Settlement and Capacity of Piles Under Large Number of Cyclic Loads

This study reports a group of field tests on cyclically loaded piles installed in soft clay in Huzhou, China. Two 29.5 m long pipe piles were instrumented with transducers to measure the accumulated settlement at the pile-head, the pore water pressure and total pressure at the pile-soil interface, and axial load at the pile end, respectively. The major objective of the field testing is to gain a better understanding of the evolution of the pile-head settlement and the effective stress at the pile-soil interface. The results of cyclic loading tests under different combinations of static load and cyclic load are discussed with reference to changes in the pile capacity, the permanent settlement, and the radial stresses. It is found that the permanent settlement of piles can be characterized as quickly stabilized (QS), progressively developing (PD), and dramatically failed (DF) patterns. Under low-level loading (QS pattern), the pile-shaft earth pressure is nearly undisturbed, final gains in effective stress are observed due to slight dissipation of pore pressure. For intermediate-level loading (PD pattern), significant reductions in pore pressure, earth pressure, and effective stress are observed after cyclic loading. Regarding high-level loading (DF pattern), the quick accumulation of pore water pressure leads to a slight increase in earth pressure, resulting in a continuous decrease in effective stress.