Axial load transfer for piles in sand. I. Tests on an instrumented precast pile

A precast concrete pile was driven 11.0 m into a sand deposit and subjected to three compression and one tension static loading tests. By means of strain-gage instrumentation, the loads imposed in the pile during the tests were determined. The observed load distributions appeared to suggest the existence of a critical depth. However, when the load data were supplemented with the residual load acting before the start of the tests, the appearance of critical depth disappeared. Instead, the analysis of the tests showed that the load distribution was a function of the effective overburden stresses in the soil over the full pile length, with β-ratios ranging from 0.40 through 0.65 and a toe bearing coefficient of 30. The shaft resistance degraded slightly from test to test. The shaft resistance in tension was about equal with the shaft resistance in compression. The β-ratios and the toe bearing coefficient derived from the test were applied unchanged to the results of compression tests on a second test pile, a 15 m long identical pile, and the calculated capacity agreed with the capacity found in the static loading test. Key words : instrumented pile, sand, loading test, residual load, load transfer.