Taking the express way tunnel in Zhejiang Province as project background and using MARC Software, the paper simulated whole procedures of dynamic construction of NATM tunnel by the use of 3D FEM. The influence of construction procedures and construction techniques all settlement of arch crown and internal force of structure is studied in the paper. Especially, the mechanical behaviors of steel pipe umbrella and rockbolts are deeply investigated in detail.
Construction is the most important phase for the stability of surrounding rock of tunnel. Therefore, researchers are interested in the influences of different approaches of tunnel construction on the stability of surrounding rock during excavation. The task of tunnel construction analysis is to studied the influences of construction procedures construction techniques and construction rate on internal force of support or lining. The first one who studied the mechanics of tunnel construction is Pro. Wittke (1976). Liu Huaihuan (1983) suggested the influences of tunnel construction analyzed using stress releasing coefficient in planar strain analysis. The analysis of structural stress during construction is also used to find the best procedures of construction or large underground structures. In order to obtain the stress of a certain section in a single tunnel, theoretically, the stress increment of every step of excavation should be accumulated from the beginning of excavation to the end of construction. All the time researchers have been trying to find out a simple and fine way to analyze the influences of construction. At first, people considered it as planar problem and by using releasing coefficient of radial displacement to take account of the change of "Virtual supporting force" in radial direction (Yu Xuefu et al. 1983, Zhang Wugong et al. 1990, Pant 1982a.b). Later the method using two and a half dimensional method to analyze three dimensional problem was developed, but it was still refined by initial assumptions. Someone used "step-by-step forward analysis" and "coupled FEM~BEM" to simulate the state of the surrounding rock around advance face and these kinds of methods can be well employed in the case that the axial direction of tunnel disagrees with the direction of principal earth stress (Sun Jun & Zhu Hehua 1993, Ohnishi et al, 1982, Swobooda et al. 1986). However the "air-element" employed in this method cannot simulate the excavation steps of non-linear problem. Some people did much research on the "space lime effect" during excavating by the use of "Generalized virtual supporting force method" and boundary element method (Zhu Hehua & Yang Linde 1994, Zhu Hehua 1991, Zhu Hehua et al. 1991). At present, there are few studies on three-dimensional simulation of the whole process of tunnel construction. Moussa& Wager (1997) studied the effects of construction speed on the mechanical behaviors of NATM tunnel by the use of three- dimensional FEM. They took account of the construction factors which can be reference to other three-dimensional analysis of tunnel construction.
Shotcrete and rockbolts are broadly used in NATM tunnels as supports.
