An experimental study of dynamic behaviors of rock under stepwise cyclic loading

The aim of this study is to investigate the responses of dynamic elastic modulus of rock on stress amplitude and stress level. Stepwise cyclic loading tests are conducted on sandstone, conglomerate and sandy conglomerate using a WDT-1500 reactive material testing machine. The variations of dynamic elastic modulus and dissipated energy with stress amplitude, stress level and moisture content are determined. The results show that the dynamic elastic modulus gradually decreases with the increase of energy dissipated. It is observed that the higher the stress level, the greater the dynamic elastic modulus and dissipated energy; the greater the moisture content and stress amplitude, the lower the dynamic elastic modulus, but the greater the dissipated energy. Ducan-Chang model is capable of describing the stress-strain relationship of rock under stepwise cyclic loading. Thus, a dynamic elastic modulus evolution model is proposed by taking into account the stress amplitude, stress level and moisture, and the methods to determine parameters of the model are discussed. Then, based on an empirical rule of energy dissipation, a dissipated energy evolution model is developed. The results show that the proposed models are able to describe correctly the characteristic of energy dissipation of rocks under stepwise cyclic loading.