This report describes the results of mineralogical analysis of a suite of sedimentary rocks from the Lias Group of England. The work was carried out as part of the ongoing BGS research programme, ‘Engineering Geology of UK Rocks and Soils.’
The first part of the report gives an introduction to the Lias Group geology and a summary of previous mineralogical studies of these rocks. A summary of analytical methods employed (X-ray diffraction analysis and surface area determinations) is then provided and the results discussed with reference to their likely effect on the engineering performance of the Lias Group.
While analyses are in general agreement with previous studies, important differences in terms of swelling clay mineral species and carbonate content are highlighted between samples taken from the northern Cleveland Basin and the southern Worcester and Wessex Basins. Such differences in clay mineralogy also provide important information on the burial histories of the Lias Group across England.
The detection of pyrite in almost all the samples analysed together with sporadic gypsum and jarosite means that any concrete engineering sited in the Lias Group rocks risks corrosion by acidic groundwaters and the formation of thaumasite