Termination criteria for and behaviour of jacked piles in completely decomposed granite

Pile jacking is a piling method that provides a noise- and vibration-free environment in the construction site. In this thesis, field tests and centrifuge tests were conducted to improve termination criteria for pile jacking and understanding of the behavior of jacked piles. In the field test, four steel H-piles were instrumented, installed and load tested at a weathered soil site. A set of termination criteria proposed by the Housing Authority was applied to the test piles. These criteria include a minimum SPT blow count of 120, a specified final jacking force, a minimum of four loading-unloading cycles at the final jack force, and a specified maximum rate of pile settlement at the final jacking force. All of the four test piles passed the required acceptance criteria. Punching shear failure occurred at the failure load of RJP-1 and PP1B1-6 piles. The shaft resistance of the piles contributed to approximately 80% of the pile capacity. Based on the field tests, loading and unloading cycles do not have significant effects on the capacity for these long piles. In the centrifuge, two series of tests were conducted to investigate the effect of pile penetration on the ratio of final jacking force PJ to required pile capacity Pult, which is defined by Davisson's criterion (1972), and the effect of the number of loading-unloading cycles at the final jacking force to the pile behaviour. Based on the results of the field and centrifuge tests and data collected from a large number of field tests in Guangdong, China, a relation between the PJ/Pult ratio and the pile slenderness ratio is established. The PJ/Pult ratio is smaller than 1.0 for long piles but is larger than 1.0 for short piles. A regression equation is established to determine the final jacking force with a given slenderness ratio. The recommended final jacking force is smaller than 2.5 times the design load for very long piles, but is larger than 2.5 times the design load for piles shorter than 42 times the pile diameter. Keywords: Pile foundations; Jacked piles; Termination criterion; Acceptance criteria; Weathered soils; Load test; Load transfer