Geotechnical Risk Management and Contingency Plan for a Sheet Pile Wall Next to an Existing Highway

A cantilever temporary sheet pile wall was designed and constructed to support a 3.5m deep excavation in soft alluvial ground for construction of a new box culvert under an existing highway on the east coast of Australia. Soil-structure interaction software Wallap was used to analyse the deflection and forces of the sheet pile wall for structural design and impact assessment of the adjacent highway with live traffic. Instrumentation and monitoring was implemented during construction to verify design assumptions and to control excavation safety. During construction the wall moved much more than the design prediction after full excavation was completed at north-west corner. Cracks were observed in the pavement behind the wall. There was major concern that the sheet pile wall could fail which would pose significant safety risks to the construction workers and road users. This paper presents how the geotechnical risks were managed and a contingency plan developed to ensure the successful completion of the deep excavation in challenging ground conditions and the subsequent two-staged installation of box culvert under the existing highway without disruption of live traffic.

Keywords: geotechnical risk management, contingency plan, sheet pile wall, excavation, soft ground, observation method.