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.