昔格达地层隧道围岩的失稳特征及变形控制工法

Instability Properties and Deformation Control Methods of Rocks Surrounding Xigeda Strata

昔格达地层是一种分布于我国西南地区的河湖相沉积半成岩,具有水稳性差,遇水易泥化、崩解等特点,在隧道开挖中易出现坍塌、围岩大变形等灾害,对隧道安全施工产生不利影响.基于此,依托攀西地区昔格达地层桐梓林、垭口以及盐边隧道工程,现场取样并进行围岩室内物理力学试验,同时建立不同含水率深浅埋昔格达地层隧道有限元模型,探究不同含水率下昔格达地层隧道围岩的失稳特征,并提出针对昔格达地层隧道施工变形控制工法.研究结果表明:昔格达地层对水较为敏感,其中浅灰色页岩夹砂岩的物理力学性质受含水率影响最大;当围岩含水率在0~20%之间时,昔格达地层隧道围岩变形呈现递增,但变形较小,自稳性较好,当含水率在20%~25%时,隧道围岩变形增大明显,失稳潜力巨大;在大埋深、高含水率的条件下,隧道仰拱隆起累计变形和掌子面挤出累计变形急剧增大,在拱顶部位,掌子面挤出变形主要发生在上中台阶交界处;针对昔格达地层隧道围岩失稳变形特征,提出在无水和有水状态下的昔格达地层页岩夹砂岩、砂岩夹页岩隧道围岩施工工法.

Xigeda strata are a type of fluvio-lacustrine deposit with half-diagenesis in southwest China,characterized by bad water stability;the deposits become mud and collapse when they come into contact with water;therefore,disasters are possible during the process of tunnel excavation.Large deformations of the surrounding rocks and collapse are the ill effects during constructions of traffic tunnels.Thus,relying on the Tong Zilin,Ya Kou,and Yan Bian tunnel engineering in the Xigeda formation in the Pan-xi region,and based on the field sampling and indoor laboratory tests of the mechanical properties of the surrounding rocks,finite element models of the shallow and deep Xigeda strata tunnels under different water content were established simultaneously to study the instability properties of the surrounding rocks of Xigeda strata for different water content and to explore the deformation control methods accordingly.The results show that Xigeda formation is sensitive to water,and the light-gray shale embedded with sandstone is most affected by water in its physical and mechanical properties.The deformation of the surrounding rocks increases when the water content ranges from 0%to 25%,but the deformation degree is small.When the water content ranges from 20%to 25%,the degree of deformation increases significantly,and there is increased possibility of instability.Under the conditions of large buried depth and high water content,accumulated deformation of the tunnel invert uplifting and tunnel face extruding increase sharply,followed by accumulated deformation of the vault.The tunnel face extruding deformation mainly occurs in the junction between the upper step and middle step.According to the instability properties of the surrounding rocks of Xigeda strata,construction methods of the surrounding rock with the rock either being shale embedded with sandstone or sandstone embedded with shale are examined for conditions where water is either present or absent.