Corrosion Protection Lining (CPL) for the Deep Tunnel Sewer System in Singapore—A Case History

Sewer systems in general undergo severe corrosion due to sulphuric acid attack which causes a serious threat to the structural integrity of the system in addition to large amount of maintenance and repair cost. Several methods and materials, such as single and double CPLs, various concrete mixes, fibre glass reinforced linings, special mortars and coatings, geosynthetic linings such as HDPE and PVC, etc are used to protect concrete from sulphuric acid attack in a sewerage environment. Typical concrete lined sewer tunnels need to function as both as ground support and Corrosion Protection Lining (CPL) systems. The CPL must be robust enough to withstand corrosion with time and thus preserve the ground support system. A CPL may be integral with the ground support system or installed separately. A composite CPL system which comprises a cast-in-situ concrete liner and HDPE or PVC lining is discussed in this paper. Attention will be given to geosynthetic HDPE CPL with respect to the technical requirements for the handling, installation and long term performance. A case history based on the Singapore Deep Tunnel Sewerage System (DTSS) project also presented.