Behaviour of Granular Soils Under Uni- and Multidimensional Drained High-Cyclic Loading

The paper summarizes a long-term experimental research program on the behaviour of granular soils under high-cyclic loading, that means a loading with many cycles (\(N \ge 10^3\)) and relatively small strain amplitudes (\(\varepsilon ^{\text {ampl}}\le 10^{-3}\)). Numerous drained cyclic triaxial and hollow cylinder triaxial tests have been performed, most of them on Karlsruhe fine sand. The effects of the stress or strain amplitude, average stress, relative density, grain size distribution curve, particle shape and a content of non-plastic fines or shell fragments on the cumulative deformations are discussed. The important role of initial fabric (sample preparation method) is demonstrated, while the geometry and dimensions of the samples seem to be of secondary importance. The effect of multiple changes of the polarization (i.e. direction) of the cycles was found less important than previously thought. The bundling of a cyclic loading with continuously changing amplitude into bundles of cycles each with a constant amplitude is demonstrated to be conservative. An interesting effect has been observed in tests with bundles of cycles interrupted by monotonic loading phases: The monotonic loading can lead to a loss of the cyclic preloading memory, and thus to an increase of the rate of strain accumulation in the next bundle of cycles. Results from tests with 1D, 2D, 3D and 4D stress and strain paths confirm the amplitude definition for multi-dimensional strain loops incorporated into a high-cycle accumulation (HCA) model. The description of the strain accumulation rates by the HCA model is discussed based on the results from the various test series.