偏压隧道洞口段衬砌多裂缝扩展有限元分析

Multi-crack Propagation Analysis of Tunnel Portal Lining under Eccentric Pressure by the Extended Finite Element Method

为降低大偏压隧道洞口段衬砌开裂风险,依托巴蕉箐公路隧道工程,对不同工况下偏压隧道衬砌裂缝扩展状态进行了分析,提出偏压隧道衬砌多裂缝扩展的可能,最终基于扩展有限元方法对不同偏压角度下隧道洞口段衬砌多裂缝扩展规律进行了分析。结果表明:随着偏压角度的增大,初始裂缝应力强度因子分布型式逐渐由扁平状转变为窄尖状,衬砌结构整体受力状态变差,易在隧道拱顶60°~90°范围内产生多条初始裂缝同时扩展,在75°位置处产生主裂缝;偏压隧道衬砌多裂缝扩展可分为应力最不利位置裂缝单独快速扩展阶段、主裂缝带动周边初始裂缝形成多裂缝同时扩展阶段和主裂缝逼近贯通衬砌破坏阶段;偏压对隧道衬砌裂缝扩展的影响显著,偏压角度越大,越易形成一条较深的主裂缝,造成衬砌结构破坏;在偏压条件下,主裂缝两侧60°~90°范围内裂缝扩展偏转率呈线性发展,说明在该范围内,离主裂缝越远,周边裂缝向主裂缝靠拢发展的趋势越大。

In order to reduce the risk of lining crack in tunnel section with large bias,this paper,relying on the project of Bajiaoqing Highway Tunnel,analyses the crack propogation status of tunnel lining under different working conditions,puts forward the possibility of multi crack propogation in bias tunnel,and finally analyses the law of multi crack expansion in tunnel section lining under different bias angles based on extended finite element.The results are as follows:with the increase of bias angle,the distribution pattern of stress intensity factor gradually changes from flat to narrow and sharp,the overall stress state of lining becomes worse,and it is easy to generate multiple initial cracks in the range of 60°to 90°at the arch waist,and the main cracks in the position of 75°at the same time.The multi-crack propagation of eccentric pressure tunnel lining can be divided into the single rapid crack propagation stage,the main crack driving the surrounding initial cracks to form the multi crack propagation stage,and the main crack approaching through lining failure stage.Under the condition of bias pressure,the bias angle of the fractures on both sides of the main fracture shows a linear development in the range of 60°~90°,indicating that within this range,the farther away from the main fracture is,the greater the tendency of the surrounding fractures to develop towards the main fracture is.