Date of Graduation

5-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Richard Coffman

Committee Member

Kyle Rollins

Second Committee Member

Michelle Bernhardt

Third Committee Member

Christopher Liner

Keywords

Deep Foundations, Downdrag, Dragload, Liquefaction, Piles, Seismic

Abstract

Deep foundation elements are typically used to transfer structural loads for multi-story buildings and large-span bridges to a competent soil layer when 1) the soil close to the ground surface has no sufficient bearing capacity, and when 2) liquefiable soils are encountered. The majority of the bridges constructed within seismic zones rely upon the stability of earthen embankments and deep foundation that are installed above or within liquefiable soil deposits. Despite large factor of safety values or different load and resistance factors being used to adequately design deep foundations within seismic areas, soil liquefaction may cause extensive damage to the structure by 1) reducing the axial geotechnical resistances, 2) reducing the lateral load capacity, 3) adding additional loads to the foundation (dragload), 4) inducing excessive foundation settlements (downdrag), and 5) causing lateral spreading on the soil surrounding the foundation.

The compressive movement of the soil caused by liquefaction affects the distribution of the load along a deep foundation. Dragloads are developed when the amount of the soil settlement is larger than the amount of foundation settlement. According to Muhunthan et al. (2017), the developed dragload may exceed the structural axial strength of the deep foundation in the extreme events. This additional load can significantly impact the axial behavior of a deep foundation. In addition, the liquefaction-induced settlements may affect serviceability of the structure by causing downdrag on the installed deep foundation element.

Many of the existing design methods to address dragload and downdrag are based on the consolidation phenomenon. Therefore, there is an immediate need for research to evaluate the impact of liquefaction-induced dragload and dragload on the performance of deep foundation elements constructed in earthquake prone areas. Full-scale axial load tests and full-scale blast-induced liquefaction tests were performed around three drilled shaft foundations and three driven pile foundations to 1) evaluate the existing design methods, and 2) investigate the effects of liquefaction-induced dragload and downdrag on deep foundations. The tested foundations were constructed at the Turrell Arkansas Test Site (TATS), located within the New Madrid Seismic Zone (NMSZ), and Mississippi Embayment.

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