Destructive field tests on mobilization of end resistance of cast-in-situ bored piles

LIU Nian-wu(刘念武)^1,2, ZHANG Zhong-miao(张忠苗)^1,2, ZHANG Qian-qing(张乾青)³, FANG Kai(房凯)^1,2

(1. Key Laboratory of Soft Soils and Geoenvironmental Engineering of Ministry of Education
(Zhejiang University), Hangzhou 310058, China;
2. Institute of Geotechnical Engineering, Zhejiang University, Hangzhou 310058, China;
3. Geotechnical and Structural Engineering Research Center, Shandong University, Jinan 250061, China)

Abstract:A series of well-designed full-scale destructive load tests were conducted on six bored piles to investigate the influence of loose debris at the pile tip on end resistance. The results show that soft debris below the pile tip will weaken the mobilization of end resistance. The ultimate tip resistance of post-grouted pile is 2.05 times that of the pile without post-grouting and the ultimate tip resistance in the second load cycle is 2.31 times that of pile in the first load cycle. The relationship between unit end resistance and displacement follows a linear model and a bilinear mode in the first load cycle and the second load cycle, respectively, whereas the unit end resistance-displacement response of post-grouted bored pile can be simulated using a bilinear mode. The critical end resistance ranges between 2 000 kN and 3 000 kN and the critical displacement ranges between 2.5 mm and 4.5 mm in the bilinear mode. As for piles rested on moderately-weathered peliticsiltstone, the socketed length has no effect on the end resistance because of the existence of loose debris.

Key words:static load test; settlement; post-grouting; end resistance; socketed depth