Numerical Simulation of the Effect of Cross Passage Excavation on Surface Settlement

Soil behavior at the intersection of a main tunnel and a cross passage is a complex, three-dimensional problem and only three-dimensional methods can provide a complete analysis of the stresses and displacements occurring in the environment surrounding the opening. The present study uses the finite element software CESAR LCPC V5 in order to investigate the surface settlement and the extent of the plastic zone generated after the excavation of a cross passage from the main tunnel. Furthermore, a parametric study was performed using different parameters such as the soil's cohesion, its young's modulus, and its friction angle, as well as different buried depth and different junction tunnel’s diameter. The results showed that the excavation of the cross passage has a significant impact on the main tunnel and the earth's surface. In comparison to the current section, the plastic zone in the intersection region was substantially larger. Moreover, the plastic zones were mainly located towards the tunnel sidewalls.