To investigate the mechanical properties and damage evolution law of layered shale under varying moisture contents, we conducted triaxial compression experiments on rock samples with different bedding angles and moisture levels. This study analyzed the variations in mechanical properties of layered shale under different conditions, and established a predicted model for elastic modulus based on different bedding angles and moisture content. Additionally, the damage constitutive model of layered shale was improved. The study revealed that shale’s mechanical properties display anisotropy, which is influenced by the bedding angles and moisture contents. The elastic modulus of the rock increases with the rise of bedding angle, exhibiting a ‘U’-shaped change. Conversely, the mechanical properties of rocks deteriorate, and their brittleness weakens with the increase in moisture content. When the confining pressure increased, the overall mechanical properties of shale were enhanced, and the influence of bedding on shale was weakened, but the deteriorating effect of water on rocks was hardly affected. Based on the above experiments, a predicted model of equivalent elastic modulus of shale considering the coupling effect of bedding and different moisture contents was proposed, which could effectively predict the elastic modulus of layered shale with different moisture content under different confining pressures. Furthermore, based on the predicted model of elastic modulus, an improved damage constitutive model of layered shale under triaxial loading was established, and the damage accumulation trend of layered shale was obtained, which showed an “S”-shaped change with strain. Under the coupling effect of bedding and different moisture contents, the damage of shale was advanced, but the accumulation rate of damage slowed down. With the increase of confining pressure, the influence of bedding and moisture content on the damage characteristics of shale decreased, and the damage curves under different conditions gradually tended to isotropy. The developed damage constitutive model for layered shale under different moisture contents provides theoretical support for the study of reservoir fracturing and wellbore stability.

中文翻译：

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不同含水率下层状页岩实验及损伤模型研究

为了研究不同含水率下层状页岩的力学特性和损伤演化规律，对不同层理角度和含水率的岩样进行三轴压缩实验。本研究分析了不同条件下层状页岩力学性质的变化，建立了基于不同层理角度和含水率的弹性模量预测模型。此外，还改进了层状页岩的损伤本构模型。研究表明，页岩的力学性质表现出各向异性，受层理角度和含水量的影响。岩石的弹性模量随着层理角度的增大而增大，呈“U”形变化。反之，随着含水量的增加，岩石的力学性能变差，脆性减弱。当围压增大时，页岩的整体力学性质增强，层理对页岩的影响减弱，但水对岩石的劣化作用几乎不受影响。基于上述实验，提出了考虑层理与不同含水率耦合效应的页岩等效弹性模量预测模型，可有效预测不同含水率层状页岩在不同围压下的弹性模量。此外，基于弹性模量预测模型，建立了改进的三轴加载下层状页岩损伤本构模型，得到了层状页岩损伤累积趋势，随应变呈“S”形变化。在层理和不同含水率的耦合作用下，页岩损伤提前，但损伤累积速度减慢。随着围压的增加，层理和含水率对页岩损伤特征的影响减小，不同条件下的损伤曲线逐渐趋于各向同性。建立的不同含水率下层状页岩损伤本构模型为储层压裂及井壁稳定性研究提供理论支撑。