Numerical simulation of true triaxial unilateral unloading effect of fractured rock

Abstract

PurposeThe interaction between rock mass structural planes and dynamic stress levels is important to determine the stability of rock mass structures in underground geotechnical engineering. In this work, the authors aim to focus on the degradation effects of fracture geometric parameters and unloading stress paths on rock mechanical properties.Design/methodology/approachA three-dimensional Particle Flow Code (PFC3D) was used for a systematic numerical simulation of the strength failure and cracking behavior of granite specimens containing prefabricated cracks under conventional triaxial compression and triaxial unilateral unloading. The authors demonstrated the unique mechanical response of prefabricated fractured rock under two conditions. The crack initiation, propagation, and coalescence process of pre-fissured specimens were analyzed in detail.FindingsThe authors show that the prefabricated cracks and unilateral unloading conditions not only deteriorate the mechanical strength but also have significant differences in failure modes. The degrading effect of cracks on model strength increases linearly with the decrease of the dip angle. Under the condition of true triaxial unilateral unloading, the deterioration effect of peak strength of rock is very significant, and unloading plays a role in promoting the instability failure of rock after peak, making the rock earlier instability failure. Associating with the particle vector diagram and crack coalescence process, the authors find that model failure mode under unilateral loading conditions is obviously distinct from that in triaxial loading. The peak strain in the unloading direction increases sharply, resulting in a new shear slip.Originality/valueThis study is expected to improve the understanding of the strength failure and cracking behavior of fractured rock under unilateral unloading.

Effect of Confining Pressure on the Macro- and Microscopic Mechanisms of Diorite under Triaxial Unloading Conditions

“…Researchers such as Li et al [32], Xiong et al [33], and Yin et al [34] have utilized PFC 2D to investigate the macroscopic mechanical behavior, crack propagation, and evolution of various energy indicators in unloaded rocks, highlighting the impact of unloading rates on microscopic structural damage and fracturing. Furthermore, studies conducted by Zhang [35], Zheng et al [36], and Uxia et al [37] using PFC 3D have explored the initiation, propagation, connectivity, and spatial distribution of microcracks in rocks during unloading, revealing that the unloading effect contributes to post-peak damage and failure in rocks. To address some of PFC's limitations in simulating rock damage processes, new contact models have been developed [38,39], enhancing the application of PFC to numerical simulations of rock unloading.…”