| Characterizing the joint system is a very significant component of investigations on fractured rock aquifers, as the secondary porosity controls the groundwater flow. It is also important to analyze the types of interactions between the joints, e.g., the types of termination and the dominancy of a certain joint set, since such information helps to understand the tectonic events that were responsible for the generation of the joint systems in the aquifer. Moreover, the current stress field is usually the most significant in controlling joint aperture, which plays a major role in groundwater flow.;The main objective of this work is to characterize an aquifer in fractured crystalline rocks with a fairly homogeneous lithology, defining a hydrogeological model of the study area, through structural surveys at different scales and hydrogeologic data analyses. This study was carried out in the Kenogami uplands, within the Saguenay graben, Quebec. It aimed to answer the following questions: (1) is there a structured joint system in the bedrock, that is, is it possible to identify preferential joint orientations and structural domains? (2) Can joint systems be defined at different scales, e.g. regional and local scales? If yes, are there any relationships between the systems observed at different scales? (3) Can any correlation between the joint system(s) and the past and present stress fields be identified? (4) Is there a relationship between the hydrogeological properties obtained from boreholes and the joint system(s)?;The structural survey involved three main phases. First, a characterization at the regional scale of the joint system is derived from air photo interpretation, lineament analysis, and a general field survey at selected sites. The latter involves the investigation of the spatial distribution of the main joint sets, and the study of the relative ages of joint sets and past stress field components conducted on horizontal outcrops. Second, a detailed structural survey of selected road cuts was carried out to define and characterize the main joint sets that compose the joint system in the study area. Third, the realization of geophysical borehole logging provided valuable information at depth, especially regarding subhorizontal joint sets. These steps allowed to answer the questions proposed in the beginning of this research.;This project allowed the characterization of an aquifer in fractured crystalline rocks, regarding the following aspects: joint systems at different scales, past stress fields, hydraulic properties and the possible relationships between these parameters. The methodology adopted may be applied to other studies on fractured rock aquifers.;Finally, a conceptual model was developed for the fractured rock aquifer in the Kenogami uplands, using the unit block approach. This model may be extrapolated to a regional scale, and it reflects the predominance of the subvertical joints in the study area. Other contributions from this work include the introduction of procedures for applying Terzaghi's correction on computers without using specialized softwares and for analyzing the orientation of the main horizontal component of past stress fields on horizontal outcrops. Moreover, it highlighted the value of characterizing a fractured media with the unit block, through a discussion of its association to hydraulic properties and their incorporation into numerical models. |
