Brazilian disc specimen is widely used in mechanical testing for geomaterials Modified Brazilian disc specimen overcomes the shortcoming of stress concentration caused by concentrated loading. Orthotropic material is a generalization of isotropic material. It is in this background that the displacement formula of flattened Brazilian disc for orthotropic material is proposed. Then the finite element software ANSYS is used to simulate the orthotropic flattened Brazilian disc specimen subjected to diametrical compression, the accuracy of the approximate formula of compression displacement is checked. The formula is further modified with a semi empirical and semi-analytical approach,and it is shown to have better accuracy than the original formula covering the whole range of orthotropic anisotropic index of rock, the error is less than 6%.Finally, the application of this displacement formula is introduced with an example, that is by recording the load-displacement plots of flattened Brazilian disc specimens loaded in two orthotropic directions and in two loading angles, respectively, the elastic constants, including two Young’s modulus, two Poisson’s ratios and the shear modulus, of an orthotropic material can be determined by the inverse slope of the straight line of the plots.
