扩体桩的作用机制与工程理论

Mechanism Analysis and Application Theory of Reamed Composite Piles

扩体桩是一种新型而有效的桩基形式,采用长螺旋置换土体灌注扩体材料后植入预制桩的方法,极大拓展了预制桩工程适用条件和应用范围。以水泥砂浆混凝土预制桩扩体桩为例,通过理论与工程实践分析,揭示了扩体桩的作用机制,提出了该桩型单桩承载力计算方法及计算参数。结果表明,混凝土预制桩与扩体材料之间具有足够的剪切强度保证两者的共同作用,桩土相互作用界面由传统预制桩相对光滑的"混凝土土"界面转变为"包裹材料土"黏结强度界面;扩体材料对内部预制桩的桩端阻力具有约束增强作用;针对不同工艺和扩体材料特点,需考虑扩体组合桩侧阻力和桩端阻力发挥进行单桩承载力计算;通过试验和数值分析,验证了模型和理论方法的可行性。研究成果可供工程设计参考。

Reamed composite piles is a new and effective type of pile foundations,in which the use of the construction method of implanting precast piles after long spiral replacement soils and infusion reamed materials,greatly expands the applicable conditions and application areas of precast piles. Taking cementmortar concrete piles as an example,the mechanism of reamed composite piles is investigated based on theoretical and practices analysis. The calculation method and parameters of single pile bearing capacity for this type of pile are also proposed. The results show that the shear strength between concrete precast pile and reamed material(cement mortar)is sufficient to ensure a joint action. The pile-soil interface changes from the relatively smooth concrete-soil interface of traditional precast piles to the reamed materials-soil bond strength interface. The reamed material also has an enhanced effect on the tip resistance of the concrete precast pile. According to the characteristics of different construction methods and reamed materials,it is necessary to consider the development of side and tip resistance of the reamed composite piles when calculating the bearing capacity. The reliability of the mechanism model and proposed calculation method are verified by experiments and numerical analysis. The research results can be used as reference for engineering design.