岩质隧道深浅埋划分方法及判别标准探讨

Discussion on Classification Method and Criterion for the Deep-buried and Shallow-buried Rock Tunnels

传统的深埋与浅埋隧道划分方法以普氏压力拱理论为基础,由于普氏理论的局限性,这种划分方法不尽合理。鉴于此,文章将有限元极限分析法应用于隧道深浅埋划分中,提出了隧道深浅埋划分的三条原则。对于Ⅳ级、Ⅴ级围岩的岩质隧道,根据隧道的破坏模式划分深埋与浅埋,破裂面贯通至地表即为浅埋隧道,破裂面没有贯通至地表即为深埋隧道,并利用有限元强度折减法求出浅埋隧道压力拱高度,以此作为深浅埋分界线;对于围岩等级高的岩质隧道,以无衬砌隧道稳定安全系数来划分深浅埋,安全系数大于等于1.5时为深埋隧道,安全系数小于1.5时还要根据破坏模式进行深浅埋判断。此外,深浅埋隧道划分还应考虑环境、施工、地质构造、不稳定块体等因素的影响,由此可能造成围岩整体塌落,形成松散压力。最后,文章建议对于深埋隧道可按弹塑性数值分析计算,而对浅埋隧道除按弹塑性数值分析外,还需按浅埋松散荷载依据荷载-结构模式分析,以确保安全。

The traditional classification for the deep-buried and shallow-buried tunnels is based on the Protodyakonov′s pressure arch theory and not reasonable enough due to its limitation of this theory.In view of this the finite element limit analysis method was applied to the classification for the deep-buried and shallow-buried tunnels,and three principles were put forward.For the rock tunnel with surrounding rock ofⅣandⅤ,the classification for the deep-buried and shallow-buried tunnels is based on the failure modes of tunnel,it is defined as the shallow-buried tunnel if the fracture plane cuts through ground surface while it is defined as the deep-buried one if the fracture plane doesn′t cut through ground surface,the height of pressure arch of the shallow-buried tunnel obtained by using FEM strength reduction method can be taken as the dividing line for the shallow-buried and deep-buried tunnels.For the rock tunnel with surrounding rock of higher grade,the deep-buried and shallow-buried tunnels are defined according to the stability safety factor of the unlined tunnel,it is defined as the deep-buried tunnel when the stability safety factor is more than or equals 1.5 while the failure mode should also be considered to define them when the stability safety factor is less than 1.5.In addition,the division of deep-buried and shallow-buried tunnels should still consider the effects of environment,construction,geological structure,unstable block,which will cause the surrounding rock collapse and form loose pressure.At last,it is suggested that for the deep-buried and shallow-buried tunnels it can be calculated by elastic-plastic numerical analysis method,but for the shallow-buried tunnel it should also be analyzed according to the load-structure model to ensure safety.