Drained cyclic behaviour and state-dependent stress-dilatancy relationship of sand in direct simple shear tests

Direct simple shear tests were conducted to investigate the cyclic behaviour, dynamic properties, and stress-dilatancy relationship of fine-grained silica sand for a wide range of constant vertical stresses, including low stresses. Multi-stage cyclic tests were conducted by increasing the shear strain amplitude from low to high values in subsequent loading stages. Test results show that the volumetric strain is related to the vertical stress and shear strain amplitude. The cyclic shear modulus decreases and the damping ratio increases with shear strain amplitude, and they are influenced by the low-amplitude cyclic loading history. The volume change is related to the cyclic stress-dilatancy relationship, which depends on the vertical stress, shear strain amplitude, number of cycles, and shearing direction. In some tests, the stress-dilatancy relationship can be represented by two parallel lines for unloading and reloading, except for the initial parts. The increase in density with cyclic loading reduces the contractive behaviour and increases the dilative response in the large-amplitude loading cases, which reduces the rate of volumetric compaction with the number of cycles.