Bearing Capacity Characteristics of Deep Foundations in Homogeneous Soil under Lateral Loads

对均质粘土和砂土中的模型桩(深基础)在水平荷载作用下的挠度和承载特性进行了理论和试验研究。对具有不同抗弯刚度Ep(E：桩的弹性，I：桩的截面积惯性)的二维和三维模型桩进行了水平荷载试验，得到了荷载(P)-桩顶水平挠度(Y)关系和桩身应变分布，并观察了水平荷载作用下桩轴线的挠度性状。根据试验，提出了一种新的试验方法。观察到了Broms的塑性铰链，随着EI值的降低，它们的位置接近地面。对于粘土，当Vesic的无量纲长度Betal表示相对弯曲刚度小于约2时，桩被认为是刚性的(短桩)，而Betal大于约2时，桩被认为是柔性的(长桩)。另一方面，对于砂土，当表示相对抗弯刚度的Rifaat无量纲长度Etal小于2时，桩被认为是刚性的(短桩)，而Etal大于约4时，被认为是柔性的(长桩)。在塑性变形区，P/D(D：桩宽)-y关系在双对数曲线图上表现为直线，有限元分析认为土体是弹性的。粘性土和砂土中短桩和长桩的极限水平承载力实验值与Broms理论计算值吻合较好。

The deflection and bearing capacity characteristics of model piles (deep foundations) under lateral loads in homogeneous clay and sand have been investigated theoretically and experimentally.Both two-dimensional and three-dimensional model piles which have various flexural rigidity EP (E: elasticity of pile, I: inertia of sectional area of pile) were used for lateral loading tests to obtain the load (P)-horizontal deflection at the free top of piles (y) relationship and the strain distribution on the pile shafts, and to observe the deflection behavior of pile axis under lateral loads.According to the experiment, the Broms's plastic hinges were observed and the places of them approached to the ground surface with decreasing in the value of EI. In the case of clay, when Vesic's dimensionless length betaL which indicated the relative flexural rigidity was less than about 2, piles were considered rigid (short piles), while betaL being greater than about 2, piles were considered flexible (long piles). On the other hand, in the case of sand, when Rifaat's dimensionless length etaL which indicated the relative flexural rigidity as in clay was less than about 2, piles were considered rigid (short piles), while etaL being greater than about 4, piles were considered flexible (long piles).In the region of the plastic deformation, P/D (D:breadth of pile)-y relationships were expressed as straight lines on the double logarithmic plots as expected by the FEM analysis in which the soil was considered elastic. The experimental values of ultimate lateral bearing capacity for both short and long piles in clay and sand were in good agreement with the calculated values by the Broms's theory.