Relationship between cleavage orientation, uniaxial compressive strength and Young’s modulus for slates in NW Spain

Slates from North Western Spain have been studied to establish the influence of the cleavage orientation on the uniaxial compressive strength (UCS) and Young’s modulus (E). Slate, sandstone and intercalated slate/sandstone lithologies were tested and the higher strengths were always obtained when the load was applied parallel, or close to parallel, to the slaty cleavage. This study suggests the following empirical relationships for unweathered slates in saturated conditions UCS = 0.037β ² − 7.622(β + 200.6, E × 10⁴ = 0.002β ² − 0.134β + 3.453. E can be estimated from UCS values using E × 10⁴ = 429,56 (UCS)^0.9122. These empirical equations will assist in geotechnical studies in this area of NW Spain where slate quarrying is an important industry.