Kuching City on Sarawak has a population of 500,000 – yet currently lacks a centralised sewer system. As a result, surrounding rivers such as Sungai Bintangor and Sungai Maong are heavily polluted by the discharge of partially treated and untreated sewerage.

The Kuching City Centralised Sewer Project, overseen by the Sewerage Services Department of Sarawak, aims to create a high quality sewer system composed of sewers and wastewater plants, ensuring that only Standard A wastewater is discharged into the surrounding environment.

The project is divided into four packages. Package 1, worth RM530 million ($US 165.3 million), commenced in October 2008. Hock Seng Lee Bhd (HSL), a Malaysian engineering and construction firm, was awarded the contract for the project, and will construct a Central Sewage Treatment Plant and install 64.1 km of sewers. This includes a 7.7 km trunk sewer, 5.4 km of secondary sewer, and 51.4 km of tertiary sewer, which will be 450–1,500 mm in diameter.

Microtunnelling will play a key role in these construction works. The sewer system will adopt a gravity flow system, making it imperative for the sewers to be installed deep underground, at depths ranging from 6 to 27 m.

While property connections will be installed via conventional open cut methods, sewers greater than 2.5 m underground, which account for most of the network, will be installed by a tunnel boring machine (TBM). Accordingly, in 2009, HSL invested RM22 million ($US 6.9 million) in the purchase of four advanced TBMs.

Jacking shafts of 8 m diameter and receiving shafts of 7 m diameter are being constructed at the site of future manholes. The TBMs are lowered into the jacking shaft and start boring towards the receiving shaft, while the sewer pipe is jacked into the bored tunnel. For sewers between 2.5 and 6 m in depth, an auguring method is being used, in which soil from the TBM is removed by an augur train. For sewers installed at 6 m and deeper, and in hard rock conditions, a slurry method is adopted.

The TBM will also be used to install the 340 m section beneath the Sungai Sarawak, a river which traverses the city, tunnelling 4 m below the river bed.

As of April 2010, construction work on Package 1 was 13 per cent complete, and the entire package is scheduled for completion in the second quarter of 2012.