Modeling Single Piles Subjected to Evolving Soil Movement

To design passive piles, it is critical to incorporate the impact of lateral soil movement (w_s) 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 (l_m) 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 l_m = 0.29l) are as follows. First, the limiting resistance per unit length (at pile-tip level; p_b) increases from uniform to inverse triangular and further to arc movement profiles at an increasing magnitude of w_s. These profiles may be superimposed together to mimic evolving soil movement profiles. Second, the p_b attains 30−60% of that on laterally loaded piles and increases by 22−60% owing to the vertical load. The p_b is proportional to the ratio of pile-head displacement (w_g) 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 w_g = 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 w_g of 1.5d (d = pile diameter) without failure. For the deep sliding of 0.57l, the p_b 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.