Study of Damaged Zone around Circular Opening Using Acoustic Emission Technique

One of the methods used to investigate the damaged zone in rock structure is the acoustic emission method. This method is based on receiving the elastic waves that are produced by deformation and cracking of the rock mass around the underground excavation. In this research, a study is conducted on the rock samples by a numerical method to investigate the damaged zone caused by the excavation of circular space on it. For this purpose, 33 cube samples of three different material types including sandstone, concrete, and cement-plaster mortar are prepared. A circular hole is drilled in the center of each sample. The hole diameter is 20 or 25 mm. The samples are loaded uniaxially or biaxially with different stress rates. It is tried to study the acoustic events occurring in the samples during the test, and their locations are investigated. Then the experiments are evaluated by a numerical method using the FLAC3D software and some developed codes. The relation between the sample damaged zone where the acoustic events have occurred during the loading period and the numerical elements that reach a degree of tensile and shear yield is studied. The results obtained show that the amount of cumulative acoustic parameters in cement-plaster mortar specimens is more than the others. In fact, the finer grains, the more amounts of energy and counts will be produced. Also, the results show that with increase in the lateral pressure and loading rate, the amount of cumulative energy and counts decreases.