Design Lessons from Load Tests on Open- and Closed-Ended Pipe Piles

Both the driving response and static bearing capacity of open-ended piles are affected by the soil plug that forms inside the pile during pile driving. In order to investigate the effect of the soil plug on the load capacity of pipe piles in general, field pile load tests were performed on instrumented open- and closed-ended piles driven into sand. For the open-ended pile, the soil plug length was continuously measured during pile driving, allowing calculation of an incremental filling ratio, IFR for the pile. The cumulative hammer blow count for the openended pile with final IFR of 77.5% was 16% lower than for the closed-ended pile. The limit unit shaft and base resistances of the openended pile were 51% and 32% lower than the corresponding values for the closed-ended pile. It was also observed, for the open-ended pile, that the unit soil plug resistance was only about 28% of the unit annulus resistance

Load Tests on Pipe Piles for Development of CPT-Based Design Method

This research focused on the drivability and load-carrying capacity of both open and closed-ended steel pipe piles. Two pipe piles (one open-ended, the other closed-ended) were installed in a sandy soil to the same depth. The site was extensively characterized. SPT and CPT tests were performed both before and after pile installation. A variety of soil indices and shear strength parameters (such as the constant-volume friction angle) were measured in the laboratory. The piles were fully instrumented, permitting separate measurement of shaft and base capacity for the closed-ended pile and shaft, annulus and soil plug capacities for the open-ended pile. The results are presented in a variety of ways. In particular, values of pile resistance are presented normalized with respect to CPT cone resistance values both along the shaft and base of the piles for quick reference. The test results for the openended piles are quite unique. Two design methods are proposed for open-ended piles based on the field load test as well as on results found in the literature. In one method, pile resistances are referred to either the soil plug length or incremental filling ratio. In the other method, pile resistances are correlated to the CPT cone resistance. Comparisons of the proposed methods with the load test results and with methods currently in use are quite favorable. The present research suggests current pile design methods may be excessively conservative. It seems that cost savings from similar research, where complete measurement of all variables of interest both for the piles and for the soil deposit where the piles are installed are done, can be very substantial if the methods proposed here are validated further. It appears that such savings would be in the interest of DOT\u27s and the FHWA