关键词:  , 陡崖, 危岩体, 交叉作业, 斜交, 半边护拱, 小导洞

Abstract: Foyansi Tunnel is a large-angle oblique entry-exit tunnel structure with steep slope and dangerous rock mass.The location of the tunnel entrance crosses the Laziyu Bridge at the bottom of the ditch.The construction site is narrow and the construction safety risk is high.In order to prevent the collapse accident of dangerous rock slope，safety protection measures are set up in the transitional section of cross operation，and active protective net is applied to reinforce dangerous rock mass at the top of the cave.Considering the large angle of oblique intersection between the topography of the left tunnel entrance and the tunnel body，half arch protection is applied outside the tunnel，construction executed from the right tunnel to the left tunnel through the traveling cross-hole，the small guide tunnel is excavated backward，and then preliminary expansion is formed according to Three-bench Seven-step Excavation Method.According to the monitoring data of the construction process，the maximum displacement of tunnel is less than the specification.The effect is remarkable.The construction scheme effectively reduce the safety risk，the safety quality of construction is guaranteed.The paper provides reference for the similar construction difficult issues.

Key words: steep cliff, dangerous rock mass, crossing operation, oblique intersection, half arch protection, small pilot hole