| In concepts for the underground storage of nuclear fuel waste, the primary rock mechanics concern is the development of damage around excavations. By controlling the extent of the excavation damage zone, the potential for transport of radionuclides, either by diffusion or by groundwater flow within this zone, can be controlled. To this end, it is first necessary to demonstrate that the fundamental behaviour of the rock mass around underground openings is understood. The measurement and interpretation of excavation-induced displacements around openings plays a key role in this respect. For example, in the absence of appreciable excavation-induced damage, displacements have been used extensively to back calculate in situ stresses. In rock damaged during excavation, displacement measurements, in combination with numerical models and in situ characterization, are also important as a means of determining the extent and characteristics of the damaged zone, and the processes responsible for its development. These two applications tend to be mutually exclusive.;Using AECL's Mine-by Experiment as the field study, this thesis considers the problems associated with analysis and interpretation of displacement measurements taken during excavation of a cylindrical tunnel in a massive, highly stressed, brittle rock mass. A technique using the radial displacement response from within one diameter of the tunnel face is developed to back analyze the in situ stress tensor in conditions where extensive excavation damage is evident in parts of the tunnel. The estimated stress tensor is, in turn, used in conjunction with observations and results from field characterization, and numerical modeling, to determine the extent and characteristics of excavation damage around the tunnel. The relationship between displacement, stress and excavation damage is also explored through comparison of results from numerical modeling and field characterization.;The main contributions represented by this thesis are: (1) An in situ stress back analysis technique based on radial displacement measurements taken within the tunnel diameter of the face. (2) General approximating functions to describe the relationship between radial displacement and tunnel face position (i.e., the spliced logistic function), and between radial displacement and radial distance for positions within one diameter of the tunnel face. (3) Parametric functions describing the characteristic radial displacement surfaces associated with components of a partitioned unit stress tensor. (4) An interpretative methodology for displacement measurements in highly stressed brittle rock, including a correction methodology for face curvature and stepped longitudinal tunnel geometry. (5) An assessment of the limitations of posterior-type displacement monitoring instruments, such as convergence arrays, and the assumptions inherent in interpreting results from them. (6) An estimate of in situ stress conditions and material properties at the 420 Level of AECL's Underground Research Laboratory. (7) An interpretation of the extent and characteristics of the damaged zone around the Mine-by Experiment test tunnel, and the processes responsible for its development. |
