Water Inrush Events Research Articles

Hydrogeological analysis and remediation strategies for water inrush hazards in highway karst tunnels

Geological hazards, particularly water inrush, pose frequent challenges in tunnel constructions within karst regions. Drawing from the engineering experiences in addressing multiple large-scale water inrush hazards in the Dejiang tunnel, a combined method of field investigation and theoretical analysis was employed for qualitative and quantitative analyses of water inrush mechanisms. The regional geological investigation highlighted the formation of strong and weak aquifers due to alternating weak limestone and mudstone in the synclinal strata, creating favorable conditions for large-scale karst conduit. Atmospheric precipitation water connects karst cavities through groundwater-eroded karst conduit, establishing a recharge system for water inrush hazards. Three empirical formulas are adopted to investigate the influence of rainfall on the tunnel’s actual water inflow. Importantly, it was found that considering only the influence of rainfall or surface water cannot reasonably predict the inflow in this area. The disaster’s primary causes are attributed to the heavy rainfall, karst conduit, underground river, and weak strata, which have contributed to the persistent nature of water inrush events. The principle of “drainage and blockage” was used to address the issue of water inrush. Proposed remediation strategies during construction, including the innovative membrane bag high-pressure grouting, have proved to be effective in addressing the connected karst conduits. The drainage and blockage effects were achieved by installing drainage pipes during the grouting reinforcement process. Finally, the water pressure-resistant structure was employed to enhance the stiffness of the lining. As validated by monitoring data, the measures serve as crucial methods to guarantee the safety of tunnel structures, effectively prevent water inrush and amplify the ecological benefits of water-rich areas.

Integrating Microseismic Monitoring for Predicting Water Inrush Hazards in Coal Mines

The essence of roof water inrush in coal mines fundamentally stems from the development of water-bearing fracture zones, facilitating the intrusion of overlying aquifers and thereby leading to water hazard incidents. Monitoring rock-fracturing conditions through the analysis of microseismic data can, to a certain extent, facilitate the prediction and early warning of water hazards. The water inflow volume stands as the most characteristic type of data in mine water inrush accidents. Hence, we investigated the feasibility of predicting water inrush events through anomalies in microseismic data from the perspective of water inflow volume variations. The data collected from the microseismic monitoring system at the 208 working face were utilized to compute localization information and source parameters. Based on the hydrogeological conditions of the working face, the energy screening range and its calculation grid characteristics were determined, followed by the generation of kernel density cloud maps at different depths. By observing these microseismic kernel density cloud maps, probabilities of roof water-conducting channel formation and potential locations were inferred. Subsequently, based on the positions of these roof water-conducting channels on the planar domain, the extension depth and expansion direction of the water-conducting channels were determined. Utilizing microseismic monitoring data, a quantitative assessment of water inrush risk was conducted, thereby establishing a linkage between microseismic data and water (inrush) data, which are two indirectly related datasets. The height of microseismic events was directly proportional to the trend of water inflow in the working face. In contrast, the occurrence of water inflow events and microseismic events exhibited a specific lag effect, with microseismic events occurring prior to water inrush events. Abnormalities in microseismic monitoring data partially reflect changes in water-conducting channel patterns. When connected with coal seam damage zones, water inrush hazards may occur. Therefore, abnormalities in microseismic monitoring data can be regarded as one of the precursor signals indicating potential floor water inrushes in coal seams.

Experimental and Theoretical Study of Seepage Models under Confining Pressure for a Single Rock Fracture

The engineering water inrush events were affected by the hydraulic characteristics of the fractures. In order to quantitatively study the seepage characteristics of the fractures, the experimental analysis of artificial fracture of shale was carried out under different confining pressure (22 MPa – 38 MPa) to explore the influence of confining pressure on seepage characteristics. Three theoretical constitutive formulas to describe the characteristics of seepage were proposed based on cubic law and fracture constitutive equation (Bandis model, Rong model, Sun model), and these theoretical constitutive formulas all had good fitting results to experiment results which indicated that the derived formulas are feasible. The parameters for the three models were compared, among which the Rong model was more suitable to describe the connection between (Q) and (Pc). Rong model and Sun model were highly descriptive to the relationship between (Pc) and (Ps). The formulas that based on three theoretical models can provide quantitative calculation for the influence of in-situ stress change on the seepage of fractures in engineering practice.

Mass-loss effects on the non-Darcy seepage characteristics of broken rock mass with different clay contents

A seepage testing system was designed and a series of seepage experiments on broken rock was conducted using different original porosity conditions and clay contents. The mass-loss process of the broken rock and the change in water flow velocity were investigated. After the mass-loss test, the non-Darcy seepage characteristics of the broken rock were tested through a step-by-step pressure-reduced seepage test. The experimental results show that the mass-loss and water velocity evolution during the water inrush could be divided into four stages: acceleration, stable with slight fluctuations, reacceleration, and stable. The lost-mass and change in water velocity were positively correlated with the clay contents and negatively correlated with the original porosity. By introducing the evolution equation of the Kozeny-Carman equation and the liquid limit index which characterises the effective particle size, the prediction model of the permeability coefficient was built. Six prediction models of the non-Darcy coefficient were verified against the testing results. The prediction model of the critical flow velocity from a Darcy flow to a non-Darcy flow using the Forchheimer number was also established. The results could provide an important reference for understanding water inrush mechanisms, adopting effective control measures for water inrush events, and calculating the water influx of tunnels.

Hydrogeochemical evolution of Taiyuan Formation limestone water under the disturbance of water inrush from karst collapse column in Taoyuan Coal Mine, China

Abstract The project implementation of water inrush and its treatment ensures the safe mining of coal mines, but also causes certain disturbance to the hydrogeochemistry of primary limestone water. Based on the water inrush event in Taoyuan Coal Mine of Huaibei coalfield in 2013, the water rock interaction mechanism of Taiyuan Formation limestone water (namely, ‘Taihui water’) was discussed. The results showed that: (1) the relationship of cation mass concentration before and after water inrush was Na+ + K+ > Ca2+ > Mg2+; the correlation of anionic mass concentration before water inrush was SO42− > HCO3− > Cl−, while it was HCO3− > SO42− > Cl− after the event. Before the event, the main water quality types were SO4•Cl-Ca and SO4•Cl-Na; after the event, they mainly included HCO3-Na and SO4•Cl-Na; (2) There is a strong positive correlation between mineral saturation index and pH value, that is, minerals are easy to dissolve under acidic conditions, while alkaline conditions will inhibit the dissolution and transformation of minerals; (3) The hydrogeochemical processes of limestone aquifer mainly included cation exchange, carbonate dissolution, pyrite oxidation, sulfate and silicate dissolution.

Mechanism Analysis of Delayed Water Inrush from Karst Collapse Column during Roadway Excavation Based on Seepage Transition Theory: A Case Study in PanEr Coal Mine

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.

Field monitoring and numerical analysis of tunnel water inrush and the environmental changes

Groundwater inflow during tunnel excavation and its influences on the hydro-geological environment (HGE) are vital to green construction and environmental sustainability. To evaluate these issues in completely weathered granite formation, a water inrush event occurred in Junchang tunnel is introduced to investigate the changes in HGE including groundwater level, ground surface settlement, surface fractures as well as the tunnel settlement. Then, a seepage-erosion coupling model is developed to predict water inrush and its influences on the HGE changes. This model can describe the characteristics of nonlinear seepage and particle erosion for water inrush and its effectiveness is verified by the field results. Using this model, the potential water inrush and the changes in HGE are evaluated for future excavation in various high-risk positions. Consequently, the real-time water inrush process, the HGE changes and the practical implications are discussed with the field and numerical results. The main research findings include: (1) the evolution direction, mutation time and the volume of the water inrush, and (2) the influenced region, evolution time and the extend of the changes in HGE. These findings can provide references for the early warning, monitoring and prevention for future constructions.

Introduction to Special Issue on Mine Water Inrushes: Risk Assessment, Mitigation, and Prevention

Water inrush is a hazard that affects safety and production in many coal mines in China. Chinese mining engineers and scientists have made significant progresses in predicting, preventing, detecting, and mitigating this unique water hazard. The approximately 20 papers in this special issue present the latest research results and practices in six aspects: water inrush risk assessment, numerical simulation for water inrush prediction, high-resolution site characterization technique, rapid determination of water inrush point and water sources, early warning monitoring techniques, and engineering measures that have been used to prevent and mitigate water inrush events.

Application and Evaluation of Regional Control Technology of Limestone Water Hazard: A Case Study of the Gubei Coal Mine, North China

The coal-forming period is mainly Permian and Carboniferous in the North China coalfield, which is one of the main coal accumulating areas in China. It is characterized by high coal rank, abundant reserves, and varieties. However, water outburst accidents originating from karst aquifers under the coal seam floor have become a terrible disaster in accompany with the deep coal exploited progressively. Water inrush events of the deep limestone have often occurred during excavation in mines. To decrease the risk of high confined water from the coal seam floor and ensure the mining under the safe water pressure of limestone aquifers, the comprehensive exploration and regional treatment are all implemented, such as drainage depressurization, curtain grouting, and grouting transformation of aquifers. Through the comprehensive treatment of the ground and underground, the water channel will be effectively filled with slurry to prevent limestone water bursting into the roadway, and the value of water-inrush coefficient is decreased below the critical value. In the study, utilizing COMSOL Multiphysics based on the finite element method to verify and determine the real layout of grouting parameters, the result shows the design plans satisfy the engineering requirements. 13321 working face located in South No.1 mining area has analyzed the effect of water hazard prevention and control. On the basis of the analysis of geophysical prospecting and validation boreholes, it is concluded that the fracture is filled with grouting slurry to block water-conducting channel effectively. In turn, the rational design parameters of grouting are confirmed as well. Finally, the water-inrush coefficient of Taiyuan formation limestone and Ordovician limestone water is calculated, respectively. The result shows that water-inrush coefficient is less than the critical value after treatment, the safety of excavating coal seam can be further assured.

A New Quantitative Method for Risk Assessment of Coal Floor Water Inrush Based on PSR Theory and Extension Cloud Model

In order to scientifically and reasonably assess the risk of water inrush from the coal seam floor, considering the influence of natural environmental factors such as hydrogeology, mining, and human intervention, the PSR model of ecosystem health evaluation was introduced, and the risk evaluation indicator system of water inrush from the coal seam floor was established. In order to solve the randomness and fuzziness of water inrush event evaluation, the evaluation model is constructed based on extension cloud theory and is applied in the 12123 working face of Pan Er coal mine of Huainan Mining Group. The application results show that the evaluation results are basically consistent with the actual situation, which shows that the model can be used in the actual evaluation work and is scientific.

Mechanism and Control of Water Inrush from Separated Roof Layers in the Jurassic Coalfields

Theoretical analysis, numerical simulation, and borehole drilling were used to study the mechanism of four large-scale water inrush events that occurred during the mining of the 1121 working face in the Hongliu coal mine in the Ningdong mine area. We concluded that the working face inrush was induced by water in the bed separations formed by overlying strata movement caused by the mining process. To control such inrushes, the location, size, and hydrogeological properties of the 18 m thick key aquiclude were investigated. We determined that the best time to drain the bed separation water was between when the beds separated and the roof caved, before water inrush occurred. The best place to drain water from was directly above the key aquiclude. These results should be useful for other sites with similar mine conditions.

Evaluation of changes in groundwater quality caused by a water inrush event in Taoyuan coal mine, China

The effects of a water inrush event on the chemical composition of groundwater in a coal measures sandstone aquifer that is important for water supply was investigated at the Taoyuan coal mine in the Huaibei region in China. Changes in groundwater quality caused by the inrush event were investigated using statistical techniques, a Piper trilinear diagram, saturation index, ion combination ratios and a fuzzy comprehensive evaluation method. These investigations indicated that Na+ + K+ and SO42− were the main cation and anion, and the average contents were 272 mg/L and 732 mg/L before water inrush, and 394 mg/L and 779 mg/L after water inrush, respectively. The concentrations of anions in groundwater before the inrush event were in the order SO42− > HCO3− > Cl− and the cation concentrations were in the order Na+ + K+ > Ca2+ > Mg2+. The chemical composition of groundwater was mainly SO4·Cl–Ca·Mg before water inrush event, and SO4·Cl–Na and Na–HCO3–Cl after this event. According to the saturation index method, gypsum, calcite, magnesite, and aragonite controlling the chemical composition of groundwater were reactive minerals in groundwater system. The oxidation of pyrite, dissolution of sulfate and carbonate minerals were main geochemical process before and after the event; while the oxidation of pyrite and cation exchange were enhanced after the water inrush event. The fuzzy comprehensive evaluation results showed that the type V water accounted for a large proportion of poor-quality groundwater. Groundwater quality in the aquifer near the mine generally deteriorated after the water inrush event.

Study on recognition of mine water sources based on statistical analysis

Models for recognizing the source of underground mine water is the basis for real-time monitoring of the water source in active underground mines. Real-time monitoring of the water source is of great significance for predicting water inrush and controlling flooding disasters. This study used the hydrochemistry data of the main aquifers of the Ningtiaota Coal Mine, Jiaozuo Coal Mine, Xieyi Coal Mine, and Huacheng Coal Mine. Through contrast experiments, the influence of dimension reduction processing of discriminant indexes and the selection of discriminant analysis methods in the recognition of the ability of the mine water source model were analyzed for different sample sizes for hydrochemistry data. The research shows that when the sample size is small, the dimension reduction processing using stepwise discriminant analysis and principal component analysis can significantly improve the model’s ability to recognize the mine water source. The recognition accuracy of the model using the distance discriminant method is significantly lower than that of the other two methods, and the recognition ability of the Bayes model is slightly better than that of the Fisher model. When the sample size is large enough, the dimension reduction processing can no longer improve the recognition ability of the model, and all three methods have the same recognition ability. This study can provide an important reference for the establishment and optimization of mine water source recognition, and it is expected to be significant for the prediction and prevention of coal mine water inrush events.

Model test for water inrush caused by karst caves filled with confined water in tunnels

In this study, a water inrush model test system for high ground stresses and hypertonic tunnels is developed to examine the evolution process of karst cave water inrush events induced by tunnel construction and rainfall. A 3D fluid-solid coupling model test is performed to simulate the tunnel excavation and increasing karst cave water pressure, and the evolutionary mechanism of karst water inrush induced by tunnel construction is revealed. The results indicate that seepage occurs during the tunnel excavation, and water seepage ceases after timely support. During hydraulic loading, the experiment successively obtained the stages corresponding to the occurrence of partial dripping, water streams, support bulging, partial and complete support block falls, and water inrush. The influence of tunnel excavation on the stability of the surrounding rock of the monitoring surface increases sharply when the distance between the tunnel excavation surface and the monitoring surface is approximately 0.5–1 times the diameter of the tunnel. The research results are significant for studies examining the water inrush mechanism and the prevention of tunnel water inrush disasters.

Study on the mechanisms and prevention of water inrush events in a deeply buried high-pressure coal seam—a case study of the Chensilou Coal Mine in China

Coal mine formations are becoming increasingly threatened by water inrush accidents resulting from high-pressure water conditions in limestone formations below mines with increasingly greater mining depths. This paper focuses on the floor of a deeply buried coal seam and the high-pressure fully mechanized mining faces of the Chensilou Coal Mine in China. Based on systematic observations and analysis of the geological and hydrogeological conditions in the study area, this study conducts theoretical analyses, numerical simulations, and underground observations in a comprehensive manner. Accordingly, a systematic and substantive investigation of the deformation and failure of the deep mining floor and the water inrush mechanism (i.e., the high hydraulic pressure within ash-filled fissures) in the Chensilou Coal Mine is carried out. The burial depth is deeper than 761.4 m, and the water pressure in the limestone of the Taiyuan Formation exceeds 4.95 MPa. Furthermore, the mining depth of the working face is 34.25 m. Based on data on water inrush events and subsurface mining failure depth, the water inrush mechanism in the floor of the coal seam in the Taiyuan Formation is analyzed. The end hole depth of the working face is composed of the L8 limestone, and transient electromagnetic detection technology is used to test the grouting effect of the working face floor and ensure the mining safety of the three working faces tested in this study.

Numerical Simulation and Risk Assessment of Water Inrush in a Fault Zone that Contains a Soft Infill

A numerical model was established to simulate the activation of the fault zone with a soft infill during a water inrush event. Distribution of the failed areas at different times was acquired. Then, a parametric sweep analysis was conducted to see the influence of permeability. By analyzing the results, a new parameter called the “activation coefficient” was proposed to characterize the fault zone activation process. A functional relationship was established between the activation coefficient and permeability. A series of numerical cases with different conditions were calculated to determine the parameters in the function. A method to evaluate the risk of water inrush is proposed, based on these results. By comparing the acceptable and actual values of the activation coefficient, the activation speed of the fault zone, and time for excavation and support can be determined; thus, the risk of water inrush can be evaluated. The research results were used during construction of line 1 of the Qingdao subway tunnel engineering project in China, which provided valuable data for assessing the risk of water inrush in a mine.

Experimental and numerical study of the water inrush mechanisms of underground tunnels due to the proximity of a water-filled karst cavern

The mechanism of lagging water inrush in underground tunnel constructions due to the proximity of a karst cavern with confined water is investigated via large-scale physical three-dimensional (3D) model testing and 3D numerical simulations. A new method is proposed for the preparation of modeled karst caverns filled with confined water. The physical 3D model testing is divided into two stages: tunnel excavation and hydraulic pressure loading. Multivariate information is obtained at the two stages using multiple measurement techniques. The results indicate that the displacement, hydraulic pressure, and the developmental trend of the damage zone in the tunnel excavation process are related. It is evident from the physical 3D model testing results that the process of water inrush can be divided into three stages, which include the initiation of group cracks, the formation of a water inrush channel, and the complete collapse of the water-resistant slab. The 3D model testing in conjunction with the 3D numerical simulations reveal that the disturbance due to excavation has an obvious impact on water inrush channel formation. However, an increasing hydraulic pressure in the karst cavern has a greater impact on the collapse of the water-resistant slab. These test results can provide support and guidance for tunnel construction under conditions that are susceptible to water inrush events.

Mechanism and Treatment Technology of Three Water Inrush Events in the Jiaoxi River Tunnel in Shaanxi, China

AbstractWater inrush events in tunnels are geological hazards that pose a special engineering problem for tunnel construction in water-rich areas. To clarify the engineering background and hydrogeo...

An application of hydraulic tomography to a deep coal mine: Combining traditional pumping tests with water inrush incidents

Water inrush incidents threaten the safety of coal mining. Understanding of hydrogeologic parameter distributions is critical for preventing water-related hazards in coal mines. During the deep mining (>1000 m) under the North China Plain, water from water-bearing strata discharges into coal seams through geologic conduits (i.e. water inrush) due to the fractured zone under the floor of working faces. In this study, a water inrush incident was exploited as an active stimulus. A 3D groundwater flow model was built for the eighth member of the Middle Ordovician system in Xingdong coal mine. Using this model and an inverse approach, we first checked if the data from the incident and an independent pumping test carry non-redundant information about the heterogeneity of the mine. Afterward, we combined these datasets to conduct a large-scale (approximately 10 km) hydraulic tomography (HT) analysis. The estimated hydraulic conductivity distribution from the HT analysis is found consistent with the distribution of known geologic faults. That is, a cluster of faults is characterized as a high-conductivity zone. A high conductivity zone is identified at locations close to the water inrush location, which is the high cement consumption zone during the grouting project. Finally, results of this study promote exploiting the water inrush events as a HT survey for mapping geologic structures over a large area.

Alteration characteristics of granite contact zone and treatment measures for inrush hazards during tunnel construction – A case study

Several large-scale mud and water inrush events occurred during excavation of the Denghuazhai Tunnel at a depth of 175 m in the contact zone between geodic granite and tuff. By analyzing the inrush process, the characteristics of the inrush hazards, such as high pressure, abundant water, high mud and sand content and strong destructive power, were revealed. In addition, the inrush hazards were intermittent, uncertain and sudden. An intrusive contact zone between geodic granite and tuff was revealed by regional geological investigation. Large-scale alteration occurred both in geodic granite and tuff near the contact zone. Petrographic analyses indicated that alteration to albite, sericite and kaolinite occurred in geodic granite, and alteration to quartz and montmorillonite took place in tuff gradually toward the contact zone. Furthermore, the changes were gradational within and between various alteration grades. The closer to the contact zone, the higher degree of alteration, the less the primary minerals including quartz, K-feldspar and plagioclase, the more the secondary minerals such as sericite and clay minerals. Tests on porosity, saturated water content and uniaxial compressive strength indicated that alteration led to significant deterioration of physical and mechanical properties of rocks (except for silicified tuff). Especially, for the zonal clay in the central area of contact zone, the physical and mechanical properties were poor and obvious swelling, disintegration and argillation were observed. Tunnel excavation triggered swelling, disintegration and argillation of clay, leading to several large-scale inrush events. In terms of treatment of inrush hazards, first of all, a comprehensive exploration method based on petrographic analyses, geophysical detection and borehole drilling was established according to the alteration characteristics, so as to identify the scale and composition of the altered zone. The principle of “consolidation before removal” was adopted to deal with the inrush deposits for breach sealing and reinforcement. Energy release and stress reduction during tunnel construction and regular drainage during operation were achieved by dewatering measures, namely, “drainage supplemented by sealing, water drainage and solids remaining”. Reinforcement measures, including full-face curtain grouting and double-layer pipe sheds, were adopted to reinforce and seal the highly disturbed rock and soil in advance. Finally, technical measures, including “bench excavation, enhancement of support stiffness and timely installation of secondary support”, were employed to effectively prevent large deformation in disturbed rock masses. With the above measures, the left and right tunnels of the Denghuozhai Tunnel have passed through the altered zone successfully.