REVIEW OF METHODS FOR ESTIMATING PILE CAPACITY

The first phase of an investigation of methods for construction control of pile driving and determination of pile capacity has been completed for the Washington State Department of Transportation. A literature review covering the use of dynamic pile driving equations, wave equation methods, and pile analyzers has been conducted. In addition, a survey of current practices by state transportation departments has been completed. The literature review has shown that dynamic formulas provide the least reliable pile capacity predictions. Of the numerous formulas studied, no single dynamic pile driving formula was found to be superior to all others. However, the Hiley, Janbu, and Gates equations appear to be among the best in published comparisons of formula predictions versus pile load test results. The Engineering News formula and its modified versions were found, with one exception, to be among the worst predictors of pile capacity. When wave equation methods were included in comparisons of predicted-to-measured capacity, the wave equation prediction was consistently equal to or better than the best formula. Pile analyzer results can be excellent; however, the ability of the operator is a crucial factor in its successful use. Recommendations have been made for the improvement of current procedures used by the Washington State Department of Transportation for construction control and estimation of pile capacity. These recommendations also are applicable to many other state transportation departments, as well as private contractors and consultants who are involved in the construction control of pile driving.