Landmark onsite assembly of Robbins double shield completed

Mar 31, 2008

Onsite assembly of a massive 10.0 m (32.8 ft) Double Shield TBM has been completed in Andhra Pradesh, India. A ceremony was held on March 18, 2008 to mark the official launch of the Robbins machine - the first of two TBMs to bore a 43.5 km (27.0 mi) long water tunnel for the Alimineti Madhava Reddy (AMR) Project.

Initial onsite assembly, rather than pre-assembly in a manufacturing facility, has been proven on previous projects by saving time on the construction schedule and money to the contractor. "The assembly has gone quite smoothly, with some minor mismatch problems that were worked out. Even with that, the assembly at site has resulted in cost savings in terms of transportation," said Mr. Anil Kamat, Project Manager at Jaiprakash Associates Ltd., the contractor for AMR. Crews worked 24 hours a day to accomplish the aggressive schedule in approximately four months.

Comprehensive planning by both Robbins and Jaiprakash resulted in the successful completion of the TBM, back-up system, and continuous conveyor assemblies. The AMR machine was built in a large launch pit using gantry cranes to hoist components into place.  Machine parts including the cutterhead, gripper system, forward shield, and telescopic shield were assembled in a concrete "cradle". The assembled TBM and back-up then crawled forward by reacting against invert segment pieces installed progressively up to the tunnel entrance.

The second Robbins machine will be assembled onsite later in 2008 and launched from the opposite end, at the inlet portal.  After excavation of the entire tunnel is completed, a drill and blasted disassembly chamber will be used for removal of each TBM and back-up. The chamber will include poured concrete inverts and installed 170-metric-ton (187 U.S. ton) gantry cranes.

Geological conditions during the tunnel bore consist of quartzite zones up to 450 MPa (65,000 psi) UCS, layered and separated by shale for approximately 50% of the length, with granite (160 to 190 MPa/ 23,000 to 28,000 psi UCS) for the  remaining 50%. Both machines feature back-loading 20-inch diameter cutters for longer cutter life. Other design modifications include specially designed drive motors to run each machine at a higher than normal rpm for optimal penetration rates in the hard rock.

Once finished, the AMR Project will transfer surplus water from the Srisailam Reservoir to the plains of the Nalgonda District for the Andhra Pradesh Government.  The entire project is expected to take about 60 months to complete, and should be operational by December 2012.

The Robbins Company
Brianna Home, Marketing Director
29100 Hall Street
Solon, OH 44139
Tel: +1 253.872.4484

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