Some engineering implications of chemical weathering of pyritic shale

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Abstract
Summary: Previous research at the site of a landslip at Mam Tor, Derbyshire, has linked the oxidation of pyrite in Edale Shale to the generation of acid groundwater. Chemical analysis of surface seepages suggests that reactions occur between this acid water and sedimentary minerals, including clays. The objective of the present research is to relate changes caused by chemical weathering to modifications of the engineering properties of those materials. It has been found that in closed system acid leaching experiments, some constituents of shale react very rapidly. In order to quantify these changes in terms of the residual shear strength of shale, a Bromhead Ring Shear apparatus has been modified so that the composition of pore solutions may be altered during shearing. These tests indicate that the residual shear strength of the shale is sensitive to modification of pore solution composition. The changes are rapid, reversible and apparently chemically analogous to those at Mam Tor. Since the bulk properties of weathered shale depend both on the type of solid material and the pore solutions present, the weathering of Edale Shale is discussed in terms of solid and solution phase modifications.

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