分别考虑桩和土水平向位移的被动桩简化算法

Simplified method of passive piles with independent lateral displacement of piles and soil

筒仓堆料或路堤填筑产生的地表超载往往会引起地面下一定深度范围内土体侧向位移,使临近桩基产生附加变形与内力。当前基于Winkler地基梁的简化计算方法中,不论是采用应力加载或是位移加载的设计方法,均假设桩基和桩周土体水平方向位移大小一致,即不考虑桩土脱开与土体绕桩流动的情况。考虑桩与桩周土体水平位移不同的情况,提出了水平方向双位移体系的计算分析模型,给出了刚度矩阵的具体拼装方法。针对典型的上海软土地基分布形式,分别尝试了应力加载和位移加载的m法、p-δ刚度法、Mindlin解、布辛奈斯克（Boussinesq）解等8种方法,探讨了土体反力刚度取值和加载方式对计算结果的影响。以此为基础,提出了一种基于布辛奈斯克解土压力和自由场位移反算土体反力刚度的位移加载的设计计算方法。通过多个算例,演示了方法的应用过程,验证了方法的可行性与可靠性。

Soil lateral movement induced by surcharge load, e.g. banking in silos or embankment construction, leads to additional deformation and internal force on adjacent piles. Current Winkler foundation based methods （ either stress loading method or displacement loading method） assume that the passive pile and the surrounding soil undergo the same horizontal displacement, which fails to account for the gap developed between the passive pile and surrounding soil, or the lateral flow of ground soil around the passive pile. This paper considers the relative movement between the passive pile and surrounding soil, proposes a simplified method with two independent lateral displacements of the passive pile and surrounding soil, and presents the assembling method of the stiffness matrix. With regard to Shanghai clayey ground condition, comparison and discussion are conducted on 8 models in total including soil springs with m method, p-6 method, Mindlin＇ s solution and Boussinesq＇ s solution through both stress loading and displacement loading. By comparison of the effect of spring stiffness values and loading type, a displacement loading method is recommended for engineering design, which is based on the soil reaction estimated with Boussinesq＇ s stress solution and the lateral stiffness back-analyzed with free field displacement. Finally, case studies are performed to demonstrate the design procedure of the proposed method, which proves this method＇ s feasibility and reliability.