Design of shaft linings to resist time dependent deformation in evaporite rocks

Abstract

Potash, a fertiliser currently in demand worldwide, lies beneath beds of salt and other evaporites deep within the ground. The ground support challenge encountered when excavating through these strata is that of time dependent (creep) deformation control. The deformation is radial, causing the shaft excavation to close up over time, eventually loading the permanent lining with the full geostatic pressure and causing lining failure. In order to achieve a significant design life for an economical shaft lining in creeping rocksalt strata, a deformation zone filled with a compressible material is employed between the excavation and permanent lining. This helps resist the ground pressure, and reduce the magnitude and velocity of creep deformation. Optimum lining designs have been developed by predicting the creep deformation at a given time and by considering the behaviour of different compressible materials available to fill the deformation zone. Foamed concrete is the favoured material for an intermediate compressible lining.

Keywords

Potash Mining Creep deformation Deep shafts Evaporites Foamed concrete

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