Load Transfer in a Step-Taper Pile

A pile load test on an instrumented, concrete-filled, step-taper pile reveals that the soil support at each step, as well as the frictional resistance developed along the pile, are significant factors in transferring load from the pile to the surrounding soil. The test pile was constructed from an 8-ft length of 10-3/4 in. O.D. pipe at the tip end and continued for 41.5 ft with varying lengths of corrugated shell of increasing diameter to the butt end where the diameter was 17-5/16 in. The pile was driven through 38 ft of dense sand and gravel and 8 ft of weathered shale with the point bearing on firm shale. Field observations disclosed that only 20% of the applied load reached the tip of the short, stiff, supposedly point-bearing pile. Concrete stresses were found to be consistent in the upper half of the pile and to decrease sharply toward the tip. Calculations of the theoretical load transfer are presented and are found to be in reasonably fair agreement with the field data.