Evaluation of crushing stress at critical state of granulated coal ash in triaxial test

A series of triaxial compression tests was performed on three types of granulated coal ash (GCA) to investigate their shear and crushing behaviour. The experimental results show that GCA displays different dilatancy characteristics to other natural granular materials due to excessive breakage even at low stresses. A simple constitutive model for crushable soils with the ability to predict the mechanical and deformation behaviour of GCA is introduced. This constitutive model uses a new strength parameter, the so-called reference crushing stress, which affects the evolution of the failure state curve. The mean stress when the peak stress ratio reduces to the critical state stress ratio and the mean stress when the peak friction angle reduces to the critical state friction angle were employed to determine the peak strength of GCA in combination with relative density and confining pressure. These three parameters, defined using the critical state concept within the framework of triaxial testing, are examined and their linear correlations are shown. It is also noted that the reference crushing stress strongly correlates with the single particle strength for a given type of GCA and, as such, has some specific mechanical meaning.