In order to explore the specimen failure characteristics during rock‐burst under different gradient stress conditions, in this paper, a novel experimental technique was proposed; a common series of tests under two gradient stress paths were conducted on rock similar material specimens using the true‐triaxial gradient and hydraulic‐pneumatic combined test apparatus. And plaster was used as the rock similar material. In the experimental process, several rock‐burst debris with area sizes of 100 mm² were collected, and the fractal dimensions of typical detrital section crystal contours were analyzed and calculated using a scanning electron microscopy (SEM) method. The results showed that the specimens’ failure characteristics which had been induced by the two gradient stress processes were various. Also, the mesoscopic morphology of the rock‐burst detrital section had effectively reflected its macroscopic failure characteristics. It was found that the fractal dimensions of the crystal contours of the specimen’s detrital section had fractal characteristics, and the box‐counting dimension based on the SEM image could quantitatively describe the rock‐burst failure characteristics. Furthermore, under the same magnification, the fractal dimensions of the crystal contours of the splitting failures were found to be relatively smaller than those of the shearing failures.

Among the factors affecting rock mass failure, the stress state has the greatest influence on the mechanical behavior of rock. The mechanical behavior of rock depends on the change of stress path, and the stress of rock mass is closely related to deformation and failure. In order to study the influence of surrounding rock stress state on the failure mode of surrounding rock, based on the theory of elastic mechanics and fracture mechanics, this paper analyzed the stress state of surrounding rock element and crack propagation of surrounding rock, and estimated the potential failure mode of surrounding rock in different areas of a phosphate mine in Yichang. The results showed that: the surrounding rock element is affected by the gradient stress, and a larger stress gradient corresponds to a larger principal stress ratio and variation direction of the surrounding rock. The failure mode of surrounding rock is affected by the coupling effect of principal stress ratio and principal stress direction. Under the action of certain crack angle and appropriate confining pressure, different fracture mechanisms may occur in the surrounding rock compression. But the partition of surrounding rock failure mode region can predict the surrounding rock failure mode to a certain extent.

Reinforced concrete structures play a pivotal role in island and reef engineering projects. Given the resource constraints typical of island regions, substituting traditional manufactured sand aggregate with reef limestone not only reduces reliance on river sand but also addresses the issue of disposing of waste reef limestone slag generated during excavation. However, the performance characteristics of reef limestone concrete, particularly its bond strength with reinforcing steel, warrant further investigation. This is particularly true for the bond–slip behavior of the reinforcement. This study aims to elucidate the effects of various parameters on the bond performance between steel and reef limestone concrete through central pullout tests. These parameters include the type and diameter of the reinforcement, bond length, and loading rate. The investigation encompasses the analysis of load–slip curves, bond failure modes, and variations in bond stress. Additionally, using the Abaqus software, a numerical simulation was conducted to analyze the mesoscopic stress characteristics, thereby revealing the mechanisms of bond formation and failure modes between steel reinforcement and reef limestone concrete. The results indicate that the bond–slip curve for reef limestone concrete reinforced with ribbed rebars and Glass Fiber-Reinforced Polymer (GFRP) rebars can be broadly categorized into four phases: minor slip, slip, decline, and residual, with the residual phase exhibiting a wave-like pattern. The predominant failure modes in reef limestone concrete are either pulling out or splitting. The bond stress in reef limestone concrete decreases with an increase in rebar diameter and bond length; conversely, it increases with the loading rate, although the ultimate slip decreases. The mesoscopic failure characteristics of reinforced reef limestone concrete, as simulated in Abaqus, are consistent with the experimental outcomes.