Numerical analysis of the mechanical properties of rock materials under tiered and multi-level cyclic load regimes

Abstract

In engineering practice, it is a common that rocks are subjected to cyclic loading. The mechanical properties of rock materials under tiered, single-level, and multi-level cyclic load regimes (i.e., with different frequency, minimum stress, and amplitude) were numerically investigated by using a dynamic constitutive model for rock materials. A comparison between these loads from the aspects of stress-strain curve, modulus, damage, and strength was undertaken. The results indicate that the model can effectively reflect the different mechanical properties of rock materials under different cyclic load regimes. Under the action of tiered and multi-level cyclic loading, the area and width of the hysteresis loops become larger with increasing applied stress, but the slope of stress-strain curve, area and width of the hysteresis loops, maximum strain, and the irreversible deformation vary under different loads. The loading deformation modulus decreases with the increase of applied stress and the reductions therein are different when subjected to tiered, single-level, and multi-level cyclic loading. With increasing applied stress, the damage evolution in rock specimens subjected to tiered cyclic loading present an increasing trend and the trend likes an approximately inverted “s” -shape. Under multi-level cyclic loading, the damage variables increase rapidly at the first level, then become relatively stable and increase slowly as the applied stress increases. Furthermore, the peak strength of rock differs under different load regimes, and results indicate that cyclic loading has both strengthening and damaging effects on rock strength.