Influences of confining pressure and bedding angles on the deformation, fracture and mechanical characteristics of slate

Abstract The physical properties of slate in buildings are affected by its bedding angle and confining pressure. A total of 74 slate specimens with seven bedding angles and five levels of confining pressure were tested in uniaxial and triaxial compression tests. The effects of bedding angle and confining pressure on the mechanical behaviour of the brittle slate were quantified. The test results showed that, with the increase of confining pressure, the compressive strength of rock increased significantly. The variation in compressive strength of slate under confining pressure could be described by the parabolic Mohr-Coulomb strength criterion. The strength of slate is the lowest when the bedding angle is 45°–60°, and greatest when it is below 15°. When unconfined, the fracture angle of slate is 65°–90°. With increased confining pressure, the fracture angle of slate tends to 45° from above. As the bedding angle increases from 0° to 90°, the fracture angle of slate presents a U-shaped curve. When the bedding angle is 75°–90°, the deformation modulus of slate is greatest, and is minimised when the bedding angle is 45°–60°. Even if the confining pressure is low, the deformation modulus of slate is significantly increased compared to that in unconfined conditions. It proves that shotcrete treatment of the rock surrounding a tunnel will greatly improve the supporting effect thereon.