组合荷载作用下扩底基础地基土体破坏模式及滑动面几何特征分析

Analysis on the Failure Mechanism of Soil and Sliding Surface Geometric Feature of Expanding Bottom Foundation under Combined Loads

上拔稳定性分析是输电线路杆塔基础优化设计的关键,直接影响线路工程的安全运行及经济造价。目前电力行业标准DL/T5219-2005给出了原状土扩底基础上拔承载力"剪切法"计算公式,然而该公式是基于仅仅承受竖向荷载作用下上拔土体呈对称状的圆弧形回转面的假设条件下得出的,而实际基础同时承受水平荷载作用,并对基础的稳定性产生非常大的影响。针对这一问题,基于弹塑性理论,采用有限差分方法,对戈壁滩地基土中扩底基础地基土体的变形破坏进行了数值分析,提出了地基土体达到极限平衡状态时的判定准则,并分析得出上拔和水平组合荷载作用下扩底基础周围土体滑动面几何形态的概化模型。该研究成果可为输电线路杆塔基础上拔承载力计算方法的修正和完善提供理论依据。

The uplift stability analysis of the transmission tower foundation is the key to the optimization design of the foundation, vital to the operation and cost of the transmission line. The present technical standard for the tower foundation design （DL/T 5219-2005） in China, however, only provides the calculation model of the uplift bearing capacity of the undisturbed soil foundation, namely the ＂Shear Method＂, which is only based on the assumption that pullout soils around foundation shows rotary surface of symmetric circular-arc. To address this problem, based on the elastic-plastic theory, the numerical analysis based on the finite difference method is used to study the deformation and failure of soils around foundation in Gobi, and a new criterion [or judging the soils around expanding bottom foundation in the limit balance state is proposed. Furthermore, generalized model of sliding surface of pullout soils around foundation under combined loads is obtained. The study results obtained herein provide a theoretical basis for correction and perfecting of the calculation method of the uplift bearing capacity of transmission line tower foundation under combined loads.