Study on mesoscopic failure mechanism of grout-infilled sandstone under uniaxial compression using an improved AE localization technique

Abstract

In this paper, to study the influence of grouting on meso-failure mechanism, acoustic emission (AE) localization technique was used to monitor the micro-cracking during the uniaxial compression tests on single flawed sandstone specimens with or without grouting. Due to the inhomogeneous geometrical structure of the flawed specimens, the mesoscopic damage evolution is also inhomogeneous during the loading process. As a result, the wave velocity of the specimens varied temporally and spatially, which greatly increased the difficulty in accurate AE localization. To solve this problem, the wave velocities versus the axial load for the studied sandstone were first measured, and the stress concentration effect near the flaw was also theoretically analyzed. Accordingly, the localization arithmetic was also improved to match the complex wave velocity field. Results show that compared to the specimens without grouting, more microcracks (particularly the shear microcracks) are induced in the grout-infilled specimens prior to the final failure of the specimens. Moreover, the effect of grouting on microcrack initiation also varies with the oblique angle of the flaw. For θ (flaw inclination) ≤30°, grouting significantly increases the shear microcrack at macrocrack propagation stage which states that the axial tensile cracking was limited by the supporting effect of the grout material and made the failure mode trend to shear mode. For θ = 45° and 60°, grouting improved the ratio of shear microcrack during the whole failure process, indicating that the direction of maximum shear stress is close to the flaw direction. Hence, failure develops in stable shear mode. For θ = 75° and 90°, the primary microcrack generated during the first macrocrack initiation changed to shear mode, but the grouting has little influence on the subsequent crack propagation. So that, the reinforcement effect is poor in this set of specimens.