Liang Yanxu, She Haicheng, Ding Wangji, She Haidong
School of Urban Construction, Yangtze University, Jingzhou, China.
Key Laboratory of Reservoir and Dam Safety Ministry of Water Resources, Nanjing, China.
PLoS One. 2025 Sep 10;20(9):e0329437. doi: 10.1371/journal.pone.0329437. eCollection 2025.
To reveal the microscopic damage evolution law of rocks under the effect of unloading disturbances with different amplitudes, electron microscope scanning, nuclear magnetic resonance (NMR), and triaxial compression tests were carried out. The evolution patterns of surface and internal pore types and mechanical properties of rock specimens after unloading perturbation were analyzed. In this paper, a classification of the ratio of dmax/dmin (dmax and dmin refer to the maximum and minimum pore size of each pore, respectively) is proposed to examine the pore and crack evolution extension development on the surface of the specimen. Meanwhile, the T2 energy spectrum with pore size classification is used to examine the damage quantification law of the pore and crack extension evolution inside the specimen. Finally, the statistical damage model of unloaded disturbed rock is established through theoretical derivation, and the accuracy of the model is verified by experimental data. The study shows that: (1) With the increase of unloading amplitude, there is an increase in the number of nascent cracks and a tendency to expand, which is caused by shear extension cracks; with the increase of unloading amplitude, there is a tendency for the microporosity to shift to the mesoporosity, and the mesoporosity has a tendency to shift to the macroporosity, and there is a decrease in the number of micropores as a whole, which indicates that there is almost no new pore sprouting. (2) When the unloading amplitude is less than 20MPa, with the increase of the unloading amplitude, the pore ratio and expansion rate of the specimen increase slowly; when the unloading amplitude is more than 20MPa, with the increase of the unloading amplitude, the pore ratio and expansion rate of the specimen have a significant tendency to increase. (3) With the increase of unloading amplitude, the shale shear strength limit value decreases more slowly, the modulus of elasticity and shear strength also show a similar pattern of change, and the same way to derive the rock Poisson's ratio does not change much.
为揭示不同幅度卸荷扰动作用下岩石的细观损伤演化规律，开展了电子显微镜扫描、核磁共振（NMR）以及三轴压缩试验。分析了卸荷扰动后岩石试件的表面和内部孔隙类型演化模式及力学性能。本文提出了dmax/dmin（dmax和dmin分别指每个孔隙的最大和最小孔径）比值分类法，以研究试件表面孔隙和裂纹的演化扩展发育情况。同时，采用按孔径分类的T2能谱来研究试件内部孔隙和裂纹扩展演化的损伤量化规律。最后，通过理论推导建立了卸荷扰动岩石的统计损伤模型，并利用试验数据验证了模型的准确性。研究表明：（1）随着卸荷幅度的增大，新生裂纹数量增加且有扩展趋势，这是由剪切扩展裂纹引起的；随着卸荷幅度的增大，微孔有向中孔转变的趋势，中孔有向大孔转变的趋势，整体微孔数量减少，表明几乎没有新的孔隙萌生。（2）当卸荷幅度小于20MPa时，随着卸荷幅度的增大，试件的孔隙率和膨胀率缓慢增加；当卸荷幅度大于20MPa时，随着卸荷幅度的增大，试件的孔隙率和膨胀率有显著增加的趋势。（3）随着卸荷幅度的增大，页岩抗剪强度极限值下降较慢，弹性模量和抗剪强度也呈现类似的变化规律，推导岩石泊松比的方式变化不大。
