United States Department of Transportation
i
Testing Protocol for Predicting Driven Pile Behavior Within Pre-Bored Soil: [Tech Summary]
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2016-02-01
[PDF-123.48 KB]
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Abstract:The Louisiana Department of Transportation and Development (DOTD) uses deep foundations, consisting of precast concrete piles, open- or closed-end steel pipe piles, steel H-piles, or auger-cast piles to support buildings, highway bridges, and other infrastructure systems. The piles at a project site derive their load carrying capacity from “side bearing” along their embedded lengths as well as from “end resistance.” Pre-boring is a method used to facilitate driving of large displacement piles in hard/dense soils. A pilot hole, generally smaller in size than the pile to be installed, is fi rst bored to a specifi ed depth. By pre-boring a pilot hole, the “end bearing” and “side friction” within the pre-bore zone are reduced, thus aiding the driving of the pile. However, pre-boring complicates the prediction of long-term pile capacity (specifi cally side friction) within the pre-bored zone and the Wave Equation Analysis of Pile (WEAP) analysis, which aims to predict pile drivability. It is assumed that long-term end bearing within the pre-bored zone will not be an issue, as current DOTD specifi cations prohibit predrilling to the pile tip elevation. However, there are three major unknowns that accompany the pre-bored zone: (1) reduction of end bearing as it pertains to pile driving within the zone, (2) reduction of side friction as it pertains to pile driving within the zone, and (3) reduction of side friction as it pertains to long-term pile capacity within the zone.
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