Abstract
In order to investigate the relationship between rock microfracture mechanism and acoustic emission (AE) signal characteristic parameters under split loads, the MTS322 servo-controlled rock mechanical test system was employed to carry out the Brazilian split tests on granite, marble, sandstone, and limestone, while FEI Quanta-200 scanning electron microscope system was employed to carry out the analysis of fracture morphology. The results indicate that different scales of mineral particle, mineral composition, and discontinuity have influence on the fracture characteristics of rock, as well as the b-value. The peak frequency distribution of the AE signal has obvious zonal features, and these distinct peak frequencies of four types of rock fall mostly in ranges of 0–100 kHz, 100–300 kHz, and above 300 kHz. Due to the different rock properties and mineral compositions, the proportions of peak frequencies in these intervals are also different among the four rocks, which are also acting on the b-value. In addition, for granite, the peak frequencies of AE signals are mostly distributed above 300 kHz for granite, marble, and limestone, which mainly derive from the internal fracture of k-feldspar minerals; for marble, the AE signals with peak frequency are mostly distributed in over 300 kHz, which mainly derive from the internal fracture of dolomite minerals and calcite minerals; AE signals for sandstone are mostly distributed in the range of 0–100 kHz, which mainly derive from the internal fracture of quartz minerals; for limestone, the AE signals with peak frequency are mostly distributed in over 300 kHz, which mainly derive from the internal fracture of granular-calcite minerals. The relationship between acoustic emission signal frequency of rock fracture and the fracture scale is constructed through experiments, which is of great help for in-depth understanding of the scaling relationship of rock fracture.
Highlights
From a microscopic point of view, solids are made up of strong and rigid phases or crystalline grains, especially ceramic, rock, and concrete materials
The parameter b describes the size distribution scaling, which is often referred to as b-value, and the spatial and temporal variations of b-value are always regarded as an essential clue for earthquake precursor
AdB is the maximum amplitude of an acoustic emission event expressed in decibels: AdB = 20lg Amax where Amax is the maximum amplitude value of AE event expressed in microvolts
Summary
From a microscopic point of view, solids are made up of strong and rigid phases or crystalline grains, especially ceramic, rock, and concrete materials. Such elastic waves are derived from microscopic dislocations; twinned crystals; crystal interfaces and the slip; and separation of macroscopic mineral grains, joints, and other weak planes; all of these are referred to as AE activity [2,3,4,5,6] It is because of the complex composition of rock material that the cracks inside the rock sample, from microscopic to macroscopic level, will be in different scales and have different fracturing mechanisms under various loading conditions. The combination of SEM and AE technology will provide excellent insights into the microscopic fracture mechanism and the characteristics of corresponding AE signals For this purpose, four types of rock materials were used to perform Brazilian splitting tests for this study: granite, marble, sandstone, and limestone.
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