Full Scale Field Study of Jack-In Piles

The prediction of pile-bearing capacity to include installation effects is a very complex problem, especially for jack-in piles. This paper describes a series of full scale pile load tests that shed light on the effects of jack-in force on the ultimate bearing capacity of jack-in piles. Three spun piles were installed in similar soil conditions under different jack-in forces. The extensive in-situ investigations, including standard penetration test (SPT), pressuremeter test (PMT), and piezocone penetration test (CPTU), were conducted in the experimental site to get better understanding of the soil condition around the test piles. The results of the tests show that the different jack-in forces did not affect the shaft friction significantly and that the difference in behaviors between test piles is caused by the difference in the toe stiffness response. The data show that the larger the jack-in force, the larger the stiffening effect, which is due mainly to the increase in volumetric compression of the bulb of soil below the toe of the piles.