The Parameters Research Of Large Cross-section Tunnel In Weak Rock With Bench Construction Method

The three-bench seven-step excavation method has been more and more popular among all the excavation methods of mountain tunnel in weak surrounding rock because of it’s unique advantages. However, the research of the main construction parameters about this method is not in-depth enough, which is still a important subject to be solved in the construction of big cross section of weak surrounding rock.This study is based on the first tunnel of Fuyan which is located in Jilin province, and researches the construction parameters of large-section and V level soft-rock tunnel through the research method of combining theoretical analysis and numerical simulation. It’s conducive to choose suitable construction parameters and provide a degree of reference and guidance to this and similar tunnels.The main research contents include:1) This paper summarizes the development present situation and the basic mechanical characteristics of the big cross section of weak surrounding rock, states the applicability of the three-bench seven-step excavation method to make prepare for the later research of construction parameters;2) This paper introduces the construction process of the three-bench seven-step excavation method, and determines the main parameters to be researched, including the bench length and the height of top bench. By checking the post-processing results and making detailed comparison, this paper got the influence law of each construction parameters;3) According to the influence law of the beach length and the height of the top beach, this paper further studied on the negative impact of the footage to the tunnel. Then, the following study moves forward to several parameter combinations which change two parameters at the same time. Through the comparison and analysis to the law of the tunnel displacement and stress, we are able to obtain a parameter combination which can improve the excavation footage and the deformation and stress no increase. In this case, the increase of excavation footage is beneficial to shorten the construction period and decrease the cost.