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A numerical solution has been developed using a finite difference formulation to simulate the one-dimensional impact wave propagation behavior and subsequent static load test performance. Based on this solution, the importance of residual driving stresses in properly interpreting pile behavior under axial loads is examined. This paper (1) briefly describes the analytical procedure developed by the authors to incorporate residual stresses explicitly, (2) applies the procedure to a documented pile load test to demonstrate the concepts developed, (3) examines the consequences of ignoring residual driving stresses in interpreting/predicting pile behavior under axial loads, and (4) demonstrates the influence of various parameters on the predicted pile performance.

As part of the I-15 Corridor Reconstruction Project through downtown Salt Lake City, nine sets of full-scale load tests were performed at locations selected as representative of the subsurface conditions along the corridor alignment. Static compression, uplift, and lateral load tests were conducted at each test site location. The test program included dynamic monitoring of pile installation and restrike events using high-strain testing and analysis methods. Dynamic test results from restrike events on companion piles compared well with the measured static axial compression load test capacities. Subsurface conditions along the alignment range from deep clays to dense alluvial sands above the groundwater table. The piles derive their support from shaft friction or a combination of shaft friction and endbearing, depending on the strata present. The test and subsequent production piles are consistently indicating large capacity gains with time (setup), regardless of the subsurface conditions. The setup in the soft to stiff lakebed clays is attributed to remolding of the clays during pile driving and subsequent reconsolidation. The setup in the dense sands is comparable with setup described by others in dense marine sands. Relationships were developed to predict long-term pile capacity based on dynamic test results from the end of installation and on data from the beginning of restrike. These relationships are being used during production pile installation and restrike events as an integral part of pile evaluation, troubleshooting, and quality control/quality assurance acceptance procedures.