Brief emergency road works were required in early June above the first tube on the Kowloon Southern Link, in Hong Kong, following the loss of compressed air through a zone of unexpectedly weak soil.

Early on Sunday, 3 June, two of the three westbound lanes on Salisbury Road, in the short section between Kowloon Park Drive and Hankow Road, were closed for repairs on a 3m by 4m area, said client Kowloon-Canton Railway Corp (KCRC). The 1m deep hole was backfilled within hours and one lane re-opened, the other remaining temporarily closed for monitoring.

The emergency works were launched above where the first 1.1km drive for the rail link turned into the home run to the reception shaft. Monitoring by the contractor, Link 2000 JV, highlighted ‘a potential ground disturbance’, said KCRC. The client told T&TI that ‘the cause of the sink hole is still under investigation but preliminary assessment points to a local weakness within the soil’. The compressed air was lost during a compressed air intervention. There was ‘minimal effect to the tunnelling works below’ because the ring had been built, it added. Public safety was not at risk and the eastbound lanes stayed open, though a gas main was shut down as a precaution.

Last August saw the official launch of the 7.99m Ø, 2,400kW Herrenknecht slurry TBM but the the machine did not start driving below Canton Road towards Salisbury Road until November. The geology in the area generally consists of reclaimed fill overlying superficial deposits, below which is completely decomposed granite over bedrock.

Once the first drive is completed, the TBM will be relaunched later this year to bore the parallel tube. The tunnels will run parallel mostly, except where the proximity of foundations has one tube briefly over the other. Excavation on the package is due to be finished by early 2008.

Link 2000 JV is building the link as part of a project to join the East and West metro lines by 2009. The JV contractor consists of Leighton, Balfour Beatty, Kumagai, and John Holland, which won the US$258M design and build tender to build West Kowloon station and the tunnels – the largest of three tunnel contracts on the 3.8km long link.

Works on the US$1.06bn link started in late 2005.