A physically based model of rebound in South Crofty tin mine, Cornwall
A physically based model of rebound in South Crofty tin mine, Cornwall
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DOI：
10.1144/gsl.sp.2002.198.01.06
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
R. Adams;P. Younger
中科院分区：
文献类型：
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作者：
R. Adams;P. Younger
最近，欧洲最后一个在开采的南克罗夫蒂锡矿关闭，引起了人们对可能的环境后果的质疑。在几个世纪的运营中，矿井通过位于矿井不同水平的一系列泵进行脱水。靠近地表的老工作区被一系列排放到附近河流和小溪的平硐排干。从这些浅部巷道排出的水的质量一般良好，不需要处理。然而，由于附近的Wheal Jane锡矿的不良经验，英国环境局对地下水反弹完成后预计从较深工作区排放的水的质量和数量表示担忧。为了解决这一问题，并作出预测的时间和量的放电，计算机模拟使用的SHETRAN/VSS-NET模型进行了。该模型已被应用于模拟英国几个煤田的地下水反弹。然而，煤矿的水文地质特征与South克罗夫蒂煤矿有很大不同。该矿围岩为花岗岩和变质板岩，透水性极低，储集性极低。因此，大部分地下水流是在开采锡矿的“巷道”和采场中。在其运行过程中，流入矿山进行了映射和量化，并发现主要是头部依赖。这些流入通常来自岩石中的断层带，也来自附近废弃和淹没的工作区，这些工作区围绕着现代矿井。回弹期间的水位预测与主井中的观测水位进行了比较，这些水位是自矿井关闭以来测得的。然后，该模型被用来预测表面放电可以预期开始的日期。预测的主要局限之一是采矿计划记录中的“空白”深度间隔，这可以用两种可能的方式解释：（一）该区域在世纪中期被开采，但计划丢失;或（二）该区域从未被开采过。当地专业意见赞成解释（i），认为最有可能的预测情景是基于这样的假设，即与采矿有关的特定产出值在这一“空白区间”中与适用于下面更好地绘制的区间的产出值类似。在这种情况下，上述（ii）似乎是真实的情况，导致反弹曲线在反弹的后期阶段明显变陡，表面排放开始于2000年11月，比大多数其他预测提前了一年。回顾性模拟假设非常低的特定收益率在“空白间隔”证实，流体动力学，否则成功地模拟使用SHETRAN/VSS-NET代码。
Abstract The recent closure of the South Crofty tin mine, the last working mine of this type in Europe, has raised questions over possible environmental consequences. During several centuries of operation, the mine was dewatered by a series of pumps located at different levels in the mine. Older workings near the ground surface were dewatered by a series of adits that discharge into nearby rivers and streams. The quality of water draining from these shallow workings is generally good and no treatment is required. However, because of bad experiences at the nearby Wheal Jane tin mine, the UK Environment Agency were concerned about the quality and quantity of water which was expected to discharge from the deeper workings when groundwater rebound was completed. In order to address this problem and make predictions of the timing and volume of the discharge, computer simulations using the SHETRAN/VSS-NET model have been carried out. This model has already been applied to the simulation of groundwater rebound in several UK coalfields. However, the hydrogeological characteristics of coal mines differ considerably from the South Crofty mine. In this mine, the country rocks comprise granite and metamorphic slates, strata that have negligible transmissivity and very low storativity. Most of the groundwater flow is therefore in the ‘drives’ and stopes from which tin ore was extracted. The inflows to the mine during its operation were mapped and quantified, and were found to be mainly head-dependent. These inflows usually originated from fault zones in the rock, and also from nearby disused and flooded workings, which surround the modern mine. Predictions of the water level during rebound are compared with the observed water levels in the main shaft which have been measured since the mine closed. The model was then used to predict the dates when surface discharges could be expected to commence. One of the main limitations of the predictions was a ‘blank’ depth interval in the mine plan records, which could be interpreted in two possible ways: (i) the zone was worked in the mid-nineteenth century but the plans were lost; or (ii) the zone was never worked. Local professional opinion favoured interpretation (i), and the prediction scenarios considered most probable were based on the assumption that mining-related specific yield values would be similar in this ‘blank interval’ to those applicable in better-mapped intervals below. In the event, (ii) above appears to have been the true case, resulting in a marked steepening of the rebound curve during the later stages of rebound, with surface discharge commencing in November 2000, as much as a year in advance of most other predictions. A retrospective simulation assuming very low specific yield in the ‘blank interval’ confirms that the hydrodynamics were otherwise successfully simulated using the SHETRAN/VSS-NET code.