基于围岩压力及结构力学特征测试的隧道初期支护时机探讨

台阶法施工的隧道工程，上台阶的开挖支护是关键工序，其施工效率影响整个隧道施工的进度。因此，以黔张常铁路吴家边隧道为依托，基于现场测试结果，对Ⅳ级围岩隧道上台阶的开挖进尺和初期支护时机进行了探讨，重点研究了不同开挖进尺和初期支护时机工况下围岩压力的变化特征、初期支护的内力演变特征及其安全性。通过研究得到:Ⅳ级围岩地段上台阶开挖进尺最长可到6 m，再进行相应的支护体系施作，可提高机械设备的工作效率，加快施工进度；支护结构在刚度相同的情况下，结构内力按时间分配；二次衬砌基本不承担围岩压力，只是作为安全储备。

Discussion on Tunnel Primary Supporting Opportunity Based on the Surrounding Rock Pressure and the Test of Structural Mechanics Characteristics

In the tunnel construction with bench cut method, the excavation and support of the upper bench are the key process, and its construction efficiency affects the progress of the whole tunnel construction.This paper analyzes the excavation footage and primary supporting opportunity of the upper bench in surrounding rock tunnel of class Ⅳ relying on Wujiabian tunnel of Qianjiang-Zhangjiajie-Changde Railway based on field test results and focuses on the change characteristics of surrounding rock pressure, the evolution characteristics of the internal force of the primary support and its safety on different excavation footages and primary supporting opportunities. The results show that the longest excavation footage of the upper bench can be up to 6 m in surrounding rock of class Ⅳ, and then constructing the corresponding supporting system, which can improve the work efficiency of the machinery and equipment and speed up the construction progress; When the stiffness of supporting structure is under the same conditions, the internal force of supporting structure distributes according to the time; the secondary lining basically does not take pressure from the surrounding rock, just as the safety reserves.