31 - Flexural Toppling of Siltstones During a Temporary Excavation for a Bridge Foundation in North Devon

Abstract

This chapter discusses flexural toppling of siltstones during a temporary excavation for a bridge foundation in North Devon. The rock mass flexural toppling failure at the Port Lane Overbridge was investigated and analyzed, and the remedial works were completed within 12 weeks. The design of the temporary works utilized established empirical relationships, which were refined by limit equilibrium methods that took into account site-specific features pertinent to the Port Lane site. The flexural toppling failure at the Port Lane Overbridge was kinematically feasible from the post-failure discontinuity surveys. Fracture characteristics, rock type, and lithology can display significant variation over the span of a particular structure or group of structures forming an interchange. Rock stress is always problematical to measure routinely, and groundwater can fluctuate with both rainfall and season, requiring long-term monitoring to generate representative data for design. With the introduction of more observational design philosophy to rock engineering, site investigation costs can be optimized by targeting the ground works to identify the potential risks.