Deep Tunnel Sewerage System Phase 2 (DTSS2) Contract T11


The Deep Tunnel Sewerage System (DTSS) is a used-water superhighway conceived to meet Singapore’s long-term needs for used water collection; treatment; reclamation; and disposal.

Upon the completion of DTSS Phase 2 (DTSS2), existing intermediate pumping stations and conventional Water Reclamation Plants (WRPs) will no longer be required—freeing up land for other developments. Making use of deep tunnels, water will be able to be transported entirely using gravity to treatment plants located at coastal areas.

DTSS2 Contract T11 is a design-and-build contract, which consists of South Sewer Tunnel of 6 kilometres running along Ayer Rajah Expressway (AYE) and Southern Region Sewer Tunnel of 5.5 kilometres running along West Coast Highway and Alexandra Road. The bored tunnel alignment covers a total length of 11.5 kilometres with tunnel diameter of 3.0 metres and 3.3 metres.

Overview of Contract T11

The pioneering deployment of innovative technology, Vertical Shaft Sinking Machine (VSM) for Contract T11, is the first in Asia for circular shaft construction.

The VSM is the inverted form of conventional partial-face excavation machines used in horizontal tunnel boring, i.e., from horizontal to vertical. Compared to the traditional caisson construction method, it increases safety, compact site space utilisation and efficiency of excavation in difficult ground conditions.

Illustration of the caisson shaft lining and telescopic excavation arm of VSM

To achieve a 100-year design life, all the permanent structures are integrated with a corrosion protection system to provide a minimum durability of 100 years. For example, the cast in-situ secondary lining for permanent structures were designed with microbiologically influenced corrosion (MIC) resistant concrete of grade C50/60 in addition to high-density polyethylene (HDPE).

Project Name
Deep Tunnel Sewerage System Phase 2 (DTSS2) Contract T11
Southern region of Singapore
Status of Construction
In progress
Expected Completion
Public Utilities Board (PUB)
Architecture Firm
Urban 3 Architects
Civil & Structural Engineer
Surbana Jurong Consultants
Mechanical & Electrical Engineer
Surbana Jurong Consultants
Landscape Architect
COEN Design International
Main Contractor
Shanghai Tunnel Engineering Co
KTP Consultants

This is an excerpt. The original article is published in
Construction+ Q2 2023 Issue: Infrastructure & Transport.
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