Study Of The Effect Of Stress Paths On The Deformation Behavior Of Sand

The behaviors of sand depend not only on its relative density but also on the consolidation pressure. It is shown that, under the same consolidation pressure, sand in a dense state will exhibit dilative response, and it will exhibit contractive response when it is in a loose state. However, sand with the same density will show volume expansion subjected to a low consolidation pressure and it maybe show contractive response under a high consolidation pressure. With regard to the sand samples with the same initial state, their stress-strain relationship, strength and dilatancy are different under different stress paths. Unfortunately, most of the existing constitutive models are based on the routine triaxial tests and do not consider the effect of states and stress paths of sand. One has to use different parameters for sand with different densities.In order to study the effect of stress paths on the deformation behavior of sand, three sand samples with different densities were prepared by use of standard sand, and then were isotropically consolidated under two kinds of pressures by use of the CKC Triaxial System. Six stress paths tests were conducted on these samples under drained conditions. The effect of the initial states (the density and consolidation pressure) as well as that of stress paths was studied.By analyzing and comparing all the test results, it is found that the stress path can have great effect on the stress-strain relationship, the strength and the dilatancy of sand. Sand with the same initial states shows more contractive response in triaxial extension tests than in triaxial compression tests. Both the strength and dilatancy of sand increase with the density under the same initial effective mean normal stress. In the same way, the strength and compressibility of sand with the same density increase with the initial effective mean normal stress and the ultimate value of volume expansion decrease correspondingly. Then, the critical state lines are provided based on the test results of different stress paths.Finally, the state-dependent dilatancy constitutive model for sand was introduced in detail. After determining all the model parameters according to the test results, numerical calculation of the whole test procedure was studied by applying FORTRAN programs. The model simulations are in agreement with the test results under different stress paths, in terms of both the shear stress-strain response and volumetric characteristics, and the present model can reflect the deformation behaviors of sand.