Analysis of surface settlements induced by tunnel excavation with EPB-TBM

Abstract

Purpose. To investigate the efficiency of various approaches to predict surface settlements due to tunnel excavation. Methodology. To appreciate the surface displacements, our study is focalized on the case of a real tunnel in a layered ground (Algiers’s Metro), where a tunnel boring machine was driven for the first time in this country. Firstly, the surface settlement trough was calculated with empirical, analytical, and numerical (FEM) methods. Secondly, a set of numerical analyses was carried out to inspect the evolution of surface settlement as the TBM progresses. Finally, a parametric study was performed to examine the construction step most productive for surface settlement. Findings. FEM is a useful tool for predicting surface displacements due to tunnelling, especially when assigning an adequate and sophisticated behaviour model. Originality. A reference numerical model which represents well the construction procedures of the Algiers tunnel has been established. Practical value. This study illustrates that the results obtained by FEM with the use of Hardening Soil as a constitutive model to represent the soil are almost identical to those measured during the tunnel excavation. On the other hand, the empirical formulas available in the literature are not always efficient to predict surface movements.