Development of Residual Forces in Long Driven Piles in Weathered Soils

A large-scale field-monitoring program for studying residual forces in long-driven piles is described. Eleven steel H-piles, 34.2–59.8 m in embedded length, were instrumented with vibrating-wire strain gauges, installed and subjected to static loading tests in a building site in Hong Kong. The residual forces in these piles during and after pile installation were recorded. The development of residual forces as it relates to the pile penetration depth during construction, and in time after the piles were installed, is presented. The measured load transfers in the piles from static loading tests are reported and the effect of the residual forces on the interpretation of load-transfer behavior is studied. The field measurements show that residual forces increase approximately exponentially with penetration depth. The residual forces continue to increase with time after pile driving due to secondary compression of disturbed soils around the pile shaft and other factors. The large residual forces in the long piles significantly affect the interpretation of the pile load distributions. The effect of residual forces on the shaft resistance is significant at shallow depths. Bearing-capacity theory tends to overpredict the true toe resistance of the long piles founded in weathered soils.