Abstract
Meso-structure is an important factor affecting the characteristics of rock fracture. To determine the factors influencing the internal meso-structural characteristics upon the crack generation and extension, rock samples were tested under uniaxial cyclic loading and unloading and examined using computed tomography (CT) scanning. CT scanning was used to visualize and investigate the entire process of fracture source generation and its development in three dimensions, and finally the location information of the fracture source was determined. The mineral composition and structure along the fracture path inside the specimen were studied by using a polarizing microscope, and the evolution of fracture propagation around mineral particles was revealed based on its mineralogical characteristics. Results indicate that based on the fracture source around different rock meso-structure types, the initial fracture source can also be divided into different types, namely, the primary porosity type, the micro-crack type, and the mineral grain type. The strength characteristics of mineral grains can determine whether the crack extends around the gravel or through it. The hard grains at the crack-tip promote the transformation of tensile stress to shear stress, which lead to the change in the direction of crack extension and bifurcation. The spatial shape of the cracks after rock fracture is related to the initial distribution of minerals and is more complicated in areas where minerals are concentrated. The crack extension around gravel particles also generates a mode of failure, affecting large grains with gravel spalling from the matrix. The findings provide a study basis for identifying the potentially dangerous areas and provide early warning for the safety of underground engineering construction operations.
Highlights
Thespecimens specimens were tested with uniaxial press after they were pre-treated. (b) The specimen was taken into the computed tomography (CT) machine for uniaxial press after they were pre-treated. (b) The specimen was taken into the CT machine for scanning after it had been loaded and unloaded. (c) The 3D reconstructed model of the specimen scanning after it had been loaded and unloaded. (c) The 3D reconstructed model of the specimen was obtained after a series of processing of the rock images from the CT scan. (d) Slices in different was obtained a seriesby of using processing of the rockplane images from the software
The sizes of most of the specimens studied by scholars have been small, Lubricating silicone grease was applied to the upper and lower loading surfaces of the which means that many meso-structural features are not included, so larger specimens rock samples, and pads made from polytetrafluoroethylene (PTFE) sheets were used to were chosen for the present study
To maximize theduring information gleaned from CT scanning as to fracture source formation and crack expansion, rock specimens were tested under uniaxial cyclic loading and unloading and CTtimes scanning: the of circulating
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Some scholars studied the internal meso-structure, e.g., initial defects, mineral types, and particle size, to reveal the relationship between meso-structure and macro-fracture [8,9,10]. Most scholars studied the fracture initiation process and mechanical mechanism of fracture by prefabricating holes and fractures, but the reality is that there are multiple meso-structures within the rock, and the combination of these structures leads to fracture source generation and fracture extension. To study the crack generation and propagation during rock fracturing on a meso-structural scale, a multi-stage loading experiment and CT scanning were performed. The influence of initial pores and micro-cracks and mineral particle distribution and strength were studied and discussed on the generation and propagation path of fracture sources
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