Workreport 2007-32



Geological Data Acquisition for Site Characterisation at Olkiluoto: a Framework for the Phase of Underground Investigations


Milnes, A. G., Aaltonen, I., Kemppainen, K., Mattila, J., Wikström, L., Front, K., Kärki, A., Gehör, S., Paulamäki, S., Paananen, M. & Ahokas, T.



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“Geological data acquisition” is a general term for the collection of observations and measurements by direct observation of exposed bedrock in the field (i.e. in natural outcrops and trenches, in drillholes, and in tunnels and other underground excavations). Only field-based data acquisition is included in this report: laboratory-based investigations will be continued, based on the field data and sampling, and all the data will be subject to discipline-specific processing, as the project proceeds. The ultimate aim of geological data acquisition is to provide the necessary data base for geological models of the bedrock of the Olkiluoto site, in connection with the construction of an underground rock characterisation facility, ONKALO, and a repository for spent nuclear fuel, at about 500m depth. Geological data acquisition plays a central role in site characterisation and modelling, and is intended to provide a solid platform on which the other disciplines (rock mechanics, hydrogeology, seismic risk assessment, etc.) can base their investigations.

Based on consideration of a series of guidelines (e.g. modelling scale, source of data, level of investigation, national and international experience, special conditions at Olkiluoto, need for process understanding), a project-oriented “framework” has been developed as a background to the different projects within the geological data acquisition programme. Each project will require its own system of data acquisition (methodology, spreadsheets, protocols, etc.), as described in the corresponding reports; the present report concentrates on the general principles which lie behind the different methodologies and data sheets.

These principles are treated under three main headings: characterization of intact rock (Chapter 2), characterization of deformation zone intersections (Chapter 3), and characterization of individual fractures (Chapter 4). Geological mapping of natural outcrops and trenches at Olkiluoto, and lithological logging of more than 40 rock cores, have already provided a broad basis of experience for detailed site characterisation. In addition to the lithological data acquisition, other areas of geological data acquisition are also treated here in more detail, particularly with respect to classification schemes, parameterization, and qualitative characterisation for increasing geological site understanding. Important areas which are discussed in detail include:

  • systematic characterisation of foliation and related small-scale heterogeneities, according to type, orientation and degree of development, including the assessment of their rock mechanics significance
  • identification and description of hydrothermal and other rock alteration phenomena
  • identification and parameterisation of deformation zone intersections, and their classification in terms of the scientifically established Sibson-Scholz fault zone model (brittle, semi-brittle, low-grade ductile and high-grade ductile deformation zone types)
  • detailed consideration of brittle deformation zone architecture, with particular focus on the characterisation of the core and damage zones, and kinematic parameters
  • classification and parameterisation of individual fractures, as a background for systematic geological studies as well as systematic data acquisition for rock quality estimation (Q-system) and Discrete Fracture Network modelling


Geological data acquisition, characterization, geological mapping, deformation, Olkiluoto


Geological Data Acquisition for Site Characterisation at Olkiluoto: a Framework for the Phase of Underground Investigations (pdf) (2.5 MB)


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