Concrete Pile Design in Tidewater Virginia

Recommendations are presented for determining unit point and shaft resistances for precast prestressed concrete piles embedded in the Yorktown Formation, the bearing stratum for most major structures in tidewater Virginia. The soil is subject to loss of strength during performance of the Standard Penetration Test (SPT) due to the creation of excess pore pressures that result in a significant reduction of the SPT resistance values. Pile driving has a similar effect on the soils, and this was documented in the study. Thus, ultimate pile capacities determined by dynamic methods will be significantly underestimated. New design parameters are developed by load testing three instrumented piles and correlating the results with the SPT resistance. The SPT correlation factors are then used to reevaluate the capacity of previous load tests and provide good estimates of ultimate pile capacity. The design parameters are considered applicable for use through the region with the few exceptions noted.