Study on Splitting Intensity and Acoustic Emission Characteristics of Brazilian Deep Gray Sandstone at Different Scales

Abstract

In order to determine the influence of size on the mechanical properties of sandstone and acoustic emission damage characteristics, the Brazilian splitting test of 6 sandstone samples with diameters of 25mm, 37mm, 50mm, 69mm, 80mm and 100mm was carried out by using the rock weak surface direct shear instrument and acoustic emission monitoring system The effects of size change on the splitting strength, deformation, acoustic emission activity and damage characteristics of rock samples are discussed. The results show that the larger the specimen size is, the more original defects are contained in the specimen, which has a great influence on the development trend of stress-strain curve, peak strength and peak strain during loading. With the increase of sample size, the peak strength and peak strain become smaller and smaller, and the ratio of peak compressive strain to peak tensile strain remains in the range of 2~4 times. According to the development characteristics of acoustic emission signals, the whole process of rock damage is divided into four stages: micro-crack compaction stage, new crack generation and expansion stage, crack rapid expansion stage and failure stage. The diameter sample of 69mm~100mm showed almost no AE signal at the beginning of test loading, and the activity of acoustic emission signal is intense at the moment of failure.The larger the specimen size, the larger the stress value and b value corresponding to the fracture entering the instability expansion stage. Tensile microcracks are the main types of cracks in the splitting test, and with the increase of the size, the shear microcracks gradually decrease, and the tensile microcracks increase.