Experimental study on anisotropic unloading mechanical behavior of bedded sandstone

Area of Science:

• Geotechnical Engineering
• Rock Mechanics
• Materials Science

Background:

• Sandstone, a prevalent rock mass in engineering, presents challenges in excavation due to its deformation and strength characteristics.
• Understanding the mechanical response of bedded sandstone under stress is crucial for safe and efficient engineering practices.

Purpose of the Study:

• To investigate the influence of varying bedding angles (β) on the deformation and strength of sandstone during triaxial unloading tests.
• To characterize the failure modes of bedded sandstone under triaxial unloading conditions.

Main Methods:

• Conducted triaxial unloading tests on sandstone specimens.
• Systematically varied the bedding angle (β) across seven different orientations.
• Analyzed elastic modulus, deformation modulus, axial strain rate, peak strength, cohesion, and internal friction angle.

Main Results:

• Elastic modulus increased with bedding angle; deformation modulus exhibited a U-shaped distribution.
• Axial strain rate showed an inverted U-shaped distribution with increasing bedding angle.
• Peak strength, cohesion, and internal friction angle decreased initially then increased with bedding angle.
• Confining pressure reduced the anisotropy of bedded rock masses.
• Identified four distinct failure modes, with bedding plane failure occurring at large intersection angles.

Conclusions:

• Bedding angle significantly influences sandstone's mechanical properties, including deformation and strength, under triaxial unloading.
• The observed U-shaped and inverted U-shaped distributions highlight complex stress-strain behaviors related to bedding orientation.
• Confining pressure plays a role in mitigating rock mass anisotropy, and failure modes are predictable based on bedding-unloading angle interactions.