Proving a landslide: ground behaviour problems at Pissouri, Cyprus

The residential area of Limnes in Pissouri, SW Cyprus has experienced significant ground behaviour problems since heavy winter rainfall in 2011/2012. These problems have comprised cracking and displacement to the ground, pavements, roads, walls and buildings, leading to the abandonment of the most seriously-affected houses. Nicosia marl comprises the underlying lithology, a material that is associated with volume change upon wetting and drying and has led to foundation problems elsewhere in the country. Various explanations have been given to account for the observed phenomena at Limnes, including the effects of underground water , settlement, slope instability, cyclical shrink-swell, seepage erosion and dissolution. Raised water tables, caused by residential waste-water discharges, applied loads from residential buildings, and inadequate ground investigation and foundation design, are other contributory or causal factors that have been cited. A geomorphological study was undertaken in 2017 and early 2018 that combined field observations with aerial photograph interpretation, and a review of available ground investigation data, to yield an explanation and develop a preliminary ground model. The conclusion drawn was that the Limnes area had been affected by ancient (possibly Late Pleistocene-Early Holocene) deep-seated failure and that slope instability had subsequently been reactivated at a shallower depth within the failed material as a result of loss of material strength and high water tables. The properties of the Nicosia marl, while important in controlling the behaviour of the ground on a site-by-site basis, were considered to be aggravating factors in the context of the landslide displacement(s) affecting the slope as a whole. InSAR satellite movement monitoring data were analysed for the Limnes area and the outcome vindicated the geomorphological interpretation and helped strengthen the ground model that embodied slope failure as the underlying cause of damage.