Abstract: Three kinds of strength theory for anisotropic rocks are reviewed: classic Coulomb's shear strength theory,Griffith's crack theory,and empirical theory.Calculation formulas and methods are derived.A comparison of these strength theories is made with the experiments on Casper sandstones and Green River oil shales by the author during his visit to the US.Two minimums in peak strength are present at bedding angle between 0° and 90°.The failure criteria of Hoek-Brown and empirical Mohr-Coulomb are the best ones to predict the peak strength of anisotropic rocks.On account of their complexity,the author presents a new empirical criterion
σ₁=A_1,2β⁴+B_1,2β³+C_1,2β²+D_1,2β+E_1,2
which is simpler and agrees well with experimental data.