Monitoring the construction of a deep energy-from-waste bunker in soft clay and peat

Abstract

This paper describes the monitoring of the construction of a deep underground waste storage bunker for the PROTOS energy-from-waste facility in Chester, UK. A key element of the construction process was a 12 m deep excavation in soft clays and peats which was supported by a complex ‘combi-wall’ cofferdam comprising alternate tube and sheet piles, a reinforced concrete (RC) capping beam and two levels of internal bracing. The permanent bunker RC structure was constructed within the excavation using a bottom-up approach. The primary aim of this monitoring programme was to assess the performance of the composite support system through measured cofferdam wall deflections, bracing member loads, and site and bunker water levels. An additional objective of the monitoring was to provide the site team with real-time feedback to inform the construction process. Interpretation of the monitored data allows for a quantitative assessment of the influence of various construction activities on the responses of the support system. The monitored behaviour shows that the high stiffness and embedment depth of the supporting structure, combined with careful control of groundwater levels, significantly reduced risks associated with deep excavation construction in challenging ground conditions.