Comparative Study On Stratum Pre-reinforced For Shallow Tunnels Construction In Urban Subway

In recent years, with the increasing scale of urban subway construction, the pre-reinforcement technology has been greatly developed. This paper will make a study about the pre-reinforcement methods of the city shallow tunnels by combining theory and practice.By reading a lot of literatures, firstly, this paper summarizes the main factors of pre-reinforcement.According to the probability of occurrence and loss levels of risk caused by different factors, the project risk is divided into four levels. Based on the above work, the paper makes a risk classification matrix and determines risk acceptance criteria and control countermeasures of various grades.Secondly, the paper will make a series of comparisons for three pre-reinforcing methods, including the cost, effectiveness and reinforcement principle. Then, with the help of FLAC3D,I will make the numerical calculation. The specific method is following: based on the key program of Beijing Subway Line, the tunnel from Guanghua Road Station to World Trade Center Station, by setting ten kinds of reinforcement schemes, I will contrast reinforcement effect for the above three pre-reinforcing methods (pipe roof support, horizontal rotary jet grouting pile, grouting reinforcement) through six aspects, including the settlement of surface, the change of stress, the horizontal convergence, analysis of arch floor heave, the impact of bridge piles and the plastic zone. In particular, the grouting reinforcement technology is focused on the analysis by changing the thickness and strength of the grout.Finally, I will make the applied research on the soft flow plastic strata by selecting the three subway project instances and define the formation conditions.I believe that the research results will have a important guidance for the selection of pre-reinforcement technology, design and construction.