深埋隧道轴线合理布置与衬砌结构稳定性研究

深埋隧道常处于构造应力状态,且水平应力分布并不均匀。采用数值模拟和模型试验方法,研究自重应力场、水平大主应力与洞线平行和垂直、不同围岩级别隧道轴线选择对围岩和衬砌结构稳定性影响。水平大主应力与洞轴平行时,围岩最不利位置发生在边墙;水平大主应力与洞轴垂直时,围岩最不利出现在拱顶。水平地应力使得二次衬砌受力特征发生很大改变,自重应力条件下,衬砌首先发生裂缝部位为拱顶,发生压弯破坏,建议加强衬砌拱顶内侧纵向配筋,提高正截面抗拉能力。当大主水平应力与轴线垂直时,关键控制部位为墙脚,出现压剪破坏,应增设墙脚箍筋,提高抗剪承载力。规范提出隧道轴线宜与水平大主应力方向一致原则,是有适用条件的。研究成果可为深埋隧道设计、施工提供参考。

STUDY ON THE AXIS ORIENTATION AND STABILITY OF LININGS FOR DEEP TUNNELS

Deep tunnels are often subjected to tectonic stress. This horizontal stress is not homogeneous. Numerical simulation and model tests were carried out to investigate the stability of tunnels and lining induced by self-weight stress, the horizontal maximum principal stresses parallel and perpendicular to the axis, and surrounding rock grades. When horizontal tectonic stress is parallel to the axis, plastic zones appear at the wall. When the horizontal tectonic stress is perpendicular to it, plastic zones take place at the arch mostly. Horizontal stress has a great influence on mechanical characteristics of the lining. Under conditions of self-weight induced stress, the first crack and compressive-bent failure take place at the arch. Loop reinforcement inside the arch are increased to improve the tensile load-bearing ability of the cross section. When the horizontal tectonic stress is perpendicular to the axis, compressive-shearing appears at the wall-footing, which is deemed to be the controlling position. Stirrups at the wall-footing should be supplemented to upgrade shear capacity. In Chinese design codes, there is a basic principle that tunnels’ long axes should be parallel to the horizontal maximum principal stress. The results can provide references for design and construction of deep tunnels.