Study On Medium Partition Mechanical Behavior And Stability Of Large Section Continuous Arch-tunnel

With the rapid development of China’s national economy, the multi-arch tunnel with large span section has been widely used as a new type of structure. However, due to its small structural proportion of height and width, and its large span, the stress during multi-arch tunnel construction process is more complicated than that of general arch construction process. Mid-partition is the core component of multi-arch tunnel structure stress, accompanying with tension, pressure, bending, shear and torsion. At the same time, the effect of the holes distributed in the construction is difficult to grasp,which increases the construction control of the deformation and stability. The mechanical behavior of mid-partition is directly related to the stability of the tunnel structure. Therefore, the deep analysis of the factors in the simulation, which influence the mechanical properties and deformation characteristics and stability of the middle wall, has a guiding significance for the design and the construction of large span section multi-arch tunnel.Depending on the Guiyang Zunyi road tunnel project, the thesis is on the basis of six form of middle wall generally used at home and abroad, under the same condition of supporting parameters, wall width, height, and surrounding rock category, it uses ANSYS12.0 to set up four two-dimensional plane finite element model, and analyze their mechanical deformation rules and structural safety coefficient. Then it also establishes the three-dimensional space finite element model for the mid-partition of multi-arch tunnel during construction process and analyzes the interaction, produced in multi-arch tunnel excavation, of mechanical behavior and deformation characteristics of the wall around the hole. Meanwhile, based on original construction steps, this paper analyzed the stability of mid-partition in three situation(top and right side back-fill, top back-fill and right side not back-fill, top not back-fill and right side not back).The main research results include:1 Collecting section forms of arch tunnel’s mid-partition and then analyzing the advantages, disadvantages and conditions of each form, which provided a reference to the selection of multi-arch tunnel’s mid-partition section.2 Through the two-dimensional simulation for the six forms of mid-partition, it has concluded that the end of the mid-partition construction is in a state of bias, layered straight wall bias force is the largest, and the mid-partition structure is safe and thewhole wall safety coefficient is the largest, hollow straight wall is in the minimum safety coefficient.3 Mid-partition has been in a biased state during the construction process, its vertical stress appears stepped convergence, the influence of each construction process on vertical stress in middle wall recesses varies the largest, its influence on bottom vertical stress varies the smallest,the influence on middle wall’s center point of each section varies gently.4 When using the middle hole- step excavation method, the left holes excavation constraint reach 18 m, the right hole excavation is 24 m. Therefore, the reasonable tunnel face distance of two holes excavation in large section multi-arch tunnel with weak surrounding should be 2B(span of single tunnel excavation is 15m).5 When using the middle hole- step excavation method, the influence range of left holes construction to mid-partition stress is 18 m, but the right holes construction to mid-partition stress is 27 m.6 Based on original construction steps, this paper took three situation(both top and right side back-fill, top back-fill but right side not back-fill, neither top no right side back-fill) to simulate and analyze factors which influence the stability of mid-partition, reaches the conclusion that top and right side both back-fill has positive influence on the stability of the mid-partition.