Design of Secondary High-Capacity Support to Large-Section Tunnel with Fractured Surrounding Rock Excavated on High-Stress Condition

To design high capacity support to deep large-section tunnel excavated in high-stress condition with fractured surrounding rock, for different section patterns of supports, the stresses and displacements of tunnel surrounding rock were analyzed with the change of lateral pressure coefficients. Particularly, the effect of height of double-layered I-section beam on the bearing capacity was investigated. As a result, an arched support with bottom arch superimposed and fully-closed I-section beam was developed with horse-shoe shaped structure. The bearing capacity of developed structure is 2.5 times higher than that of support using I-section beam. Underground field test shows that the deformation of the surrounding rock could be effectively controlled when the proposed secondary arched support is adopted.