Corrosion Protection Linings for the Strategic Tunnel Enhancement Program, Abu Dhabi

Abu Dhabi Sewerage Services Company (ADSSC) commissioned development and delivery of the Strategic Tunnel Enhancement Programme (STEP), which intercepts flows upstream of existing pumping stations and conveys the sewage via gravity through a new tunnel sewer network. The tunnel was designed using precast concrete segments as its permanent structural lining. In order to mitigate internal corrosion to the structural lining, a Corrosion Protection Lining (CPL) system was required, which comprises a mechanically anchored high density polyethylene (HDPE) lining cast into an unreinforced cast-in-place concrete secondary lining. Following construction, various CPL defects were observed. After field inspections and review of information on similar systems, it was determined that all bulging defects were related to workmanship issues with the CPL concrete secondary lining, with no indications that the HDPE membrane was failing. The conclusion reached was that the installed CPL system remains a robust solution to meet the required 80-year design life.