SHEAR WAVE VELOCITY DEVELOPMENT IN NATURAL SAND UNDER TRIAXIAL LOADING

Accurate definition of shear wave velocity (Vs) and small shear modulus (Gmax) is of high importance for solving any kind of geotechnical problems using modern software solutions. Abundance of experimental results have been accumulated to define the initial maximum shear modulus, however the interpretation of shear wave data measured in deformed/sheared soil has not been considered so far. This study used a triaxial apparatus equipped with bender elements to monitor the development of Vs during triaxial experiments of the cohesionless natural sand. Sandy soil specimens were prepared using wet-tamping method varying the initial relative densities, from Dr=30% to Dr=80%, then confined at four levels of initial effective stress p0 = 50, 100, 200 and 400kPa before application of loading. Loading rate of 0.2mm/min was applied in drained and undrained conditions, while the Vs was monitored during the tests for defined points of axial deformation. The experimental results revealed that the Vs values for the specimens in drained conditions tend to approach each other and merge at large axial strains. Additionally, the axial strains at which the peak Vs is measured is found to be aligned with the axial strain at which the specimen transfers for compaction to dilation. In the case of undrained monotonic test, the peak values of Vs are occurring for higher axial strain values, while the merge of results is not measured at least not within the observed range of 15% axial strain. For both sets of results significant density dependence is noticed, more pronounced in the case of undrained conditions.