2. Experimental SRST

2.1 Material

Glass beads in size ranges of 30-50µm (Polysciences Inc. 18901-100, lot 685012) and 150-210µm (Polysciences Inc. 05483-250, lot A760996) were acquired from Polysciences Inc. A particle density of 2500kg/m3 is used in both the DEM simulation and experimental analysis, consistent with averaged reported values from vendor specifications.
Prior to testing, samples were screened using a #100 US standard sieve (150µm opening). Images of each bead type were taken at 200x magnification using a Keyence VHX-2000 optical microscope. Binary blends of small and large glass beads were prepared at ratios of 3:1, 1:1, and 1:3 on a mass basis, and prepared at a 30g scale. Weighed and screened materials were transferred to a 135ml glass container and mixed using a Turbula mixer at 32rpm for 5min.

2.2 Shear testing

Ring shear testing of each blend was performed on the Schulze RST-XS using the XS-MV4 shear cell. The shear cell is annular in shape with an inner diameter of 32mm and an outer diameter of 64mm. The initial gap between the base and the lid is 4mm; the size of this gap decreases as pressure is applied to the shear cell and particle mixtures are compressed. The shearing bar of the XS-MV4 cell is pyramidal in shape and covers the surface of both the base and the lid.
Shear measurements were performed using a shear rate of 0.004s-1 and a 2000 Pa pre-shear load, with subsequent consolidation loads of 400, 700, 1000, 1300, and 1600 Pa. For this work, the shear data and the solid fraction data taken at the pre-shear condition were used to compare to the DEM simulation. Two replicates were performed for each blend condition, with new particle mixtures prepared to generate the replicate data.
The segregation of the binary blend is very apparent. After blending, there are regions in the glass jar where the small and large beads are separated. Given the large size ratio (approximately 4.5), it is very difficult to mix the particle into a random mixture. Segregation is an inherent factor to the shear test and it was not possible to completely eliminate from our experiment. The shear cell was filled by taking multiple scoops of blend from the bulk mixture, with each scoop taken from a random location within the blending vessel. Segregation is observed even when filling the shear cell, the area of segregated particle can be seen when preparing the shear cell. Figure 1 presents an image taken on the surface of the shear cell before testing. All shear tests were performed on the material as is. Due to the method of fill for the shear cell (scooping from a mixture prone to segregation), the content of the shear cell is emptied out after the shear test. The content is again sieved through a #100 US standard sieve, separating them into smaller (<150µm) and larger (≥150µm) segments. The mass of each sample is then determined to verify the mixture composition.