昔格达组地层大断面隧道施工工法比选分析

Comparative Analysis on Construction Methods of Large Section Tunnels in Xigeda Formation Strata

昔格达组地层是一种分布于我国西南地区的河湖相沉积半成岩,水稳性差,遇水易泥化、崩解,强度大幅度降低,在隧道开挖过程中易产生围岩大变形、初期支护结构开裂、掉块、坍塌冒顶等灾害事故,严重影响着交通隧道工程的建设。以改建铁路成都~昆明线米易~攀枝花段桐梓林隧道为工程背景,运用FLAC3D数值仿真软件,建立5种施工工法模型。从隧道围岩变形时空效应特征角度,对比分析昔格达组地层在不同施工工法中的变形响应。研究结果表明,不同施工工法对隧道拱顶沉降影响最大;当隧道设计预留变形量为10~15cm时,建议优先选择三台阶临时仰拱法;当隧道设计预留变形量为10cm以内时,建议优先选择CRD法;最先行开挖面最大挤出变形量与最先行开挖面面积近似呈线性正相关;采用预留核心或增加较大刚度的临时闭合支撑有利于控制掌子面挤出变形。

Xigeda formation strata is a kind of fluvio-lacustrine deposits＇ half-diagenesis in southwest of China, which is also a kind of soft rocks with poor engineering properties. Its water stability is bad, so it is easy to mud and disintegrated with the strength greatly reducing in the presence of water. In the process of tunnel excavation, some emergencies is easy to produce, such as large deformation of surrounding rock, the initial support structure cracking supporting, sloughing and collapsing etc. These seriously affect the construction of transportation tunnel engineering. In the paper based on the Tongzilin Tunnel located on MPZQ-2 Section of the reconstructed railway from Chengdu to Kunming, FLAC3D is used to establish 5 numerical models of construction methods. From the characteristics of time and space effects of surrounding rock deformation, comparison and analysis are made on the deformation response of different construction methods in Xigeda formation strata. The results show that： different construction methods make a biggest effect on crown settlement in Xigeda formation strata, when the rational deformation of tunnels ranges from 10cm to 15cm, three-step temporary inverted arch method is recommended to choose; when the rational deformation of tunnels is less than 10cm, the CRD method is recommended to choose. The maximum extrusion deformation of the first excavation face is approximately linearly positive correlated with the first excavation face area, and the reservation core or increasing the stiffness of temporary supports is propitious to control the tunnel face extrusion deformation.