Site investigation, monitoring and stability analysis of a built-up slope involved by gas pipeline explosion

The paper describes the results of site investigations, monitoring and stability analyses of a build-up slope located near Pineto (Italy). In March 2015 the explosion of a gas pipeline in the upper portion of the slope caused extensive damage to existing buildings and lifelines. Soon after the event, a site investigation and monitoring program was planned. The site investigation included 3 boreholes (25-30 m depth) and 3 flat dilatometer tests DMT (15 to 30 m depth) carried out inside the boreholes by use of the "torpedo" system. The boreholes were instrumented for inclinometer and piezometer measurements. A detailed topographic survey was carried out to reconstruct the ground profile. Hydrological data were analysed for possible critical rainfall events. The slope is formed by OC clay, covered with an upper, 10-14 m thick clayey-sandy silt colluvial layer. The stability of the slope was analysed both in pre- and in post-explosion conditions. The pre-explosion conditions were back-analysed assuming different levels of the groundwater table (at the time of the explosion presumably close to the ground surface). The analyses, in agreement with field observations, indi-cated that the slope is unstable and possibly slope movements may have been one concurrent cause of failure of the pipeline. The profiles of the DMT horizontal stress index KD helped identify multiple slip surfaces.