Assessing heterogeneity of in situ stress for the design of nuclear waste repositories

Javaid MA, JP Harrison, D Mas Ivars and H Kasani. Assessing heterogeneity of in situ stress for the design of nuclear waste repositories. Published in proceedings of GeoNiagara 2021 – Creating a Sustainable and Smart Future, September 26-29, Niagara Falls, ON, Canada

Abstract: An essential part of the investigations supporting the design of nuclear waste repositories are campaigns to determine thestate of in situ stress, usually by application of measurement techniques such as hydraulic fracturing and borehole overcoring. Such measurements often display spatial variability, which is indicative of stress heterogeneity. Although the term “stress heterogeneity” is commonly found in the rock engineering literature on in situ stress, a consistent and universally agreed definition of it seems to be missing. Similarly, a formal means of characterising a stress field as either homogeneous or heterogeneous is also absent. In this paper we review concepts of stress homogeneity and heterogeneity as they have been presented in the literature. From this, and using exemplar stress fields together with concepts from multivariate statistics and cluster analysis, we propose new definitions of stress heterogeneity. We finally indicate how these considerations may usefully be applied to the design of nuclear waste repositories.