Graduation Year

2024

Document Type

Thesis

Degree

M.S.C.E.

Degree Name

MS in Civil Engineering (M.S.C.E.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Gray Mullins, Ph.D.

Committee Member

Michael J. Stokes, Ph.D.

Committee Member

Zachary Haber, Ph.D.

Keywords

Dragload, Embankment, Negative Skin Friction, Pile Foundations, Software

Abstract

Embankments are commonly used for bridge approaches, with mechanically stabilized earth (MSE) walls being the preferred choice in Florida. However, the construction of embankments leads to the settlement of the underlying soil, regardless of soil type. When piles are driven before embankment construction, the initial settlement of the original soil creates relative movement between the pile and the surrounding soil, introducing frictional forces. When the existing soils move downward relative to the pile, a downward-oriented side shear known as downdrag is introduced. While downdrag is addressed in current codes and textbooks, it is often only briefly mentioned and primarily in the context of clay soils, with little to no mention of sandy soils. Additionally, current codes and textbooks lack comprehensive procedures and computations for incorporating downdrag into designs. Consequently, existing design aids, such as SPT97 and FB-Deep, do not account for downdrag in their calculations. This thesis aims to address this gap by investigating the design process of end bent driven piles with downdrag and proposes an Excel-based program for incorporating downdrag into pile design. The study involved compiling essential background information on downdrag, including soil settlement prediction models, pile capacity models, and implementation methods. The developed Excel program, Pile Embankment Assessment Tool (PEAT), integrates these downdrag considerations into the design process. Its effectiveness was tested through three case studies, by comparing the software’s predictions with field data from Sandridge Road, Paseo Al Mar Boulevard, and Henley Road bridge construction projects in Florida. Discrepancies between PEAT predictions and the measured data were analyzed, with variations attributed to uncertainties from thermal variations, soil profile improvements, and data bias. The study concludes that downdrag effects should be considered in the design of end bent piles, even in predominantly sandy soils, and recommends further research is needed to establish appropriate load factors to address variability and uncertainties in predictive efforts.

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