ABSTRACT
The paper takes a single geological phenomenon – clay mylonites – and uses case histories to illustrate their effect on some engineering constructions where slope failure has occurred. The term „clay mylonite“ is used here to refer to the zone of disturbed material along and adjacent to bedding plane shears and in intraformational shears and bedding plane crush seams. It was as a result of the study of one such horizon at Walton’s Wood that the concept of residual strength was developed in the early 1960s. The paper emphasises the importance of these weak zones in Coal Measures strata for both road construction and open cast pit stability and notes that they also occur in other strata, from Lower Palaozoic to Tertiary in age. Four ways in which clay mylonites are created are postulated, although it is likely that more than one mechanism may have been involved at any one location.
