Interaction behaviours between parallel tunnels in soft ground

Abstract

This paper describes a study of the influence of shield tunnel construction on the displacements and stresses induced in the linings of existing nearby parallel tunnels. The paper presents a brief review of a set of laboratory scale model test research programme investigated the influence of tunnel proximity and alignment, liner stiffness on the nature of the interactions between closely spaced tunnels in clay. A total of two sets of carefully controlled physical model tests were performed. A cylindrical test tank was developed and used to produce clay samples of Speswhite kaolin. In each of the tests, three model tunnels were installed in order to conduct two interaction tests that have been carried out to investigate the interaction problem between parallel tunnels. The results of these tests are compared with the results of finite element analysis to investigate the techniques that must be used to obtain reliable numerical solutions to this type of problem. The results presented here are limited to the comparison between the results of physical model test and the corresponding finite element back-analysis. The results of the physical model tests generally indicate that interaction effects are greatest on the pillar springline and crown of the instrumented tunnel. It was also generally observed that the total stresses acting on the instrumented tunnel decreased immediately after a non-instrumented tunnel had been installed. These stresses tended to increase in the long term as pore-pressure dissipation occurred. These results also indicate that significant bending moments were induced in the instrumented tunnel by installation of the new tunnels. In both cases, the numerical and model test data agree well. It is also found that the closer new tunnels are constructed to an existing tunnel, the larger additional moment is developed at the pillar springline of the existing tunnel liner. The physical model tests show that for closely spaced tunnels the distortions and moments of the liner may be important. The values of the bending moments induced in the liners appear to be particularly significant. It is shown that interaction between tunnels is unlikely to be significant unless the spacing between the tunnel centres is less than about two tunnel diameters. Elastic finite element analysis with a hydrostatic gap modelling procedure gives results that appear to be in good agreement with the results of the physical model tests. Based on the results of finite element analyses performed to verify experimental procedure, it is suggested that the procedures adopted in the model tests of using one clay sample to carry out two interaction experiments is reasonable. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.