Anizotropní řešení při stanovování napjatosti v horninovém prostředí pomocí uvolňovací metody CCBO

Abstract

The CCBO method is used to determine the stress tensor in the rock using a special conical probe installed at the end of the borehole. This strainmetric probe is overcored, causing relaxation of the stress originally acting at the location. The full stress tensor at the idealised point is determined from the strains measured on strain gauges placed on the probe in specific directions. The thesis deals with the determination of the necessary relationship between stress and strain, called the distribution matrix. This distribution matrix is determined on the basis of numerical modelling, where the model simulates a probe placed in a borehole and its overcoring under the action of certain stresses. The rock surrounding the probe is assumed to be homogeneous and linearly elastic. An integral part of the numerical model is information about the deformation characteristics of the rock environment. Deformation characteristics are most commonly determined in the laboratory under the assumption that the material is isotropic. In most cases, the rock material shows signs of anisotropy and the use of an isotropic material model in the numerical model introduces error into the process of determining the distribution matrix. Scientific output from underground research laboratories around the world is changing the way we look at what constitutes a basic standard. This is becoming the established complete stiffness matrix for assuming a transversely isotropic material and its use in determining the complete stress tensor in the rock mass. The most recent trend in this area is the sensitivity analysis of the resulting stress tensor to hypothetical variants of the rock stiffness matrix. This dissertation deals with the sensitivity analysis of the resulting stress tensor to the scientifically based results of laboratory testing on Grimsel granite from the GTS underground research laboratory. For an oriented rock sample taken in the vicinity of the CCBO probe, the complete material stiffness matrices are determined along with the principal axis directions for the three load cases. Considering that similar sensitivity analyses have been carried out worldwide only on the basis of hypothetical variants of material stiffness, the practical part of this thesis offers unique and scientifically based results.