A Numerical Model to Study the Response of Piles under Lateral Loading in Unsaturated Soils

Abstract

The interaction between a laterally loaded pile and the surrounding soil is typically limited to the shallower soil layer. Often, this zone is above the water table and therefore the interaction takes place under unsaturated conditions. The available evidence is scarce but suggests that unsaturated conditions play a major role on the pile’s response. The actual mechanisms governing the soil–pile interaction under unsaturated soil conditions are not understood entirely, and this paper provides a useful insight on this topic. The analysis is carried out with a fully coupled three-dimensional numerical model, the soil behaviour is simulated with a Modified Cam Clay Model extended to unsaturated conditions. The model accounts for the increase in stiffness and strength of unsaturated soils as well as the volumetric collapse upon wetting. The constitutive model is calibrated on the laboratory data and validated against centrifuge data with satisfying agreement. The results highlight the substantial differences in the soil reaction against the pile depending on different water saturation profiles. The study also shows that the influence of unsaturated conditions on the pile response increases as the pile’s flexibility increases. Comparing the findings with currently available design methods such as the p–y curves, it is found that these do not adequately describe the unsaturated soil reaction against the pile, which opens the door for new research in the field. The proposed numerical model is a promising tool to further investigate the mechanisms underlying the soil–pile interaction under unsaturated soils.

Impact of Suction on the Near Surface Lateral Soil Response using Centrifuge Modeling

“…For the unsaturated soil test, suction stress significantly affected the failure wedge mobilized in front of the pile as it displaced laterally, leading to greater values of lateral resistance on the p-y curves. The results were consistent with those of Lalicata et al [29]. They observed that the lateral resistances along the p-y curve showed an increasing trend in the unsaturated soil condition but were closer to steady lateral resistance values for the fully saturated soil at similar values of lateral displacements.…”

Seismic behavior of pile foundations in unsaturated soils

“…Less attention has been paid to the effect of unsaturated soil conditions on the response of laterally loaded piles; however, it is well known that pile behavior is greatly affected by the mechanical properties of soil layers near ground surface [1], which is frequently above the water table. To the best of the authors' knowledge, only a few studies [2][3][4][5] have explored the effect of soil suction on the response of laterally loaded piles in unsaturated soils. Mokwa et al [6], for example, proposed a method for calculating the load versus lateral displacement curves for unsaturated soils based on the results of five full-scale load tests.…”

An analytical method to evaluate the capacity of laterally loaded piles in unsaturated soils

“…Consideration of lateral forces is crucial, for example, in the design of tall buildings, bridge abutments, earth-retaining structures and wind turbines. Experimental, analytical and numerical studies show that the response of flexible piles is largely influenced by the pile-soil stiffness ratio whereas, for short and rigid piles, the behaviour is governed by both stiffness and slenderness ratio [1]. The non-linear soil behaviour also strongly influences design parameters such as head displacement, maximum bending moment and critical length.…”