Method for observing rock and soil sample shear band inclination angle evolution rules under two types of formation conditions

The invention provides a method for observing rock and soil sample shear band inclination angle evolution rules under original and real-time formation conditions. The method includes acquiring a digital image, comprising speckle surfaces, of a sample by shooting devices under a loading condition; by a digital image correlation method, acquiring maximum shear strain fields of the sample under the original and real-time formation conditions; by an interpolation method, acquiring maximum shear strain fields good in smoothness in an area comprising measured shear bands; deleting redundant data according to roughly-estimated widths and inclination angles of the measured shear bands to acquire positions of all points on center lines of the measured shear bands, and acquiring inclination angles of planer shear bands and spatial shear bands by a fitting method. The method has the advantages that the rules that the shear band inclination angles evolve according to stress, strain and time under the original and real-time formation conditions can be acquired; automated, rapid and accurate measurement of the shear band inclination angles can be achieved; the method is suitable for measuring the inclination angles of plane inclination strain concentration bands and spatial shear planes of various materials.