城市轨道交通暗挖洞桩法车站拱顶矢跨比对钢管桩受力和地面沉降的影响分析

Impact Analysis of Arch Vault Rise-span Ratio on Steel Pipe Pile Stress and Land Subsidence in Urban Rail Transit Covered PBA Method Stations

[目的]拱顶矢跨比影响着城市轨道交通暗挖洞桩法车站的建筑高度,以及车站设计的合理性和施工的安全性,需对拱顶矢跨比对钢管桩的受力以及地面沉降的影响进行研究。[方法]构建城市轨道交通车站拱顶结构力学模型,分析不同拱顶矢跨比下的结构内力。通过数值模拟分析软件建立车站-地层三维数值模型,结合地面沉降数值模拟值和现场监测值进行对比分析,论证模型的合理性。同时研究了暗挖洞桩法施工时钢管桩的力学特性,以及其对地面沉降的影响。[结果及结论]拱顶矢跨比从0.20到0.40变化时,拱顶结构的最大弯矩、最大轴力及最大剪力均呈递减趋势,钢管桩的最大轴力呈先减少后增大的趋势;当拱顶矢跨比为0.30时,中桩轴力为最小;随着拱顶矢跨比的增大,地面沉降呈先减少后增大的趋势,地面沉降控制最优的拱顶矢跨比为0.30,比拱顶矢跨比为0.20时减少了34%。导洞施工和扣拱施工是地面产生沉降最明显的两个阶段,合理的拱顶矢跨比会提高导洞施工和扣拱施工阶段地面沉降量的占比,进而减弱后续车站主体结构土体开挖对土层的扰动。

[Objective]The arch vault rise-span ratio not only affects the building height,design rationality,and construction safety of covered PBA(pile-beam-arch)method urban rail transit stations.Therefore,it is necessary to study the impact of arch vault rise-span ratio on the stress of steel pipe pile and land subsidence.[Method]A mechanical model of urban rail transit station arch vault structure is constructed to analyze the structural internal forces under different arch rise-span ratios.A 3D station-stratum numerical model of the station and surrounding soil is established using numerical simulation analysis software,and the rationality of the model is verified by comparing numerical simulation results of land subsidence and field monitoring data of land subsidence.The study also examines the mechanical properties of steel pipe piles and their impact on land subsidence during covered PBA method construction.[Result&Conclusion]When the arch rise-span ratio varies from 0.20 to 0.40,the maximum bending moment,maximum axial force,and maximum shear force of the arch vault structure show a decreasing trend.The maximum axial force of the steel pipe piles decreases initially and then increases;the middle pile axial force is the minimum with the arch vault rise-span ratio of 0.30.As the arch vault rise-span ratio increases,land subsidence first decreases and then increases.The optimal ratio for controlling land subsidence is 0.30,resulting in a 34%reduction compared to the arch vault rise-span ratio of 0.20.The stages of pilot tunnel and arch closure construction cause the most significant land subsidence.An appropriate arch rise-span ratio increases the proportion of land subsidence induced during these two stages,thereby reducing the disturbance to the soil layers from the subsequent station main structure excavation.