Optimal Lower Step Height of Tunnel Excavation Designs by Using the Non-Dominated Sorting Genetic Algorithm-II

In order to control the stability of tunnel surrounding rock, reduce the construction cost, and improve the construction schedule, the deformation behavior and instability mechanisms of tunnel surrounding rock are studied by numerical simulation and field monitoring methods according to the engineering characteristics of the fractured slate zone under construction of Longshu Tunnel in the central Yunnan water diversion project. The results show that step excavation technology can effectively control the deformation of the tunnel surrounding rock. The deformation range of the top and bottom of the tunnel is 32 mm~35 mm, the deformation range of the left shoulder is 25 mm~28 mm, and the deformation range of the right shoulder is 26 mm~29 mm. The stability range of the tunnel surrounding rock is about 25 m away from the palm surface, and the concentrated stress on both sides of the tunnel is at a low level.