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The Erzhuangke landslide is a typical landslide affected by the rainy season. Rainfall changes the seepage pattern with the pre-existing landslide, weakening matric suction and soil shear strength, leading to the formation of tension cracks internally. This triggers overall sliding and localized extensive deformations. Existing studies seldom considers the interaction between the seepage field and stress field of the Erzhuangke landslide. Therefore, based on the actual engineering geological disaster scenarios, supported by on-site monitoring data and terrain physical parameters, a geometric computational model is established, and hydraulic coupled numerical simulations are conducted. By investigating variations in saturation and pore pressure within the landslide, the paper explores the rainfall infiltration patterns. It examines the impact of rainfall intensity on landslide reactivation from the perspective of stress displacement. In addition, in order to validate the accuracy and feasibility of the method, selected measurement points from the landslide are matched with corresponding positions in the numerical model. Comparative analysis is performed on displacement, soil pressure, and saturation aspects, confirming that the numerical model effectively reflects the actual situation. Through coupling numerical simulations and the study of the reactivation mechanism of the old landslide under rainfall conditions, the paper interprets field data, analyzes the reactivation process, and provides theoretical foundations and technical guidance for subsequent engineering early warning and disaster mitigation works.

Objective Recently, the seismic damage of an actual bridge structure in a frozen soil area has shown that the presence of frozen soil will increase the lateral stiffness of the bridge foundation, which may cause more serious seismic damage to the bridge structure, but there is a lack of research on the frozen soil-pile interaction effect of frozen soil bridge structures under seismic loadings and the corresponding seismic responses. Methods The present paper proposed efficient nonlinear numerical models to consider the effect of the frozen soil-pile interaction on the seismic responses of structures. First, the relationship between the depth of frozen soil and surface temperature was constructed. Then, the p-y spring modelling approach was presented to simulate the seismic behavior of frozen soil. Several as-recorded ground motions were selected as the seismic input. The seismic responses of piers and bearings of regular bridges with different depths of frozen soil under seismic loadings were investigated. Results The results show that the proposed efficient nonlinear numerical model can be adopted to model the seismic behavior of bridges considering frozen soil. And the proposed p-y curves for frozen soil can accurately predict the p-y relationship from the existing tests. When the PGA is relatively small, the pier curvature increases slightly; by contrast, in the case of large PGA, frozen soil can significantly increase the curvature demands, which can make the pier enter into the inelastic behavior. When the depth of frozen soil is small (the temperature is -5℃), the bearing displacement increases significantly, which increases the probability of unseating under seismic loadings. Moreover, frozen soil can transfer to the adverse locations of structural systems under seismic loadings. Conclusion Therefore, the conclusions of this paper can provide the necessary theoretical basis and data support for studying the seismic performance and corresponding seismic design methods of frozen soil bridge structures in China, which is of great significance for promoting the development and engineering application of disaster prevention and mitigation of bridge engineering in frozen soil areas in China.

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Objective Monitoring natural attenuation (MNA) is a widely used, economical and effective remediation technique for soil and groundwater contamination. The migration of nonaqueous phase liquid (NAPL) in heterogeneous strata is an important element in the assessment for the efficiency of MNA. Methods Based on three consecutive years of dynamic groundwater quality monitoring data, the purpose of this study is to accurately characterize the biodegradation processes of multiphase fluids at a typical phenol contaminated site in northern China. A multiphase flow numerical model of phenol transport considering Monod biodegradation processes based on TOUGH3/TMVOCBio software was developed and applied. The model depicted the spatial distribution and temporal variation of phenol under the current conditions well and analysed the sensitivities of the adsorption and biodegradation parameters. The paper also discussed the removal contributions of dissolution, volatilization, adsorption and biodegradation effects under uncertainty of adsorption and microbial degradation parameters and predicted two different natural attenuation scenarios for source disposal. Results The contribution of phenol removal varies over a range under the influence of parameter uncertainty, with 17.91% to 58.02% for biodegradation, and precipitation conditions affect the seasonal variation in phenol concentrations. In the future 20 years, under the conditions with complete removal of the phenol source and the present leakage model, the total mass removal rate of phenol will arrive at 98% and 80% at the end of the 20th year, respectively. Conclusion This paper identifies the biodegradation parameters with high sensitivity in the multiphase flow model, which provides a reference for the numerical simulation of the organic matter biodegradation process at petrochemical sites and can also provide a theoretical basis for the application of MNA technology in China.

Prediction of water inflow of a sub-sea tunnel under the blasting vibration effect is still a difficult subject. This paper takes the sub-sea tunnel between the Wawuzhuang Station and Guizhou Road Station of the Qingdao Metro Line 1 as the engineering background. Based on the equivalent continuum model, the mirror image method is used to deduce the calculation formula for the water inflow of the sub-sea tunnel considering the damage area factor. Through forward modeling and inversion, combined with numerical simulation results and actual engineering monitoring results, the correctness of the formula is comprehensively verified, and the influence mechanism of damage area factors on water inflow is analyzed. The results show that the squeezing effect caused by blasting vibration makes the pore water pressure of surrounding rock around the tunnel rise rapidly in a short time. After reaching the peak value, it began to decline slowly with the weakening and disappearance of blasting vibration. Under the influence of damage zone factors, the water inflow of the tunnel increases gradually with the increasing thickness of the damage zone, but it will not increase continuously with the increase of the coefficient of permeability in the damaged area. Through numerical simulation calculation, the ratio of tunnel water inflow considering blasting damage area is 1.4, and the error is only 4.1% compared with the calculation result of 1.342 deduced in this paper. The calculated results in this study are only 0.53 m3/(d·m) less than the field measured results, and are closer to the measured results than those with the traditional calculation formula, indicating that the calculation formula in this paper is suitable for the calculation of tunnel water inflow considering the factor of damage zone, and are of high engineering application value.

The borehole transient electromagnetic method is used to detect the long-range water-bearing bodies around the borehole wall by using the advanced water exploration borehole in the heading roadway, which avoids the “one’s opinion in one hole” because the normal logging methods can only detect the rock layer of the borehole wall. At present, because of the whole space effect, the current borehole transient electromagnetic method cannot distinguish the orientation of abnormal bodies by the received single-component response, and it can approximate the orientation of abnormal bodies by multi-component response, but it is difficult to precisely locate and interpret the profiles by the visual and effective means such as imaging. Based on the theory of borehole transient electromagnetic method and azimuthal electromagnetic logging, this paper proposes a borehole transient electromagnetic positioning method with azimuthal coil scanning detection. The azimuth coil is used as the detection device to reduce the mutual inductance of the coil and enhance the detection effect of the borehole transient electromagnetic method. At the same time, by changing the rotation angle of the coil, the borehole wall is scanned by 360° to form a radial all-round detection of the borehole, aiming at a precise localization and profile interpretation of low-resistance abnormal bodies in the rock mass at the periphery of the borehole wall. Firstly, the authors derive an analytical expression for the mutual inductance of an azimuth coil, discuss the effect of azimuth angle on azimuth coil mutual inductance, and determine the optimum azimuth angle by numerical calculation. Secondly, a full-space 3D geological-geophysical model of the borehole with homogeneous medium and low-resistance abnormal bodies are established respectively and the numerical simulation of transient electromagnetic field is carried out. The multi-component response characteristics of the azimuthal coil scanning detection transient electromagnetic response are analyzed, and the law of transient electromagnetic response of azimuthal coil scanning detection is summarized, and the borehole transient electromagnetic positioning method with azimuthal coil scanning detection is determined. Namely, through the transient electromagnetic response characteristics of the axial and radial directions of the borehole, the position of the low-resistance abnormal bodies in the rock body at the periphery of the borehole wall is determined. Finally, by establishing the geological-geophysical model with two low-resistance bodies and using azimuth coils set to the best azimuth angle for numerical experiments, it is verified that the method can intuitively and effectively determine the orientation of low resistance abnormal bodies. The study shows that the azimuth coil scanning detection results of the borehole transient electromagnetic method can better reflect the transient electromagnetic field anomaly caused by the low-resistance abnormal bodies in the rock body at the periphery of the borehole wall, and the resolution of the full-space apparent resistivity imaging results is high. Based on the transient electromagnetic response characteristics of the axial and radial directions of the borehole, the borehole transient electromagnetic positioning method with azimuthal coil scanning detection has a high resolution and localization accuracy for the low-resistance abnormal bodies in the rock body at the periphery of the borehole wall. The research results provide a theoretical basis for the practical application of the borehole transient electromagnetic positioning method with azimuthal coil scanning detection.

Objective The great demand for urban landscape improvement and reconstruction has required increasing dredging practices for waterfront buildings, particularly antique buildings. To effectively protect such antique buildings, the influence of dredging on the ground deformation of antique buildings needs to be carefully considered in the dredging operations. Methods To obtain a better understanding of the effect of dredging activities on antique buildings, the influence of dredging depth, dredging slope shoulder width and dredging slope ratio on the displacement and stress distribution of an antique stone bridge on soft ground via a three-dimensional model of the bridge body and its ground strata was studied in this paper. Based on the calculated results, mechanistic explanations of dredging on the ground deformation of antique stone bridges were proposed. Results The simulated results show the following: ① Dredging effects on the antique stone bridge mainly appeared as giving rise to the displacement of the bridge and the near strata, changing the stress distribution, and forming a plastic zone in the adjacent area of strata. As a result, dredging activities render a more complex stress and displacement distribution to the bridge and the strata around the bridge. ② Different dredging parameters have different effects on the displacement fields and stress fields of the bridge and its surrounding area. The dredging depth primarily affects the displacement magnitude of the soil, and the dredging slope shoulder width is the crucial factor affecting the scope of the dredging effect, whereas the dredging slope ratio and the dredging slope shoulder width jointly manipulate the change in the soil displacement curve and the development of the plastic zone. ③ In dredging projects, the setting of dredging parameters should not only meet the requirements of engineering practicability and economy but also reasonably determine the dredging parameters and control the impact of dredging on adjacent ancient buildings and take into account the width of the dredging slope shoulder width and the dredging slope ratio when determining the designed dredging depth. Conclusion The results in this work are of practical significance for dredging activity in antique building protection.

Objective The Kuncheng Tunnel of the Central Yunnan Water Diversion Project crosses the Heilongtan and Bailongtan areas, the major headwater regions in the Chenggong District of Kunming City. Methods Tunnel water inrush may seriously threaten the safety of the urban water supply. In this paper, based on hydrodynamic data and hydrochemical data during tunnel construction, the characteristics of the karst water system, the origin of the springs, and the impact of tunnel construction were analysed. Then, a three-dimensional groundwater flow model for the Heilongtan-Bailongtan Section was developed and calibrated to simulate and predict groundwater level changes during the construction of the Kuncheng Tunnel, and the water environment effect of tunnel construction was evaluated. Results The results show that both the Heilongtan and Bailongtan springs are mainly recharged by the same karst P1q+m aquifer. However, controlled by aquitard P1d and the Hunshuitang fault downstream of the Sanjiacun Depression, the two springs actually belong to two relatively independent karst water systems. In addition, the excavation of the Kuncheng Tunnel has changed the regional groundwater flow field and cut off the flow of Bailongtan, while it has negligible impact on Heilongtan. Conclusion This study discusses the genetic relationship of karst spring, and quantitatively analyzes the impact of tunnel excavation on water environment, which has reference significance for preventing water inrush in tunnel construction.

Objective Monitoring natural attenuation (MNA), as a low cost remediation method for groundwater pollution that does not produce secondary pollutants and has little impact on the polluted site environment, has high application value and development prospects, and is worth practicing and studying. Methods This paper adopts a groundwater-contaminated site in Baiyun District of Guangzhou to assess the applicability of MNA. Based on the analysis of hydrogeological conditions and pollution status, a groundwater numerical simulation program MODFLOW was used to establish a groundwater flow model for contaminated sites. The pollutant migration numerical simulation program MT3DMS was used to establish a pollutant migration model for the site. The migration processes of groundwater flow, main pollutants total petroleum hydrocarbons (TPH), and heavy metal nickel (Ni) were simulated, respectively. Based on the model, the performances of the MNA alone and the MNA combined with pump and treat methods were compared. Results The results show that TPH and Ni are both sensitive to changes in the Freundlich constant and Freundlich exponent. The TPH shows good natural attenuation effect and can be substantially attenuated by the MNA alone. The concentration of TPH decreased from the initial value of 1.52 mg/L to the target (0.3 mg/L) after 850 days. Ni decay is relatively slow and it is suitable to adopt to a natural attenuation scheme under monitoring combined with the pump & treat method. The concentration of Ni decreased from the initial value of 0.13 mg/L to the target (0.02 mg/L) after 300 days. For a contaminated site with large natural attenuation capacities and/or low groundwater flow velocities, MNA alone is an appropriate remediation strategy. In contrast, for a contaminated site with low natural attenuation capacities and/or high groundwater flow velocities, the MNA combined with pump and treat may be a better remediation strategy. Conclusion This study provides an appropriate reference for the application of MNA to groundwater pollution remediation.

Sgnificance To quantitatively study the impact of various nonlinear factors in the coastal zone on groundwater flow and solute transport processes, MARUN (Marine Unsaturated) software for simulating groundwater flow in the coastal zone was developed. Progress This paper reviews the research and application progress of MARUN from the aspects of model principles, algorithm characteristics, literature review, and case analyses. The software is suitable for numerical simulations of two-dimensional vertical profiles of groundwater flow and solute transport reactions in the coastal zone. MARUN implements a finite element algorithm for variable saturation and density flow and solute transport, mass-consistent implicit difference discretization, and Picard, Newton, and Newton-Picard numerical solution methods, covering many nonlinear factors such as tides, waves, evaporation, rainfall, and load effects. It is characterized by its high professionalism, good flexibility, and high fault tolerance, but it does not have a graphical user interface. MARUN has achieved a number of highlighted research results in scenarios such as bioremediation of crude oil pollution on beaches, seawater-groundwater circulation processes in shallow aquifers in intertidal zones, and the evolution of regional groundwater flow systems. Conclusion and Prospects In the future, MARUN needs to be further expanded into three-dimensional space and coupled with physicochemical processes with random characteristics to improve its performance level of simulating groundwater flow and solute transport in coastal aquifers.

During the process of developing and utilizing geothermal resources, various challenges are encountered. One such challenge is the decrease in temperature and pressure of the geothermal reservoir as a result of the increasing geothermal exploitation and duration. In addition, the discharge of geothermal tail water poses a risk of thermal pollution, leading to environmental concerns. To address these issues effectively, reinjection of geothermal fluids into the reservoir can be implemented as a viable solution. Prior to initiating the geothermal development and utilization, it is crucial to conduct scientifical and rational planning of the layout of production and reinjection wells. This involves exploring optimal strategies for the production-reinjection scheme that prevents the premature thermal breakthrough and maximize the efficient utilization of geothermal resources, thereby extending the lifespan of the geothermal reservoir. The Fengpei Basin, a Cenozoic rift basin that developed since the Paleogene period, exhibits a widespread distribution of geothermal reservoirs, primarily composed of the Ordovician limestone with karst and fracture characteristics. Building upon the geothermal resource exploration results in the Anguo Town in Peixian County in Jiangsu Province, this study utilizes key parameters obtained from pumping tests and reinjection experiments, such as well spacing and the reinjection-to-production ratio. This paper establishes a 3D coupled numerical model of geothermal water seepage and heat transfer by using the Feflow6.2 software. The recoverable reserves of geothermal fluid within the geothermal reservoir are simulated and predictd, specifically the Ordovician limestone formation. Furthermore, a simulated optimization of the development and utilization scheme for the production-reinjection wells is conducted. The results reveal that an appropriate well spacing of 389 m between the producing well (RPX01) and the reinjection well (RPX02) is recommended. Moreover, the reinjection-to-production ratio, namely the ratio of average aquifer hydraulic conductivity, is determined to be 1.29, supporting a sustainable approach of one-for-one pumping and reinjection. With a stabilized drawdown of 50.61 m, the production well has a capacity to recover 1000 m3/d of geothermal resources. Under the conditions of a production rate and a reinjection rate of 1000 m3/d, as well as a reinjection temperature of 40 °C, the simulation predicts a decrease in groundwater level by 45.49 m and a temperature reduction of 1.44 °C after ten heating seasons. This represents the optimal cyclic development and utilization scheme among the simulated scenarios. The above results provide a scientific basis for decision-making in the construction of the clean energy heating demonstration area in rural northern Jiangsu. They contribute to the establishment of a scientifically sound and sustainable approach for utilizing geothermal resources, while considering the challenges associated with the thermal breakthrough and the environmental impact of geothermal tail water discharge.

Restricted by the surface smoothness and topography, it is impossible for some high-speed railways on mountainous regions to avoid parts of rockfall development sections, posing great safety challenges to construction projects and railway operations. In light of that, this paper laid its focus on the rockfall situated by the entrance of Xinghuayu Tunnel along the proposed Jinan-Zaozhuang Railway project, and leveraged the power of drone-captured 3D aerial photography to perform digital geological survey and mapping so as to accurately identify the development characteristics, scale, as well as modes of deformation and failure of said rockfall. Next, by cross-referencing the results of 3DEC numerical simulation with those from analytic hierarchy process (AHP), color-coded maps highlighting the scope of influence and danger levels of potential rockfalls induced were obtained. Using said maps, zone-by-zone hazard and risk assessment were then performed, based on which corresponding prevention and control measures were put forward. The findings show that among the 12 dangerous rock belts identified from the drone-captured 3D aerial photography model, only Belt No. 5 would threaten the safety of the tunnel entrance and bridge abutments, for which the combination of anti-rockfall passive protective netting and an open-cut tunnel structure was recommended as a comprehensive solution. By virtue of the solution’s effectiveness, this study can offer reliable references for not only zone-by-zone hazard and risk assessment for rockfalls, but also railway route selection and disaster prevention and mitigation.

To explore the accuracy of the calculation method of the jacking force of circular curved pipe jacking under different pipe-soil contact characteristics, in combination with the curved steel pipe jacking project of Gongbei Tunnel of Hong Kong-Zhuhai-Macao Bridge, this paper adopted several commonly used jacking force calculation formulas for the curved pipe jacking at home and abroad and jacking force finite element analysis model with consideration of grouting effect and the pipe-soil contact range established with ABAQUS to calculate the jacking force. It was found by contrast with the pipe jacking force data: ①The calculated value of jacking force: JMTA formula≫Shanghai normative formula>Shimada formula, where it was considered that the calculated value of the lower limit of Shimada formula of 1/3 pipe-soil contact was relatively close to the measured value. ②Through numerical simulation, it was found that the simulated jacking force of 1/3 pipe-soil contact characteristics was gradually close to the one of 1/2 pipe-soil contact characteristics; in the grouting state, the previously measured jacking force was close to the one of 1/2 pipe-soil contact characteristics. When the jacking force tended to be stable, the measured jacking force was close to the one of 1/3 pipe-soil contact characteristics. Therefore, the numerical model could predict the jacking force of the pipe jacking under the same working condition and had a certain guiding significance for actual construction.

The Shuitoushang landslide in Ershe in Qijiagou Village of Xinchang Town in Tongjiang County is a typical red-bed terrace landslide in eastern Sichuan. There are few studies on the seepage analyses of such landslides in this area, but similar slopes are widely distributed in the area. In this paper, on the basis of a large number of field investigations, surveys and data collection of disaster sites, the satellite remote sensing, UAV aerial photography, airborne LiDAR, indoor tests and other technical means are comprehensively used to analysis the landslide. Based on the mathematical model of Fredlund & Xing soil-water characteristic curve, the SEEP/W module in Geo-Studio is used to conduct the seepage analysis, and the analysis results at different time stages are coupled with the SLOPE/W module. Then the dynamic relationship between the stability coefficient, rainfall and time is obtained, revealing the deformation process and formation mechanism of the landslide. The results show that: (1) the continuous rainfall causes the groundwater level to rise and the slope stability to decrease, eventually leading to the overall instability and failure of the Shuitoushang landslide. (2) The deformation process of the landslide and the characteristics of groundwater exposure are basically consistent with the results calculated by Geo-Studio, indicating that the results based on Fredlund & Xing model can provide more accurate simulation results in similar areas. (3) Reclamation of terraced fields (paddy fields) will reduce slope stability. The results can provide theoretical support for hidden danger investigation and active prevention of similar landslide disasters in mountainous areas of Sichuan, and provide a reference for disaster prevention and mitigation.

In order to study the slope deformation law during and after the construction of the sandstone bed-cut high slope support project and the effect of the treatment project, this paper relies on a slope support project in Beijing to analyze the axial force of the anchor cable and the slope during the construction process. The slope displacement is monitored and analyzed, and the results show that the change of the axial force of the anchor cable is mainly divided into the acceleration loss stage, the fluctuation stage and the continuous stable trend stage; the change of the axial force of the anchor cable can well reflect the change of the internal force of the slope; the change of horizontal displacement and vertical settlement can reflect the change law of the deep displacement of the slope and the stability of the slope, has a better support effect. The finite element analysis software was used to simulate the excavation and support process of the sandstone-layered high slope. It was found that with the excavation of the slope, the displacement of the slope developed along the slope angle of the weak sliding surface, and the stability of the slope decreased. The monitoring results and the simulation results are compared and analyzed, and it is found that the change trends of the two are basically the same, which proves that the slope support system can effectively control the deformation of the slope. The research results can provide reference for the design and construction of similar slopes in the future.

In order to discuss the future development trend of structural and unstructured dynamic grid technology in the field of unsaturated-saturated groundwater numerical simulation, this paper summarizes the research status of unsaturated-saturated coupled numerical simulation, introduces the principle of dynamic grid technology and the deformation method of moving boundary structure and unstructured grid, summarizes the application status and shortcomings of dynamic grid technology in the unsaturated-saturated interface, and discusses the future development trend of related research. The review shows that both structural dynamic grids and unstructured dynamic grids have their inherent advantages and disadvantages, and the combination of structural/unstructured hybrid grids and multiple dynamic boundary treatment methods has important application value in the research of unsaturated-saturated coupling numerical simulation. When simulating the change of phreatic surface, a variety of mesh deformation methods can be combined. When the change of the position and shape of the phreatic surface is small, the spring method is used to update the mesh; When the position of the water table changes significantly but the shape changes little, the overlapping structure dynamic grid technology or the overlay method is used to update the grid; If the shape of the water table changes greatly, the grid reconstruction method is used to update the grid, so as to more accurately simulate the change and movement of the unsaturated-saturated interface. Relevant research provides scientific guidance for the coordinated prevention and control of unsaturated zone soil and saturated zone groundwater of the site.

The Jinjiling landslide was obviously deformed after the rainstorm, and preliminary conclusions were drawn through on-site investigation, drilling, geophysical prospecting, deep displacement monitoring and horizontal displacement monitoring. On this basis, in order to further find out the genesis mechanism of the landslide, this paper interprets the existing survey and monitoring data, combines the Midas-GTS software to analyze the seepage field, displacement field, and stability calculation of the landslide under different working conditions, and comprehensively evaluates its genesis mechanism. The results indicate that (1) geophysical interpretation shows that the Jinjiling landslide is a rock-soil mixed, water-bearing landslide, and the sliding surface is located at the boundary between T2b1 marlstone and T2b2 mudstone. (2) Deep displacement monitoring data reveals that the landslide occurs in a superficial soil mass, and the position of the slip surface is consistent with the location of the slip surface obtained by geophysical exploration. (3) The horizontal displacement monitoring shows that the superficially distributed Houbang landslide and Panjialing landslide have fast deformation rates and stronger deformation. (4) The numerical simulation results show that the Jinjiling landslide is currently in a basically stable state; it is in a basically stable state when the groundwater is drained; it is in a less stable state under heavy rain conditions, which may cause overall slippage, and the Panjialing and Houbang landslides produce secondary soil slippage. (5) The topography, geological structure, stratigraphic lithology of the Jinjiling landslide provide provenance and site conditions for the formation and development of the landslide. Torrential rain and human engineering activities are the inducing factors, which further aggravate the deformation of the landslide. The research results will provide a theoretical basis for the analysis of the genetic mechanism and stability of similar landslides in the Three Gorges Reservoir area, and have important guiding significance for the later control measures.

Slope kinematics is normally used to evaluate the temporal and spatial evolution of landslides. The inverse velocity method (INV) is an important tool for predicting the initiation of landslide, but its correlation with the physical and mechanical mechanisms of multiple physical fields inside the landslide need to be further clarified. In this paper, the slope deformation and geological characteristics of the Lijie Beishan landslide in Zhouqu, Gansu Province was investigated. The inverse velocity method, velocity threshold method and numerical simulation based on unsaturated soil theory were used to study the kinematic characteristic of slope. The results showed that after the lowest value of the inverse velocity on June 3, 2021, a stable stage lasted for approximately 60 days and then suddenly accelerated on September 20. The velocity became more than 200 mm/d over 20 days, and the deformation did not converged. There was an obvious acceleration point in the time-dependent inverse velocity curve. The end of the landslide life cycle was obtained by extending the straight line after the onset of the acceleration point. The prediction period was within 8 days compared to the actual instability startup, and the landslide was predicted 130 days in advance. According to the post analysis of the whole time-dependent velocity curve, the multi-level speed thresholds of v1=20 mm/d, v2=60 mm/d, and v3=100 mm/d were set up. Because there were two peaks of velocity, the prediction of landslide triggering was lagging compared to the inverse velocity method. The coupling of slope stresses, deformation and pore water transportation was simulated. The results showed that the inflection point of the time-dependent deformation curve was correlated with the increase in precipitation intensity, and the cumulative precipitation was negatively exponentially correlated with the safety factor. The cumulative deformation obtained by numerical simulation was 2 250 mm, the velocity of deformation was 10-35 mm/d, and the inverse velocity was 0.03-0.12 d/mm, which were close to the actual monitoring data. However, there was still a deviation between the prediction of the inflection point of slope deformation and the actual situation.

The development of clean, stable, and renewable hot dry rock geothermal energy is significant for alleviating the energy crisis, reducing environmental pollution, and improving human health. Enhanced geothermal system (EGS) is an advanced technology for developing geothermal energy efficiently by stimulating hot dry rock reservoir. This technology involves a complex hydro-thermal coupling process. A numerical approach is usually applied for analyzing heat extraction. In this paper, taking the geothermal reservoir of the Cooper basin in Australia as the research object, two models–a 3D zonal homogeneous permeability model and a heterogenious permeability model – are established based on the measured microseismic data of hydraulic fracturing. The latter one is inversed from microseismic data. The temperature field, seepage field and thermal performance of the reservoir are numerically studied, and their differences are compared and analyzed. The results show that with the same injection-production flow rate, fluid flows more quickly from the injection well to the production well while the temperature drops relatively more rapidly in the inhomogeneous model due to the dominant channel revealed by dense microseismic events near the wellbore. In the homogeneous model, the dominant flow channel is not as pronounced as in the previous model, and the temperature decreases more slowly. During the operation of the geothermal reservoir model, the change in heat recovery of the zonal homogeneous model is relatively stable, with a decline of 3.74%, and that of the inhomogeneous model is rather obvious, with a decline of 12.72%. Compared with the inhomogeneous model, a smaller temperature drop and a higher heat recovery exist in the homogeneous model. However, the permeability in the actual reservoir is uneven, and the simulated heat recovery of the zonal homogenization model is higher than the actual recovery. Therefore, the simulation results of the inhomogeneous model have more reference significance for practical engineering.

Water resources are scarce and ecological environment is fragile in the arid regions of northwest China. How to scientifically deal with the relationship between production water and ecological water has always been one of the hotspot and difficult issues in the field of water resources development and utilization in northwest arid areas. However, there are few quantitative studies on the relationship between the ecological water conveyance from the middle and upper reaches of the basin to the downstream terminal lake (wetland) and the area of the terminal lake (wetland). In this paper, Qingtu Lake, the terminal lake of the Shiyang River Basin in Gansu Province, is taken as an example. A coupled model of surface water and groundwater is established using GSFLOW software, among which, LAK module and SFR2 module are used to treat the lake and water channel, respectively. Based on this, the changes of surface area of the Qingtu Lake under different ecological water conveyance schemes are predicted. The appropriate range of ecological water conveyance to the Qingtu Lake is determined. The results show that the current ecological water conveyance of 3100×104 m3/a can ensure the highest water level of Qingtu Lake of 1212.23 m (the average water level of 1211.68 m) and the corresponding water surface area of 16.27 km2. The relationship between ecological water conveyance and water surface area is as follow. When the water delivery is in the range of 2000×104−3700×104 m3/a, the water surface area increases obviously and the area change rate is relatively stable with the increase of water conveyance; when the water delivery is in the range of 3700×104−4500×104 m3/a, the increasing water surface area gradually decreases and the area change rate gradually decreases with the increasing water conveyance; and when the water conveyance is more than 4500×104 m3/a, the increase of water surface area with the increasing ecological water conveyance is very small, especially when the ecological water conveyance is more than 5500×104 m3/a, the change rate of water surface area tends to 0. Considering the demand for maintaining the current water surface area of the Qingtu Lake and the benefits of ecological water conveyance, the ecological water conveyance volume from the Hongyashan reservoir to the Qingtu lake should be in range of 3100×104−4500×104 m3/a. The results are of certain reference value in determining the local ecological water demand and maintaining the coordinated and sustainable development of local ecology, economy and society.

The horizontal well multi-fracture development technology, which is well-developed in the oil and gas industry, can significantly improve the economics of enhanced geothermal systems (EGS). In this paper, a three-dimensional horizontal-well multi-fracture physical model is established for EGS. The performances of EGS under different reservoir characteristics of well spacing and fracture spacing are analyzed by CFX simulation, and the influence mechanism of different reservoir characteristics on the heat recovery process of the EGS reservoir is revealed. The results show that: ①The fracture spacing is the key factor affecting the operating life and mining rate of EGS engineering. Under the same water injection flow, the larger the fracture spacing, the smaller the possibility of forming thermal permeability, the longer the system operation life, but the lower the reservoir recovery rate. The smaller the fracture spacing, the higher the thermal permeability, the shorter the system life, and the higher the reservoir recovery.②The well spacing has a significant effect on the fluid velocity in the fracture. As the well spacing increases, the temperature of the flow-producing fluid increases continuously during the same mining time, and the life of the system also increases. The increase in well spacing also means that the reservoir volume becomes large, so there is more geothermal energy for exploitation and longer life for the system for operating. The research can provide theoretical guidance for the construction of EGS reservoirs and provide theoretical preparation for the commercial exploitation of geothermal energy.

The depth and plane position of the goaf control the deformation characteristics of the mining slope with gently inclined layered structure and directly affect the overall stability of the mining slope. In recent years, scholars have carried out a large number of studies on the deformation of the overlying rock mass caused by underground coal mining, but the influence of goaf characteristics on the key positions of slopes has not been revealed deeply enough. The Jianshanying deformation body in the Faer Coal Mine in Guizhou Province is a typical gently-inclined layered mining slope, which has the steep upward and gentle downward, and hard upward and soft downward characteristics. The Jianshanying Deformation Body is chosen as the subject of the study in this paper. The effects of multi-layer mining and single-layer mining at different depths on the slope deformation are studied by qualitative analyses of the geological process mechanism and numerical simulation method. The width, depth and depth ratio of goaf have an important influence on the slope deformation characteristics. The results show that the multi-layer mining leads to the destruction of the slope toe and the overall collapse, which will cause the slope to produce a significant horizontal displacement, resulting in the vertical displacement of the multi-layer mining being much greater than the total thickness of the coal seam mining. The goaf crossing the slope toe, which makes the depth-to-thickness ratio decrease sharply and the mining cracks are more likely to extend to the surface, is an important factor for the destruction of the rock mass near the slope toe. When the width of the goaf increases or the multi-layer mining operation is carried out, the slope deformation increases significantly. When the depth of the goaf increases, the slope deformation value decreases, but the deformation range increases. It is beneficial to slope stability by optimizing the layout of the working face to prevent the sharp decrease of the depth-to-thickness ratio, controlling the width of the goaf, avoiding repeated mining and increasing the depth of mining, when mining in the strong terrain areas.

In the early 1960s, Tóth obtained hierarchical groundwater flow systems by using analytical solution based on given-head upper boundary, which is a milestone breakthrough in hydrogeology and successfully solved a series of theoretical and practical problems.However, the defects of Tóth's analytical solution have been followed for a long time such as focusing solely on mathematical simulation and ignoring the physical mechanism; taking terrain control of water table as a universal law; and ignoring the distortion of the mathematical simulation based on given-head upper boundary.These shortcomings, especially the lack of the physical mechanisms exploration, not only hindered the development of Tótian theory itself, but also made the theory difficult to be understood, so that the theory has not being widely applied yet by the international hydrogeological community.This paper proposes an expression for the minimum energy consumption rate of groundwater flow referring to the principle of minimum energy consumption rate applied in river dynamics.Based on the exited results of "numerical simulation of groundwater flow patterns using flux as upper boundary", the physical mechanism is further explored, and it is concluded that groundwater flow follows the principle of minimum energy consumption rate.

In order to study the working characteristics of energy pile groups, based on the Abaqus finite element simulation, assigns the average temperature of the heat transfer stable stage to the pile body for steady-state thermo-mechanical coupling calculation, and proposes a simplified analysis method for the bearing characteristics of energy pile groups.The reliability of this research method is verified through the comparative analysis with field data.Combined with an example, this method is used to analyze the bearing characteristics of energy group piles under the action of pure mechanical load and thermal coupling.The results show that the non-uniform settlement of the distributed symmetrical arrangement of energy piles in the pile group foundation is significantly less than that of the centralized arrangement, and the layout has a great influence on the response characteristics of the pile foundation structure.Under the condition of equal stiffness of pile foundation, the control effect of pile group tilt is better by increasing pile diameter and decreasing pile spacing.The research results of this paper can provide some reference value for the engineering application of energy pile group.

Shale reservoirs are well developed in Southeast Chongqing, of which the Longmaxi Formation is the main reservoir.Compared with other types of reservoirs, structural fractures are very well developed in this type of shale reservoirs, making this area potential for shale exploration.In this paper, based on the field survey data and typical regional geological sections, structural characteristics of the study area were analyzed.On this basis, a geological model for the shale reservoir was established.In order to restore the process of structural evolution within the study area of the Himalayan period, further, the finite element analysis software Ansys 15.0 are used.Simulation results fit the actual structural development well.Based on the results as well as Griffith fracture criterion and Coulomb-Moore fracture criterion, multiple influencing factors of shale reservoirs were comprehensively analyzed, and comprehensive fracture development coefficient IF were used to quantification of the fractures distribution prediction in shale reservoirs.The larger comprehensive fracture development coefficient IF is, the more developed the shale reservoir fractures would be.Therefore, shale reservoirs in the study area are classified into three categories: fracture favorable zone Type Ⅰ(IF ≥ 3.0, fracture very well developed), fracture favorable zone Type Ⅱ(3.0, 2.0], fracture good developed) and fracture favorable zone Type Ⅲ(2.0, 1.0].

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.

The research on the mechanism of hydrothermal transfer and transformation and bare soil evaporation is of great significance for water balance and surface energy transformation in surface-groundwater systems. In this paper, based on long-term observations of in situ lysimeter test and numerical simulation, two cases for lysimeter with initial groundwater depths of 80 cm (shallow groundwater depth) and 290 cm (deep groundwater depth) are used to examine the dynamic process of hydrothermal transformation in the variable saturation zone with its effect on bare soil evaporation in the “wind-blown sand area” of the Ordos Basin in China. The results indicate that soil water movement in the variable saturation zone is driven by the head gradient and temperature gradient, showing different movement modes under different groundwater depths. For the situation of shallow groundwater depth, the capillary height can reach the surface, soil water transports upwards with little temperature effects driven by capillary force under the effects of head gradient under the evaporation conditions, and there is no zero flux plane in the soil. When the groundwater depth is less than the capillary height, groundwater directly contributes to soil evaporation driven by capillary force. For the situation of deep groundwater depth, head and temperature are the key factors in the soil water movement, and there is an isolated zero flux plane located at 18 cm below the ground surface, which prevents the upward soil water movement and leads to a decrease in evaporation. When the groundwater depth is greater than 1.6 times the capillary height, groundwater no longer directly involves in soil evaporation, but indirectly affects the water conversion in the unsaturated zone. Therefore, during the simulation period, the cumulative bare soil evaporation of the shallow groundwater depth was about 4 times that of the deep groundwater depth.

Seawater intrusion (SI) has become a global concern for groundwater environment. SI not only seriously threatens freshwater resources in coastal aquifers, but also undermines the balance of coastal ecosystem and further restricts the socioeconomic development. This paper simulates the SI process in a 2D synthetic aquifer constructed from sandbox experiment using the simulator SEAWAT-2000. The transport phenomenon of the brackish water interface is investigated by altering the location and injection rate of a recharge well and the layout of the physical barrier. The results show that when the recharge well is located near the toe of the salt water wedge of 40 cm from the coastline and 5 cm from the surface, the optimal performance of the recharge scheme is achieved with the repulsion rate up to 21.5%. When the physical barrier is located 10 cm from the coastline and the penetration depth is 35 cm, the toe of saltwater wedge is effectively driven to the coastline with the repulsion rate up to 81.8%. Moreover, we simulate the variable-density groundwater flow and transport in a typical two-dimensional section of coastal aquifer in the Longkou District of Shandong Province. The SI model is established to evaluate the influences of different management schemes (i.e., physical barrier and recharge well) on the prevention of seawater intrusion. The results show that when the physical barrier is located 600 m from the coastline and the penetration depth is 18 m, the toe of salt water wedge is effectively driven back to the coastline with the repulsion rate up to 28.4%. The results reveal the influence of hydraulic and physical barriers under different settings on the migration rule of the brackish water interface. The findings may provide insights into the optimization suggestions for coastal groundwater management under site conditions.

Focusing on the uneven settlement of surrounding buildings caused by deep foundation pit dewatering in loess area, this study analyzed the mechanism of ground settlement induced by foundation pit dewatering, deduced the simplified calculation formula of ground settlement caused by dewatering based on the layer-wise summation method and shear displacement method. First, the equation of the cone of depression was derived from Dupuit formula by ignoring group well effect and lateral displacement. The soil around the pit was divided into a drained zone and a saturated zone by the precipitation curve. Then introduce modification factor, and the effective stress increment caused by the reduction of pore water pressure in different loess layers was corrected. Finally, the constraint function of lateral friction located in soil-pile interface towards soil settlement was considered. The settlement at different distances from the dewatering well was calculated respectively, the actual settlement was the sum of the both. Instance calculates was performed based on an engineering example of foundation pit dewatering by finite element software Abaqus, and comparative analysis was carried out between numerical results and measured field data. The research results show that the position where the constraint effect of lateral friction became most significant was at the interface of soil and pile; the accuracy of settlement calculation in this paper was much higher than that of the normative method in the range of 1.5 times of precipitation depth, which can better predicted the ground settlement at different distances around the foundation pit in loess region during dewatering. The study could provide reference for calculating ground subsidence in similar phreatic aquifers.

The prediction of the geothermal field is an important prerequisite for the evaluation of geothermal resources. Much attention has been paid to the research on coupled temperature field of percolation-heat transfer in deep fractured rock mass. The Zhuolu Basin is a graben-type faulted basin of the Cenozoic era. There are many hot springs on the surface and rich geothermal resources. In this paper, a three-dimensional non-parallel multi-fractured geological model of the Zhuolu Basin for large scale was established based on the actual geological survey results and the geological structure section interpreted by 3 geophysical survey lines. Parameters have been assigned or adjusted, a mathematical model of permeate-heat transfer in multi-fractured rock mass considering groundwater flow was obtained. After the model was verified, the internal temperature field of the basin was calculated and indicated. The geothermal anomaly area is concentrated in the center of the Jixian group (around 70℃) and the north- eastern part of the Changcheng group (90~98℃), the internal temperature field of basin have been analyzed at different hydraulic reaolients. The study results provide a certain basis for the exploration, evaluation, development and utilization of geothermal resources in Zhuolu Basin or similar areas.

Compared with water, CO2 has larger expansibility, lower viscosity and lower reaction degree with rock.As an enhanced geothermal system (EGS) seepage heat transfer fluid, CO2 has higher heat transfer efficiency than water.This paper summarizes the research status of fluid/rock interaction in CO2-EGS from three aspects: theoretical research, experimental research and numerical simulation.The changes of reservoir rock properties are evaluated from mineral composition, micro pore structure and mechanical properties.The results show that the main reaction minerals of CO2-water-rock interaction are quartz and feldspar, and the precipitation minerals are montmorillonite, illite and calcite.The interaction of CO2-water-rock will lead to the decline of mechanical properties of reservoir rocks and the change of pore structure characteristics.Finally, the existing problems and development trend of CO2-water-rock interaction in CO2-EGS are discussed, which provides a reference for the development and research of CO2-EGS in the future.

Bedding rock slopes with soft-hard interlayers have complicated failure types and are difficult to prevent. In view of the prone and frequent occurrence of such slope geological disasters, research is carried out from the aspects of slope angle, rock formation tendency and combination form, and joint distribution.Slope physical model testing is an important means to reveal the mechanism of slope deformation and failure.Based on similarity theory, this paper takes the Sunjia landslide in Wanzhou District, Chongqing City, as the engineering support and designs the indoor slope physical model test according to the geological exploration report of the landslide area.The test simulates gravity loading through a jack-up model box and explores the relationship between the front slope angle and the weak interlayer inclination when the bedding rock slope slope is damaged.Combined with the finite element analysis software Plaxis 2D, multiple sets of numerical simulation tests were performed on the physical model to verify the failure mechanism of bedding rock slopes with soft-hard interlayers. The results show that for a bedding rock slope, when the inclination angle of the weak interlayer is approximately 22°, the leading edge excavation slope angle is about 58°, the bedding rock slope is prone to sliding, and the sliding surface is the joint surface of the trailing edge and the weak interlayer. Through the surface.Therefore, the stability of a bedding rock slope is controlled by the density of the layer and the joint surface. When the slope contains multiple weak layers, it is easy to break along the layer and the back edge of the joint. As the number of weak surfaces increases, the slope stability coefficient gradually decreases.The research results can provide a theoretical basis for the instability mechanism and stability evaluation of bedding rock slopes caused by road excavation and slope cutting, and provide support for the prediction of the bedding rock slope instability.

Containment property is the key to ensuring the safe operation of groundwater-sealed caverns.At present, the main difficulty in studying the water sealing property of groundwater-sealed caverns lies in the strong heterogeneity and anisotropy of fractured rock aquifer.In this paper, a discrete fracture network model is established based on the measured fracture geometry parameters to analyze the fracture development characteristics.Based on the understanding and assumption of the basic law of fracture seepage, a high-precision heterogeneous and anisotropic seepage model is established, and the permeability characteristics of the study area are analyzed.Through the establishment of heterogeneous anisotropic seepage model, the water seal performance of water curtain system is discussed and compared with the traditional homogeneous isotropic seepage model.The model can make up for the deficiencies of the traditional homogeneous isotropic seepage model, and more accurately evaluate the storage leakage risk caused by the heterogeneity and anisotropy of fractured rock mass.