With the data gleaned from the geological investigation, Robbins was able to advise Afcons on the optimal operating parameters to get through the difficult conditions, including cutterhead rotation speed, thrust pressure, penetration rate and cutterhead torque. The data not only assisted the crew in operating the TBM, but also provided a comprehensive geological record for the second drive. Robbins India provided a geologist who carried out face mapping for the whole of the first drive, in both hyperbaric and open mode conditions on a daily basis. The unexpectedly hard rock caused high cutter consumption rates and slowed advance.Ī crew of Robbins Field Service personnel and engineers assisted Afcons in remedying the problem. The TBM bored into mixed face conditions that contained varying strengths of granite, from weathered to hard granite of 150 MPa (21,700 psi) UCS. ![]() The TBM was launched on its initial drive in January 2012 from a 28-m (92-ft) deep starting pit. Launched from a 28-m (92-ft) deep starting pit, the EPB experienced challenging ground nearly from the outset that required help and analysis from Robbins India. Small grippers located around the circumference of the machine’s shield allowed for cutterhead stabilization in harder ground, while additionally reacting the forces needed to pull the cutterhead back from the face in difficult conditions. diameter disc cutters, as well as soft ground tools. The specialized design utilized a combination of 17-in. The 6.65-m (21.8-ft) diameter Robbins EPB was designed to excavate granite, sand, silt and clay with boulders up to 300 mm (12 in.) in diameter. RELATED: Twin Robbins TBMs Play Key Role in Austrian Hydro Project ![]() ![]() We didn’t record any water leakage or settlement at the surface, and we have demonstrated a high standard of safety in the tunnel during construction,” said Gopal Dey, Senior Manager for Afcons. reflected on the breakthrough: “We are really proud of our executing team, which has maintained a high standard of quality. The 1,027-m long second drive for the machine was part of Lot UAA-01 on Line 1 of the city’s metro, consisting of two parallel 1.0-km (0.6-mile) tunnels running from the Washermanpet area toward Chennai International Airport.Ĭontractor Afcons Infrastructure Ltd. 27, 2016, a Robbins mixed ground EPB TBM broke through at Chennai Metro in India, finishing up a challenging second drive that saw the full gamut of difficult conditions.
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