Single Arch Four-lane Highway Tunnel Structure Optimization Study

With the rapid development of economy highway traffic volume increases severely, single small cross-section tunnel cannot satisfy the requirements of highway traffic. In order to solve this problem effectively, large-span tunnel, for instance, single-arch four-lane road tunnel is constructed. How to build safe, economical and practical single-arch four-lane road tunnels by using existing design theory and practical experience is a problem which the technological workers and engineers always concerned. According to present design specification of highway tunnel and combining with optimization technique, structural optimization of single-arch four-lane road tunnel which is based on Long Tou Mountain Tunnel is investigated in this paper, and specific works are as follows:(1) The influence factors of large-span tunnel on mechanical characteristics are analyzed. Then the change law of the mechanic response and stability for surrounding rock with difference span-ratio section is obtained by using numerical simulation. The influences of invert on stability of tunnel structure are analyzed, and the feasibility of removal invert under good surrounding rock condition is discussed based on numerical analysis. Ultimate bearing capacity of arch lining structure is studied, the results show that ultimate bearing capacity of arch lining structure is related to rise-span ratio and boundary conditions, ultimate bearing capacity is determined by the restriction of arc tip; the exerting degree of bearing capacity of arch is controlled by rise-span ratio.(2) Optimization of cross-section for tunnel is achieved by employing FORTRAN program. By introducing the complex method in optimization theory and building optimal numerical model, the reasonable shape of cross-section is obtained through optimization calculation, and the state of mechanical for lining structure at wall footing improved. Moreover, by analyzing the relationship between soft rock and the stability of tunnel structure, the load on the inverted arch is determined. Combining with the construction technology of inverted arch, a mechanics model of three hinged arch is built and the equation of reasonable axial line and formula for internal force of inverted arch are given. Applying heuristic algorithm and Combining with design specification of highway tunnel, tunnel structural optimization model which is took the construction cost of tunnel lining for objective function is established to realize the optimum design of tunnel lining.(3) Cross-section optimization objectives are analyzed. Analytic Hierarchy Process (AHP) and Entropy Method are employed in multi-objective optimization decision, then its rationale and steps are introduced. The inner section optimum process base on excavation area, stress concentration factors, convergence around tunnel and plastic zone is analyzed.