Lateral Response of Piles in Unsaturated Sandy Soils

Date of Award

Summer 2023

Project Type

Dissertation

Program or Major

Civil Engineering

Degree Name

Doctor of Philosophy

First Advisor

Majid Ghayoomi

Second Advisor

Jean Benoît

Third Advisor

Fei Han

Abstract

Laterally loaded piles are usually analyzed to adequately interact with the soil around them. The response of piles to lateral forces is a vital consideration when designing deep foundations for tall buildings and retaining structures. Many building failures have been linked to the failure of piles to withstand lateral loads, thus leading to excessive soil-pile displacement. It is essential to ensure that the laterally loaded pile is designed with sufficient bending stiffness to withstand the moments developed along the pile shaft while ensuring that the soil does not reach its ultimate lateral resistance. Furthermore, the nature of the soil and its saturation can greatly influence the pile lateral response. In many cases, the water table usually lies somewhere along the embedded pile length, thus leading to a laterally loaded pile in an unsaturated-saturated soil mix. The strength and stiffness of the unsaturated soil vary from those of dry or fully saturated soils because of inter-particle suction and three-phase material response. This becomes critical when dealing with fluctuating groundwater levels within different vadose zone thicknesses, and ignoring such conditions may lead to inaccurate performance assessment of the laterally loaded pile. Thus, this dissertation focuses on assessing how changes in groundwater levels impact the interactions between soil and laterally loaded piles, considering the effect of pile-head fixity conditions.A series of theoretical and experimental studies were conducted to evaluate the lateral response of piles in unsaturated cohesionless soils. The theoretical ultimate lateral resistance of the cohesionless soil commonly predicted using p-y curves was modified to incorporate unsaturated soil mechanics. Key variables impacted by the degree of saturation in the soil were adjusted, and new mathematical models describing the p-y curves were presented. A set of sensitivity analyses was performed based on soil water retention characteristics and flow rate to show the influence of fluctuating water levels on pile lateral response in the soil. Additionally, centrifuge experiments were performed on different pile physical models, which were the single free-head pile, the single fixed-head pile, and pile groups with 3D and 5D spacings, to investigate the influence of the unsaturated soil on pile lateral response. Experimental findings indicate that the unsaturated soil and pile head fixity conditions can considerably affect lateral soil-pile interactions. Results showed that the pile lateral loads for the unsaturated-saturated soil mix were higher than the fully saturated soil at the maximum displacement. Also, the single free-head pile experienced lower lateral load values than the single fixed-head pile and leading piles of the fixed-head pile group when the water level decreased. Soil lateral resistances from the experimental results were compared to the theoretical models from the p-y curve formulation in the unsaturated cohesionless soil to show how well they compare and to better understand the lateral behavior of piles in unsaturated soil conditions.

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