A geotechnical survey of some British Coal Measures mudstones, with particular emphasis on durability

Abstract

Samples of fresh mudstones were obtained from near Tow Law and Kirkheaton, and of weathered mudstones from near Wrexham. The mineral composition of these mudstones was similar, kaolinite being the principal clay mineral, the clay mineral fraction dominating. Quartz was the chief non-clay mineral present. Some basic geotechnical and index properties were determined. The fresh mudstones from near Tow Law had a low plasticity, as did the moderately and highly weathered mudstones from near Wrexham. However, the completely weathered mudstones from the latter area possessed intermediate plasticity. The strength of the fresh mudstones from near Kirkheaton was notably higher than that of the mudstones from near Tow Law. Both groups of fresh mudstones displayed significant anisotropy ratios when they underwent axial and diametral point load testing. This, no doubt, was due to the influence of lamination. As durability is one of the most important engineering properties of mudstone, it was assessed by a number of tests. One cycle slake durability testing did not appear to offer an acceptable indication of the durability of mudstones when compared with cyclic wetting and drying, cyclic freezing and thawing, and geodurability classification. Cyclic slake durability testing and comparison with unconfined compressive strength would seem to be a more reliable way of determining durability. Both fresh and weathered mudstones underwent little expansion when subjected to swelling tests. However, in the case of the weathered mudstones, the amount of swelling stress and strain could be related to basic geotechnical properties.