Experimental investigation and empirical model on damping properties of rock under multistage cyclic loading

Abstract

The dynamic shear modulus and damping ratio of rock are the main indicators that reflect the dynamic characteristics of rock masses under seismic and dynamic action. The multistage cyclic triaxial compression test is performed on granite and red sandstone under different confining pressures with two stress paths. To reasonably describe the dynamic characteristics of rock, a modified Hardin hyperbolic model is proposed to describe the backbone curve. The relationship between the dynamic shear modulus, damping ratio and cyclic shear strain is analysed under different confining pressure conditions with variable and same amplitude. Furthermore, an empirical formula is established for estimating the dynamic shear modulus and damping ratio. The obtained results show that with increasing shear strain, the damping ratio of red sandstone and granite decreases and then increases under the condition of variable amplitude. When the shear strain is constant, the damping ratio of red sandstone and granite is less affected by the confining pressure. Under the same amplitude conditions, as the shear strain increases, the dynamic shear modulus under different confining pressures shows an increasing trend. The two established empirical formulas can be used to predict the dynamic shear modulus and damping ratio under multistage cyclic loading. This has important reference significance for studying the dynamic characteristics of rock.