STUDY OF THE STRENGTH REDUCTION DDA METHOD AND ITS APPLICATION TO MOUNTAIN TUNNEL

The stability of tunnel surrounding rock is the mainly concerned content during tunnel design and construction procedure. It is one of the main tasks for researchers to accurately estimate the stability of tunnel surrounding rock. Generally, determined by its engineering geological features, surrounding rock of mountain tunnel is cut by joints into discontinuous blocks, which can be more accurately analyzed by discontinuum-base numerical methods, e.g., the discontinuous deformation analysis (DDA) method. In addition, progress of deformation and failure of tunnel surrounding rock is often a nonlinear catastrophe behavior, so that it is feasible to determine the tunnel stability by the catastrophe theory. The strength reduction method can be used to simulate failure progress development in its computation procedure by reducing the strength parameters. Based on the DDA method, the strength reduction method and the catastrophe theory are adopted to study the stability of tunnel surrounding rock. Firstly, the strength reduction method is used to obtain the function of displacement and the reduction factor varies, and then the catastrophe theory is used to judge the critical state of surrounding rock based on the function curve. The reduction factor at this critical point is defined as the stability safety factor of the tunnel. Thus the stability status of the surrounding rock can be determined. Jinjishan multiple-arch tunnel is a big span tunnel with eight traffic lanes, which is a very important project of the second phase project of Fuzhou city airport. This method is put into application of this project to guarantee safety of the tunnel.