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| Granular discrete element research on semi-circular bending fracture characteristics of anisotropic sandstone under asymmetric loading |
| CHEN Yanan1，2，BIAN Kang1，2，LIU Jian1，2，CUI Deshan3，LI Yiran3 |
| (1. State Key Laboratory of Geomechanics and Geotechnical Engineering，Institute of Rock and Soil Mechanics，Chinese Academy of Sciences，Wuhan，Hubei 430071，China；2. University of Chinese Academy of Sciences，Beijing 100049，China；3. Faculty of Engineering，China University of Geosciences(Wuhan)，Wuhan，Hubei 430074，China) |
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Abstract Reservoir resources often occur in anisotropic jointed rock mass and fracture mode of anisotropic reservoirs is relatively complex，which make it difficult to carry out efficient exploitation only based on engineering experiences. To better understand the fracture characteristics of anisotropic reservoirs，to realize the control and prediction of fracture expansion morphology，and hence，to collect reservoirs more scientifically，this paper uses the discrete element method(DEM) to study fracture characteristics of the anisotropic sandstone by semi-circular bending test under asymmetric loading. By adjusting the asymmetric degree of the bottom bearing， the control of rock mass fracture from pure I mode to pure II mode can be achieved. The main results are as follows：(1) The peak load of the semi-circular bending samples shows obvious anisotropy，showing distribution forms of “W” and “increasing-stable-increasing” with increasing the joint angle，and a trend of “precipitous drop-stable” with increasing the asymmetric coefficient. (2) SCB samples with different notch angles and joint distributions show different failure modes mainly including offset type，bedding type，cut-bedding type and composite bedding type. With increasing the asymmetric coefficient，the stress field in the samples changes，making fracture path of the samples deviate along the movement direction of the bearing. (3) The fracture toughness of the samples obtained by solving the geometric factor，which is obtained based on the calculation of J-integral and by which 3 kinds of asymmetric loading ways of pure II mode，pure I mode and compound mode are designed，shows obvious anisotropy with the change of the joint angle and presents a trend of “precipitous drop and stable” with increasing the asymmetric coefficient. (4) Impacted by the joints，the initial crack angles of pure I mode and pure II mode are respectively distributed in the range of 0°–36.9°and 47.68°–76.12°，which are not exactly the same as the theoretical values.
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2021, Vol. 40 
