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| Field pull-out test and design method of the short pile and anchor composite foundation in the Karst area |
| CUI Qiang1,XING Ming2,YANG Wenzhi1,DING Shijun1 |
(1. China Electric Power Research Institute,Beijing 102401,China;
2. Foshan Electric Power Design Institute Co.,Ltd.,Foshan,Guangdong 528000,China) |
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Abstract In this paper,a composite foundation combining short pile and anchor was proposed for the complex foundation conditions with overlying thick soil layer(4–7 m) and underlying moderately weathered rock in the Karst area for overhead transmission line project. In order to reveal the bearing mechanism of the composite foundation and to establish the corresponding design method to facilitate the better application to projects,the foundation with overlying silty clay and underlying weakly weathered limestone at the typical Karst area of Yangchuan in Guangdong province was selected as the site of field test. Six full-size foundations(1∶1) with different embedded depths and different anchor numbers were designed according to the uplift load on the tower hanging the transmission line of 110–1 000 kV voltage in China. The load-displacement curves,ultimate uplift bearing capacities and foundation failure modes of the tested foundations were obtained in the pull-out tests on the site. It was concluded from the test results and theoretical analysis that the failure of the composite foundation is controlled by the ultimate uplift displacement when the anchor appears damaged. On this basis,a formula for calculating the uplift bearing capacity of the composite foundation was established,and the methods to determine the failure displacement and the allocation coefficients of bearing capacity of the composite foundation were proposed respectively. The correctness of the methods was verified by comparing with the field test results.
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