Borehole Resistivity Imaging Method for the Disaster Evolution Process of Tunnel Seepage Instability-Induced Water Inrush

Applicability Analysis of Microseismic Technology in Tunnel Water Inrush Monitoring

Water or mud inrush has become a common geological disaster during tunnel construction in karst areas. To study forming process and mechanism of water and mud inrushes through a filled karst conduit, water inrush and mud inrush model tests were carried out with a self-developed 3D model test system. The results show that the forming processes of water inrush and mud inrush have different forming modes. For water inrush, the forming process follows: flowing instability of filling material particles—formation of water inrush channel—water inrush occurring; while for mud inrush, the forming process follows: stability—sliding instability of the whole filling material suddenly—mud inrush occurring. Accordingly, a local instability model of critical hydraulic pressure causing water inrush and an integral sliding instability model of critical hydraulic pressure causing mud inrush were established respectively. The two analytical models reveal the mechanism of water inrush and mud inrush experiments to an extent. The calculated critical hydraulic pressures for water inrush and mud inrush are in good agreement with the test results. The distinguishment of water inrush and mud inrush through a karst conduit was discussed based on the critical hydraulic pressure and the evolution law of seepage water pressure in tests, and a criterion was given. The research results might provide guidance for the forecast of water and mud inrush disasters during the construction of tunnels in karst area.

By using the principles of porous media seepage mechanics and solute transport theories, a seepage–erosion theory model was developed to uncover the dynamics of mud and water inrush in fault rupture zones during the construction of tunnels. This model consists of a mass conservation equation, a flow transformation equation, a porosity evolution equation, and a permeability evolution equation. These components illustrate the interaction between seepage–erosion particle loss and the transformation of seepage flow patterns throughout the mud and water inrush evolution in the fault fracture zone. This model proves to be effective in illustrating the catastrophic process of mud and water inrushes within tunnels located in fault rupture zones. To address the spatial and temporal variations, the implicit difference and Galerkin finite element schemes were utilized, and the Newton–Raphson iteration method was applied to handle the nonlinear attributes of the equations. The theoretical model underwent further development and numerical simulations were performed using COMSOL multi-field coupling software. A comparison with existing indoor water inrush mud model test results validated the effectiveness of our model. The theoretical model was then applied to the Yong Lian tunnel scenario within the fault rupture zone. This computational analysis exposed the sequence of flow pattern transformations and the instability in seepage–erosion evolution within the fault rupture zone, ultimately leading to the emergence of mud and water inrush disasters. The findings of this study offer valuable insights for addressing tunnel engineering challenges related to underwater inrush disasters.

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.

Borehole resistivity images and dipole sonic data analysis helps a great deal to identify fractured zones and obtain reasonable estimates of the in-situ stress conditions of geologic formations. Especially when assessing geologic formations for carbon sequestration feasibility, borehole resistivity image and borehole sonic assisted analysis provides answers on presence of fractured zones and stress-state of these fractures. While in deeper formations open fractures would favour carbon storage, in shallower formations, on the other hand, storage integrity would be potentially compromised if these fractures get reactivated, thereby causing induced seismicity due to fluid injection. This paper discusses a methodology adopted to assess the carbon dioxide sequestration feasibility of a formation in the Newark Basin in the United States, using borehole resistivity image(FMI™ Schlumberger) and borehole sonic data (SonicScaner™ Schlumberger). The borehole image was interpreted for the presence of natural and drilling-induced fractures, and also to find the direction of the horizontal stress azimuth from the identified induced fractures. Cross-dipole sonic anisotropy analysis was done to evaluate the presence of intrinsic or stress-based anisotropy in the formation and also to obtain the horizontal stress azimuth. The open or closed nature of natural fractures was deduced from both FMI fracture filling electrical character and the Stoneley reflection wave attenuation from SonicScanner monopole low frequency waveform. The magnitudes of the maximum and minimum horizontal stresses obtained from a 1-Dimensional Mechanical Earth Model were calibrated with stress magnitudes derived from the ‘Integrated Stress Analysis’ approach which takes into account the shear wave radial variation profiles in zones with visible crossover indications of dipole flexural waves. This was followed by a fracture stability analysis in order to identify critically stressed fractures. The borehole resistivity image analysis revealed the presence of abundant natural fractures and microfaults throughout the interval which was also supported by the considerable sonic slowness anisotropy present in those intervals. Stoneley reflected wave attenuation confirmed the openness of some natural fractures identified in the resistivity image. The strike of the natural fractures and microfaults showed an almost NE-SW trend, albeit with considerable variability. The azimuth of maximum horizontal stress obtained in intervals with crossover of dipole flexural waves was also found to be NE-SW in the middle part of the interval, thus coinciding with the overall trend of natural fractures. This might indicate that the stresses in those intervals are also driven by the natural fracture network. However, towards the bottom of the interval, especially from 1255ft-1380ft, where there were indications of drilling induced fractures but no stress-based sonic anisotropy, it was found that that maximum horizontal stress azimuth rotated almost about 30 degrees in orientation to an ESE-WNW trend. The stress magnitudes obtained from the 1D-Mechanical Earth Model and Integrated Stress Analysis approach point to a normal fault stress regime in that interval. The fracture stability analysis indicated some critically stressed open fractures and microfaults, mostly towards the lower intervals of the well section. These critically stressed open fractures and microfaults present at these comparatively shallower depths of the basin point to risks associated with carbon dioxide(CO2) leakage and also to induced seismicity that might result from the injection of CO2 anywhere in or immediately below this interval.

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.

In tunnel construction, water and mud inrush disasters are prone to occur when the tunnel traverses water-rich faults, which leads to structural damage and tunnel instability, which is one of the most severe hazards in tunnel excavation and construction. This paper proposes a method of combining AHP and TOPSIS. The weights are determined through the analytic hierarchy process utilizing expert scoring. The determined weights are evaluated and predicted by TOPSIS for water inrush risk. The Jiaozhou Bay Subsea Tunnel is used as a case to carry out the tunnel crossing the fault zone. Water inrush risk prediction provides a new idea for water inrush risk prediction.

This paper presents a case study of the countermeasures of water and mud inrush disasters in the Junchang Tunnel in Guangxi, China. This tunnel was constructed in a weathered granite formation, and four serious water and mud inrush disasters occurred during construction. The geological and hydrological conditions are first reviewed to understand their effects on the water and mud inrush disasters. Four potential causes of the serious water and mud inrush disasters in the Junchang Tunnel were proposed, including the poor stability of the completely weathered granite, the high groundwater level and large groundwater flow rate, insufficient pre-reinforcement of the surrounding rock and the disturbances caused by tunnel construction. Water-sealing and ground reinforcement measures were suggested before excavation to improve the stability of the surrounding rock and plug the water outflow channels, and full-face curtain grouting was considered as the first choice. Furthermore, several improvements, including the combined utilization of various grouting materials, supplementary grouting with steel pipes in collapsed boreholes and dynamically optimized grouting methods, were implemented to solve the serious water inflow and collapse problems experienced during the drilling and grouting work. A detailed curtain grouting scheme was proposed and applied in practice. A comprehensive evaluation based on inspection borehole investigations and P–Q–t analysis indicated that the curtain grouting method yielded satisfactory performance in water sealing and ground reinforcement. In addition, the groundwater level and settlement data collected in the field validated the effectiveness of the proposed countermeasures.

a modified SPH framework of for simulating progressive rock damage and water inrush disasters in tunnel constructions

With the rapid development of the transportation industry in China, the number and scale of tunnel construction are increasing. Tunneling through fault zones and other complex geological environments is becoming more and more common. In the construction of highway tunnels, due to the special geographical environment and complex geological conditions, mud and water inrush often occur in the tunnel. Water inrush disasters pose a major risk to the construction of highway tunnels and affect the normal construction of highway tunnels. This paper combines the engineering background of the tunnel mud and water inrush accidents, carries out evaluation on the accident treatment measures and the treatment efficiency, and summarizes the main concerns in the construction process and the technical guidelines for dealing with the tunnel mud and water inrush.

Experimental and numerical research on the evolution law of precursor information of rock apparent resistivity during the process of water inrush in metal mines

Water inrush disasters in mining frequently occur under the influence of confined water‐bearing fault zones. Therefore, investigating the fault water inrush mechanism is necessary to reduce the number of occurrences of this type of disaster. In fault zones, the rock is highly fractured, and the mechanism of water conduction is complex. In this research, the seepage mechanism of fractured sandstone in fault zones is studied through experiments, and the results indicate that the permeability coefficient of fractured sandstone depends on the axial stress and particle size. The relationship between the permeability coefficient and axial stress was an exponential relationship. Then, a water‐rock coupled model is proposed based on the experimental results, which considers the different water flow patterns during water inrush disasters. Finally, a numerical simulation combined with the water‐rock coupled model is conducted to investigate the fault water inrush mechanism of a case study, and the results reveal that when water inrush disasters occur during mining, two types of conditions are required. One is that the connection among the fractured zone of the coal seam roof, fault fracture zone, and aquifer fails, and the other is that the connection among the fractured zone of the water inrush prevention pillar, fault fracture zone, and aquifer fails. This study contributes to an increased understanding of the mechanism of water inrush disasters and the design of water inrush prevention pillars.

Water inrush disaster is one of the major disasters affecting the production safety of coal mines following roof caving, fire, gas outburst, and dust explosion disasters. It is urgent to reveal the water inrush mechanism and take effective measures to prevent the disasters. More than 80% of water inrush accidents occur around geological structural zones such as faults and karst collapse columns (KCCs). The water inrush events from KCCs caused huge economic losses and heavy casualties, and the water inrush process often shows certain hysteresis characteristics. Taking the water inrush disaster from a KCC during roadway excavation in PanEr Coal Mine of Huainan Mining Area as the case study, the delayed inrush mechanism of KCC was analyzed from the aspects of floor failure, KCC activation, seepage transition, and water inrush development characteristics. The results show that the rock mechanical properties and the excavation depth are the main factors affecting the floor failure characteristics. The seepage transformation from pore flow to fracture flow and pipeline flow, with the change in internal composition structure, is the internal mechanism of the delayed water inrush from KCC. The research is of great significance for the prediction and prevention of water inrush disasters from KCCs.

Tunnel construction in mountain areas, especially in karst regions, is challenging due to complex hydrogeological conditions in such regions, such as water inrush disaster induced by water-bearing structures that may jeopardize tunnel construction safety. To identify potential water inrush sources, this study first analyzed regional hydrogeological conditions of the Yuelongmen tunnel that cross under the river. Then, the tunnel-induced polarization method was employed to probe three-dimensional (3D) spatial location and distribution of water-rich areas. Based on detection results, numerical simulation was carried out to study the corresponding velocity and pressure for each probing line set in the numerical model, and flow characteristics after water inrush were summarized. Finally, optimized evacuation routes were designed to minimize the potential damage caused by the water inrush. Research results may provide critical implications for water inrush analysis and reduce casualties during tunneling in karst regions in China.

Water inrush hazard seriously threatens construction safety of subsea tunnels in unfavorable geological areas. In recent years, a large number of subsea tunnels have been built worldwide, some of which have experienced many water inrush disasters, especially in Japan and Norway. In this paper, a systematic methodology is proposed to rigorously review the current literature about water inrush in subsea tunnels. Emphasis is placed on recorded causes and evolution processes of water inrush, as well as relevant mitigation measures. In particular, the geological conditions that generate such water inrush hazards are initially discussed by counting cases of tunnel water inrush in the past decades (43 cases of water inrush hazards in tunnels (including mountain tunnels)). The process of formation of failure modes of water inrush, and the corresponding research methods (including theoretical, numerical and experimental) are reviewed, and can be used to pave the ways for hazard prevention and future research. This is followed by a summary of the prevention methods and mitigation measures used in practice, and a short discussion of the achievements and limitations of each method. Then combined with the evolution characteristics of the failure area, the water inrush process of different modes is divided into three stages, with a proposed a grouting scheme for each stage. Finally, concluding remarks, current research gaps and future research directions on subsea tunnel water inrush are provided and discussed.