Sand behavior from anisotropic and isotropic static and dynamic triaxial tests

Liquefaction behavior of reconstituted samples of saturated loose Nevada and medium dense lone sands is investigated through isotropically and anisotropically consolidated, static and cyclic, drained and undrained triaxial tests.Various modes of the triaxial test are performed on sands to simulate, approximately, conditions anticipated in the field. However, more complex response is shown, herein, to be obtainable from the appropriate application and interpretation of simpler, routine tests, tests that are within the capability of most geotechnical labs. Anisotropically consolidated sand sheared under both drained and undrained conditions can be determined from isotropically consolidated drained and undrained tests. Ko-consolidated drained axial compression behavior is successfully assessed from isotropically consolidated drained axial compression tests. Anisotropically consolidated undrained axial compression behavior is similarly assessed from isotropically consolidated undrained axial compression tests once the appropriate consolidation ratio is established from analytical computation. In turn, undrained isotropic behavior is assessed from drained isotropic tests. Under uniform cyclic deviator stress, isotropically consolidated undrained cyclic behavior is governed by undrained lateral compression behavior. Meanwhile, anisotropically consolidated undrained cyclic behavior of sands is controlled by its undrained axial compression response. In such tests, porewater pressure builds up at the end of each cycle. The amount of pore pressure build-up is based on monotonic stress - strain - strength behavior. As part of the current work, a modified Hooke's Law is used to assess such build-up. The undrained cyclic behavior of sand also depends upon the magnitude of the applied cyclic deviator stress and the rate of loading (frequency). The relationship between cyclic stress ratio and number of cycles required to cause liquefaction of loose Nevada and medium dense lone sands is developed from Series of undrained cyclic triaxial tests. It is shown that in the post liquefaction state of such loose sand, strength can be regained under monotonic axial compression loading at large axial strain. This too can be assessed from drained triaxial test response.