Abstract：
The deformation and failure mechanism of surrounding rock passed through by the running tunnel of the Beijing metro is studied by a model test regarding different depths of overburden in a clay stratum. The results show that overburden depth directly affects ground deformation and settlement, and that the rock failure process is similar no matter what the overburden depth is, which means that rock shear-slide failure initiates at the tunnel springing and develops upward gradually, ultimately causing tensile-shear failure at the tunnel crown. As for an overburden depth＜2.5D(D =tunnel diameter), the rock collapse will develop to the ground surface in ashape of an arch. It is recommended that, for the first case, two or three rows of locking anchors are installed at the tunnel springing and one row of dense grouting condulets or two rows of grouting condulets are installed at the tunnel roof to consolidate the ground. For the second case, the pre-support measures with one row of locking anchors and grouting condulets are proposed.
2013, Vol. 50 