Field Experiments on Cyclic Behaviors of Axially Loaded Piles Jacked in Soft Clay

Pipe piles are increasingly used to support embankments of high-speed railways. This study presents a series of static and cyclic axial loading tests on two industrial prestressed-concrete pipe piles installed on a field site with soft clay in Huzhou, southeastern China. The 29.5-m-long preinstrumented piles were subjected to different loading combinations of static load ($5–400\mathrm{kN}$) and cyclic load ($50–400\mathrm{kN}$) to maximum numbers of 50,000 cycles. The geotechnical details of the testing site and the instrumentations were explored before characterizing the accumulated displacement at the pile head. Preliminary results reveal that pile compressive capacities increased significantly after cyclic loadings. The cyclic behaviors of the pile-head displacement are classified into three patterns: quickly stabilized, progressively developing, and dramatically failed. Correspondingly, cyclic stability criteria are identified as stable zone, metastable zone, and unstable zone. Stable utilization line, critical utilization line, and ultimate utilization line are proposed to divide these three zones. For some cases under the same total load, the accumulated settlements of the piles are, however, different, depending largely on the cyclic loading level.