Granule shape effect on the shear modulus and damping ratio of mixed gravel and clay

Gravel-Clay mixtures are abundant materials in nature and are frequently used in certain civil engineering projects such as earth dams, levees and landfills. The advantage of using these soils lies in their low permeability owing to clay fraction along with the high shear strength due to the presence of the non-cohesive granular part. Karkheh dam is an example where these soils were used as the impervious core of the embankment. To date, little research has been carried out to investigate the performance of these soils, and therefore, their behavior under cyclic loading is still not well known. In order to investigate the cyclic behavior of gravel-clay mixtures, 51 cyclic and monotonic triaxial tests were performed on specimens with 11 different mixtures and under various confining pressures. Two different types of gravel, i.e. angular and round grains, were utilized to prepare specimens with the same gravel content in order to investigate the effect of the granule shape on the cyclic behavior of the mixtures. All the specimens were prepared with a constant compaction effort. Normalized shear modulus and damping ratio data showed differences in the behavior of mixtures with different kinds of gravel. Based on samples of macro structure performance under cyclic loading, two different mechanisms for the behavior of angular and round granules at contact level were hypothesized. The importance of the sampling method and specimen size for intermediate soils was also noticed.