(2)

Fracture (fault) reactivation can lead to dynamic geological hazards including earthquakes, rock collapses, landslides, and rock bursts. True triaxial compression tests were conducted to analyze the fracture reactivation process under two different orientations of Q2, i.e. Q2 parallel to the fracture plane (Scheme 2) and Q2 cutting through the fracture plane (Scheme 3), under varying Q3 from 10 MPa to 40 MPa. The peak or fracture reactivation strength, deformation, failure mode, and post-peak mechanical behavior of intact (Scheme 1) and pre-fractured (Schemes 2 and 3) specimens were also compared. Results show that for intact specimens, the stress remains nearly constant in the residual sliding stage with no stick-slip, and the newly formed fracture surface only propagates along the Q2 direction when Q3 ranges from 10 MPa to 30 MPa, while it extends along both Q2 and Q3 directions when Q3 increases to 40 MPa; for the pre- fractured specimens, the fractures are usually reactivated under all the Q3 levels in Scheme 2, but fracture reactivation only occurs when Q3 is greater than 25 MPa in Scheme 3, below which new faulting traversing the original macro fracture occurs. In all the test schemes, both epsilon 2 and epsilon 3 experience an accumulative process of elongation, after which an abrupt change occurs at the point of the final failure; the degree of this change is dependent on the orientation of the new faulting or the slip direction of the original fracture, and it is generally more than 10 times larger in the slip direction of the original fracture than in the non-slip direction. Besides, the differential stress (peak stress) required for reactivation and the post-peak stress drop increase with increasing Q3. Post-peak stress drop and residual strength in Scheme 3 are generally greater than those in Scheme 2 at the same Q3 value. Our study clearly shows that intermediate principal stress orientation not only affects the fracture reactivation strength but also influences the slip deformation and failure modes. These new findings facilitate the mitigation of dynamic geological hazards associated with fracture and fault slip. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

来源平台：JOURNAL OF ROCK MECHANICS AND GEOTECHNICAL ENGINEERING