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The acoustic emission (AE) characteristic signal can reveal the mechanical properties of rock materials and the development characteristics of internal microcracks. Rocks with different mineral development characteristics produce different AE signals during fracture. This study selected variable metagabbros with varying feldspathic development for AE tests under splitting load. The results demonstrated that the characteristics of AE ringing counts during the Brazilian fracture of metagabbro were closely correlated with the content of felsic minerals. The cumulative AE ringing count of metagabbros with feldspar nondevelopment exceeded 250 000, while those of metagabbros with feldspar development did not reach 200 000. As the feldspathic mineral content increases, the AE ringing counts of metagabbro exhibit an increasing trend in the high-energy (1e6–+∞ aJ) and high-amplitude (90–100 dB) intervals. With the development of feldspar minerals, the fracture mode of metagabbro gradually changed from shear failure to tensile failure. The higher the development of felsic minerals, the higher the stress level corresponding to the maximum fractal dimension, the greater the energy released by rock failure, and the more severe the damage. This study is of great significance for revealing the mechanism of rock rupture. [ABSTRACT FROM AUTHOR]

Feldspar vein-intrusive metagabbro is a special geological structure, and different stress angles have an important influence on the fracture mode and deformation characteristics of metagabbro. A Brazilian splitting test on feldspar vein-intrusive metagabbro was performed using three distinct stress angles (0°, 45°, and 90°), and acoustic emission signals and strain characteristics were monitored synchronously during the test. The results showed that the damage pattern of the feldspar vein-intrusive metagabbro was related to the feldspar mineral perforation damage on the main rupture surface. With the increase in stress angle, the percentage of high peak frequency increased gradually. The phenomenon of strain lagging stress appeared in the rock samples before the peak damage. The feldspar minerals played a controlling role in the expansion of microcracks in the feldspar vein-intrusive metagabbro. Significant differences in the local deformation coordination of rocks under different stress angles were observed. The deformation coordination of rock samples with a stress angle of 0° was much lower than that of other rock samples. This study is of great significance for the understanding of the deformation and damage laws of similar geological structures and also provides an important theoretical basis for the stability of deep chambers. [ABSTRACT FROM AUTHOR]

Taking the weakly cemented sandstone of Ordos, China, as the research object, the evolution law between the relative stress of weakly cemented sandstone and the multiparameters of the acoustic emission under different dry-wet cycles was explored, and the critical failure identification mode of weakly cemented sandstone under dry-wet cycle was established. The results show that as the number of dry-wet cycles increases, the wave velocity loss rate gradually increases. Overall, the longitudinal wave loss rate is larger than the shear wave loss rate, indicating that the longitudinal wave is more sensitive to the degradation of weakly cemented sandstone. With an increase in the number of dry-wet cycles, the crack is mainly caused by the main crack penetration failure, and the secondary crack is significantly reduced. The fractal dimension decreases with an increase in the dry-wet cycles and reaches its maximum at 0 dry-wet cycles, which means that 0 dry-wet cycles witness the most complex morphology of fractures within the weakly cemented sandstone. This finding indicates that the dry-wet cycle inhibits the generation and expansion of fractures. The event rate appears to be close to 0 before the rupture, and then the platform oscillates, followed by a sudden increase. The acoustic emission b value is relatively high during the initial stage and then decreases, which is the initial damage process. The elastoplastic phase rises again, the peak stage decreases rapidly, and the weakly cemented sandstone undergoes unstable damage. The change in the acoustic emission entropy value is exactly the opposite of the b value change law. When the weakly cemented sandstone reaches the critical failure state under different dry-wet cycles, the relative stress value is 95%. The test results provide new methods and a basis for the damage evolution mechanism and fracture prediction of weakly cemented sandstone under dry-wet cycles. [ABSTRACT FROM AUTHOR]

During the microstructural analysis of weakly cemented sandstone, the granule components and ductile structural parts of the sandstone are typically generalized. Considering the contact between granules in the microstructure of weakly cemented sandstone, three basic units can be determined: regular tetrahedra, regular hexahedra, and regular octahedra. Renormalization group models with granule- and pore-centered weakly cemented sandstone were established, and, according to the renormalization group transformation rule, the critical stress threshold of damage was calculated. The results show that the renormalization model using regular octahedra as the basic units has the highest critical stress threshold. The threshold obtained by iterative calculations of the granule-centered model is smaller than that obtained by the pore-centered model. The granule-centered calculation provides the lower limit (18.12%), and the pore-centered model provides the upper limit (36.36%). Within this range, the weakly cemented sandstone is in a phase-like critical state. That is, the state of granule aggregation transforms from continuous to discrete. In the relative stress range of 18.12%– 36.36%, the weakly cemented sandstone exhibits an increased proportion of high-frequency signals (by 83.3%) and a decreased proportion of low-frequency signals (by 23.6%). The renormalization calculation results for weakly cemented sandstone explain the high–low frequency conversion of acoustic emission signals during loading. The research reported in this paper has important significance for elucidating the damage mechanism of weakly cemented sandstone. [ABSTRACT FROM AUTHOR]