深埋大断面黄土隧道初期支护受力特征分析

为避免初期支护局部破坏对深埋黄土隧道安全产生危害，依托甘肃省境内早胜3号隧道施工开展深埋大断面黄土隧道初期支护受力规律的现场试验研究。通过埋设振弦式传感器对围岩与初期支护接触压力、喷射混凝土应变、钢拱架应变、相邻钢拱架间作用力进行监测，同时建立模拟隧道施工的有限元计算模型，分析得到初期支护内力分布特点。结果表明： 1) 初期支护受力随时间表现出迅速增长—缓慢增长—逐渐稳定的特点，曲线在二次衬砌闭合12 d后基本稳定； 2)应力空间分布上部大下部小，偏压特性明显，荷载理论计算值偏小； 3) 拱顶及边墙区域为初期支护薄弱部位，需采取措施并加强监控量测； 4)数值计算表明锚杆末端轴力较小，设计中可考虑适当缩短锚杆长度。

Mechanical Characteristics of Primary Support of Deep buried Large Cross-section Loess Tunnel

In order to avoid the damage of deep buried loess tunnel caused by partial failure of primary support, field test on primary support force of deep buried large cross section loess tunnel is carried out based on the construction of Zaosheng No.3 Tunnel in Gansu Province. The vibrating wire sensor is embedded in primary support to monitor the contact pressure between surrounding rock and primary support, the strain of shotcrete and steel arch and the active force between neighboring steel arches; the finite element calculation model is established to simulate tunnel construction; and the distribution characteristics of primary support internal force are obtained. The results show that: (1) The primary support stress experiences 3 stages with the variation of time, i.e. rapid growth, slow growth, and gradual stability; and the curve turns basically stable after the secondary lining has been closed for 12 days. (2) For space distribution, the upper part of stress is larger than that of the lower part, which shows that the characteristic of biasing is obvious, and the calculated value of load is too small. (3) The crown and sidewall area are the weak parts of primary support, thus measures should be taken and monitoring measurement should be strengthened. (4) According to numerical calculations that the axial force at the end of the bolt is small, the length of the bolt can be appropriately shortened in the design.