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Application of the Hybrid Finite Element Mixing Cell method to an abandoned coalfield in Belgium
Abstract
The Hybrid Finite Element Mixing Cell (HFEMC) method is a flexible modelling technique particularly suited to mining problems. The principle of this method is to subdivide the modelled zone into several sub-domains and to select a specific equation, ranging from the simple linear reservoir equation to the groundwater flow in porous media equation, to model groundwater flow in each sub-domain. The model can be run in transient conditions, which makes it a useful tool for managing mine closure post-issues such as groundwater rebound and water inrushes.
The application of the HFEMC method to an abandoned underground coal mine near the city of Liege (Belgium) is presented. The case study zone has been discretised taking advantage of the flexibility of the method. Then, the model has been calibrated in transient conditions based on both hydraulic head and water discharge rate observation and an uncertainty analysis has been performed. Finally, the calibrated model has been used to run several scenarios in order to assess the impacts of possible future phenomena on the hydraulic heads and the water discharge rates. Among others, the simulation of an intense rainfall event shows a quick and strong increase in hydraulic heads in some zones coupled with an increase in associated water discharge rates. This could lead to stability problems in local hill slopes. These predictions will help managing and predicting mine water problems in this complex mining system.
... Figure 2 shows a simplified plain view (2a) and cross section (2b) of the modeled mine. [39,40] is the finite element numerical code we used to develop the groundwater numerical model. This code solves the groundwater flow equation (Equation (1)) based on a mixed formulation of Richard's equation proposed by Celia et al. [41] using the control volume finite element (CVFE): ...
... The main reason we choose SUFT3D is because it has certain capabilities specifically designed for modelling underground mines, improving the realism and the results of the groundwater numerical model. Specifically, underground cavities were simulated as linear reservoirs using the hybrid finite element mixing cell (HFEMC) method [39,40] implemented in the SUFT3D code [44][45][46]. This method combines physically-based and spatially distributed models as well as black-box models. ...
... Single mixing cells were used to discretize the underground cavities (i.e., chambers) that are modelled as linear reservoirs, which is similar to the box model approaches that consider a mean hydraulic head for the whole cell. The groundwater exchange between the domains modelled as linear reservoirs and those modelled as porous medium varies linearly [47] and is governed by the following internal dynamic Fourier boundary condition (BC) [40]: ...
Featured Application
This work evaluates the influence of groundwater exchanges occurring in the context of underground pumped storage hydropower using abandoned mines on the efficiency and on the environment. The findings are useful to define (1) design criteria of future underground pumped storage hydropower plants and (2) screening methodologies to choose the best places to construct them.
Abstract
Underground pumped storage hydropower (UPSH) is an attractive opportunity to manage the production of electricity from renewable energy sources in flat regions, which will contribute to the expansion of their use and, thus, to mitigating the emissions of greenhouse gasses (GHGs) in the atmosphere. A logical option to construct future UPSH plants consists of taking advantage of existing underground cavities excavated with mining purposes. However, mines are not waterproofed, and there will be an underground water exchange between the surrounding geological medium and the UPSH plants, which can impact their efficiency and the quality of nearby water bodies. Underground water exchanges depend on hydrogeological features, such as the hydrogeological properties and the groundwater characteristics and behavior. In this paper, we numerically investigated how the hydraulic conductivity (K) of the surrounding underground medium and the elevation of the piezometric head determined the underground water exchanges and their associated consequences. The results indicated that the efficiency and environmental impacts on surface water bodies became worse in transmissive geological media with a high elevation of the piezometric head. However, the expected environmental impacts on the underground medium increased as the piezometric head became deeper. This assessment complements previous ones developed in the same field and contributes to the definition of (1) screening strategies for selecting the best places to construct future UPSH plants and (2) design criteria to improve their efficiency and minimize their impacts.
... The groundwater numerical model is developed using the finite element numerical code SUFT3D [35,36]. This code uses the Control Volume Finite Element (CVFE) method to solve the groundwater flow equation based on the mixed formulation of Richard's equation proposed by Celia et al. [37]: ...
... The underground cavities, in this case the underground chambers of the Martelange slate mine, are modelled as linear reservoirs taking advantage of the Hybrid Finite Element Mixing Cell (HFEMC) method. The HFEMC method [35,36], which is implemented in the SUFT3D code [40][41][42], is a flexible method combining advantages of black-box models together with physically based and spatially distributed models. Basically, the HFEMC method allows dividing the domain into different subdomains according to their nature. ...
... These linear reservoirs are equivalent to a box model technique where only a mean hydraulic head is calculated. In terms of hydraulic behaviour, the linear reservoirs are equivalent to zones discretised with finite elements with a very high hydraulic conductivity and a porosity of 1. Groundwater exchange between linear reservoirs and porous medium varies linearly as function of the water level difference between them [43] according to an internal dynamic Fourier BC [36] defined as follows: ...
Underground pumped-storage hydropower (UPSH) is a promising technology to manage the electricity production in flat regions. UPSH plants consist of an underground and surface reservoirs. The energy is stored by pumping water from the underground to the surface reservoir and is produced by discharging water from the surface to the underground reservoir. The underground reservoir can be drilled, but a more efficient alternative, considered here, consists in using an abandoned mine. Given that mines are rarely waterproofed, there are concerns about the consequences (on the efficiency and the environment) of water exchanges between the underground reservoir and the surrounding medium. This work investigates numerically such water exchanges and their consequences. Numerical models are based on a real abandoned mine located in Belgium (Martelange slate mine) that is considered as a potential site to construct an UPSH plant. The model integrates the geometrical complexity of the mine, adopts an operation scenario based on actual electricity prices, simulates the behavior of the system during one year and considers two realistic scenarios of initial conditions with the underground reservoir being either completely full or totally drained. The results show that (1) water exchanges may have important consequences in terms of efficiency and environmental impacts, (2) the influence of the initial conditions is only relevant during early times, and (3), an important factor controlling the water exchanges and their consequences may be the relative location of the natural piezometric head with respect the underground reservoir.
... Groundwater modelling in mining contexts is challenging because they correspond to mixed contexts involving porous media and large voids (Adams and Younger, 2001;Ghasemizadeh et al., 2012;Rapantová et al., 2007;Sherwood and Younger, 1994;Surinaidu et al., 2014). The Hybrid Finite Element Mixing Cell (HFEMC) method (Brouyère et al., 2009;Wildemeersch et al., 2010), implemented in the SUFT3D code (Brouyère, 2001;Brouyère et al., 2004;Carabin and Dassargues, 1999), is a flexible method combining advantages of black-box models together with physically based and spatially distributed models. The HEFMC method allows working with mixing cells corresponding to linear reservoirs and finite elements of porous medium together in the same mesh. ...
... The HEFMC method allows working with mixing cells corresponding to linear reservoirs and finite elements of porous medium together in the same mesh. Interactions between zones are considered thanks to internal boundary conditions (Brouyère et al., 2009;Wildemeersch et al., 2010). ...
... A full description and verification of the HFEMC method was presented by Brouyère et al. (2009). Wildemeersch et al. (2010) used the method for a mined area in Belgium. The principle is to divide the modeled zone into several subdomains. ...
In the actual evolving energy context, characterized by an increasing part of intermittent renewable sources, the development of energy storage technologies are required, such as pumped storage hydroelectricity (PSH). While new sites for conventional PSH plants are getting scarce, it is proposed to use abandoned underground mines as lower reservoirs for Underground Pumped Storage Hydroelectricity (UPSH). However, the hydrogeological consequences produced by the cyclic solicitations (continuous pumpings and injections) have been poorly investigated. Therefore, in this work, groundwater interactions with the cyclically fill and empty cavity were numerically studied considering a simplified description of a slate mine. Two pumping/injection scenarios were considered, both for a reference slate rock case and for a sensitivity analysis of variations of aquifer hydraulic conductivity value. Groundwater impacts were assessed in terms of oscillations of piezometric heads and mean drawdown around the cavity. The value of the hydraulic conductivity clearly influences the magnitude of the aquifer response. Studying interactions with the cavity highlighted that seepage into the cavity occurs over time. The volume of seeped water varies depending on the hydraulic conductivity and it could become non-negligible in the UPSH operations. These preliminary results allow finally considering first geological feasibility aspects, which could vary conversely according to the hydraulic conductivity value and to the considered groundwater impacts.
... Estanislao Pujades et al. used the finite element numerical code SUFT 3D to establish a numerical model of groundwater flow. Considering the two actual initial conditions of complete depletion and complete injection of water in the groundwater reservoir, they evaluated the hydraulic exchange effects of the mine reservoir and roadway surrounding rock when the power station was in operation for a long time [21][22][23]. Based on the flow equation of air and water under different operating conditions of the abandoned mine pumped storage power station, Ye Peng [24] used the Fluent software to conduct numerical simulation and analyzed the influence of different geometric designs on water-air flow characteristics as well as water energy utilization rate under each operating conditions. ...
The roadway of an abandoned mine is an ideal site for the construction of underground pumped storage hydropower, but the operation of the power station is deeply restricted by the structural characteristics of the roadway. With the common double-bend roadway of an abandoned mine as the research object, this study conducted numerical simulations based on the theory of mass conservation and momentum conservation and explored the law of the flow field characteristics and energy loss of a double-bend roadway with the roadway structure and angle. The results showed that a velocity gradient and a pressure gradient form from the outer wall to the inner wall when the fluid flows through the two bends of the roadway. The low-speed zone and maximum positive pressure appeared at the outside of the bend, while the high-speed zone and maximum negative pressure appeared at the inside of the bend. As the angle rose, the peak value of positive pressure increased correspondingly when the fluid flowed through Model A, whereas the negative pressure displayed a fluctuating trend of increasing first and then decreasing and reached its peak when β = 45°. By contrast, when the fluid flowed through Model B, the velocity gradient was symmetrically distributed at the two bends. The peak value of the positive pressure of the first bend increased, and the other positive and negative pressures displayed a trend of “first increasing and then decreasing” when the angle increased, and they reached their peak when β = 45°. When β ≥ 60°, the fluid formed a backflow zone when it flowed through each bend. With an increase in the angle, the area of the backflow zone increased correspondingly. The head loss of the two models increased with the angle. At the same angle, the head loss of Model B was greater than that of Model A. According to the requirement of abandoned mine pumped storage, the roadways with a bend angle of 15° or 30° in Model A and 15° in Model B can be used. The research results can provide some reference for the underground space exploitation and utilization of abandoned mine pumped storage.
... In the long-term struggle against water inrush, coal mine hydrogeologists have obtained promising research results. The theories and methods of predicting water inrush include the down three zones theory beneath the coal seam (Li 1999), the key stratum theory (Qian et al. 1996), the strong seepage theory (Ye and Liu 2005), the three maps-two predictions method (Wu et al. 2007), the vulnerable index method (Wu et al. 2009), artificial neural networks , the analytic hierarchy process (AHP) (Wu et al. 2017a), physically based and spatially distributed techniques (Boyaud and Therrien 2004), the hybrid finite element mixing cell technique (Wildemeersch et al. 2010), ground penetrating radar (Singh 2015), and so on (Rapantova et al. 2007;Rutter et al. 2013;Zhang et al. 2017;Yin et al. 2019b). Evaluating the risk of seam floor water inrush with the above theories and methods is a complex process for coal mine technicians. ...
The mining of stratigraphically low coal seams in North China-type coalfields is subject to water inrush from the underlying Ordovician limestone aquifer. The water-inrush coefficient method that is currently used for the evaluation of the water-inrush risk has inherent shortcomings, because it takes into account only the aquifer head pressure and the aquiclude thickness. Therefore, an improved water-inrush coefficient (IWIC) model is proposed. Based on the normalized water-inrush parameter, water-resisting parameter and structural parameter, the IWIC model is established using a linear weighting method. The first-order weights of each parameter are determined by the analytic hierarchy process, and the second-order weights are determined by the trapezoidal fuzzy number technique. Contour maps of the water-inrush risk calculated with the IWIC model are then obtained. The water-inrush risk grades are classified by thresholds derived via the Jenks natural breaks technique. The IWIC model is applied to the Longgu coal mine, as a typical coal mine in China, to evaluate the water-inrush risk of the lower four coal seams (L4CS). The evaluation results show that the risk of water inrush in the L4CS can be divided into five grades: safe, slightly safe, slightly dangerous, dangerous, and extremely dangerous. Overall, the L4CS mining in the Longgu coal mine is seriously threatened by the underlying Ordovician limestone aquifer. As the depth increases, the risk of water inrush increases from the No. 151 to No. 182 coal seams. Among the L4CS, No. 17 and No. 182 have the highest grade of water-inrush risk, and it is proposed that these two coal seams should not be mined to prevent water-inrush accidents.
... HUANG et al [15] studied the variation characteristics of stress field and seepage field in Dongtan Coal Mine with the numerical calculation software FLAC 3D and revealed the mechanism of water inrush by simulating the whole process of water inrush around the collapse column. WILDEMEERSCH et al [16] simulated the formation of water-inrush channels caused by the coupling effect of water pressure in the mining process. Taking Sima Coal Mine as the engineering background, WANG et al [17] analyzed the water inrush of hidden depressed column in the confined coal seam under the fluid-solid coupled interaction. ...
Through rock mechanics test, similar simulation experiment, borehole photographic observation of rock fissure, numerical simulation calculation of plastic zone distribution and deformation monitoring of rock mass during undersea mining, the fractal evolution mechanisms of rock fracture in undersea metallic deposits of Sanshandao Gold Mine were studied by fractal theory. The experimental researches on granite mechanics test in undersea deposit indicate that with the increase of load, the granite deformation energy and the fractal dimension of acoustic emission (FDAE) increase gradually. However, after reaching the peak stress of specimen, the fractal dimensions of acoustic emission (FDAEs) decrease and the granite specimen fails. Therefore, the fractal dimension evolution of rock failure can be divided into four stages, which are fissure inoculation stage, fissure growth stage, fissure expansion stage and fracture instability stage, respectively. By calculating and analyzing the damage photographs of rock specimens in Sanshandao Gold Mine, the fractal dimension of rock fissure is 1.4514, which is close to the average value of FDAE during granite destruction, i.e., 1.4693. Similar simulation experiments of undersea mining show that with the excavation proceeding, the FDAE in rock stratum increases gradually, and when the thickness of the isolation roof is less than 40 m, the FDAE begins to decrease, and meanwhile the sign of water inrush emerges. The numerical simulation researches on the plastic zone distribution of undersea mining in Sanshandao Gold Mine indicate that the fractal dimension of plastic zone (FDPZ) where the failure characteristics occur is 1.4598, close to the result of similar simulation experiment of 1.4364, which shows the sign of water inrush. Meanwhile, the thickness of the isolation roof for undersea mining should be more than 40 m, which is consistent with the results of similar simulation experiment. In Sanshandao Gold Mine, the rock fissures in undersea mining were observed by borehole photography and the rock mass deformation was monitored by multi-point displacement meters, and at the same time the fractal dimensions of strata borehole fissure distribution and energy release ratio (ERR) of rock mass were calculated by fractal principle, which are 1.2328 and 1.2685, respectively. The results demonstrate that rock deformation and fissure propagation are both in the second stage of fissure growth, and have not reached the fourth stage of fracture instability. Therefore, the conclusion can be obtained that the undersea mining in Sanshandao Gold Mine is safe at present.
... Further, Li et al. (2011) performed a numerical investigation of groundwater outbursts near faults in underground coal mines, providing highly meaningful guides for investigating the mechanism and preventing groundwater outbursts induced by faults in practice. Many other methods to evaluate and predict mine water inrush have been developed (Wildemeersch et al. 2010;Li CP et al. 2013;Li T et al. 2013;Shi et al. 2014;Wu et al. 2016;Bai et al. 2016;Qi et al. 2017). Most of the methods mentioned are multi-factor comprehensive evaluation methods. ...
Risk assessment of water inrush from a coal seam floor is essential for safety in many coal mines. From the point of view of mechanics, such water inrush forms on the floor when the aquiclude breaks under the action of continuous water pressure within a certain period of time. Consequently, the water from the aquifer below the aquiclude gushes along the rupture surface into the goaf. In this study, to clarify the water inrush mechanism, a time-related function f(P, H, q) is developed (where P, H, and q are the aquifer water pressure, aquifuge thickness, and aquifer specific yield, respectively). Hence, the likelihood of water inrush can be determined. Data collected from 150 cases are used to determine the related parameter thresholds. The influence of P, H, and q on water inrush occurrence is analysed based on the time-related function. Finally, a P-H-q evaluation system is proposed and successfully applied. The P-H-q evaluation system not only facilitates realistic risk assessment for water inrush, but also elucidates the water inrush mechanism in underground mining. The results also provide a reference for evaluating the risk of water inrush in other coal fields.
... The finite element numerical code SUFT3D (Brouyère et al., 2009;Wildemeersch et al., 2010) is used to model the underground reservoir and its interaction with the porous medium. This code uses the Control Volume Finite Element (CVFE) method to solve the groundwater flow equation based on the mixed formulation of Richard's equation proposed by Celia et al. (1990). ...
Underground Pumped Storage Hydropower (UPSH) using abandoned mines has been
considered as a potential high capacity Energy Storage Systems. In UPSH
plants, the excess of electricity is stored in the form of potential energy
by pumping water from an underground reservoir (abandoned mine in this paper)
to a surface reservoir, while electricity is produced (when the demand
increases) discharging water from the surface into the underground reservoir.
The main concerns may arise from the water exchanges occurring between the
underground reservoir and the surrounding medium, which are relevant in terms
of environmental impact and UPSH efficiency. Although the role of the water
exchanges has been previously addressed, most studies are based on synthetic
models. This work focuses on a real abandoned slate mine located in
Martelange (Belgium). The effects of different rehabilitation works to
prepare the mine as an underground reservoir are assessed in terms of
groundwater exchanges and their associated consequences.
... S. Wildemeersch et. Al [9] performed an uncertainty analysis based on both the hydraulic head and water discharge rate observation using the Hybrid Finite Element Mixing Cell (HFEMC) method. Q. Wu et. ...
Water inrush disaster is an important factor in restricting safe production of the coal mine. Taking the roadway in seam in Danhou Coal Mine, as the engineering background, according to the spatial relationship of the roadway, the impermeable layer, the fault and the loading conditions, the fault activation mechanical model under the roadway excavation disturbance was built, and the fault activation conditions, roadway water inrush criterion and water inrush three modes were put forward. A three-dimensional numerical calculation models were built by using FLAC3D. Through fluid-solid coupling calculation, the surrounding rock damage and failure, the water inrush channel formation, and the evolution process of water inrush of the roadway excavation approaching the fault were analyzed. Moreover, the displacement field, the stress field and the surrounding rock plastic failure characteristics of the roadway were revealed. Furthermore, under the conditions of different water pressure, impermeable rock thickness, fault displacement, and fault dip angles, the roadway water inrush modes and their evolution characteristics were comparatively analyzed.
... Ce réseau est, entre autres, destiné à servir de système d'alerte pour d'éventuels coups d'eau dans les galeries d'exhaure en vallée de la Meuse. Ces études des conséquences de l'après-mine ont permis de collecter de nombreuses et diverses données hydrogéologiques (Berger et al, 2003 ;Gardin et al, 2005 ;Dingelstadt & Drevet, 2007) et de modéliser ce comportement particulier (Brouyère et al., 2009 ;Wildemeersch et al., 2010). ...
... Physically based and spatially distributed models are also very timeconsuming due to the complicated parameterisation and being prone to numerical problems such as instability and numerical dispersion. The innovative HFEMC ('hybrid finite element mixing cell') method (Brouyère et al. 2009;Wildemeersch et al. 2010;Orban et al. 2010), implemented in the SUFT3D code (Carabin and Dassargues 1999;Brouyère 2001;Brouyère et al. 2004), is a compromise between black-box models and physically based and spatially distributed models, and which offers a pragmatic solution to the issues encountered in groundwater flow and transport modelling at the regional scale. The deterministic approach developed here allows estimating the space-time fate of nitrate in groundwater quite rapidly. ...
Models are the only tools capable of predicting the evolution of groundwater systems at a regional scale, by taking into account a large amount of information. This study presents the association of a water balance model (WetSpass) with a groundwater flow and solute transport model (SUFT3D, saturated and unsaturated flow and transport in 3D) in order to simulate the present and future groundwater quality in terms of nitrate in the Upper Dyle basin (439 km2) Belgium. The HFEMC (hybrid finite element mixing cell) method implemented in the SUFT3D code is used to model groundwater flow and nitrate transport. Spatially distributed recharge, modelled with WetSpass, is considered for prescribing the recharge to the groundwater flow model. The feasibility of linking the WetSpass model with the finite-elements SUFT3D code is demonstrated. Time evolution and distribution of nitrate concentration are then simulated using the calibrated model. Nitrate inputs are spatially distributed according to land use. The spatial simulations and temporal trends are compared with previously published data on this aquifer and show good results.
Complex underground flow processes can occur in flooded mine workings. As the groundwater rebounds, outbreaks, flooding, and slope stability problems can occur where hydraulic pressures build up in less drained areas. A time-series statistical analysis was conducted to understand how exploited areas in an abandoned coalfield were connected and to calculate groundwater response times to rain events by spatially and temporally correlating piezometric levels and discharge rates. Ten years of flow rate and water level data were statistically analyzed for an abandoned coalfield in Liège (Belgium). Then, the results were compared to results from physically-based simulations (a 3D groundwater flow model) based on data from the first 2 years of monitoring. The statistical approach gives qualitative indications on the interconnections between the different areas of the coalfield, as well as on the storage capacity/transmissivity of the aquifer. Improved understanding of this hydrogeological behavior can be used to prevent post-mining accidents and assess the associated risks.
Mine water inrush is very common in China and can cause hysteresis and severe damage. The entire process of crack formation, concealed fault propagation, and evolution of a water inrush channel with high pressure water directly beneath the mine floor was physically simulated based on fluid–solid coupling mechanics and solid materials research. Activated materials were used to simulate fault damaged rock, including soybeans, sand, Vaseline, and calcium carbonate. The results indicate that water channels are mainly caused by the connection between tectonic rock zones and coal floor cracks, which are the direct cause for water inrush. Furthermore, the lagging water inrush mechanism from the coal floor in a confined water body under both a stress field and a seepage field were revealed. The formation of the water inrush path with temporal and spatial variations was analyzed by interpreting the monitoring data and phenomena. The data showed that the floor stress in front of the working face increased and was affected by the abutment pressure, and that floor stress under the mined-out area began to decrease simultaneously. The stress of the upper wall showed a drastic drop while the stress of the footwall continued to decline and then stabilized after the water inrush. This work provides new approaches and knowledge for research on deep mining water inrush structures.
Underground Pumped Storage Hydropower (UPSH) is a potential alternative to manage electricity production in flat regions. UPSH plants will interact with the surrounding porous medium through exchanges of groundwater. These exchanges may impact the surrounding aquifers, but they may also influence the efficiency of the pumps and turbines because affecting the head difference between the reservoirs. Despite the relevance for an accurate efficiency assessment, the influence of the groundwater exchanges has not been previously addressed.
Two construction schemes were optimized for the soft rock tunnel under complex conditions, and the deformation effects of the two construction schemes were verified by the field test. The evolution process of water inrush of the roadway excavation approaching the fault was analyzed and the reliability analysis of the shallow hydraulic tunnel structure stability was evaluated. The disturbance deformation effect on the existing tunnel was revealed based on the physical model test and numerical experiments. The principal stresses distribution and energy dissipation were analyzed according to the nonuniform stress field of the circular tunnel. The evolution characteristics of the pressure-arch of the highway tunnel under different stress states were analyzed, and the skewed distribution of the pressure-arch in a double-arch tunnel, induced by step-by-step excavation, was revealed.
Underground pumped storage hydroelectricity (UPSH) plants using open-pit or deep mines can be used in flat regions to store the excess of electricity produced during low-demand energy periods. It is essential to consider the interaction between UPSH plants and the surrounding geological media. There has been little work on the assessment of associated groundwater flow impacts. The impacts on groundwater flow are determined numerically using a simplified numerical model which is assumed to be representative of open-pit and deep mines. The main impact consists of oscillation of the piezometric head, and its magnitude depends on the characteristics of the aquifer/geological medium, the mine and the pumping and injection intervals. If an average piezometric head is considered, it drops at early times after the start of the UPSH plant activity and then recovers progressively. The most favorable hydrogeological conditions to minimize impacts are evaluated by comparing several scenarios. The impact magnitude will be lower in geological media with low hydraulic diffusivity; however, the parameter that plays the more important role is the volume of water stored in the mine. Its variation modifies considerably the groundwater flow impacts. Finally, the problem is studied analytically and some solutions are proposed to approximate the impacts, allowing a quick screening of favorable locations for future UPSH plants.
The height of the water flowing fractured zone and the extents of water inrush caused by coal mining are the main influence factors on groundwater systems. Utilizing the empirical equation analysis approach combined with analogy method, taking a typical coal mine in taiyuan as example, the effects of coal mining on the overlying and underlying aquifers was analyzed by the estimation of the development height of the water flowing fractured zone and water inrush coefficient. The results are shown that the development heights of the water flowing fractured zone in coal seams No.9, No.11 and No.13 would be 80.25~97.5m, 5.25~20.25m, 4.5~34.5m respectively. The developed water flowing fractured zone in the No.9 coal seam would reach the Neogene aquifer, and the aquifers in the weathering crust and Neogene system would be influenced with a total area of 0.9 km2; the water inrush coefficients of coal seams No.9, No.11 and No.13 would be 0.028~0.051 MPa/m,0.031~0.057MPa/m and 0.037~0.072MPa/m respectively, apart from the danger zone with an area of 0.33km2 in the West bound of No.13 coal seam around G02, it would be safe from water inrush when mining the No.9 and No.11 and most areas of No.13 coal seams.
Some specific features and problems of numerical modelling applications in mining environment are briefly discussed and three
modelling case studies are presented. Two of the applications are aimed at mine dewatering problems in active coal mines.
The first represents the underground hard coal mining region in the Czech part of the Upper Silesian Coal Basin. The second
example is focussed on optimisation of the dewatering regime of open pit mining of brown coal in the Most sub-basin of the
North Bohemian Coal Basin. The third example describes how mathematical modelling can be applied to solve issues associated
with the intensive use of mine waters from the flooded Olsi-Drahonin mine as a source of uranium to shorten the time necessary
for the purification of mine waters discharged into watercourses.
Dewatering operations often stop at mine closure. The ground water rebound can have undesirable consequences, which numerical models can help one understand and manage. However, classical modelling techniques are relatively unsuitable to these contexts. While spatially distributed and physically based models suffer difficulties due to the lack of data and the complexity of geological and hydrogeological conditions, black-box models are too simple to deal with the problems effectively. A new modelling method is proposed to simulate ground water environments in which water flows through mined (exploited) and unmined (unexploited) areas. Exploited zones are simulated using a group of mixing cells possibly interconnected by pipes. Unexploited zones are simultaneously simulated using classical finite elements. This combined approach allows explicit calculation of ground water flows around the mine and mean water levels in the exploited zones. Water exchanges between exploited zones and unexploited zones are simulated in the model using specifically defined internal boundary conditions. The method is tested on synthetic cases of increasing complexity, and first results from a real case study are presented.
Minimizing negative impacts associated with water rebound in decommissioned mines requires a quantitative assessment of the process. An innovative modeling approach has been developed to simulate mine water rebound, where three-dimensional flow in fractured rock is fully coupled to one-dimensional flow occurring inside mine conduits. This approach has been tested against a documented case of mine water rebound at the Saizerais mine, in northeastern France. The model adequately reproduces the temporal evolution of hydraulic head inside the mine during and after rebound, as well as trends of water overflow at the ground surface. Overestimation of overflow discharge by the model suggests that the fractured rock units adjacent to the mine do not behave as equivalent porous media.
Nonlinear regression was introduced to ground water modeling in the 1970s, but has been used very little to calibrate numerical models of complicated ground water systems. Apparently, nonlinear regression is thought by many to be incapable of addressing such complex problems. With what we believe to be the most complicated synthetic test case used for such a study, this work investigates using nonlinear regression in ground water model calibration. Results of the study fall into two categories. First, the study demonstrates how systematic use of a well designed nonlinear regression method can indicate the importance of different types of data and can lead to successive improvement of models and their parameterizations. Our method differs from previous methods presented in the ground water literature in that (1) weighting is more closely related to expected data errors than is usually the case; (2) defined diagnostic statistics allow for more effective evaluation of the available data, the model, and their interaction; and (3) prior information is used more cautiously. Second, our results challenge some commonly held beliefs about model calibration. For the test case considered, we show that (1) field measured values of hydraulic conductivity are not as directly applicable to models as their use in some geostatistical methods imply; (2) a unique model does not necessarily need to be identified to obtain accurate predictions; and (3) in the absence of obvious model bias, model error was normally distributed. The complexity of the test case involved implies that the methods used and conclusions drawn are likely to be powerful in practice.
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