In February, Taisei’s second Kawasaki TBM holed through at Botanical Gardens station on Phase 4 of the Circle Line (CCL) project – a month after the first 6.63m diameter slurry machine.
The shields, TBMs 4 & 3, respectively, were launched from Bukit Brown on 2,269m westbound drives to Botanical Gardens station in June 2006, and the average weekly rates were 26.5m on 24-hour operation for each. They are being refurbished for relaunch on the final, twin 900m long mixed faced drives to Farrer station.
Geology along the route of contract C854 comprises fresh granite, soft residual soils and significant sections of mixed face conditions. Cover ranged from 20m-25m through residential areas and under transport links and utilities. The next drives will negotiate an area of piled foundations and the Deep Tunnel Sewer with 1.8m clearance.
Each TBM has nominal torque of 3120kNm, 1500kW drive power and 43,000kN thrust. The operating slurry face pressures generally equated to 20kPa over pore water pressure and consequent volume losses were approximately 0.5% and surface settlement were about 5mm-15mm, said Samuel Adair McChesney, project manager for Singapore Government’s metro developer Land Transport Authority (LTA), which is supervising the works directly.
With a cut diameter of 6.72m, the TBMs are building a segmental bolted lining (5+1) that is 275mm thick and sealed with gaskets. McChesney said the lining performed ‘extremely well’ with negligible cracking, spalling or leakage.
In December, two identical shields – TBMs 1 & 2 – completed successive 1.1km long eastbound drives to Thomson and Marymount stations after being launched from Bukit Brown in February and May 2006, respectively. The lead machine, TBM1, achieved 19m/week and TBM2 advanced on average 24m/week. The shields have been stripped out and the skins left in place.
Celebrations after the second breakthrough at Botanical Gardens, Circle Line, Singapore Taisei’s second Kawasaki 6.72m diameter TBM breaks through
