Methods and storage media for external reinjection and safety optimization assessment of open-pit mine drainage curtains

Abstract

This invention belongs to the field of mining engineering technology, specifically disclosing a method and storage medium for the evaluation of curtain-type recharge and safety optimization of open-pit mine drainage systems. The method involves identifying groundwater source inflows, establishing a hydrogeological model of open-pit mine drainage systems, and defining boundary conditions and model scope; using monitoring data combined with guide points and regularized inversion to perform heterogeneous inversion of model parameters; extracting water levels at observation points from all simulation examples and interpolating to identify the critical time for curtain-type overflow. t lim The invention employs particle tracking to determine the safe reinjection zone; based on batch numerical simulation results, it utilizes three measures—coordinated optimization of curtain extension, addition of drainage wells, and coordinated pumping-injection control—to determine the optimal parameter combination; and uses the water balance method to assess the change in groundwater evaporation caused by reinjection under the optimal parameter combination, thereby determining the risk of regional salinization. This invention can effectively prevent curtain overflow and increased mine water inflow while ensuring the scale of drainage and reinjection.

Description

Technical Field

[0001] This invention belongs to the field of mining engineering technology, specifically relating to a method and storage medium for external reinjection and safety optimization assessment of drainage curtains in open-pit mines. Background Technology

[0002] In open-pit coal mining, to ensure the safety of operations and slope stability, groundwater is often actively drained using engineering methods such as dewatering wells and drainage ditches. This method is particularly prevalent in arid and semi-arid ecologically fragile areas. However, long-term, large-scale groundwater drainage can easily create significant groundwater drawdown cones in and around the mining area, leading to a series of ecological and environmental problems such as surface water degradation, vegetation deterioration, and soil desertification. This results in regional water resource imbalance and severely restricts the green development and sustainable development of open-pit mines. Therefore, achieving reasonable replenishment of drainage water and protecting groundwater resources while effectively preventing mine water hazards has become a core technical problem that urgently needs to be solved in the field of open-pit mining engineering.

[0003] To reduce mine water inflow and slow the decline in groundwater levels, some open-pit mines have begun constructing cutoff curtain projects in recent years. Engineering practice shows that cutoff curtains can, to some extent, block the flow of groundwater into the mine pit and raise the groundwater level outside the curtain, playing a positive role in mine water hazard prevention and water resource protection. However, due to limitations imposed by mining rights boundaries, mining area planning, and engineering investment, open-pit mine cutoff curtains often fail to form a completely closed structure. Problems such as flow bypass at the curtain ends and difficulties in properly managing drainage from the side walls exist, significantly reducing the effectiveness of cutoff curtains in water hazard prevention and water resource protection.

[0004] To balance mine water hazard prevention and control with regional groundwater resource protection, the practice of reinjecting open-pit mine drainage into Quaternary loose aquifers outside the cutoff curtain, creating a coordinated "drainage-reinjection" operation model, has gradually become an important direction for industry research and engineering applications. Theoretically, this model can effectively mitigate the decline of groundwater levels outside the cutoff curtain and achieve the recycling of water resources in the mining area. However, in practical engineering applications, it still faces many key technical challenges: Firstly, the groundwater level rise caused by reinjection can easily lead to overflow at the top of the cutoff curtain or bypass flow along the curtain ends, which not only increases the mine water inflow but also threatens the safety of the cutoff curtain structure. Secondly, there is a lack of systematic and quantitative assessment methods for the impact of different reinjection scales, layouts, and combinations of engineering measures on mine water inflow patterns, regional groundwater level evolution, and ecological environmental effects, making it difficult to guide engineering practice.

[0005] Current technological research and engineering practices largely focus on single drainage or interception measures. Methods for identifying the risks of curtain flow and bypass flow under drainage and recharge conditions are inadequate, failing to clearly define the safety threshold for recharge operations and easily leading to blind decision-making in recharge projects. Furthermore, there is a lack of technical pathways to coordinate and optimize measures such as recharge parameter control, curtain structure adjustment, and drainage well placement, making it difficult to systematically evaluate the comprehensive effects of various water control engineering measures and achieve the synergistic goal of water hazard prevention and water resource protection. In addition, there is a lack of operational quantitative assessment methods for whether the groundwater level rise caused by recharge will enhance regional groundwater evapotranspiration and induce secondary ecological problems such as soil salinization, thus restricting the large-scale application of drainage and recharge technology.

[0006] Among existing related technologies, although some solutions propose aquifer-internal circulation and recharge systems for open-pit mine drainage water, which reduce external drainage by arranging drainage wells and fracture recharge wells around the mining area to achieve local recharge of drainage water, they do not consider the risks of overflow and bypassing of the cutoff curtain and are not applicable to open-pit mine scenarios with existing cutoff curtains. Other solutions have constructed open-pit mine drainage water recharge and water retention models to determine the recharge volume and predict water level changes, thus optimizing the recharge volume, but they do not quantitatively identify the water hazard risks caused by recharge, nor do they form a collaborative optimization strategy for multiple engineering measures. Still other solutions propose a combined horizontal and vertical well drainage method, which only focuses on improving groundwater drainage efficiency and does not involve the recharge utilization of drainage water and water resource protection.

[0007] Therefore, it is urgent to study a method for evaluating the recharge and safety optimization of open-pit mine drainage curtains under existing cutoff curtain conditions, so as to achieve the synergistic goal of groundwater resource replenishment and open-pit mine water hazard prevention and control, and provide technical support for green mining in arid and semi-arid ecologically fragile areas. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a method for evaluating the external reinjection and safety optimization of drainage curtains in open-pit mines, and also provides a computer storage medium.

[0009] The open-pit mine drainage curtain external recharge and safety optimization assessment method of the present invention is implemented as follows: it includes the steps of model construction, model calibration, simulation and safety scheme identification, water hazard prevention optimization, and ecological impact identification. The specific contents of each step are as follows:

[0010] A. Model Construction: Based on the stratigraphic structure, hydrogeological conditions and engineering layout of the open-pit mine, the groundwater source sinks are identified through the model generalization method, the hydrogeological data of the site are obtained, the hydrogeological model of the open-pit mine drainage is established, and the boundary conditions and model range of the aforementioned model are defined.

[0011] B. Model calibration: Using groundwater level and mine water inflow monitoring data from hydrogeological data, combined with guide point and regularized inversion methods, the parameters in the hydrogeological model of open-pit mine drainage are inverted in a heterogeneous manner to achieve the calibration of the hydrogeological model of open-pit mine drainage.

[0012] C. Simulation and Safety Scheme Identification: Conduct batch numerical simulations of open-pit mine drainage being reinjected into the Quaternary loose aquifer outside the cutoff curtain. Using Python, different operating conditions including reinjection flow rate, reinjection location, curtain extension, and drainage wells are combined to extract the water balance term and observation point water level from the output file. Then, the critical time for curtain overflow is identified by interpolation methods for the observation point water levels in all simulation examples. t lim ; and / or use the PATH3DU particle tracking method to identify the groundwater seepage path and bypass flow rate after reinjection, and determine the safe reinjection zone;

[0013] D. Water hazard prevention and control optimization: Based on the batch numerical simulation results of step C, three engineering measures are adopted: collaborative optimization of curtain extension, addition of drainage wells, and pumping-injection coordinated control. The optimal parameter combination that meets the requirements of reducing mine water inflow, curtain safety, and water resource replenishment is determined.

[0014] E. Ecological impact identification: The water balance method is used to assess the changes in groundwater evaporation caused by recharge under the optimal parameter combination, and to determine the risk of regional salinization.

[0015] Furthermore, in step A, the groundwater source collection includes rainfall infiltration, mine drainage, and dewatering well volume, and the hydrogeological data includes atmospheric precipitation infiltration, river seepage, mine drainage and evaporation, groundwater level, mine inflow, and groundwater evaporation.

[0016] Furthermore, the specific process in step A includes:

[0017] A10. Constructing a hydrogeological model for open-pit mine drainage:

[0018] Based on the geological structure, hydrogeological conditions, and engineering layout of the open-pit mine, groundwater sources and sinks are identified, on-site hydrogeological data are obtained, and groundwater flow is generalized into a hydrogeological model of open-pit mine drainage:

[0019]

[0020] In the formula: μ For water supply, dimensionless; h The head is measured in meters (m). K xx , K yy , K zzAquifer x , y , z The permeability coefficient component in the direction of the direction, in m / d; The rate of change of water head over time, expressed in m / d; These represent the rates of change of the seepage parameters in three directions of the Cartesian coordinate system, in units of 1 / m; The aquifers are respectively in x , y , z Hydraulic gradient in direction; W Source and sink items per unit time, with the unit being 1 / d; x , y , z represents spatial Cartesian coordinates, with units of meters (m). t Time, in days (d).

[0021] A20. Identify the initial and boundary conditions of the model:

[0022] Initial conditions:

[0023] Given head boundary:

[0024] Waterproof boundary:

[0025] In the formula: h ( x , y , z , t )| t=0 To simulate the initial head distribution at each spatial point within the study area at the initial time (t=0), the unit is meters; h ( x , y , z , t )| Γ1 Let Γ1 be the head value of the spatial point on the given head boundary Γ1 at any time, in meters; Γ2 is the rate of change of water head along the outer normal direction of the impermeable boundary, and 0 indicates that no seepage passes through it. It is dimensionless. h 0 represents the initial head in meters (m); Ω represents the spatial domain; Γ1 and Γ2 represent the given head and the impermeable boundary, respectively; n is the unit vector of the boundary normal.

[0026] River seepage Q r for:

[0027]

[0028] In the formula:Q r The unit is m 3 / d; C river The equivalent hydraulic conductivity of the riverbed is expressed in meters (m). 2 / d; h river The water head of a river is measured in meters (m).

[0029] The excavation face of the Quaternary strata on the edge of the mine can be generalized as free drainage: if the groundwater level is higher than the bottom elevation of the drainage ditch, the drainage volume is proportional to the difference in water head between the two; if the groundwater level is lower than the bottom elevation of the drainage ditch, the drainage volume is zero; that is:

[0030]

[0031] In the formula: Q d This refers to the water inflow from the mine, expressed in cubic meters (m³). 3 / d; C drain The water conductivity coefficient of the drainage ditch is expressed in meters. 2 / d; d b This is the elevation of the bottom of the drainage ditch, in meters (m).

[0032] The groundwater evaporation rate ET is:

[0033]

[0034] Where: ET max This represents the maximum evaporation rate, expressed in m / d. z surf This is the ground elevation, in meters (m). z lim This is the evaporation limit elevation, in meters (m).

[0035] A30. Model Mesh Processing:

[0036] The open-pit mine drainage hydrogeological model was divided into grids, and the grids were densified near the mine boundary, rivers, curtains, drainage wells and reinjection wells in the aforementioned model.

[0037] A40. Generalization of Drainage and Recharge:

[0038] During the drainage process, to prevent the groundwater within the numerical grid from drying up, the actual pumping volume in the pumping wells is... Q well for: Q well = min( Q pump , Q max ),

[0039] in,

[0040] In the formula: Q pump The set pumping capacity, in meters (m). 3 / d; Q max The maximum drainable volume in the grid, in meters. 3 / d; Q ex For traffic exchange between adjacent grids, the unit is m. 3 / d; A cell This represents the current grid cross-sectional area, in meters (m). 2 ;z bot The current grid's base elevation, in meters; Δ t The time step is expressed in seconds (d).

[0041] Furthermore, in the A30 sub-step, the open-pit mine drainage hydrogeological model is meshed using the Voronoi unstructured mesh of MODFLOW USG.

[0042] In the A40 sub-step, the saturation thickness threshold is used. d 0 Determine whether the groundwater within the numerical grid has dried up, i.e. h - z bot < d 0 At the time of assessment, the groundwater level is considered to be dry, and the hydraulic conductivity is set to zero. When pumping or recharge stops, the groundwater level within the grid will recover. Whether it has recovered is determined by the groundwater level of adjacent grids: if the groundwater level of an adjacent grid is greater than z... bot + d When the water level reaches 0, the current grid is reactivated, and the grid water level is re-wetted. h re Represented as:

[0043]

[0044] In the formula: h re The unit is meters (m). χ The rehumidification coefficient is between 0 and 1. h a The water level is for adjacent grids, in meters (m).

[0045] Furthermore, in step B, the heterogeneous inversion process of the parameters in the open-pit mine drainage hydrogeological model is as follows:

[0046] Using the PEST program combined with Pilot Points and the Tikhonov regularization method based on singular value decomposition, parameters including aquifer permeability coefficient, infiltration recharge intensity, river leakage, and drainage boundary in the hydrogeological model of open-pit mine drainage were inverted. Then, the minimum value Φ of the objective function was solved based on the Gauss-Levenberg-Marquardt algorithm. min ;

[0047] Wherein, the objective function Φ is the weighted sum of variances between the simulated values ​​obtained by MODFLOW groundwater numerical simulation software and the observed values ​​monitored in the field:

[0048]

[0049] In the formula, y obs These are groundwater level observations, in meters (m). f (p) is the model response function, in units of m, p = ( p 1, p 2, p 3, …, p Np ) are the parameters in the model. N p is the number of parameters; Q = diag( w 1 2 , w 2 2 , …, w n 2 Let be a diagonal matrix of squared observation weights. n The number of observation points;

[0050] To ensure a good fit between groundwater level and mine water inflow, the variances of both are considered in the objective function, and Tikhonov regularization deviation and smoothing constraints are added. The final objective function Φ is:

[0051]

[0052] In the formula: w These are the weighting coefficients; h i obs , h i sim The first i The observed and simulated water heads at each observation point are in meters (m). Q d obs , Q d simThese represent the observed and simulated water inflow rates, respectively, in m³ / d; λ is the regularization weighting factor. p j ref For the corresponding number j Reference parameter values ​​for each guide point p j , p m , p n These are the model parameter values ​​for the j-th, m-th, and n-th derivative points, respectively, in m / d; m , n ) represents a pair of adjacent guide points; N is the set of all adjacent guide points. w h , w Q , w r,j , w mn These are the head fitting weight coefficients, the inflow fitting weight coefficients, and the first... j The weighting coefficient of the deviation of each guide point parameter from the reference value, and adjacent guide points. m , n The weighting coefficients of the parameter smoothing constraint are dimensionless.

[0053] Furthermore, in step C, Python is used to batch extract the water levels of all observation points in the simulation examples. Then, two times when the water level of an observation point reaches the curtain elevation are found between adjacent observation points. Based on the aforementioned two times, linear interpolation or cubic spline interpolation is used to accurately obtain the critical time for overflow. t lim Then determine the water level at the observation point. h Is it lower than the top elevation of the curtain? Z top ,Right now h < Z top Reinjection is safe if it occurs within the critical time for the corresponding water volume.

[0054] Furthermore, in step C, the PATH3DU particle tracking method is used to identify the groundwater seepage path and flow rate after reinjection, and to determine the reinjection safety zone. Formula (1) is used to solve the three-dimensional seepage velocity field.

[0055]

[0056] In the formula: v x , v y , v zThese are the pore velocity components of the aquifer in the x, y, and z directions, respectively, in m / d; θ Effective porosity; The aquifers are respectively in x , y , z Hydraulic gradient in a certain direction.

[0057] Furthermore, in step D, the curtain extension measure involves extending the cutoff curtain at the boundary of the mining rights or at the end of the curtain, and comparing the mine water inflow and groundwater uplift range under different extension lengths.

[0058] The measure of adding drainage wells involves setting up drainage wells around the perimeter of the mine pit to form a water-pumping curtain, which works in conjunction with the reinjection system.

[0059] The pumping-injection coordinated regulation is to control the rate of groundwater level rise by adjusting the matching relationship between the pumping volume and the reinjection volume of a single well, thereby avoiding curtain flow and reducing the amount of water flowing into the mine.

[0060] Furthermore, step E involves, after obtaining the optimal parameter combination, evaluating whether external recharge would lead to a significant rise in regional water levels by combining numerical simulation results. Then, the water balance method is used to further evaluate the changes in groundwater evaporation caused by recharge under the optimal parameter combination, thereby determining the risk of regional salinization.

[0061] The computer storage medium of the present invention is implemented as follows: it stores a computer program, which, when executed by a processor, implements the aforementioned method for external reinjection and safety optimization assessment of open-pit mine drainage curtain.

[0062] The present invention has the following beneficial effects:

[0063] 1. This invention breaks away from the traditional single mode of "external discharge and consumption" of open-pit mine drainage. It recharges the drainage into the Quaternary loose aquifer outside the intercepting curtain. By constructing a coordinated operation system of "drainage-recharge", it not only realizes the resource recovery of drainage, but also replenishes regional groundwater resources. It effectively alleviates the contradiction between water shortage and waste in open-pit mines in arid and semi-arid regions, and provides a stable water source for production, domestic water use and ecological water replenishment in mining areas.

[0064] 2. This invention accurately identifies the critical time of curtain overflow by combining batch numerical simulation with interpolation methods, and uses the PATH3DU particle tracking method to clarify the groundwater seepage path and bypass flow after reinjection, forming a scientific criterion for the reinjection safety zone and safety threshold. This avoids the risks of curtain overflow and end bypass caused by reinjection from the source, avoids the increase of mine water inflow and damage to the curtain structure, and provides technical support for the safe implementation of reinjection projects.

[0065] 3. This invention innovatively adopts a multi-measure synergistic optimization strategy of "curtain extension + drainage well addition + pumping-injection coordinated control". By systematically simulating the implementation effects of different engineering measures combinations, the optimal parameter combination for reducing mine water inflow, curtain safety and water resource replenishment is determined. Compared with single prevention and control measures, it can more efficiently control the rate of groundwater level rise, further reduce mine water inflow, and maximize the efficiency of groundwater replenishment, achieving the dual goals of water hazard prevention and water resource protection, thereby effectively improving the comprehensive effect of water hazard prevention and control.

[0066] 4. This invention uses the water balance method to quantitatively assess changes in groundwater evaporation caused by recharge, which can accurately determine the risk of regional salinization and make up for the shortcomings of existing technologies in assessing the secondary ecological problems caused by recharge. At the same time, groundwater recharge can effectively slow down the decline of regional groundwater levels, alleviate ecological problems such as the decline of surface water systems and vegetation degradation, provide strong support for the ecological environment restoration of open-pit mine areas, and promote green and sustainable mining.

[0067] 5. This invention constructs a hydrogeological model for open-pit mine drainage based on a general numerical platform, uses Voronoi unstructured mesh to densify key areas, and combines guide points and regularized inversion methods to improve model calibration accuracy. The modeling approach is clear, the parameter inversion is reliable, and it can be adapted to open-pit mine scenarios with different hydrogeological conditions, mining scales, and curtain layouts. Moreover, the operation process is standardized and highly quantified, requiring no complex special equipment, and is easy for engineering technicians to master. It has broad application value in open-pit mine water hazard prevention and water resource protection projects in arid and semi-arid ecologically fragile areas.

[0068] In summary, this invention, through quantitative numerical simulation and water hazard risk assessment, rationally controls the scale of reinjection and coordinates and optimizes various water control engineering measures. While effectively avoiding curtain overflow, bypass flow, and increased mine pit water inflow, it also achieves synergistic improvement in economy, ecology, and safety, providing key technical support for green mining in open-pit mines. Attached Figure Description

[0069] Figure 1 This is a flowchart of the open-pit mine drainage curtain external recharge and safety optimization assessment method of the present invention;

[0070] Figure 2 This is the hydrogeological model and grid division for open-pit mine drainage in this embodiment of the invention;

[0071] In the figures: Figure 2a shows the model boundary conditions, Figure 2b shows the distribution of geological boreholes, Figure 2c shows the numerical grid division, Figure 2d shows a local magnification, and Figure 2e shows the curtain and the remaining wells on the outer side;

[0072] Figure 3 These are the model calibration results in the embodiments of the present invention;

[0073] In the figures: Figure 3a shows the simulated flow field and error bars, Figure 3b shows the comparison between the observed water level and the simulated value, and Figure 3c shows the sensitivity of the model parameters;

[0074] Figure 4 In this embodiment of the invention, the curtain flow and overflow generated by the recharge of the abandoned drainage well are used;

[0075] Figure 5 The variations in water level and mine water inflow under different reinjection schemes are illustrated in the embodiments of the present invention.

[0076] In the figure: Figure 5a shows the water level change caused by reinjection from the legacy well; Figure 5b shows the critical time for overflow caused by reinjection from the legacy well; Figure 5c shows the simulation of water level control by pulse reinjection from the legacy well; Figure 5d shows the influence of the selection of the reinjection well location on the change of water inflow.

[0077] Figure 6 This invention illustrates the influence range of mine water inflow and water level rise under different curtain extension lengths in this embodiment.

[0078] In the figures: Figure 6a shows the effect of extending the curtain on increasing the water inflow in the reinjection pit, and Figure 6b shows the effect of extending the curtain on the range of water level rise in the reinjection pit;

[0079] Figure 7 These are simulation results of curtain flow and mine water inflow under the condition of simultaneous injection and extraction in this embodiment of the invention;

[0080] In the figure: Figure 7a shows the evolution of the groundwater flow field during simultaneous pumping and injection; Figure 7b shows the critical time distribution of curtain flow under different pumping / injection flow rates; Figure 7c shows the change of mine water inflow over time under different pumping / injection flow rates.

[0081] Figure 8 These are the simulation results of groundwater evaporation under different single-well recharge flow rates in the embodiments of the present invention;

[0082] In the figures: Figure 8a shows the evolution of evaporation over time under different water injection rates; Figure 8b shows the evaporation rate in areas with a water level depth of less than 6m. Q in =5000m 3 / d, t =5000d). Detailed Implementation

[0083] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this does not limit the present invention in any way. Any changes or improvements made based on the teachings of the present invention shall fall within the protection scope of the present invention.

[0084] like Figure 1As shown, the open-pit mine drainage curtain external recharge and safety optimization assessment method of the present invention includes the following steps: model construction, model calibration, simulation and safety scheme identification, water hazard prevention optimization, and ecological impact identification. The specific contents of each step are as follows:

[0085] A. Model Construction: Based on the stratigraphic structure, hydrogeological conditions and engineering layout of the open-pit mine, the groundwater source sinks are identified through the model generalization method, the hydrogeological data of the site are obtained, the hydrogeological model of the open-pit mine drainage is established, and the boundary conditions and model range of the aforementioned model are defined.

[0086] B. Model calibration: Using groundwater level and mine water inflow monitoring data from hydrogeological data, combined with guide point and regularized inversion methods, the parameters in the hydrogeological model of open-pit mine drainage are inverted in a heterogeneous manner to achieve the calibration of the hydrogeological model of open-pit mine drainage.

[0087] C. Simulation and Safety Scheme Identification: Conduct batch numerical simulations of open-pit mine drainage being reinjected into the Quaternary loose aquifer outside the cutoff curtain. Using Python, different operating conditions including reinjection flow rate, reinjection location, curtain extension, and drainage wells are combined to extract the water balance term and observation point water level from the output file. Then, the critical time for curtain overflow is identified by interpolation methods for the observation point water levels in all simulation examples. t lim ; and / or use the PATH3DU particle tracking method to identify the groundwater seepage path and bypass flow rate after reinjection, and determine the safe reinjection zone;

[0088] D. Water hazard prevention and control optimization: Based on the batch numerical simulation results of step C, three engineering measures are adopted: collaborative optimization of curtain extension, addition of drainage wells, and pumping-injection coordinated control. The optimal parameter combination that meets the requirements of reducing mine water inflow, curtain safety, and water resource replenishment is determined.

[0089] E. Ecological impact identification: The water balance method is used to assess the changes in groundwater evaporation caused by recharge under the optimal parameter combination, and to determine the risk of regional salinization.

[0090] In step A, the groundwater source collection includes rainfall infiltration, mine drainage, and dewatering well volume, and the hydrogeological data includes atmospheric precipitation infiltration, river seepage, mine drainage and evaporation, groundwater level, mine inflow, and groundwater evaporation.

[0091] The model boundary conditions in step A include the impermeable boundary and the given head boundary, and the model range is determined by the model boundary.

[0092] The specific process in step A includes:

[0093] A10. Constructing a hydrogeological model for open-pit mine drainage:

[0094] Based on the geological structure, hydrogeological conditions, and engineering layout of the open-pit mine, groundwater sources and sinks are identified, on-site hydrogeological data are obtained, and groundwater flow is generalized into a hydrogeological model of open-pit mine drainage:

[0095]

[0096] In the formula: μ For water supply, dimensionless; h The head is measured in meters (m). K xx , K yy , K zz Aquifer x , y , z The permeability coefficient component in the direction of the direction, in m / d; The rate of change of water head over time, expressed in m / d; These represent the rates of change of the seepage parameters in three directions of the Cartesian coordinate system, in units of 1 / m; The aquifers are respectively in x , y , z Hydraulic gradient in direction; W Source and sink items per unit time, with the unit being 1 / d; x , y , z represents spatial Cartesian coordinates, with units of meters (m). t Time, in days (d).

[0097] A20. Identify the initial and boundary conditions of the model:

[0098] Initial conditions:

[0099] Given head boundary:

[0100] Waterproof boundary:

[0101] In the formula: h ( x , y , z , t )| t=0 To simulate the initial head distribution at each spatial point within the study area at the initial time (t=0), the unit is meters; h ( x , y , z , t )|Γ1 Let Γ1 be the head value of the spatial point on the given head boundary Γ1 at any time, in meters; Γ2 is the rate of change of water head along the outer normal direction of the impermeable boundary, and 0 indicates that no seepage passes through it. It is dimensionless. h 0 represents the initial head in meters (m); Ω represents the spatial domain; Γ1 and Γ2 represent the given head and the impermeable boundary, respectively; n is the unit vector of the boundary normal.

[0102] River seepage Q r for:

[0103]

[0104] In the formula: Q r The unit is m 3 / d; C river The equivalent hydraulic conductivity of the riverbed is expressed in meters (m). 2 / d; h river The water head of a river is measured in meters (m).

[0105] The excavation face of the Quaternary strata on the edge of the mine can be generalized as free drainage: if the groundwater level is higher than the bottom elevation of the drainage ditch, the drainage volume is proportional to the difference in water head between the two; if the groundwater level is lower than the bottom elevation of the drainage ditch, the drainage volume is zero; that is:

[0106]

[0107] In the formula: Q d This refers to the water inflow from the mine, expressed in cubic meters (m³). 3 / d; C drain The water conductivity coefficient of the drainage ditch is expressed in meters. 2 / d; d b This is the elevation of the bottom of the drainage ditch, in meters (m).

[0108] The groundwater evaporation rate ET is:

[0109]

[0110] Where: ET max This represents the maximum evaporation rate, expressed in m / d. z surf This is the ground elevation, in meters (m). z lim This is the evaporation limit elevation, in meters (m).

[0111] A30. Model Mesh Processing:

[0112] The open-pit mine drainage hydrogeological model was divided into grids, and the grids were densified near the mine boundary, rivers, curtains, drainage wells and reinjection wells in the aforementioned model.

[0113] A40. Generalization of Drainage and Recharge:

[0114] During the drainage process, to prevent the groundwater within the numerical grid from drying up, the actual pumping volume in the pumping wells is... Q well for: Q well = min( Q pump , Q max ),

[0115] in,

[0116] In the formula: Q pump The set pumping capacity, in meters (m). 3 / d; Q max The maximum drainable volume in the grid, in meters. 3 / d; Q ex For traffic exchange between adjacent grids, the unit is m. 3 / d; A cell This represents the current grid cross-sectional area, in meters (m). 2 ;z bot The current grid's base elevation, in meters; Δ t The time step is expressed in seconds (d).

[0117] It should be noted that the initial model condition in step A20 is the model surface elevation, which is used to ensure that the model can run; the given water head boundary is mainly the river (in the embodiment, the Laoha River and the Yingjin River). The mine water inflow in this application refers to the sidewall water inflow. Since the water quality of the Quaternary sidewall water is relatively good, while the bedrock fissure water at the bottom of the pit is polluted, the reinjection in this application refers to the reinjection of the Quaternary sidewall water.

[0118] In step A20, the curtain uses the HFB package in MODFLOW software to calculate the leakage through the head difference between adjacent units. The inter-grid permeability characteristic parameter (HC) is set to be very small, which can ensure a function similar to "waterproofing" to achieve generalization. HC is determined by dividing the curtain's permeability coefficient by the thickness of the curtain's waterproof wall.

[0119] In the A30 sub-step, the open-pit mine drainage hydrogeological model is meshed using the Voronoi unstructured mesh of MODFLOW USG.

[0120] In the A40 sub-step, the saturation thickness threshold is used. d 0 Determine whether the groundwater within the numerical grid has dried up, i.e. h - z bot < d 0 At the time of assessment, the groundwater level is considered to be dry, and the hydraulic conductivity is set to zero. When pumping or recharge stops, the groundwater level within the grid will recover. Whether it has recovered is determined by the groundwater level of adjacent grids: if the groundwater level of an adjacent grid is greater than z... bot + d When the water level reaches 0, the current grid is reactivated, and the grid water level is re-wetted. h re Represented as:

[0121]

[0122] In the formula: h re The unit is meters (m). χ The rehumidification coefficient is between 0 and 1. h a The water level is for adjacent grids, in meters (m).

[0123] It should be noted that the conductivity in the A40 sub-step is the permeability coefficient multiplied by the saturation thickness, which is different from the conductivity of the drainage ditch and the equivalent conductivity of the riverbed.

[0124] In step B, the heterogeneous inversion process of the parameters in the hydrogeological model of open-pit mine drainage is as follows:

[0125] Using the PEST program combined with Pilot Points and the Tikhonov regularization method based on singular value decomposition, parameters including aquifer permeability coefficient, infiltration recharge intensity, river leakage, and drainage boundary in the hydrogeological model of open-pit mine drainage were inverted. Then, the minimum value Φ of the objective function was solved based on the Gauss-Levenberg-Marquardt algorithm. min ;

[0126] Wherein, the objective function Φ is the weighted sum of variances between the simulated values ​​obtained by MODFLOW groundwater numerical simulation software and the observed values ​​monitored in the field:

[0127]

[0128] In the formula, y obsThese are groundwater level observations, in meters (m). f (p) is the model response function, in units of m, p = ( p 1, p 2, p 3, …, p Np ) are the parameters in the model. N p is the number of parameters; Q = diag( w 1 2 , w 2 2 , …, w n 2 Let be a diagonal matrix of squared observation weights. n The number of observation points;

[0129] To ensure a good fit between groundwater level and mine water inflow, the variances of both are considered in the objective function, and Tikhonov regularization deviation and smoothing constraints are added. The final objective function Φ is:

[0130]

[0131] In the formula: w These are the weighting coefficients; h i obs , h i sim The first i The observed and simulated water heads at each observation point are in meters (m). Q d obs , Q d sim These represent the observed and simulated water inflow rates, respectively, in m³ / d; λ is the regularization weighting factor. p j ref For the corresponding number j Reference parameter values ​​for each guide point p j , p m , p n These are the model parameter values ​​for the j-th, m-th, and n-th derivative points, respectively, in m / d; m , n ) represents a pair of adjacent guide points; N is the set of all adjacent guide points. w h , w Q ,w r,j , w mn These are the head fitting weight coefficients, the inflow fitting weight coefficients, and the first... j The weighting coefficient of the deviation of each guide point parameter from the reference value, and adjacent guide points. m , n The weighting coefficients of the parameter smoothing constraint are dimensionless.

[0132] It should be noted that, due to the method of recharge of open-pit mine drainage into the Quaternary loose aquifer outside the cutoff curtain, the following two situations may occur: First, the rise in water level after recharge may cause overflow, which is harmful because the hydraulic gradient on the mine side is large, and the groundwater overflowing the curtain will cause scouring and erosion of the inner wall structure and strata, reducing the stability of the curtain wall; Second, some planned recharge wells are close to the corners of the existing curtain, and bypass flow may occur after recharge, which is harmful because the bypass flow outside the curtain will cause the water level in the pit to increase, leading to an increase in the mine's water inflow.

[0133] In step C, Python is used to batch extract the water levels of all observation points in the simulation examples. Then, two times when the water level of an observation point reaches the curtain elevation are found between adjacent observation points. Based on the aforementioned two times, linear interpolation or cubic spline interpolation is used to accurately obtain the critical time for overflow. t lim Then determine the water level at the observation point. h Is it lower than the top elevation of the curtain? Z top ,Right now h < Z top Reinjection is safe if it occurs within the critical time for the corresponding water volume.

[0134] In step C, the PATH3DU particle tracking method is used to identify the groundwater seepage path and flow rate after reinjection, and to determine the safe reinjection area. Formula (1) is used to solve the three-dimensional seepage velocity field.

[0135]

[0136] In the formula: v x , v y , v z These are the pore velocity components of the aquifer in the x, y, and z directions, respectively, in m / d; θ Effective porosity; The aquifers are respectively in x , y , z Hydraulic gradient in a certain direction.

[0137] It should be noted that the particle position update of the aforementioned PATH3DU particle tracking method adopts the Lagrange tracking method, and the calculation adopts the time step method to obtain the migration path of the simulated reinjection water after entering the aquifer. Furthermore, based on the batch simulation of reinjection and pumping, a reinjection safety zone is obtained.

[0138] In step D, the curtain extension measure involves extending the cutoff curtain (up to 2.4 km) at the boundary of the mining rights or at the end of the curtain, and comparing the mine water inflow and groundwater uplift range under different extension lengths.

[0139] The measure of adding drainage wells involves setting up drainage wells around the perimeter of the mine pit to form a water-pumping curtain, which works in conjunction with the reinjection system.

[0140] The coordinated regulation of pumping and injection is achieved by adjusting the matching relationship between the pumping volume and the reinjection volume of a single well (i.e., by determining the total amount of reinjection wells to ensure that the pumping volume meets the reinjection requirements), thereby controlling the rate of rise in the groundwater level, avoiding curtain flow, and reducing the amount of water flowing into the mine.

[0141] In step D, the optimal parameter combination that satisfies the requirements of reducing mine water inflow, curtain safety, and water replenishment is determined by maximizing reinjection, ensuring no curtain overflow, and minimizing curtain bypass (so as not to increase mine water inflow).

[0142] Step E involves, after obtaining the optimal parameter combination, assessing whether external recharge will lead to a significant rise in regional water levels by combining numerical simulation results (i.e., obtaining the height and range of water level rise through numerical simulation). Then, the water balance method is used to further assess the changes in groundwater evaporation caused by recharge under the optimal parameter combination, thereby determining the risk of regional salinization (i.e., determining whether the groundwater depth is less than the estimated value; if it is less than the estimated value, the groundwater will evaporate directly; and then by comparing the evaporation with the rainfall, if the evaporation is greater than the rainfall, salinization will occur).

[0143] Example

[0144] Optimize the prevention and control of shallow recharge water hazards outside the drainage curtain at the Yuanbaoshan open-pit mine in Inner Mongolia.

[0145] S100: Based on the stratigraphic structure, hydrogeological conditions, and engineering layout of the open-pit mine, the research object is determined, groundwater sources are identified, and on-site hydrogeological data including atmospheric precipitation infiltration recharge, river seepage, mine drainage and evapotranspiration, groundwater level, mine inflow, and groundwater evaporation are obtained. An open-pit mine drainage hydrogeological model is established, and the model boundary conditions and model range are defined. The aforementioned model primarily focuses on Quaternary loose aquifers, with the underlying bedrock considered as a weakly permeable or impermeable boundary. The model range covers the mine pit, the cutoff wall, and the surrounding recharge influence area.

[0146] The study area has a multi-year average potential evapotranspiration of 1434 mm / a and a precipitation of 364 mm / a. Based on the CMA-RA / Land global land surface-atmosphere reanalysis product from the China Meteorological Administration, precipitation (Pr), potential evapotranspiration (ET0), and actual evapotranspiration (ET) of the study area were obtained. a Snowmelt equivalent water volume (SWE) and air temperature ( T air ).

[0147] The coal-bearing strata are a floodplain and lacustrine clastic formation, with the main coal-bearing strata being the Lower Cretaceous Fuxin Formation, primarily composed of grayish-white coarse sandstone, interbedded with medium-fine sandstone, conglomerate, grayish-black mudstone, and coal seams. The coal-bearing strata are 250–470 m thick, with an average thickness of 340 m, containing 12 complex coal seams, with a cumulative average mineable thickness of 84.29 m. The main aquifer in the study area is a Quaternary loose gravel layer formed by alluvial processes, with a thickness of 38–75 m, a unit yield of 24–143 L / (s·m), and a maximum permeability coefficient of 637 m / d. The nearby surface water systems are mainly the Yingjin River and the Laoha River, with average flows of 12.80 m³ / d and 12.80 m³ / d, respectively. 3 / s and 13.6m 3 / s. Among them, the Yingjin River flows past the edge of the mine pit and joins the Laoha River about 4km southeast of the open-pit mine. Exploration data shows that the Quaternary aquifer is replenished by seepage from the Laoha River and the Yingjin River, and the water level and water-bearing capacity in the near-river section have increased significantly.

[0148] The specific process in step S100 includes the following sub-steps:

[0149] S110. Constructing a hydrogeological model for open-pit mine drainage:

[0150] Based on the geological structure, hydrogeological conditions, and engineering layout of the open-pit mine, groundwater sources and sinks are identified, on-site hydrogeological data are obtained, and groundwater flow is generalized into a hydrogeological model of open-pit mine drainage:

[0151]

[0152] In the formula: μ For water supply, dimensionless; h The head is measured in meters (m). K xx , K yy , K zz Aquifer x , y , z The permeability coefficient component in the direction of the direction, in m / d; The rate of change of water head over time, expressed in m / d; These represent the rates of change of the seepage parameters in three directions of the Cartesian coordinate system, in units of 1 / m; The aquifers are respectively in x , y , z Hydraulic gradient in direction; W Source and sink items per unit time, with the unit being 1 / d; x , y , z represents spatial Cartesian coordinates, with units of meters (m). t Time is expressed in days (d).

[0153] S120. Identify the initial and boundary conditions of the model:

[0154] Initial conditions:

[0155] Given head boundary:

[0156] Waterproof boundary:

[0157] In the formula: h ( x , y , z , t )| t=0 To simulate the initial head distribution at each spatial point within the study area at the initial time (t=0), the unit is meters; h ( x , y , z , t )| Γ1 Let Γ1 be the head value of the spatial point on the given head boundary Γ1 at any time, in meters; The rate of change of water head along the direction of the outer normal to the boundary, which is 0 indicates that no seepage passes through, and is dimensionless; h 0 represents the initial head in meters (m); Ω represents the spatial domain; Γ1 and Γ2 represent the given head and the impermeable boundary, respectively; n is the unit vector of the boundary normal.

[0158] River seepage Q r for:

[0159]

[0160] In the formula: Q r The unit is m 3 / d; C river The equivalent hydraulic conductivity of the riverbed is expressed in meters (m). 2 / d;h river The water head of a river is measured in meters (m).

[0161] The excavation face of the Quaternary strata on the edge of the mine can be generalized as free drainage: if the groundwater level is higher than the bottom elevation of the drainage ditch, the drainage volume is proportional to the difference in water head between the two; if the groundwater level is lower than the bottom elevation of the drainage ditch, the drainage volume is zero; that is:

[0162]

[0163] In the formula: Q d This refers to the water inflow from the mine, expressed in cubic meters (m³). 3 / d; C drain The water conductivity coefficient of the drainage ditch is expressed in meters. 2 / d; d b This is the elevation of the bottom of the drainage ditch, in meters (m).

[0164] The groundwater evaporation rate ET is:

[0165]

[0166] Where: ET max This represents the maximum evaporation rate, expressed in m / d. z surf This is the ground elevation, in meters (m). z lim This is the evaporation limit elevation, in meters (m).

[0167] S130, Model Mesh Processing:

[0168] The open-pit mine drainage hydrogeological model uses MODFLOW USG's Voronoi unstructured mesh for mesh generation. The mesh is fined near the mine boundary, rivers, curtain flows, and wells, with a minimum mesh size of 2m. Geological borehole and pit elevation data are integrated to achieve accurate modeling of the side slopes, enabling precise assessment of curtain flow and overflow phenomena that may occur during water injection. The open-pit mine drainage hydrogeological model and mesh generation are shown below. Figure 2 As shown.

[0169] S140, Generalization of Drainage and Recharge:

[0170] During the drainage process, there is a possibility that the groundwater within the numerical grid may be depleted if the flow rate of the pumping wells is too high. To prevent the groundwater within the numerical grid from drying up, the actual pumping volume in the pumping wells should be controlled. Q well for: Q well = min( Qpump , Q max ),

[0171] in,

[0172] In the formula: Q pump The set pumping capacity, in meters (m). 3 / d; Q max The maximum drainable volume in the grid, in meters. 3 / d; Q ex For traffic exchange between adjacent grids, the unit is m. 3 / d; A cell This represents the current grid cross-sectional area, in meters (m). 2 ;z bot The current grid's base elevation, in meters; Δ t The time step is expressed in seconds (d).

[0173] The curtain is generalized using HFB (Horizontal Flow Barrier), and the permeability characteristics of HFB are determined by dividing the curtain's permeability coefficient by the wall thickness; in this embodiment, a value of 2×10 is used based on the actual water-resistant performance of the curtain. -4 d -1 Since the aquitard and coal seam do not contain groundwater, the model only considers Quaternary aquifers and weakly permeable layers.

[0174] Further consideration is given to rewetting the dewatering numerical grid to accurately simulate the changes in aquifer state caused by mine drainage.

[0175] In step S140, the saturation thickness threshold is used. d 0 Determine whether the groundwater within the numerical grid has dried up, i.e. h -z bot < d 0 If the groundwater level is considered to be dry, the hydraulic conductivity is set to zero and removed from the numerical solution coefficient matrix. When pumping or recharge stops, the groundwater level within the grid will recover. Whether it has recovered is determined by the groundwater level of adjacent grids: if the groundwater level of an adjacent grid is greater than z... bot + d When the water level reaches 0, the current grid is reactivated, and the grid water level is re-wetted. h re Represented as:

[0176]

[0177] In the formula: hre The unit is meters (m). χ The rehumidification coefficient is between 0 and 1; in this embodiment, it is set to 0.8. h a The water level is for adjacent grids, in meters (m).

[0178] S200: Using groundwater level and mine inflow monitoring data from hydrogeological data, combined with guide point and regularized inversion methods, heterogeneous inversion is performed on the hydrogeological model of open-pit mine drainage, including aquifer permeability coefficient, infiltration recharge intensity, riverbed leakage and drainage boundary parameters, to achieve calibration of the hydrogeological model of open-pit mine drainage.

[0179] The heterogeneous inversion process for parameters in the hydrogeological model of open-pit mine drainage is as follows:

[0180] The study area included 20 effective observation points for water level, 6 observation points inside and outside the curtain, and the average mine inflow (8.44 × 10⁴ m³) as of March 2023. 3 / d) Using the observation dataset, the PEST program combined with Pilot Points and the Tikhonov regularization method of singular value decomposition was used to invert the heterogeneous parameters in the hydrogeological model of open-pit mine drainage. Then, the minimum value Φ of the objective function was solved based on the Gauss-Levenberg-Marquardt algorithm. min .

[0181] Wherein, the objective function Φ is the weighted sum of variances between the simulated values ​​obtained by MODFLOW groundwater numerical simulation software and the observed values ​​monitored in the field:

[0182]

[0183] In the formula, y obs These are groundwater level observations, in meters (m). f (p) is the model response function, in units of m, p = ( p 1, p 2, p 3, …, p Np ) are the parameters in the model. N p is the number of parameters; Q = diag( w 1 2 , w 2 2 , …, w n 2 Let be a diagonal matrix of squared observation weights. n The number of observation points;

[0184] To ensure a good fit between groundwater level and mine water inflow, the variances of both are considered in the objective function, and Tikhonov regularization deviation and smoothing constraints are added. The final objective function Φ is:

[0185]

[0186] In the formula: w These are the weighting coefficients; h i obs , h i sim The first i The observed and simulated water heads at each observation point are in meters (m). Q d obs , Q d sim These represent the observed and simulated water inflow rates, respectively, in m³ / d; λ is the regularization weighting factor. p j ref For the corresponding number j Reference parameter values ​​for each guide point p j , p m , p n These are the model parameter values ​​for the j-th, m-th, and n-th derivative points, respectively, in m / d; m , n ) represents a pair of adjacent guide points; N is the set of all adjacent guide points. w h , w Q , w r,j , w mn These are the head fitting weight coefficients, the inflow fitting weight coefficients, and the first... j The weighting coefficient of the deviation of each guide point parameter from the reference value, and adjacent guide points. m , n The weighting coefficients of the parameter smoothing constraint are dimensionless.

[0187] In the PEST inversion process, the water level simulation error is assumed to be ±1m, while the inflow error is set to ±500m. 3 / d, with weights set to 1 and 0.002 respectively. The main parameters involved in the steady-state model inversion are the horizontal permeability coefficient (HK), the average infiltration recharge intensity (RCH), and the equivalent hydraulic conductivity coefficient of the riverbed seepage ( C river), equivalent hydraulic conductivity coefficient of mine boundary drainage ( C drian ) and maximum evaporation (ET) max (HK and RCH were achieved using guide point assistance, and the initial parameter values ​​and ranges were determined through model trials, as shown in Table 1. The maximum permeability coefficient of the Quaternary gravel layer was set to 300 m / d to ensure parameter rationality. The evaporation limit depth was set to 6 m, and the specific yield was set to 0.2 during the unsteady flow simulation.)

[0188] Table 1. Model parameters involved in the inversion and their value ranges

[0189]

[0190] The groundwater simulation error bars and comparison with observed values ​​of the PEST-calibrated open-pit mine drainage hydrogeological model are shown below. Figure 3 Figures 3a to 3c show that the vast majority of observation errors are less than 1m, indicating that the water level simulation error is very small.

[0191] S300: Conduct batch numerical simulations of open-pit mine drainage being reinjected into Quaternary loose aquifers outside the cutoff curtain. Using Python, different operating conditions including reinjection flow rate, reinjection location, curtain extension, and drainage wells are combined. Water balance terms and observation point water levels are extracted from the output files. Then, the critical time for curtain overflow is identified using interpolation methods for the observation point water levels in all simulation examples. t lim ; and / or use the PATH3DU particle tracking method to identify the groundwater seepage path and bypass flow after reinjection, and determine the safe reinjection zone. Among them, the batch numerical simulation may have the following two situations: First, the rise in water level after reinjection may cause flooding, the harm of which is that the hydraulic gradient of the mine pit side is large, and the groundwater will scour and erode the inner wall structure and strata after flooding the curtain, reducing the stability of the curtain wall; Second, some planned reinjection wells are close to the corners of the existing curtain, and bypass flow may occur after reinjection, the harm of which is that the bypass flow of reinjection outside the curtain will cause the water level in the pit to increase, which will lead to an increase in the mine pit water inflow.

[0192] In order to quantitatively determine whether reinjection is safe, the specific steps are as follows:

[0193] S310. Use Python to batch extract the water levels of all observation points in the simulation examples. Then, find the two times when the water level of an observation point reaches the curtain elevation. Based on the two times, use linear interpolation or cubic spline interpolation to accurately obtain the critical time of the overflow. t lim Then determine the water level at the observation point. h Is it lower than the top elevation of the curtain? Z top ,Right nowh < Z top Reinjection is safe if it occurs within the critical time for the corresponding water volume.

[0194] In this embodiment, the critical time for overflow is identified by using the intersection of the monitored water level and the top elevation of the curtain. t lim At the critical time corresponding to the water volume t lim Recharge within the specified area is safe. Therefore, the constructed open-pit mine drainage hydrogeological model can be used to conduct simulations of different recharge and pumping batches to obtain a safe recharge area.

[0195] S320. The PATH3DU particle tracking method is used to identify the groundwater seepage path and flow rate after recharge. The three-dimensional seepage velocity field is solved using formula (1) to determine the safe area for recharge.

[0196]

[0197] In the formula: v x , v y , v z These are the pore velocity components of the aquifer in the x, y, and z directions, respectively, in m / d; θ Effective porosity; The aquifers are respectively in x , y , z Hydraulic gradient in a certain direction.

[0198] In this embodiment, the eastern section of the curtain is located inside the pit, with its top elevation at 450m, lower than the pit edge at 472m. After recharge, the rising water level may cause overflow. Furthermore, some planned recharge wells are close to the existing curtain's corners, which may cause bypass flow after recharge.

[0199] The 16 drainage wells remaining outside the curtain were used as the first phase of reinjection wells to minimize economic costs. The same reinjection flow rate (Qin) was assumed for each well. The seepage trajectory after reinjection was displayed using PATH3DU particle tracking, showing the bypass and overflow flows generated under different reinjection flow rates. Figure 4 As shown.

[0200] The water level changes at observation points near the curtain area due to different reinjection flow rates are shown in the figure. Figure 5 Figure 5a shows that in the numerical simulation, the curtain is at the same elevation as the top of the grid at its location, preventing groundwater from directly overflowing through the curtain. However, by extracting the time it takes for the water level to reach the curtain elevation, the critical time point for curtain overflow can be accurately identified. t lim ,like Figure 5 As shown in Figure 5b. When the single-well recharge flow rate is 3500 m³ / h... 3 At a rate of / d, continuous recharge for approximately 330 days results in a water level approaching 450m. Based on the critical time point, the maximum duration of pulse recharge and different pause intervals can be set, such as... Figure 5 As shown in Figure 5c, simulation results indicate that pulsed recharge can effectively control water level rise, but the different pause times in the pulsed recharge scheme have little impact. With long-term pulsed recharge, the groundwater level will still slightly exceed the curtain elevation by up to approximately 1.7m, indicating that the first peak water level during pulsed recharge should be below 450m, which can be controlled by adjusting the recharge flow rate and pulse duration.

[0201] S400: Based on the batch numerical simulation results of step S300, three engineering measures are adopted: collaborative optimization of curtain extension, addition of drainage wells, and coordinated pumping-injection control. The optimal parameter combination that meets the requirements of reducing mine water inflow, curtain safety, and water resource replenishment is determined.

[0202] The following engineering measures are introduced and combined for optimization:

[0203] S410, Curtain Extension Measures: Extend the cutoff curtain (maximum 2.4km) at the boundary of the mining rights or at the end of the curtain, and compare the mine water inflow and groundwater uplift range under different extension lengths.

[0204] Using the above method, according to Figure 5 The simulation results in Figure 5b show that the design curtain extends northeastward, and the groundwater rise in areas with different curtain extension lengths is compared. The water level rise Δ... h =1.0m is used as the identification boundary for water level rise. Further data is obtained from the above simulations showing the mine water inflow and the range of water level rise under different curtain extension lengths, such as... Figure 6 As shown, when the curtain is not extended, the water level rise caused by the recharge has a relatively small impact range, approximately 12.9 km. 2 However, when the curtain was extended by only 400m, the average mine water inflow decreased by approximately 10.8%, and the area affected by the water level rise increased to 44.3km. 2 As the curtain was subsequently extended further, the rate of decrease in mine water inflow slowed, and the area affected by the water level rise stabilized. This result indicates that extending the curtain by 400m yielded the best effect.

[0205] S420, Drainage Well Installation Measures: Drainage wells are installed around the mine pit to form a pumping curtain, which works in conjunction with the reinjection system.

[0206] Without increasing the curtain length, 49 drainage wells are designed, with a minimum planned well spacing of 100m; 39 existing wells and planned recharge wells are located on the east side. The designed pumping and injection flow rates for each well are 1000~5000m³. 3 / d, with 8 pumping volume values ​​and 15 injection volume values, resulting in 120 batch simulation examples with free combinations. The pumping volume reaches 5000m³. 3 When the flow rate is / d, due to the influence of the permeability coefficient, some pumping wells cannot meet the set pumping capacity and are thus drained, such as... Figure 7 As shown in Figure 7a.

[0207] S430, Pump-Injection Coordinated Control: By adjusting the matching relationship between the pumping volume and reinjection volume of a single well, the rate of groundwater level rise is controlled, curtain flow is avoided, and the mine water inflow is reduced.

[0208] Under conditions of simultaneous pumping and injection, the critical time of curtain flow under different single-well pumping and injection rates was obtained by extracting the water level at observation points between the reinjection well and the curtain. Linear interpolation was then used to obtain the distribution cloud map. The results are shown in [Figure number missing]. Figure 7 Figure 7b shows the blank area, which represents the condition zone where curtain flow does not occur. The results show that increasing the pumping rate of a single well leads to... t lim The decrease, while the increase in water injection volume per well led to t lim Increase. The final result, showing the change in mine water inflow over time under different injection conditions, is shown in [reference needed]. Figure 7 Figure 7c shows that simultaneous pumping and injection can effectively optimize the pumping and injection volumes of a single well, thereby avoiding curtain overflow.

[0209] S500: After obtaining the optimal parameter combination, the system assesses whether the external recharge will lead to a significant rise in the regional water level, based on the on-site conditions (i.e., by numerical simulation, the height and range of the water level rise are obtained). Then, the water balance method is used to further assess the change in groundwater evaporation caused by recharge under the optimal parameter combination, thereby determining the risk of regional salinization (i.e., determining whether the groundwater depth is less than 6m, based on empirical values; if it is less than 6m, the groundwater will evaporate directly; then, by comparing the evaporation with the rainfall, if the evaporation is greater than the rainfall, salinization will occur).

[0210] Based on groundwater level observation data, the groundwater depth in the study area is generally greater than 10m, exceeding the evaporation limit. Therefore, evapotranspiration has little impact on the regional groundwater level; drainage and recharge primarily affect the regional groundwater resource reserves. Due to mine excavation and curtain wall recharge, some areas near the mines have groundwater depths less than 6m, and water level fluctuations affect evaporation. In the above recharge scheme, considering only the recharge of 8 existing wells and planned wells, the temporal variation of evaporation under different single-well recharge flow rates is as follows: Figure 8 As shown in Figure 8a, the initial evaporation rate is approximately 170.9 m³. 3 / d, when Q in = 6000m 3At / d, the simulated maximum evaporation over 5000 days increased by 3.5 times, equivalent to 0.53% of the mine water inflow at the same time, which is negligible. (Based on a single well of 6000m...) 3 Even with continuous recharge for 5000 days, evaporation only occurs at the mine boundary and the confluence of the Yingjin River and the Laoha River downstream. Figure 8 As shown in Figure 8b.

[0211] In conclusion, due to the good permeability of the aquifer in the study area, the curtain-style recharge design proposed in this paper will not cause a significant rise in the regional water level and increase evaporation, thus it will not lead to salinization and will not have a large-scale impact on the surface vegetation.

[0212] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for evaluating the external reinjection and safety optimization of drainage curtains in open-pit mines, characterized by: The process includes model building, model calibration, simulation and safety scheme identification, water hazard prevention optimization, and ecological impact identification. The specific details of each step are as follows: A. Model Construction: Based on the stratigraphic structure, hydrogeological conditions and engineering layout of the open-pit mine, the groundwater source sinks are identified through the model generalization method, the hydrogeological data of the site are obtained, the hydrogeological model of the open-pit mine drainage is established, and the boundary conditions and model range of the aforementioned model are defined. B. Model calibration: Using groundwater level and mine water inflow monitoring data from hydrogeological data, combined with guide point and regularized inversion methods, the parameters in the hydrogeological model of open-pit mine drainage are inverted in a heterogeneous manner to achieve the calibration of the hydrogeological model of open-pit mine drainage. C. Simulation and Safety Scheme Identification: Conduct batch numerical simulations of open-pit mine drainage being reinjected into the Quaternary loose aquifer outside the cutoff curtain. Using Python, different operating conditions including reinjection flow rate, reinjection location, curtain extension, and drainage wells are combined to extract the water balance term and observation point water level from the output file. Then, the critical time for curtain overflow is identified by interpolation of the observation point water levels in all simulation examples. t lim ; and / or use the PATH3DU particle tracking method to identify the groundwater seepage path and bypass flow rate after reinjection, and determine the safe reinjection zone; D. Water hazard prevention and control optimization: Based on the batch numerical simulation results of step C, three engineering measures are adopted: collaborative optimization of curtain extension, addition of drainage wells, and pumping-injection coordinated control. The optimal parameter combination that meets the requirements of reducing mine water inflow, curtain safety, and water resource replenishment is determined. E. Ecological impact identification: The water balance method is used to assess the changes in groundwater evaporation caused by recharge under the optimal parameter combination and to determine the risk of regional salinization. The specific process in A includes: A10. Constructing a hydrogeological model for open-pit mine drainage: Based on the geological structure, hydrogeological conditions, and engineering layout of the open-pit mine, groundwater sources and sinks are identified, on-site hydrogeological data are obtained, and groundwater flow is generalized into a hydrogeological model of open-pit mine drainage: In the formula: μ For water supply, dimensionless; h The head is in meters (m). K xx , K yy , K zz Aquifer x , y , z The permeability coefficient component in the directional direction, with units of m / d; The rate of change of water head over time, expressed in m / d; These represent the rates of change of the seepage parameters in three directions of the Cartesian coordinate system, in units of 1 / m; The aquifers are respectively in x , y , z Hydraulic gradient in direction; W Source and sink items per unit time, with the unit being 1 / d; x , y , z represents spatial Cartesian coordinates, in meters; t Time, in days (d). A20. Identify the initial and boundary conditions of the model: Initial conditions: Given head boundary: Waterproof boundary: In the formula: h ( x , y , z , t )| t=0 To simulate the initial head distribution at each spatial point within the study area at the initial time (t=0), the unit is meters; h ( x , y , z , t )| Γ1 Let Γ1 be the head value of the spatial point on the given head boundary Γ1 at any time, in meters; Γ2 is the rate of change of water head along the outer normal direction of the impermeable boundary, and 0 indicates that no seepage passes through it. It is dimensionless. h 0 represents the initial head in meters (m); Ω represents the spatial domain; Γ1 and Γ2 represent the given head and the impermeable boundary, respectively; n is the unit vector of the boundary normal. River seepage Q r for: In the formula: Q r The unit is m 3 / d; C river The equivalent hydraulic conductivity of the riverbed is expressed in meters (m). 2 / d; h river The water head of a river is measured in meters (m). The excavation face of the Quaternary strata on the edge of the mine can be generalized as free drainage: if the groundwater level is higher than the bottom elevation of the drainage ditch, the drainage volume is proportional to the difference in water head between the two; if the groundwater level is lower than the bottom elevation of the drainage ditch, the drainage volume is zero; that is: In the formula: Q d This refers to the water inflow from the mine, expressed in cubic meters (m³). 3 / d; C drain The water conductivity coefficient of the drainage ditch is expressed in meters. 2 / d; d b This is the elevation of the bottom of the drainage ditch, in meters (m). The groundwater evaporation rate ET is: Where: ET max This represents the maximum evaporation rate, expressed in m / d. z surf This is the ground elevation, in meters (m). z lim This is the evaporation limit elevation, in meters (m). A30. Model Mesh Processing: The open-pit mine drainage hydrogeological model was divided into grids, and the grids were densified near the mine boundary, rivers, curtains, drainage wells and reinjection wells in the aforementioned model. A40. Generalization of Drainage and Recharge: During the drainage process, to prevent the groundwater within the numerical grid from drying up, the actual pumping volume in the pumping wells is... Q well for: Q well = min( Q pump , Q max ), in, In the formula: Q pump The set pumping capacity, in meters (m). 3 / d; Q max The maximum drainable volume in the grid, in meters. 3 / d; Q ex For traffic exchange between adjacent grids, the unit is m. 3 / d; A cell This represents the current grid cross-sectional area, in meters (m). 2 ;z bot The current grid's base elevation, in meters; Δ t The time step is expressed in seconds (d). In C, Python is used to extract the water level of all observation points in the simulation examples in batches. Then, two times when the water level of the observation point reaches the curtain elevation are found between adjacent observation points. Based on the two times mentioned above, linear interpolation or cubic spline interpolation is used to accurately obtain the overflow critical time tlim. Then, it is determined whether the water level h of the observation point is less than the top elevation Ztop of the curtain. That is, when h < Ztop, it is safe to recharge within the critical time of the corresponding water volume. The PATH3DU particle tracking method is used to identify the groundwater seepage path and flow around the injection point after recharge, and to determine the safe recharge zone. Formula (1) is used to solve the three-dimensional seepage velocity field. In the formula: v x , v y , v z These are the pore velocity components of the aquifer in the x, y, and z directions, respectively, in m / d; θ Effective porosity; The aquifers are respectively in x , y , z Hydraulic gradient in direction; In section D, the curtain extension measure involves extending the cutoff curtain at the boundary of the mining rights or at the end of the curtain, and comparing the mine water inflow and groundwater uplift range under different extension lengths; the drainage well addition measure involves setting up drainage wells around the mine to form a pumping curtain, which operates in coordination with the reinjection system; and the pumping-injection coordinated control measure involves adjusting the matching relationship between the pumping volume of a single well and the reinjection volume to control the rate of groundwater level rise, avoid curtain overflow, and reduce mine water inflow. The term E refers to the evaluation of whether external recharge will lead to a significant rise in regional water levels after obtaining the optimal parameter combination, combined with numerical simulation results. Then, the water balance method is used to further evaluate the change in groundwater evaporation caused by recharge under the optimal parameter combination, thereby determining the risk of regional salinization.

2. The method for evaluating the external reinjection and safety optimization of open-pit mine drainage curtains according to claim 1, characterized in that: In A, the groundwater source includes rainfall infiltration, mine drainage, and drainage well volume, and the hydrogeological data includes atmospheric precipitation infiltration, river seepage, mine drainage and evaporation, groundwater level, mine inflow, and groundwater evaporation.

3. The method for evaluating the external reinjection and safety optimization of open-pit mine drainage curtains according to claim 2, characterized in that: In the A30, the open-pit mine drainage hydrogeological model is meshed using the Voronoi unstructured grid of MODFLOW USG. In A40, the saturation thickness threshold is used. d 0 Determine whether the groundwater within the numerical grid has dried up, i.e. h - z bot < d 0 At the time of assessment, the groundwater level is considered to be dry, and the hydraulic conductivity is set to zero. When pumping or recharge stops, the groundwater level within the grid will recover. Whether it has recovered is determined by the groundwater level of adjacent grids: if the groundwater level of an adjacent grid is greater than z... bot + d When the water level reaches 0, the current grid is reactivated, and the grid water level is re-wetted. h re Represented as: In the formula: h re The unit is meters (m). χ The rehumidification coefficient is between 0 and 1. h a The water level is for adjacent grids, in meters (m).

4. The method for evaluating the external reinjection and safety optimization of open-pit mine drainage curtains according to claim 1, characterized in that: In section B, the heterogeneous inversion process of the parameters in the hydrogeological model for open-pit mine drainage is as follows: Using the PEST program combined with Pilot Points and the Tikhonov regularization method based on singular value decomposition, parameters including aquifer permeability coefficient, infiltration recharge intensity, river leakage, and drainage boundary in the hydrogeological model of open-pit mine drainage were inverted. Then, the minimum value Φ of the objective function was solved based on the Gauss-Levenberg-Marquardt algorithm. min ; Wherein, the objective function Φ is the weighted sum of variances between the simulated values ​​obtained by MODFLOW groundwater numerical simulation software and the observed values ​​monitored in the field: In the formula, y obs These are groundwater level observations, in meters (m). f (p) is the model response function, in units of m, p = ( p 1, p 2, p 3, …, p Np ) are the parameters in the model. N p is the number of parameters; Q = diag( w 1 2 , w 2 2 , …, w n 2 Let be a diagonal matrix of squared observation weights. n The number of observation points; To ensure a good fit between groundwater level and mine water inflow, the variances of both are considered in the objective function, and Tikhonov regularization deviation and smoothing constraints are added. The final objective function Φ is: In the formula: w These are the weighting coefficients; h i obs , h i sim The first i The observed and simulated water heads at each observation point are in meters (m). Q d obs , Q d sim These represent the observed and simulated water inflow rates, respectively, in m³ / d; λ is the regularization weighting factor. p j ref For the corresponding number j Reference parameter values ​​for each guide point p j , p m , p n These are the model parameter values ​​for the j-th, m-th, and n-th derivative points, respectively, in m / d; m , n ) represents a pair of adjacent guide points; N is the set of all adjacent guide points. w h , w Q , w r,j , w mn These are the head fitting weight coefficients, the inflow fitting weight coefficients, and the first... j The weighting coefficient of the deviation of each guide point parameter from the reference value, and adjacent guide points. m , n The weighting coefficients of the parameter smoothing constraint are dimensionless.

5. A computer storage medium storing a computer program thereon, characterized in that: When the computer program is executed by the processor, it implements the open-pit mine drainage curtain external recharge and safety optimization evaluation method as described in any one of claims 1 to 4.

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