Recent Progress in Rock Mechanics in Mining

Abstract

A brief introduction is given in this paper of some of recent researches in rock mechanics in mining both at home and abroad. To provide information of fundamental importance explanation is given of stresses and strains in homogeneous elastic ground and also in anisotropically elastic ground, of the theory of brittle fracture of rock, of the meaning of shear stress, of the comparison of static and dynamic properties of rock, the barodynamic tests, and of the model test of underground cavities.For technical purposes introduction is given to the instrument used for civil engineering and mining purposes to measure accurately the travel time of elastic waves, to the crack coefficient and ground soundness, to the use of sonic techniques to explore cracks and fracture, and to the techniques of measuring the earth's pressure.Concerning the rock fracture, explanation is given of Griffith's theory of brittle fracture and the modified theory accounting for the effects of closure of the Griffith cracks in compression.Equation (7) is the Griffith's fracture criterion, that is the relationship between the major principal stress σ1 (Fig. 1) at fracture, the principal stress ratio k1 and the uniaxial tensile strength of the material σt.The resulting fracture criterion for a brittle material in which crack closure has occurred is given by equation (8).By measuring the principal stress changes and the direction (p, q and θ) with respect to the original principal stresses (σ1, σ2), the final principal stresses and the direction (σ1', σ2' and α) can be calculated by using equation (11). The relationship between the stresses on rock (principal stresses, S and T) and the deformation (U1, U2, U3, 60°respectively) of a borehole diameter (d) is given by equation (12). Therefore, we can calculate the absolute principal stresses (S and T) in rock by measuring the deformation (U1, U2, U3) of a borehole diameter (d) accompanied by the relaxation method.