The Impact of Soil Anisotropy on Surface Settlements Induced by Tunnelling: A Revealing Parametric Study and Nomogram Development to Improve Modelling Practice

ABSTRACT Natural soils often exhibit clearly anisotropic mechanical properties, yet this characteristic is frequently overlooked in numerical models due to the practical challenges of determining anisotropic parameters. As a result, the influence of anisotropy remains difficult to anticipate, and engineers have limited tools to incorporate it into design procedures. However, accounting for anisotropy is essential for producing accurate predictions of ground settlements caused by tunnelling. This paper aims to enhance the understanding of cross‐anisotropy effects on the ground surface response. A parametric analysis is performed using the finite element software CESAR‐LCPC. The study shows that anisotropy in elastic properties significantly affects key parameters of surface settlement distributions, particularly the maximum settlement and the width of the settlement trough. To assist with practical evaluations, the paper provides abacuses (design charts) and analytical approximation formulas that illustrate how the maximum settlement and trough width vary with different values of the anisotropy ratios. These results offer valuable insights and practical tools for geotechnical engineers aiming to incorporate anisotropic behaviour into settlement analysis. To further assess the practical applicability of the approach, a case history from the TULIP tunnelling project was analysed. Despite the complexity of real conditions—including three‐dimensional effects, staged excavation, and multi‐layered soils—the predictions obtained with the proposed method to take into account the soil anisotropy showed good agreement with field monitoring data, confirming its potential for use in preliminary design.