Secondary lining thickness optimization of road tunnel

Engineering analog method was adopted to take the secondary lining thickness optimum design of Yushugou tunnel, shallow-buried Ⅱ class rock, Ⅲ class rock and Ⅳ class rock, which are three different kinds of composite lining structure types, were selected, the software FLAC was used to take analog computation on the surrounding rock and primary support's strained condition after the tunnel was excavated, then the software ANSYS was used to take analytical computation on the strained condition of the secondary lining.Computation result indicates that the secondary lining's internal forces of three different kinds of lining structure types are less, the maximal stress is 165 kN, the maximal bending moment is-15.97 kN·m, and both of them happen in the section of shallow-buried Ⅱ class rock, the safety factor of the secondary lining is large; the maximal circumjacent displacement of the lining occurs in the situation of shallow buried Ⅱ class rock, the maximal displacement (18 mm) of the surrounding portal happens in spring, the surrounding rock displacement in side wall has a less convergence, the better the surrounding rock is, the smaller the circumjacent displacement is.The result of monitoring measurement indicates that the convergence of tunnel inner perimeter is far smaller than allowed convergence, the measured pressure values of contact surface in the secondary lining are smaller than the calculated values in specification, the secondary lining has good work condition and its safe provision is enough, so tunnel structure is safe when reducing the thickness of secondary lining.