Sway, sliding and back-rotation of piles subjected to pulse-like soil movement

Abstract

Back-rotation and hinges were detected in in situ piles during lateral spreading, but they were not reported in model tests. This paper presents, for the first time, model tests on vertically loaded capped piles subjected to pulse-like soil movement. The study reveals (i) modes of pile–soil interaction, including sway at a sliding depth (SD) of 0.286l (l = pile embedment), back-rotation at SD = 0.57l and sliding of the piles at either SD; (ii) the evolution rule of yielding moments at the ground level (Moy) and maximum bending moment (Mm) of the pile body for each mode. Expressions are synthesised from the tests to estimate Mm, to define the ultimate state as a rotation angle exceeding 0.8–1.2 times that of free-head piles, to gain limiting soil movement wf* (that incurs hinges) and residual displacement of piles. The simple expressions offer a good estimation of limiting soil movement and permanent displacement for the piles underpinning bridges in Christchurch, New Zealand. They are useful to complement the three-layer modelling of the response of piles incurred by sliding, sway and back-rotation.