OasisLMS

Abstract: A case study of the construction of a diaphragm wall situated within complex site conditions to form the tunnel access shaft retention structure as part of Melbourne, Australia’ s most ambitious rail infrastructure project. The diaphragm wall structure consisted of 57 No. 1000mm reinforced concrete panels with excavated depths ranging from 24m to 31m with 38 No. of the panels being constructed within uncontrolled fill. The location of the site is approximately 27km South-East of Melbourne’ s CBD and was a former sand quarry that had been backfilled with uncontrolled fill to a depth of approximately 13m with underlying dense sands with a high-water table. All fill material was determined to be contaminated with non-friable asbestos. The site conditions presented significant risk to the project both commercially and from a constructability perspective. The documented history of the fill used to backfill the quarry was limited which provided uncertainty for the presence of inground obstructions, the stability of the fill, and management of the bentonite support fluid. The presence of asbestos required the workforce to conduct the works under strict conditions. The panels were all constructed using diaphragm wall hydraulic grabs under bentonite support fluid. The ground conditions required the placement of concrete to be executed as soon as possible once excavations were completed which posed as a problem due to the asbestos working conditions. To accelerate this process, stop-end lengths were reduced, and reinforcement cages were installed in single lengths up to 24.5m. While several problems became present during the works and needed to be carefully managed, the structure was completed on time, within budget and without major collapse.

Mr. Clayton James Price

Annual Conference Proceedings