From the report summary:
Although exploratory borings and engineering studies during design are an integral part of foundation engineering, the axial resistance of a driven pile foundation is ultimately determined by the criteria used to decide when to stop driving the pile during construction. The use of test piles for the purpose of developing the pile installation criteria can be instrumental in building driven pile foundations that are reliable and cost-effective. Nationwide practices for developing pile driving criteria range from the use of very simple formula without any test pile verification to the use of pre-production test piles with dynamic measurements during installation and static load testing. Many agencies employ a range of technologies and methods based on the size of the project, the type of pile, and the predominant ground conditions. However, this issue is handled differently from state to state based on local experience, economics, and other factors.
This synthesis provides a survey of the current practices used by transportation agencies to develop pile driving criteria, with special attention placed on the use of test pile data. The survey consists of questionnaires sent to all 50 state departments of transportation plus the District of Columbia and Puerto Rico; 44 of the 52 agencies provided responses. In addition, a Phase II Survey was performed by telephone interview with nine agencies representing a broad geographical distribution of large states that have extensive pile foundation construction projects.
The information collected indicated that practices used by transportation agencies to develop pile driving criteria for production pile installation can be described as highly variable in terms of the level and sophistication of the testing performed. To some extent, such variability in test pile requirements may reflect the inherent variety in project size, complexity, ground conditions, pile type, etc. However, a significant component of the variation in pile driving criteria may be related to the pace of implementation of new approaches to pile testing and variation among agencies with respect to training, experience, and acceptance of new technology.