Field Tests of Super-Long and Large-Diameter Drilled Shaft Pile Foundations

Abstract

This study investigated the compressive behaviour of super-long pile foundations with large diameters. Three 52 m, 73 m, and 83 m long piles with a diameter of 1500 mm, 1500 mm, and 1800 mm were cast and tested, respectively. Given that large loading was required, an improved compressive static load test was introduced, and the load transfer mechanism, shaft resistance development, and distribution were analysed. This study found that the transferred load decreased along the pile during each applied load, but the gradients were different. For most layers, when increasing the load, the shaft resistance developed in the upper layers first, while the shaft resistance from the lower part did not always fully develop. Moreover, the "mutual compensation"phenomenon was discovered, which was when the shaft softening occurred from one soil layer, the shaft hardening of the other soil would occur simultaneously. Under consideration of the soil layer differences around these piles, it was recommended that shaft and base grouting should be applied on 52 m and 73 m piles, while only shaft grouting should be applied on the 83 m pile. For this longest pile design, whose toe resistance was discovered to be very small, increasing the pile length was not appropriate; thus, it was preferable to increase the pile diameter to increase the ultimate bearing capacity.