Posiva publishes Working Reports and Posiva Reports. From the year 2006 nearly all the reports have been published on our webpage and they can be found in the databank. In the databank you can also find our Annual Reviews and some other publications as well. You can also find print-quality pictures and useful links in the databank.

Recent publications

Workreport 2016-23



Rock Mechanics Parametrization of Fractures and Brittle Deformation Zones in ONKALO Based on the Mapping Data


Salminen, P., Mas Ivars, D., Mattila, J., Nordbäck, N.



Page count:



In this report, the rock mechanical parameters of fractures and brittle deformation zones are estimated for the ONKALO facility and its surroundings. Parameters are derived from the mapping data of ONKALO tunnels and shafts and from the drill core data.

ONKALO is located in Olkiluoto, in the western Finland. It is an underground rock characterisation facility, which is one element of the site investigations conducted at Olkiluoto. In addition, ONKALO provides an opportunity to develop excavation and final disposal techniques in realistic conditions and it will ultimately become part of the final disposal facility.

Parametrization of fractures and brittle deformation zones have previously been provided in four working reports (Kuula 2010, Mönkkönen et al. 2012, Simelius 2014, Salminen & Simelius 2016). This report is not a continuation to these previous reports – instead, this report provides a new rock mechanics parametrization covering the entire ONKALO facility (tunnels and shafts). Drill cores in the area of ONKALO and in the vicinity of ONKALO are also investigated to some extent. Drill cores provide a way to investigate brittle deformation zones outside of the tunnels and shafts.

This report provides a parametrization of the mapped fractures outside of the brittle fault and joint zone intersections. This parametrization of the fractures is mainly based on the mapped Q (Q´) parameters, including RQD, Jn, Jr and Ja. The Q mapping system delivers qualitative presentation of fractures, but for the purposes of the spent nuclear fuel repository and associated modelling of discontinuities, more accurate parameters (e.g. quantitative representations) are necessary. However, as long as the basis of the characterisation is of qualitative nature, some uncertainties are transmitted to the quantified numbers as well.

Fracture orientations, fracture lengths, fracture terminations, fracture undulation and fracture mineralogy are also analysed and JRC1 m and JCS values are estimated for the fractures. In addition, fracture stiffness parameters, instantaneous cohesion, instantaneous friction angle and peak dilation angle are calculated for three fracture length categories and for three effective normal stress levels (representing three different depth levels); within these length categories and effective normal stress levels, all defined fracture sets and fractures outside of the sets are also considered separately.

For parametrization of the fractures, ONKALO tunnels are first divided into 23 different domains. This division is chiefly based on the fracture orientations, fracture intensities and lithology; significant amount of foliation is also taken into account in the domain formation. These domains are further grouped in to three discrete units based on their fracture orientations, RQD values and fracture mechanical properties. Unit I includes Domains 1-8, Unit II Domains 9-15 and Unit III Domains 16-23. Unit I clearly differs from other two units: compared to Units II-III, fractures in Unit I are more altered, rougher and more undulating, RQD values are commonly lower and fracture orientations are more variable. Differences between Units II and III are smaller: the major differences are in fracture orientations and in Jr values of ≥1 m long fractures.

In total 30 brittle deformation zones are also analysed for their mechanical properties. These zones were, based on their size, classified as either site-scale or repository scale brittle fault zones. The strength and deformability properties of these brittle fault zones are estimated on the basis of the mapped Q´ parameters obtained from the fault core zones.


Nuclear waste disposal, Olkiluoto, ONKALO, rock mechanics, fracture, brittle deformation zone, mechanical properties, Q mapping


WR 2016-23_web (pdf) (19 MB)


Share article:
This website stores cookies on your computer. These cookies are used to improve our website and provide more personalised services to you.


To make this site work properly, we sometimes place small data files called cookies on your device. Most big websites do this too.

1. What are cookies?

A cookie is a small text file that a website saves on your computer or mobile device when you visit the site. It enables the website to remember your actions and preferences (such as login, language, font size and other display preferences) over a period of time, so you don’t have to keep re-entering them whenever you come back to the site or browse from one page to another.

2. How do we use cookies?

A number of our pages use cookies to remember your actions and preferences (such as login, language, font size and other display preferences.)

Also, some videos embedded in our pages use a cookie to anonymously gather statistics on how you got there and what videos you visited.

Enabling these cookies is not strictly necessary for the website to work but it will provide you with a better browsing experience. You can delete or block these cookies, but if you do that some features of this site may not work as intended.

The cookie-related information is not used to identify you personally and the pattern data is fully under our control. These cookies are not used for any purpose other than those described here.

3. How to control cookies

You can control and/or delete cookies as you wish – for details, see You can delete all cookies that are already on your computer and you can set most browsers to prevent them from being placed. If you do this, however, you may have to manually adjust some preferences every time you visit a site and some services and functionalities may not work.