Experimental Study on the Spatial–Temporal Failure Characteristics of Red Sandstone with a Cemented Structural Surface under Compression

Abstract

A geological structural surface frequently appears in underground engineering and it significantly affects the stability of engineering structures. To elucidate the spatial–temporal failure characteristics of discontinuities between rocks, red sandstone with a firmly cemented discontinuity was investigated under uniaxial compression. The results revealed that adding a strong binder to rock discontinuities can improve the shear strength and stability of rock mass. The stress curve indicated that red sandstone specimens had elastic–brittle failure characteristics without obvious plastic deformation. The acoustic emission ring counts did not have large fluctuations, and its values were smaller (less than 2.5 × 10 4 /s) at elastic deformation stage, which was termed as the “quiet period”. The acoustic emission ring counts initially exhibited an obvious jump increase phenomenon at the forthcoming brittle failure stage before stress curve produced an obvious turning point, and then, it entered the “relatively quiet period”. Based on the acoustic emission index (rise angle and average frequency), at the initial destruction stage of rocks, the types of internal fractures were simple and clearly (tensile cracks or shear cracks), and the fracture location was also relatively scattered inside specimens. Subsequently, the internal fracture developed into mixed tensile and shear cracks, and then, the fracture location exhibited a progressive evolution trend in the vertical space of specimens.

Spatio-Temporal Distribution of the Sources of Acoustic Events in Notched Fiber-Reinforced Concrete Beams under Three-Point Bending

“…In other words, it makes it possible to localize the points where the damage mechanisms are activated, at any time instant from the onset of loading up to the final macroscopic fracture. The spatial evolution of the position of the sources of the acoustic events has been used as a tool for the localization of the areas of intense microcracking activity by many researchers worldwide [ 1 , 25 , 26 , 27 , 28 ], as well as an index for the quantification of the degree of spatial concentration or dispersion (or, in other words, of the spatial “density”) of the sources of microcracking [ 29 , 30 ].…”