Stability (Post-operational Phase)
Post-closure phase
The Quarries Regulations 1999 require that …."the operator shall ensure that in the event of the abandonment or ceasing operations at a quarry, the quarry is left, so far as is reasonably practicable, in a safe condition" (Regulation 6(4)). Unless this requirement is anticipated in the quarry design, it can be difficult to achieve, especially if the quarry is deep and has very steep faces to which access is no longer possible for stabilisation measures or buttressing. In these cases, filling the void or buttressing the slopes with fill materials or, if that is not possible, secure fencing and restricting access can be the only options for landowners who assume the liabilities once the operation has ceased.
Most modern planning permissions incorporate an approved scheme of working and restoration that has been demonstrated to be environmentally acceptable and to incorporate final excavated and tip slopes that are stable and compatible with the intended after-use. Often, final restoration landforms (comprising excavated and fill elements) are created progressively throughout the life of the quarry by placement of site-derived or imported material and spreading of soils in worked-out areas of the site (e.g. sand and gravel workings) and/or progressive formation of final rock slopes with associated planting and stabilisation/containment measures. Where the formation of final geometry is progressive during the life of the operation, it is possible to assess the performance of restoration slopes and planting proposals and make any necessary amendments in the light of accumulated knowledge of appropriate parameters influencing stability. In some cases, the proposed after-use for a quarry will change during or Post-operation. In these circumstances, revisions may be required to proposed or existing final slopes to render them suitable for the new after-use (e.g. the incorporation of rockfall prevention or containment measures where built development or other public access is proposed).
The ALSF research projects Integrating non-agricultural afteruses with the design and planning of quarries L0127 and Secure and sustainable final slopes for SME aggregate quarries L0056 provide considerable details on all of the issues relevant to the post-quarrying phase of aggregates quarries.
Additional Information, References and Bibliographies
Geoffrey Walton Practice (1991). Handbook on the design of tips and related structures. For the Department of the Environment. HMSO (ISBN 0 11 752539 1).
Geoffrey Walton Practice in association with the Department of Mining Engineering, Nottingham University (1988). Technical review of the stability and hydrogeology of mineral workings. For the Department of the Environment. HMSO (ISBN 0 11 752133 7).
Geoffrey Walton Practice (1988). Handbook on the hydrogeology and stability of excavated slopes in quarries. For the Department of the Environment. HMSO (ISBN 0 11 752726 4).
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