Statistical Analysis and Modelling of Olkiluoto Structures

Transkriptio

1 Working Report 24-5 Statistical Analysis and Modelling of Olkiluoto Structures Pirjo HeiHi Tiina Vaittinen Pauli Saksa.Jorma ummela JP-Fintact Oy ovember 24 Working Reports contain information on work in progress or pending completion. The conclusions and viewpoints presented in the report are those of author(s) and do not necessarily coincide with those of Posiva.

2 Hella, P., Vaittinen, T., Saksa, P. & ummela, J. 24. Statistical analysis and modelling ofolkiluoto structures. Eurajoki: Posiva Oy. 56 p. Working Report ABSTRACT Posiva Oy is carrying out investigations for the disposal of the spent nuclear fuel at the Olkiluoto site in SW Finland. The investigations have focused on the central part of the island. The layout design of the entire repository requires characterization of notably larger areas and must rely at least at the current stage on borehole information from a rather sparse network and on the geophysical soundings providing information outside and between the holes. n this work, the structural data according to the current version of the Olkiluoto bedrock model is analyzed. The bedrock model relies much on the borehole data although results of the seismic surveys and, for example, pumping tests are used in determining the orientation and continuation of the structures. Especially in the analysis, questions related to the frequency of structures and size of the structures are discussed. The structures observed in the boreholes are mainly dipping gently to the southeast. About % of the sample length belongs to structures. The proportion is higher in the upper parts of the rock. The number of fracture and crushed zones seems not to depend greatly on the depth, whereas the hydraulic features concentrate on the depth range above -loo m. Below level - m, the hydraulic conductivity occurs in connection of fractured zones. Especially the hydraulic features, but also fracture and crushed zones often occur in groups. The frequency of the structure (area of structures per total volume) is estimated to be of the order of 1/lOOm. The size of the local structures was estimated by calculating the intersection of the zone to the nearest borehole where the zone has not been detected. Stochastic models using the Fracman software by Golder Associates were generated baseq on the bedrock model data complemented with the magnetic ground survey data. The seismic surveys (from boreholes KR5, KR1, KR14, and KR1) were used as alternative input data. The generated models were tested by comparing the modelled and observed structural intersections in boreholes KRl - KR2. t was observed that the number of structural intersections is much more sensitive to the intensity of structures and orientation than to the size of the zones. The intersections with the OKALO tunnels down to -42 m and the characterization tunnel at that level were calculated. t is estimated that approximately 2 structures similar to the bedrock model would be intersected by the tunnels. The seismic data overestimate the number of structures observed in the boreholes. This suggests that many of the reflectors originate actually from other variations in rock properties than fractured zones, like lithological contacts. Assessment of the seismic surveys and its limitations revealed that the most reliable sets of seismic results to be used in modeling of structures are sub-horizontal reflectors, which can be verified with borehole data, and steeply dipping reflectors strong in amplitude, which can be observed within large volumes of rock. Keywords: bedrock modelling, nuclear fuel waste, site characterisation, simulation

3 Hella, P., Vaittinen, T., Saksa, P. & ummela, J. 24. Olkiluodon rakenteiden tilastollinen analyysi ja mallinnus. Eurajoki: Posiva Oy. 56 s. Tyoraportti TVSTELMA Posiva Oy tutkii Olkiluodon kallioperaa ydinjatteiden loppusijoittamista varten Tutkimukset ovat keskittyneet saaren keskiosaan. Loppusijoitustilan suunnittelua varten tarvitaan kuitenkin tietoja laajemmalta alueelta. Tahan asti suunnittelu on pohjautunut kaytettavissa olevaan alueen kokoon nahden harvahkoon kairanreikatietoon ja geofysikaalisiin mittauksiin rei' ista j a reikien valilla. Tassa tyossa on analysoitu Olkiluodon kalliomallin rakennetietoja. Kalliomalli perustuu paaasiassa kairanreikatietoihin, joskin seismiikan ja esimerkiksi koepumppausten tuloksia on hyodynnetty rakenteiden suuntien ja jatkuvuuksien mallintamisessa. Analyysissa on keskitytty rakenteiden esiintymistiheyteen ja niiden koon arviointiin. Kairanrei'issa tavatut rakenteet ovat kaadesuunnaltaan paaasiassa loivasti etelakaakkoon viettavia. oin % kokonaisreikapituudesta on luokiteltu rakenteisiin kuuluvaksi. Osuus on korkeampi kallion ylaosassa. Rako- ja rikkonaisuusrakenteiden lukumaara ei juurikaan nayta riippuvan syvyydesta, sen sijaan hydrauliset piirteet keskittyvat syvyysvalille - -1 m. Syvyyden - m alapuolella hydraulisia piirteita ei kaytannossa tavata, vedenjohtavuutta esiintyy kuitenkin rikkonaisuusrakenteiden yhteydessa. Erityisesti hydrauliset johteet, mutta myos rako- ja rikkonaisuusrakenteet esiintyvat ryhmissa. Rakenteiden esiintymistiheys (rakenteiden pinta-ala tilavuuden suhteen) on suurusluokaltaan 1 m. Paikallisten rakenteiden kokoa arvioitiin laskemalla rakenteiden leikkaus lahimpaan reikaan, jota sen ei ole tulkittu leikkaavan. Stokastisessa mallinnuksessa kaytettiin Fracman-mallinusohjelmaa (Golder Associates). Mallej a generoitiin perustuen kalliomalliin, taydennettyna maanpintamagneettisten mittausten tuloksilla. V aihtoehtoisena lahdeaineistona kayettiin seismiikan tuloksia rei'ista KR5, KR1, KR14 ja KR1. Generoituja malleja arvioitiin vertailemalla mallinnettuja ja havaittuja rakenneleikkauksia rei'issa KR1 - KR2. Mallinnuksen perusteella havaittiin, etta rakenteiden esiintymistiheys ja suuntaus vaikuttavat voimakkaammin kuin rakenteiden koko reikalavistysten maaraan. Rakennelavistyksia OKALOn ajotunnelissa tasolle -42 m ja ko tasolle suunnitellussa ajotunnelissa arvioitiin myos. Tunnelien arvioidaan leikaavan noin 2 nykyisen kalliomallin mukaista rakennetta. Seismiikan havainnot yliarvioivat rakenteiden maaraa. Osa heijastajista johtuukin todennakoisesti muista kallion ominaisuuksien vaihteluista kuin rakenteista, esim kivilajivaihtelusta. Rakennemallinnuksen kannalta seismiikan tuloksia voidaan luotettavimmin kayttaa lahes vaaka-asentoisten, reikalavistyksilla varmennettujen rakenteiden mallintamiseen seka sellaisten piirteiden mallintamiseen, joista on saatu voimakas signaali laajalta alueelta,. Avainsanat: kalliomallinnus, ydinjatteet, karakterisointi, stokastinen

4 PREFACE This work has been done under Posiva's commission 71//KJOK. The authors wish to thank the contact persons at Posiva's side, Liisa Wikstrom and Kimmo Kemppainen, for their interest and comments on the work. Discussions before starting and during the work with Jukka-Pekka Salo, Sami iiranen, Aimo Hautojarvi and Turo Ahokas have provided an important contribution in defining the scope of the work. The authors wish to thank also Johan Andersson, JA Streamflow Ab and Lasse Koskinen, VTT Processes for their valuable comments on the report. Pirjo Hella has co-ordinated the work, done the data analysis of the bedrock model and defined the data sets to be used in the simulations, taking into account the comments and suggestions of Tiina Vaittinen. Tiina Vaittinen has assessed the possibility to use seismic data in the analysis (Chapter.2) and has written Chapter 2.2 about the Olkiluoto bedrock model used as the main source of input data. The Fracman simulations have been conducted by Pirjo Hella and Tiina Vaittinen. Jorma ummela has produced additional information on the Olkiluoto bedrock model in CAD and done the visualizations of the simulated models. Pauli Saksa has assessed the uncertainties related to the seismic data (Chapter 2.). The report is written by Pirjo Hella, except for the chapters mentioned above.

5 1 COTETS Abstract Tiivistelma Preface 1 lntroduction... 2 Approach General Bedrock model Seismics Magnetic ground survey data Simulation Defining input data for the simulations Olkiluoto bedrock model v. 2/ Frequency of occurrence Orientation Size Seismic data... 4 Modelling results Models Results... 5 Conclusions... 5 References... 55

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7 1 TRODUCTO Posiva Oy is carrying out investigations for the disposal of the spent nuclear fuel at the Olkiluoto site in SW Finland. Currently, the investigations are focusing on the volume to host the underground research facility, OKALO. The layout design of the entire repository requires characterization of notably larger areas and must rely at least at the current stage on borehole information from a rather sparse network and on the geophysical soundings providing information outside and between the holes. The Olkiluoto bedrock model presents the rock type distribution and locations of the fractured and hydraulically conductive zones. The bedrock model provides basic information, among other things, for the layout design of the underground facilities. t can be used to locate suitable areas for the repository and to estimate the volume needed for it. The limitations in the data coverage and uncertainties in the available data mean that the area to be characterized should be larger than the repository itself and flexibility is required in the layout design. This work aims to complement the Olkiluoto bedrock modelling results. The current bedrock model includes crushed, fractured and major hydraulically conductive zones (structures), which are either intersected by boreholes, by the investigation trenches on the ground surface or detected by geophysical soundings. n other words, the bedrock model contains features, of which there are direct or at least indirect observations. The criteria used to define the features which are modelled as fracture or crushed zones and changes, for example, in the way the zone size is modelled affect the output of modelling. Many boreholes intersect local features, the location of which has not been predicted by the near-by boreholes or surface observations. Accordingly, the features encountered in neighbouring boreholes have not been combined. The fact that the borehole distances are less than 2 m, in some cases only tens of meters, suggests that some of the observed zones do not have very large extensions. There are naturally difficulties in recognizing the features in different boreholes to be the same due to ambigious structure properties and uncertainty in zone orientation, for example. n many areas interesting for the repository layout, the distance between boreholes is of the order of 5 m or they lie outside the area covered by boreholes. n these areas, many of the features similar to those in the current bedrock model have certainly remained unobserved and thus not included in the current bedrock model. n addition to the areal coverage of the boreholes, also the borehole orientation affects the possibility to observe zones in certain directions, both by diminishing the chance to intersect the zone and by resulting in unfavourable measurement geometry. The objective of this work is to provide data to estimate the amount and properties of the structural features for the needs of technical planning and construction, different modelling purposes and performance analysis. n this work, the analysis is based mainly on the bedrock model v. 2/1 (Vaittinen et al. 2). Also, the seismic data and magnetic ground survey data are used as additional, alternative input data for statistical modelling. To visualize the possible distribution of fractured zones in the areas not covered by boreholes, simulations are done based on the results of the analysis. For the simulations, Fracman software by Golder Associates is used (Dershowitz et al. 14).

8 4 The Fracman software package was used already in a similar work done as part of the bedrock model version 21/1 (Vaittinen et al. 21). t has also been widely used for modelling the fracture scale features; see e.g. Poteri (21), Poteri & Taivassalo (14), iemi et al. (1) and Bossart et al. (21). La Pointe & Hermansson (22) have used discrete fracture network models for the estimations of the rock movements caused by future earthquakes.

9 5 2 APPROACH 2.1 General The structural data according to the current version of the Olkiluoto bedrock model (v. 2/1 by Vaittinen et al. 2, in the latter part of the text this version is shortly referred to as bedrock model) is analyzed in this work. Especially, questions related to the frequency of structural occurrence and structural size are discussed. The bedrock model strongly relies on the borehole observations. On the other hand, parts of the repository are planned in areas with hardly any borehole data available (see Figure 2-1). The model contains only features of which there are direct or indirect observations, thus giving an impression of good-quality rock with no fractured or hydraulically conductive zones in the areas with no borehole information available. The results of the analysis of the bedrock model are used to generate realizations of the structural zone distribution also in the areas with poorer borehole coverage. The realizations should give a picture of how the rock would look like in the areas with no borehole data, should there be similar structural behaviour as observed in the boreholes. Fracman software by Golder Associates is used (v. 2.4, Dershowitz et al. 14) for the simulations. Most of the structures observed in the boreholes are interpreted to have a gentle dip towards SSE. Anyhow, there are some hints of the possibility of sub-vertical zones observed, for example, by seismics and by magnetic ground surveys. Especially, the seismic surveys (VSP and HSP) provide a comparable data set to the bedrock model, covering large volumes and observing features in the same scale as those included in the bedrock model, although the seismic features are not necessarily all presenting fractured zones. This study is based on the analysis of the borehole intersections of the zones, their occurrence, orientation and estimated continuity as interpreted in the bedrock model v. 2. The study covers site scale features as the bedrock model having an extension ranging approximately from 1 m to 1 m. The boreholes encountered range from borehole KR1 to KR2; the same as used to compile the bedrock model (see Figure 2-1). Close to several of the lately drilled boreholes, a shorter B-borehole is drilled to ensure the core sample also from the shallow parts of the rock. n this study the actual hole and the B hole are considered as one.

10 6 Figure 2-1. The current boreholes, the OKALO characterization tunnel and the area designed for the repository (in grey), both at z = -42m (Tanskanen & Palmu (ed.) 2). 2.2 Bedrock model The bedrock model of the Olkiluoto site consists of the lithological model, the structural model, and the hydro geological model. n the present version 2/1, the structural model includes 2 fracture and crushed zones, and the hydrogeological model 75 zones with high hydraulic conductivity. Of these, 22 structures belong to both models. The total number of directly observed structures, i.e. structures with at least one borehole intersection, is 145 (excluding the alternative interpretations). The bedrock model contains also some structures from which there are indirect indications by e.g. geophysical measurements or lineament interpretation, but these are excluded from the study. Cross sections of the bedrock model are presented in Figures These figures are comparable with Figures presenting the modelling results later in Chapter 4. The structural intersections in boreholes are defined based on fracture frequency, hydraulic conductivity and mapped fracturing class according to the conventional Finnish engineering geological classification. The primary criterion for a fracture zone is that the fracture frequency exceeds 1 fractures/m on at least 2 m continuous interval. The fracture data is based on the core sample mapping done by the drilling contractor. The zone margins are defined as the location where the fracture frequency is less than 7 fractures/m for at least 2 m. The rock belonging to fracturing class Ri ll is fracture structured and densely fractured (over 1 fractures per meter), but there is only little

11 7 filling in fractures. These sections are called 'fracture zones'. The rock classified as Ri V- Ri V is crush or clay-structured, abundantly or densely fractured and the fractures are filled with clay or there is abundantly clay material in the rock mass. These sections are called 'crushed zones'. Also, all mapped Ri V and Ri V intersections are modelled as structures, regardless of their intersection length. Hydraulic features are defined as zones for which the fracturing does not fulfil the criteria used but which have hydraulic conductivity K 2 m greater than m/s. Figure 2-2. Horizontal intersection at z=-42 m, the planned level for the OKALO main level characterization tunnel and planned repository depth. The area planned for the repository is shaded grey. The fracture zones are in green and the crushed zones in grey. The locations of the cross sections in Figures 2- and 2-4 are shown. The location of the boreholes at z=-42 m is marked with a circle.

12 Figure 2-. Vertical cross-section along a north-south line, view towards west, see the location of the cross section in Figure 2-2. Figure 2-4. Vertical cross-section along the first long tunnel section, view towards northeast, see the location of the cross section in Figure 2-2.

13 r n this study two classes are used: hydraulic features, called also hydraulic zones in this text, are as in the bedrock model but crushed and fracture zones are combined to form one data set. This is because the number of crushed zone intersections is not very large, making separate statistical analysis inappropriate. t should be noted that the fracture or crushed zones can also be hydraulically conductive. The hydraulic criterion, K2m higher than 5 1 o- 7 m! s, is met also in about two thirds of the correlated, fracture or crushed zones where these high transmissivities are observed. On the other hand, only in 1 % of the local zones met in one borehole only, both the fracturing and the transmissivity criteria are fulfilled. f the fracture criteria, at least ten fractures/m, would be lowered, some of the zones defined now as hydraulic features would be classified as fracture or crushed zones. Anyhow, it is not unusual that high conductivities are observed also along sparsely fractured borehole sections and that along even frequently fractured sections, high conductivities are not observed. Loosening the criteria would not necessarily increase the number of correlated structures, as the correlation is mainly based on observed connections between structural intersections. n this study the structure intersections and interpretations are taken as in the bedrock model v. 2/1. The summary of the structural intersections for each borehole is shown in Table 2-1. The orientation of structures is mostly based on the mean orientation of fractures within the zone, determined either from the core data as presented in the original drilling reports or from optical borehole images. Seismic measurements are another important source of orienting information. The advantage is that information is gained from greater distances from boreholes. Seismic results are used especially in the orientation of gently dipping correlated structures. The third method to orientate structures has been borehole radar data but radar measurements have not been carried out since borehole KR1. Orientation has not been assigned to 4 structures out of 145 due to lack of data. The continuity of structures in the model is assessed on the basis of geological properties, observed hydraulic responses, seismic measurements, and galvanic charged potential data. Structures with only one borehole intersection are called local structures and those with more than one borehole intersection or the ones between a borehole intersection and the ground surface data are called correlated structures. There is no reliable information on the lateral extension of structures; therefore structures have been modelled according to their observed trend and depth extension. Most of the structures (126 in all) are modelled to intersect only one borehole, whereas 1 correlated structures are interpreted. Crushed zones are modelled to have greater extension than other structural types. This is possible because the geological properties of the crushed zones are more distinct and thereby easier to identify in different boreholes. The local structures are described as discs with constant diameter of 1 m, except in adjacent boreholes KR15- KR1 with diameter of 1 m. n the bedrock model, adjacent intersections along the same borehole are sometimes combined, see Figure 2-5. Combined intersections occur within correlated structures interpreted to have larger continuities. n this study, each of the intersections are counted as one sample when analysing the intensity and orientation of the zones, but in defining the size of the zones, the correlated structures formed a separate set. For some borehole intersections alternative structure interpretations are presented. n this study only the first alternative is considered.

14 1 OL-KR5 ructur ton. stwctur model: Oriented ff"<1ctures Op si Tt!> rt si Clay ldl.xl Grain tll.xl Equnl ore lower hemisphere projection: Structurnl secti on. hydr. mo el : L lnt G r Rt-cl b D Rtlll Hy rl uhe etto, Depth 1:5 Figure 2-5. Example of combining the adjacent structure intersections along a borehole. The example is from the intersection of structure RH21 with borehole KR5. The orientations of the structures in the present bedrock model are concentrated in the range 14-1 for the dip direction and - 5 for the dip angle corresponding to the observed fracture orientation in the boreholes. The thickness of the structures is typically a few metres, the mean thickness being 6.2 m and the median.6 m. The hydraulic features, which form about one third of all the structures, have mostly an intersection length equal to the measurement interval (2 m), lower than the mean thickness. n fact, the thickness of the hydraulic features is even less, because even a single fracture can cause the observed high conductivity. The mean transmissivity of hydraulic features is. 1-6 m 2 /s, of fracture zones 5. 1" m 2 /s and of crushed zones m 2 /s. About 2 % of all structure including both hydraulic and fractured zones, have a transmissivity higher than 1 1 o m 2 s.

15 : Table 2-1. Summary of the borehole structure intersections in the Olkiluoto bedrock model v. 2. Bore hole n total Fracture and crushed zones Hydraulic features d sample borehole count length length count length length count length length length orientation (m) (%) (m) (%) (m) (%) (m) dip direction/dip (degrees) KR / KR / KR / KR KR / KR / KR / KR / KR / KR1 574./ KR 62 1./ KR / KR / KR14 5./ KR15 + KR15B / KR16 + KR16B 171./ KR17+ KR17B 161./ KR1+ KR1B./ KR1+ KR1B / KR2+ KR2B 4 2./ KR / KR22+ KR22B / KR2+ KR2B 2.5/ total Seismics The seismic survey is an investigation method enabling observation of features which do not necessarily intersect boreholes and may be located rather far away from the boreholes or from the ground surface. Vertical Seismic Profiling (VSP) and Horizontal Seismic Profiling (HSP) can be used as reference source data for statistical bedrock modelling because the scale of observed seismic reflectors is comparable with modelled structures. VSP surveys have been carried out in many boreholes since the 1s. VSP reflectors from boreholes KR5, KR1, KR14, and KR1 were selected as an alternative, reference input data because the interpretation procedure has been the same in these boreholes (Cosma et al. 2). Afterwards, the reprocessed reflectors observed in boreholes KR and KR4 were checked and they supported the representativity of the

16 12 selected data set. n Figure 2-6, a D view showing the sub-horizontal reflectors observed in boreholes KR5, KR1, KR14 and KR1 is presented. Seismic reflections are caused by variations of physical properties in the rock. Rock bulk density, P and S wave velocities influence directly the wave reflection, refraction and transmission as well as wave attenuation. Physical variations are geologically related to changes in the rock type (mineral composition), intensity of fracturing, type of fracturing, orientation and magnitude of stress field, weathering, porosity, alteration and foliation (anisotropy) in crystalline bedrock. For example, increase of weathering degree and increased porosity lower the rock density and seismic wave velocity and thus cause variations of physical properties, which further give rise to seismic reflections. Fractured zones, fracturing and also lithological variations can be a significant source of anomalies. There are limitations related to the seismic surveys. Coverage of the VSP survey is a geometric issue, meaning areas and volumes within subsurface space where the reflection can be obtained with specified borehole - shot points - reflector -geometry. Factors affecting the coverage area include the relative orientation of the reflector to the borehole and shot point distances. For example, Figure 2-7 presents the areas at the planned repository depth -42 m, from which reflections of sub-horizontal features have been possible to obtain with a typical borehole - shot point geometry used in surveys at Olkiluoto. KR14 KR1 KR5 KR1 Figure 2-6. n D view of the seismic reflectors, the sub-horizontal set of reflectors is shown.

17 1 Figure 2-7. An example of the seismic coverage analysis, areas from which reflections can be obtained from horizontal structures at the depth -42 m. Another main limitation related to the seismic surveys is the observability related to the rock mass and property variation. Seismic wave attenuates when it propagates through the rock. Due to attenuation, the recorded signal can be close to the ambient noise level or limit of instrument dynamics, and it cannot be observed from recordings although the reflection may have geometrically (in terms of coverage) taken place. Reflectivity describes how large portion of the seismic wave energy reflects from the surface towards the detector. Typical values are a few per cent. n typical Olkiluoto bedrock conditions (wave velocity m/s, frequency 15-5Hz, wave length 1-4 m, seismic Q-value about ), it is known that observation range can be quite large in favourable situations. n homogeneous rock mass, 4-5 m radius around the borehole or even more has been within the observational range. Major fracture zones at Olkiluoto (thicker, intensively fractured) are normally good wave reflectors, too. The ones smaller in extension, thinner and less intensively fractured zones have also considerably weaker reflection characteristics. So many minor type of fracture zones or zones laying in positions and orientations are not covered by VSP surveys. Other features affecting the reliability of the seismic results are as follows: Strength and coherency of the reflection event have influence on how reliably the seismic reflection trace is visible and can be interpreted from the results.

18 14 Continuity of the reflection trace. The best case is that the reflector can be followed close to the borehole and that (same) reflection can be identified in several timedepth sections. n this case the reflection has likely been used in deterministic bedrock modelling. Extrapolation of the reflectors observed far from the borehole and possibly at the same time covered only by a relatively small reflecting surface area to boreholes or surface are unreliable. ntersection angle between reflector and borehole line. When intersection angle is small, small changes of reflector geometry may change the intersection point significantly and evaluation with borehole data becomes more difficult. There may be several possible origins to choose from and uncertainty ncreases. Most reliable sets of seismic results and orientations, which can be used in modelling of fractured zones, are horizontal and gently dipping reflectors, which can be verified with borehole data to represent major fracture zones, and steeply dipping seismic reflectors strong in amplitude, which can be observed within large volumes of rock and can represent major fracture zones. On the basis of seismic data, alternative orientation distribution and feature frequency can be determined. Size of the reflectors is not as useful, because the observed trace is strongly dependent on the orientation of the feature relative to the borehole. Also, when the observation frequency is compared, it has to be taken into account that the VSP method cannot observe features close to the ground surface and part of the reflectors present other features than fractured structures. 2.4 Magnetic ground survey data The fact that most of the boreholes are steeply inclining restricts the possibility to observe sub-vertical features. On the other hand, sub-vertical fractures form a major data set observed on the outcrops. The results of the magnetic surveys were included in the study. The surface magnetic and aeromagnetic anomalies have a trend similar to the seismic reflectors. Only the trend of the anomalies is known, but they are assumed to be vertical as they are likely to be connected to lineaments and faults. Also the VSP reflectors with similar trend and the fractures observed on the outcrops and investigation trenches are vertical (Posiva 2). The results are presented in Figure 2-. The interpretations are by Turo Ahokas, Posiva Oy, and are used here at his suggestion and permission.

19 15 Figure 2-. Anomalies observed in the magnetic ground survey (purple) and aeromagnetic studies (red). 2.5 Simulation The results of the analysis of the bedrock model are used to define the input parameters for statistical modelling. By simulation it is possible to generate realizations of the structure zone distribution to get an idea of the occurrence also in the areas not so well covered with investigations. For the simulations, Fracman software by Golder Associates is used (v. 2., Dershowitz & al. 14). The Fracman software package is designed for geometric modelling of fractures and other discrete features. t also provides stochastic simulation and exploration simulation tools, which are used in this context. Fracture orientation, size, intensity and preferably some properties like transmissivity and thickness distributions are defined and several conceptual models can be selected to generate the fracture models. An arbitary example of a generated structure network by Fracman is given in Figure 2-. The parameters required for the simulations include intensity of the zones, orientation and size distribution of the zones. The intensity is a measure of the frequency of the zones. t can be given either as a desired number of features, as the proportion of the zone area to the total modelling volume (P2 = AzonesiYtotaJ) or as the proportion of the zone volume to the total modelling volume (P = YzonestotaJ). n this work, the proportion of the zone area to the total modelling volume, P 2, was used as a measure of the zone intensity because it can be estimated with the least amount of assumptions. The ideas about the total number of the zones are very vague. The value of P requires an estimation of the zone thickness, which is strongly dependent on the definitions used for

20 16 structure identification. Therefore, although the thicknesses are reported by Vaittinen et al. (2), it was decided not use the thickness values or the volume proportion of the structures in this study. Estimation of the P 2 is not straightforward either, but some conclusions can be made from the observed structure frequency in the boreholes. n this work, P 2 was calculated using the following equations: P2 = A1/ Vr, (Dershowitz et al. 14) Equation 2-1. P2 = 1 ( s cos( a)), (Poteri & Taivassalo 14) Equation 2-2. Here Ar means the surface area of the zones, Yt the total volume, s the mean feature spacing in borehole and a the angle between the borehole and the mean pole (normal) of the fracture set. The values for parameters in the Equations 2-1 and 2-2 were estimated based on the respective data; bedrock model and seismic data. The same applies to the orientations and size distribution. The way these parameters were analyzed is discussed in Chapter. The intensity is assumed to be independent of the fracture size. n the simulations, zones were modelled to a volume extending 4 m along both orth-south and East-West axes and m depth., a volume large enough to cover the planned repository volume. The zones were modelled as hexagons having an equal area to a circle with the given radius (Enhanced Baecher with 6 edges). For each defined model data set, realizations were generated. The number of simulations is not very large, but gives already idea of the variation in the simulation results. Some of the modelled sets were transferred to the ROCK -CAD modelling system because of better visualization possibilities and to be able to view the results along with the bedrock model. The zones in the models exported to ROCK -CAD were modelled as Poisson rectangles with size and width parameters equal to the diameter of the Baecher model, i.e. as rectangles with equal area to the hexagons in the Baecher model. The Poisson rectangles were used, as the import routines to ROCK-CAD for this model type were available. The observed structural intersections in boreholes KR1 - KR2 as in the bedrock model v. 2/1 were compared to the modelling results. Also the number of structural intersections with the new boreholes KR24 - KR2 not yet included in the bedrock model and along the planned OKALO tunnel line down to -42 m level and on the main characterisation tunnel at -42 m level was calculated. The OKALO layout used is according to Posiva 2b.

21 Figure 2-. An example of generated structural model with Fracman software. The parameters used are the following: orientation 16 /2 with dispersion 7, size log normally distributed with mean 1 m and standard deviation 1 m, and constant intensity P 2.1. The size of the box is 1 km and the viewing direction is downwards to northwest.

22 1

23 1 DEFG PUT DATA FOR THE SMULATOS.1 Olkiluoto bedrock model v. 2/1.1.1 Frequency of occurrence Amount From the total core sample length of nearly 1 km, roughly 1% belongs to structures. A summary of the borehole-structure intersection data is presented in Table 2-1. Close to 2 structure/borehole intersections have been observed, from which about one third were correlated with other borehole(s). There are altogether 1 structures with several borehole intersections or both borehole and surface observations. The sample length belonging to correlated structures, i.e. larger-scale fractures with several borehole intersections, is slightly less than half of the total borehole length belonging to structures. There is a rather large variation of the number of structures intersected by a borehole or the structure intersection length in the boreholes, see Figure.1 and Table.1. Three depth intervals z > -1 m, - m < z < -loom and z < - m were considered separately. n the analysis, one borehole is counted as one sample. So the count of samples is 2, except for 1, when z < - m, as five of the boreholes do not extend below - m. Boreholes KR12 and KR22 are clearly more fractured than the other boreholes, whereas borehole KR14 and KR16 present the other end of the range. Typically less than 5% of the borehole length belongs to structures, but especially in the upper part of the rock over 2% of the sample length can belong to structures. One reason for variation is that boreholes are drilled with a special target in mind. Some have been intended to intersect certain structures, whereas some are drilled to rock estimated to be of good quality. aturally also borehole length and orientation affect the number of structures intersected. From many boreholes, the sample is missing from the first tens of meters of the hole, so no structures can be observed, either. This is likely to have an effect on the variation of especially the number of hydraulic zones in the upper parts of rock. n the third depth interval below z = - m, boreholes have very varying lengths. Only one hydraulic zone is observed below z = - m. Hydraulic conductivity is observed also at deeper depths, but there in connection of the fractured or crushed zones. Although the number of hydraulic zones is rather high in the upper parts of the rock, their proportion is notably less than that of the fractured features. Even though the hydraulic zones are always modelled to have at least 2 m borehole intersection length, regardless of the length of the actual conductive borehole interval, their proportion of the sample length is actually less. n cases where there is only one fracture with high conductivity, the actual length can be just few centimetres or even less.

24 2 Fracture and crushed zones z > -1 m Hydraulic zones z > -1 m , *--+ 1 ' ' :::;==-----t..6.6! f c= = r () > >2 Proportion of sarrple length belong to structures (%) c:::j Count Cum frequency ProporUon of sarrple length belong to structures (%) 1- Count Cum frequency Fracture and crushed zones - m < z < -1 m Hydraulic zones z < -1 m , ()'..6! " n r 1 n >2 > () == ' [ 6! E _,_J L_ >4 Proportion of sarrple length belong to structures(%) c:::j Count Cum frequency Proportion of sarrple length belong to structures(%) 1- Count Cum frequency Fracture and crushed zones z < - m ()' ()' = i! o +-+--L >2 Proportion of sarrple length belong to structures(%) c:::j Count Cum frequency Figure -1. Distributions of proportion of the borehole length belonging to fracture and crushed zones and hydraulic zones at three depth intervals a) z > -1 m (number of samples, i.e. boreholes 2), b) - m< z < -1 m (number of samples, i.e. boreholes 2) and c) z < - m (number of samples, i.e. boreholes 1). The scaled frequency is presented as bars and the cumulative frequency as line.

25 21 Table -1. Summary of the length proportion analysis. Set Count of boreholes in the M in Max Average Median Stdev depth interval (%) (%) {%) (%) (%) Fracture and crushed zones z > -1 m Fracture and crushed zones -1 m < z < - m Fracture and crushed zones z < - m Hydraulic zones z > -1 m Hydraulic zones m < z < - m Depth dependency The depth dependency of the structure occurrence was calculated. The results are normalized by the borehole number at the corresponding depth. The normalizing has been done by counting the structure as one if all 2 boreholes cover the depth interval of the structure midpoint. f only 12 boreholes cover the depth, the structure has been counted as two, see Figure -2. The depth dependency of the structure occurrence is presented in Figure.. O 2 6 M W W m -2-4 l l.t 1 This depth S COY red by all 2 borehole s so the weighting lac pr is - -6.s c. 4> " -1 This depth is covered by 6 boreholes so the weighting factor is 2/6 =. Figure -2. ormalizing the results of the structure depth analysis by the number of boreholes at corresponding depth.

26 22 Fracture and crushed zones Hydraulic features c: ai _g : ,.-"' j j! c:: l ]l v = o:,o oc.j: '-'----'-'-'-'-"-' j. c 5.4 c E.2 a c: , -ai _g : Y =-.1-5-Bln( - x) ,--+-l j! _ R' _= _.54_1_--r g - iv.6..4 (.) c E ::J (.) A'-' depth (m, belo sea le-.el) depth (m, belo sea le-.el) Figure -. Depth dependency of the structure intersections. The depth shown in the figure is the depth of the midpoint of the structure below sea level. The frequency is scaled by the number of boreholes at the corresponding depth. The hydraulic features concentrate on the first hundreds of metres below ground level. Already at approximately 1 m depth, their number diminishes rapidly and after m only one hydraulic feature is observed. The occurrence of hydraulic features seems to be roughly proportional to the logarithm of the depth. On the other hand, fractured zones occur rather evenly regardless of the depth. Comparing these results to those presented in Figure -1 suggests that the zones close to the surface have a larger width, although there is no great difference in their number compared to larger depths. As the fracture frequency close to surface is higher, the fact that the borders of the structure intersections are defined using the criterion 7 fractures/m can increase the zone thicknesses in the upper parts of the rock. For the simulations, it was decided to use two depth intervals both for the fractured and crushed zones ( - -1 m and > -1 m) and for the hydraulic features ( - -1 m and - m< z < -1 m). The depth z = -1 m was used as a limit, because in the depth range - -1 m the borehole sample length varies a lot, because in many boreholes no sample is available from the first tens of meters. n that depth range, seismic reflectors are hardly observable and the number of hydraulic features is clearly higher than in the deeper parts of the rock. Spacing The spacing between structures is calculated along borehole for each intersection. The distance to the both neighbouring zones is calculated, see Figure -4. The two distances are denoted as the min dist, i.e. the distance to the closest zone, and the max dist for the longer distance, in the opposite direction. The latter distance describes how long sections of averagely fractured rock can lie between structural intersections. The intervals between borehole top or bottom and the structure are excluded. The structure type is taken into account. For the hydraulic zones, the spacing is calculated to the next intersection regardless of its type. n the spacing calculation for the fracture and crushed zones, the hydraulic zones are excluded.

27 2 Figure -4. Definition used in calculation of the spacing between zones. The intersection for which the values are determined is the middle one marked with the arrowhead. On the left hand side, the calculation is shown in case of a hydraulic feature and on the right in case of a fracture or crushed zone, here the hydraulic features are excluded. The blue line denotes the m in dist, i.e. the closest intersection, and the red line the max dist, i.e. the distance to the neighbouring structure in the opposite direction. The Figure -5 shows the observed spacing distributions for the fracture and crushed zones and for the hydraulic features. Over % of the hydraulic features lie within 2 m distance from another structure. The fracture and crushed zones also occur in groups. n case of fracture and crushed zones, many of the distances falling to the smallest category are between intersections, which have been later modelled as one larger scale feature. The largest intervals with no structure intersections are over m.

28 24 Fracture and crushed zones, rrin distance Hydraulic zones, rrin distance 1.2. i.6 U:.4.2 f- f- / r-4<-. -, 1 rl > > u f.- i.6 i- U:.4 f.-.2 i- i > u.2 distance to the neighbouring structure (m) c:::j Count -+- Cum frequency distance to the neighbouring structure (m) 1- Count -+- Cum frequency j Fracture and crushed zones, rmx distance Hydraulic zones, rrax distance i.6 U: distance to the neighbouring structure (m) c:::j Count -+- Cum frequency > u.2..6 ll distance to the neighbouring structure (m) 1- Count -+- Cum frequency > 1 > u.2 Figure -5. Spacing between structures along borehole calculated separately for the fracture and crushed zones (sample size 1 ) and for the hydraulic zones (sample size 6). Both the minimum distance, i.e. distance to the next, closest structure intersection and also the longer one describing how long sections of averagely fractured rock lie between the structure intersections. ntensity value for the simulation The intensity value P 2 was calculated by using the Equations 2-1 and 2-2. As the area of fractures is not known, the following equation given by Dershowitz et al. (14) was used to approximate P 2, the proportion of fracture area per volume, from the borehole data. Equation -1. n the equation above, s is the expected value of spacing between zones, the same as used in Equation 2-2. Cp is a constant depending on the orientation of the features relative to the line along which spacing is measured. For the value of Cp Dershowitz et al. (14) suggest the value 2, adding that values 1- are normally appropriate. Value 2 was used. The spacing was calculated by dividing the sample length by the number of features. n case of fracture zones, the obtained intensity values presented in Table -2 are comparable with the mean values suggested for spacing in Figure -5, keeping the effect of combined intersections in mind. The angle between borehole and the mean zone orientation a in Equation 2-2 was assumed to be, i.e. the structures perpendicular to the boreholes. This is true for most of the borehole intersections and it

29 gives a reasonable approximation. The value is not very sensitive to changes in the value of a, because the angle can vary up to 2 resulting in an only 5% change of the intensity value. Table -2 gives a summary of the intensity values to be used in Fracman model generation. t can be seen that as a consequence of setting the value Cp to 2 in Equation -1 and a to in equation 2-2, the intensity according to Equation -1 is two times higher than the one according to the Equation 2-2. ntensity of both the fracture and hydraulic zones is higher in the depth range z > -1 m than deeper. n this depth range the intensity of the hydraulic is even higher than the frequency of fracture zones. For reference, La Pointe & Hermansson (22) use for Olkiluoto P2 value.12, which they further apportion to three sets. Table -2. The intensity values (P 2 proportion of the area of the zones to the total volume) used in simulation. Set count of Sample Spacing P2 according to P2 according to features length (m) (m) Equation -1. Equation 2-2. Fracture and crushed zones z > -1 m Fracture and crushed zones z < -1 m Hydraulic zones z > -1 m Hydraulic zones m< z <- 1 m.1.2 Orientation The orientation of the zones has been mainly determined to be parallel to the main fracture orientation within the zone as described in Chapter 2.2. n some cases a couple of close-lying structure intersections are combined to form a single structure intersection of a larger-scale feature. n this study the original, distinct features were used to form a sample. f intersections are combined, only the combined section has an interpreted orientation. n the analysis, the same orientation is used for the distinct parts, which means that the variation in orientation can be slightly underestimated. Table - summarizes the available orientation data of the structural intersections at different depth intervals and for different structural types. The orientation data of hydraulic zones is not as extensive as that of the fractured zones. Figure -6 and -7 present the orientation distribution on equal-area, lower hemisphere stereoplots. For the simulation, it is assumed that the variation (,) from the mean orientation follows the Fisher distributionf(,) with the dispersion coefficient K (Derschowitz et al. 14): f(,) = Ksin ekcose (21t (ek -1), < < rt/2, < < 27t Equation -2

30 26 For each set, the value of parameter K is calculated by the following equation given by Dershowitz & al. (14): K=(-/R/) Equation -. n the equation above, is the total number of zones in the set and RJ is the sum of the unit vectors presenting the zone orientation, if all the zones were parallel R would be equal to and K would be infinite. K is a measure of variation around the mean orientation; a larger value means less variation in the orientation. The resulting values of parameter K are presented in Table - along with the mean orientation for each set. The effect of leaving the duplicates, i.e. counting the combined intersections as one, out of estimation of K was tested. t would have lowered the K of the set fracture and crushed zones z > -1 m and hydraulic zones z < -1 m by one integer. The structures in the bedrock model have practically only one orientation, dipping gently to SE. A couple of steeply dipping features do occur. The dominance of the features dipping gently to SE is enhanced by giving the parts of the combined structure sections the global zone orientation. Many of these sections belong to structures RH21 and RH2A-C. As can be seen from the dispersion coefficient, there is more variation in the zone orientation below z < -1 m both in fracture and in hydraulic zones. Table -. Summary of the orientation data. Duplicate means a structural intersection which was later combined with another and has only one orientation definition for the combined intersection. Set Oriented Duplicates Mean Distribution total Count Count orientation parameter K (Proportion) (Proportion from Dip direction oriented) dip Fracture and crushed zones (7 %) (17 %) z > -1 m Fracture and crushed zones (2 %) (1 %) z < -1 m Hydraulic zones oo 12 z > -1 m (52%) (5 %) Hydraulic zones z < -1 m (2 %) ( %)

31 27 A) n=24 max. dens.=24. (at /66) min. dens.=o.oo Contours at:., 6.,., 15., 1., 21., (Multiples of random distribution) B) n=6 max. dens.=27.76 (at 2/72) min. dens.=o.oo Contours at:., 6.,., 15., 1., 21., 27., (Multiples of random distribution) Figure -6. Orientation of fracture and crushed zones a) at depth range - 1 m and b) at depths greater than 1 m.

32 2 A) n=22 max. dens.=47.71 (at /) min. dens.=o.oo Contours at:., 6.,., 15., 1., 21., 27.,., (Multiples of random distribution) B) e n= max. dens.=4.5 (at2/72) min. dens.=o.oo Contours at: 2., 4., 6., 1., 12., 14., 1., 2., (Multiples of random distribution) Figure -7. Orientation of hydraulic zones at the depth range a) - 1 m and b) 1 - m on a lower hemisphere equal-area stereo plot.

33 Size There is very little information available about the size of the structures. Some rules of thumb how to correlate the observed zone width to the zone length or size have been presented. For example, Munier & Hermansson (2 1) suggest the length to be,.., 1-2 times the width. The deviations from the rule can still be large. Some conclusions can be made by studying the continuity or non-continuity of the structures between boreholes, although the reasoning suffers from the uncertainties related to the structure correlation and an uneven distribution of the boreholes. As a first approximation of the structural size, the distance from a certain structure intersection to other boreholes was calculated. Both the horizontal distance and the distance along the structure were calculated. Anyhow, the resulting distributions did not differ significantly from each other due to the dominance of the sub-horizontal zones. For the un-oriented structures, dip direction/dip / was assumed (equal to the horizontal distance). Also the investigation trenches (TK 1-TK) were used in the calculations, but the closest intersection was never with the trenches and therefore the trenches are left out from the analysis presented here. Figure - shows schematically, how the structural size is estimated. Figure -. Estimation of the structural size; calculating distance to the closest borehole (in red). The distance is calculated along the structure. n the figure, also distances to other boreholes lying close by are shown.

34 n the analysis, the fractured zones were divided in two groups, to local structures, i.e. those with just a single borehole intersection (named KR *), and those with several borehole intersections, i.e. correlated structures (named R */RH*/H*). The first group was mainly used in the size estimation, whereas the other group is used to get an idea of a possible relation between the closest observation and the actual size. The size of the correlated structures was here assumed to equal the maximum distance between correlated borehole intersections. The distribution of the distances between the observed borehole intersection and the nearest uncorrelated borehole is presented in Figure -1. The size of the correlated structures is presented in Figure - together with the distribution of the closest correlated distance for each intersection. The size here is equal to the distance between borehole intersections belonging to the structure located furthest apart. Correlated structures ( <" >75 distance (m) c:::j Closest correlated distance, freq. - Size of the correlated fracture, freq. +- Closest correlated distance, cum ---*-- Size of the correlated fracture, cum Figure -. Distribution of the distance to the closest borehole from the structure borehole intersection of correlated structure (count 6) and the size of the modelled structure (count 1). The structural size here is equal to the distance between borehole intersections belonging to the structure located furthest apart.

35 1 Local structures >75 distance to the closest borehole (m) c::::::j Fracture& crushed zones, frequency - Hydraulic zones, freq. '"' Fracture& crushed zones, cum Hydraulic zones, cum Figure -1. Distribution of the distance to the closest borehole from the structural intersection of local structures with single borehole intersection. The total number of fracture and crushed zones is 7 and that of hydraulic zones 47. Structural size distribution for simulation Handling the data in this way gives an opportunity to estimate the maximum continuity of the structures. The result presented in Figure -1 is calculated for the structures with single borehole intersection. The mean distance to the closest borehole is in the range of 2-25 m. The result depends strongly on the borehole geometry. Presumably, the size of the zones is smaller than the mean distance between boreholes. This is suggested already by the definition, but also supported by the behaviour of the correlated structures. As the simulation gives an opportunity to test the effect of the size distribution, the distribution was modified by using a smaller mean value than the one obtained from the closest borehole analysis. The effect of variation in size was also tested by using smaller variation. The size distributions used in the modelling are presented in Figure - for the fracture and crushed zones and in Figure -12 for the hydraulic zones and the parameters are summarized in Table -4. For the fracture zones, the size was assumed to be lognormally distributed and two mean and standard deviation values (in logarithmic scale) and their combinations were tested. n the arithmetical scale, the mean size varies from 1 m to m and the deviation from 1 m to 4 m. The size of hydraulic features was modelled using the log-normal and power-law distribution. The hydraulic features were assumed to have a smaller size than the fracture zones.

36 2 Table -4. Summary of the distribution types and parameters used for describing the structural size. Fracture and crushed zones Structural size Distribution type Mean Standard deviation Log-normal arithmetical m arithmetical 4 m logarithmic (n) 5. logarithmic (n) 1. Log-normal arithmetical 25 m arithmetical 2 m loqarithmic (n) 5. logarithmic (n).7 Log-normal arithmetical 1 m arithmetical 1 m loqarithmic (n) 4.6 logarithmic (n).7 Log-normal arithmetical 16 m arithmetical 21 m loqarithmic (n) 4.6 logarithmic (n) 1. Hydraulic zones Distribution type Mean Standard deviation Log-normal arithmetical 7 m arithmetical 7 m logarithmic (n). logarithmic (n). Distribution type x min B Power-law 2 m 1.6 Fracture and crushed zones Fracture and crushed zones ! == =---.!.6 -l r -----;, l L-----.,.,..4L size, radius (m) size, radius (m) - logn(,4) - logn(25,2) logn(1,1 ) - logn(,4) - logn(25,2) logn(1,1) - logn(16,21) o closest bore hole - logn(16,21) o closest borehole Figure -. Modified size distribution of fractured and crushed zones, on the left the frequency distribution and on the right the cumulative distribution i.15.::.1.5. ' \. Hydraulic zones /. 2 4 size (m) J -, 2 Hydraulic zones size (m) 6 - logn(7,7) - power-law (1.6, 2 ) closest bore hole - logn(7,7) - power-law (1.6, 2) closest bore hole Figure -12. Modified size distribution of hydraulic zones, on the left the frequency distribution and on the right the cumulative distribution.

37 .2 Seismic data VSP reflectors from boreholes KR5, KR1, KR14, and KR1 were selected as source data for a reference study. The exploitable parameters of the VSP data are frequency of occurrence and orientation. The size of the interpreted reflectors is strongly dependent on the orientation of the reflector and cannot be used for statistical study. Two sets of realizations were created with differing size definition. Set VSP1 was generated with constant size of elements. The radius of elements was 1 m. n the VSP2 set the size of elements followed lognormal distribution with mean value 25 m and standard deviation 2 m. Orientation The orientation of the reflectors is shown on an equal-area lower hemisphere plot in Figure -1. Based on the distribution, three reflector sets were determined: 1) 165 /25, 2) 145 /7, and ) 24 /7. The first set has an orientation equal to the main orientation of the features in bedrock model. The seismic data has been used to define the orientation of the structures, when it has been possible to correlate seismic reflectors with fractured zones met in boreholes. Equal area projection, lower hemisphere Maximum density.7 % at 165/25 Figure -1. Reflector orientation in boreholes KR5, KR1, KR14, and KR1. Frequency of occurrence For the reflectors, the intersection depths along borehole or along extension ofborehole are reported (Cosma et al. 2). The reflectors were divided in three sets. For each set the distance along borehole between the reflectors in that particular set was calculated. The spacing to be used in the intensity determination (Equation 2-2) was defined as a median distance for each reflector set. The distribution of the distance between reflectors of each reflector set is presented in Figure -14. Similarly, the median

38 4 intersection angle of each reflector set and boreholes were determined. The median spacing and intersection angle of the reflector sets were 1) 1 m., 2) 7 m 5, and ) 175 m , Orientation 165/ M:> re Distance between reflectors, m Frequency OJmulative % 1 -,--- -, r 1.2 Orientation 145/ M:lre Distance between reflectors, m Frequency OJmulative % Orientation 24/7 1. >- g Q) ::::l er 4 u M:lre Distance between reflectors, m Frequency OJmulative % Figure -14. The distribution of the spacing of reflectors for each fracture set.

39 MODELLG RESULTS 4.1 Models Based on the statistics presented in the previous chapter, stochastic models of the possible structure realizations were generated. Table 4-1 summarizes the model variations and the parameters used in individual models. The generated stochastic models covered a volume with a range of 4 m in the orth South and East-West directions and reaching from + 1 m to -1 m vertically. To avoid margin effects, the modelled volume is set larger than the volume covered by the boreholes, which is roughly 2 m along orth-south axis, m in East-West direction and 1 m vertically (only four boreholes go deeper than - m). The fracture and crushed zones, hydraulic zones and seismic reflectors were modelled separately. For the different models, different depth ranges were used according to their occurrence, see Table 4-1 for details. For each of the models, realizations were generated. The geometry of the structures was modelled as Enhanced Baecher models with 6 sizes. Termination of the features was not taken into account. The generated realizations were tested by calculating the structural intersections with the boreholes KR1 - KR2 and by comparing those to the observed ones. Also the intersections with the new boreholes KR24 - KR2 and the tunnel to the depth of -42 m were calculated. The location of boreholes KR24 - KR2 is shown in Figure 2-1 and the tunnel sections used in the sampling in Figure 4-1. For the sampling, the tunnel sections having the same orientation and belonging to a depth range modelled with similar rock properties were combined. The combined sections were numbered 2-4 and are shown in Figure 4-1 with the orientation and length.

40 6 Table 4-1. The models used in Fracman simulations. Model Description Set ntensity Dip direction Size (radius, m) Depth range Distribution p2 Mean type Distribution type (Mean, st.deviation) Fracture BRM1-1 m /25 Fisher(14) lognormal, Fracture BRM1 >1 m.2 16/2 Fisher(?) log normal, Fracture BRM2-1 m /25 Fisher(14) log normal 25, Fracture BRM2 >1 m /2 Fisher(?) lognormal 25, Fracture BRM -1 m /25 Fisher(14) lognormal 1, Fracture BRM >1 m /2 Fisher(?) lognormal 1, Fracture BRM4-1 m /25 Fisher(14) lognormal 16, Fracture BRM4 >1 m /2 Fisher(?) lognormal 16, Fracture BRM5-1 m /25 Fisher(14) lognormal, Fracture BRM5 >1 m /2 Fisher(?) lognormal, Fracture BRM6-1 m /25 Fisher(14) lognormal 25,2-1-1 Fracture BRM6 >1 m /2 Fisher(?) lognormal 25, Fracture BRM7-1 m /25 Fisher(14) log normal 1, Fracture BRM7 >1 m /2 Fisher(?) log normal 1, Fracture BRM -1 m.15 15/25 Fisher(14) lognormal 16, Fracture BRM >1 m /2 Fisher(?) lognormal 16, Hydraulic BRM1 <1 m.45 6/ Fisher(12) power law xmin=2, b= Hydraulic BRM1 1- m /2 Fisher(6) power law xmin=2, b= Hydraulic BRM2 <1 m / Fisher(12) log normal 7, Hydraulic BRM2 1- m /2 Fisher(6) log normal 7, Hydraulic BRM5 <1 m / Fisher(12) power law xmin=2, b= Hydraulic BRM5 1- m /2 Fisher(6) power law xmin=2, b= Hydraulic BRM6 <1 m / Fisher(12) lognormal 7, Hydraulic BRM6 1- m /2 Fisher(6) lognormal 7, VSP1 165/ /25 Fisher( 54) constant 1, VSP1 145/ /7 Fisher(2) constant 1, VSP1 24/ /7 Fisher(2) constant 1, VSP2 165/ /25 Fisher( 54) log-normal 25, VSP2 145/ /7 Fisher(2) log-normal 25, VSP2 24/ /7 Fisher(2) log-normal 25, Vertical GEOF ESE-WW / constant constant 5, -1-1 Vertical GEOF2 ESE-WW / constant constant 5, -1-1 Vertical GEOF SW-E.2 5/ constant constant 5, -1-1 Vertical GEOF4 SW-E 4.1 5/ constant constant 5, -1-1

41 7 l}:)r>j Oj'O '=' ' ' <.' <Yo <o <o c:,'='? a, '{?. / % 7. \6' <.6' % 6' <o"' a ra7. ra % c:,r-v i.yc2 "' rr}<o' rr}<o' rp - -1m rp -1- -m c:,<o '=' m Figure 4-1. Tunnel sections numbered 2-4 used in the model testing. The length and orientation of each of the sections is given in parenthesis.

42 4.2 Results The structural borehole/tunnel intersections according to models are presented in Figures The value shown is the average of the realizations generated for each model, and the lower and upper bounds are defined to be equal to the observed standard deviation. When applicable, the observed number of intersections of the corresponding type of structures at the modelled depth range is also shown for comparison. The results show (see Figures 4.2, 4. and 4.6 based on the bedrock model results) that using Equation 2-1 for the intensity determination overestimates the number of intersections of structures per borehole. The intensity value calculated according to the Equation 2-2 seems to be of the correct order as the simulated number of structures per borehole is close to the oberved one (see Figures 4.4, 4.5 and 4.7). The size of the structures does not seem to have a great influence on the number of intersections. The orientation of the zones does have an effect on the intersection frequency. For example, the intensity of the zones having a trend SSE-W has to be high before they are observed in the boreholes, see Figures 4., 4. and 4.1. The frequency of the seismic reflectors is clearly higher than the observed frequency of the structures (see Figures 4. and 4.). n the figures, each reflection set is shown separately and in the fourth figure, the reflector sets are combined and compared to the observed structural frequency. The comparison with the observations is based on structural intersections determined below -1 m due to the fact that VSP method is not applicable close to the ground surface. t can be seen that the number of intersections of generated elements is roughly twice as high as the number of observed structural intersections. There is a strong possibility that the reason for high intensity of elements is due to the fact that apart from the fracture zones there are other features causing VSP reflectors, e.g. lithological variation. The following observations can be made based on the comparison of the simulation results and the borehole observations: n the depth range - -1 m Boreholes KR5, KR14, KR15, KR16 and KR17 are less fractured than average rock whereas boreholes KR12, KR1 and KR22 are more frequently fractured. Hydraulic features are less frequent in boreholes KR2, KR, KR7, KR1 and KR22, but frequent in boreholes KR, KR and KR15. At depths below -1 m Boreholes KR1, KR4, KR, KR14 and KR15 are less fractured. KR12, KR1 are more frequently fractured than the average rock. Hydraulic zones are frequent in borehole KR4. The reason for deviations can be that the borehole is located in a rock where properties differ from the average. Also the borehole orientation and the purpose of drilling can be a reason for the differences in the results. For example, boreholes KR15, KR16 and KR17 were drilled to rock estimated to be less fractured. Borehole KR12 is the only borehole towards East, and it can, therefore, reach features with different orientation than the dominant orientation. Borehole KR1 is less inclined and structures having dip

43 7-75 are observed, although such structures are not present in close-lying borehole KR2 with a parallel orientation. The conclusions presented above are based on comparing the results of models BRM5 - BRM to the observed values. The borehole is considered to differ from the general trend if the observed value differs from the average simulated value more than the standard deviation. Summing up the results for the OKALO tunnels in depth range - 42 m based on models BRM5- BRM, it is estimated that the OKALO would intersect a fracture or crushed zone similar to the ones included in the current bedrock model approximately twenty times. The estimated number of intersections with hydraulic zones is very low, less than ten, because according to the bedrock model the hydraulic features are subhorizontal and close to the tunnel orientation decreasing the intersection probability. Should there be a set similar and with an equal intensity to the VSP2 set 6 (24/7), the number of tunnel intersections with such features would also be roughly 2. Some of the generated models were transferred to ROCK -CAD modelling system for better visualisations. The results are shown in Figures The models shown in the figures include sets defined according to the bedrock model. n addition, one of the VSP sets (set o 6 with dip direction/dip 24 /7 ) is added to depict the effect of a possible sub-vertical set to the structure distribution. This set was selected because its trend coincides with the one of the surface magnetic results. This orientation is also the one most poorly detectable in the boreholes considered in this study. For the CAD visualisations, the models were generated using Poisson rectangle model with orientation and size equal to the Enhanced Baecher model used in the simulations otherwise. The model type was changed because procedures to transform Poisson models to CAD were readily available. The visualisations show possible situations of structural occurrence. The modelled structures do not have an exact location, but in the following Figures , the outline of the Olkiluoto island, the planned area for the repository, the OKALO main level tunnels and borehole intersections are shown as reference. The realizations of the same models are shown to depict the variation possible in the simulated models generated with the same parameters. t can be seen that the structures can form groups leaving areas with just a few structures. Hydraulic features occur only close to the surface. The size of the structures is probably still too large. t would be likely to get better realizations by using the statistical technique only to the local structures and by modelling the correlated structure in a deterministic way, as in the bedrock model. Also the frequency of the structures based on the VSP observations is too high because the set probably includes also other features than structures. For reference, the structures of bedrock model v. 2/1 along the same sections are shown in Figures

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53 4 Figure 4- a. Horizontal intersection at z=-42, the planned level for the OKALO main level characterization tunnel and planned repository depth. The area planned for the repository is shaded grey. Two realizations including sets 25 (bedrock model) in brown are shown.

54 5 Figure 4- b. Horizontal intersection at z=-42, the planned level for the OKALO main level characterization tunnel and planned repository depth. The area planned for the repository is shaded grey. Two realizations including sets 25 (bedrock model) in brown and 6 (VSP reflectors dipping south-west) in green are shown.

55 51 Figure Vertical cross-section in orth-south direction, view towards west. The realization in the upper Figure includes sets 25 in brown (bedrock model), 26 and 27 in blue (hydraulic zones) and the lower Figure in addition also set 6 in green (VSP reflectors dipping towards south-west). OKALO tunnels are shown in grey.

56 52 Figure 4-1. Vertical intersection along the first long tunnel section, view towards northeast. The realization in the upper Figure includes sets 2 5 in brown (bedrock model), 26 and 27 in blue (hydraulic zones) and the lower Figure in addition also set 6 in green (VSP reflectors dipping towards south-west). OKALO tunnels are shown in grey.