Stress‒dilatancy behaviour of calcareous sand

Calcareous sands are a special geomaterial primarily composed of calcium carbonate or other insoluble carbonate materials susceptible to breakage. Therefore, breakage has a crucial impact on the change of calcareous sand granulation and the shape of individual grains during shear. By analysing some triaxial tests results of some calcareous sands presented in the literature in the light of the Frictional State Concept (FSC), it can be shown that the stress‒dilatancy relationship in different shear phases can be approximated with straight lines. These lines are defined by a critical frictional state angle and two material parameters of the FSC. These parameters express the deviation between the stress‒dilatancy relationship for tested soil and the stress‒dilatancy relationship for isotropic granular material shear deformed without non-coaxiality of the stress tensor and strain increment tensor, breakage, and other effects affecting energy dissipation during shear. It will also be shown that the points representing failure states in the η - D plane lie on a straight line with a much higher slope than for silica sands due to the breakage effect. Using the FSC, the stress‒dilatancy relationship can be simply described in different shear phases and used to build new elasto-plastic models of calcareous sand in the future.