Dynamic behavior of granular materials

An experimental technique has been developed that is capable of (1) controlling the triaxial stress state in the specimen, (2) dynamically loading the specimen in multiaxial compression, and (3) allowing the recovery of the sample after loaded by a single and well-defined pulse for the characterization of the failure mode. Hydrostatic pressure is introduced to the test section of a compression Kolsky bar to create dynamic triaxial loading conditions on sand specimens. Both the test section and the free end of the transmission bar in a Kolsky bar setup are fitted with two hydraulic pressure chambers. After a desired hydrostatic pressure is applied to the specimen, an impact-generated axial load is applied through the incident bar for characterizing the dynamic shear response. Quasi-static and dynamic triaxial compression experiments have been performed on Quikrete #1961® fine grain dry sand. The sand specimens are confined triaxially and the amount of confining pressure (25-150 MPa) is varied by controlling hydraulic pressure. The profile of the dynamic loading pulse is controlled through pulse shaping such that the specimens deform at constant axial engineering strain rates under uniform dynamic stresses. The experimental results show that the compressive stress-strain response of the sand is sensitive to hydrostatic pressure levels but insensitive to strain rates. After test, specimens are investigated using gradation, particle breakage factor and surface morphology. The effect of dynamic loading on the failure behavior of sand grain shows ductile to brittle failure transition