直墙式隧道衬砌背后空洞影响下结构开裂机制研究

Study on the structural cracking mechanism under the influence of voids behind straight-wall tunnel lining

为探究直墙式隧道衬砌背后空洞条件下衬砌开裂机制,以某直墙式隧道为背景,采用扩展有限元方法对拱部背后空洞影响下直墙式隧道衬砌开裂机制进行分析。研究结果表明:直墙式隧道衬砌拱脚外侧应力集中显著,无论空洞存在与否,衬砌首先在拱脚外侧裂损;在正常状态下和空洞环向范围小于30°时,直墙式隧道在拱脚底部及内侧各出现1条张拉裂缝,且裂缝扩展经历3个阶段;随着空洞范围继续增大,拱顶外侧和边墙底部相继出现拉裂缝;空洞改变了围岩-支护之间的力学传递模式,使拱顶成为最不利位置并在拱顶出现贯穿裂缝,衬砌承载能力大幅降低。

In order to investigate the lining cracking mechanism in the conditions of voids behind straight-wall tunnel lining,an extended finite element method is used to analyze the straight-wall tunnel lining cracking mechanism under the influence of cavity behind arch,taking a straight-wall tunnel as the background.The results show that the stress concentration outside the arch foot of the straight-wall tunnel lining is significant.Regardless of whether there is a void,the lining first cracks on the outside of the arch.In normal conditions and when the circumferential range of the void is less than 30°,the straight-wall tunnel has one tensile crack at the bottom of the arch and one at the inner side,and the crack propagation goes through three stages.As the scope of the void continues to expand,cracks appear at the outside of the vault and at the bottom of the sidewall one after another.The void changes the mode of the mechanical transfer between the surrounding rock and the support,which puts the apex of arch at the most disadvantaged place and causes transverse crack on the apex,thus greatly reducing the carrying capacity of the lining.