Anisotropic deformation in Muzhailing railway tunnel, Gansu, China

摘要

Muzhailing railway tunnel is excavated mainly in fault zones,carbonaceous slate and sandstone using the drilling-blasting method.Geotechnical problems encountered in the tunnel during construction,such as large squeezing deformation with long duration and collapse of arch crown.The monitoring data shows the ratio between the maximum cumulative horizontal and vertical displacements reaches to 4 to 10,which shows an anisotropic deformation.Meanwhile,serial hydraulic fracture stress tests we conducted in tunnel indicate that coefficient of lateral pressure k approaches to 3,compared to the ratio of in-situ stress which is about 1.The geological analysis and the numerical simulation show that the special rock mass with layered structure presents an appearance of heterogeneous condition which affects the redistribution of stress in tunnel and takes major responsibility for the large horizontal deformation of tunnel.In addition,blasting excavation and groundwater also caused some problems during the excavation of the tunnel.