Centrifuge modeling of torsional response of piles in sand

Abstract

Centrifuge model tests were performed to investigate the torsional behavior of a well-instrumented model pile jacked into loose and dense sand. The whole process of pile jacking, torsional loading, and pile extraction was conducted in-flight at 40g using a four-axis robotic manipulator. The torsional response at the pile head, distributions of torque and shaft friction along the pile shaft, torsional load transfer, and loading rate effects were studied. The shaft resistances along the pile during torsional loading, compression loading, and tension loading were compared. The shear stress – local pile movement curves obtained from the present torsional load tests were found to be approximately hyperbolic and similar to those obtained from axial load tests reported in the literature. The torsional shear stress distribution along the pile shaft was influenced by stress degradation effects, particularly in the loose sand. A criterion was proposed to define pile failure under torsional loading. Torsional loading rates in the range of 1–8°/s had little effect on the torsional resistance of the pile. Depending on the initial state of the soil around the pile, the shaft resistance under torsional loading may be greater than that under axial loading when the horizontal stress is larger than the vertical stress, but smaller when the horizontal stress is smaller than the vertical stress.Key words: centrifuge modeling, compression test, loading rate, load transfer, pile foundations, tension test, torsional test.