Revisiting Tavenas (1971): Tests on Piles in Sand-Article

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Bengt H. Fellenius reanalyzes François Tavenas’s 1968 static load tests on instrumented precast concrete and H-piles driven into compact sand in Quebec. Each pile was tested at successive embedment depths, with telltales used to estimate axial compression and distinguish shaft and toe behavior.<br /><br />Tavenas’s original interpretation suggested that shaft and toe resistance became constant below a “critical depth.” Fellenius argues that this apparent pattern resulted from residual forces left in the piles after driving, combined with errors in estimating applied loads from hydraulic-jack pressure. The tests were also conducted in an excavated and partly backfilled site, so the effective overburden stress differed from that of undisturbed ground.<br /><br />By accounting for residual force, jack-load overestimation, and excavation effects, Fellenius’s back-analysis found that pile response followed effective overburden stress throughout the sand layer, rather than leveling off below a critical depth. The analysis estimated similar shaft and toe resistance parameters for both pile types, despite their different shapes and materials. Residual forces were fully mobilized along roughly the upper half of each pile, and repeated driving did not appear to change the shaft-resistance parameter.<br /><br />The study highlights the value of preserving original test records and cautions that reliable pile-test interpretation requires directly measuring applied load with a load cell.

Keywords

Bengt H. Fellenius

François Tavenas

static load tests

instrumented piles

precast concrete piles

H-piles

compact sand

residual forces

shaft resistance

toe resistance