Design and construction of a commercial building on a closed municipal solid waste landfill in Takapuna, Auckland

Ground engineering works on closed municipal solid waste landfills provide challenges beyond those related to construction on other brownfield sites within the urban environment. Design and construction of a multi-level commercial building on the closed Barrys Point landfill site in Auckland presented challenges for foundation design, durability, and mitigation of hazards (refuse, gas, and leachate) related to landfill material. Geotechnical inputs for the new building included deep-piled foundations and landfill gas protection measures. Engineering observation of construction for the gas protection measures was required to comply with stringent consent conditions. This paper describes challenges, during detailed design and construction of the new building, posed by the complex ground conditions on-site. The challenges included the development of pile installation methods that would not contribute to leachate migration, and construction of the passive landfill gas protection system. Permanent design features of the building includes deep-driven steel piles, and landfill gas mitigation measures entailing a specifically designed gas manifold system and a subfloor slab with high-density polyethylene (HDPE) geo-membrane to prevent ingress of landfill gas into the new building.