复合式衬砌隧道的总安全系数设计方法探讨

Discussion on Design Method of General Safety Factor of Composite Lining Tunnel

研究目的:铁路、公路等交通隧道常采用复合式衬砌,其中初期支护一般采用地层-结构法或工程类比法进行设计,二次衬砌采用荷载-结构法进行设计,由于二者采用的分析方法不同,难以统一评价整体结构的安全性。现有隧道设计规范仅提出了二次衬砌的安全系数要求,但复合式衬砌并非单一结构,有必要研究初期支护和二次衬砌的总安全系数。同时为建立总安全系数设计法,有必要研究初期支护的荷载-结构模型。研究结论:(1)对于采用喷锚支护的复合式衬砌隧道结构,围岩压力随埋深的增加而增加,隧道支护参数应根据埋深进行相应调整;(2)采用荷载-结构模型可以建立复合式衬砌初期支护和二次衬砌的统一设计方法;(3)复合式衬砌隧道的总安全系数应包含初期支护和二次衬砌各自的贡献,当二次衬砌为钢筋混凝土时,总安全系数建议不低于3.0,否则不低于3.6;(4)不同设计方法所建议的初期支护和二次衬砌的安全系数分配可按表2采用;(5)采用本文设计方法对现有高速铁路隧道结构安全性进行再分析,结果表明,在埋深为300 m左右时,Ⅲ、Ⅳ级围岩支护参数有进一步优化的空间;(6)本研究结果可为复合式衬砌隧道结构设计提供思路和方法。

Research purposes： Composite lining is often used in the railway, highway and other traffic tunnels, and the primary support is generally designed by layer structure method or engineering analogy method, while the secondary lining is usually designed by load structure method, so it is difficult to evaluate the structural safety uniformly due to the difference of analysis methods. The current tunnel design code only specifies the safety factor requirements of secondary lining, but the composite lining is not a single structure, so it is necessary to study the general safety factor of primary support and secondary lining. And it is necessary to study the load - structure model of primary support to establish the design method of total safety coefficient. Research conclusions： （ 1 ） For composite lining structure with shotcrete and rock bolt support, the surrounding rock pressure increases with the increase of the buried depth, therefore the tunnel support parameters should be adjusted according to the buried depth. （2） The unified design method of composite lining including primary support and secondary lining can be established by the load - structure model. （3） The general safety factor of composite lining tunnel should include the safety contribution of both primary support and secondary lining. When using steel reinforced concrete as secondary lining, the general safety factor should be not less than 3.0, or else not less than 3.6. （4） Different distribution of safety factor on primary support and secondary lining suggested by different design methods is shown in table 2. （5） The result of reanalysis on the structural safety of existing high - speed railway tunnel using this design method shows that when the buried depth is about 300 m, the supporting parameters of tunnel in surrounding rock of m and Ⅳ grade can be further optimized. （6） The research results can provide ideas and methods for structural design of composite lining tunnel.