Rheological properties of siltstone-like fissure specimens in different environments

Joints and fissures in deep enclosing rocks impact the stability of the rock mass considerably. Therefore, understanding the deformation and damage mechanics of deep fissured soft rocks is crucial to ensuring the safety and efficiency of any project that involves them. Similar material testing is a commonly used method used to study rock strength and fissure evolution. In this study, we performed orthogonal tests to determine the similar material ratio of cement:sand:water:talc as 2:2.5:2:2 for the siltstone-like material found in the water-rich soft rock roadway enclosing rock in the fault fracture zone of the Hongqingliang coal mine. In addition, a fabrication method for prefabricated fissure specimens with appropriate water stability was designed based on sodium glutamate crystals. Subsequently, triaxial compression tests with high confining pressures were carried out on the prefabricated siltstone-like fissure specimens with different integrity indices. It was found that the peak stress of the specimens decreased with the decreasing integrity index, while the plasticity increased. As the integrity index decreases, the probability of decay in compressive strength also decreases, and the compressive strength shows a negative exponential correlation with the integrity index. The modulus of elasticity of the specimens at each integrity level shows varies directly with the confining pressure. In the case of a specimen with low integrity index, this phenomenon is obvious with certain fluctuations. Both Poisson’s ratio and the internal friction angle show a good linear correlation with the integrity index, whereas cohesion shows a clear exponential decay trend. These results are of great significance in the study of rock strength damage and fissure evolution.