On the simplified method for evaluating tunnel response due to overlying foundation pit excavation

Abstract

Foundation pit excavation may cause excessive uplift displacement and structural damage to the underlying shield tunnel. In this paper, the rationality of the excavation-induced inputs in the current force-based and displacement-based methods is analyzed theoretically and verified by comparing the elastic finite element method (FEM) and the elastic continuum solution. Then, the force input is modified by the load amplification factor to obtain a reasonable tunnel response, and the calculation method of the load amplification factor is given. Based on the mechanism of tunnel-soil interaction, the difference between Winkler subgrade moduli under active and passive conditions is analyzed. It is recommended that the active and passive Winkler subgrade moduli should be adopted under the force and displacement inputs, respectively. By comparing the elastic continuum solution and the Winkler solution, the validity of the Winkler subgrade moduli under active and passive conditions is verified. Thus, a force-based Winkler solution with modified force input is proposed. Finally, the proposed method is applied to a case study, and its applicability is verified by comparing the measured results and the FEM analysis with the HS-Small model.