软弱围岩浅埋大断面公路隧道支护结构参数比选

Analysis of the influence of deep cuttingconstruction on the safety of the existing tunnel structure below

以乐汉高速为工程背景,借助有限元软件MIDAS分别构建地层结构模型和荷载结构模型,研究不同支护参数下隧道围岩变形及结构受力特征,结合结构安全系数,比选出隧道最为合理的支护体系。研究结果表明,不同初支厚度下结构受力均呈现边墙>拱腰>拱顶的分布规律,围岩变形呈现仰拱>拱顶>拱腰>边墙的分布规律,随着初支厚度的增加,结构受力及围岩变形均逐渐降低,但跌幅较小,在15 cm厚初喷C25支护下结构受力及围岩变形均满足工程要求。对于软岩浅埋公路隧道,结构安全系数最小值位于隧道拱顶,且随衬砌厚度增加而逐渐提高,采用45 cm,55 cm,65 cm厚C30钢筋混凝土结构安全系数及裂隙宽度均满足规范要求,为了节省经济,减少工程投资,二衬可选择45 cm厚C30钢筋混凝土。

In this paper,taking Lehan Expressway as the engineering background,the stratum structure model and load structure model are constructed by means of the finite element software MIDAS,and the deformation and structural stress characteristics of tunnel surrounding rock under different supporting parameters are studied.Combined with the structural safety factor,the most reasonable supporting system of the tunnel is selected.The results show that the stress of the structure under different initial support thicknesses shows the distribution law of side wall>arch waist>vault,and the deformation of surrounding rock shows the distribution law of inverted arch>vault>arch waist>side wall.With the increase of the thickness of the initial support,the stress of the structure and the deformation of the surrounding rock are gradually reduced,but the decrease is small.The stress of the structure and the deformation of the surrounding rock under the support of the 15 cm thick initial spraying C25 meet the engineering requirements.For soft rock shallow buried highway tunnels,the minimum structural safety factor is located at the tunnel vault,and gradually increases with the increase of lining thickness.The safety factor and crack width of 45 cm,55 cm and 65 cm thick C30 reinforced concrete structures meet the requirements of the specification.In order to save economy and reduce engineering investment,45 cm thick C30 reinforced concrete can be selected as the secondary lining.