Study On The Tunnels Stability Influence Of Caverns In Arch In Surrounding Rock

With the growing scale of China’s highway construction, there had been a significant development in the tunnel construction. However a various factors (suchas the geological conditions, terrain conditions.climatic conditions and the errorof tunnel’s design, construction, operation) make some effects on the wall rock behind many highway tunnel lining. These defects somehow can produce diseaseon varying degrees that can cause potential safety hazard.Based on Cimu mountain tunnel, this paper mainly studies the mechanical behavior of the tunnel structure with the difform and varisized cavity behind thevault lining and calculates the safety coefficient of tunnel structure with the difform and varisized cavity by the method of finite element strength reduction. Andthe overall stability of the tunnel structure has been comprehensive evaluated.The construction of cavity with different shapes and different sizes is complex. This paper uses numerical simulation to analyze the three-dimensional elastic-plastic.The paper mainly analyzes the cavity with different shapes(trapezium shape, rectangle shape, triangle shape) in the tunnel cross-section. For every cavity shape, this paper establishes cavity simulation models under different overhead height, different width and different length of longitudinal axis circumstances. According to the simulation models, when the wall rock in different working conditions,the law of displacement stress variation and the compressive and tensile stressvariation of primary support under the cavity can be got. When the cavity exists behind the lining structure, the stress of wall rock is distributed again that makes the law more complex. So only taking the stress and strain of the construction into account is not enough. This paper introduces a special method of finiteelement strength reduction and uses particular convergence criterion to calculate the safety coefficient of tunnel structure and to study the effect of cavity on theinstability of wall rock structure.In order to analyze how the cavity affects the wall rock, this paper analyzesthe deformation and force characteristics of the wall rock and the support structure under the different cavity conditions. Research calculation results show that:under the condition of grade Ⅳ wall rock, the existence of part cavity behind the lining has not much affect the displacement of the entire structure and the co mpressive stress of wall rock near the cavity. The primary support stress under the cavity reduces on varying degrees when the all the direction size of cavity reduces. In all direction size, the variation of toroidal size has a great effect on the force of the primary support. When the toroidal direction size of cavity reaches4meters, the force of the tunnel construction has a reduction.The final conduction is as follows: in all direction size, the toroidal direction size has the biggest influence on structural safety coefficient, then the longitudinal direction size, last the height direction size. And the safety coefficient has an obvious reduction when the toroidal width of cavity reaches4meters (the central angle is30°).