COVER STORY
AN ALTERNATIVE METHOD FOR CONNECTING BORED TUNNEL
SEGMENTS TO BOOST PRODUCTIVITY by David Ng C C, Executive Director, Victor Ong C W, Managing Director, Choong N H, Principal Engineer, and Anthony Ng, Resident Engineer, One Smart Engineering Pte ltd It reduces the installation time whilst maintaining the quality of construction. The 22 km Murnane Pipeline is a major water infrastructure project by PUB, Singapore’s National Water Agency. It was designed to meet future water demand in the city area. The Murnane Water Pipeline project involves the installation of pipelines inside a pre-installed segmental bored tunnel with very tight curvature. A tunnel boring machine was used to construct a segmental bored tunnel with an outer diameter of 4.2 m, at depths ranging from 45 m from the launching shaft to 55 m at the receiving shaft, as temporary tunnel to facilitate the installation of the proposed water pipelines. One Smart Engineering Pte Ltd was appointed by Tiong Seng Contractors (Pte) Ltd as their consultant to carry out engineering design for the proposed 2200 mm/1600 mm diameter potable water pipeline, from Jalan Kampong Chantek to Marina South and River Valley Road, under Package 5 (P5), for PUB, the Client.
In the P5 project, there were many challenges in terms of the alignment and ground conditions. The P5 bored tunnel was launched from the P5-5 shaft which was 43 m deep and in Bukit Timah Formation with varying degrees of weathering, with depth. The bored tunnel passes under the MRT tunnels of the Thomson East Coast Line (TEL) Contract T220 and Fort Canning Station of the Downtown Line. In this project, the main challenges were the design and construction of the P5-5 shaft and the sophisticated interfaces of the bored tunnelling with the existing MRT tunnels, MRT station, CTE tunnels, Singapore River, and adjoining buildings. Among other mitigation measures to protect these structures and ensure the safety of the bored tunnelling under the Singapore River, one of the ways was to increase the productivity and speed of bored tunnelling and installation of the tunnel segments. An innovative dowel connection system for the tunnel segment has been adopted and was found to be working effectively.
Plan showing the alignment of the bored tunnel for the P5 Project. THE SINGAPORE ENGINEER March 2020
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