2005 – RIPPABILITY: A Case Study – Wivenhoe Alliance

Philip Styles, Brett Stephens, Stephen Perrett

The Wivenhoe Dam Spillway Augmentation Project involved the construction of an additional spill way on the right abutment of the main dam. The right abutment is located in massive sandstones and siltstones of Jurassic and Upper Triassic age.

Seismic refraction surveys and borehole drilling conducted at the design stage for the project indicated that part of the spillway area was likely to be marginally rippable to unrippable using a Caterpillar D9 bulldozer or equivalent. Further assessment and rock strength testing was conducted during the initial stages of excavation where D9 and D10 bulldozers were in operation. The results from this further work indicated that a section of the spillway extending from the proposed position of the ogee crest to approximately 100m further upstream were unlikely to be unrippable for a D9 dozer and marginally rippable for a D10.

Excavation options considered for this section included full scale blasting and load out, limited small scale ‘popping’ combined with ripping or the use of larger ripping equipment. Based on an assessment of cost-benefit, and given the availability of larger ripping equipment, it was decided touse a combination of D10 dozers and a Komatsu 475A bulldozer (D11 equivalent) equipped with single tine ripping tools. The use of this equipment proved successful with better than anticipated production rates being achieved. This resulted in significant cost and time savings for the project and reduced the likelihood of potential adverse impacts on the existing dam grout curtain, environment,travelling public and residents that may have occurred during blasting.

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