3D DEM simulation of hard rock fracture in deep tunnel excavation induced by changes in principal stress magnitude and orientation

• Published in: Journal of Rock Mechanics and Geotechnical Engineering Vol. 16; no. 10; pp. 3870 - 3884
• Main Authors: Wang, Weiqi, Feng, Xia-Ting, Wang, Qihu, Kong, Rui, Yang, Chengxiang
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2024; Elsevier
• Subjects: Deep hard rock tunnel; Fracture mechanism; Magnitude and orientation of principal stress; Three-dimensional (3D) discrete element model (DEM); Transient unloading; Fracture mechanism; Deep hard rock tunnel; Magnitude and orientation of principal stress; Transient unloading; Three-dimensional (3D) discrete element model (DEM)
• ISSN: 1674-7755
• DOI: 10.1016/j.jrmge.2023.12.003

To achieve the loading of the stress path of hard rock, the spherical discrete element model (DEM) and the new flexible membrane technology were utilized to realize the transient loading of three principal stresses with arbitrary magnitudes and orientations. Furthermore, based on the deep tunnel of China Jinping Underground Laboratory II (CJPL-II), the deformation and fracture evolution characteristics of deep hard rock induced by excavation stress path were analyzed, and the mechanisms of transient loading-unloading and stress rotation-induced fractures were revealed from a mesoscopic perspective. The results indicated that the stress–strain curve exhibits different trends and degrees of sudden changes when subjected to transient changes in principal stress, accompanied by sudden changes in strain rate. Stress rotation induces spatially directional deformation, resulting in fractures of different degrees and orientations, and increasing the degree of deformation anisotropy. The correlation between the degree of induced fracture and the unloading magnitude of minimum principal stress, as well as its initial level is significant and positive. The process of mechanical response during transient unloading exhibits clear nonlinearity and directivity. After transient unloading, both the minimum principal stress and minimum principal strain rate decrease sharply and then tend to stabilize. This occurs from the edge to the interior and from the direction of the minimum principal stress to the direction of the maximum principal stress on the ε1-ε3 plane. Transient unloading will induce a tensile stress wave. The ability to induce fractures due to changes in principal stress magnitude, orientation and rotation paths gradually increases. The analysis indicates a positive correlation between the abrupt change amplitude of strain rate and the maximum unloading magnitude, which is determined by the magnitude and rotation of principal stress. A high tensile strain rate is more likely to induce fractures under low minimum principal stress.