Calculation of safety factor of tunnel structure based on Duncan-Fama convergence curve

Firstly, convergence-confinement curve of circular tunnel surrounding rock is established based on the Duncan-Fama convergence function and characteristic functions for rock bolt, shotcrete and metal net. Meanwhile, how to convert noncircular section into circular section of a tunnel is solved, and the dynamic development relationship between the surrounding rock and the supporting system based on the convergence-confinement curve is also analyzed. Then, the longitudinal deformation profile (LDP) is introduced and the development process of excavation, support and information feedback about rock mass is formed in conjunction with the convergence-confinement curve. Finally, the expressions for stable safety factor of tunnel surrounding rock are proposed, and the method for determining the relevant supporting time is discussed. The effect of the initial location of the supporting system on constraining force of rock mass after tunnel excavation is analyzed. Using the above mentioned achievements, the existing shortage that the design method for support of underground structure based on classification system of rock mass can not quantitatively evaluate the degree of safety is investigated. Two practical cases show the implementation of the proposed method, and its availability is also verified.