Gypsum-related sinkhole remediation Magdalen Road, Ripon, Yorkshire UK

不幸的是，最近发生在里彭Magdalen路的天坑（2016年11月10日）并不是第一个影响里彭的天坑。埋藏的石膏溶解的影响在这个地区是臭名昭著的（Cooper 1998）。它是由于产生的落水天坑可能对建筑物和基础设施造成重大破坏而造成的。里彭下面的地质包括二叠纪泥灰岩、白云化石灰岩和石膏，覆盖着大约10米的冰川沉积物。可溶性石膏在深部的溶解导致了埋藏的空洞，这些空洞以天坑的形式传播到地表。塌陷坑如何形成的细节还不完全清楚（石膏中形成的溶解开口的大小和位置）。这是因为这些空洞难以进入，而且充满了水。一旦天坑形成，它附近的地面就不稳定了；进入天坑是不可能的，任何侵入性的调查（如钻孔）都有可能进一步破坏地面的稳定。因此，通常会对天坑进行补救，使其尽快安全。历史上，微重力地球物理技术已被证明是探测与溶蚀有关的埋洞和扰动地面的首选技术。在这里，我们建议使用一系列地球物理技术来监测修复（填充空腔），并记录整个天坑深度的地面状况变化，以便更多地了解其几何形状和深度，从而了解可能的形成过程。与此同时，我们建议使用国家地球科学数据中心保存的钻孔记录来生成Ripon地区的三维地质数据，并将其与天坑的几何形状和相关的扰动区联系起来，以进一步了解天坑的地质背景，即与主沉积物和地下水位的分布有关。除了有助于过程理解外，该方法还将(i)允许对一系列地球物理技术（微重力、电阻率和地震）进行比较，以评估其在空隙探测和补救监测方面的可行性，这将有助于为任何后续事件提供指导；（ii）它将反馈信息，为任何未来发展的建议提供调查要求。

Unfortunately the recent sinkhole in Magdalen Road, Ripon (10 November 2016) was not the first to affect Ripon. The impact of the dissolution of the buried gypsum is notorious (Cooper 1998) in this area. It results from the generation of drop-out sinkholes with a potential to cause significant damage to buildings and infrastructure. The geology beneath Ripon comprises Permian marls, dolomitised limestones and gypsum, capped by approximately 10 m of glacial deposits. Dissolution of the soluble gypsum at depth results in buried voids that propagate to the surface as sinkholes. The detail of how the sinkholes develop is not fully understood (size and position of the dissolutional openings that develop in the gypsum). This is because the cavities are inaccessible and water filled. Once a sinkhole develops the ground adjacent to it is unstable; access to the sinkhole is not possible, and any intrusive investigation (such as boreholes) have the potential to further destabilise the ground. Consequently, the sinkholes are usually remediated to make them safe as soon as possible. Historically, microgravity geophysical techniques have been demonstrated to be the preferred technique for detecting buried cavities and disturbed ground associated with the dissolution. Here we propose to use a range of geophysical techniques to monitor the remediation (infilling of the cavity) and record changes to the condition of the ground throughout the depth of the sinkhole in order to learn more about its geometry and depth and hence the likely formational processes. In parallel we propose to use the borehole records held by the National Geoscience Data Centre to generate a 3d geological of the Ripon area and attribute this with the geometry of the sinkhole and the associated zone of disturbance in order to further the understanding of the geological context of the sinkhole, i.e. in relation to the distribution of the host sediments and the groundwater table.As well as contributing to the process understanding, this approach will (i) allow the comparison of a range of geophysical techniques (micro-gravity, electrical resistivity and seismic) to assess their viability for void detection and remediation monitoring, which will help inform guidance for any subsequent events and (ii) it will feed back to inform investigation requirements for proposals for any future developments.