The Lateral Strain Response has been used in the uniaxial test, yet there is little research with its applicability and application conditions in the triaxial test. We studied it with 2 kinds of extensometer in different calibration accuracy by the uniaxial and triaxialAE (acoustic emission) tests data. Determine the crack initiation by using the LSR method. Combined with the stress-strain data and acoustic emission data in the compression test, we can get the crack initiation from theAE date. Comparing these crack initiations in different calibration accuracy, we can get the following conclusions: The two different crack initiations which we get from the LSR method and the AE method are with the correlation coefficient of more than 0.90 on the condition that the calibration accuracy is 0.001 um. The LSR method can be applied to determine the crack initiation in the triaxial test in this situation; The LSR method cannot be used on the condition that the calibration accuracy is less than 0.1 um.
Granite is a kind of hard and low-porosity rocks. Researchers in all over the world[1–6] processed many studies on damage of the granite one of the typical brittle solids, and the results insist that the stress-strain curve of the brittle solids before the peak stress could be separated in 4 phases: I phase is the stage when the primary fissures are closed within the rocks. II phase is the linear elastic deformation stage, III phase is the crack steady expansion stage. IV phase is the crack unsteady expansion stage. Crack initiation, as the first step of the low-porosity rocks' rupture, it is an important theoretical significance to the research of crack initiation of the rocks, and it could be important to determine the crack initiation of granite cracks for deep underground engineering practice. Some recent research suggested that the crack initiation could be used for analysis of the in situ fracture strength, which is usually observed at the underground excavation caves of brittle rocks with medium and large fissures. However, there is no stress test recommendation from ISRM for the crack initiations.
