Modeling Single Piles Subjected to Evolving Soil Movement

Abstract

To design passive piles, it is critical to incorporate the impact of lateral soil movement (ws) and its profiles. This may be conveniently realized by using appropriate input parameters and a three-layer analytical model developed by the first author. In this paper, 25 (1-g) model tests were conducted on single piles in sand, subjected to a uniform (U), inverse triangular (T), or arc (A) profile of sand movement, to a final sliding depth (lm) of either 0.29l (l = pile embedment) or 0.57l, respectively. The measured response is subsequently simulated using the three-layer model to gain the input parameters and pile–soil interaction mechanism. The main conclusions (for lm = 0.29l) are as follows. First, the limiting resistance per unit length (at pile-tip level; pb) increases from uniform to inverse triangular and further to arc movement profiles at an increasing magnitude of ws. These profiles may be superimposed together to mimic evolving soil movement profiles. Second, the pb attains 30−60% of that on laterally loaded piles and increases by 22−60% owing to the vertical load. The pb is proportional to the ratio of pile-head displacement (wg) over the soil movement. The on-pile pressure is larger on smaller diameter piles. Third, the thrust taken by piles reduces by 50% from a uniform to a linearly increasing modulus. The bending moment (at approximately 4 times larger movement) is 2.3−7.5 times larger under the T movement (worst-case scenario) than those induced under U movement. Bending capacity based on wg = 10 mm needs to be approximately tripled to warrant the safety of passive piles at a rotation angle of 5°. Finally, moving soil imposes rotational restraining and reduces bending moment and pile displacement. It may push the piles to a wg of 1.5d (d = pile diameter) without failure. For the deep sliding of 0.57l, the pb values may be doubled, and the arc profile may inflict the worst-case scenario as well. The results from model tests work well for three instrumented piles in glacial tills and clay, respectively, independent of evolving soil movement profiles.