Mechanical behavior of granite under cyclic loading after a seawater cyclic thermal shock

The ocean, islands, and coastal areas represent significant potential for geothermal energy development, owing to the abundant seawater resources serving as an efficient heat exchange medium. To study the mechanical behavior of granite under cyclic loading after cyclic thermal shock, a laboratory triaxial cyclic loading and unloading test was carried out. This paper presents the results of a study on the deformation behavior, mechanical properties, and failure modes of granite after 0–30 cycles of seawater thermal shock at 400 °C. The experimental results show that the axial and circumferential plastic deformations increase monotonically with the number of cycles ( N ), while the elastic modulus changes nonlinearly. The computed tomography (CT) results indicate that seawater thermal shock cycles cause the formation of cracks on the granite surface. With an increase in the number of thermal shock cycles, the cracks gradually increase and expand inwards, resulting in a rise of 93.84% in axial strain and a decrease of 29.02% in failure strength ( σ c ). Furthermore, the occurrence of shear failure is predominantly observed in the damaged granite, and shear-induced cracks form along the shear fractures when the number of thermal shock cycles exceeds 6. However, after three cycles of thermal shock, the failure surface of the granite exhibits characteristics of shear splitting failure, and the σ c increases by 14.96%.