Abstract：Wushaoling long and deep-buried tunnel passes through the east foot of Qilian Mountain，with the length of 20 050 m and the maximum burial depth of 1 050 m. During the excavation of tunnel in the soft rock such as phyllite，plywood rock and tectonic breccia，the surrounding rock was deformed severely，with the maximum horizontal deformation magnitude of 1 034 mm and the arch top subsidence magnitude of 1 053 mm，which led to that not only supports lost their effects，but steel frames were distorted heavily. Moreover，the deformation lasted and could not converge. The testing results of original field stress show that these tunnel sections are under the action of clear modern tectonic stresses with the maximum principal stress of 20–22 MPa，and that the general feature of modern ground stress field is that sH≥sV＞sh. According to the analysis，it is considered that the strong deformation of surrounding rock of tunnel results from the joint actions of rather strong tectonic stress and vertical gravity stress；and that the tunnel has not be supported in time and soft surrounding rock can not bear such actions，which causes continuous large rheological deformation. Engineering practice indicates that the stress state of surrounding rock is the basis of support design；and that the timely support is very critical. However，proper deformation of surrounding rock is allowed，which can make the stress of surrounding rock release properly. Carrying out lining support construction in time when the large rheological deformation has not been formed and the surrounding rock has not lost its bearing capacity is of great significance to assure the stability of surrounding rock and the safety of supports.
