Stress redistribution around cross passages in shallow tunnels

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Construction of cross passages is a standard practice in tunneling, functioning as adits between the running tunnels for emergency access, maintenance, and equipment storage. The effect of cross-passage excavation on the running tunnels is poorly understood and sparsely documented. This study investigates the stress redistribution around cross passages by performing centrifuge experiments on a scaled model at 50g. Uni-directional strain gauges, installed near the crown and springlines of the cross-passage opening, were used to measure the hoop and longitudinal strains and back-calculate the changes in stress in the parent tunnel. The results from centrifuge tests were then compared with three-dimensional finite element analyses considering the parent tunnel lining as linearly elastic and using the Mohr-Coulomb failure criterion to model the soil.

Results indicate that linear strain gauges provide a reliable method of estimating stress changes in the hoop and longitudinal directions. Current experiments show that the increase in hoop force near the opening is about 2.68 times and 1.72 times for C/D = 0.5 and C/D = 1.0 respectively. While some agreement with numerical results is observed, some values significantly differ in experiments as compared to numerical values. Bending moments show irregular results in model experiments, possibly due to the end supports interference. The shortcomings of the current model tests are discussed and remedies are to be implemented in future works.

5th European Conference on Physical Modelling in Geotechnics (ECPMG2024)

Geotechnical infrastructure