A strain applied method for FEM-2D modelling of TBM tunnels in coarse-grained soils with comparative analysis of case histories

Abstract

• The “Strain applied method” is proposed. • The method applies to finite-element plane-strain analyses. • The method allows the prediction of surface settlements induced by mechanised tunnelling. • The method includes “Predictive lines” particularly useful for Class A predictions. • The “Predictive lines” are calibrated for mechanized tunnelling in coarse-grained soils. The paper focuses on the prediction of tunnelling-induced settlements in greenfield conditions. The main components of ground deformation are investigated with approaches based on both empirical and numerical solutions. In particular, the study analyses five well documented case histories of shield-driven tunnels bored in coarse-grained soil deposits and compares the predicted and measured settlements. A specific approach for FEM-2D modelling of soil-shield interaction (called “ Strain Applied Method ”) has been implemented and its potential for the prediction of the settlement trough has been discussed. The analyses were performed for the green field conditions with the Finite Element software Plaxis. The mechanical behaviour of the soil has been modelled by both the usual linear elasto-plastic model ( Mohr-Coulomb, MC ) and the advanced Hardening Soil model with small strain stiffness ( HSs ). The comparison of results shows that the settlements calculated by the HSs model are generally in better agreement with the field measurements. Then, the analysis has been focused on the volume loss obtained for the five case histories, finding some significant correlations between volume loss and the specific parameters required by the proposed FEM-2D model. The predictive capabilities of the 2D model, with parameters estimated by specific correlations, were demonstrated by applying the proposed method for two new case histories, not included in the initial set utilized to find the correlations.

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