Analysis of piles in a residual soil—The ISC'2 prediction

The 2nd International Conference on Site Characterization (ISC'2), held in 2004, included a seminar for prediction of pile capacity involving three 6 m embedment length test piles, one 350 mm square driven concrete pile, and two 600 mm diameter, strain-gage instrumented, bored piles. Invited predictors were provided with results of in situ, laboratory tests and dynamic tests. Test layout, soil information, and pile data are presented with calculations of pile capacity and load distribution, submitted predictions, and results of the static loading tests. The CPT-calculated capacities show considerable scatter—total values ranged from 500 to 1400 kN for the driven pile and from 1000 to 1900 kN for the bored piles. The static loading test on the driven pile showed an offset limit load of 1200 kN and a plunging capacity of 1500 kN. Despite pile movements of 100 mm for 1200 kN of applied load, neither of the bored piles showed signs of having reached an ultimate resistance value. Effective stress analysis of strain measurements for the bored piles showed the data to correlate to a β coefficient of 1.0 and a toe coefficient of 16. Most submitted predictions underestimated the capacity of the driven pile and overestimated the capacities of the bored piles.Key words: pile capacity, effective stress analysis, shaft and toe resistances, β coefficient, CPTU, dynamic testing.