Abstract
To study the shear damage and failure characteristics of red sandstone under different normal stress conditions, the failure process of sandstone under three different shear angles (50°, 55°, 60°) were studied by using variable angle shear test device. The shear stress-deformation curves and failure characteristics of sandstone were obtained, and the relationships between shear cracks and acoustic emission impact times, amplitude, peak frequency were established. With the increase of shear angle, the normal stress, shear stress and peak shear stress decrease gradually. The development of micro-cracks in the shear plane appear more earlier. The rock spalling mainly occur in the penetrating area of main and secondary cracks surrounding the two ends of specimen. The spalling degree was obviously weakened with the increase of shear angle. In acoustic emission monitoring,the high frequency signal decreases significantly, which may have a significant corresponding relationship with the rock friction and shear effect. The failure mode of rock changes from plasticity to brittleness. The amplitude changes are concave, and more acoustic emission energy is released at compaction stage and plastic(failure) stage. The results have important guiding value for judging and predicting the instability mechanism of rock engineering.
Highlights
Shear failure is the most common failure form in rock engineering
The shear failure process of sandstone was studied by using variable angle shear test device, the failure and acoustic emission characteristics of sandstone under different normal stress conditions were obtained by using PCI-II acoustic emission system
By observing the development of secondary cracks in the loading process, it was found that the rock spalling mainly occur in the penetrating area of main and secondary cracks surrounding the two ends of the specimen
Summary
Shear failure is the most common failure form in rock engineering. Usually, the shear failure in rock engineering is not the pure shear modebut the shear stress related to normal stress exceeds the limit equilibrium (Jia 2011). The shear failure process of sandstone was studied by using variable angle shear test device, the failure and acoustic emission characteristics of sandstone under different normal stress conditions were obtained by using PCI-II acoustic emission system. According to the analysis of the above literature, domestic and foreign scholars have done amount of work on rock failure characteristics under shear conditions and AE events under different mechanical conditions, the study on rock failure and AE characteristics under different normal stress conditions is few. The shear failure process and acoustic emission characteristics of sandstone under different shear angles were studied in this paper The characteristic parameters such as AE event count, cumulative count, amplitude and peak frequency were used to analyze the mechanical behaviors, and the evolution laws of rock damage were discussed. The achievements of this paper can provide theoretical support for the establishment of shear instability theory and site monitoring of sandstone engineering
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