Lessons Learned on Singapore's DTSS

In this article the authors offer some conclusions regarding the completion of Singapore’s recent Deep Tunnel Sewage System (DTSS) excavation project. The tunnels of the new system will carry wastewater by gravitational inertia to two recently built water reclamation plants (WRP). Eight earth pressure balance boring machines (EPBM) were used for the project. Local geology consisted of old alluvium, granite, and soil-like materials. An overview of the advance rates of each machine is presented with speed, problems with intrusion, and cutterhead replacement rates due to abrasion. The structural lining used was bolted, precast concrete in segments with full grouting for the annular void. A review of the project is structured into the following sections: the design/build contracts, preliminary design detail, locations of permanent maintenance shafts, tunneling beneath major roadways, and aspects related to the tunnel boring machines (TBM) used.