Mechanical Properties and Failure Mechanism of Granite with Maximum Free Water Absorption under Triaxial Compression

Abstract

Granite in underground water-sealed storage caverns has usually been immersed for a long time. The immersion affects the mechanical properties and failure mechanism of granite with maximum free water absorption; therefore, it is crucial to study the behavior of granite under different confining pressures for engineering construction. A triaxial compression test with maximum free water absorption was conducted on granite and its mechanical properties were analyzed. A fracture scanning electron microscope test was carried out to analyze the microstructural characteristics and reveal the failure mechanism. The test results showed that the differential stress-axial strain curve can be divided into the initial compaction stage, the elastic deformation stage, the plastic deformation stage, and the post-peak strain-softening stage. With an increase in confining pressure, the duration of the initial compaction stage decreased, while the plastic deformation stage and the peak strength and peak strain stages increased. For the confining pressure range of 0–20 MPa, the peak stress difference of granite with maximum free water absorption was between 146.0 and 307.6 MPa. The elastic modulus was between 31.36 and 44.18 GPa. The cohesion (c) of the rock sample studied was 26.84 MPa and the internal friction angle (φ) was 51°. The failure mechanism of granite is tensile–shear composite failure, predominantly with tensile failure under low confining pressure regimes, and the inclined fracture surface is mainly due to shear failure under high confining pressure conditions. These research results provide updated reference data for rock engineering involving granitic mechanical properties and failure mechanisms in submerged caverns.