Geotechnical design and construction methodology of a deep basement cut next to sensitive buildings

The Maritime Apartment Building is a proposed 16 level building over 2 basement levels to be constructed on a steep site with neighbouring buildings on 3 sides. The primary challenge of this site is limiting movement at the western boundary, which is within 1 metre of a 5-storey sensitive historic building located at the crest of the slope. The basement structure retains approximately 13-metres and has been designed collaboratively by the structural and geotechnical engineers. Coffey has undertaken geotechnical analysis to assess the design soil loads and soil-pile interactions. To limit deflections the basement soldier piles are very stiff and are supported with a capping beam, diaphragm slab and associated wing wall. However, poor pile drill rig access to the top of the site and the requirement to install the perimeter soldier piles and pile cap before excavation presents constructability issues. By working closely with the main contractor a temporary works methodology was developed that was both constructible and ensured the stability of the site and neighbouring structures. The proposed solution comprises the construction of a geogrid reinforced ramp to the top of the site where a temporary platform founded on piles would be constructed to support the permanent pile drilling rig. A detailed monitoring plan was prepared as a key risk treatment during construction.