（1 河北工业大学土木与交通学院， 天津 300401； 2 河北省土木工程技术研究中心， 天津 300401；3 中冶京诚工程技术有限公司， 北京 100176； 4 吉林大学建设工程学院， 长春 130012）

［摘要］利用柱锤冲扩干硬性混凝土形成桩端夯扩体是柱锤夯实扩底灌注桩的特色，桩端夯扩体的性状对单桩承载力有显著影响。通过现场开挖试验研究了夯扩体的形状和构造特点；通过工程实例分析和现场静载荷试验研究了柱锤夯实扩底灌注桩单桩承载特性。开挖试验表明，采用平底柱锤施工形成的夯扩体为竖向高度略大于水平投影直径的椭球体，试桩A,B的夯扩体的水平投影面积分别为理论投影面积的0-81倍和0-83倍；在地下水位以下，先行夯填碎砖可形成包围夯扩体的干燥不透水层；夯扩体施工过程中形成的凹形夯坑可以保证上部桩身和夯扩体的可靠连接；根据开挖试验结果，对承载力设计方法进行了改进。针对某工程地基填土层厚、填垫时间短的特点，采用柱锤夯实扩底灌注桩结合柱锤冲扩素土桩对深厚的软土层进行处理，取得了良好的效果，承载力达到设计要求，同时验证了承载力设计方法的适用性，为深厚、大面积软弱地基处理提供了新的方法。

［关键词］夯扩体； 单桩承载力； 开挖试验； 设计方法

中图分类号：TU473-1+2文献标识码：A文章编号：1002-848X(2019)03-0108-05

Study on field investigation and design approach of enlarged base pile rammed by column-hammer

Wu Mai1,2, Zhao Xin1,2, Qiu Feng3, Geng Jun4

(1 School of Civil and Transportation Engineering, Hebei University of Technology, Tianjin 300401, China；2 Civil Engineering Technology Research Center of Hebei Province, Tianjin 300401, China；3 Capital Engineering & Research Incorporation Ltd., Beijing 100176, China；4 Construction Engineering College, Jilin University, Changchun 130012, China)

Abstract: Forming the pile base with dry concrete by column-hammer is the character of enlarged base pile rammed by column-hammer. The property and shape of the enlarged base is of great effect on the bearing capacity of the pile. Site excavation test was conducted to investigate shape and construction character of the pile; project case analysis and field static load test data was adopted to study the bearing behaviors of the pile. The excavation  test indicates that the enlarged base is approximate an ellipsoid with the vertical axis of the ellipsoid be slightly longer than horizontal axis. The horizontal projection area of the  enlarged base of test pile A and test pile B is 0-81 times and 0-83 times of the theoretical projection area, respectively. Below the ground water level, the bricks rammed in advance can form a dry and impermeable layer which surrounds the enlarged base. In the construction process of the dynamic compaction, the concave hole was formed which can ensure the reliable connection between the upper pile body and the enlarged pile end. According to the excavation test results, the bearing capacity design method was improved. According to the engineering characteristics of thick soil filling and short filling time of foundation in a project, the combination of enlarged base pile and compacted soil pile were applied to treat the thick soft soil layer. Ideal treatment results were achieved and the bearing capacity met the design requirement. The method to estimate the bearing capacity was verified to be applicable, which provides a new method for deep and large area soft and weak foundation treatment.

Keywords:enlarged base; bearing capacity of single pile;  excavation test; design approach

作者简介：吴迈，博士，副教授，Email:wumaitj@126.com。