对形变压力的认识--隧道围岩挤压性变形问题探讨

The Key Way is to Release the Genuine Rock Pressure—Discussion on Problems of Tunnelling in Squeezing Ground

在高地应力背景下,隧道开挖造成岩体应力大幅度变化,软弱围岩松弛阶段的变形将达到很大的量级,这就是挤压性大变形的本质所在。国际隧协曾归纳总结的隧道结构设计模型中的"收敛-约束"模型可以十分贴切地说明支护和围岩在松弛变形发展过程中的相互作用。支护在同围岩共同变形中承受的荷载有别于隧道设计规范中规定的由离散岩体重量产生的"离散压力",可以称为"形变压力"。囿于对离散压力荷载的认识,很难找到处治挤压性大变形的合理途径。文章从形变压力的特性出发,对挤压性围岩隧道工程中的若干问题进行探讨,着重论述通过围岩变形的适度释放来缓解形变压力的处治理念以及与之相应的可让型支护和岩体锚固技术。

Squeezing of weak rock is essentially associated with creep caused by exceeding a limiting shear stress.In case of high in-situ stress,large deformation of surrounding rock may occur.During the deformation,a so called“genuine rock pressure”builds up and acts on the support structures according to“convergence-confinement”mod⁃el.The load jointly borne by support and rock mass is different from the“discrete pressure”due to weight of dis⁃crete body and it might be called“genuine pressure”.Restrained by the understanding of discrete pressure load,it is difficult to find the reasonable means to deal with squeezing deformation.Several issues of the tunnel in squeezing rock mass are discussed in terms of the characteristics of genuine pressure,and it points out that the feasible solu⁃tion in heavily squeezing ground is to release the genuine rock pressure by application of a yielding support system in combination with a certain amount of over-excavation,whereas the amount of over-excavation may be reduced by use of untensioned rock bolts.