浅埋偏压隧道施工工法研究与非对称设计优化

Construction Methods and Asymmetric Design Optimization for Shallow-Buried Tunnels Subjected to Unsymmetrical Loads

为探究偏压隧道的适宜工法并针对偏压特性对支护结构进行非对称优化,基于九绵高速福隆隧道,通过现场监测深浅埋侧非对称周边收敛与地表变形,建立三维山体隧道模型,进行不同工法围岩、支护结构受力变形比选分析以及初期支护厚度、锚杆长度与倾角的非对称优化设计。相关研究表明:1)现场监测发现,地表沉降与周边收敛非对称特性明显,随着离隧道正中距离的增大,深埋侧地表沉降较浅埋侧数值减小较慢。深埋侧上拱腰收敛数值最大且波动较大,浅埋侧下拱腰收敛增速较慢。2)偏压隧道较适宜工法为CD法,能有效控制围岩支护结构变形、锚杆应力、初期支护压应力以及塑性区分布。3)初期支护非对称优化结果为将浅埋侧初期支护厚度减小2cm,深埋侧增大2cm,能将二次衬砌拉应力控制在较小数值。4)锚杆长度非对称优化结果为将浅埋侧锚杆长度减小0.5m,深埋侧增大0.5m,使锚杆受力更为均匀并减小右上拱肩与左下拱脚的塑性区。初期支护应力在右上拱肩与左下拱脚处存在显著偏压,通过将右上拱肩处锚杆朝深埋侧倾斜能一定程度减小初期支护受力不均匀。

To explore the suitable construction methods for tunnels subjected to unsymmetrical loads and asymmetrically optimize supporting structures,a case study is conducted on Fulong tunnel on Jiumian expressway.According to the field monitoring results of asymmetric surrounding convergence and surface settlement,a three-dimensional mountainous model is established to perform comparative analysis on different construction methods and deformation of support structure and asymmetric design optimization for primary support thickness,anchor rod length,and inclination.The results show the following.(1)The on-site monitoring shows that both the surface settlement and the surrounding convergence are significantly asymmetric.As the distance from the tunnel center increases,the surface settlement reduction on the deep-buried side is slower than that on the shallow-buried side.The upper arch waist of the deep-buried side has the largest convergence value and large fluctuations,while the lower arch waist of the shallow-buried side has a slower convergence rate.(2)The center diaphragm method is more suitable for unsymmetrically-loaded tunnel,which can effectively control the displacement of the soil and supporting structure,the anchor rod stress,the primary support compressive stress,and the distribution of the plastic zone.(3)The thickness of the primary support on the shallow-buried side is reduced by 2 cm,and that on the deep-buried side is increased by 2 cm in asymmetric design optimization of primary support,which can control the tensile stress of the secondary lining within a small value.(4)The length of the anchor rod on the shallow-buried side is reduced by 0.5 m,and that on the deep-buried side is increased by 0.5 m in asymmetric design optimization of anchor rod,which can uniform the anchor rod stress and reduce the plastic zone on right upper arch shoulder and the left lower arch foot.The primary support stress on the right upper arch shoulder and left lower arch foot unsymmetrically distributes,the situation can be improved by tilting the anchor rod at the right upper arch shoulder towards the deep-buried side.