卤水井开采对铁路桥梁群桩的影响分析

摘要

为研究卤水井开采对德州—大家洼铁路沿线桥梁安全性的影响,在现场监测数据的基础上,采用有限差分软件FLAC3D建立多口卤水井开采条件下带承台群桩的三维计算模型,分析井内不同地下水位降时的桩土沉降特性及各单桩的内力分布规律.结果表明:随着地下水位的下降,地面沉降范围逐渐增大且呈漏斗状分布,沉降漏斗的中心位于群井的中心,地面沉降范围在距群井中心100 m内;群桩沉降主要发生在地下水位从-9m下降至-33.1 m的过程中,此阶段群桩沉降量占工后总沉量的64.7％;随着地下水位的下降,各桩的轴力沿桩身先增大后减小,桩身上部负摩阻力的作用区域逐渐增大,且负摩阻力沿桩身先增大后减小,各桩最大轴力所在截面和中性点不断下移;在相同的地下水位降条件下,各桩轴力和负摩阻力的大小顺序为角桩＞侧桩＞近井中桩＞中桩;抽水结束且群桩沉降达到稳定后,角桩桩底侧面受到的正摩阻力最大,为75 kPa.%To study the influence of brine well mining on the safety of bridges along Dezhou-Dajiawa railway,the three-dimensional calculation models of group piles with pile caps were established on the basis of field monitoring data by finite difference software FLAC3D under the condition of different brine well mining.The settlement characteristics of pile and soil as well as the internal force distribution law of each single pile were analyzed under different groundwater level drop in the well.Results show that the surface subsidence area increases gradually and assumes a funnel-shaped distribution with the decrease of groundwater level.The center of the subsidence funnel is located at the center of group wells and the range of surface subsidence is within 100 m from the center of group wells.The settlement of pile group mainly occurs in the course of groundwater level dropping from-9 m to-33.1 m,and the settlement of pile group accounts for 64.7％ of the total settlement amount after construction in this stage.As the level of underground water drops,the axial force of each pile increases first and then decreases along pile body.The negative friction resistance of the upper part of pile body increases gradually.The negative friction resistance increases first and then decreases along pile body.The section of the maximum axial force and the neutral point of each pile moves downward constantly.Under the condition of the same groundwater level drop,the axial force and negative friction resistance of each pile are in the order of corner pile＞side pile＞near borehole center pile＞center pile.When the pumping is finished and the settlement of pile group is stable,the maximum friction resistance at the bottom side of corner pile arrives at the maximum,which is 75 kPa.