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.
Over the last 10 years, construction of tunnels has increased in mountainous regions of high geological complexity and tunneling in tectonic zones has become common and necessary. The special property and structure of rock mass has been recognized as an important triggering factor that leads to various engineering problems (E. Button & G. Riedmüller et al, 2004; S. Dalgı ç, 2003). Large deformation in weak rocks and rock burst in hard rocks which are mainly hazards of tunneling excavation, have caused great losses in many areas of the world (Singh B. & Goel R.K., 2006). Compared to rock burst in hard rocks, it is still insufficient to understand the failure mechanism of large deformation.
Large deformation in tunnels is currently very frequent in China, accompanying different engineering activities, such as high way and railway construction, dam construction and mining, which caused numbers of large deformation in tunneling excavations (Guo Q L & Wu F Q et al. 2006). It is agreed upon the researchers in China that the large deformation can be divided into three categories: stress induced, structure induced and swelling induced (Wang CH &Sha P et al. 2011). The structure induced deformation becomes a highlighted problem among the three types, which is due to the variety and complexity of property and structure of rock mass. Hence, to examine and analyze the characteristic and reasons of some typical cases, it is important to better understand the structure induced deformation in tunnel and to provide valuable references for enhancing the connection between design, construction and investigation.
