DEVELOPMENT OF DESIGN PROCEDURES FOR ESTIMATING CAPACITY AND DEFORMATION OF PILE GROUPS. VOLUME 4: A CENTRIFUGAL STUDY OF AXIALLY LOADED MODEL PILES AND PILE GROUPS IN REID-BEDFORD SAND. INTERIM REPORT

To obtain a better understanding of single pile and pile group behavior, 50 model pile and pile group tests were conducted in the centrifuge. The main objectives of this study were to provide load-deformation responses of single and group piles in sand and to determine the depth of influence below the pile tip for the model piles tested. Furthermore, two different methods of pile installation were tested to determine the influence on the load-deformation response of the models, and some preliminary tests were conducted using a miniature cone penetrometer. It was found that the depth of influence for single piles increases from 14 to 30 pile diameters, as the relative density increases from 30% to 75%. Based on tests conducted on two different model pile sizes, the depth of influence appears to be a function of pile diameter and soil density. The ultimate capacity of a modelled 10 in. diameter, 20 ft long steel pipe pile showed a strong dependency on the relative density of the test sand. The capacity increased threefold for an increase in relative density from 40% to 65%. The pile group efficiency was found to be less than one for a relative density greater than 40%. The method of pile installation, pushed incrementally or driven, does not seem to have any influence on the load-deformation response of the single model piles. Insufficient data were obtained to judge installation effects of pile groups. The load distribution between tip load and side friction of the piles appeared to be independent of soil density.