The first ever segmentally lined tunnel to be constructed in Sarawak, East Malaysia, has broken through. The 2.2km long, 2.2m i.d., Miri Raw Water Transfer Tunnel was excavated by contractor McConnell Dowell Kelena using a Herrenknecht shielded roadheader MHSM21 and took 15 months.
The tunnel was driven through intermittent bands of mudstone, claystone and water bearing sandstone of varying thickness. The ground conditions did not permit regular rates of progress and the weekly rate varied with the water inflows through the strata interfaces. However, rates of over 70m/week were achieved.
The lining is composed of more than 13 000 trapezoidal reinforced concrete segments cast locally. Each ring was formed from six equal segments, the invert segment having a formed sill to locate the rail track. The rings were built within the tailskin of the machine and the annulus around the ring was filled with pea gravel, cement grouted at a later stage, to give immediate support.
No experienced local labour was available so all workers, who were mainly from a local indigenous race known as the Iban, had to be fully trained in all aspects of the construction process.
Finishing work is under way within the tunnel and project completion, including outlet culvert and inlet piping, is expected in January 2000.
