The most widely accepted approach to long-term storage of nuclear waste is to design and construct a deep geological repository, where the geological environment acts as a natural barrier to radio nuclide migration. Sedimentary rocks, particularly argillaceous formations, are being investigated by many countries because of favorable isolating qualities (laterally continuous and low permeability) and the ability of self-sealing of fractures. Underground construction creates a damage zone around the excavation. The depth away from the excavation surface of the damage zone depends on the rock mass properties, the stress field, and the construction method. This research investigates the fracture development process in sedimentary rocks and evaluates continuum modelling methods to predict the damage zone dimensions. At the laboratory scale, a complete classification system for samples of carbonate and siliciclastic rocks has been developed, with geotechnical considerations, which when applied narrows the variability of the mechanical properties. Using this system, crack initiation (CI) shows the most uniform range in each class, particularly for mud rocks. Tensile strength was found to be higher for the Brazilian method than Direct method of testing. Brazilian reduction to Direct values was found to be rock type dependent. Laboratory testing results are also influenced by the orientation of bedding. Bedding and other structures were also found to influence the excavation behaviour as observed at the Niagara Tunnel Project in a mudstone and in excavations in the Quintner limestone of Switzerland. The conceptual stages of damage development and the potential fracture networks in sedimentary rocks are used to summarize the understanding of excavation damage developed in this thesis. Using a continuum based modelling approach, a set of predictive damage depth curves were developed for the different excavation damage zones. This approach was found to be most sensitive to the tensile strength used as an input. Back analysis of the Niagara Tunnel Project and forward prediction of the excavation damage around a shaft in the Queenston Formation are used to illustrate the importance of this research. The prediction methods were also applied to cut-off design analysis. This research has enhanced the understanding of excavation damage development in sedimentary rocks and provided a methodology to predict the dimensions of the excavation damage zones using a continuum based approach. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2014-01-29 16:08:58.022

The intent of this thesis is to contribute to the understanding of the origin of fractures in rock. The man-made fracturing from engineering activities in crystalline rock as well as the fracturing induced by the natural process of meteorite impacts is studied by means of various characterization methods. In contrast to engineering induced rock fracturing, where the goal usually is to minimize rock damage, meteorite impacts cause abundant fracturing in the surrounding bedrock. In a rock mass the interactions of fractures on the microscopic scale (mm-cm scale) influence fractures on the mesoscopic scale (dm-m scale) as well as the interaction of the mesocopic fractures influencing fractures on the macroscopic scale (m-km scale). Thus, among several methods used on different scales, two characterization tools have been developed further. This investigation ranges from the investigation of micro-fracturing in ultra-brittle rock on laboratory scale to the remote sensing of fractures in large scale structures, such as meteorite impacts. On the microscopic scale, the role of fractures pre-existing to the laboratory testing is observed to affect the development of new fractures. On the mesoscopic scale, the evaluation of the geometric information from 3D-laser scanning has been further developed for the characterisation of fractures from tunnelling and to evaluate the efficiency of the tunnel blasting technique in crystalline rock. By combining information on: i) the overbreak and underbreak; ii) the orientation and visibility of blasting drillholes and; iii) the natural and blasting fractures in three dimensions; a analysis of the rock mass can be made. This analysis of the rock mass is much deeper than usually obtained in rock engineering for site characterization in relation to the blasting technique can be obtained based on the new data acquisition. Finally, the estimation of fracturing in and around two meteorite impact structures has been used to reach a deeper understanding of the relation between fracture, their water content and the electric properties of the rock mass. A correlation between electric resistivity and fracture frequency in highly fractured crystalline rock has been developed and applied to potential impact crater structures. The results presented in this thesis enables more accurate modelling of rock fractures, both supporting rock engineering design and interpretation of meteorite impact phenomena. / QC 20100709

Prior to an underground excavation a site investigation is carried out. This includes reviewing and analysing existing data, field data collected through outcrop mapping, drill core logging and geophysical investigations. These data sources are combined and used to characterise, quantify and classify the rock mass for the tunnel design process and excavation method selection. Despite the best approaches used in a site investigation, it cannot reveal the required level of detail. Such gaps in information might become significant during the actual construction stage. This can lead to; for example, over-break due to unfavourable geological conditions. Even more so, an underestimation of the rock mass properties can lead to unplanned stoppages and tunnel rehabilitation. On-the-other-hand, the excavation method itself, in this case, drill and blast, can also cause severe damage to the rock mass. This can result in over-break and reduction of the strength and quality of the remaining rock mass. Both of these attributes pose risks for the tunnel during excavation and after project delivery. Blast damage encompasses over-break and the Excavation Damage Zone (EDZ). In the latter irreversible changes occur within the remaining rock mass inside this zone, which are physically manifested as blast fractures. In this thesis, a number of methods to determine blast damage have been investigated in two ramp tunnels of the Stockholm bypass. Herein, a comparison between the most common methods for blast damage investigation employed nowadays is performed. This comparison can be used to select the most suitable methods for blast damage investigation in tunnelling, based on the environment and the available resources. In this thesis Ground Penetrating Radar, core logging (for fractures) and P-wave velocity measurements were applied to determine the extent of the blast damage. Furthermore, the study of the two tunnels in the Stockholm bypass shows a significant overestimation of the actual rock mass quality during the site investigation. In order to gain a more accurate picture of the rock mass quality, Measurement While Drilling (MWD) technology was applied. The technology was investigated for rock mass quality prediction, quantifying the extent of blast damage, as well as to investigate the potential to forecast the required rock support. MWD data was collected from both grout and blast holes. These data sets were used to determine rock quality indices e.g. Fracture Indication and Hardness Indicator calculated by the MWD parameters. The Fracture Index was then compared with the installed rock support at the measurement location. Lastly, the extent of the damage is investigated by evaluating if the MWD parameters could forecast the extent of the EDZ. The study clearly shows the capability of MWD data to predict the rock mass characteristics, e.g. fractures and other zones of weakness. This study demonstrated that there is a correlation between the Fracture Index (MWD) and the Q-value, a parameter widely used to determine the required rock support. The study also shows a correlation between the extent of the blast damage zone, MWD data, design and excavation parameters (for example tunnel cross section and charge concentration).