USE OF UNIAXIAL COMPRESSION TEST-RESULTS IN STRESS MODELING AROUND OPENINGS IN NONLINEAR GEOMATERIALS

A phenomenological approach extending linear elastic constitutive equa tions to nonlinear materials is presented and applied to stress analys is around circular openings. This extension uses stress-dependent Lame parameters instead of fixed values: a mean effective stress-dependent compressibility modulus C(sigma') and a shear stress-dependent invert ed shear modulus, D(tau(2)) = 1/G(tau(2)). Both C(sigma') and D(tau(2) ) are expressed as power series, allowing several typical pre-peak mat erial nonlinearities to be described with reasonable accuracy. A simil ar, strain-dependent model is also provided. In the strain-dependent v ersion, the model uses volumetric strain-dependent bulk modulus K(epsi lon) and shear strain-dependent shear modulus, G(gamma(2)). Material p arameters of these nonlinear models can be identified from uniaxial co mpression tests. Numerical examples showing linear and nonlinear stres ses around openings in different rocks are presented. It is shown that a model without yield does not necessarily have to underpredict openi ng stability. Underpredictions depend on the convexity of the rock com pression curve and on the degree of rock nonlinearity. (C) 1998 Elsevi er Science B.V. All rights reserved.