AXIAL CAPACITY OF AUGERED DISPLACEMENT PILES AT AUBURN UNIVERSITY

A comparative study as performed at the Auburn University's Spring Villa NGES test site aimed at quantifying the effects of grouping and amelioration on the axial capacity of augered displacement piles. Amelioration is defined as the addition of sand or stone during drilling to "improve" the pile-soil interface. The test site lies in the Piedmont geologic formation and is comprised of residual soils best classified as silty-clay to clayey-silt. The test piles were specialized, full displacement continuous flight auger piles. The scope of testing involved quick load compression tests on five different pile configurations: isolated single pile; isolated single pile ameliorated with sand; isolated single pile ameliorated with #89 crushed stone; single pile centered in symmetric #5 pile group; single pile centered in symmetric #5 pile group ameliorated with sand. Previous studies of this test site indicated low variability across the site with respect to stratigraphy and soil strength. The test quantified substantial increases in axial capacity with both grouping and amelioration. The nature of the full displacement piles is such that the group effect substantially increases lateral soil stresses over the depth of the pile, resulting in higher side friction with the installation of adjacent piles. Amelioration with either the sand or the crushed stone also resulted in an increase in capacity, though quantitatively not as much as the group effect. While both grouping and amelioration provided marked increases in capacity, their combined effects were not as substantial.