Field test on vertical compressive bearing characteristics and time-dependent effects of jacked piles in layered soil

Abstract

This study aims to investigate the characteristic and time-dependent effects of jacked PHC (pre-stressed high-strength concrete) pile's bearing capacity in quaternary soil. The static load test and the re-pressed tests during different resting periods were carried out on the jacked pile. This study analyzes variation in the jacked pile's pile-sinking resistance, pile tip resistance, and pile side friction resistance. The correlation between bearing capacity and resting time after pile-sinking is investigated, and the ultimate bearing capacity by the curve fitting method is predicted. The research findings show that the pile-sinking resistance is more strongly influenced by the softness and hardness of the soil layer. The pile tip resistance variation during the pile-sinking process essentially reflects the nature of the changing soil layer and the development of the pile side friction resistance is strongly associated with the nature of the soil layer. The pile tip resistance in the static load test decreases by about 5 % compared with that in the pile-sinking process and the pile side friction resistance improves by about 27 %. The pile side friction resistance was the main factor restricting the jacked pile's bearing capacity time-dependent effect. The test pile's repressure value gradually increased with the increase of the resting time. The final repressure value was about 1.15 times the final pressure value when the pile-sinking process was completed. Through the fitting of the test pile's bearing capacity curves, the fitting results agree well enough to be used for predicting the jacked pile's ultimate bearing capacity.