Assessing the effect of the anisotropy of rocks on the accuracy of stress determination by the relief method

Abstract

To solve the problems associated with the design of underground constructions, the correct interpretation of geophysical data, and the study of tectonic conditions in various layers of the Earth's crust, we must know the stress in the virgin rock.The simplest and most reliable way of determining the stress in the rock is the relief method, first employed in mining by the All-Union Scientific Research Mine Surveying Institute (TsNIMBA) in 1935. The basis of the method is the use of the characteristics of the elastic restoration of d~e shape of an element of the rock when we separate it from the main body of the rock. The method is used for rocks for which specimens retain their shape separation from the main body.The vertical stress o z and the horizontal sUess o x are calculated, in accordance with [1], from formulas of the theory of elasticity for a plane problemwhere E is the elasticity modulus of the specimen being relieved; /~ is d~e Poisson's ratio; and s are the relative deformations of the end face of the relieved core.Equation (1) is correct for an/sotropic material~ but most rocks are anisotropic -usually ~ansversely isotropic. It is therefore of interest to assess the effect of anisotropy on u~e accuracy of rock suess determinations. An anisetropic medium displays different elastic properties in different directions; these are shown for certain rocks in Table 1.