Sarah Mobley, P.E., doctoral student, and Kelly Costello, E.I., doctoral candidate, from the department of civil and environmental engineering at the University of South Florida, are the winners of the 2017 DFI and DFI Educational Trust Student Paper Competition.
Their winning paper, “The Effect of Slurry Type on Drilled Shaft Cover Quality,” presented the findings of laboratory experiments performed on 24 tremie-placed concrete specimens that investigated the correlation between slurry type (bentonite, polymer and natural slurry) and laitance channel formation.
Concrete placed in a drilled shaft using the tremie method first fills a portion of the shaft within the reinforcement cage prior to flowing beyond the cage and radially outward into the annulus. Depending on slurry type, the radial flow may produce laitance-filled creases or channels that project the reinforcing cage configuration to the outer surface of the shaft.
The flow pattern (and creases) can affect filter cake thickness, cover quality and propensity for corrosion. A direct correlation between the use of bentonite slurry and laitance channel formation was identified, which indicated a high propensity for corrosion and lower strength. The drilled shafts constructed using polymer behaved in a similar manner to the shafts constructed using water, neither of which indicated a heightened propensity for corrosion or reduction in strength.
Two runners-up were also selected for the 2017 Student Paper Competition: Jennifer Ostrowsky, P.G., Utah State University for “A New Approach for Evaluating the Ductility, Volumetric Stiffness and Permeability of Cutoff Wall Backfill Materials,” and Martijn van Wijngaarden, M.Sc., Delft University of Technology, for “Gravity Based Foundations for Offshore Wind Turbines: Cyclic Loading and Liquefaction.”
In addition, four student papers received special recognition.
- “Statistical Analysis of Design Method for the Axial Capacity of Single Driven Piles in Glacial Tills,” by Markus Jesswein, EIT, Ryerson University
- “Physical Modelling of Lime Stabilisation in Soft Soils Around Deep Excavations,” by Jignasha Panchal City, University of London
- “Challenges Associated with the Regional Calibration of Resistance Factors for Drilled Shafts,” by Philippe Kalmogo, Iowa State University
- “Field Study of Blast‐induced Liquefaction Dragloads on Drilled Shaft Foundations,” by Elvis Ishimwe and Richard A. Coffman, associate professor, University of Arkansas
The awards were presented at the DFI 42nd Annual Conference on Deep Foundations in October 2017 in New Orleans, where Mobley and Costello presented the winning paper to conference attendees. Each of the winners and runners-up will have their papers published in a future issue of the DFI Journal. All of the award recipients received a library of up to 20 DFI publications along with a gratis two-year DFI Individual Membership. The special recognition winners received a plaque and their papers will be considered for the DFI Journal as well.