拱北隧道多台阶分部 暗挖方案研究

拱北隧道暗挖段开挖断面约337m2，在管幕-冻结复合帷幕作为超前支护下，进行多台阶分部开挖。原设计采用5台阶15部开挖工法，结合科研成果和现场可操作性，通过方案比选，对暗挖方案进行了优化，推荐采用5台阶14部竖撑方案，并采用台阶法进行开挖。本文利用数值分析软件对五台阶15分区方案，五台阶14分区斜撑方案，五台阶14部竖撑方案进行了对比，研究了各工况下隧道结构受力规律及安全性。分析结果表明：1）采用三种开挖方案均能满足结构安全要求，但五台阶14分区斜撑和竖撑方案更有利于机械化开挖施工；2）斜撑方案相对竖撑方案受力较大，且拼装难度大，精度要求高，施工安全性低；3）采用台阶法相对于侧壁导坑法，边脚部的初期支护变形更小，有利于冻土与管幕的协同变形，提高复合帷幕的封水安全。

Study on a Multi-propped Excavation of Gongbei Tunnel

Gongbei Tunnel, with an excavation cross section area of 337 m2 , is an ultra-shallow tunnel. The tunnel is to be constructed using the bench method under the protection of a freezing-sealing pipe roof. In the original design, the tunnel is constructed using a five-bench 15-step method. Combined with scientific research and the feasibility of construction, the tunnel is constructed using a five-bench 14-step method with vertical support. This paper presents a numerical study of the structural internal force and safety of the tunnel constructed using a five-bench 14-step method with diagonal support and five-bench 14-step method with vertical support. The following conclusions are drawn: 1) All of the methods meet the structural safety requirements of the tunnel; however, the five-bench 14 step-method with diagonal support and five-bench 14-step method with vertical support are more convenient for mechanized excavation construction. 2) If the tunnel is constructed using the five-bench 14 step method with diagonal support, the support has a more difficult assembly and bears a large internal force; therefore, the five-bench 14-step method with diagonal support has a low safety performance. 3) If the tunnel is constructed using the side heading method, the deformations of the initial support, frozen soil wall, and steel pipes increase; therefore, the side heading method has a low safety performance.