Study on the Characteristics of Acoustic Emission Quiet Period in Rocks with Different Elastic Modulus

To study the characteristics of the quiet period of acoustic emission (AE) during the rock failure process, rock models with an abnormal elastic modulus were established based on PFC2D. The calibration of the mesoscopic parameters was performed by the macroscopic mechanical parameters of granite samples obtained in uniaxial compression tests. An abnormal area of 2 × 100 mm2 was set at the center of the model and had two to six times the elastic modulus of the normal area. The evolution law of cracks and the characteristics of the AE quiet period were analyzed in detail. The main conclusions are as follows: (1) The axial stress of the abnormal area rises to the maximum value before the occurrence of the main fracture; in the AE quiet period, the axial stress in the abnormal area of elastic modulus increased by 2%–5%, then decreases rapidly after the AE quiet period. (2) As the elastic modulus increases, the interval time of the AE quiet period is prolonged by one to five times. Furthermore, many cracks occurred mainly in the abnormal area, and then a few cracks were generated before the AE quiet period. Cracks mainly focus on the elastic modulus abnormal area and propagate beyond the normal area after the AE quiet period. (3) The Z value is used as the indicator of the significance of the AE quiet period, and it changes with the elastic modulus of the abnormal area. The Z value without an abnormal area is the minimum of 1.1, and the elastic modulus of the abnormal area was set to three times the normal area, the Z value reaches the maximum of 6.08, and the Z value changes with the elastic modulus. The distribution of different elastic modulus is an important factor concerned with the characteristics of the AE quiet period