An Innovative Acousto-optic-Sensing-Based Triaxial Testing System for Rocks

Abstract

The failure mechanisms of rocks as a result of hydro-mechanical coupling effects have not been fully understood due to the limited abilities of conventional triaxial test equipment in measuring both the internal and external damage of rocks simultaneously in real time. This study presents an innovative triaxial testing system for detecting the internal and external damage of rocks. The system consists of an innovatively designed built-in acoustic emission sensor, an optical measurement system and a fully transparent pressure chamber. This work shows that the developed system can capture the internal and external damage behaviour of rocks using triaxial tests. The results demonstrate that the developed built-in acoustic emission sensors can measure the internal damage of rock specimens in an aqueous environment during a load test, while the proposed configuration of the optical measurement system together with the developed imaging construction technique can capture the surface crack development of samples. In addition, the acoustic ring-down counts and event counts can be used to detect the internal damage of the rock specimens, and the ring-down counts reach a significantly high level when the maximum axial force is reached. Furthermore, damage to rock specimens due to triaxial loading first occurs internally, and damage then extends externally. The critical failure point of a specimen can be determined when large fluctuations in the crack fractal dimension and ring-down counts occur simultaneously.