Foundation piles are subject to downdrag forces whenever the soil surrounding them settles. The settlement of thick compressible soils under embankments can cause downdrag forces significantly larger than the structural load the pile must carry. This additional load may result in unacceptable settlements of the piles or even failure of part of the pile group. Downdrag forces have been reduced by coating the piles with bitumen. Several approaches for predicting and reducing downdrag forces have been published, but little verification of design methods and material properties is available. The overall objective of this research was to develop practical guidelines for use of bitumen-coated piles including: (1) coating material specifications and tests, (2) design techniques, and (3) construction practices.

Two reports "Design and Construction Guidelines for Downdrag on Uncoated and Bitumen-Coated Piles" and "Research on Uncoated and Bitumen-Coated Piles Subjected to Downdrag" have been reviewed and approved by the project panel. The guidelines have been published as NCHRP Report 393, "Research on Uncoated and Bitumin-Coated Piles Subjected to Downdrag." The second report and a video are available for purchase on request. A software program, "PILENEG," that helps apply the guidelines is presently available from the linked World Wide Web homepage of the Texas Transportation Institute at https://ceprofs.tamu.edu/briaud/.