Load Tests on Long Bearing Piles

Abstract

Load tests were performed on corrugated step-tapered piles with pipe extensions and pipe piles driven through 120 ft of slightly overconsolidated, medium-to-stiff, fissured clays 1 to 10 ft into dense fine sands and silty sands. Failure loads for the bearing piles of 10¾ to 12¾ in. tip diameter varied from 180 to 280 tons. Design dead loads up to 90 tons, which could be temporarily carried in friction in the upper compressible soils, were expected to be eventually transmitted to the sand stratum. The bearing capacity of the sand was evaluated by subtracting friction in the upper clays, as measured by piles stopped above the sand, from the total load carried by the bearing piles. The developed friction capacity was uncertain because of variations in soil strength between load test locations. However, the following conclusions are indicated by the test data and wave equation analyses of the driven piles: (1) the corrugated step-tapered piles developed frictional resistances in the clays equal to or greater than the minimum undrained shear strength determined by unconfined compression tests, (2) pipe piling frictional resistances were about two thirds of the corrugated pile values, and (3) the bearing capacity of the sand was overestimated 70 to 100 percent by wave equation analyses of the ultimate resistance of bearing piles driven to practical refusal and 150 to 400 percent by bearing capacity formulae using full overburden pressures and bearing capacity factors for laboratory-measured angle of internal friction of the sand.

Model Studies of Long Piles in Clay

“…3) Skin friction development and proportioning at increasing penetrations: 4) The influence of tension loading on the development of skin friction: 5) Verification of a soil-to-soil failure; and 6) Evaluation of driveability studies using model piles.…”