| With the rapid development of the traffic construction in our country, the highway extends to the mountain area constantly. The construction of highway tunnels in mountainous areas will inevitably be subject to the restrictions of the terrain. Double-arch tunnel has a lot of advantages such as mall floor area, space higher utilization, convenient management and so on, which makes it widely adopted in special terrain. Affected by the topography, geology and the construction method, the double-arch tunnel often has the unsymmetrical loaded problem. Compared with the separated tunnel, the unsymmetrical loaded double-arch tunnel construction is complex. It is difficult to grasp that different construction sequence exerts negative influences on unsymmetrically loaded tunnel structure and surrounding rock. Therefore, the study on surrounding rock stability, excavation sequence, the way of supporting for unsymmetrical loaded double-arch tunnel construction safety has important significance.The project of Liu Gang tunnel in the highway of Rong Wu as the background, through the field investigation, to understand the engineering geological characteristics and engineering geological evaluation of the tunnel area, through the spot to follow up the construction of arch tunnel, to understand the tunnel construction methods and processes. According to the stratum structure method, based on the theory of finite element analysis, and the unsymmetrical loaded double-arch tunnel construction process was simulated by the Midas GTS NX finite element software to analysis that different excavation sequence exerts negative influences on the stress and deformation characteristics of tunnel surrounding rock and support structure, select the reasonable construction sequence. Based on the numerical simulation results of the tunnel construction, the reasonable optimization of the initial supported structure of the unsymmetrical loaded double-arch tunnel was carried out. The following research is mainly carried out by numerical calculation and field investigation:(1) In the process of the construction of unsymmetrical loaded double-arch tunnel, the tunnel surrounding rock and supporting structure stress condition is complex and changeful. With different construction sequence, through comparative analysis the status of the tunnel surrounding rock, the center pillar and support structure, we can see, first excavating shallow measurement is better than the first excavation of the deep buried side according to analysis of the tensile stress and displacement of the surrounding rock, the plastic zone of surrounding rock tunnel, the tensile stress and displacement of the center pillar, the status of the support structure. There was no significant difference between them according to compressive stress and shear force analysis.(2) Through the analysis of tunnel construction process, due to the influence of bias in the process of tunnel construction, the center pillar partition showed to shallow buried side dumping trend. The center pillar as an important part of tunnel structure, its partition stability is directly related to the stability of the whole structure of the tunnel. Therefore, in the construction process, we should focus on the center pillar deformation characteristics, timely monitor displacement of the center pillar to prevent the center pillar dumping.(3) According to tunnel engineering geological conditions and bias tunnel condition, reduce parameters of initial supported structure of the shallow-buried side, and cancel the systematic bolts on both sides, two initial supported structure is tested by the force situation which is analyzed here to reach that initial supported structure optimization is reasonable. Initial supported structure optimization can speed up the progress of construction, and to ensure that the premise of the construction safety of the tunnel reduced the total cost of the project, to achieve the purpose of economic construction of the tunnel. |
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