Fly Ash Effects on the Stress-Dilatancy Relation of Coarse Soils: Particle Morphology Role

The influence of the overall regularity and gradation characteristics on the stress-dilatancy relations of a river sand amended with fly ash material is discussed in this paper. To achieve this goal, a series of direct shear tests was carried out on reconstituted samples at an initial relative density (D-r = 87 +/- 3%) and subjected to three normal stresses (sigma(n) = 0.1 MPa, 0.2 MPa and 0.3 MPa). The obtained results confirm that the fly ash binder improved significantly the mechanical performance of the tested materials resulting in a noticeable increment of its shearing resistance. In addition, the analysis of the generated results proves that the particle shape (Angularity "A", Sphericity "S" and overall regularity "OR") and granulometric characteristics (effective and mean particle diameters "D-10 and D-50" and coefficient of uniformity "C-u") correlate very well with stress-dilatancy properties for the tested sand-fly ash assemblies. Moreover, the overall regularity parameter (OR) and the related granulometric characteristics (D-10, D-50 and C-u) appear as pertinent parameters for the prediction of the maximum dilatancy friction angle (psi(max)) of the used materials. This experimental research points out the relevance of particle shape and particle size parameters in the studying and evaluation of the strength-dilatancy relationships of river sand-fly ash mixtures.