Numerical calculation and stress analysis of crack evolution in coal with a central hole under nonuniform load

摘要

The initiation and evolution of the cracks around the hole in coal specimens with a central hole under different uniform loads are studied by the rock failure process analysis software RFPA2D. The results show that homogeneity not only has an influence on the peak strength of coal specimens, but also on the crack propagation directly. The lower homogeneity, the more extensive the stress concentration areas, the rougher the surface crack, and the more irregular the crack propagation path. However, homogeneity has a certain impact on acoustic emission (AE) number and instantaneous effective coalescence rate of cracks, but the influence degree is significantly lower than that under nonuniform load gradient and original cracks. Nonuniform load can cause the obvious stress concentration on the higher load area of the coal specimens (right side), which mainly reflects the micro-crack initiation in the area, and the greater the nonuniform load gradient, the more significant is this trend. The peak stress of models does not change with the change of load forms (the change from uniform load to nonuniform load), but nonuniform load will accelerate the effective coalescence of the surface crack, and the larger the nonuniform load, the shorter the time to achieve the effective coalescence of the surface crack. The original cracks with a certain inclination weaken the stress concentration around the hole. When the dip angle of original crack reaches a certain range (such as 45 degrees), this trend will be more obvious. But it is not closely related to the homogeneity of the coal and the size of the load gradient, and has a certain universal applicability. Finally, the stress around circular tunnel is analyzed based on the theory of elastic mechanics, and a criterion for judging the crack initiation around the laneway is proposed.