中文摘要：

根据实际工程中单桩受力特点,对足尺桩基进行等比例缩尺,考虑不同埋深、砂土颗粒级配等影响因素,开展室内小尺寸模型单桩的竖向拉拔、水平推移和竖向压载试验,分析桩身变位、变形、轴力等参数与桩基埋深、桩周砂土特性等因素的相互关系,探究钙质砂地基中单桩在不同受力方向下的承载性状,进而剖析钙质砂中桩-土相互作用机制。研究表明,钙质砂地基中,单桩变位、变形特点随着受力方向、埋深、桩周砂土特性等的变化存在明显差异;增大桩的埋深对竖向抗拔桩的意义大过竖向抗压桩;相同条件下桩在承受竖向抗压荷载时,增大埋深的作用主要体现在加载初期,随着荷载的逐渐增大,最终差别将逐渐减小;竖向抗压桩承载过程由以侧摩阻力承载为主发展为以桩端阻力承载为主;颗粒破碎和重分布会引起抗拔桩εmax在加载后期出现衰减;宽级配钙质砂中桩的抗拔能力较强,而单一粒组的钙质砂则在维持桩身稳定方面占优势;桩侧剪碎时的桩侧阻力衰减是随着颗粒破碎逐渐发生的,而桩端压碎时的桩侧阻力衰减主要发生在砂土被压碎瞬间。研究结果对钙质砂地基中的不同功能桩基的优化、设计和施工具有重要指导价值。

英文摘要：

According to the mechanical characteristics of a single pile, the full-size pile is proportionally minified. A series of experiments is conducted on the model piles under various vertical uplift static loads, horizontal static loads and vertical compressive static loads, with considering various pile lengths and surrounding sands. Relationship among parameters such as deflection, displacement, axial force and burial depth, grain gradation of surrounding sand is clarified. The influence of loading direction on the bearing capacity of single pile in calcareous sand is explored. Pile-sand interaction mechanism in calcareous sand is analyzed. It is shown that, the displacement and deformation of a single pile vary significantly with the loading direction, burial depth and grain gradation of the surrounding sand. To increase the burial depth is more favorable for uplift pile than for compression pile. The effect of increasing burial depth is more pronounced in the early loading stage, and gradually diminishes as the load increases. When a stepwise load is applied to the top of the model pile, the bearing form alters from side friction beating to tip resistance bearing. Particle breakage and redistribution can result in a degradation in εmax of uplift pile within the late loading stage. The bearing capacity of a single pile is larger in a wider-grading calcareous sand and the stability of the pile is better in the singleness-size sand. A decrease in side friction of the model pile would occur due to the shear-induced particle breakage in the vicinity of the pile; but at the moment the particles at pile tip crush, an instantaneous reduction in side friction would occur. The research results can provide a guidance for pile optimization, design and construction in calcareous sand.