软弱围岩浅埋隧道二衬结构设计探讨

在软弱围岩浅埋地段（特别是洞口段）,为了确保隧道施工安全,通常采用较强的超前支护措施,比如超前大管棚支护、超前小导管注浆等,这些超前工法极大地提高了地层围岩参数,改善了隧道稳定性。但设计中这些地段的二次衬砌结构配筋偏多,材料性能得不到有效利用。结合工程实际,借助数值模拟手段,分析了某隧道衬砌的受力特点并对内力进行检算,发现二次衬砌各截面均有较高的安全储备,墙脚是二衬配筋的控制部位。因此提出降低钢筋直径、增加钢筋间距,适当加长仰拱与边墙部位搭接钢筋的长度等措施,最终可以既减小全断面配筋面积、又充分发挥钢筋的作用效果,数值模拟验证了这一措施具有可行性。

An Exploration into the Structural Design of the Secondary Lining of a Shallow-Depth Tunnel in the Soft Surrounding Rock

With shallow-depth tunnels in soft-rock areas,especially the entrance sections,some strong leading support measures are usually adopted to ensure the safety of the tunneling construction,such as the pipe-roof support,leading small-pipe-grouting.These leading support methods may greatly improve the parameters of the surrounding rock and eventually improve the stability of the tunnel being built.However,the designed structural reinforcement of the secondary lining of the tunnel in such sections is often found to have too many steel bars provided,in which case the performance of the materials is not efficiently used.With some engineering projects as practical examples,the numerical stimulation method is used to analyze the mechanical characteristics of the lining of a certain tunnel in the paper,with its internal forces checked up.It is found that the various cross-sections of the secondary lining of the tunnel all have greater margin of safety than is needed,and the weakest section of the secondary lining is the foot of the side wall.So it is suggested that the design of the secondary lining should adopt the following technical measures such as reducing the diameter of the steel bars,and properly increasing the space between steel bars and the length of the overlap steel bars in the sections of the inverted arch and the side wall.Practice shows that these technical measures may not only reduce the area of the cross-section of the steel bars but also give full play to the performance of the steel bars.The numerical stimulation proves the technical measures feasible.