Microtunnelling Design Utilising All Significant Rock Properties
Dr Bill Bamford
Abstract
Although most microtunnelling machines (MTBMs) use slurry to support the face and transport the muck, they may also be used open faced when boring through soft to medium strength sedimentary rocks, in relatively dry states. Bamford Rock Testing Services (BRTS) has recently developed the capability to numerically model the predicted behaviour (thrust and torque requirements, and advance rates) for cutting rock tunnels with MTBMs using drag picks or mini-discs, from the measured rock mechanical properties. The machine torque has to overcome the frictional resistances of cutters, scraping across the rock face, as well as the cutting forces in the rock. Previous authors have guessed at the appropriate friction coefficients, but we have now developed a technique to accurately measure the friction coefficient of any cutter material scraping across any rock. Some recent results measured for different cutters on several rock types are presented. Numerical examples demonstrate the results of modelling MTBM performance, using the friction coefficients measured on some local rock types, versus the range of previously-guessed friction coefficients. .
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