Advanced acoustic emission analysis of brittle and porous rock fracturing

Abstract

Abstract. Analysis of Acoustic Emission (AE) induced during brittle and porous rock fracturing at variety of loading conditions has been performed. On the base of advanced analysis of AE parameters, ultrasonic velocities and mechanical data we found that regardless of applied loading conditions the process of rock fracture can be separated into two main stages: (A) accumulation of non-correlated cracks localized almost randomly in the whole volume of uniformly stressed rock. (B) Final stage of sample fracturing could be characterized by appearance of AE nucleation site followed by initiation and propagation of the macroscopic fault. Contribution of tensile sources is reduced significantly, shear type and pore collapse type events dominate during propagation of a fracture process zone through the sample regardless of applied loading conditions. In the case of porous rock, nucleation of compaction bands could be clearly identified by the appearance of AE clusters inside the samples. Microstructural analysis of fractured samples shows excellent agreement between location of AE hypocenters and faults or the positions of compaction bands, confirming that advanced AE analysis is a powerful tool for the process of rock fracture investigation.

The effects of intermediate principle stress on the mechanical behavior of transversely isotropic rocks: Insights from DEM simulations

“…Similarly, when σ 3 = 70 MPa, the ratio increased from 1.75 (at σ 2 = σ 3 ) to 2.44 (at σ 2 = σ 1 ). Similar findings have also been reported in other studies . Stanchits et al performed conventional triaxial tests on intact samples of granite and sandstone rocks under different confining pressures of σ 3 = 10 and 60 MPa and employed acoustic emission to study the impact of the confinement on the tensile and shear components of cracking in the rock samples.…”

“…Similar findings have also been reported in other studies . Stanchits et al performed conventional triaxial tests on intact samples of granite and sandstone rocks under different confining pressures of σ 3 = 10 and 60 MPa and employed acoustic emission to study the impact of the confinement on the tensile and shear components of cracking in the rock samples. They observed a larger contribution of shear cracks relative to tensile cracks with higher confining pressure, along with compaction bands, owing to grain crushing and pore collapse.…”

Microearthquakes preceding a M4.2 Earthquake Offshore Istanbul

“…A plethora of laboratory rock deformation experiments, for example, are known to show sequences of much smaller failures preceding a through-going rupture 2 , 3 . These laboratory tests also showed that shortly before failure the spatial correlation of small failures increased significantly 4 . In the past, such small-scale failure processes have not been commonly observed for natural earthquakes along plate boundaries.…”

Microearthquakes preceding a M4.2 Earthquake Offshore Istanbul

“…A plethora of laboratory rock deformation experiments, for example, are known to show sequences of much smaller failures preceding a through-going rupture 2,3 . These laboratory tests also showed that shortly before failure the spatial correlation of small failures increased significantly 4 . In the past, such small-scale failure processes have not been commonly observed for natural earthquakes along plate boundaries.…”