Termination criteria for jacked precast high-strength prestressed concrete pipe piles

Precast high-strength prestressed concrete pipe piles installed by the jacking method have received wide use as deep foundations in China. Adoption of appropriate termination criteria during installation is the key issue to ensure design capacity or avoid conservative design for jacked piles. A database including 1228 field load tests on jacked concrete pipe piles is collected in this study to establish empirical correlations between the final jacking force and the ultimate capacity. Using the pile slenderness ratio as the fundamental parameter, a total of 14 correlations are derived to apply for various categories of soil conditions. Among them, the ratio of pile capacity to jacking force for piles in stiff clay and firm clay exhibits the greatest magnitude and trend of increase with increasing pile slenderness ratio. Moreover, two jacked concrete pipe piles in silty clay are instrumented and load-tested as an independent case to examine the consistency of the proposed correlations. The two test piles are installed in accordance with a double-control termination criterion that involves the requirements of both final penetration and final jacking force. The load transfer behaviour of the piles has revealed that their performances satisfy all the design requirements.