Effect of Particle Size and Morphology on Laboratory Maximum Density Determination of Sands

Determining the minimum and maximum density of sands is critical to accurate estimation of relative density-a key parameter in comparison of laboratory and field test data. Current ASTM methods (ASTM D4253) recommend the use of a vibratory table for maximum density determination. However, studies have shown that different specimen reconstitution techniques can lead to maximum density values that are above the value determined using the ASTM vibratory table method. This discrepancy can lead to an overestimation in the calculated relative density of reconstituted specimens. To further investigate, a sand rainer system composed of a nozzle and a series of stacked sieves was developed with the capability of achieving a wider range of densities. Preliminary results using the sand rainer system showed that densities in excess of the ASTM vibratory method were possible. This study further investigates this exceedance by examining the impact of particle morphology (i.e. angularity) and particle size on the achievable maximum density. Four different uniform sands were tested, including two angular and two rounded at coarse and fine particle sizes. Particle roundness and sphericity values were computed using digital images and computational methods. Minimum and maximum densities for each sand were evaluated using the ASTM method and the custom-built sand rainer system. Results show the importance of particle morphology and size on the maximum achievable density for the two different methods.