Abstract:

Large deformation and collapse are easily occurred in shallowburied tunnels due to soft soils. In order to solve the problem of surrounding rock deformation and the selection of excavation method during tunnel excavation, the crown top settlement, hance convergence and inverted arch settlement of Zizhi Tunnel are monitored; and the monitored data and influencing factors are analyzed. The results show that: (1) The crown top settlement of tunnels constructed by CRD method in mucky soft soil and that by 4bench method in highly weathered silty siltstone are relatively large. (2) The dismantling of support will also cause large crown top settlement, which accounts for 14.63% of total crown top settlement. (3) Elliptical deformation would occur when tunnel is located in silty soft soil; and overall settlement would occur after completion of secondary lining because of insufficient bearing capacity of the tunnel base. (4) The rainfall will overload the upper soil and weaken the strength of surrounding rock, which leads to increase of crown top settlement. (5) The change of soil conditions and construction methods will affect the crown top settlement obviously; and the risk of excavation by CRD method in areas where tunnel deformation is strictly controlled or in mucky soft soil is still high.

Key words: shallowburied mined tunnel, soft soil, large crosssection, crown top settlement, surrounding convergence