Host rock classification

Working Report 2003-04 Host rock classification Phase 2: Influence of host rock properties Annika Hagros Kari Aikas Tim McEvven Pekka Anttila Febr...
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Working Report 2003-04

Host rock classification Phase 2: Influence of host rock properties

Annika Hagros Kari Aikas Tim McEvven

Pekka Anttila

February 2003

POSIVA OY .:J

FIN-27160 OLKILUOTO, FINLAND Tel. +358-2-8372 31 Fax +358-2-8372 3709

Working Report 2003-04

Host rock classification Phase 2: Influence of host rock properties

Annika Hagros Kari Aikas Tim McEvven Pekka Anttila

February 2003

Working Report 2003-04

Host rock classification Phase 2: Influence of host rock properties Annika Hagros, Kari Aikas Saanio &

Riekkola Consulting Engineers Tim McEvven SAM Ltd Pekka Anttila Fortum Engineering Ltd

February 2003 Base maps: ©National Land Survey, permiss i on 41 /MYY/03

Working Reports contain information on work in progress or pend ing completion .

The conclusions and v iewpoints presented in the report are those of author(s) and do not necessarily co inc ide with those of Posiva .

INSINOORITOIMISTO

SAANIO & RIEKKOLA OY

SAATE 29.11.2002

SAATE TYORAPORTIN TARKASTAMISESTA JA HYVAKSYMISESTA

TILAAJA

Posiva Oy 27160 OLKILUOTO

TILAUS

9577/02/AJH, 9649/02/AJH, 9734/02/A~

YHTEYSHENKILOT

TYORAPORTTI

j

Jo/t.t.z. Z~3 ~d~~ A1mo Hautojarvi Kari Aikas

Posiva Oy Saanio & Riekkola Oy

HOST ROCK CLASSIFICATION. PHASE 2: INFLUENCE OF HOST ROCK PROPERTIES Working report 2002-:XX

LAATIJAT

Annika Hagros Kari Aikas TimMcEwen Pekka Anttila

Saanio & Riekkola Consulting Engineers Saanio & Riekkola Consulting Engineers SAMLtd F ortum Engineering Ltd

/

LAATUOIDENPUOLESTA

~~ Annika Hagros

TARKASTAJA

~~ie t..:::o;.: l:.-.....a --e::-- lE-08 m/s) occur only sparsely in the intact rock mass, and they can be avoided when locating the deposition holes. Their spatial distribution in the rock mass can be studied from detailed underground investigations, but the current borehole data are not sufficient to establish the spatial distribution of K values in the intact rock mass. It should be noted that in the current bedrock model of Olkiluoto all borehole sections with a very high conductivity (> 5E-07 m/s) have been assigned to modelled fracture zones, the avoidance of which is discussed in Chapter 7.2. Secondly, the hydraulic conductivity of the rock mass surrounding the repository can be influenced by sealing measures, for example by grouting with a water-cement suspension. The cement is expected to remain in the fractures of the rock mass for thousands of years (Alcom et al. 1992). Although the intact rock mass at Olkiluoto has a low conductivity, the intersection of hydraulically conductive local fracture zones and fractures by the repository cannot be avoided. The sealing of these by grouting is important, in order to keep the total inflow into the repository as low as possible. This is necessary for controlling the risk ofupconing of saline groundwater.

It may prove difficult to locate the zones of inflow for the purposes of grouting before driving a tunnel, if they are channelled. Observing them beforehand would be important because sealing can best be achieved by pre-grouting. The more channelled these zones of inflow are, the larger the number of probe holes will be required to find and grout them. The groutability of such zones should be taken into account when orienting the tunnels - if possible, they should be oriented with respect to hydraulically conductive fracture zones and fractures so that these features can be easily intersected by pregrouting holes. 7.2

Hydraulic properties of fracture zones

The hydraulic properties of fracture zones are generally described by means of their transmissivity, which is defined as the product of their mean hydraulic conductivity and their thickness. The unit of transmissivity is m2/s. Because fracture zones are likely to be weathered and more densely fractured than the surrounding rock mass and often also continuous, they usually constitute the main groundwater flow routes in the rock mass. If a fracture zone contains significant amounts of clay or the fractures are otherwise non-conductive, its transmissivity may also be low. The transmissivities of the fracture zone intersections in the site investigation boreholes and used in the Olkiluoto bedrock model2001/2 (Saksa et al. 2002) are shown in Figure 7-2 (Sievanen 2002). The transmissivities measured from the cemented fracture zone

73

intersections (those intersections that had to be stabilised during drilling) have been increased in the figure by a factor of 10, because it has been estimated that cementing reduces the transmissivity by a factor of 10 (a rough approximation). The depthdependence of transmissivity has been estimated from the data and illustrated by three visually fitted curves that have been used to defme three transmissivity classes of fracture zones, A, B and C (these classes were chosen subjectively for the purposes of flow modelling). It can be seen from the figure that the depth-dependence of transmissivity is significant in the upper part of the bedrock, but reduces with depth. The transmissivity seems to decrease by about two orders of magnitude from the surface down to a depth of500 m.

2

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log (T, m /s)

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Excavation (Drilling, Blasting)

Repository Layout and Location

Far-field

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