Translational Slope Instabilities in Weak Rock

ABSTRACT: This paper examines the problem of translational slope instabilities occurring in complex geological formations of weak rock as are typical of the Langhe region in Italy. Unstable rock volumes slide along slightly dipping planar surfaces that are formed where adjacent layers of marl and sand are in contact. Four sites were identified and examined. Special attention was devoted to the development of a laboratory method able to simulate the behaviour of the thin layer of marl which is deemed to play an active role in these phenomena in conjunction with the sand layers providing a preferential path for groundwater circulation. Direct shear tests were carried out and the results obtained show that the fundamental role played in instability phenomena by the de-structuring effect of water on marl cannot be taken into account through the customary laboratory techniques.