Research On The Dynamic Process Of The Construction Of The Shallow-buried Biasing Entry Section Of The Close Distance Xiang Er Mountain Tunnel

In the longterm construction of the mountain highway tunnel, the construction of entry section is often difficult in the whole process of construction. As the throat of tunnel, the entry section has many common features such as longterm destruction by weathering, universal broken surrounding rock which is generally mixed with soil layer. The covering layer is general thin and, besides, its thickness is general not uniform. It is easy to develop a shallow biasing section. So the arching effect is difficult to play a role in this circumstance. So it urgently need to solve some problems such as how to establish the construction plan and monitoring scheme which is suitable for the local conditions, how to ensure safety, how to improve the economic benefit of the project, how to reduce the disturbance of surrounding rock on the basis of the requirement of period.This essay is based on the shallow-buried biasing entry section of the close distance XiangEr mountain tunnel. According to the actual landform and geological conditions of the entry project, and the actual construction plan(reserving core soil and excavating in three benches and seven steps, and deep side as the first, shallow side as the second, and for the pilot hole in the same level bench, the right side as the first, the left side as the second), this essay designs three other plans: reserving core soil and excavating in three benches and seven steps in the same way, but altering the sequence of two tunnels and the pilot holes.According to the comparison of the monitoring result and the simulative result, this essay analyzes the dynamic mechanical evolvement of the excavating process. According to the evolvement of the strain change of surrounding rock, and the evolvement of the plastic zone of surrounding rock, and the evolvement of the stress of surrounding rock, and the evolvement of the stress of primary support, this essay analyzes the different disturbing results of surrounding rock of different entry plans.According to the comparison, it is concluded that the better plan of entry construction is that deep side tunnel as the first, shallow side tunnel as the second, and for the pilot hole, the right side as the first, the left side as the second, but it need to combine together the middle bench and the under bench while excavating the pilot holes.The achievement of this study can provide some guidance and advices to the construction of the shallow-buried biasing entry section of the close distance XiangEr mountain tunnel. What’s more, it also can provide some scientific guidance for the construction of some similar tunnel to ensure the safety of construction.