtained. The equation can also be used to calculate the critical pumping rate of pumping wells in coastal areas without seawater intrusion. In this paper, the groundwater flow network diagram at a certain time in the process of unstable well flow under the above conditions is given. Compared with the flow network of well flow near the river, which is commonly seen in the literature, the flow network has obvious characteristics.
2021, 48(6): 13-23.   doi: 10.16030/j.cnki.issn.1000-3665.202010061
Abstract(64) HTML(20) PDF (3139KB)(43)
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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 high-level radioactive waste (HLW) disposal repository. There are many numerical simulation methods for groundwater flow in deep geological disposal of 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.
2021, 48(6): 24-33.   doi: 10.16030/j.cnki.issn.1000-3665.202012061
Abstract(69) HTML(14) PDF (6742KB)(24)
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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.
2021, 48(6): 34-43.   doi: 10.16030/j.cnki.issn.1000-3665.202012018
Abstract(53) HTML(9) PDF (13293KB)(17)
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The objective of the Integrated Planning of Rational Water Resources Utilization and Ecological Protection (2011-2020) issued by the State Council is to relieve the contradiction of reasonable water resource utilization and ecological protection. After the implement of the planning in recent years, visible water area is added, and the necessities of the planning is doubted. Groundwater is an important water source, and is also one of key factors affecting the ecology in the Xihu Nature Protection Area. Aiming at an quantitative analysis of the tempo-spatial changes of groundwater levels under different transferred scenarios, this study establishes a three-dimensional groundwater flow numerical model, and calibrates and verifies the model using much data such as long-term observation well data and additional water level data obtained through field investigation. The model results show that groundwater storage in the study area is under a negative equilibrium state with a yearly average value of 0.04×108 m3, mainly distributed in the Danghe alluvial fan and the north part of the Dang River irrigation area. The yearly averaged groundwater storages in this irrigation area and the core region of the West Lake Protected Area have the decrement of 2.62×106 m3 and 9.99 ×106 m3, respectively. Scenarios analysis based on the different amount of water transferring project, which are 0.8×108 m3/a, 0.9×108 m3/a, 1.0×108 m3/a and 1.2×108 m3/a, are carried out by using the established model, and the results indicate that groundwater levels are increased around 5.0～20.0 m in the Danghe alluvial fan and 7.0～15.0 m in the Crescent Moon Spring area after 50 years. However, groundwater levels in the West Lake Protected Area has a slow increase trend of 0.5 m in the predication period. Subsurface runoff is important and sustainable recharge sources in the West Lake Protected Area, but the water transferring project may improve the slow recovery groundwater levels in the West Lake Protected Area. The results of this study will provide important references for argument of the implement of the water transferring project.
2021, 48(6): 44-53.   doi: 10.16030/j.cnki.issn.1000-3665.202104019
Abstract(52) HTML(12) PDF (4694KB)(13)
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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.
2021, 48(6): 54-63.   doi: 10.16030/j.cnki.issn.1000-3665.202010017
Abstract(38) HTML(15) PDF (4505KB)(21)
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Infiltration of current in unsaturated soil is essentially a two-phase flow problem of water displacing air in the process of infiltration. The accuracy of traditional two-phase flow research methods cannot meet the needs of engineering, and it is not conducive to repetitive research. In contrast, the numerical simulation method of multiphase flow at the meso-scale can better simulate the whole dynamic process of water flooding. Mao Huan, Qren and others have achieved great results in the field of pore meso-scale research, but on the one hand, most of them focus on the study of rock multiphase flow, and there are some differences between the research object and the actual pore structure. On the other hand, the widely used pore network model method cannot directly show the change of particle velocity at any time and cannot present the phase interface movement state. In view of this, in order to reveal the dynamic percolation mechanism of water-gas two-phase displacement of unsaturated granite residual soil, this paper selected undisturbed granite residual soil in Fuzhou as the research object and studied the dynamic characteristics of two-phase displacement of undisturbed soil samples by using industrial CT scanning images and Level Set method. The results show that the Level Set method can properly capture the interface position between two immiscible fluids for meso-scale water-gas two-phase displacement simulation. The water-gas two-phase displacement process has the characteristics of large pore preferential flow, and the ‘low around’ phenomenon can easily appear in the higher ground of porosity roundness in general. The displacement rate is mainly controlled by the tortuosity of the channel, displacement speed is relatively high in the straight and wide channel. There is an obvious phenomenon of ‘preferential passage’, and its seepage time is positively correlated with the first rapid and then slow characteristics, and the maximum and minimum growth rate are 10.77 % and 1.90 %, respectively. The velocity distribution of the pore cross-section is related to the pore structure, and the phenomena of ‘reflux’ and ‘flow around’ cause the displacement velocity to drop sharply, whose decreasing degree can reach 21.62 %. The maximum displacement resistance appears at the hole wall, and the narrower the hole, the greater the resistance. The displacement efficiency is directly proportional to the displacement pressure difference, and the initial pressure growth effect is significant (up to 25.49 %, and only 1.47 % later). The research results can provide a theoretical basis for the study of the water migration mechanism of porous slopes, and also can enrich the theoretical basis of rainfall-induced landslides and are helpful in preventing natural disasters.
2021, 48(6): 64-71.   doi: 10.16030/j.cnki.issn.1000-3665.202012045
Abstract(30) HTML(24) PDF (4431KB)(4)
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Due to the characteristics of large reserves, loose structure and low strength, an inner dumping site in the open pit coal mine is prone to erosion or overall instability under the rainfall conditions. The analysis of rainfall infiltration is quite important to estimate the stability of a dump. The inner dump of the Yuanbaoshan open pit coal mine is taken as the prototype, the physical model test is carried out according to the similar theory to study the characteristics of rainfall infiltration, and the classic Green-Ampt infiltration model is improved. The results show that during the process of rainwater infiltration, with the downward migration of the wetting peak, the erosion of the slope surface starts from the splash groove, gradually transits to runoff erosion, and finally appears as traceable erosion damage, showing the characteristics of shallow landslide parallel to the slope surface. The existence of unsaturated wetting layer above the wetting peak leads to the inaccurate calculation results if the classical Green-Ampt model is used. Based on consideration of the thickness of the infiltration layer and cumulative infiltration amount, an improved Green-Ampt model is derived. The improved Green-Ampt model is a piecewise function, which can reflect the actual characteristics of the transition from unsaturated to saturated slope caused by rainfall infiltration. The validation results show that the prediction accuracy of infiltration depth and cumulative infiltration volume is significantly improved. Because of the erosion damage and the difference in the initial water content, the prediction accuracy of the improved model decreases for the later stage of the rainfall, but it is of great significance for the stability analysis of an open pit coal mine dump at the initial stage of rainfall. The calculation result of the improved model is closer to the measured data.The improved infiltration model can provide an important reference for the studies of rainfall infiltration and slope stability of open-pit coal mine inner dumping sites.
2021, 48(6): 72-80.   doi: 10.16030/j.cnki.issn.1000-3665.202108065
Abstract(51) HTML(22) PDF (8502KB)(27)
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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 rockslides caused the most catastrophic consequence in China since 1920’s, and were 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 did 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 on the northern slope of the source area before the 1965 rockslides, evidencing the precursors there, 2) the 1965 rockslide first occurred on the northern slope, and subsequently induced the rockslide on the southern slope next day resulted from its strong impact, 3) rapid granular flows of the two rockslides 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 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.
2021, 48(6): 81-88.   doi: 10.16030/j.cnki.issn.1000-3665.202103006
Abstract(38) HTML(28) PDF (3870KB)(23)
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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.
2021, 48(6): 89-96.   doi: 10.16030/j.cnki.issn.1000-3665.202012033
Abstract(38) HTML(45) PDF (3800KB)(31)
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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.
2021, 48(6): 97-104.   doi: 10.16030/j.cnki.issn.1000-3665.202012029
Abstract(53) HTML(11) PDF (4826KB)(27)
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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-gravel mixture generally has two particle size fractal dimensions: the coarse sand particle size fractal dimension value and the gravel particle size fractal dimension value. The closer the fractal dimension of sand and gravel particle size is, the greater the shear strength and internal friction angle. When the values are equal, the sand-gravel mixture has 1-D fractal dimension, at this time the uniformity is the best, the shear strength and internal friction angle are the largest. The axial coefficient is an important parameter to describe the shape of gravel. With the increasing axial coefficient, the gravel shows obvious needle-like properties. In the direct shear test, the anti-rotation ability is enhanced and the amount of surrounding contact is increased, leading to the continuous increase of shear stress and internal friction angle.
2021, 48(6): 105-112.   doi: 10.16030/j.cnki.issn.1000-3665.202012060
Abstract(44) HTML(35) PDF (3503KB)(37)
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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.
2021, 48(6): 113-121.   doi: 10.16030/j.cnki.issn.1000-3665.202012015
Abstract(18) HTML(4) PDF (6259KB)(11)
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Geogrid reinforced soil slope is a new type of slope supporting structure, which is of great significance for improving the slope stability, saving construction land and preserving the ecological environment. In order to provide the optimal design solution of the reinforced soil slope for high fill slopes, a case study is conducted on the No.6 slope at the northwest corner of the airport runway. Three design schemes with different slope ratios are carried out firstly based on the geological conditions of the slope and the field situation of the high fill slope. Secondly, the simplified Bishop method, Spencer wedge method and Morgenstern price method are used to calculate the stability factors of the reinforced slopes under the natural, rainstorm and earthquake conditions. Finally, the deformation characteristics of the slope and tensile force in reinforcements are investigated based on the finite element method under the natural conditions. The results show that all the proposed design schemes can meet the requirements of slope stability under different working conditions. A zigzag distribution of the tensile force in reinforcements in the multi-stage reinforced soil slope is observed along the slope height, and the maximum axial force of reinforcement increases abruptly at the toe of each slope. Compared with the design scheme of the gentle reinforced soil slope with the slope ratio of 1∶1.5, the reinforced retaining wall with the slope ratio of 1∶0.25 shows obvious advantages in reducing the slope height, consumption of geosynthetics, filling and excavation amount as well as slope protection area. The key issues including the slope stability, construction cost and duration are comprehensively considered, and the design scheme of the reinforced earth wall is reasonable.
2021, 48(6): 122-130.   doi: 10.16030/j.cnki.issn.1000-3665.202101022
Abstract(41) HTML(5) PDF (4010KB)(38)
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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 Scanning Electronic Microscopy (SEM), 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.
2021, 48(6): 131-139.   doi: 10.16030/j.cnki.issn.1000-3665.202101018
Abstract(54) HTML(14) PDF (3804KB)(29)
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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.
2021, 48(6): 140-150.   doi: 10.16030/j.cnki.issn.1000-3665.202009025
Abstract(37) HTML(15) PDF (4614KB)(7)
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Debris avalanches are frequently occurred in the mountainous region along the Sichuan-Tibet Railway in the Tibetan Plateau. These disasters are characterized by high and steep slope, huge energy and intense impact at the slope toe. In order to study the propagation behaviours and dynamic mechanisms of the debris avalanche, a series of laboratory experiments that grains aggregation freefall and impact on the horizontal plane then settle on it was conducted. In laboratory experiments, we consider the influences of the collision on the propagation and deposition features of debris avalanches. Images and quantitative data of the propagation and deposit features of the grains aggregation under the conditions of different particle sizes, volumes and falling height are obtained. The results show that (1) the bottom of the grains aggregation first hits the ground, then the particles are squeezed to form a shear surface. The particles move along the shear surface, spread and eventually deposit; (2) During the collision phase, the significant momentum transfer between the particles cause the particles at the front edge of the grains mass to move faster and farther, resulting in dispersive deposit; (3) From the center of the mass to the frontal edge of the deposit, the thickness gradually decreases; the shape is nearly circular at the beginning of the movement, and the final form is nearly diamond. The mechanical process leads to the occurrence of stress ridges; (4) The smaller the particle size of the grains aggregation is and the larger the volume is, the larger the maximum deposit thickness, the farther the travel distance of the main body, and the larger the main body cover area, the faster the spreading speed; the smaller the falling height is, the larger the maximum deposit thickness, the slower the spreading speed, which leading to a decreasing trend of the main body cover area; (5) Volume have the greatest influences on the deposit features of debris avalanches, followed by particle size, and the falling height has the least influence.
2021, 48(6): 151-160.   doi: 10.16030/j.cnki.issn.1000-3665.202010041
Abstract(121) HTML(8) PDF (4081KB)(19)
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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.
2021, 48(6): 161-170.   doi: 10.16030/j.cnki.issn.1000-3665.202011032
Abstract(23) HTML(8) PDF (3860KB)(5)
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Considering the fact that the optimization function of the critical slip surface search problem has many variables, complex constraints and many local extremum points, it is difficult for the traditional optimization method to achieve better search results. Therefore, a genetic algorithm based on double mutation strategy is proposed to search the critical slip surface of slope. On one hand, the algorithm improves the local optimization ability of the algorithm by detecting mutation operation and the global optimization ability of the algorithm by direct mutation operation. The combination of detection mutation operation and direct mutation operation enables the algorithm to achieve a good balance between the breadth and depth of the search. On the other hand, the algorithm adopts adaptive crossover probability and adaptive mutation probability considering individual fitness value and evolution times, so that the algorithm can increase the diversity of population in the early stage of evolution. The algorithm can protect the better individuals from destruction in the later stage of evolution. The algorithm is combined with the simplified Bishop method to calculate the examination questions provided by ACADS and a seawall slope problem. The results show that (1) for both homogeneous and heterogeneous slopes, this method can accurately search the critical slip surface of the slope and calculate the corresponding safety factor. (2) Compared with genetic algorithms that only carry out direct mutation or detect mutation, the double mutation genetic algorithm has stronger global search ability and better robustness, and has a broad application prospect.
2021, 48(6): 171-179.   doi: 10.16030/j.cnki.issn.1000-3665.202008010
Abstract(60) HTML(14) PDF (15542KB)(44)
Abstract:
Rapid and accurate 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.
2021, 48(6): 180-186.   doi: 10.16030/j.cnki.issn.1000-3665.202104028
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Abstract:
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.
2021, 48(6): 187-195.   doi: 10.16030/j.cnki.issn.1000-3665.202107017
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Abstract:
Deqin County is one of the areas suffering the most serious geological disasters in Yunnan Province. Based on the development characteristics of the debris flow in the Zhixi River, this study identifies five disaster-generating modes for the debris flow in the Zhixi River: Collapse - clastic flow, rock landslide-clastic flow, soil-rock mixture landslide-clastic flow, loose accumulation layer -bedrock contact surface landslide-clastic flow and landslide in loose accumulation layer-clastic flow. The FLO-2D model is used to simulate the debris flow movement in the Zhixi River under the rainstorm cycle of 10, 20, 50 and 100 years, and the maximum flow velocity, the maximum accumulation depth, the accumulation distance and the volume scale in different rainfall return periods are quantitatively analyzed. The results show that the debris flow is characterized by high acceleration, fast velocity, strong destructive force, and long circulation area when it erupts. When the debris flow occurs once in 100 years, its maximum velocity reaches 3.07 m/s, the maximum mud depth is 2.27 m , the volume of debris flow washed out is 84419 m3, and the disaster area reaches 91600 m2. The results provide quantitative data reference for the prevention and control of debris flow disasters in Zhixi River, and also provides an important basis for the design of disaster prevention and mitigation projects in Deqin County.
2021, 48(6): 196-205.   doi: 10.16030/j.cnki.issn.1000-3665.20201043
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Abstract:
CO2 geological 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 mean while produce 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 practices is lacking. Based on the evaluation results of the suitability of CO2 source - sink matching in the eastern Junggar Basin and the geological data 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 study the potential of the CO2-EWR technology. The results show that the the oretical 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 CO2 geological 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.
2021, 48(6): 206-212.   doi: 10.16030/j.cnki.issn.1000-3665.202010056
Abstract(70) HTML(28) PDF (3347KB)(23)
Abstract:
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.

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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010-60850926 (汪老师)
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