An estimation equation for the TBM thrust force in creeping rock

Abstract

Shield jamming due to insufficient thrust force poses a critical hazard in mechanised tunnelling through squeezing ground. The time-dependency of squeezing due to creep can substantially alter the thrust force requirements, and the use of existing design tools that neglect it might therefore be misleading for the feasibility assessment of mechanised tunnelling or the design of the tunnel boring machine (TBM). This paper develops an equation for estimating the required thrust force in creeping rock under squeezing conditions during ongoing TBM advance, as well as during construction standstills. The method uses and extends the applicability of existing design nomograms through design equations established via multiparametric nonlinear regression, considering the results of 12,300 transient numerical simulations that cover a wide range of in-situ stresses and ground, TBM, and creep parameters relevant in tunnelling practice. The proposed method approximates the numerical results with sufficient accuracy to provide a reliable basis for decision-making during design and a valuable tool for fast assessments of the shield jamming risk. Its versatility and suitability in practical situations are demonstrated via two application examples from the Fréjus safety gallery and the Gotthard base tunnel.