The Study On Mechanism Of Crack Initiation, Propagation And Connection With Ordered Multiple Cracks In Rocklike Material

The failure mechanism and crack propagation of multi-fractured rock mass under pressure is an important research topic in the field of geotechnical engineering. Generally, most of unstable failures are related to crack propagation and the interactions between cracks. Precious researches achieved some results, but there are still many research problems which are not solved yet, due to the limitation of test conditions. Therefore, the research of multi-fractured rock mass with different geometric parameters is still a hot topic in rock fracture mechanics.In this paper, the main research method is experimental study, based on precious studies. The uniaxial compression test for rocklike specimens is conducted with nine cracks on it. According to the result, we will discuss the orders of micro-cracks appeared on the tip of pre-existing cracks and crack coalescence, displacement of the crack initiation, and the pressure and displacement of crack coalescence. Crack initiation types, crack coalescence types, failure mode, stress-strain curve, crack initiation stress, peak stress and peak strain will be discussed and analyzed in detail with considerations of changing crack angle, crack row spacing, crack spacing, and the materials compounding. Meanwhile, we will use the XJTUDIC three-dimensional digital speckle dynamic strain measurement and analysis system to collect the information from thousands of images and to record the dynamic information during the whole process from crack initiation to failure. Based on this study, we obtain the following results:(1)Besides the geometric distribution and the materials compounding are constantly changing, it was found that the wing-crack initiation still was the mainly crack initiation mode. In the ductility group, the crack initiation are influenced by angle.(2)In this paper, there are three crack coalescence types: tensile mode, shear mode and tensile-shear mode. The main crack coalescence type for most of specimens is tensile mode. A small number of specimens' main crack coalescence type is shear mode. The change of angle influences the main crack coalescence type, especially in the ductility group.(3)The main types of failure mode are tensile failure and tensile-shear failure. The change of angles also has a significant effect on failure mode.(4)The change of angles and the cementing material content influence the crack initiation stress and peak stress significantly. Crack initiation stress and peak stress decrease as the angle decreases and increase as the cementing material content increases.(5)According to the displacement nephogram of y axis and strain nephogram, we obtain the displacement of each point on the surface of specimens, the path of crack propagation and the level of crack. from displacement nephogram, the path of crack propagation and strain concentration situation are also obtained.