现浇X形桩桩-土荷载传递规律现场试验研究

现浇X形混凝土桩（简称X形桩）是为了更好地满足沿海、沿江软土地基处理应用而开发的一种新桩型。该新型桩具有比表面积大、侧向摩阻力高，施工便捷，经济效益高等技术经济优势；但针对其在复合地基中桩-土荷载传递规律特性的研究却相对较少。结合某污水处理厂软基处理工程，开展了X形桩复合地基中桩-土荷载传递规律的现场试验，测得了荷载-沉降关系，桩-土荷载分担比、桩-土应力比，以及桩身轴力等发展情况，分析了不同工况下复合地基中桩-土协调相互作用和中性点位置规律；并将等混凝土用量圆形桩和X形桩的单桩静载荷试验作为对比分析。研究结果表明，本文试验条件下复合地基中X形桩桩侧正、负摩阻力转化发生在0.2倍桩长处，桩侧正摩阻力最大值约为其负摩阻力最大值的140 %；相同桩长情况下桩-土应力比随竖向荷载等级增长速率随桩间距的增加而减小。

Field test study of pile-soil load transfer characteristics of X-shaped cast-in-place pile

A new pile type,X-shaped cast-in-place concrete pile(XCC pile) was developed for coast or river soft soils treatment.XCC piles have many technical and economic advantages,such as large surface area,high shaft friction,conveniently construction,and high economic effects.But there were relative little studies focused on the pile-soil load transfer characteristics of XCC pile composite foundation.Based on a sewage treatment plant soft ground improvement engineering,field tests for the pile-soil load transfer of XCC pile composite foundation were carried out.The load-settlement,pile-soil load sharing,pile-soil stress ratio,and the distributions of axial force of pile shaft were measured.Then the pile-soil interaction and neutral plane of XCC pile under different conditions were analyzed.In order to do comparative analysis,the static load tests for circular pile which has the same concrete amount with that of XCC pile were carried out.The results show that,the neutral plane of XCC pile in composite foundation is mainly occurred in 0.2 times of pile depth.The maximum value of positive skin friction is about 140 % of those of negative skin friction.The pile-soil stress ratio of XCC pile in composite foundation is increased with the decreasing of pile spacing under the same pile length.