Overview

Conduct geotechnical design of driven pile foundations, and all related considerations, per AASHTO LRFD Bridge Design Specifications Article 10.7. Piling design should consider skin friction and may consider point bearing as well. Because piling has small tip areas and is generally placed in softer soil, the point bearing contribution is modest and is often disregarded in static design. Exception should be made when tipping a driven pile into bedrock or very competent, hard founding material. In these cases, end bearing is crucial, and piles could be designed exclusively from tip resistance or using a combination of tip and side (depending on pile type used).
Technical specifics of many common driven pile types can be found in FHWA GEC-12 Design and Construction of Driven Pile Foundations – Volume I (
FHWA-NHI-16-009
), Chapter 6, Section 6.1. These can be used when making preliminary pile type selection in design.
Driven piles are not designed nor accepted based solely on static analysis. The nominal bearing resistance of all driven piles must be calculated and accepted based on Hammer Formula (Item 404, Section 3.5, for dynamic bearing resistance), wave equation analysis (e.g., drivability analysis and final driving acceptance criteria by GRLWEAP), dynamic measurements with signal matching (PDA/CAPWAP), or full-scale load testing results.
On refusal, assume that the piling has developed the maximum allowable service load for the pile. If required, perform a drivability study to establish a hammer & driving system that can install the pile without overstressing. Include this study in Geotechnical Design Report.
Design based on process outlined in Section 1 with additional steps:
  • Specify resistance factors to use based on field methods to use dynamic formulas for pile acceptance (or refer to Item 404 Section 3.5 specification for Hammer Formula Method of Bearing Evaluation to determine the allowable dynamic bearing resistance).
  • Perform a pile drivability analysis to obtain required tip elevations (
    if required
    ). Pile acceptance based on the pile driving analyzer (PDA) is for projects where it is cost effective on large number of friction piles or where high pile driving stresses are predicted and require monitoring
Pile design resistance should meet or exceed the requirements specified for each limit state, both in static analysis and dynamically.
Design with caution when designing piling in areas with shallow hard or dense soils. If piling cannot be driven through these areas, the contractor will need to pilot hole or jet the piling to achieve the desired penetration. Jetting should avoid an area with existing foundations and utilities. Excessive pilot holes and jetting may affect the foundation capacity.