Experimental Investigation of the Fatigue Damage and Strength Characteristics of Heterogeneous Rock Mass under Cyclic Loading

Rock fractures filled with cementation inevitably lead to rock mass heterogeneity and affect its mechanical properties. The cementation is usually regarded as a defect due to its strength is lower than that of the surrounding rock. To investigate the influence of the defect on fatigue damage and strength of the rock mass under cyclic loading, the defect area ratio was obtained and a series of static and cyclic loading uniaxial tests were carried out. The experimental results reveal that tensile failure with few secondary cracks occurs under static loading. However, microcracks are widely developed in the samples after cyclic loading, especially at the defect interface. The compressive strength decreases with increasing defect area ratio. During cyclic loading, the fatigue damage for samples with small defect area ratios (<10%) is similar to that of intact rock. However, multiple sudden increases in the residual strain and dissipation energy occur when the defect area ratio is greater than 10%. In addition, cumulative residual strain, cumulative acoustic emission (AE) count and cumulative dissipation energy increase with increasing defect area ratio. Cyclic loadings significantly reduce the rock mass strength, and the strength reduction increases with increasing defect area ratio. It is inferred that the incompatible deformation in the heterogeneous rock mass is the main reason for the sample damage and the strength reduction, and the unloading has an essential effect on the initiation, propagation and coalescence of microcracks.