Cowi to design tunnel for Singapore’s Cross Island Line

In November last year Nishimatsu was awarded the S$446m (US$328m) contract for the design and construction of the 2.9km tunnel between Tampines North and Defu stations. The package of work also includes 300m-long cut and cover tunnels and a two-storey building to house mechanical and electrical services for the tunnel.

A 12.6m diameter TBM – one of the largest ever used in Singapore – will bore a single tunnel with two tracks. The cut and cover tunnels will extend 45m deep and the bored tunnel depth will vary from almost 50m underground at its deepest to less than 12m cover at its shallowest. Tunnelling will be carried out mostly in old alluvium, a predominantly soil-like material comprising sandy and silty clay.

Jotham Vizard, senior vice-president in COWI's international transportation unit, said the company was “immensely proud” to assist Nishimatsu in creating the state-of-the-art metro in Singapore.

“As TBM technology improves, large diameter tunnels are becoming more common, and this project maintains our leading position in the large diameter market,” he said.

Vince Goh, managing director for COWI in Singapore, said the project involved several exciting technical challenges other than the large diameter tunnel itself.

“The tunnel will go underneath a military airport with sensitive fibre-reinforced pipe, runway, taxiway, apron, and airport structures which increase limitation in ground movement during both bored and mined tunnelling operation. Moreover, any TBM cutterhead intervention beneath the airbase will need to be pre-planned and in hyperbaric environment due to the depth. Multiple closely spaced adits for future underground infrastructure are also part of the challenge. The tunnel will also go under public roads and will under cross the Sungei Serangoon vehicular bridge and Kallang-Paya Lebar Expressway viaduct,” said Goh.

Construction works are expected to start in June.