![]() Finite element analysis or equations given in codes for different shapes of tunnels can be used to find the stresses of the tunnel. This load can be applied to the tunnel as a gravity load. For example, consider massive moderately jointed rock, rock load is 0.5B. Depending on the rock condition, fracture spacing and RQD value, rock load can be selected. The above figure is extracted form EM 01. It provides a guideline to design tunnels depending on different ground conditions. “ EM 01 Tunnels and Shafts in Rock” one of the most commonly used standards that can be reffed for our designs. In tunnel designing books or design standards, it can be found the load that needs to be considered for the lining design depending on the rock type. Rock quality and the type of rock shall be inspected at the site and then the design should be carried out. Lining design is done considering the type of rock. If the rock is not fairly good or it can not be stabilized with shotcreeting (reinforced or un-reinforced), we have to have a lining that can bear the external loads. When adequate rock cover is present, we need not worry about the total collapse of the tunnel. But if the rock is weak we have to consider the rock quality for the design. If we have good quality rock, we can have an unlined tunnel. When an adequate rock cover presents, we can do the design of the tunnel with lining or without lining. Design of a Section with an adequate rock cover They normally find the distance that the unlined section can be continued and the rest of the length is lined. Most of the tunnels designers come across this situation. However, at the outlet, the tunnel has to be lined by a steel liner or a concrete liner if there is no adequate rock cover. Generally, tunnels with having good quality rock cover are not lined by reinforced concrete in addition to the shotcreating. In addition, the area around the tunnel can be a collapse in the tunnel.ĭepending on the type of surrounding material, a tunnel design can be carried out. ![]() When the tunnel is lined we have to consider the loads on the tunnel and it should be designed considering those factors. Especially when a rock cover is smaller we have to check whether the overburden is sufficient to take that load when the tunnel is unlined. When the tunnel carries water with a large head, it exerts water head on the surrounding area. However, tunnels carry water are design for both external and eternal loads. It could be constructed in rock or soil.įor example, a tunnel constructed for a highway is designed for external loads which are applied from the rock cover or any other overburden material. Tunnel design is done in reservoirs or underground roads are not constructed every day like other structures.
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