Geotechnical design and construction performance of abutment modification

M. P. Chan and M.Y. Broise

Many civil engineering structures rely on geotechnical input to provide practical and innovative solutions, often in the face of uncertainty. In a recently completed major roadway widening project in Melbourne, a geotechnical alternative design was proposed to modify an existing bridge spill-through abutment to improve the functionality of the roadway by enabling the construction of two traffic lanes rather than a single lane proposed in the reference design. The solution involved removing the spill-through abutment and slicing through the counterfort buttress retaining wall and its foundations to form a continuous vertical face, transforming the retention system into a monolithic blade wall laterally supported by soil nails and rock bolts. This paper describes the alternative solution that was adopted and identifies the construction risks that had to be managed during construction. The importance of real-time and continuous geotechnical monitoring as a means to control the excavation sequence and verify abutment performance throughout the construction works is emphasised.