Water-rich Fault Research Articles

Study on Mechanism of Water and Mud Inrush in Deep-Buried Large-Section Tunnel Crossing Water-Rich Fault Fracture Zone

Study on Mechanism of Water and Mud Inrush in Deep-Buried Large-Section Tunnel Crossing Water-Rich Fault Fracture Zone

Catastrophe Information Characteristics and Prevention Measures of Water Inrush in Tunnel Approaching Fault with Different Water Pressure

In order to ensure the safety of the tunnel approaching the fault and prevent water inrush disasters, and then take reasonable protective measures, a fault-tunnel-surrounding rock is established by using a three-dimensional (3D) discrete element numerical analysis method, which takes into account the fluid-structure coupling effect. Based on the method of control variables, the catastrophe information characteristics of displacement and water pressure of the surrounding rock of the tunnel face and the corresponding characteristics of changes before the occurrence of water inrush disasters were studied under different fault water pressures during the excavation of the tunnel approaching the water-rich fault. The results show that, during excavation at the same step, displacement and its magnitude in the surrounding rock escalate as fault water pressure increases. The maximum pressure of the water in the surrounding rock is also constantly increasing. As tunnel excavation progresses, at constant fault water pressure, longer excavation distances result in greater axial displacement of the surrounding rock mass and increased water pressure at corresponding positions within the surrounding rock, leading to higher magnitude increases. As excavation proceeds, the displacement and water pressure in the surrounding rock and the increase of its amplitude continue to increase. Pre-reinforcement grouting techniques and pipe umbrella support systems that are very effective protective measures can be determined by a comprehensive approach integrating advanced geological forecasting methods, real-time water pressure detection, and the analysis of stress-strain and seepage pressure field variations in the surrounding rock mass.

Study on Catastrophic Evolution Law of Water and Mud Inrush in Water-Rich Fault Fracture Zone of Deep Buried Tunnel

Study on Catastrophic Evolution Law of Water and Mud Inrush in Water-Rich Fault Fracture Zone of Deep Buried Tunnel

Modeling the Seepage-induced Damage in Water-Rich Fault Zones at Tunnel Faces by Double Point Material Point Methods

During tunnel construction, crossing water-rich fault fracture zones leads to water influx hazards at the tunnel face. Excavation exposes the fault, causing disturbances and changes in the hydraulic gradient. Thus, the tunnel face becomes a low hydraulic head surface. The naturally high permeability of the fracture zone provides a pathway for groundwater flow, resulting in water seepage along the fracture zone and subsequent water influx at the tunnel face. To investigate this interaction, a two-phase double-point material point method was employed aimed at developing a coupled fluid-solid numerical model for excavating submarine fault tunnels. The model incorporates solid-liquid phase interaction, including rock mass permeability, water viscosity, and tunnel geometry. It analyzes the changes in the liquid-phase flow velocity, pore water pressure, and particle trajectories in the fractured zone ahead of the working face after the fracture zone is exposed, revealing the dynamic evolution of water influx following excavation. Additionally, this study discusses the impact of the solid-liquid phase permeability coefficients on the range of water influx hazards. The research findings demonstrate that the two-phase double-point material point method effectively captures the seepage and water influx processes, offering valuable insights into the mechanisms of sudden water influx in tunnel engineering.

Evolution Law and Grouting Treatment of Water Inrush in Hydraulic Tunnel Approaching Water-Rich Fault: A Case Study

Tunnel construction adjacent to the fault fracture zone is prone to water inrush disasters, which pose a serious threat to the safety of tunnel construction. To provide theoretical support for the early warning and prevention of water inrush disasters of the tunnel adjacent to the water-rich faults, a numerical analysis based on the three-dimensional discrete element method (DEM) was performed to study the evolution of the displacement and seepage fields of the water-resistant rock mass of a tunnel adjacent to a water-rich fault during the water inrush process by taking the Xianglushan tunnel as the research project. With reference to the obtained results, a grouting reinforcement scheme was developed, and its effectiveness was evaluated. The results indicated that as the tunnel face approached the water-rich fault fracture zone, the effect of water pressure gradually became obvious, and the displacement at the face continuously increased. When the tunnel face was excavated to the position 5 m from the fault, the displacement at the center of the face changed suddenly with a sudden increase in water pressure. The water-resistant rock mass ahead of the center of the face was damaged, and a water inrush disaster occurred in the tunnel. Numerical simulation results demonstrated the feasibility of the grouting reinforcement scheme. The assessment based on the borehole acoustic waves, borehole TV, geological radar detection, and convergence monitoring as well as the excavation results confirmed that the water inrush disasters in the 2# adit of Xianglushan tunnel adjacent to the water-rich fault were effectively prevented and controlled, which can provide a reference for the prevention and treatment of the frequent water inrush disasters in underground projects constructed in the water-rich fault area.

Evolution mechanism of water-conducting fractures in overburden under the influence of water-rich fault in underground coal mining

Based on the 7618 working face in Yaoqiao coal mine of Datun mining area, the activation mechanism of water-rich faults and the development characteristics of water-conducting fractures in overlying strata under the influence of faults are studied by theoretical analysis, numerical simulation and field measurement in this paper. The research results show that Anderson model and Mohr–Coulomb strength criterion are combined to establish the fault failure mechanical model, and the fault activation criterion under the influence of mining is obtained. FLAC3D numerical simulation results show that with the advance of the working face, the fault begins to be affected by the mining effect of the working face at the distance of 20 ~ 30 m from the fault. Meanwhile, with the advance of the working face, the overburden shear failure range also expands, and the fault fracture gradually expands from top to bottom. The failure zone of the working face roof is connected with the fault fracture zone. Then the fault is "activated" and causes the fault to become a water gushing channel, and finally the water gushing disaster occurs. Through numerical simulation and comparative analysis, the development height of water-conducting fracture is 73.2 m in the absence of fault, and 73.7 m in the presence of fault, indicating that the fault has little influence on the maximum development height of water-conducting fracture. The actual development height of the water-conducting fracture zone in the 7618 working face is 73.97 m and the fracture production ratio is 13.7. The research results can provide theoretical reference for the safe mining of similar working faces across faults.

Mechanical Behaviors and Structure Safety of a Tunnel Crossing a Water-Rich Fault Fracture Zone—A Case Study

To study the potential disasters caused by tunnels crossing water-abundant fault areas, this study takes the Jinyunshan Tunnel as an example, and studies the groundwater flow law between different rock layers, the interaction between surrounding rock hydrostatic pressure and soil pressure, and the mechanical features and safety of the lining during construction by combining field tests and finite element simulation analysis. The results show that the displacement change rate of the tunnel vault reaches 2.8 mm/d, and the maximum earth pressure and hydrostatic pressure are 2.3 MPa and 1.15 MPa, respectively, both at the bottom of the tunnel in section II. When the tunnel enters the fault fracture zone from the V surrounding rock, the bending moment of the lining increases by 222.78% at the left haunch and 60.87% at the bottom of the right wall. The axial force of the right spandrel increases by 2579.2%, and the left spandrel increases by 221.18%. The safety factor of the two sections is greater than 2.4, indicating that the overall structure is in a safe state, but the safety factor of the second right shoulder is 2.54, which is close to the safety threshold of 2.4. The research results provide a basis for the safety design and construction safety of tunnels through water-rich sections in similar fault fracture zones, and provide a reference for reducing groundwater loss and protecting ecological vegetation.

Evaluating construction parameters of HB and CD methods for super large section tunnel: a case study

The double sidewall guide pit and centre cross diagram (CRD) methods are often used for the construction of large-section tunnels through water-rich fault fracture zones due to their long construction time and high construction cost. To shorten the construction period and save costs, the top heading and benching method (HB) and centre diaphragm (CD) can be chosen for construction. The construction parameters of the step and CD methods are optimized to ensure the surrounding rock stability and tunnel safety. By relying on the Tongzi Tunnel, we simulate the excavation of different step heights in the construction of the top heading and benching method (HB) and CD methods through numerical simulation, the laws of tunnel vault settlement, and changes in the surrounding rock stress, initial support axial force, bending moment and safety factor. The study shows that as the height of the upper step increases, the settlement of the vault and the convergence of the periphery increase, the initial support safety factor decreases, and the plastic zone of the surrounding rock increases at 30 m from the target face. The step height for the top heading and benching method (HB) of construction is optimized as follows. The ratios of the upper, middle and lower step heights are 0.45H, 0.35H and 0.2H, respectively. The CD method construction step height is optimized to the left (right) upper and left (right) lower step height ratios of 0.5H and 0.5H, respectively.

A New Quantitative Evaluation Index System for Disaster-Causing Factors of Mud Inrush Disasters in Water-Rich Fault Fracture Zone

The Yonglian tunnel in China has experienced 15 instances of severe water and mud inrush disasters, resulting in a total volume of 53,000 m3 of gushing water and mud. These disasters have caused irreversible environmental damage, including hilltop collapse and soil erosion. To achieve early warning and early management of such disasters, the paper introduced the Fuzzy Comprehensive Evaluation Method into the Analytic Hierarchy Process to establish a new quantitative evaluation index system for the causal factors. As the evaluation method involves expert participation in scoring, it inherently presents certain subjective elements. To further substantiate the validity of our approach, we conducted a series of model tests. Then, the accuracy of the quantitative evaluation indexes was verified through these model tests, indicating that the quantitative evaluation system has important guiding significance for safe tunnel construction, allowing for early warning and management of potential disasters.

Coupled hydro-mechanical analysis for water inrush of fractured rock masses using the discontinuous deformation analysis

Water inrush is one of the most frequent geohazards during tunnel or mining excavation, and the study of the water-resisting stratum is of great significance in mitigating and preventing this disaster. Aiming at the fractured water-resisting rock mass ahead of the tunnel face, the discontinuous deformation analysis (DDA) coupled hydro-mechanical method was adopted to shed light on the failure process of the water-resisting stratum. The coupled method was implemented, including introducing single fracture flow equations, assembling the global conductivity equation, coupling seepage force, and updating the discrete fracture network. Then, after validating the coupled method by comparing the numerical results with theoretical solutions and experimental measurements, a real inrush case of Yonglian tunnel in a water-rich fault fracture zone was simulated to study the influence of the thickness of the water-resisting structure, stratum stress, and seepage force on the evolution characteristic of the geohazard. The simulation results could well depict the failure mechanism of the water-resisting structure, and the obtained results considering the progressive damage were more correspond to practice than those based on continuous assumption, showing the capacity of the coupled method for studying practical engineering geohazards.

Analysis method of the water inrush and collapse in jointed rock mass tunnels: A case study

Water inrush disaster occurs easily when the tunnel is close to the water rich fault fracture zone. To clarify the disaster evolution process and the critical thickness of the water-resistant rock mass is the key problem of the prevention and control of water inrush disaster in jointed rock tunnel. However, the water inrush disaster in jointed rock tunnels involves solid-fluid interaction, and the conventional single-phase numerical method is difficult to realize the real simulation of the disaster. To solve this problem, we gave full play to the advantages of the discontinuous deformation analysis method (DDA) in simulating solid motion and the smoothed particle hydrodynamics method (SPH) in simulating fluid motion, and the two-dimensional DDA-SPH (2D DDA-SPH) method was used to simulation the solid-fluid interaction in the water inrush disasters. Firstly, the 2D DDA-SPH method was used to replicate the solitary wave experiment, named Scott Russell's wave generator, and the result of the simulation was almost the same with experiment, which verified the accuracy of 2D DDA-SPH method in simulating solid-fluid interaction dynamic problems. Secondly, taking the Yonglian Tunnel as the research object, we simulated the water inrush disaster in the F2 fault of Yonglian Tunnel under the condition of different thickness of water-resistant rock mass. Based on the results of the simulation, the critical thickness of water-resistant rock mass was determined, which was about 5m. Lastly, we analyzed the process of the water inrush disasters based on the movement state of the fluid near the water-resistant rock mass. And we divided the process of the water inrush disasters in the jointed rock mass into three stage, which were mutation stage, cataclysmic stage and stable stage, which provided a theoretical basis for the prevention and control of water inrush in jointed rock tunnel.

Numerical simulation of the fluid-solid coupling mechanism of water and mud inrush in a water-rich fault tunnel

This study developed a new model, a 3D coupled computational fluid dynamics (CFD)-discrete element method (DEM) model, by coupling two software programs, ABAQUS and PFC3D, to solve problems related to fluid-solid interaction systems. The complete governing equations and the two-way coupling process between the two software are presented herein. Via Transmission Control Protocol (TCP) socket communication with Python scripting, information between the two software is exchanged in real-time. Then, the classic example in the PFC5.0 documentation was used to verify the model. In the end, the ABAQUS-PFC3D model was employed to simulate the process of water and mud inrush in a water-rich fault tunnel, which could reflect the evolution process of water and mud inrush and track particle movement in a fault zone. The results show that the particles that collapsed inside the fault formed an ellipsoidal distribution during the water and mud inrush in a water-rich fault tunnel. With the continuous loss of particles in the fault into the tunnel, the migration of particles is discontinuous, and a large void appears inside the fault zone. The rapid change of the groundwater flow velocity caused the negative pore pressure. The pressure arch force structure is formed above the ellipsoidal collapse area inside the fault. The principal force field of the fault areas changes from close to the dip of the fault to close to the perpendicular to the fault.

Research on the Safety Thickness of Tunnel Outburst Prevention in Water-Rich Fault Fracture Zone Based on Janssen’s Theory

In the construction of tunnel in water-rich fault fracture zone, when the thickness of outburst prevention is insufficient, it is very easy to cause water and mud inrush engineering accident. Therefore, it is very necessary to study the safety thickness of outburst prevention for this type of tunnel. In this paper, the expression of in situ stress in water-rich fault fracture zone is derived based on Janssen’s theory. Two mechanical models of outburst prevention rock mass are established, and according to the shear balance theory, the calculation formula for the safe thickness of outburst prevention is determined and the parameter sensitivity analysis is carried out. Finally, it is verified by engineering examples and numerical simulation. The results show that: (1) the calculation formula of outburst prevention thickness proposed in this paper is more perfect and shows good prediction effect for deep- and shallow-buried tunnels; (2) the greater the angle α between tunnel axis and fault zone and the dip θ of fault fracture zone, the smaller the critical safety thickness of outburst prevention and the safer it is for tunnel construction; (3) when the fault fracture zone inclines inward relative to the tunnel face, the gravity of the rock mass in the fault zone will lead to an increase in the safety thickness of outburst prevention, and reinforcement measures should be taken during actual construction.

Impact of Water Gushing Influenced by the Relationship between Fault and Tunnel Position

In order to analyze the influence of the position relationship between the fault and the tunnel on the water inrush, the fault is regarded as a constant head boundary, the bounded aquifer is transformed into an unbounded problem by the reflection method, and a simplified calculation model of the tunnel water inrush is constructed. Based on the theory of groundwater mechanics, Darcy’s law, and the linear superposition principle, the calculation expressions of water inflow and structural external water pressure are derived, and degradation analysis is performed. The correctness of the model is verified by numerical simulation and field test data. Afterward, the sensitivity of the characteristic parameters is studied, and the influence mechanism of the grouting structure and faults on the tunnel water gushing is discussed. The research results show that in order to ensure the safety of the secondary support structure of the tunnel, appropriate grouting circle thickness and a permeability coefficient should be set, and the permeability coefficient of the secondary support structure should be appropriately increased. When the seepage is stable, the tunnel water inflow will increase nonlinearly with the increase of the fault dip, and the sensitivity will gradually increase; when the fault dip is fixed, with the increase of the distance from the tunnel, the restriction of the fault on the tunnel is weakened, and the water inflow decreases continuously. In the case project, the theoretical and measured water inflows of the unfaulted section, single-faulted section, and combined-faulted section differ by 13.36%, 12.79%, and 10.85%, respectively. The difference between the theoretical value and the measured value of the outer edge water head height of the secondary support structure was 10.7%, 10.51%, and 13.87%, respectively. The research results can provide a theoretical basis for the calculation and structural design of tunnels in water-rich fault areas.

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.

Optimization Of Curtain Grouting Range for Water-Rich Fault Tunnel

When the tunnel is excavated through the water-rich fault, it is easy to cause the problems of water surge and the instability of the face of the tunnel. The advanced curtain grouting can effectively improve the rock mass quality and water permeability of the fault broken zone, and ensure the safety of the construction. In view of this, MADIS-GTS finite element software is used to establish dynamic excavation models under the conditions of no curtain grouting and curtain grouting. The deformation and water seepage characteristics of the palm surface were compared and analysed to determine the fortification length, optimal grouting thickness and optimal grouting length of the curtain grouting before the fault. The results show that :(1) The timing of the connection between rock mass and fault plastic zone in front of the palm head is roughly the same as the timing of the deformation of the palm head face and the surge of seepage velocity. When the palm head face is about 0.5 times the tunnel diameter from the fault plane, the fortifications length of the curtain grouting should also be 0.5 times the tunnel diameter. (2) The increase of grouting length and thickness will reduce the risk of instability of the palm face. When the grouting length exceeds 12m and the grouting thickness exceeds 3m, the influence on the palm face is not obvious. The research results can provide reference for the curtain grouting design of tunnel through fault in the future.

Analysis of Water and Mud Inrush in Tunnel Fault Fracture Zone—A Case Study of Yonglian Tunnel

Water and mud inrush disaster is easily induced during tunnel construction through water-rich fault fracture zones. In this paper, based on the field data, the process of water and mud inrush in tunnels is introduced in detail, and generation conditions and evolution mechanisms have been analyzed. Results show that the key factors of water and mud inrush include poor strata lithology, abundant groundwater and tunnel excavation disturbance. These key factors provide material conditions, source power and start-up conditions for water inrush, respectively. The evolution process of water and mud inrush can be divided into three stages: generation, development and occurrence. During generation stage, a seepage channel expands continuously, with water flow increasing gradually until a large range of loose zone is formed. During the development stage, a large amount of groundwater and a large range of softened muddy rock mass accumulates around the tunnel. During the occurrence stage, the “protective layer” and initial supports suddenly lose stability and are destroyed. These research results could provide some references for the effective prediction and forewarning of similar engineering disasters.

2D Magnetotelluric forward modelling for deep buried water-rich fault and its application

Water inrush is a common geological disaster during the tunnel construction in the broken zone of deep buried water-rich faults. In order to improve the exploring accuracy of this water-rich faults, we first design four water-rich fault models with different inclined angle (22.5°, 45°, 67.5° and 90°) in 2D Magnetotelluric (MT) forward modelling using the finite element method. The simulation results show that the contour lines of apparent resistivity and impedance phase in these four models have a sparse concave feature, which increases with the inclined angle of the water-rich fault. However, the lateral resolution for the inclined fault in TM mode is better than that of TE model. We finally arranged two MT exploring lines in rocky mountainous area of southwest China to detect the deep buried water-rich fault. The inversion results show four significant low resistivity zones in the two MT measured lines. Combine with the geological data, we found that each two low resistivity areas are coherence with the fracture fault zone. Moreover, considering the forward modelling of the faults, we infer that two fracture faults spread in our study area. One fault F1 is northwest tilt with the inclined angle ~60°, and the other fault F2 is southeast tilt with the inclined angle ~80°. All these were also confirmed by the drilling data. The detections of two tilt water rich faults can effectively avoid potential hazards at this area and the forward numerical simulation can provide abundant theoretical reference for the field measured data.

Semi-analytical solution for water inflow into a tunnel in a fault-affected area with high water pressure

This paper studies the water inflow problem when a tunnel is excavated in the area affected by a water-rich fault from an analytical perspective, and a seepage model considering the influence of the fault boundary is established. In the model, the inclined fault is equivalent to the vertical fault by regarding the volume of water inflow and the distribution of water head as the standard of measurement; then, the image superposition principle is used to transform the seepage problem with a finite boundary into a seepage model in semi-infinite space. In the process of solving the model, the stratum adopts a conformal mapping coordinate system, and the lining and grouting circle adopt the polar coordinate system, both of which are jointly solved. Then, the distribution formula of the water head in the stratum and the semi-analytical solution to water inflow are obtained, and the rationality of the semi-analytical solution is proven by degenerate checking, numerical simulation calculation and engineering case. Finally, the paper analyzes the sensitivity of the water inflow to various influencing factors and finds that the effect of the distance between the tunnel and the water table is less than that of the construction quality of the waterproof measures and more than that of the distance between the tunnel and the fault.

Research on water inrush and mud inrush from water-rich fault fracture zone of deep tunnel in mountainous area

Taking the potential risk of water and mud inrush in the construction of a water conveyance tunnel of a hydropower station as the engineering background, based on the field investigation and data collection, the whole process of tunnel construction is simulated and analyzed by using 3D finite element Midas. The results show that because the tunnel passes through the strong water rich fault fracture zone, the filling material in the fault fracture zone has obvious stress concentration under the coupling action of high stress, high pressure seepage and construction disturbance, and the displacement of the filling material has increased significantly. After the fault fracture zone is exposed, the seepage speed has increased significantly, indicating that water and mud inrush disaster has occurred here. It is suggested that when the tunnel passes through complex water-rich fault, monitoring and early warning and excavation support measures should be strengthened to prevent water and mud inrush accidents. The research results have a certain guiding role for the safe construction of the tunnel project.