Many constitutive models are available nowadays to predict soil-structure interaction problems. It is sometimes not very easier for engineers to select a suitable soil model to carry out their design analyses in terms of complexity versus accuracy. This paper describes the application of three constitutive models to back-analyse a well-instrumented centrifuge model test, in which the effect of basement excavation on an existing tunnel was simulated. These three models include a linear elastic-perfectly plastic model with the Mohr-Coulomb failure criterion (called MC model), a nonlinear elastic Duncan-Chang model (DC) and a hypoplastic model (HP), the last of which can capture path-dependent and strain-dependent soil stiffness even at small strains. By comparing with measured data from the centrifuge model test, it is found that the HP model yielded the best predictions of tunnel heave among the three models. Not only the gradient but also the magnitude of tunnel heave is predicted well by this HP model. This can be explained by the fact that the HP model can capture the path-dependent and strain-dependent soil stiffness even at small strains but not the MC and DC models. However, all three models underestimated the change in tunnel diameter and the maximum tensile bending strain in the transverse direction.

Basement excavation inevitably causes stress changes in the ground leading to 38 soil movements which may affect the serviceability and safety of adjacent tunnels. Despite 39 paying much attention to the basement-tunnel interaction, previous research has mainly 40 focused on the influence of tunnel location in relation to the basement, tunnel stiffness and 41 excavation geometry. The effects of sand density and basement wall stiffness on nearby 42 tunnels due to excavation, however, have so far been neglected. A series of three-dimensional 43 centrifuge tests were thus carried out in this study to investigate these effects on the complex 44 basement-tunnel interaction. Moreover, three-dimensional numerical analyses and a 45 parametric study by adopting hypoplastic sand model were conducted to improve the 46 fundamental understanding of this complex problem and calculation charts were developed as 47 a design tool. When the basement was constructed directly above the existing tunnel, 48 excavation-induced heave and strain were more sensitive to a change in soil density in the 49 transverse direction than that in the longitudinal direction of the tunnel. Because a looser sand 50 possesses smaller soil stiffness around the tunnel, the maximum tunnel elongation and 51 transverse tensile strain increased by more than 20% as the relative sand density decreased by 52 25%. Moreover, the tensile strain induced along the longitudinal direction was insensitive to 53 the stiffness of the retaining wall, but that induced along the transverse direction was 54 significantly reduced by a stiff wall. When the basement was constructed at the side of the 55 existing tunnel, the use of a diaphragm wall reduced the maximum settlements and tensile 56 strains induced in the tunnel by up to 22% and 58%, respectively, compared with the use of a 57 sheet pile wall. Under the same soil density and wall stiffness, excavation induced maximum 58 movement and tensile strains in the tunnel located at a side of basement were about 30% of 59 the measured values in the tunnel located directly beneath basement centre. 60

No abstract

No abstract

No abstract