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Materials 2017, 10(11), 1310; https://doi.org/10.3390/ma10111310

Anisotropic Failure Strength of Shale with Increasing Confinement: Behaviors, Factors and Mechanism

1,2,3
,
1,2,3,* and 4
1
Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
2
Institutions of Earth Science, Chinese Academy of Sciences, Beijing 100029, China
3
College of Earth Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
4
Institute of Crustal Dynamics, China Earthquake Administration, Beijing 100085, China
*
Author to whom correspondence should be addressed.
Received: 25 October 2017 / Revised: 13 November 2017 / Accepted: 13 November 2017 / Published: 15 November 2017
(This article belongs to the Special Issue The Brittle Failure of Different Materials)
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Abstract

Some studies reported that the anisotropic failure strength of shale will be weakened by increasing confinement. In this paper, it is found that there are various types of anisotropic strength behaviors. Four types of anisotropic strength ratio ( S A 1 ) behaviors and three types of anisotropic strength difference ( S A 2 ) behaviors have been classified based on laboratory experiments on nine groups of different shale samples. The cohesion c w and friction angle ϕ w of the weak planes are proven to be two dominant factors according to a series of bonded-particle discrete element modelling analyses. It is observed that shale is more prone to a slight increase of S A 1 and significant increase of S A 2 with increasing confinement for higher cohesion c w and lower to medium friction angle ϕ w . This study also investigated the mechanism of the anisotropic strength behaviors with increasing confinement. Owing to different contributions of c w and ϕ w under different confinements, different combinations of c w and ϕ w may have various types of influences on the minimum failure strength with the increasing confinement; therefore, different types of anisotropic behaviors occur for different shale specimens as the confinement increases. These findings are very important to understand the stability of wellbore and underground tunneling in the shale rock mass, and should be helpful for further studies on hydraulic fracture propagations in the shale reservoir. View Full-Text
Keywords: shale; anisotropic failure; strength anisotropy; confinement; cohesion and friction angle of weak planes shale; anisotropic failure; strength anisotropy; confinement; cohesion and friction angle of weak planes
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Cheng, C.; Li, X.; Qian, H. Anisotropic Failure Strength of Shale with Increasing Confinement: Behaviors, Factors and Mechanism. Materials 2017, 10, 1310.

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