软岩隧道初期支护沉降变形分析及控制方法

目前存在对软岩隧道初期支护变形的错误认识,造成施工成本的浪费、安全风险的增大、进度被严重制约等不利影响,所以非常有必要对隧道初期支护变形进行研究分析并控制。首先以“矿山法”工程实践证明软岩隧道预留变形量是不必设置的,再通过各种权威文献说明以容许变形来实现围岩自承的观念是对“新奥法”的曲解,是错误的,需要找出支护变形的真正原因并控制。通过总结分析隧道支护常见的6 种位移及其组合,得出为控制初期支护变形需要解决支护底脚地基承载力和支护结构强度2 方面问题。于是建立以“分布锚杆+钢架+喷射混凝土且系统分布锚杆模拟为具有法向和切向作用力的链杆支座的结构力学模型”,可计算出支护结构底脚应力及截面最大应力等值,由此可得出对地基承载力和支护结构强度要求的明确标准,或对改善支护底脚抗力提供数值依据。计算结果表明: 系统分布锚杆能极大地降低支护结构的弯矩、轴力内力和底脚应力,从而增强支护结构的承载力和降低基底应力,使变形和沉降得以有效控制。

Analysis and Control Method of Settlement Deformation of Initial Support in Soft Rock Tunnel

At present, there is a wrong understanding of the deformation of the initial support of the soft rock tunnel, which results in the waste of construction cost, the increase of safety risk, and the adverse effect of the progress being seriously restricted. Therefore, it is very necessary to study, analyze and control the deformation of the initial support of the tunnel. In this paper, the engineering practice of "mining method" proves that the reserved deformation of soft rock tunnel does not need to be set. Then, through various authoritative documents, it is explained that the concept of realizing the self bearing of surrounding rock with allowable deformation is a misinterpretation of " New Austrian Tunneling Method", which is wrong. Therefore, it is necessary to find out the real cause of support deformation and control it. Based on the analysis of six common displacements and their combinations of tunnel support, it is concluded that two problems need to be solved, i. e. the bearing capacity of the foundation and the strength of the support structure, in order to control the deformation of the initial support. Therefore, a structural mechanical model of chain link bearing with normal and tangential forces is established by" distributed anchor + steel frame + shotcrete and systematic distributed anchor simulation", which can calculate the stress of the support structure foot and the maximum stress of the support structure section, so as to obtain a clear standard for the bearing capacity of the ground base and the strength of the support structure, or provide a basis for improving the resistance of the support foot. Numerical basis. The results show that the systematic distribution of bolts can greatly reduce the bending moment, the axial force and the foot stress of the supporting structure, so as to enhance the bearing capacity of the supporting structure and reduce the stress of the base, and effectively control the deformation and settlement.