Cross passages between twin tunnels. Preliminary design schemes
When a project includes two parallel tunnels, cross passages linking both tunnels are normally constructed for safety reasons during tunnel exercise. Design and construction of the cross passages is a challenging issue in tunnelling design. Excavating cross passages through rock, soft ground, and mixed face conditions presents very different challenges as well as handling groundwater creates additional difficulties. Excavation of the main running tunnels, having a relatively larger dimension compared to the cross-passages, usually involves in the use of full-face mechanized excavation to mitigate the impacts of difficult subsurface conditions. For cross passages, access is usually limited, excavation is implemented through traditional methods preceded by treatments if required. Different scenarios were selected and afterwards by changing the geometrical data of main tunnels, cross-passage, overburden and geotechnical parameters, a series of threedimensional numerical analyses (FLAC 3D) were performed. The aim of this ongoing parametric study is to obtain some abacuses useful in engineering practice.