Weathering and brittleness in shale fill dams and embankments

Abstract

Research and industrial concern has been expressed about the behaviour of mudrocks when used in engineering structures. In particular the loss of strength in shale fills caused by chemical weathering processes and by progressive failure arising from overstressing and brittleness is an important consideration in design. A literature review into use of the term 'brittleness' to describe this loss of shear strength has revealed infrequent references, but those that were found refer to a wide scope of failures including liqufaction events and long term slope stability problems. The use of large size shear box equipment has been reviewed as an appropriate method of testing the brittleness of shale fills in the laboratory. A range of materials, from fresh shale to shales retrieved from dams of different ages in the north east of England, has been collected for shear strength testing and for chemical and mineralogical examination to determine the condition of the fill. Research has concentrated on such rocks as it was possible to obtain. Although the samples have not exhibited wide lithological and geotechnical variations the work has highlighted several significant features including the need for resolving appropriate methods of testing. The results of the work were generally in accordance with earlier research on Carboniferous rocks by suggesting similar material trends in, on the one hand, Namurian shale dams and associated spoil heaps and, on the other hand, colliery spoil heaps of Westphalian shale as had been previously observed.