Mine-induced sinkholes over the U.S. Strategic Petroleum Reserve (SPR) storge facility

摘要

The initial sinkhole at the Weeks Island SPR site that was first observed in May 1992 gradually enlarged and deepened, concurrent with the increasing dissolution of salt over the mined oil storage area below. A second and much smaller sinkhole was first noticed in early 1995 on an opposite edge of the SPR mine, but with a very similar geological and mine mechanics setting. The cracks become flowpaths for brine incursion, wherein after time it is released into mined openings. Undersaturated ground water gradually enlarges the cracks in salt, leading to further dissolution and eventual collapse of the overlying sand to form sinkholes. Other geologic conditions may have been secondary factors in controlling both mining extent and sinkhole location. An en echelon alignment of sinkholes over other mine edges has been observed. Thus most likely areas of future occurrence at Weeks Island are adjacent to the existing sinkholes; surface inspections are now concentrated at those locations.