Experiment Research On The Fracture Failure Mechanism Of Rock-like Material With Fissures Under Uniaxial Compression

Aiming at the compression fracture properties of rock containing joint fissures, the uniaxial compression experiments were made on the rock-like material with transfixion fissures in indoor experiment. The comprehensive and in-depth research and analysis were done on the failure process and mechanism of fissure bodies, and the main fracture laws under uniaxial compression were obtained and mastered.Firstly, using the cement mortar material similar with natural rock, the specimens containing transfixion fissures with different distribution state were made by pulling out the greased metallic shims inserted in the specimen beforehand at the early stage of maintenance. The uniaxial compression experiments were accomplished on the Electro-Hydraulic Servo Control Testing Machine cooperating with DCS-200 operating software, and the loading speed was 200N/s. The initiation and propagation process of branch cracks at the tips of prefabricated fissures was observed and recorded by digital devices during experimental process.Secondly, based on the properties of experimental materials, the strain-softening model had been built with the help of numerical analysis procedure - FLAC3D. The new experimental phenomena found during the tests and the changing rule of experimental results were investigated and analyzed by this model. Combining with the experimental results, the failure process and mechanism of fissure bodies were studied from the view of numerical simulation.Finally, based on the author's recognition, the views and opinions about this field's development direction were put forward to help follow-ups work it smoothly.In this paper, the main researches include:(1) The change law of stress distribution at the tips of fissure with different inclination angle was explained quantitatively by the application of sliding crack model. And, considering the friction effect of fissure surface, the calculation formula of stress intensity factor at the tips of fissure was deduced under uniaxial compression.(2) According to the theory of progressive stress at the tips of fissure, the mechanical response mechanism of horizontal fissure had been studied under uniaxial compression. In the condition of compression, the stress concentration at the tips of horizontal fissure still existed, but which had relationship with the relative fracture aperture. And the stress concentration would weaken with the increasing of the relative fracture aperture. It was found that:when the relative fracture aperture was equal to 0.005, the stress concentration began to appear. With the relative fracture aperture changing from strong to weak, fissure tip yield failure and fissure central tension failure appeared in order.(3) The fissure inclination angle played a leading role in influencing damage mode of fissure bodies, and the initiation and propagation mode of micro-cracks at the tips of prefabricated fissure was influenced by the fissure distribution.(4) During the loading experiment on specimens with two fissures, single-fissure transfixion failure, two-fissure transfixion failure, and non-fissure transfixion failure appeared in order with the increasing of fissure inclination angle. When the transfixion failure of two fissures occurred on specimens, the failure mode could be divided into tensile failure, shear failure, and tensile-shear compound failure according to the different rock-bridge angle.(5) When the failure occurred on the specimens with ordered multi-fissures, the uniaxial compressive strength would reach the minimum with the fissure inclination angle being a certain value. When the prefabricated fissures were opened, the certain value was 45°, and when they were closed, the value was less than 45°. The reduction of the value was equal to half of the friction angle of fissure surface. And the strength would increase with the increasing (or decreasing) from this value of fissure inclination angle. When the inclination angle of fissures decreased, the added strength was limited, which was just a little larger than the minimum. But when the inclination angle of fissures increased, the strength would increase until it was close to the strength of complete specimen made by this kind of material. And the increasing rate of the strength would increase with the increasing of the fissure inclination angle.