Acoustic emissions (AE) and elastic wave (P-wave) velocities were measured on granite and marble under triaxial compression. The triaxial chamber capable of accommodating many AE sensors was made and transducer vessels measuring seismic wave velocities in axial and lateral direction simultaneously were devised. The measured AE parameters such as AE hit and amplitude were analyzed synthetically and quantitatively to determine the fracture process of rock. Moreover, AE source locating was carried out by considering the anisotropy and change of elastic wave velocity according to the applied stress state. The Kaiser effect was verified at constant confining pressure as well as at multistage confining pressures. Experimental MethodRock Specimen. Rock specimens used in the test were granites and marbles from Korea. Specimens were NX core of diameter 53-54 mm and length to diameter ratio was about 2. Both ends of specimens were ground parallel to within 0.02 mm and specimens were dried at 105°C before testing. Physical properties of rock specimens used in the test are shown in Table 1.Testing Method. Tests were carried out on a 200 ton capacity universal testing machine. Specimens were mounted in triaxial chamber as shown Fig. 1.Two strain gages and six AE sensors (Piezoelectric transducer, PZT) were attached to the specimen. Small size of the PZT allows many AE channels to be set in the limited space of triaxial chamber. The specimen was coated with silicon in order to prevent hydraulic oil penetrating the rock specimen. Signals from strain gages and PZT are transmitted from the chamber by plugs.

The objective of this study is to investigate acoustic emission (AE) characteristics of rock-concrete interfaces under shear loading. AE was monitored in direct shear tests of split tension under constant normal load. The locations of AE sources distributed over the entire shear zone before the shear stress reached the converged residual value. After the residual shear stress had been attained, the sources were localized. In the initial stages of the shear tests, under a condition of low shear stress, the rates of AE counts and energy were proportional to the shear stress. The maximum rates of AE counts and energy were observed when the stress dropped after peak shear stress. The surface asperity failure and the occurrence of shear displacement could be observed by measuring AE counts and energy.

Brazilian test which also known as indirect tensile test is widely used to evaluate the tensile strength of rock. Discrete element method (DEM) together with finite element method (FEM) approach was used to investigate numerically the response of granite material under Brazilian test for indirect measurement of tensile strength of rocks. The calibration analysis performed in this study using the commercial software LS-DYNA. It has been attempted to calibrate the micro-parameters in bonded particle model of granite rock for numerical modelling. In hybrid DEM-FEM simulation, the rock specimen was modelled in DEM while the steel plates were simulated using FEM. This numerical analysis is compared to experimental data of Brazilian test. It shows that the combination of numerical methods simulation could reproduce the trends of experimentally observed stress-strain curve of granite rock under tensile loading. Besides that, the hybrid DEM-FEM simulation also shows the same failure mode of granite specimen. Comparison between experimental data and numerical analyses is presented and discussed.

To investigate failure and damage mechanisms in rock, a moment tensor inversion procedure named the SiGMA (Simplified Green's function for Moment tensor Analysis) was applied to acoustic emission (AE) data measured during uniaxial compression and three-point bending tests. In addition, the relative crack volume estimated from the moment tensor analysis was used as the damage index. This paper reports the applicability of the moment tensor analysis to estimate failure planes in rock, as well as to investigate rock failure mechanisms.

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