Abstract
The cracking behavior of precracked rocks under mechanical-hydraulic loading is of great significance in underground openings or petroleum engineering. In this study, an advanced in-house finite element code PANDAS proved to be effective in simulating coupled fracturing processes under complex geological conditions was used to simulate the cracking propagation of the precracked rocks under mechanical loading and mechanical-hydraulic loading with different strength parameters. The simulation results demonstrated that (1) the cracks initiate by the induced stresses, and multiple types of tensile cracks originate from the preexisting flaws; (2) crack propagation patterns under mechanical-hydraulic loading were studied with different strength parameters, and the multiple patterns of pure tensile, main tensile, tensile-shear, main shear, and pure shear were observed; and (3) the timing of hydraulic loading has a significant impact on the fracturing process: when hydraulic loading was carried out in the phase of main crack propagation, the tensile fracture was promoted and the shear fracture was inhibited; when hydraulic loading was carried out in the phase of shear crack propagation, the shear fracture and tensile fracture were stimulated. The numerical simulation results are in good agreement with the experimental results by previous studies. The research on the cracking behavior of precracked rocks under mechanical and hydraulic loading will expand the application prospect in the fields of coal seam gas reservoir and tunnel water inrush.
Highlights
In the process of underground engineering construction such as traffic tunnel excavation, water conservancy project, and coal and oil exploitation, the geological environment of high ground stress and strong seepage pressure is becoming more and more complex
Some studies suggested that tensile cracks are initially originating from flaws under compressive loading, and the tensile cracks are subsequently followed by shear cracks [5]
Some more complex conditions of the actual work need to be further considered to simulate the cracking behavior and propagation mechanism of precracked rock, such as different strength parameters and hydraulic coupling. To address this knowledge gap, this study was based on the porous mechanical-hydraulic coupled finite element methods (FEM) and the continuum damage theory, and an in-house finite element code PANDAS was used to simulate the cracking behavior of precracked rock [21,22,23]
Summary
In the process of underground engineering construction such as traffic tunnel excavation, water conservancy project, and coal and oil exploitation, the geological environment of high ground stress and strong seepage pressure is becoming more and more complex. Some more complex conditions of the actual work need to be further considered to simulate the cracking behavior and propagation mechanism of precracked rock, such as different strength parameters and hydraulic coupling. To address this knowledge gap, this study was based on the porous mechanical-hydraulic coupled FEM and the continuum damage theory, and an in-house finite element code PANDAS was used to simulate the cracking behavior of precracked rock [21,22,23]. The cracking behaviors that originate and propagate from the flaws with different strength parameters in rock samples were investigated in this study On this basis, how the crack behaviors propagate under the mechanical-hydraulic loading and the influence of hydraulic action time sequence was examined. This research is expected to enhance the awareness of the instability process of crack damage evolution under complex stress environments, as well as the mechanism of crack formation and propagation
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