Ribbed supporting system has been used for many years to support tunnels. The ribbed supporting system is based on steel ribs supporting tunnels. The implementation of this system involves the installation of rolled steel sections around the circumference at specified spaces. The formation of gaps between the steel ribs and the ground is very common.
These gaps should be suitably wedged to avoid excessive deformation of the ground. It is essential to ensure that the loads are distributed evenly by the steel support around the tunnel profile. Subjecting of steel support to point load will significantly reduce their ultimate capacity.
The steel ribs can be combined with shotcrete concrete. The shotcrete concrete will be applied before the erecting of ribs. The applying of a layer of shotcrete concrete will reduce the problems of gaps between ribs and surrounding ground, which minimize the wedging problems.
Then another layer of shotcrete can be applied after the installation of ribs that combine the steel ribs and concrete together. This will improve the ultimate capacity of the supporting system.
Generally, the legs of the steel arches are placed on concrete to ensure the efficient distribution of the loads to the ground and prevent settlement. Lattice girders can also be used instead of rolled steel sections. Lattice girder can be installed with a combination of shotcrete concrete, as shown in figure no:2.