Ultimate bearing capacity and failure mechanism on cyclic lateral loaded pile group

(1)为研究轴载混凝土桩在循环侧向荷载作用下的破坏机理，在离心（50G）条件下对群桩模型进行了试验。用钢琴线和类似于实际现浇混凝土的圆形黄铜环加固的砂浆桩约为2毫米。在以往的试验中已经发现，桩的损伤首先发生在桩顶，随着循环位移幅度的增大，桩的损伤也发生在地表以下深处。本文研究了轴向荷载对桩基破坏行为的影响。试验结束后，还观察到桩的裂缝。(2)在地震作用下，软土地基通常要承受侧向循环荷载。在大地震中，认为桩基础及其周围地面的力学行为是非线性的是合理的。近年来，极限状态设计方法在收费桥梁和其他结构的基础设计中占主导地位。因此，研究横向循环荷载作用下桩基达到极限状态时的受力特性，对设计方法提供依据具有十分重要的意义。本文采用三维弹塑性有限元分析（DGPILE-3D）对直径为1.2m的9桩基础进行了循环侧向荷载至极限状态的实尺现场试验模拟。本文采用轴向力滞回模型对钢筋混凝土桩的非线性行为进行了模拟。同时，采用Drucker-Prager模型对地面土壤进行了模拟。本文的目的是提供一种适用的数值方法来评估在循环横向荷载作用下直至极限状态的桩基础的力学行为。

(1) In order to investigate the failure mechanism of the axially loaded concrete piles under cyclic lateral loading, the model of group pile is tested under centrifugal condition (50G). Mortar piles reinforced with piano wires and circular brass rings which are analogous to real cast-in-place concrete is about 2 mm. It was already found in the former tests that the damage occurred at the pile head first and when the magnitude of cyclic displacement became larger, damage of pile also took place at the depth under ground surface. In this paper, the influence of axial load on the failure behavior of the pile ground are investigated. After the test, cracks of piles are also observed.(2) Pile foundation in soft ground usually will be subjected to a lateral cyclic loading during an earthquake. In a major earthquake, it is reasonable to think that the mechanical behavior of a pile foundation and the surrounding ground is nonlinear. In recent year, the limit state design method became predominant in the design of foundations of toll bridges and other structures. The investigation on the mechanical behavior of the pile foundations subjected to lateral cyclic loadings up to an ultimate state, therefore, is very important to provide evidences for the designing method. In this paper, a real scale field test of 9-pile foundation, with a diameter of 1.2m, subjected to cyclic lateral loading up to an ultimate state, is simulated using a 3-dimensional elasto-plastic finite element analysis (DGPILE-3D). The nonlinear behavior of RC pile is simulated with an axial-force depend hysteretic model proposed in this paper. Meanwhile, the soil of the ground is simulated with Drucker-Prager model. The purpose of the paper is to provide an applicable numerical way of evaluating the mechanical behavior of a pile foundation subjected to cyclic lateral loading up to an ultimate state.