Interpretation of Pile Load Test Considering Residual Stresses

The results of an instrumented pile load test program, including uplift and compression tests, are presented. The purpose of the pile load test is to determine ultimate bearing and skin friction design parameters. Vibrating wire strain gauges mounted on the steel H‐piles allow measurement of load transfer behavior along the pile length. Residual driving stresses and their distribution along the pile are also measured. Measured skin friction and endbearing stresses are found to vary significantly depending on whether or not residual stresses are accounted for in the analyses of the test data. Residual stresses are reduced significantly, but not completely, after one or two uplift load cycles. Since the design conditions are transient earthquake uplift loads, which are likely to change the residual stresses from those noted in the test piles, it is necessary to account for the residual stresses in the interpretation of the load test results.