Temporary support of vertical excavation in weathered sedimentary deposits

During a stage of construction for the Boulcott Street Underpass in the Shell Gully section of the Wellington Urban Motorway, the Contractor, Wilkins and Davies Construction Company Limited, was required and instructed to make a temporary open excavation into a steep hillside slope to provide working space for construction of the western abutment. The site boundary, outside which the Contractor could not operate, was located only 12 feet beyond the back face of the abutment pile cap location. Ground surface level on the boundary ranged up to 50 feet above the proposed base of pile cap level. Thus the flattest open batter slope which could be created was on the order of 1/2 horizontal to 1 vertical.