EXPERIMENTAL AND THEORETICAL STUDY OF SIZE EFFECT OF ROCK MATERIAL

Uniaxial compression tests with marble specimens of different length-to-diameter ratios were carried out on a servo-controlled testing machine. The effect of the specimen length on the unconfined strength and the failure pattern was investigated. There is no clear effect of the specimen length on the deformation before stress peak, whereas there is significant effect after stress peak. The longer the specimen length is, the more brittle the material becomes after the stress peak. Failure of rock specimens changes from splitting pattern into shear pattern with the increase of length. The length effect results from the friction between the end faces of rock specimens and the loading platens, not the heterogeneity of rock material. A theoretical model of size effect of marble material, F₀=F₂expa+b(D/L), is brought forward, which is verified by experimental data. Physical parameter a reflects the sensitivity of mechanical parameters on the size; b reflects the relation between mechanical parameters and sizes, which shows negative pertinence if b>0, positive pertinence if b<0, and no pertinence if b=0.