Continous Conveyors

Conveyors at the Lower Northwest Interceptor Project

1 California, USA’s Lower Northwest Interceptor sewer tunnels used a
continuous conveyor system to haul clay, silt, and sand at 6 % upgrade with over 90 % system availability

2 The conveyor system was assembled for an initial 610 m long tunnel, then disassembled and transported in 3 days for a second section of the same length

3 A 5.8 km long conveyor system was used at California’s nearby UNWI tunnels, resulting in both TBM and conveyor system availability of above
90 %

4 Clay and sand mixed with additive was conveyed using a fabric belt
conveyor that emptied onto a stacker

5 The 5.8 km long UNWI tunnel was completed in December 2009, after the TBM achieved record advance rates for a soft ground machine in the 4 to 5 m diameter range

6 The UNWI sewer tunnel was completed with record rates by the Traylor/Shea JV, who attributed the high advance rates, in part, to the continuous conveyor system

While continuous conveyors have become the muck removal system of choice in long, hard rock TBM tunnels, they have gained
acceptance in soft ground tunnels only
recently. Several successful projects in Sacramento, California/USA have proven them to be a favorable alternative to muck cars,
producing record rates with high system availability.

The absence of muck cars allows for continual operation behind TBMs, factoring into recent weekly EPB advances as high as 210 m.

“The Robbins-supplied tunnel conveyor system performed remarkably well throughout the drive. The availability of the TBM and associated sub-components was in turn very high for a tunnel heading operating 24 hours a day, 5 days per week,” said Jeremy Theys, Project Manager for the Traylor/Shea JV (contractor for Sacramento’s Upper Northwest Interceptor (UNWI) sewer project).

The design of such systems must, however, take into account the differences in material between...