Investigation of a slow-moving landslide in Cretaceous bentonitic clay

Abstract Bentonitic clays are characterised by extremely high plasticity due to their high smectite content. As such, they exhibit very low values of residual friction angles and are often a leading cause of landslides in many parts of the world, even in gently sloping ground. This paper presents a case study of a slow-moving landslide in bentonitic clays in southwestern Cyprus. These bentonitic clays, which are of Maastrichtian age, are intensely folded and highly fissured. Landslide movement was first observed a few years after the completion of a residential development project at its head, and since then it evolved with an average slippage rate of the order of 5 cm per year, causing severe damages to the buildings. In order to investigate the causes and the mechanism of the landslide, back-analyses are performed using the finite element method. The findings reveal that the landslide is most likely part of an old palaeolandslide, the geomorphological characteristics of which have been attenuated with time due to erosion. The fissures of the clay play also a key role by allowing rainwater and wastewater to generate a relatively shallow phreatic level.