Generalized Hoek-Brown dynamic strength criterion incorporating strain rate effect

The mechanical behavior of rock material is strongly influenced by confining pressure and strain rate. It is of great significance to establish a unified strength criterion taking account of complex stress state and strain rate in the rock dynamics analysis. A series of strength data obtained from uniaxial compression test, triaxial compression test, Brazilian test on sandstone under strain rates of 10(-5)-10(2.32) s(-1), are applied to assess the applicability of generalized Hoek-Brown strength criterion and to analyze the strain rate effect on the material parameters. The results show that the strength rule of sandstone can be reasonably described by the generalized Hoek-Brown strength criterion from low tensile stress region to relatively high compressive stress region under the same strain rate. The parameters both uniaxial compressive strength sigma(c) and parameter a show a slight increase at lower strain rate, and show a dramatically nonlinear increase at higher strain rate, whereas parameter m almost does not change with different strain rates. Therefore, the function relationships between the material parameters sigma(c) and a of the generalized Hoek-Brown dynamic strength criterion and strain rate can be established. On this basis, a new generalized Hoek-Brown dynamic strength criterion is proposed taking account of strain rate from the region of 10(-5)-10(2.32) s(-1). The physical mechanisms of strain rate and confining pressure effects on dynamic strength of sandstone are further studied.