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（1 河北工業(yè)大學土木與交通學院， 天津 300401； 2 河北省土木工程技術研究中心， 天津 300401；3 中冶京誠工程技術有限公司， 北京 100176； 4 吉林大學建設工程學院， 長春 130012）
［摘要］利用柱錘沖擴干硬性混凝土形成樁端夯擴體是柱錘夯實擴底灌注樁的特色，樁端夯擴體的性狀對單樁承載力有顯著影響。通過現場開挖試驗研究了夯擴體的形狀和構造特點；通過工程實例分析和現場靜載荷試驗研究了柱錘夯實擴底灌注樁單樁承載特性。開挖試驗表明，采用平底柱錘施工形成的夯擴體為豎向高度略大于水平投影直徑的橢球體，試樁A,B的夯擴體的水平投影面積分別為理論投影面積的0-81倍和0-83倍；在地下水位以下，先行夯填碎磚可形成包圍夯擴體的干燥不透水層；夯擴體施工過程中形成的凹形夯坑可以保證上部樁身和夯擴體的可靠連接；根據開挖試驗結果，對承載力設計方法進行了改進。針對某工程地基填土層厚、填墊時間短的特點，采用柱錘夯實擴底灌注樁結合柱錘沖擴素土樁對深厚的軟土層進行處理，取得了良好的效果，承載力達到設計要求，同時驗證了承載力設計方法的適用性，為深厚、大面積軟弱地基處理提供了新的方法。
［關鍵詞］夯擴體； 單樁承載力； 開挖試驗； 設計方法
中圖分類號：TU473-1+2文獻標識碼：A文章編號：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
作者簡介：吳邁，博士，副教授，Email:wumaitj@126.com。
