Huang Tianzhu, Xu Xiaoliang, Wang Lehua, Li Jianlin, Xu Jianwen
Key Laboratory of Geological Hazards On Three Gorges Reservoir Area, Ministry of Education, China Three Gorges University, Yichang City, 443002, Hubei Province, China.
College of Civil Engineering and Architecture, China Three Gorges University, Yichang City, 443002, Hubei Province, China.
Sci Rep. 2024 Sep 6;14(1):20779. doi: 10.1038/s41598-024-71680-0.
Rocks exhibit various mechanical properties under different stress conditions, with changes during unloading having significant implications for geological engineering safety. This study carried out triaxial loading and unloading mechanical tests on sandy slate to investigate its mechanical properties, deformation characteristics, and failure mechanisms at different initial stress levels and stress paths. The results showed that during the unloading process, the deformation modulus (E) of the sandy slate decreased, and the Poisson's ratio (μ) gradually increased. This indicates that significant volume expansion of the rock is the dominant factor in its deformation and failure. The exponential function can be used to describe the evolution of E and μ with confining pressure during unloading. The damage stress of the rock under unloading conditions was lower than that under loading conditions, suggesting that unloading led to an earlier onset of volumetric expansion in the sandy slate. Under conditions where the initial axial stress level approached the damage stress, the mechanical properties were most significantly affected by unloading. Compared to loading conditions, when the initial axial stress level was at 70% of the peak strength, the cohesion (c) decreased by 15.77 to 29.37%, while the internal friction angle (φ) increased by 1.88 to 5.14%. The rock's failure process can be divided into four stages based on the development of microcracks. Unloading during the stages of microcrack initiation and propagation can lead to tensile cracks of varying degrees, resulting in different mechanical properties and failure characteristics under loading and unloading conditions.
岩石在不同应力条件下呈现出各种力学性质，卸载过程中的变化对地质工程安全具有重要影响。本研究对砂质板岩进行了三轴加卸载力学试验，以研究其在不同初始应力水平和应力路径下的力学性质、变形特征及破坏机制。结果表明，在卸载过程中，砂质板岩的变形模量（E）减小，泊松比（μ）逐渐增大。这表明岩石显著的体积膨胀是其变形和破坏的主导因素。指数函数可用于描述卸载过程中E和μ随围压的演化。卸载条件下岩石的损伤应力低于加载条件下的损伤应力，这表明卸载导致砂质板岩更早地开始体积膨胀。在初始轴向应力水平接近损伤应力的条件下，力学性质受卸载的影响最为显著。与加载条件相比，当初始轴向应力水平为峰值强度的70%时，黏聚力（c）降低了15.77%至29.37%，而内摩擦角（φ）增大了1.88%至5.14%。基于微裂纹的发展，岩石的破坏过程可分为四个阶段。在微裂纹萌生和扩展阶段进行卸载会导致不同程度的拉伸裂纹，从而在加卸载条件下产生不同的力学性质和破坏特征。
