Abstract:

At present, there is lack of experience in the construction of tunnels located in talus deposits and it is random to choose the excavation cycle length for tunnels located in talus deposits. The entrance portal section and exit portal section of Zhaojiawu tunnel on MaZhao highway in Yunnan, China are located in talus deposits. In the paper, the calculation formulas for the excavation cycle length of the shallow portal section of Zhaojiawu tunnel are proposed on basis of silo theory, and the appropriate excavation cycle length of the portal section in talus deposits under the condition of different core soil lengths and different mechanical parameters of the talus deposits are analyzed. Conclusions drawn are as follows: 1) Whatever the excavation cycle length is, during the construction of tunnels located in talus deposits, the safety coefficient of the tunnel face is small and the tunnel face may lose its stability if no advance support or reinforcement measures are taken; 2) Core soil kept can improve the stability of the tunnel face significantly; 3) The excavation cycle length is sensitive to the cohesion of the surrounding rock, which is unfavorable for the stability of the tunnels located in talus deposits. 

Key words: talus deposit, shallow tunnel, excavation cycle length, ultimate analysis method, stability of tunnel face