Study on grey feature of surface strain field during deformation and failure of coal rock mass

In order to characterize the deformation and failure law of coal rock, this paper carries out uniaxial compression tests of coal rock specimens, and obtains grey scale images of surface strain field by using digital speckle observation system. Based on the grey scale images of the surface strain field, the grey scale histogram was calculated and the grey scale parameters were extracted to analyze the grey scale evolution characteristics, and then characterize the deformation and damage of the coal rock. The results showed that the specimens were classified into slow failure, instantaneous failure and interval failure according to the time sequence of the appearance of cracks on the surface of the specimens. During the damage process, the grey scale histograms show a tendency to move from high grey level to low grey level, and there are obvious differences in the changes of the grey scale histogram wave peaks of the samples of different damage types; the change of grey scale smoothness can effectively reflect the evolution law of the fissure, while the grey scale energy and grey scale entropy reflect the complexity of the deformation and destruction process of the coal rock and the degree of destruction.