Study on Stability and Initial Support Optimization of Multi-tunnel Based on Bearing Characteristics
(1.Key Laboratory of Underground Engineering, Fujian University of Technology, Fuzhou 350118; 2. Department of Civil Engineering,Fujian University of Technology, Fuzhou 350118; 3.Fujian Provincial Key Laboratory of Advanced Technology and Informatization in Civil Engineering, Fuzhou 350118; 4.School of Civil & Architectural Engineering, East China University of Technology, Nanchang 330013; 5.China Railway 24th Bureau Group Fujian Railway Construction Co. Ltd., Fuzhou 351111)
Abstract：
Based on a large-span four-tube small-clearance tunnel (the two-tube traffic tunnel in the middle is a two-way eight-lane tunnel) passing under an expressway in Fujian Province, this paper carries out an overall optimization study taking into consideration the bearing characteristics of each tube to achieve a more scientific design. By means of the strength reduction limit theory method, this paper evaluates the stability of each tube and explores the determination method and failure mode of multi-tunnel instability in combination with the deformation of surrounding rock, the development of the plastic zone of middle rock pillar and the failure process of the tube. Based on the concept of equal-strength design of each tube, the implicit relationship between the safety coefficient of each tube and the thickness of the initial support is fitted through a mathematical function model, and the support thickness is optimized through a genetic algorithm. The results show that the plastic zone of the surrounding rock develops and penetrates from near to far with the increase of the strength reduction coefficient, and there is room for optimization as the safety reserves of large-span vehicular and pedestrian tunnels are different. In combination with the stability and failure development process of each tube, three dominant failure modes of multi-tunnel system are summarized,i.e. through failure in the plastic zone of middle rock pillar, through failure in the plastic zone of arch springing and surface, and combined failure of the above two. The calculation results show that the thickness of the initial supports for pedestrian and vehicular tunnels can be reduced by 4~12 cm, and there is room for optimization ranging from 16.7% to 26.7%. The deformation and stress of the typical section in the optimized scheme and the original scheme are consistent with the measured values on site and are less than the specified values, and the structure is stable, indicating that the optimized support and surrounding rock can work well together, which verifies the rationality of the calculation method and optimization scheme. This optimization method, which comprehensively considers the bearing characteristics of each tube, the economy of supporting parameters and the overall stability of the multi-tunnel,better deals with the dialectical relationship between engineering safety and engineering cost, and is more scientific than the traditional engineering analogy method.
YAO Zhixiong1,
2,
3 LIU Mengfei1 WU Bo4 LIU Yaoxing1 CHEN Ximao5 ZHENG Guowen5 LUO Zhiyi1
.Study on Stability and Initial Support Optimization of Multi-tunnel Based on Bearing Characteristics[J] MODERN TUNNELLING TECHNOLOGY, 2023,V60(1): 119-129
2023, Vol. 60 