Pleistocene deposits of the South Wales Coalfield and their engineering significance

Abstract

Abstract The importance of glaciation in the modification of landscape in the South Wales coalfield has long been acknowledged. The effect of periglacial conditions has never been fully assessed, even though these are of enormous relevance to the geomorphology and to the prediction of the engineering characteristics of the superficial deposits. Examination of field relationships and sedimentology has proved the presence, in valley-floors, of glacial lodgement tills, meltout tills and associated water-lain deposits. On lower valley-sides, however, a large proportion of the drift has moved downslope by gelifluction or as mudflows. These redistributed sediments contain silt bands which can cause side-slope collapse in cuttings. They also extend over valley-floors and may conceal glaciolacustrine deposits which can contain water at artesian pressures. Higher valley-side slopes and hilltops show extensive modification by periglacial processes, and there are solifluction terraces and nivation hollows. A good understanding of depositional processes is required for any investigation of slope stability.