采动影响下输电线塔桩基础侧摩擦阻力演变规律
Evolution of shaft friction resistance in pile foundations of transmission towers under mining influence
-
摘要: 针对采动作用下输电线塔桩基础侧摩擦阻力(简称“摩阻”)演化及桩土变形关系不明确的问题,采用FLAC3D建立单桩—土体相互作用模型,设置0、200、400、600 kN桩顶竖向荷载,分析工作面推进过程中桩侧摩阻应力、摩阻中性点及桩土轴向相对位移的变化,并结合界面剪切关系解释负摩阻形成机制。结果表明:随工作面推进,桩侧摩阻总体由正摩阻主导演化为上部正摩阻、下部负摩阻,负摩阻区向上扩展,后期分区边界趋稳而摩阻幅值继续增大。在设置的工况范围内,桩顶荷载越小,负摩阻出现越早、发展范围及峰值绝对值越大;荷载由0 kN增至600 kN时,负摩阻初生的临界推进距离估计由约184 m推迟至212 m。采动引起的土体相对下沉使初始正摩阻卸载并转为负摩阻,中性点上移对应下部负摩阻区扩展。在荷载为600 kN工况下,推进350~500 m时摩阻中性点深度稳定在14.18~14.46 m内,而桩土相对位移幅值持续增大,表明分区边界趋稳不意味着界面变形停止累积。研究结果可为采动区输电线塔桩基础受力评价与变形控制提供参考。Abstract: A FLAC3D model of a single pile and its surrounding soil was established to investigate the evolution of shaft friction resistance and pile-soil deformation in transmission tower pile foundations subjected to mining-induced ground movement. Pile-head vertical loads of 0 kN,200 kN,400 kN,and 600 kN were considered. Changes in shaft shear stress,the neutral point,and the axial relative displacement between pile and soil were examined as the working face advanced,and the formation of negative skin friction was explained based on the interface shear transfer relationship. The results show that shaft friction generally evolves from being predominantly positive to a state of positive friction in the upper pile and negative skin friction in the lower pile. The negative skin friction zone extends upward; its boundary subsequently stabilizes while friction magnitudes continue to increase. Within the range of conditions investigated,lower pile-head loads lead to earlier onset,greater extent,and larger peak magnitudes of negative skin friction. Increasing the pile-head load from 0 kN to 600 kN increases the estimated critical advance distance for the onset of negative skin friction from approximately 184 m to 212 m. Mining-induced downward soil movement relative to the pile unloads the initial positive shaft friction and reverses it into negative skin friction. Upward migration of the neutral point corresponds to expansion of the negative skin friction zone in the lower pile. Under a 600 kN load,the neutral point remains at a depth of 14. 18 m-14. 46 m below the pile head for working-face advance distances of 350 m-500 m,while the magnitude of relative pile-soil displacement continues to increase. Stabilization of the zone boundary therefore does not imply that interface deformation has ceased to accumulate. These findings provide a reference for assessing pile foundation response and controlling deformation in mining-affected areas.
下载: