The role of umbrella arch and face bolt as deformation preventing support system in preventing building damages

Ground settlement is the most significant environmental impact of the tunnels excavated in intensively urbanized regions. A Considerable amount of ground settlement occurs by pre-convergence, formed during the time of support setting followed by the excavation, and movement of tunnel face into the tunnel. The risk of damage on the buildings by the ground settlement can be catastrophically high. Therefore, rock engineers bear an important duty to prevent the potential damage on buildings by controlling the ground settlement while excavating the tunnels. This has been accomplished by applying umbrella arch with face bolt technique recently in various important areas. In this method, the ground settlements can substantially be decreased by limiting the tunnel face movement into the tunnel, by creating a pseudo shell around the tunnel face with umbrella arch and then increasing the stability with face bolts. In this study, as part of the 2nd phase of Izmir metro construction in densely populated Poligon district of Izmir the effects of umbrella arch-face bolt applications on ground settlements have been determined using numerical modeling and in situ measurements. Results indicated that the umbrella arch and face bolt applications have significantly diminished the risk of settlement damage on buildings by reducing the ground settlements and convergence as 69% and 57%, respectively.