Abstract
Three-dimensional crack propagation in a rock mass was investigated using a specifically designed material with good transparency and elastoplasticity. The material has properties that are similar to those of the nature sandstone. Hydromechanical tests were conducted to simulate pore pressure in the paper to study the influence of the angle of the primary crack and the water pressure on the mechanical stability of the rock mass. The results indicated that the water pressure accelerated the crack propagation and the failure of the samples. The influence of water pressure on initiation crack strength was not significant but had a significant impact on the peak strength. With the increase in water pressure, the crack initiation strength, penetration strength, and peak strength all decrease in varying degrees. The penetration strength did not only depend on the pore pressure but also exhibited high sensitivity to the inclination angle of the primary crack. The extended finite element method is used to simulate hydraulic fracturing. The simulation results show that the stress near the tip exhibited a cycle of energy accumulation-crack expansion-stress relaxation as the crack expanded, and this finding was consistent with Griffith’s energy theory.
Highlights
Rocks contain a large number of primary joints and fractures, which are the result of long-term geological processes.e existence of joints, cracks, and other structural planes in the rock mass provides natural channels for the flow of groundwater and play a major role in underground oil and gas exploitation. e presence of high-pressure groundwater has negative effects on rock mass engineering projects. e water pressure often causes local tensile stress concentration near rock mass cracks, which results in instability and failure of the rock mass engineering.In 1920, Griffith [1, 2] made important breakthroughs in theoretical and experimental research and laid the foundation for fracture mechanics of brittle materials
When the water pressure is increased to 4 modulus (GPa) Compressive strength (MPa), the expansion speed is obviously accelerated
When the water pressure reaches 6 MPa, the crack grows rapidly, and water inrush is easy to occur in the project
Summary
Rocks contain a large number of primary joints and fractures, which are the result of long-term geological processes.e existence of joints, cracks, and other structural planes in the rock mass provides natural channels for the flow of groundwater and play a major role in underground oil and gas exploitation. e presence of high-pressure groundwater has negative effects on rock mass engineering projects. e water pressure often causes local tensile stress concentration near rock mass cracks, which results in instability and failure of the rock mass engineering.In 1920, Griffith [1, 2] made important breakthroughs in theoretical and experimental research and laid the foundation for fracture mechanics of brittle materials. E existence of joints, cracks, and other structural planes in the rock mass provides natural channels for the flow of groundwater and play a major role in underground oil and gas exploitation. E water pressure often causes local tensile stress concentration near rock mass cracks, which results in instability and failure of the rock mass engineering. Sneddon [4] established an analytical model of the induced stress around a plane with a single crack, which has become the cornerstone of subsequent studies. Considerable achievements have been made in the study of rock mass fractures and mechanical-hydraulic coupling. Waters et al [6] and Dahi Taleghani and Lorenzo [7] believe that widely used techniques such as microseismic methods may show the effect of natural fractures on hydraulic fracture growth only qualitatively and not quantitatively.
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