Set-up effect in long piles in weathered soils

Field tests were conducted to study set-up effects in long driven piles founded in completely decomposed granite (CDG). Two steel H-piles 56 m and 58 m in embedment depth were fully instrumented with vibrating-wire strain gauges and installed. Several restrike dynamic tests were carried out on each test pile from 1 day and up to 95 days after the end of initial driving. Static load testing was later carried out to substantiate the dynamic tests. The test programme is described in detail. Changes with time in pile capacity and in the shaft and toe resistances were studied based on the results of the pile tests. The development of the shaft resistance set-up with depth and time was studied in particular. It was found that setup took place in the shaft resistance and relaxation in the toe resistance. The overall set-up was found to be at the lower bound of the values found with concrete piles. More significant set-up in shaft resistance was observed in the shallower fill and alluvium layers. The dimensionless set-up factor A for shaft resistance in CDG ranged from 0·53 to 1·06, and the set-up factor decreased with depth and with increasing blow count in the standard penetration test.