The normal stress acting around a piled or anchored foundation is a governing parameter in the mobilized skin friction capacity. The radial effective stresses acting on a pile or anchor can decrease over the course of its service life due to cumulative soil contraction during cyclic loading (e.g. from wind, wave, and tide action, or service-related vibrations) which may result in degradation of the skin friction capacity. The magnitude of this degradation has been previously shown to depend on the stress path imposed on the soil-structure interface in terms of the magnitude and sequence of applied shear stresses. However, quantification and prediction of this effect remains difficult to achieve. This paper presents the results of a series of laboratory load-controlled interface shear tests performed using constant normal stiffness boundary conditions to model the soil mass surrounding a pile. The investigation is aimed at determining the evolution of normal stress and shear resistances and the accumulation of shear and volumetric deformations experienced by sand-structure interfaces during cyclic loading of varying amplitude and number of cycles. The results presented highlight the effect of cyclic stress amplitude and sequence on the degradation of normal stress, cyclic strength, and post-cyclic strength. Implications of the results presented herein are discussed, with emphasis on the evolution of skin friction capacity of offshore structures.
Kyle B. O'Hara, M.S., S.M. ASCE and Alejandro Martinez, Ph.D., A.M. ASCE
Keywords: soil-structure interface, cyclic loading, skin friction, degradation
Publisher: DFI