Ground Stress Field Research Articles

Integrated approach of predicting rock stability in high mountain valley underground caverns

High mountain valleys are characterized by the development of intricate ground stress fields due to geological processes such as tectonic stress, river erosion, and rock weathering. These processes introduce considerable stability concerns in the surrounding rock formations for underground engineering projects in these regions, highlighting the imperative need for rigorous stability assessments during the design phase to ensure construction safety. This paper introduces an innovative approach for the pre-evaluation of the stability of surrounding rocks in underground caverns situated within high mountain valleys. The methodology comprises several pivotal steps. Initially, we conduct inverse calculations of the ground stress field in complex geological terrains, combining field monitoring and numerical simulations. Subsequently, we ascertain stress-strength ratios of the surrounding rocks using various rock strength criteria. To assess the stability characteristics of the surrounding rocks in the 1# spillway cave within our project area, we employ numerical simulations to compute stress-strength ratios based on different rock strength criteria. Furthermore, we undertake a comparative analysis, utilizing data from the 5# Underground Laboratory (Lab 5) of Jinping II Hydropower Station, aligning the chosen rock strength criterion with the damage characteristics of Lab 5′s surrounding rocks. This analysis serves as the cornerstone for evaluating other mechanical responses of the surrounding rocks, thereby validating the pre-evaluation methodology. Our pre-evaluation method takes into account the intricate geological evolution processes specific to high mountain valleys. It also considers the influence of the initial geostress field within the geological range of underground caverns. This comprehensive approach provides a robust foundation for the analysis and assessment of the stability of surrounding rocks, especially in high mountain valley areas, during the design phase of underground engineering projects. The insights derived from this analysis hold substantial practical significance for the effective guidance of such projects.

Effects of microstructure on hydraulic fracturing and gas–water production in coal reservoirs: A case study of the Dahebian coalbed methane block in Western Guizhou, China

AbstractThe development of coalbed methane (CBM) in China is susceptible to the influence of microstructure. Therefore, it is crucial to understand the extension laws of hydraulic fractures and engineering responses in coal reservoirs affected by microstructure development. Utilizing the Dahebian block in western Guizhou as the study area, this investigation examines the coal reservoir characteristics, fracturing, and drainage engineering analysis of the well DC1 group in the region. The aim is to discuss the spatial distribution characteristics of hydraulic fractures, geological controlling factors influenced by microstructure, and their corresponding engineering responses. The results indicate that, for coal reservoirs unaffected by microstructure, the extension laws of the fracture network in both longitudinal and planar directions are influenced by burial depth and the regional stress field. In the microstructural belt, tectonic stress dominates, causing changes in the ground stress field. Consequently, the hydraulic fracture network deviates from the direction of the maximum principal stress during the extension process. When a secondary fracture is nearby, the hydraulic fracture network extends towards the shortest path radial secondary fracture direction, leading to a rapid increase in fracture width per unit length until it intersects with the secondary fracture. Additionally, the presence of secondary joints near the microfault structure decreases fracturing pressure and results in a dense distribution of the fracture network. This promotes the formation of a complex fracture network, favorable for fracturing. The extension of the fracture network in complex structural development areas is influenced by the microfault structure between wells, which is reflected in the fracturing construction pressure and fluid output. This accounts for the significant variations in the early drainage performance of CBM wells.

Research on stress field inversion and large deformation level determination of super deep buried soft rock tunnel

Understanding the characteristics and distribution patterns of the initial geo-stress field in tunnels is of great significance for studying the problem of large deformation of tunnels under high geo-stress conditions. This article proposes a ground stress field inversion method and large deformation level determination based on the GS-XGBoost algorithm and the Haba Snow Mountain Tunnel of the Lixiang Railway. Firstly, the hydraulic fracturing method is used to conduct on-site testing of tunnel ground stress and obtain tunnel ground stress data. Then, a three-dimensional model of the Haba Snow Mountain Tunnel will be established, and it will be combined with the GS-XGBoost regression algorithm model to obtain the optimal boundary conditions of the model. Finally, the optimal boundary condition parameters are substituted into the three-dimensional finite-difference calculation model for stress calculation, and the distribution of the in-situ stress field of the entire calculation model is obtained. Finally, the level of large deformation of the Haba Snow Mountain Tunnel will be determined. The results show that the ground stress of the tunnel increases with the increase of burial depth, with the maximum horizontal principal stress of 38.03 MPa and the minimum horizontal principal stress of 26.07 MPa. The Haba Snow Mountain Tunnel has large deformation problems of levels I, II, III, and IV. Level III and IV large deformations are generally accompanied by higher ground stress (above 28 MPa) and smaller surrounding rock strength. The distribution of surrounding rock strength along the tunnel axis shows a clear "W" shape, opposite to the surface elevation "M" shape. It is inferred that the mountain may be affected by geological structures on both sides of the north and south, causing more severe compression of the tunnel surrounding rock at the peak.

The Distribution Law of Ground Stress Field in Yingcheng Coal Mine Based on Rhino Surface Modeling

The distribution law of the ground stress field is of great significance in guiding the design of coal mine roadway alignment, determining the parameters of roadway support, and preventing and controlling the impact of ground pressure in coal mines. A geostress inversion method combining Rhino surface modeling and FLAC3D 6.0 numerical simulation software is proposed. Based on the geological data of the coal mine and the results of on-site measurements, a three-dimensional geological model of Yingcheng Coal Mine is established for the geostress inversion, and the distribution law of the geostress field in Yingcheng Coal Mine is obtained. Research shows the following: (1) The horizontal maximum principal stress values of the Yingcheng Mine are between 33.9 and 35.3 MPa, the horizontal minimum principal stress values are between 23.6 and 25.4 MPa, and the direction of the horizontal maximum principal stress is roughly in the southwest to west direction; (2) the three-way principal stress magnitude relationship is σH > σv > σh, indicating that the horizontal stress dominates in the study area, which belongs to the slip-type stress state; (3) The maximum principal stress of No. 3 coal seam is 33.1–34.8 MPa, the middle principal stress is 27.5–29.2 MPa, and the minimum principal stress is 17.3–22.9 MPa. Due to the influence of topography and burial depth, there is a phenomenon of stress concentration in some areas. By comparing the inversion values with the measured values, the accuracy of the geostress inversion is high, and the initial geostress inversion method based on Rhino surface modeling accurately inverts the geostress distribution pattern of the Yingcheng coal mine.

Study on the Mechanism of Water and Sand Leakage in a Foundation Pit Retaining Structure Based on the Computational Fluid Dynamics–Discrete Element Method

The existence of defects in the enclosure structure is the primary cause of water and sand leakage in foundation pits, as well as being a significant source of danger in pit construction, but current research lacks an in-depth investigation of the generation mechanism and gestation process. In this paper, which comprehensively considers the microscopic particles and macroscopic level, the development mechanism of a water and sand leakage disaster in a foundation pit with a water-rich sand layer was studied using the principle of computational fluid dynamics and discrete element method coupled analysis (CFD–DEM); moreover, based on the anisotropy of the particle force and fluid energy analysis, the deformation of the stratum and ground stress field were analyzed. The results show that the stress field will produce a plugging effect at a certain distance from the defect, and the strata exhibit a dominant displacement tendency in the vertical direction, resulting in the emergence of a gradually concave stress relaxation zone and an elliptical contour in the strata displacement map near the defect. The fluid energy describes the displacement of the sand layer very well, and it is separated into the sand layer’s centralized loss region and the major loss area based on the high and low levels of the fluid energy class. The impact of fluid at the defect reaches the maximum kinetic energy, which penetrates the structural weakness and causes the loss of sand particles, and the cross-section of the water influx near the defect gradually expands with the loss of particles, indicating that there is a danger of further expansion of the defect under the impact of water flow. These results have technical implications for the management of water and sand leakage disasters in foundation pit engineering.

Numerical simulation and application of ground stress field in ultra-deep strike-slip faults—taking the FI12 fault zone in the Fuman Oilfield as an example

This study carried out a research on the distribution characteristics of the geostress field of ultra-deep strike-slip faults, aiming to improve the exploration efficiency and development benefits of ultra-deep fault-controlled reservoirs. This study combines multiple geological information, drilling information, seismic data, and seismic attribute analysis. Taking the FI12 fault zone in the Fengman Oilfield as an example, it carried out numerical simulation of the geostress field, clarified the distribution pattern of geostress, analyzed the effectiveness of fracture mechanics, and proposed a reservoir quality evaluation method and production increase strategy based on geostress analysis. The study includes the following three aspects: 1) research on the heterogeneity of fault-controlled fractured carbonate reservoirs: Due to the existence of faults, fractures, and pores, carbonate reservoirs exhibit strong heterogeneity. These discontinuous structures lead to local stress field decreases to varying degrees. By analyzing the changes in geostress, it is possible to infer the development of faults, fractures, and pores. This provides important basis for predicting and evaluating reservoirs. 2) research on the distribution pattern of geostress: The geostress of fractured bodies exhibits a “shell-type” distribution pattern. Inside the fractured body, the geostress values are lower, indicating that this part is a favorable reservoir body. On the outside of the fractured body, the geostress exhibits high-value concentration, and this part has relatively poor permeability and can be regarded as an unfavorable drilling target. 3) research on the relationship between fault-fracture mechanical activity and reservoir quality and production capacity: Geostress and its influence on fault-fracture mechanical activity are directly related to the quality and production capacity of fault-controlled fractured carbonate reservoirs. When deploying well locations and optimizing well trajectories, geostress factors should be fully considered, and reservoir reformation efficiency should be taken into account to promote single well production increases and reservoir economic devel.

Rock-physics modeling of deep clastic reservoirs considering the relationship between microscopic pore structure and permeability

Deep clastic reservoirs often exhibit low porosity and low permeability due to the influence of factors such as the sedimentary environment, the ground stress field, etc. The targeted seismic rock physics model can not only specify the microscopic main controlling factors that effect the macro-elastic response of rocks but also predict the shear wave velocity. Thereby, it guides reservoir prediction. Therefore, constructing a rock physics model that considers the pore-permeability relationship, pore structure, and consolidation compaction of reservoir rocks is especially crucial. However, there is the challenge of constructing direct rock-physics relationships between permeability parameters and elastic or physical property parameters. Consequently, the relationship between permeability and pore type is developed in this study using laboratory measurement data. Building upon this foundation, the calculated elastic modulus of the dry rock skeleton is further corrected by the consolidation compaction parameters and the optimization algorithm. Numerical analysis indicates that permeability parameters introduced in the modeling process can serve as guiding factors for different pore type proportions. Additionally, the compaction coefficient exerts a significant influence on the rock's elastic modulus. The applicability and effectiveness of the modeling are confirmed through the utilization of measured well data from the East China Sea.

Study on the Distribution Trend of Rockburst and Ground Stress in the Hegang Mining Area

As the depth of coal mining increases, rockbursts become more severe, and multiple rockburst accidents have previously occurred, seriously affecting coal mine production safety. With the Hegang mining area as the research object and using field measurement and numerical simulation as the research methods, the geological and tectonic characteristics of each impact mine in the Hegang mining area are analyzed to obtain the tectonic stress field distribution characteristics of each mine and the tectonic stress field distribution trend in the Hegang mining area. The maximum horizontal principal stress and the minimum horizontal principal stress on the energy field in the overrun area of the retrieval working face is analyzed via numerical simulation, and the influence trend of the ground stress on the impact ground pressure is finally obtained. Results show that using the typical working face where rockburst occurs as the geological proto-type, the influence of the direction of the ground stress field, the maximum horizontal principal stress and the minimum horizontal principal stress on the energy field in the overrun area of the retrieval working face is analyzed via numerical simulation, and the influence trend of the ground stress on the impact ground pressure is finally obtained. When the angle is 70°~90°, an energy peak in the overrun area of the working face reaches its maximum. The ratio of the minimum horizontal stress to the vertical stress is positively correlated with the energy concentration in the overrun area of the working face, but its change has a minimal effect on the energy distribution in the overrun area of the working face. When this ratio is increased from 0.6 to 1.4, the peak energy of the simulated working face only increases by 8.22%, and the energy concentration area remains basically unchanged.

Temporal and spatial variation of temperature and displacement fields throughout cross-passage artificial ground freezing

The artificial ground freezing (AGF) method exhibits advantages of non-pollution, a good effect of reinforcement, and water sealing that are widely applied in underground engineering. However, the AGF method would disturb the original ground stress field and cause frost heave and thaw settlement. Therefore, it is significant to study the development of temperature and displacement fields for better and more efficient application of the AGF method. In this paper, a complex three-dimensional model, which considers the deflection arrangement of freezing pipes, the ice-water phase change, the thermal-mechanical coupling, and the nonlinear change of soil parameters comprehensively, has been created to study the temperature and displacement variations throughout the entire construction period of a representative AGF project. The findings demonstrate that the proposed sophisticated model corresponds well with the field monitoring results, which meet the limit value required by the specification. It is determined that each AGF construction period must be taken into account in order to more accurately estimate the freezing effects and environmental influences throughout the AGF project.

Inversion and Analysis of the Initial Ground Stress Field of the Deep-Buried Tunnel Area

The detailed analysis of the initial ground stress distribution law is an important work for the safety of tunnel construction and operation. Especially, the high ground stress phenomenon in the deep-buried tunnel area is common, which has a great impact on the tunnel construction. Based on the on-site measured ground stress data, the analysis of the initial ground stress field by numerical simulation and multiple linear regression is mainly described in this study. Following the comparison and selection of three coefficient estimation methods for the regression equation, the best regression method is selected for inversion and verification. The distribution characteristic of the initial ground stress at different buried depths of the tunnel line is obtained. The inversion results of the initial ground stress in a tunnel area, in China, show that the lateral pressure coefficient gradually decreases with the buried depth increasing, while the overall lateral pressure coefficient is in the range of 1.0–2.0, showing a more significant horizontal tectonic. At the area where the tunnel passes through the fault, a small amount of horizontal tectonic stress is released. The ratio of horizontal principal stress to vertical principal stress is smaller than that on both sides, which is different from the distribution characteristic of lateral pressure coefficient without the impact of fault. It shows that faults have a great influence on ground stress. The lateral pressure coefficient in the area near the fault must be determined according to the on-site measured results.

Elastic-plastic solution of circular hydraulic pressure tunnel based on D-P criterion

This work provides new findings on the theory of D–P failure criterion applied to the study of the analytic solution of the radius and stress of tunnel plastic zone and the periphery displacement of hydraulic pressure tunnel under uniform ground stress field. It focuses on elasto-plastic rock masses with the stage of construction and operation. The results that are obtained are compared to other calculation techniques and show that: The elastic-plastic solution calculated based on the theoretical model is larger than that based on the D-P Criterion, indicating safer conditions. The principal stress varies with the internal water pressure, and it firstly decreases to zero and then gradually increase in the plastic zone. With the internal water pressure keeping increasing to a high level, the principal stress in the elastic zone changes from tangential stress to radial stress in the radial distance-enlarging direction, which tends to reach the geostress. In this condition, the radial distance is related to the value of internal water pressure. The calculation results of this study are demonstrated to be in good agreement with those of numerical simulation under the same conditions.

Time-dependent analyses for ground movement and stress field induced by tunnelling considering rainfall infiltration mechanics

The evaluation of influence of heavy rainfall on tunnel structural construction is a problem being faced by engineers around the world. Current analytical solutions on the tunnelling-induced ground movements are generally based on the normal sunny weather and provide little attention on the rainfall intensity and duration risk. In this paper, a time-dependent complex variable approach is proposed to estimate the deformation and stress of surrounding soils caused by tunnelling considering the rainfall infiltration mechanisms. The modified Green-Ampt model under the assumption of stratification is used to simulate the rainfall infiltration process and the complex function theory is employed to calculate the subregion mapping for the saturated, transitional, and natural layers. The non-uniform convergence deformation boundary is adopted at the tunnel structure opening so as to consider the displacement controlled excavation effects due to tunnelling. The analytical presented solution is then verified by comparisons with a total of three engineering case records. It is revealed that the presented complex variable solution considering the rainfall infiltration mechanism can provide a prediction of surface settlement, soil subsidence and horizontal displacement in good agreements with the field measurements. Finally, the parameters that affect the ground deformation and stress induced by tunneling in rainy day, including the rainfall intensity, saturated permeability, matric suction, initial water content, are studied. The paper contributes to provides a relatively quick and easy way of accurately evaluating the time-dependent feedback in tunnel-soil interaction system involving heavy rainfall as a potential risk in the preliminary design of tunnel structures considering the adverse weather condition.

Development and Application of the 3D Model Test System for Water and Mud Inrush of Water-Rich Fault Fracture Zone in Deep Tunnels

In order to study the evolution process, damage characteristics, and occurrence mechanism of water and mud inrush disaster in deep tunnel fault zone with infiltration instability under complex conditions, a set of the three-dimensional physical model test systems of water and mud inrush flow-solid coupling in tunnel fault zones is developed. The system mainly comprises a rigid test frame, ground stress loading system, hydraulic loading system, multiple information monitoring and acquisition system, and mud and water protrusion recovery system. The system’s main features are that it can meet the model’s simulation of the ground stress field, water pressure, and other complex environments subjected to ground stress, and water pressure gradients can be controlled. The system is characterized by high rigidity, high-pressure strength, visualization, good sealing, and expandability. Taking the water fault zone of a well in the Dazhu Mountain Tunnel of the Darui Railway as the research object, the new fault zone and surrounding rock similar materials applicable to the flow-solid coupling model test are designed using the self-developed flow-solid coupling similar materials. The system is used for model tests to reveal the spatial and temporal changes of the surrounding rock stress field and seepage field during the tunnel excavation process. The test results show that the system is stable and reliable, and the research method and results are of guiding significance to the research of the same type of underground engineering.

Numerical Simulation Analysis of Surrounding Rock Deformation of Expansive Rock Roadway under Humidity Field

Based on the measured distribution law of humidity field, according to the humidity stress field theory, the coupling of the humidity field and the ground stress field is realized, and the humidity field is systematically analyzed. Under the conditions, the influence of the expansion of surrounding rock, lining, buried depth, height-span ratio and horizontal pressure coefficient on the deformation of the surrounding rock of the roadway, the general law of the surrounding rock deformation of the swelling rock roadway is obtained. The results show that the five factors have a certain impact on the approaching amount of the two sides of the surrounding rock and the approaching amount of the roof and floor of the swelling rock roadway, but the degree of influence is different. The order of factors affecting the approach of two sides is lining > expansibility > buried depth > horizontal pressure coefficient > height-span ratio; The order of factors affecting the approach of roof and floor is lining > expansibility > height-span ratio > horizontal pressure coefficient > buried depth. The research results provide valuable suggestions and references for the selection of reasonable support schemes and related design and construction of swelling rock roadways.

Initial ground stress field regression analysis and application in an extra-long tunnel in the western mountainous area of China

The understanding of the initial ground stress field in a deep and long tunnel can help to optimize the support structure design and reduce the occurrence of collapse and other failures in tunnel construction and operation periods. Daxiangling Tunnel is a deep and long tunnel under multiple faults condition, many collapses, rock bursts, and large deformations occurring during construction. This paper presents a study of initial ground stress field regression analysis in Daxiangling Tunnel. A three-dimensional geomechanical model with faults is established first, which satisfies the deformation compatibility equation at the fault location. Then, according to the superposition principle, the distribution of regional stress field under the fault condition is obtained by the method of partition inversion. The results show that the distribution of the ground stress field in the Daxiangling Tunnel areas is mainly tectonic stress. The horizontal stress in the area is greater than the vertical stress, and the extreme value appears at the maximum excavation depth. Owing to fault extrusion shear, the stress relaxation exists in the stratum near the fault. The regression analysis results are generally consistent with the measured results, and the relative error is controlled within 10%. However, owing to the boundary effect of the finite element model, the regression stress values near the tunnel entrance and exit are distorted. This can be corrected by applying a mathematical statistical method to obtain the initial stress field of the Daxiangling tunnels with higher applicability.

Analysis of stress state of transversely isotropic weak rock stratum

In geotechnical engineering excavation and design, in-situ stress field is a factor that engineers must consider. However, in practical engineering, the testing method of in-situ stress in weak rock stratum is not mature, and how to obtain the distribution of in-situ stress field in weak rock stratum efficiently and accurately has become a research hotspot. According to the in-situ stress test results of known rock strata, based on the principle of deformation coordination of adjacent rock strata, the stress state of rock strata which is difficult to carry out in-situ stress test is deduced. It is considered that considering the transverse isotropy of rock strata will greatly improve the prediction accuracy, which is verified by ABAQUS finite element model. The results show that the transverse isotropic model is far superior to the isotropic model in predicting the distribution of ground stress field in rock strata (shale, slate, etc.) with obvious anisotropy. However, the greater the ratio of elastic modulus between horizontal and vertical direction, the smaller the ratio of elastic modulus between horizontal and vertical direction, and the greater the difference between the predicted and measured rock stress states. The obtained conclusions are applied to the estimation of ground stress of Que Ge Ka fault in Litang Tunnel, sichuan-tibet railway, which provides sufficient theoretical basis for the classification of large deformation in the process of tunnel excavation and design.

Numerical simulation of the laws of fracture propagation of multi-hole linear co-directional hydraulic fracturing

Directional rupture is one of the most important and most common problems related to rock breaking. The goal of directional rock breaking can be effectively achieved via multi-hole linear co-directional hydraulic fracturing. In this paper, the XSite software was utilized to verify the experimental results of multi-hole linear co-directional hydraulic fracturing., and its basic law is studied. The results indicate that the process of multi-hole linear co-directional hydraulic fracturing can be divided into four stages: water injection boost, hydraulic fracture initiation, and the unstable and stable propagation of hydraulic fracture. The stable expansion stage lasts longer and produces more microcracks than the unstable expansion stage. Due to the existence of the borehole-sealing device, the three-dimensional hydraulic fracture first initiates and expands along the axial direction in the bare borehole section, then extends along the axial direction in the non-bare hole section and finally expands along the axial direction in the rock mass without the borehole. The network formed by hydraulic fracture in rock is not a pure plane, but rather a curved spatial surface. The curved spatial surface passes through both the centre of the borehole and the axial direction relative to the borehole. Due to the boundary effect, the curved spatial surface goes toward the plane in which the maximum principal stress occurs. The local ground stress field is changed due to the initiation and propagation of hydraulic fractures. The propagation direction of the fractures between the fracturing boreholes will be deflected. A fracture propagation pressure that is greater than the minimum principle stress and a tension field that is induced in the leading edge of the fracture end, will aid to fracture intersection; as a result, the possibility of connecting the boreholes will increase.

穿越多断层公路隧道初始地应力场反演分析

穿越多断层公路隧道初始地应力场反演分析

Back-analysis for initial ground stress field at a diamond mine using machine learning approaches

Exact knowledge for ground stress field guarantees the construction of various underground engineering projects as well as prediction of some geological hazards such as the rock burst. Limited by costs, field measurement for initial ground stresses can be only conducted on several measure points, which necessitates back-analysis for initial stresses from limited field measurement data. This paper employed a multioutput decision tree regressor (DTR) to model the relationship between initial ground stress field and its impact factor. A full-scale finite element model was built and computed to gain 400 training samples for DTR using a submodeling strategy. The results showed that correlation coefficient r between field measurement values and back-analysis values reached 0.92, which proved the success of DTR. A neural network was employed to store the global initial ground stress field. More than 600,000 node data extracted from the full-scale finite element model were used to train this neural network. After training, the stresses on any location can be investigated by inputting corresponding coordinates into this neural network.

Parametric Study on the Ground Control Effects of Rock Bolt Parameters under Dynamic and Static Coupling Loads

Dynamic and static coupling loads (DSLs) are one of the most common stress environments in underground engineering. As the depth of a roadway increases over the life of a mine, the static load of the ground stress field increase multiplies, and the cyclic operation at the working face releases a large amount of dynamic energy. Therefore, deep roadways easily induce dynamic disasters during production. In this paper, a deep roadway numerical model was built with FLAC3D to test the deep roadway under DSLs and was simulated with 16 different support designs. The ground stability in each support condition was examined and compared in terms of the ground deformation and scope of failure. The underlying support mechanism was further analyzed with numerical modeling in view of the deformation in the surrounding rock mass induced by variations in the support parameters. The results show that shortening the bolt spacing is an effective measure to control the deformation of surrounding rock whatever DSLs or static load. Under static load, the larger the anchoring length is, the more stable the surrounding rock is. Under DSLs, end grouting length (S = 600 mm) and full grouting length (S = 1800 mm) can effectively control the deformation of surrounding rocks and enhance the stability of surrounding rocks. The results contribute to the design of supports in the field of underground coal mines and provide a basis for determining the reasonable support scheme for roadways.