Characterization of rock damage evolution and support timing under true triaxial unloading paths
Min-jie Qi , Guang-ming Zhao , Xiang-rui Meng , Chong-yan Liu , Wen-song Xu , Xin Xu , Cong-hui Zhao , Kai Sun , Bin Zhao
Journal of Central South University ›› 2026, Vol. 33 ›› Issue (1) : 442 -465.
To study the influence of support timing and support strength on the mechanical properties and deformation damage characteristics of a single-sided unloaded rock mass, a true triaxial perturbation unloaded rock testing system was used to conduct rock damage tests on sandstone with different support timing and strength paths. Based on the acoustic emission monitoring system, the spatial and temporal evolution characteristics of the whole process of rock body loaded instability under two stress paths were studied, and the mechanism of the reinforcing effect of stress support on the unloaded rock mass was analyzed. The results show that, within the scope of this study, both earlier applications of shoring and an increase in shoring strength can effectively improve the ultimate bearing capacity of the unloaded rock, which increases the ultimate bearing capacity of the unloaded rock mass by 60.31% and 54.96%, respectively; There is a phenomenon of rebound deformation of the rock mass during sudden changes in stress (single-sided unloading, stress support), which shows opposite expansion and compression platforms on the stress–strain curve; The crack evolution of unloaded rock under different stress support conditions shows the state law of “initial crack activations→middle steady state expansion→late main crack penetration”, and the lagging support significantly accelerates the crack evolution from local activation to main penetration; The single-sided unloading and stress-supporting stages have less influence on the unloading deformations σ1u, σ2u and support deformations σ1t, σ2t in the σ1 and σ2 directions, while they show significant response characteristics to σ3u, σvu and σ3t, σvt, and with the increase of the support strength, the stress-supporting stages σ3t, σvt gradually increase and exceed the deformations generated by the unloading stages σ3u, σvu; The increase of support strength can effectively compensate for the rock stress loss caused by unloading, which makes the maximum, minimum, and volumetric strain support coefficients during the loading and unloading of the rock body increase gradually while the effect on the intermediate principal strain support coefficient is small; During loading, the support strength of rock masses seeks a new bearing area by regulating stress equilibrium states. This process primarily manifests as a shift in the locations of the crushing zone and the main bearing area, accompanied by a corresponding transformation in failure patterns. Consequently, the rock mass transitions from asymmetric three-zone damage under no or weak support to approximate symmetric three-zone damage under strong support. Simultaneously, the main load-bearing area of the rock mass shifts from deep bearing in the unsupported to middle bearing under strong support as the support strength increases.
true triaxial / single-sided unloading / unloading effect / support timing / support strength
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Central South University
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