BEHAVIOR OF MEDIUM SAND UNDER VERY HIGH STRAIN RATES

摘要

Drained triaxial compression tests on crushed coral sand were performed from near-static strain rates up to approximately 1,760 %/sec. Experiments were performed on medium (Dr = 58%), dry, vacuum confined axisymmetric specimens at two different confining pressures. A gravity drop weight loading system was used to generate high strain rates. High-speed photographs of the specimen were taken through the flat sides of a square triaxial cell. Using digital image analysis, strains were locally measured near the center of the specimen to obtain the most uniform assessment. The following effects were observed with increasing strain rates: the elasto-plastic stiffness increased significantly; the failure strength increased moderately; the axial strain at peak stress decreased significantly; volumetric strains became more dilatant. Unusual behavior was observed at very high strain rates, such as: the peak stress was not associated with the maximum dilatancy rate and shear band inclination angle was noticeably reduced.