First extension for Beijing’s
Metro Line 6 opens in September

After only three months of work a Robbins 6.15 m (20.2 ft) diameter EPB machine finished its excavation task in China’s capital Beijing. The machine had bored through 2.3 km (1.4 mi) of soft soils, clay, sand, pebbles, and highly weathered rock for the contractor China Railway Engineering Corporation (CREC) Bureau 5. The breakthrough marks the completion of the last section
of Line 6 extension Phase II, further lengthening Beijing Metro’s longest subway route. The machine was launched from a 20 m (65 ft) deep shaft at Lot 15 and added 12 km (7.5 mi) to the existing 30 km (19 mi). This eastern extension of Line 6 will allow seven new stations to open in September 2014. A second western extension, planned in 2015, will make the entire route 54 km (34 mi) in length. Advance rates of 125 m (409 ft) per week were achieved with the help of consistent ground conditions, field service support, and custom EPB design. This included a spoke-type cutterhead and shaft-type screw conveyor, as well as active articulation to negotiate curves down to a 1000 m radius. Universal concrete segment rings 1.2 m in length were placed to support the variable geology.  The urban conditions made tunnelling all the more challenging: structures along the tunnel route included high voltage lines within 1.5 m of the excavation, a 30 m (98 ft) wide river, a 200 m (656 ft) long machine factory, and a variety of active utility pipes. “The ground condition in Beijing is loose, soft ground with fine sand. We reduced the torque by injecting Bentonite into the cutterhead. We were also able to maintain a good rate of advance with high-powered VFD electric motors (5 x 800 kW) and with the help of a good crew for trouble shooting,” said Andrew Han, Robbins Field Service Manager.  In ongoing efforts to alleviate traffic pressure, more extensions to Beijing’s 16 active metro lines are expected. The overtaxed system currently carries 10 million passengers daily, and will be able to add 700 000 more upon completion of Line 6, according to the municipal transport commission.