AN INVESTIGATION OF RING-SHEAR DISPLACEMENT FOR CONTROLLING SHEAR ZONE FORMATION OF SAND

As a part of a Japanese National hydrate research program (MH21, funded by METI), we performed a study on the relationship between ring-shear displacement and shear zone formation of sand. To provide of evaluating shear zone formation, we used a ring-shear apparatus to examine the relationship between shear zone conditions and shear displacement of silica sand. The effects of shear displacement on the porosity and pore-size distribution were investigated. We obtained measurements under constant effective normal stress of 8.0 MPa and in a drained condition during shearing. The shear displacement was about 2500 mm. The specimens after shearing used in analyses of microstructure (FE-SEM), grain size distribution (laser diffraction) and pore-size distribution (mercury porosimetry) were collected at the end of the experiments. The porosity after shearing decreased with increasing shear displacement up to 500 mm. Grain crushing and compaction of shear zone in specimen were observed by the microstructures and grain size distributions after large-displacement shear. Median grain size values of shear zones in the range from approximately 200 μm to 10 μm decreased with increasing shear displacement (0-2500 mm). Pore-size distribution analysis showed that pore diameter under 10 μm increased with increasing shear displacement.