Bearing Capacity for Foundations with Cyclic Loads

The paper presents a procedure to calculate the bearing capacity for foundations subjected to a combination of static and cyclic loads under undrained conditions. The term cyclic shear strength is defined, and laboratory tests are used to show how this strength and the type of failure of a soil element depend on the average and cyclic shear stresses and the number of load cycles. The calculation procedure is based on the strength determined from laboratory tests. It ensures strain compatibility of the soil elements along the potential failure surface and accounts for redistribution of average stresses during undrained cyclic loading. The procedure gives the failure load, the location of the critical failure surface, and indicates whether the foundation failure will occur as large cyclic displacements, large average displacements (e.g. settlements), or a combination of the two. The paper also presents examples with numerical values of cyclic shear strengths from triaxial and DSS laboratory tests on Drammen clay, both for given number of cycles and for typical storm loading.