A Finite Element Model to: 2. Simulate Groundwater Rebound Problems in Backfilled Open Cut Mines

A two-dimensional finite element softwate called SEEP/W can be easily modified to simulate the groundwater rebound process within the spoil of an open cut mine taking into account saturated and unsaturated flow, hydraulic conductivity, and water content (as a function of pore-water pressure). Flexibility in the model is achieved by assigning different boundary conditions. In this paper, the results of the numerical model of the ground water rebound are presented and compared with those obtained from analytical solutions, another numerical model, and with data measured at the Horsley backfilled site in the UK. This model calculates realistic results that can be used by mine operators and environmental engineers to control the quality of mine drainage in a backfilled open cut operation.     

侏罗纪煤田宝塔山砂岩含水层大流量大降深放水试验

为了在抽水试验的基础上进一步查明侏罗纪煤田宝塔山砂岩含水层的水文地质特征,开展了井下放水试验,单孔放水量平均值为237.91 m3/h,多孔放水量平均值为444.10 m3/h,宝塔山砂岩含水层地下水位下降最大值达310 m.通过大流量大降深放水试验,计算出含水层的渗透系数和单位涌水量,确定宝塔山砂岩含水层与白垩系、煤...     

Assessment and Prevention of Water and Sand Inrush Associated with Coal Mining Under a Water-filled Buried Gully: A Case Study

Mining under a water-filled buried gully risks a potentially serious water and sand inrush, especially if the bedrock is thin. A case study was conducted at a Chinese coal mine, where the thin overlying overburden was covered by widely distributed gullies. Several empirical formulas and numerical modelling indicated that the overlying strata was almost totally fractured and that all of the conditions for an inrush were met. Pre-mining dewatering and grout injection were initiated. The groundwater table was lowered by 13 surface pumping wells and 33 underground upholes that were drilled around the gully. Those located at the bottom of the gully were generally better in aquifer dewatering than those located at the banks. A barrier was constructed to avoid a water inrush by injecting a chemical grout into the bottom of the buried gully through 25 surface holes. Field observations of the water table, underground water yield, and overburden movement prove the validity of the assessment methods and treatments.     

基于数值模拟预测工作面顶板太灰含水层疏降水量

通过分析万峰矿地质及水文地质资料,研究万峰矿井太原组灰岩含水层水文地质特征,应用Visual MODFLOW软件,建立太灰含水层地下水数值模型,通过模型计算模拟太灰水流场动态特征,预测当回采工作面太灰水位疏降至含水层底板+160 m时,太灰含水层趋于疏干,工作面顶板太灰水的疏降水量为750 m³/h,为工作面安全回采及矿井排水设施的建立提供依据。     

柠条塔矿区南翼S1210工作面涌水机制分析

柠条塔煤矿作为陕北矿区中开采侏罗系延安组煤层的矿井,涌水量一般不大,但2011年5月30日发生了涌水事故,查明涌水事故原因至关重要。通过地下水位观测、水文地质钻探等手段,进行了地面水文地质条件探查,总结了地表水系水位变化情况及地下水水位动态特征;结合现场放水试验、地下水连通试验,详细分析含隔水层特性,即含水层厚度、裂隙发育、富水性及变化规律。最终确定了涌水水源是工作面上覆侏罗系中统直罗组风化基岩裂隙承压水,涌水通道为西北部连续分布粗—中粒砂岩。     

长江漫滩复杂地层条件下超大超深基坑降水设计

长江漫滩地区第四系松散层是一个巨厚的复杂含水体,地下水丰富,对深基坑施工影响极大。详细分析了南京梅子洲过江通道及青奥轴线地下交通系统工程中B2-J1区基坑降水工程的特征,分区分段进行降水设计,并根据各区段的地层特征,选用合适的降水井结构,利用全孔填滤料的方式对开挖面以上含水层进行疏导,取得良好的降水效果;针对坑内、外水位差大的区段设置坑外备用井,防止因围护结构缺陷造成基坑管涌,为基坑安全增加保障,并有效地控制了降水对周边环境破坏。     

Evaluating the Origin of Seepage Water in the Golgohar Iron Mine,Iran

The Golgohar mine produces iron ore from an open pit in south-central Iran that is now more than 100 m below the water table, and dewatering has not solved the mine’s water seepage problem. Previous studies had reported that Kheirabad (Sirjan) Playa, 13 km north of the mine, was the most probable groundwater source. A combination of geological, hydrogeological, hydrochemical, and isotopic techniques were used to evaluate the hydraulic connectivity between the mine and the lake, and to characterize the probable water sources. Thirty-two surface and groundwater samples were collected and analyzed for major and minor (Li, B, and Br) constituents. Ten water samples were analyzed for oxygen-18 and deuterium and three samples were analyzed for tritium. The results indicated that impermeable formations and very low-permeability alluvial deposits lie between lake and the pit. In addition, the chemical and isotopic signatures of the two water sources indicated different origins. Inverse geochemical modeling and the mine water’s isotopic signatures suggest that the water is coming from the surrounding alluvial aquifer, or is deep basin water from within the fractured bedrock, or a mixture of the two.     

A Study of Water-Inrush Mechanisms Based on Geo-Mechanical Analysis and an In-situ Groundwater Investigation in the Zhongguan Iron Mine,China

The Zhongguan iron mine is strongly threatened by water inrushes because of the thick Ordovician limestone aquifer and a variety of concealed faults. An inrush event occurred at ?260 m below sea level (bsl), inundating the mine during the mineral deposit developing stage. It was very important to understand why and how this occurred to prevent its recurrence. A numerical simulation of a process-based model of the excavation, together with an in-situ groundwater investigation, showed that the event was related to the normally impermeable X1 fault, which was gradually activated from the bottom of the aquifer to the mine roof as excavation developed. The activated fault transformed into an inrush channel, hydraulically connecting the aquifer and the roadway. Thus, faults and other geological structures have to be mapped before mining. Moreover, sealing possible water channels before excavation in potential inrush areas is much better than advance dewatering because of the aquifer’s transmissivity and the limited effectiveness of grout curtains.     

蒙西深部复合水体下高强度安全疏控水开采技术

针对蒙西矿区纳林河二号矿井开采深度大,主采煤层受多层含水层威胁、开采强度大的特点,在确定该矿区水害威胁类型的基础上,采用数值模拟、物理相似模拟和经验类比的方法研究了主采煤层覆岩破坏高度,分析了各含水层的充水规律,提出了复合水体下安全“疏控水”技术方案。研究结果表明：蒙西矿区开采主要防治水问题是复合水体威胁下安全采煤;预计得到纳林河二号矿井3-1煤开采垮落带高度按照垮采比4.5倍选取,裂采比按照15倍选取;提出的复合水体下“疏控水”采煤的总体方案为对于白垩系志丹群含水层采取“顶水开采”的方案,对于直罗组底部砂岩含水层采取“边回采边疏降”的控水方案,对于延安组含水层则采取“钻孔疏干或疏降与回采疏干或疏降相结合、先疏后采与边疏边采相结合”的疏水方案。     

Modelling of groundwater recovery process for prediction of land settlement in surface mines

A two-dimensional finite element model was used to simulate the groundwater recovery process under various surface mining situations. The simulation results were used to predict the rate at which soil settlement takes place. It was found that the groundwater recovery process is very fast immediately after mine closure and cessation of dewatering programmes; a significant part of mine land settlement can be measured at such times. This paper presents a method for deriving the relationship between the re-establishment of the natural groundwater regime to its equilibrium position as existed prior to the commencement of mining operations and mine spoil settlement.     

Hydrogeological Model for Groundwater Prediction in the Shennan Mining Area,China

Coal mining can seriously affect groundwater systems in aquifers that overlie the coal seam, especially in dry and water-stressed areas where protection of groundwater resources is very important. Through generalization of the hydrogeological conditions and analysis of the actual groundwater flow field in a confined weathered bedrock aquifer overlying the Shennan mining area in northern Shaanxi, a hydrogeological conceptual model and numerical groundwater flow model were established. FEFLOW finite element software was used to solve the model and dynamic groundwater data were used to validate it. The study area was hydrogeologically modeled by repeatedly adjusting the parameters. The model was then used to simulate the effect of mining on the overlying aquifer based on the mining plan for the next 5 years by adjusting the quantity of water discharged, the hydrogeological parameters of the upper water-bearing zone, the characteristics of the groundwater flow field, and the predicted water balance after 5 years. The results show that the maximum drawdown could be as high as 50 m (northeast of the Zhangjiamao Mine). A cone of depression centered on the Ningtiaota, Zhangjiamao, and Hongliulin mines will be formed that will influence more than 75% of the simulation area.     

煤炭地下气化酚污染迁移数值模拟

基于我国西部某煤炭地下气化试验,以气化特征污染物之一--挥发酚为例,建立地下水流运动和污染物迁移数学模型,对气化炉闭炉后的污染物迁移规律进行了数值模拟。结果表明： 20 a 预测期内,挥发酚具有极弱的向煤层隔水顶板上覆咸水含水层的迁移倾向,水动力弥散是其迁移的主要方式;煤层内部挥发酚的迁移只发生在燃空区附近,在气化后20 a,污染晕为以燃空区为中心的椭圆形,长轴方向大约500 m,短轴方向大约300 m,煤层的低渗透性、水力坡度小和介质的吸附作用是阻碍挥发酚在煤层内扩展的主要原因;煤层与含水层之间的水头差、燃空区上下方隔水层的破坏程度和范围以及水动力弥散作用是含水层污染评价的关键因素。地下水污染风险须通过科学选址、气化过程控污、煤层燃空区污染处理等措施进行综合防治。     

Development of the Sleeper Pit Lake

Abstract.  The Sleeper open pit gold mine operated from the mid-1980s through the mid-1990s. Operations were mostly sub-water table and extensive dewatering was required to lower groundwater levels by 180 m. Dewatering flows peaked at 930 L/s, with most flow contributed from an alluvial aquifer. After completion of mining, the pit was rapidly filled with water pumped from the alluvial aquifer to reduce the exposure time of sulfide wall rocks and waste rocks in the ultimate pit. The pumped alluvial groundwater provided a large volume of low total dissolved solids (TDS), high alkalinity water that controlled the early chemistry. The rising lake waters were amended with lime to buffer excess acidity contributed to the lake from reactive pit wall rocks during submergence. The pore water contained in submerged waste rock at the base of the pit was elevated in TDS and subsequently of higher density that the lake water. The density contrast and waste rock location limited contributions of waste rock pore water to the main body of the lake. Some stratification of the early lake occurred, with shallow water characterized by higher pH, low dissolved metals, and sulfate; deeper water had lower pH and higher dissolved metals and sulfate. The reservoir of alkalinity in the shallow layer mixed with the deeper waters and created a stabilized lake with a homogenized column that exceeded water quality expectations. Current water quality meets all Nevada primary drinking water standards with the exception of sulfate, TDS, and manganese, which are slightly elevated, as predicted. Chemistry has remained stable since development of the initial lake.     

Optimization of Water Pumping and Injection for Underground Coal Gasification in the Meiguiying Mine,China

The Meiguiying mine is a famous underground coal gasification (UCG) mine in China, but there has been a potential safety hazard since it began operating, that groundwater in the overlying aquifer might enter the mine and even extinguish the gasifier. A 3-D hydrogeological model was developed to explore the characteristics of the seepage field of the aquifer and determine an optimal water pumping and injection option for the UCG. The results indicate that more attention should be paid to control induced fractures of the roof due to the increasing water level of the aquifer, and that a pumping rate of 160 m³/day would decrease the water level to a reasonable elevation. Moreover, to maintain the groundwater table and mine safety, 120 m³/day was recommended as a reasonable and economical recharge (re-injection) rate in the study area.     

武山铜矿地下水数值模拟与矿坑涌水量预测

地下水数值模拟是矿坑疏干排水设计的基础.该文以江西武山铜矿为研究对象,根据矿区地质构造、地层分布及水文地质条件,对矿区的岩溶-裂隙含水系统进行概化,建立地下水流三维数学模型,结合现场抽水试验资料,采用MODFLOW有限差分法进行地下水模拟,预测矿井在不同设计疏干水平下,地下水流场分布及矿区涌水量大小,为矿山地下水有效防治和安全生产提供依据.     

Assessment of Dewatering Requirements and Dewatering Well Design for an Open Pit Coal Mine in Central Anatolia

The Çeltikçi Coal Basin is a newly discovered coal basin in Central Anatolia where 11 years of open-cut mining has been planned. The bulk of the mining will be conducted below the regional water table; hence, determination of the dewatering requirements and proper design of the dewatering wells plays a critical role. This study (i) defined the dewatering requirements of the open-pit mine, (ii) established a dewatering well design for the area, and (iii) assessed the anticipated impacts of the dewatering activities. For this purpose, a 3-D numerical groundwater flow model was developed using the FEFLOW software. Yearly dewatering requirements were determined under transient conditions. For the dewatering well simulations, two types of dewatering wells were considered: permanent wells located at the open pit boundary that would increase in number as the excavation proceeds and wells located at the periphery of the yearly excavated area that would be operational for about two years. The simulation results indicated that 894 wells were required to satisfy dry working conditions; the average pumping rate throughout the mine life was calculated as 322 L/s. The impacts of open-pit dewatering on groundwater resources were assessed in terms of spring discharge and base flow rates in the nearby Kirmir stream. As a result of dewatering, most of the village water supply springs and fountains will dry up in the area. In addition, the base flow rates to the Kirmir stream will be decreased by 15%.

     

Assessment of Water Supply Impacts for a Mine Site in Western Turkey

A nickel mine site located in western Turkey requires approximately 135?L/s of water for 15?years. To assess the potential impacts associated with meeting this water supply requirement, we determined alternative water resources, assessed the potential impacts associated with each resource, and selected the most feasible alternative, given the environmental and technical impacts. Three options were considered: surface water, groundwater, and treated wastewater. A low-flow analysis of Gediz River was conducted for the evaluation of using surface water. For the groundwater alternative, a three-dimensional numerical groundwater flow model of the Turgutlu-Salihli aquifer was established using MODFLOW so that the impacts of withdrawal on groundwater resources could be evaluated. The wastewater option was assessed based on the amount of wastewater generated nearby (in Turgutlu). It was determined that each option is capable of supplying the required water to the mine site. However, storage of the river water in a small dam in wet seasons for use in dry seasons and using treated wastewater would have less impact on existing water users and related ecosystems.     

Is Treatment of Mine Dewatering Water Necessary Prior to Rapid Infiltration Basin Recharge? A Case Study

In Nevada, USA, the return of mine dewatering water (MDW) to the subsurface through rapid infiltration basins (RIBs) requires treatment if the quality exceeds the state’s Division of Environmental Protection (NDEP) Profile I reference values. However, a 2019 change to the Nevada Administrative Code allows discharge without treatment if the natural background groundwater solute concentrations are not exceeded. We developed a novel approach to demonstrate that groundwater will not be adversely affected by the untreated discharge of MDW. At the Cortez Gold Mine, dewatering will discharge water to the Grass Valley RIBs with 0.045 mg/L of As, exceeding the NV Profile I reference value (0.010 mg/L) and natural background (0.015 mg/L). A MODFLOW-SURFACT groundwater model incorporated empirical hydraulic conductivities to evaluate the extent to which changes in mound water depth and quality would occur. Modeling inputs were determined using column tests to assess SO₄ leaching from the alluvium and batch tests to quantify As partition coefficients (Kd_As?=?8.9 L/kg) to the alluvium. The results indicated that Profile I will be met at all compliance wells due to dispersion and attenuation. The Kd_As was also used to calculate the attenuation capacity of the alluvial mound water by adsorption (100-years), well beyond the 13-year operational span of the RIBs. Based on this analysis, and in conjunction with a similar analysis in the adjacent Crescent Valley, where 25 years infiltration of 0.045 mg/L As had not affected groundwater quality, the NDEP concurred that a dewatering water treatment plant was unnecessary. Overall, our analysis obviated construction of four treatment plants in the area and permitted direct discharge of mine dewatering water to the subsurface.

     

A Review of Mine Water Rebound Predictions from the VSS–NET Model

Mine water rebound predictions made in the late 1990s and early 2000s were critically reviewed in light of subsequent monitoring data and available literature. The VSS–NET physically-based groundwater model simulates the rebound process by representing both laminar and turbulent flow; the latter is observed in mined out voids, including shafts, adits, and underground roadways. We found good agreement between modelled and predicted rebound rates at a coal mine (Whittle Colliery) in NE England. The rebound from an abandoned tin mine in Cornwall, England (South Crofty), which closed in 1998, took place more rapidly than initially predicted by the VSS–NET model; however, by back-fitting the storage coefficient, the observed rate was matched by the model. In a third case study from a coal mine in South Wales, we managed to reproduce the flow rate from an adit reasonably closely following rebound. However, at a fourth site, a better fit to the rebound curve was obtained using a simpler, lumped model. These studies show the value of using models to predict rebound and discharge from flooded mines, which is important since these mines can produce a long-term legacy of pollution and can cause serious environmental impacts downstream.     

神经网络的地下水类型判别系统及其应用

简要介绍了BP神经网络的理论,在此基础上根据任楼矿区含水层水化学特征,建立判别含水层的BP神经网络模型,从而建立了防突水预警系统。实践证明,该神经网络系统对防范矿井突水有重要作用。