Groundwater Inrush Research Articles

Impact of particle transfer on flow properties of crushed mudstones

Karst collapse pillar (KCP) is widespread in North China coalfields, where coal extraction above the Ordovician limestone aquifer is threatened by the abundant supply of water and a very high hydraulic pressure. KCP is composed of rock skeleton and fine fillings, which can be transferred under the effect of water flow, thus KCP usually functions as a channel for groundwater inrush. In order to investigate the mechanism of mining-induced groundwater inrush of KCP which was caused by fine fillings transfer, a self-designed particle transfer permeability testing system was used to test the crushed mudstones’ flow properties, which included fine filling particle transfer rate, porosity increase rate and permeability under the conditions of varying pore pressure, particle size mixture and compaction level (initial porosity). The tests indicate fine fillings transfer is the essential reason for mining-induced groundwater inrush (flow instability) of KCP. The flow properties changeability during fine particle transfer could be divided into four stages, i.e., initial flow stage, flow inrush stage, continued particle flow stage and stable flow stage, and flow inrush stage which is the key point to cause water inrush. Due to the crushing of edges and corners and the adjustment of the structure, the fluctuation of permeability–time relationship mainly distributed in the first two stages, which make a change to flow channel. Moreover, with the increasing of pore pressure, particle size mixture and initial porosity, the water inrush time and stable seepage time decreased more rapidly; the fine fillings, porosity and permeability increased gradually. The efficiency criteria analysis between measurement and calculation permeability shows an empirical equation can fit the relationship between porosity and permeability well, and not all of the pore structures were in flow; this means there was a part of pores that were invalid, but the effective porosity in flow can be treated as calculation value approximately.

Multi-factor evaluation for the water yield properties of coal floor aquifers, based on GIS

Groundwater inrush in mines directly threatens safe coal production. Aquifer yield plays a crucial role during water inrush. Significant accidents occur in areas where aquifer yields are strong. The yield of an aquifer is influenced by many things and, in this study, five for which data are easily acquired were selected as evaluation indices for coal-seam floor aquifer yield. They comprise specific yield, permeability, drilling fluid consumption, aquifer thickness, and fault and fold distribution. Based on these indices, a comprehensive model for evaluating water yield was constructed. Using the Ordovician limestone aquifer below the coal floor of Danhou coal mine, Hebei province, China, as an example, index data relating to aquifer yield were collected and the index weight determined. A geographic information system was used to prepare a thematic map for each driving factor and, subsequently, to superimpose them. Comprehensive water yield evaluation indexes were obtained and, finally, a zonal map of different water yield properties was developed for the research area.

Permeability variations within mining-induced fractured rock mass and its influence on groundwater inrush

This paper is concerned with the evaluation of permeability of fractured rock mass due to the cover stress re-establishment, which is a major factor in controlling water and gas flow rate induced by mining operations in fractured rock. The case study considered in this paper is based on the results of observations of groundwater inrush and a decrease in water inflow from the fractured roof strata due to mining advancing in the Taiping Coalmine, Shandong Province, China. A conceptual model of an effective porous media was used to assess the permeability distribution in the fractured zone induced by coal mining. The cover stress re-establishment in gob fractured rock mass was evaluated using an empirical formula based on the surface subsidence. A simplified conceptual model of the fractured zone was used to evaluate the deformation of fractured zone along with the evaluation of changes in the rock permeability above the gob due to the cover stress re-establishment. These data were then used to calculate the water inflow rate into the panel. Predicted water inflow rates have been found to be in good agreement with those from monitoring data. This study improved the understanding of the mechanisms of the post-mining cover stress re-establishment on permeability change of the overburden fracture rock strata. These results can then be applied for numerical simulations of the process of overburden failure and consequent groundwater inrush due to coal mining.

Effect of mining on shear sidewall groundwater inrush hazard caused by seepage instability of the penetrated karst collapse pillar

Mining-induced groundwater inrush, a type of serious hazard for underground coal extraction, occurs in tunnel or coal face combined with a large volume of groundwater gushing. It has an impartible relationship with geological structures such as karst collapse pillar (KCP), which is widely distributed in North China. To analyze the effect of coal mining on groundwater inrush caused by seepage instability of the penetrated KCP (PKCP), stress and seepage coupling equations are used to model the seepage rule, and a numerical FLAC3D model is conducted to determine the shear stress, damage zone, pore pressure, seepage vectors and effect of damage zone on seepage field development. The results indicate that when PKCP and the surrounding rocks show dislocation, shear failure may occur, which leads to a shear sidewall channel for groundwater inrush. As mining advances, the damage zone in the PKCP and its crushed area develop gradually, and the simulated damage zone development was consistent with observed thicknesses of crushed rocks. Under the effect of the support pressure and unloading of the coal face, an obvious seepage concentrate channel with greater hydraulic head and seepage vectors will form within the edge of the PKCP; then, the shear sidewall channel will gradually move to the other side with the coal face near and away. When the damage zones are crushed through, the connected fractures will become a strong seepage channel in PKCP, named as pipe flow, which may cause groundwater inrush.

An experimental investigation on the permeability of chemically grouted sands and its application for mitigating underground sand and water inrushes

This paper presents an experimental investigation on the hydraulic conductivity of coarse sand samples before and after chemical grouting. A newly developed device that applies aerostatic pressure is used to prepare the chemically grouted sand, which can also be used to simulate grouting into soil mass at different depths with different pumping pressures. A static high-pressure triaxial test system is then used to investigate the permeability of the chemically grouted sands under a high confining pressure. The experimental results show that chemical grouting obviously reduces the permeability of sand. The results also show that the hydraulic conductivity of the chemically grouted coarse sand increases with increased hydraulic gradients at a constant confining pressure. The hydraulic conductivity of the chemically grouted sand is generally reduced with increased confining pressure. However, under a high confining pressure, the hydraulic conductivity is increased with increases in the confining pressure owing to the rupture of the particles or samples. A case history is then presented, which uses chemical grouting to control groundwater seepage into a deep coalmine shaft and thus demonstrates the feasibility and durability of the use of chemical grouting as a ground treatment to prevent groundwater inrush from sand aquifers.

Compaction and seepage properties of crushed limestone particle mixture: an experimental investigation for Ordovician karst collapse pillar groundwater inrush

As mining activity rapidly develops to deeper and deeper ground, there have been an increasing number of groundwater inrush events occurring in China. The Ordovician limestone karst collapse pillar (KCP), which contains a lot of crushed rocks, usually functions as a channel for groundwater inrush. The factors, such as the geological conditions, groundwater flow and extraction percentage of coal seam in underground mines, are the main causes of recompaction and permeability change of crushed rock particles in KCP. The high permeability of rock will cause large volumes of groundwater flow, thus posing a great threat of loss of lives in the mines. It is important to take into account the compaction and seepage behaviors of the crushed rocks in Ordovician limestone KCP. The MTS815.02 system and a self-designed water flow apparatus were used to investigate the effect of particle size distribution on compaction and seepage behavior of crushed limestone particle mixture. The Reynolds number calculation of particle mixture shows that the seepage has been influenced by non-Darcy flow. Testing results indicate that the effective porosity of crushed limestone sample is strongly influenced by compaction and particle size distribution. The effective porosity decreases with the increase in compaction and decrease in larger particle size, respectively. Particle crushing during compaction is a main cause of size 0–2.5 mm materials, whereas some fine particles are washed away due to the effect of water seepage, which is a main cause of weight loss. Non-Darcy seepage properties of the crushed limestone are strongly influenced by compaction and particle size distribution. In general, during the compaction, the permeability decreases while the non-Darcy coefficient increases with the decreasing of effective porosity. The effective porosity, particle crushing and seepage properties of crushed limestone are not only related to compaction levels and mixture sizes but also to style of arrangement and initial pore structure.

Risk Assessment of Coal Floor Water Inrush from Underlying Aquifers Based on GRA–AHP and Its Application

Ground water inrush from underlying coal seam aquifers is a serious geohazard during coal mining in China. In order to effectively predict coal floor water inrush, the evaluation index system and evaluation standard for coal floor water inrush, containing quantitative indexes and qualitative indexes, is established on the base of conditions of aquifer and aquiclude, geologic structure and mining disturbance. Simultaneously, grey relational analysis and analytic hierarchy process are used to establish an evaluation model which efficiently overcomes the uncertainty between indexes of water inrush effects and really reflects the degree of importance for each index of water inrush effects. The model is applied to the typical working face of Yuzhou coalfield in the north of China to demonstrate the evaluation process. Compared to the water inrush coefficient method which is widely used for evaluating coal floor water inrush, the presented evaluation model in this paper accords more with the susceptibility of coal floor water inrush by multi-factor and is of nonlinear dynamic characteristics of highly complicated formation mechanism. This method offers a new tool in the assessment of ground water inrush in mine.

Experimental investigation on sealing efficiency of chemical grouting in rock fracture with flowing water

This paper presents an experimental investigation of the main factors that influence the sealing efficiency of chemical grouting in a permeated fracture replica. Chemical grouting has been widely used to control groundwater inrush in underground mining. However, the relationship between the sealing efficiency of grouting and its influencing factors is one of the many critical issues that still remain unsolved. The four factors tested in the orthogonal experiment include the fracture aperture width, initial water flow speed, gel time, and grout take. The sealing efficiency is evaluated and graded by the reduction of water drainage through the fracture after grouting. The experimental results of the orthogonal arrays show that two most influencing factors on sealing efficiency are the initial water flow speed and the aperture width, where the former has a higher impact than the latter. In a comparison with the two other factors, it is found that the grout take and gel time have less influence. The patterns of grout propagation are classified into four types: (1) total sealing off; (2) partial sealing off with erosion along boundaries; (3) partial sealing off with internal erosion; and (4) total erosion. The interaction between the injected grout and flowing water slows down the water flow and the grout starts to solidify at a downstream location where the retention time for grout is longer than its gel time.

In situ Measurement of Hydraulic Properties of the Fractured Zone of Coal Mines

A review of the literature on the water inrush of underground openings under a condition of water flow reveals that insufficient attention has been devoted to the measurement of hydraulic properties of fractured zones, such as faults and zones of plastic damage generated by excavation or mining. A conceptual sketch of the fractured zone is presented in Fig. 1. The zone of floor damage is a zone of deformation and failure of the floor rock formation resulting from mining. In particular, groundwater inrush from aquifers underlying mining coal seams are usually induced when uncovering the fractured zone, which is a geological structure extensively distributed in the coalfields of eastern China (Bai et al. 2013). Moreover, the Ordovician limestone underlying the coal seams of coalfields in eastern China forms a confined karst aquifer containing an abundant supply of water and having very high water pressure (Zhang 2005). In this regard, the hydraulic properties in the fractured zone are important to deep underground engineering, particularly when an aquifer surrounds an excavation, for the reason that most water inrush accidents relate to the fractured zone (Fahimifar and Zareifard 2009; Qiao et al. 2013). Laboratory tests are commonly conducted to determine the hydraulic properties of soft soils and rocks (e.g., Ponziani et al. 2011; Bo et al. 2014). There has been an increasing emergence of in situ testing methods as alternatives to laboratory testing methods for assessing the hydraulic characteristic of the fractured zone in civil engineering (Bo et al. 2014); e.g., the water injection test (WIT) is conducted to determine the hydraulic characteristics of the fractured zone (Mukai and Fujimori 2007; Kitagawa et al. 2007). However, laboratory tests of the fractured zone are subject to uncertainties due primarily to disturbances that cause an important difference in hydraulic conductivity between the in situ and laboratory test methods (Bo et al. 2014). In situ tests are particularly useful in the determination of the in situ hydraulic conductivity of the fractured zone. In situ tests have an advantage over other methods in that they effectively measure the in situ hydraulic conductivity. The key objective of this technical note is to report the measured hydraulic properties in the fractured zone under mutative water pressures by conducting an in situ WIT.

Risk Assessment of Ground Water Inrush from Underlying Aquifers Based on Fuzzy Comprehensive Evaluation and its Application

Mining operations in China are often threatened by frequent water inrushes from confined karst aquifers, We need to evaluate the risk from water-inrush from coal floors in order to have safe production in mines. water inrush risk assessment method based on fuzzy comprehensive evaluation is introduced in this paper. A secondary fuzzy comprehensive evaluation system is constructed to evaluate the risk of floor water invasion in coal mines. Four first-grade indices and fifteen second-grade indices are determined based on the principles. The weight of every index is rationally distributed by analytic hierarchy process (AHP). Finally applying the evaluation model based on fuzzy comprehensive evaluation to evaluate floor water disasters of Yuzhou coalmine in Hebei, the evaluation results are accurate. It can provide certain reference and basis for the evaluation of water-inrush from coal floor forecast for the future.

Groundwater inflow prediction model of karst collapse pillar: a case study for mining-induced groundwater inrush risk

The prediction of groundwater inflow in karst collapse pillar has an important impact on safety underground mining, and the occurrence of these groundwater disasters is likely to be controlled and decreased via establishing an accurate groundwater inflow prediction system. However, the relationship between groundwater inflow and the factors such as geological structure, hydrogeology, aquifer, groundwater pressure, groundwater-resisting layer, mining damage and so on can be highly nonlinear, so it is difficult to establish a suitable model using traditional mechanics methods to predict the groundwater inflow and inrush risk using time series data. It is appropriate to consider modelling methods developed in other fields in order to provide adequate models for rock behaviour on groundwater inflow, nonlinear grey Bernoulli model (NGBM) is a new grey prediction model which is a simple improvement of GM(1,1) together with Bernoulli differential equation. This paper presents a new parameter optimization scheme of NGBM using the genetic algorithm (GA). The power index r of Bernoulli differential equation and production coefficient of the background value are considered as decision variables, and the prediction mean absolute percentage error is taken as the optimization objective. Parameters optimization of NGBM was formulated as the combinatorial optimization problem and would be solved collectively using GA. The model can be optimized once the GA finds the optimal parameters of NGBM. NGBM with this parameter optimization algorithm is then applied in time series groundwater inflow prediction system. Results of long-term groundwater inflow prediction show that GA is an effective global optimization algorithm suitable for the parameter optimization of NGBM and the NGBM-GA model is suit for the groundwater inflow and inrush risk prediction. After grouting reconstruction, the groundwater inflow is decreased and there is no groundwater inrush risk in the process of mining.

Prediction of Groundwater Inrush into Coal Mines from Aquifers Overlying the First Coal Seam in Eastern Ningxia Coalfield, China

In the region where Eastern Ningxia coalfield locates, with the fragile eco-environment and the relative short water resources, it is significant to make clear the influence of coal mining on the groundwater in this region. According to analyses of water-filling factors for the 21 mine fields in the 7 mining areas and 1 independent mine field of Eastern Ningxia coalfield. Firstly, this paper selects the formula in the regulations on the preserving of the coal pillar and coal mining under buildings, water, rail and main shafts (regulations for short) and the Standard on the Exploration of Hydrogeology and Engineering-Geology in the Mining Area (GB12719-91) (standard for short) to calculate the height of water-flow fractured zone in the first coal seam mining, and compares the analysis results of the above formula to the observation data of 3 working faces, and determine the estimated method on the height of water-flow fractured zone, and then use “three maps-two predictions” method to complete the criterion of aquifer water-enrichment and inbreak in safety of the first coal seam. Finally, analyzing the influence of coal mining on the direction of groundwater and recharge-runoff-discharge conditions, the final comprehensive division program on the risk of the groundwater inrush is presented. The research results served as the general guidelines for the mine operations.

Mechanical behavior of a coal seam penetrated by a karst collapse pillar: mining-induced groundwater inrush risk

A karst collapse pillar (KCP) is caused by the karst subsidence that occurs in carbonate rock distribution areas. Current KCP studies focus mainly on aspects such as the cause of formation, rule of development, groundwater inrush, and structural characteristics of the pillar and sidewall rock body. However, few existing studies focus on the influences of mining activity on the damage to KCP, its surrounding rocks, and the formation of the fracture zone, especially the mechanical behavior. In this paper, a numerical fast Lagrangian analysis of continua in three dimensions model was created to understand the mechanical state of a coal seam penetrated by a KCP during mining panel extraction. The numerical results suggest that (1) because of the structure defect, the stress field strongly depends on the mining activity, and the stress distribution varies in different parts of the KCP; (2) KCP and the surrounding rocks show dislocation when the working face passes the KCP, at which point shear failure may then occur, which will lead to a sidewall channel for groundwater inrush; and (3) as mining advances, the plastic zone in the KCP and its broken area develop gradually until the upper and lower plastic zones connect when the working face passes the KCP, which will cause a channel for groundwater inrush.

Groundwater outbursts from faults above a confined aquifer in the coal mining

Groundwater outburst has an impartible relationship with geological structures such as water-conducting faults, which are widely distributed in north China. In order to study the seepage property and mechanism of water outburst from the faults above a confined aquifer in the coal mining, the simulation model of ground water inrush for fault was designed. The water outburst parameters, such as water inflow, permeability, seepage velocity, porosity and other variables under different material combination and water pressures, were obtained; the research results indicate as follows: (1) The changes of the water inflow can be divided into three stages, i.e., the water inflow slowly increases at the early stage, rapidly increases at the middle stage and keeps unchanged at the late stage. (2) The seepage process can be represented by the seepage combination types, which are composed of pore flow, fissure flow and pipe flow, and the seepage changes not only with time but also with different conditions. (3) Mining would lead to the reactivation of faults and further enhance the permeability of fault zone potentially. The tiny granules in fault would be eroded and moved to exterior as the time under the high water pressure and lead to the change of porosity parameters. In this case, the seepage velocity would increase ceaselessly, and then the seepage would convert into pipe flow and finally lead to water inrush accidents.

Typical Techniques and Equipment for Coal Mine Water Hazards Prevention and Control

Some of the most classical technologies and equipment for coal mine water hazards prevention and control are prevented in this paper. In addition, the application of these technologies and equipment is introduced. The typical technologies and equipment for coal mine water hazards prevention and control can be divided into four groups: exploration technology and equipment; monitoring technology and equipment; forecasting technology and equipment; groundwater inrush controlling technology and equipment.

Mechanical behavior of groundwater seepage in karst collapse pillars

Groundwater inrush has an impartible relationship with geological structures such as karst collapse pillars (KCPs), which are widely distributed in North China. In order to study the mechanism of groundwater inrush from coal seam floor, the variable mass dynamics and nonlinear dynamics were introduced. A mechanical model–plug model is established to describe the behavior of water seepage flow in coal-seam-floor containing KCP. The study shows that: (1) If the mass of the KCP keeps steady, the water seepage velocity in the KCP and the surrounding rocks will reach a constant value soon; (2) if the mass of the KCP and the surrounding rocks increases by grouting, etc, the seepage velocity in the KCP and the surrounding rocks will reach its minimum value gradually, and (3) if the mass of the KCP and the surrounding rocks decreases by scouring, the flow velocity in the KCP and the surrounding rocks shows a monotone increase, the water flow may change into pipe flow, especially when a large number of the mass of the KCP and the surrounding rocks enters into goaf road, which may lead to instable flow and cause groundwater inrush.

Groundwater Inrush Channel Detection and Curtain Grouting of the Gaoyang Iron Ore Mine, China

The complex hydrogeological conditions of the Gaoyang Iron Mine area were responsible for two water inrush accidents that occurred during tunneling at the horizontal level of −245 m on August 17, 2000 and August 29, 2004. Borehole computerized tomography in the key areas of the mine and groundwater level monitoring data were used to identify the main underground hydraulic channel and its characteristics. A grout curtain, designed and emplaced based on the results of this study, was highly effective in reducing the groundwater levels in the mine area and amount of water pumped from the mine.

地下水向雪山隧道的排泄对台湾北部水资源的影响

The Hsueh-Shan tunnel is the fifth longest road tunnel in the world. During the excavation, the tunnel encountered several events of groundwater inrush, causing serious delay of the construction. Data on groundwater discharge to the tunnel were gathered from the monitoring system and their spatial and temporal variations were analyzed. The results of the integrated analysis of groundwater discharge and local precipitation indicated that the discharge increased rapidly when the cumulative rainfall exceeded 85 mm. The groundwater level recession rate after a rainfall event was found to be independent of rainfall intensity. A hydrogeological conceptual model was developed to simulate the long-term groundwater discharge to the tunnel. Sensitivity analysis was first conducted to identify sensitive parameters, and then the calibration process was accomplished by the automated parameter estimation method. The calibrated model was then used to evaluate the potential impact of tunnel excavation on the Feitsui reservoir; the average percentage loss of inflow to the Feitsui reservoir from 2006 to 2010 is estimated to be 1.74 %. The developed model can provide a tool for evaluating the regional hydrogeologic setting and the influence of tunnel construction on water resources.

Water Inrush Monitoring of Zhangmatun Mine Grout Curtain and Seepage-Stress-Damage Research

Based on extensive literature review, the state of the art of coupled hydromechanical models and in-situ monitoring for groundwater inrush predictions are summarized in detail, based on which, it is proposed that the key issues for describing the seepage characteristics during groundwater inrush are to calibrate the equations for damage-induced evolution of permeability and of effective stress. Depending on in-situ experiments and numerical simulations, a new academic idea, i.e.“the rock micro seismicity induced by mining processes and water pressure disturbance is in essence the index of groundwater inrush” is put forward based on case studies, coupled hydro-mechanical theory, high-performance computing technology and microseismic monitoring. The authors propose that the tendency for analyzing and predicting the groundwater inrush is to synthetically inverse the inrush pathway formation, strata microseismic precursor and high performance computing results. And relying on the microseismic monitoring events, the groundwater inrush models are calibrated, which could be used to clarify the precursory characteristics and to locate the inrush pathway. This study will lay theoretical basis for establishing the models to predict the groundwater inrush in underground mining. Key words：rock mechanics, groundwater inrush models, calibrating, numerical simulation, microseismic monitoring

Numerical Modeling and Solution of Ground Water Inrush at the Baixiangshan Iron Mine

The Baixiangshan iron mine is a large scale underground mine under construction, and will be put into production in 2011. As hydro-geological conditions of the mine are extremely complicated, ground water inrush happened twice during excavation of the ventilation shaft in 2006 and 2009 respectively. The purpose of this paper is to control the ground water inrush and guide the safety production of the mine. Hence, the ground water state was firstly analyzed through the data of borehole and hydrologic geology. After that, hydro-geological models of the ground water system were built up. According to the hydro-geological models, mathematical models of the ground water were established. With the help of the software of Processing Modflow for Windows (PMWIN), the numerical model of the ground water was set up. Then, by using the SOR (Successive Over-Relaxation) iterative method, the numerical equations were solved. Finally, the district ground water inflow rate on the main mining levels and the dangerous districts of the ground water inrush was figured out. The results of the numerical solution are significant to the control of ground water inrush in the Baixiangshan iron mine.