Collapse of a Shaft at Bangkok Wastewater Pumping Station

A wastewater treatment plant was under construction at the Yanawa Station as part of the Bangkok Wastewater Project. The plant contained an inlet pumping station (IPS), housed in deep shaft. For the shaft, a concrete diaphragm wall was constructed, which was designed to serve as an earth-retaining wall during the excavation and later as part of the final structure. On 17 August 1997, this shaft collapsed inwards as the final stages of excavation were about to be completed, causing a landslide and the collapse of many residential houses in the neighbourhood. The investigating team visited the site just after the collapse to obtain first-hand information and gather data for further study. This article serves to highlight the findings of this investigation and the lessons learnt from the incident.