Axial Pile Capacity from CPT Data in Difficult Soil

ABSTRACT: Dynamic pile load testing was performed during the driving of 610 mm displacement prestressed concrete piles into sandy soils, and actual pile capacity was determined during end-of-drive (EOID) and at beginning of restrike (BOR) using CAPWAP procedures. The load test provided an opportunity to compare pile design techniques to measured pile performance. The soils at this site prevent the pile driving process from being completed and the required pile length and capacity were not achieved due to early refusal. An evaluation was carried out to evaluate nine Cone Penetration Test (CPT) methods based on their ability, to which predictive method would be best suited for estimating the pile capacity at a site where such soils may encountered. The study also compared the CPT methods to the results of the bearing capacity obtained from Standard Penetration Test (SPT) based methods presented in the literature for the same pile. The ratio of predicted total capacity, Qp, to measured total capacity, Qm, is presented, along with the absolute percent difference between the predicted and measured capacities. Four methods included Philipponnat (1980), De Ruiter and Beringen (1979), Price & Wardle (1982), Zhou Etal (1982) had slightly over predicted the capacities for test pile within 50% to 63% of the capacities determined by the 1-day BOR dynamic loading test. The Qp and Qm ratio was between 1.5 to 1.9 which showed good agreement between predicted and measured capacities.