Analysis of the Disc Cutter Cutting Load and Performance during TBM Tunneling in Soft-Hard Varied Strata through Laboratory Cutting Test

Tunnel boring machine (TBM) disc cutters are specially designed for breaking hard rocks and always exhibit unsatisfactory performance during the soft-hard varied stratum tunneling process. To figure out the load and cutting performance of the disc cutter and avoid unsatisfying excavation face crushing effects, a soft-hard varied strata excavation face model was made and rotary cutting tests with full-scale disc cutters were conducted. The load and cutting performance of the disc cutter under different TBM operating conditions were monitored and analyzed based on the test. It was found that the variation of the disc cutter load did not meet the CSM model completely, and the tangential force of the disc cutters in the heterogeneous areas was only about 30-40 % of that in the uniform areas of the excavation face model. An ideal criterion for the excavation face to be crushed successfully was established and the unknown parameters in it were obtained by fitting the test data. The gradation information and fractal dimension of crushing debris were obtained by the sieved-and-weighed method, which can provide indicators for the crushing effect of the disc cutters. Three different disc cutter poor performance modes in the heterogeneous strata cutting process were analyzed: (1) rotating starting failure of the disc cutters caused by tangential load insufficiency, (2) excavation face crushing failure caused by low crack extending capacities of the materials being cut and improper operating parameters (too small cutting depths or too large disc cutter spacing), and (3) adverse excavation face crushing forms (large or powdery debris). These analyses can help with the performance evaluation of disc cutters and the tunneling parameter adoption of the TBM in soft-hard varied strata tunneling engineering.