A meso-macro mechanical model of direct tensile fracture in brittle rocks under dry-wet cycles

Aiming at the engineering problems of rock damage and failure caused by long-term dry-wet cycle conditions such as the hydro-fluctuation belt in the Three Gorges reservoir area, this paper investigates the challenging issues of the micro-macro mechanical properties of brittle rocks under the combined effects of dry-wet cycles and direct tensile loading. However, due to the challenges in conducting direct tensile tests under dry-wet cycles, there is a scarcity of macro-micro mechanical models that account for both dry-wet cycles and direct tensile loading. Based on the coupled method of the theory of fracture mechanics and the experiment of dry-wet cycle, a macro-micro mechanical model of direct tensile fracture of brittle rock under the influence of dry-wet cycle conditions is proposed. The model is developed by considering the combined effects of the number of dry-wet cycles (n) and water content (ω) on fracture toughness (K_IC) and initial damage (D₀). It is then integrated with a direct tensile microcrack propagation mechanical model that considers initial microcrack damage and crack fracture toughness in rocks. The theoretical results for tensile strength, wing crack limit length l_lim, elastic modulus, and rock deterioration damage are compared with experimental data to validate the reasonableness of the model. The influence of initial crack angle φ, material parameter β, and other parameters on the variation of crack initiation stress and peak stress with the number of dry-wet cycles n is discussed. Furthermore, a comparative analysis is conducted to explore the effects of dry-wet cycles and single water content conditions on the deterioration degree of rocks.