Physical Modeling of Drilled Shaft Side Resistance in Sand
Dimensional analysis of deep foundation side resistance is used to formulate the laws of similitude for drilled shaft uplift capacity. The resulting prediction equation for dimensionless side resistance then is tested against the results of static uplift load tests on model drilled shaft foundations in sand constructed at three different scales, all satisfying the same conditions of similitude. The test results and analysis of soil response show that soil dilation, constant thickness of the soil shear zone surrounding the shaft regardless of shaft diameter, and curvature in the Mohr-Coulomb failure envelope at low normal stresses can combine to cause apparent scale effects. These mechanisms are isolated and evaluated quantitatively for the shafts of this study, and apparent scale effects are eliminated by applying correction factors to the load test results. The factors illustrated by this study are used to develop guidelines for: (1) conducting model load tests to avoid scale effects and (2) developing correction factors for small-scale models that may be affected by apparent scale effects.