Experimental study of undrained lateral and moment behavior of drilled shafts during static and cyclic loading

Abstract

This report presents the results of an experimental study of the undrained response of drilled shaft foundations in cohesive soils under lateral and moment loads. Both static and cyclic loadings typical during windstorms were included. The report offers criteria for evaluating the influence of such loadings on shaft capacity and displacements as well as guidelines for foundation design. Researchers constructed model drilled shaft foundations in three diameters and four depth-to-diameter ratios in uniform cohesive soils with overconsolidation ratios ranging from low to high. On the basis of previous wind-loading evaluations, they developed a test loading program to simulate significant windstorms. They loaded the model shafts cyclically and then to failure. These results were compared with test results obtained by monotonic lateral or moment loading. Test results showed that the lateral or moment resistance of drilled shaft foundations can be influenced significantly by cyclic loading. One-way to cyclic load levels less than about two-thirds of the static shaft lateral resistance cause small displacements or capacity reduction. Higher load levels will cause large permanent displacements and metastable behavior. On the basis of these results, design guidelines were developed to address various loading combinations.