Explanation for twin tunnelling-induced surface settlements by changes in soil stiffness on account of stress history

Abstract

In this article, a group of representative centrifuge tests were selected for numerical modelling to explain the surface settlements induced by sequential twin tunnelling. Both Modified Cam Clay model (MCC) and Three-Surface Kinematic Hardening model (3-SKH) were adopted in the simulation, which indicated the use of 3-SKH model conduced to mimicking more closely centrifuge model response. Via performing more contrastive numerical analyses with 3-SKH model, the influence of the first tunnel event on the stiffness of the soil around the second tunnel was quantitatively investigated, whereby the mechanism behind the observed surface settlements was finally made clear.

A Design Chart for the Analysis of the Maximum Strain of Reinforcement in GRPEs Considering the Arching and Stress History of the Subsoil

“…Here, it is assumed that the sag of the reinforcement is equal to the settlement of the subsoil. With the surface settlement of the subsoil quantified by Equations ( 13)-( 16), the vertical stress shared by the reinforcement was updated when substituting Equations ( 13)-( 16) into Equation (12). After that, Equation ( 6) and the updated σ r were substituted into Equation (17), and an equation for σ s was then obtained (i.e., Equations ( 18)-( 21)).…”

“…In addition, engineering practices have shown that soils with different stress histories have diverse strains under the same stress. Grammatikopoulou et al [11] and Zhang et al [12] noted that the stress history affects the soil stiffness, which in turn causes differences in soil settlement. Different stress histories would cause various consolidation coefficients of the subsoil [13], which determines the consolidation rate of the soil.…”