Record win at Qinling

Robbins claimed this month that one of its machines had broken the record advance rate for a TBM in the 10-11m range. The TBM was on the Qinling rail project in China when it broke the record. The previous advance record, also set by a Robbins machine, was set on the Tunnel and Reservoir Plan (TARP) in Chicago, USA.

The new 841.8m advance record was set in April, with a peak 235m set in week 15 by the 10.2m main beam TBM that was commissioned by contactor China Railway Tunnel Group (CRTG) 18th Bureau in December 2008. Upon arrival it began boring one of the 16.6km parallel tunnels through Qinling Mountain.

A Robbins spokesman told T&TI, “The TARP tunnels were all in Dolomitic Limestone, with strengths ranging from 103 to 222 MPa UCS. Ground at West Qinling is phyllite and limestone, ranging from 30 to 100 MPa UCS.

“While the rock is softer at West Qinling, the tunnel depths vary greatly between the two projects. The majority of the TARP tunnels are approximately 90m below the city of Chicago. The amount of cover at the West Qinling tunnels, at the time of the record rates, was approximately 1,000m.

The spokesman added, “The TARP record was set by a 10.8m main beam TBM between 1989 and 1990.

“Although both are Main Beam machines, the TARP machine was fitted with 17-inch front-loading disc cutters, while the West Qinling Machines are fitted with back-loading 19-inch disc cutters for longer cutter life in rock and more efficient cutter changes.

“The West Qinling machines are also designed with the specialised ground support system replacing roof shield fingers while the TARP machine had roof shield fingers.

Construction contracts were awarded to CRTG 18th Bureau for the ‘Left Line’ tunnel and the China Railway Construction Corporation for the ‘Right Line’ tunnel.