Distribution of residual load and true shaft resistance for a driven instrumented test pile

摘要

Foundation conditions are studied for a series of apartment buildings in a shore area reclaimed from the Nakdong River estuary delta west of Busan, South Korea, in full-scale field tests on two 600 mm, post-driving grouted, concrete cylinder piles instrumented with strain gages, driven through compressible layers and a short distance into underlying dense sand at depths of 56 m (Shinho) and 35 m (Myeongji). One test pile was provided with an O-cell so that after an initial Ocell test, a subsequent head-down test only affected pile shaft resistance. The purpose was to evaluate drivability of the piles, magnitude of the drag load due to consolidating soils, and potential settlement (downdrag) of the piled foundations. Early in the study, it became apparent that the internal process of heating and cooling of the grout during the hydration process and swelling from absorption of water affected the strain records and the assessment of residual load in the test piles during the wait time before the static loading test. The paper reports the measurements, analyses, and method for determining residual load, strain-dependent modulus of test piles, and actual load distribution in the test piles. The results are correlated to cone penetration test (CPTU) sounding data and effective stress analysis.