The Thrust-Penetration Gradient: Decoding Geomechanical Dynamics and TBM Response

The Thrust-Penetration Gradient (TPG) is an essential tool in analyzing and predicting the performance of Tunnel Boring Machines (TBMs). It evaluates TBM efficiency, reflecting geomechanical dynamics during tunneling. The TPG effectively captures the complex relationship between thrust and penetration rates across various rock masses, drawing a parallel to the CSM model (Colorado School of Mines model) but with broader applicability. Originating from the TBM's start-up phase, the TPG offers real-time, continuous insights into machine-ground interactions, highlighting non-linear gradients. It involves isolating shield friction from total thrust, a process revealing frictional variations even in consistent geological settings. TPG also accounts for supplementary losses due to cutterhead curvature. By comparing torque and thrust per cutter, it accurately determines shield friction for each stroke, using quadratic and exponential models to correlate thrust per cutter with penetration rate. More comprehensive than the Specific Penetration metric, this approach avoids linear reduction constraints, offering a more precise platform for TBM performance evaluation. TPG's utility extends to grouping gradients based on geomechanical non-linearities through a novel matrix system, facilitating forward predictions of penetration rates irrespective of project or geomechanical conditions.