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Review Article |
Halcrow Group Ltd., Deanway Technology Centre, Wilmslow Road, Handforth, Cheshire, SK9 3FB, UK(e-mail: DonnellyLJ@Halcrow.com)
Fault reactivation has been observed at several locations in almost every British coalfield. The movement of faults during mining subsidence has been known for at least 150 years, but the affects and consequences are not widely appreciated by other geologists, engineers, insurers, builders, lawyers and planners. This has lead to widespread damage to land, houses, roads, railways, engineered structures (bridges, tunnels, dams), utilities (sewers, pipelines, cables). Disputed cases of fault reactivation have resulted in lands tribunals and claims for compensation for damage to land and property, often incurring significant financial losses. These sources of data on fault reactivation includes anecdotal accounts, archive information and detailed case examples supported with surveying observations. The reactivation of a fault in an area undergoing mining subsidence may result in the generation of a fault scarp along the ground surface, accompanied by compression or fissuring. Ground deformation caused by reactivated faults varies from subtle flexures across the ground surface to steeply inclined scarps, 3–4 m high and at least 4 km long. In the latter, this may influence the morphology of an entire moorland plateaux and has a contributory role in groundwater flow and the drainage of the landscape, or the initiation (and reactivation) of landslides. Not all types of faults reactivate when subject to mining subsidence stresses. Furthermore, movement along faults does not continue indefinitely. It is usually the principal faults which cross the coalfields and define structural blocks and cells that are more prone to reactivation. Several phases of fault reactivation are possible, during multi-seam (3+) mining operations, separated by periods of relative stability. In some circumstances, such as minewater rebound or residual mining subsidence, further movements along a previously reactivated fault are possible. The objectives of this paper are to provide, for the first time, a comprehensive account of reported and recorded cases of mining-induced fault reactivation in Britain. These have been compiled over a 15 years period, from 1990 to 2005. There are 227 recorded cases of fault reactivation and this is thought to represents a large under estimation of the actual number. This may be attributed to a relatively poor understanding of geology and fault reactivation mechanisms by past investigators. There was a tendency to ignore fault reactivation cases to reduce mining subsidence compensation claims. Furthermore, relatively fewer investigations were undertaken compared to the more conventional widespread mining subsidence observations. Many cases of fault reactivation have been undocumented, not recorded or incorrectly interpreted. This paper also aims to draw attention to potential geotechnical hazards, liabilities, risks and consequences associated with faulted ground.
Key Words: discontinuities • environmental geology • geological hazards • mining geology • subsidence
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