LAUSR

Stress-induced deformation problems are often encountered in civiland mining-related rock engineering projects. In a typical situation, rock disturbance under external loading by mechanical excavation or blasting methods induces the rock to undergo a complex history of the response states of load and deformation. For instance, a number of loading, unloading and then reloading sequences can be anticipated at a certain location ahead a tunnel face. As the tunnel advances forwards, excavation promotes disturbed zones ranging from failed, damaged, disturbed and undisturbed zones (Martin 1997; Martin and Read 1996). Damage effects insights (Xu et al. 2004) and the mechanical properties (Eberhardt et al. 1999; Taheri et al. 2016a, b) of quasi-brittle rocks under uniaxial compression within the pre-peak stress–strain regime are commonly found in the literature. However, very limited studies have been undertaken on the stress–strain behaviour of rocks during post-peak cyclic loading condition. This is mainly due to the major difficulties with measuring properly postpeak stress–strain quantities associated mainly with a suitable testing method and rock brittleness (Munoz et al. 2016a, b) contrary to conventional testing methods (Wawersik and Brace 1971; Wawersik and Fairhurst 1970). In addition, post-peak cyclic loading damage evolution, i.e. the characteristics of non-localised uniformly distributed damage and localised damage, associated with localisation of strains and stiffness degradation have not been addressed yet. In this regard, very few investigations into the local deformational characteristics of rocks under uniaxial cyclic loading limited to both pre-peak regime (Dautriat et al. 2011; Hao et al. 2010; Zhang et al. 2013) and 2D DIC (Song et al. 2013, 2016; Xu et al. 2004) have been conducted. Therefore, the present study focuses primarily on studying strain localisation evolution and damage evolution characteristics of quasi-brittle porous sandstone subjected to compressive cyclic loading in post-peak regime. To do so, firstly, an innovative laboratory testing method was designed to investigate progressive damage in postpeak cyclic loading. Secondly, 3D DIC was implemented to study the insights of strain localisation evolution and damage evolution throughout the cyclic tests.