Improved Squeezing Prediction of Deep Tunnels Within Highly Fractured Rock Mass: Update of the Hoek & Marinos Curve Under Uncertainties
Résumé
In the early stages of deep tunnel design, identifying potential hazards, such as significant deformations around the tunnel after excavation, is crucial. The abacus introduced by Hoek & Marinos (2000) remains a widely used tool for estimating such deformations. This article aims to clarify the assumptions of the original abacus and updates it using numerical modeling, supplemented by a Monte Carlo simulation on input parameters to address a broader range of geological scenarios. Unlike the original approach based on analytical expressions, the new curves incorporate a generalized Hoek and Brown failure criterion, revised parameter intervals, and enhanced practical applicability. To address uncertainties in input parameters at early design stages, a “3-point method” was developed. This method propagates uncertainties through the updated curves, enabling the estimation of the median radial strain, a confidence interval—reasonably associated with a 95% range under certain assumptions—and the parameters of the probability density function. The method and updated curves were validated through a case study of the Yacambu–Quibor tunnel, demonstrating their effectiveness in estimating squeezing potential and uncertainty impacts. The updated curves offer three key advantages: (1) they eliminate the need to estimate the uncertain rock mass strength; (2) they account for variability in the elastic modulus using three modulus ratios (200, 400, 600); and (3) they rely exclusively on input parameters from laboratory tests and field investigations (σci, mi, σ0), with GSI iso-values introduced. These improvements provide a more reliable tool for assessing tunnel deformation risks while maintaining the qualitative recommendations of the original abacus.