Predicting Eccentric Stresses for Large Diameter Open Ended Pipe Piles: Fid-Bau Portal

Predicting Eccentric Stresses for Large Diameter Open Ended Pipe Piles

Webster, Scott / Robinson, Brent / Allin, Ryan / Flynn, Rory

Recent experience with dynamic pile testing results of Large Diameter Open Ended Pipe piles (LDOEP) has provided some insight to consider when such piles need to penetrate very dense soil or rock layers. In soil conditions where these piles need to penetrate such layers to achieve sufficient geotechnical resistance or fulfill lateral stability requirements, the potential for pile damage needs to be assessed. In addition to potential uniform compression stress at or near the pile toe, consideration should also be given to possible eccentric compression stress. The uniform pile toe compression stresses can be evaluated by wave equation results during the design phase of the foundations. Then, the design team can consider alternate pile diameters and wall thickness to prevent over stressing of the pile toe. During pile installations, dynamic pile monitoring can calculate the pile toe stress based upon the Case Method equations. CAPWAP analysis can further refine the calculation and location of the maximum compression stress. However, none of these methods can directly assess eccentric stresses which might occur where the pile toe encounters the dense soil or rock layer at an angle due to pile batter or sloping soil/rock layer. The paper will present examples where such stresses were encountered, and pile damage was apparent. Based upon the pile monitoring results and the evident pile damage encountered a method to calculate the apparent eccentric stresses is provided. The method proposed would be used in combination with wave equation or dynamic monitoring results to predict the combination of uniform dynamic and eccentric stress for piles driven at an angle or to soil layers with an expected slope.