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

U.S. Rock Mechanics/Geomechanics Symposium (ARMA)

Abstract

ABSTRACT: 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. 1 INTRODUCTION A non-linear correlation between the acting thrust at the cutter head and the corresponding penetration of disccutters in a specific rock mass greatly influences the performance of a Tunnel Boring Machine. This correlation is known as the Thrust-Penetration Gradient (TPG), and it reflects the disc-cutter indentation process within a specific rock type. The TPG is a specific and sensitive metric to evaluate the TBM's performance. It is considered a ground truth parameter for performance characterization, based on the Colorado School Mines Penetration Prediction for intact rock in the laboratory. The TPG represents the required work for rock mass mining and predicts performance for various rock conditions. The TPG for rock mass resembles the Colorado School of Mines model, representing the upper limit of disc-cutter indentation on massive rock conditions. A matrix notation is introduced as best practice to align specific TPGs towards rock strength and fracturing.

Authors 5

1. Marcel Schlicke

   Technical University of Munich

   Affiliation as printed

   Technical University of Munich, Munich, Bavaria, Germany

2. Konrad Nübel

   Technical University of Munich

   Affiliation as printed

   Technical University of Munich, Munich, Bavaria, Germany

3. Helmut Wannenmacher Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen, Aachen, Germany / Implenia AG, Vienna, Austria

4. Florian Amann Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen, Aachen, Germany

5. Thomas Marcher

   University of Graz

   Affiliation as printed

   Graz University, Graz, Austria