Mechanical Responses and Damage Model of Anchored Jointed Rock Mass under Fatigue Shear Load

Abstract

Cyclical impact loads will transform into low-frequency fatigue loads during propagation and will induce creep deformation of far-field rock under long-term disturbance loads. Laboratory tests of specimens under different fatigue shear loads were conducted. The mechanical responses and creep laws of the specimen were analyzed in detail. Based on the experimental results, a new constitutive model was explored. The results reveal that the stress‒strain curves of the specimen show a trend of step-path increasing under stable and fatigue load circularly. With an increase in fatigue load, the shear strength and elastic modulus of the specimens decrease gradually, while the corresponding failure strain increases gradually. The damage index composed of peak time and peak shear stress can reflect the failure of rock under fatigue loading, and the fatigue amplitude has the greatest influence on specimen deterioration. A fatigue stage in the shear creep curve occurs and is caused by the fatigue load. The fatigue creep rate increases gradually as the fatigue parameter increases. A combined nonlinear damage creep model based on the Nishihara model, elastic body, nonlinear creep body, and fatigue damage function (termed the NENF model), describing the creep responses of rock, anchor, accelerated creep, and fatigue load, respectively, was established. Compared with test data, the creep equation of the model has good accuracy in describing the whole shear creep process of specimens under fatigue loading and provides a new framework for the stability of anchoring rock masses.