## 1 Introduction  
Underground water-sealed storage caverns projects are mostly built in granite host rock and have high exacting requirements for the mechanical properties of the surrounding rock. The granite in such underground water-sealed storage caverns has been immersed in water for a long time, allowing pervasive water absorption. When granite absorbs the maximum free water content, the stability of the engineering rock mass is negatively affected. At the same time, different burial depths of the caverns result in different confining pressures of the rock mass. Therefore, it is of great significance to study the mechanical properties and failure mechanisms of granite with maximum free water absorption under different confining pressures for this type of engineering construction. At present, research on the triaxial compression of granite block mainly focuses on the basic mechanical properties and failure characteristics. [PERSON] et al. [1] summarized the stress-strain relationship of rock under the conditions of the conventional triaxial compression test, improved the classical plastic statistical damage model, and preliminarily verified the constitutive relationship expression by using the results of the conventional triaxial compression test. [PERSON] et al. [2] proposed a nonlinear empirical strength criterion based on Mohr-Coulomb criterion, which provides a new reference and method for determination of the triaxial compressive strength of rock materials. [PERSON] et al. [3] conducted triaxial compression tests under different confining pressures to study the deformation and failure characteristics and mechanisms of granite. [PERSON] [4] believed that the deformation mechanism of granite includes elastic deformation, brittle deformation, and compaction deformation. The latter two deformations are related to micro-fractures. [PERSON] et al. [5] used acoustic emission technology to carry out conventional triaxial compression tests on granite under different temperatures and confining pressures, and carried out damage analysis and characteristic stress value analysis. [PERSON] et al. [6] studied the mechanical properties of Dagangshan granite using static triaxial tests and dynamic triaxial tests, indicating that the compressive strength, Poisson's ratio, and elastic modulus of granite are related to the strain rate. [PERSON] et al. [7; 8; 9] studied the mechanical properties of granite after high temperature exposure and found that the peak strength and elastic modulus of granite after high temperature exposure decreased sharply. The P-wave velocity also decreased to varying degrees. [PERSON] et al. [10; 11; 12] conducted uniaxial and triaxial compression tests on intact granite as well as single-and double-defect granite specimens, and further studied the influence of confining pressure and fracture on rock strength and failure mode. [PERSON] et al. [13; 14; 15; 16] studied the failure process, strength characteristics, and damage evolution mechanism of Beishan granite under different confining pressures. [PERSON] et al. [17] studied the damage evolution characteristics of granite during loading and unloading through a series of triaxial tests under different confining pressures. [PERSON] et al. [18; 19; 20; 21] studied the deformation and acoustic emission characteristics of granite under different confining pressures using triaxial compression tests. [PERSON] et al. [22] studied the triaxial compression mechanical properties of granite under chemical corrosion. [PERSON] et al. [23] studied the mechanical properties of granite after the peak stage and found that after the peak, the rock exhibited plastic failure characteristics under confining pressure. [PERSON] et al. [24] studied the microscopic process of the progressive failure of granite plates and found that the occurrence and development of axial cracks eventually led to the splitting failure of the samples. [PERSON] et al.