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

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Rock Mechanics and Rock Engineering Aims and scope Submit manuscript

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.

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Abbreviations

r :

Radius of the specimen

x p, y p, z p :

Coordinate of point P

\(x_{{\text{p}}}^{'},y_{{\text{p}}}^{'},z_{{\text{p}}}^{'}\) :

Coordinate of point \({\text{P}}^{\prime}\)

\(x_{{\text{p}}}^{{''}},y_{{\text{p}}}^{{''}},z_{{\text{p}}}^{{''}}\) :

Coordinate of point \({\text{P}}^{\prime\prime}\)

\({\text{A}}'{\text{B}}'\) :

Width of the undistorted image with a length equal to arc \({\mathop{\rm AB}\limits^{\raisebox{-3pt}{$\frown$}}}\)

\({x_{\text{q}}},{y_{\text{q}}},{z_{\text{q}}}\) :

Coordinate of the camera point

d :

Distance between camera and specimen surface

l :

Width of the overlapping region

D :

Fractal dimension

\(\delta\) :

Side length of squares covering the image

\(N(\delta )\) :

Number of squares covering the image

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Acknowledgements

The research is supported by the National Key Research and Development Project (Grant no. 2017YFC1501201), the National Natural Science Foundation of China (NSFC) (Grant no. 41472257, 41530638, and 41372302), the National Key Research and Development Project (Grant no. 2017YFC0804605), the Special Fund Key Project of Applied Science and Technology Research and Development in Guangdong (Grant nos. 2015B090925016, 2016B010124007), the Special Support Program for High Level Talents in Guangdong (Grant no. 2015TQ01Z344), the Science and Technology Program of Guangzhou (Grant no. 201803030005).

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Correspondence to Zhen Liu.

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Zhou, C., Lu, Y., Liu, Z. et al. An Innovative Acousto-optic-Sensing-Based Triaxial Testing System for Rocks. Rock Mech Rock Eng 52, 3305–3321 (2019). https://doi.org/10.1007/s00603-019-01764-1

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  • DOI: https://doi.org/10.1007/s00603-019-01764-1

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