The first of three Robbins earth pressure balance (EPB) tunnel boring machines (TBMs) excavating the Moscow Metro has made its breakthrough. As well as finishing the bore early in late May, project saw a new Russian record set by the 6.2 m diameter machine, with an advance of 37.8 m being achieved in a single day in April 2013 – the greatest ever achieved for a machine in this class in the country.

Launched in the winter of 2012, the TBM achieved advance rates of 150 m per week. “The soil condition, crew experience, rigorous schedule, continuous conveyor, and the reliability of the Robbins TBM are all factors that helped achieve the record,” said Vadim Bocharov of contractor SK MOST.

The machine will now be disassembled in the receiving station site and launched on an additional 1.4 km (0.9 mi) tunnel in the last quarter of 2013. It is one of several Robbins EPBs on the massive metro project where dozens of TBMs are operating simultaneously. Two 6.6 m (21.6 ft) diameter Robbins EPBs are excavating left and right-hand tunnels, each 2.0 km in length, for contractor Engeocom. A third machine refurbished by Robbins for Engeocom, nicknamed “Julia”, is also excavating a 2 km section of tunnel.

Ground conditions in the city are said to be challenging, consisting of fine sand, gravel, loam, stiff clays and boulders. The EPBs are designed for the conditions, with active articulation to enable excavation of tighter curves without the risk of tunnel segments deforming. Two-component back-filling is being used to reduce the risk of settlement at the densely urban tunnel sites. Mixed ground cutterheads reinforced with abrasion-resistant wear plate give the option of changing the carbide knife-edge bits with 17-inch (432 mm) disc cutters, depending on the conditions.

Moscow’s Metro Development Program, unveiled in 2012 by the Moscow Government, calls for 150 km of new metro lines to be build in the next eight years. Work thus far has been around the clock, with close to 18,000 workers and specialists engaged in the projects. Their number is expected to reach 35,000 by the end of 2013.

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