Correlating Particle Shape Parameters to Bulk Properties and Load Stress at Two Water Contents

Abstract

Particle shape of prospective root-zone sands is evaluated qualitatively, but a quantitative shape determination may be more useful for sand selection. The objectives of this research were to: determine how particle shape complexity relates to bulk density, total porosity, and mechanical behavior (resistance to displacement given a vertical load); correlate quantitative shape parameters to these properties; determine how water content influences these relationships; and establish if quantitative shape parameters can be used to predict mechanical behavior in the absence of turfgrass roots. Seven materials of various shapes were separated into the medium size class (0.25 to 0.50 mm) to limit variability introduced by particle size distribution. A dynamic, digital imaging machine was used to quantify particle sphericity, symmetry, and aspect ratio. Bulk density, total porosity, and stress at multiple displacements were determined for the materials at two water contents, oven-dry and 5% gravimetric water content. As sphericity, symmetry and aspect ratio increased, bulk density increased and total porosity decreased. Sphericity, symmetry, and aspect ratio were negatively correlated with stress under a vertical load. The addition of water at compaction did not affect the correlations of the shape parameters with either bulk density or porosity; correlations of symmetry and sphericity with these were stronger at 5% water content for some displacements. Multiple regression analysis indicated that sphericity can be used to predict stress characteristics of sands compacted at 5% water content for specific testing conditions. These data indicate that particle shape complexity is related to bulk properties and has potential for predicting the stress characteristics of prospective root zone materials prior to construction.

Primary Mechanical Modification to Improve Performance of Miscanthus as Stand-Alone Growing Substrates

“…SPHT = 4π A P 2 (0 < SPHT ≤ 1) (P: measured perimeter of a particle projection, A: measured area covered by a particle projection) It is an indicator of surface roughness (an ideal sphere has SPHT value of 1) [42,43].…”

“…In all substrates, the degree of elongation increased with the increase in particle size, which was expressed as the mean value of aspect ratio at each size category (Table 5). The sphericity parameter (SPHT) describes the sphere shape, and it also indicates the roughness of particle surface [43]. The higher the SPHT values, the smoother the particle surfaces.…”