Abstract：
The instability model and criterion for the stability of tunnels in jointed rock masses have been a subject of debate, and no scientific and reasonable standard has been reached for the subject so far. The empirical value of the displacement around the tunnel and plastic zone is deemed the criterion for stability of surrounding rock; elastic modulus and the shape of a tunnel have a great influence on the displacement around the tunnel. Additionally, displacements around a tunnel are unequal at different positions. For these reasons, it is difficult to settle upon a unified criterion. The empirical value of the plastic zone is superior to the displacement around the tunnel when it comes to the stability criterion. The plastification of surrounding material reflects the plastic dynamic mechanics of continuous media, but it cannot be adopted to quantitatively evaluate the tunnel stability in a jointed rock mass in which failure is induced by a preferred structural plane. Therefore, combined with the shapes and changes of micro-joints, the instability mode and quantitative criterion for the stability of a tunnel are studied by means of UDEC, and the relationship of the mechanisms of micro-structure and macro-mechanical behavior is analyzed. The conclusions are as follows: (1) The structural plane greatly weakens the mechanic property of the rock mass and its stability. Deformation and the strength of the structural plane play the controlling role in tunnel stability; (2) In the jointed rock mass, the disturbance zone of the surrounding rock is divided into failure shape, open zone and shear and slip zone. The failure means the instability mode of the tunnel, and the open zone means that surrounding rock is under the shedding critical condition, which creates a potential landslide area; (3) The shear and slip zone is the main cause of progressive damage of rock masses, so the shear zone is proposed as the criterion for stability of a tunnel in a jointed rock mass. Based on its strict mechanical foundation, the stability of a rock mass can be evaluated quantitatively. Using the Muzhailing Tunnel of the Lanzhou-Chongqing Passenger Dedicated Line as an example, the mechanical effects of surrounding rock are investigated before and after the implementation of bolt support, which verified the reliability, rationality and feasibility of using the shear and slip zone as the criterion for stability of a tunnel in a jointed rock mass.
ZHANG Zhi-Qiang,
He-Ben-Guo,
Guan-Bao-Shu
.A Study of the Criterion for the Stability of a Tunnel in a Jointed Rock Mass[J] MODERN TUNNELLING TECHNOLOGY, 2012,V49(1): 12-19
2012, Vol. 49 