Analysis of the evolution of the instability process of a coastal cavern

This work concerns the assessment of the stability of a large cavern, which is located along the rocky coast of Polignano a Mare town (Apulia, Southern Italy) under a urbanised area. This cavern, which is located at the sea level, has been formed by an intense process of salt and wave erosion within a rock mass formed of a lower stratified limestone mass and an upper Gravina Calcarenite mass. The thickness of the cave roof, which has a dome shape, is slightly less than 10 metres in the centre and buildings are founded on the ground surface above. Field and laboratory investigations and stability assessment analyses, including simple analytical methods and numerical modelling, have been carried out in order to understand the current stability conditions of the roof and the potential evolution mechanism. In particular, a detailed geo-structural survey has firstly been carried out, together with laboratory and in-situ testing for the geomechanical characterisation of the rock materials and of the corresponding joints. A structural monitoring system has also been installed in order to measure eventual block displacements within the cavern.