Abstract
In deep mining, granite is stored with high energy duing to its structural integrity and brittleness. Rock bursts usually occur because stress changes and mining disturbances during mining, which seriously threaten safe production. Focusing on the factor -water- which may reduce the brittleness and rockburst tendency of granite, this paper quantitatively analyzes the brittleness index and AE characteristics of dry and water granite under uniaxial loading. The results show that the peak strength and elastic modulus of the water granite are reduced. The damage degree of the water sample is larger than that of the dry sample, and the brittle failure is significantly reduced. The cumulative number of acoustic emission (AE) events in water granite is significantly reduced compared to the dry sample, which is a decrease of 31.5%. However, AE event rate is higher than that of dry granite in the late loading period; AE quiet period of water granite lasts longer and is more obvious than that of dry granite. Dry granite stores and releases more energy during the whole loading process, and the proportion of high energy level AE events in the later stage of loading is higher. The b value of the two samples show a downward trend with fluctuation in the critical state of fracture and a jump increases at the moment of instability. The decrease of b values of dry granite is larger than that of water granite. Results prove that the decline of AE b value of granite can be taken as the precursor of rock burst, and water can significantly reduce the rock burst tendency of granite.
Highlights
The stress environment of underground rock mass engineering is complicated and the elastic energy accumulated in the rock mass is released in the form of elastic wave due to mining activities and frequent microseismicity breaking stress balance, which is accompanied by the change of rock mass structure and even instability (Zhao et al, 2015; Dong et al, 2018; Peng et al, 2020)
Since the b value analysis, which originated from the seismological research, was introduced into the laboratory-scale acoustic emission (AE) research, a lot of discussions have been made on the improvement of algorithms, the influencing factors, and the changes in the b value in the process of rock mass instability and failure
Acoustic emission b value is used as a measure to characterize the development of cracks
Summary
The stress environment of underground rock mass engineering is complicated and the elastic energy accumulated in the rock mass is released in the form of elastic wave due to mining activities and frequent microseismicity breaking stress balance, which is accompanied by the change of rock mass structure and even instability (Zhao et al, 2015; Dong et al, 2018; Peng et al, 2020). The effect of water on the activity and b value of AE events during rockburst incubation was emphatic discussed It is of great theoretical significance and engineering application value to study the change of the mechanical strength characteristics and the rockburst tendency of granite as a typical brittle rock mass after hydration combined with AE technology. The loading equipment was the MTS322 material test system (load the 50 mm × 50 mm × 100 mm sample) and the MTS815 Flex test GT rock mechanics test system (load the 100 mm × 100 mm × 200 mm sample), which performed the static, dynamic, normal temperature, high temperature, high pressure, and failure mechanics experiments of brittle materials such as rock and concrete It recorded load, stress, displacement and strain values in real time, and simultaneously draws loaddisplacement, stress-strain curves. Before the experiment, checked the installation of the specimen, the coupling degree of AE sensor and debugged the equipment
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