Evolution of sand microstructure during shear

Quantitative measurements of the local void ratio distribution are used to demonstrate how the microstructure throughout dilatant triaxial specimens o f uniform fine quartz sand evolves during drained axial compression loading . Shear-induced increases in the mean of the local void ratio distribution initiate at the center of the specimen and migrate toward the ends of the s pecimen as axial strain increases. At any given strain, the mean of the loc al void ratio distribution is largest near the center of the specimen, refl ecting the influence of end platen and membrane restraining effects. The re sults provide direct quantitative microstructure-based evidence that global or macro response, as conventionally used in interpreting specimen behavio r, can be misleading as to the true material response. Implications of the test results on practical issues such as the location of local strain measu rement systems are noted.