The evolution of grain-size distribution of sands under 1-D compression

Crushing of particles is a fundamental mechanisms leading to deformation of particulate materials at medium and high stresses. As crushing progresses, the grain-size distribution undergoes modifications, causing changes of the porosity, grain-to-grain contacts and of their density (”packing density” and “grain contact”). The main aim of the research is the identification of trends in the modifications of characteristic diameters (D10, D15, D25, etc.) in function of the applied stress s´v.

Results of a laboratory research programme on the crushing of dry sands compressed under one-dimensional conditions, at vertical effective stresses ′v up to 120 MPa, are reported in the paper. Tests have been carried out on calcareous bioclastic and on quartz sands, with initial coefficient of uniformity Cu ranging from 1.10 to 1.42. The crushing of bioclastic sand particles is considerable even at low stresses, whilst for quartz sands it becomes appreciable for stresses higher than 10 MPa. It is shown that the evolution of the grain-size distribution of a given sand can be effectively represented by the following relation between the absolute value of the decrement of the generic characteristic diameter Di and ′v: Di= h/(K(1+C e –hlgv)), where C, h, K are parameters depending upon the nature and the initial grain-size distribution of the sand. This Verhulst type relation properly accounts for the existence of an upper limit to Di. The analysis of published data shows that this type of relation also applies for other, quite different, sands.