Experimental investigation on deformation behavior and failure modes of limestone under coupled effects of water content and end friction

Understanding the deformation and failure behavior of rock under complex boundary and environmental conditions is critical for the design and stability assessment of geotechnical structures. In particular, the influence of water content and end friction during laboratory testing significantly affects the mechanical properties of rocks. In this study, uniaxial compression tests were conducted on dry and water-saturated limestone specimens under two end conditions: with and without a coupling agent, to investigate the coupled effects of water saturation and end friction on rock deformation and failure behavior. The results indicate that the uniaxial compressive strength (UCS) in the dry state is 84.2% higher than that in the water-saturated state, and the elastic modulus (E) shows an 84.7% increase in the dry state compared to the water-saturated state. The use of a coupling agent was found to enhance overall strain and reduce the extent of end friction effects. Radial shrinkage occurred in the early loading phase near the specimen ends and gradually weakened toward the center. Failure modes varied with test conditions: specimens without vaseline primarily exhibited X-shaped conjugate shear fractures due to strong end restraint, whereas vaseline-coated specimens showed cleavage failure characterized by more pronounced end damage. Water-saturated specimens exhibited more ductile behavior, while dry specimens showed brittle splitting. Fracture observations indicated that early crack formation and stress rebound influenced radial deformation and crack evolution.