Analysis of the intersection between tunnel, shafts and cross passages in a metro project.

The high-stress concentration, accompanied by the significant disturbance of the surrounding strata are the effects that characterise the construction of the transition areas that connect a vertical shaft with the subway tunnel by a cross passage due to the complex and irregular geometries at these intersection areas. Considering a case study of a project that includes eight ventilation\emergency shafts connected to a metro tunnel by different lengths of cross passages, this thesis studies the behaviour and the stability of the construction at the transition areas. Moreover, the good and worst scenario has been studied based on the geological conditions in the intersection areas among the eight regions. Furthermore, a suggested preliminary design for the primary support for the two geological conditions was introduced. A system of bolts and shotcrete has been chosen for stabilising the tunnel and the cross passages in the good scenario conditions, while for the stability of the shaft excavation, struts as temporary support and shotcrete as primary support until the installation of the final lining has been assumed. Whereas, for the worst scenario, a composite liner of steel sets and shotcrete for the stability of the tunnel and the cross passage, and micro piles to stabilise the excavation of the shafts in addition to the shotcrete until the installation of the final lining, turned out to be the best choice. The problem of the stress states and the displacements around the intersection areas is a clear three-dimensional problem. Therefore, the Finite-Element-Method (FEM) software RS3 (Rocscience,2022) was used to analyse the surface subsidence, the plastic zones of the surrounding rock, and the stress and displacement distribution induced by the construction at the intersection areas. Then, the suggested support systems were introduced. The considered project uses rectangular shafts and horseshoe-shaped cross passages with a slight curvature at the crown. Eventually, this thesis presented the possibility of using a recommended models for the shafts and the cross passages by using elliptical shafts and a more curved horseshoe shape for the cross passages, which helped to reduce the stress concentration and the total displacement for the excavation boundaries as well as decreases the disturbance in the surrounding strata. These recommended models are much more robust by utilising the arch effect; consequently, the need for stabilising systems is considerably minimised compared to the original model; therefore, the recommended models are anticipated to behave better, leading to a more economical solution for the project.