Working Report 2014-35
Geological 3D Model of the Investigation Niche in ONKALO, Olkiluoto, Southwestern Finland
Noora Koittola
Posiva Oy
July 2014
Working Reports contain information on work in progress or pending completion.
ABSTRACT
The main goal of this Master of Science Thesis was to create a geological 3D-model of the investigation niche 3 and its surroundings. The model were created for the needs of the rock mechanical back analysis. This study is a part of Posiva's regional studies for characterization of the bedrock. Totally 4 models were created: lithological model, foliation model, fracture model, and physical rock property model. Besides the modeling, there was also made a study of the migmatite structures in the niche. Used geological and geophysical methods were drill core loggings, tunnel mapping, ground penetration radar, mise-á-la-masse and drill hole geophysics.
Four rock types exist at the niche area: veined gneiss, pegmatite granite, diatexitic gneiss and quartz gneiss. The lithological units were modeled primary with the drill core loggings, tunnel mapping and ground penetrating radar. The major lithological units followed the main foliation direction (south dipping). So the continuations were fairly easy to model in the walls and roof, where the data was lacking.
Foliation and fractures were modeled as discs, with mid-points at the measurement points of the structure. There were two main foliation directions 164/46 and 62/39. Fractures were more scattered but three fracture sets can be separated: 156/34, 270/85 and 342/83. The first set is mainly from the drill core loggings, second and third from tunnel mapping. Used methods in foliation model were drill core loggings, tunnel mapping and drill hole geophysics. In fracture model used data was from drill core loggings, tunnel mapping, mise-á-la-masse measurements and drill core geophysic.
Four anomalous zones were detected with the drill hole geophysics. Three of these zones were associated with intensely fractured zones and one was connected to exceptionally high mica content in the gneiss.
Rocks of Olkiluoto are divided into gneisses and magmatic rocks in the geological mapping. Actually almost all Olkiluoto's rocks are more or less migmatites. The migmatite classification is created at the moment so it was reasonable also study the migmatite structures. The recognized structures were schlieren, homophanous, veined and the border of metatexite and diatexite.
Besides the modeling, there was also made a quality control of the used data and methods. During the modeling was also located a slickenside fracture set under the niche. There is a possibility that this fracture set is connected to one of the brittle fault zones (bfz-265). Despite this, these structures cannot be combined before additional studies.
Keywords: Olkiluoto, ONKALO, final disposal of nuclear waste, Surpac, 3D-model, structural geology, geophysics, rock mechanic, POSE experiment, back analysis, lithology, foliation, fracture, anomaly, migmatite, quality inspection, bfz-265.
Geologinen 3D malli ONKALO:n tutkimuskuprikasta 3, Olkiluodossa
TIIVISTELMÄ
Tutkimuksessa luotiin 3D-malli tutkimuskuprikka 3:sta ja sen lähialueen geologiasta. Mallit luotiin erityisesti kalliomekaanisen takaisinlaskennan tarpeisiin. Tutkimus toimii- kin osana Posiva Oy:n aluetutkimuksia, joiden tavoitteena on karakterisoida Olkiluodon kallioperää. Malleja luotiin yhteensä 4 kappaletta: litologiamalli, foliaatiomalli, rakoi- lumalli ja malli kiven fysikaalisista ominaisuuksista. Mallinnuksen lisäksi kuprikasta tehtiin migmatiittirakenteiden tutkimus. Mallinnuksessa käytettyjä geologisia ja geofy- sikaalisia metodeja olivat kairasydänloggaukset, tunnelikartoitus, maatutkaus, lataus- potentiaalimittaukset ja kairareikägeofysiikka.
Litologiamalliin mallinnettiin solideina kuprikan alueella esiintyneet neljä kivilajia: suonigneissi, pegmatiittigraniitti, diateksiittinen gneissi ja kvartsigneissi. Yksiköt mal- linnettiin ensisijaisesti kairasydänloggausten, tunnelikartoituksen ja maatutkausten avul- la. Suurimmat kivilajiyksiköt seurasivat vallitsevaa foliaatiosuuntaa (etelään kaatuva), joten jatkeita oli helppo mallintaa myös kattoon ja seiniin, joista data oli puutteellista.
Foliaatio ja rakoilu mallinnettiin disc-tasoina, joiden keskipiste sijaitsee rakenteen mit- tauspisteessä. Foliaatiosuuntia ilmeni kaksi: 164/46 ja 62/39. Rakoilu oli epäsäännölli- sempää, mutta kolme päärakosuuntaa erottui: 156/34, 270/85 ja 342/83. Näistä ensim- mäinen on määritelty lähinnä kairasydänloggauksista ja kaksi viimeistä ovat tunnelikar- toituksesta. Foliaatiomallin luonnissa käytettiin dataa kairasydänloggauksista, tunneli- kartoituksesta ja kairareikägeofysiikasta. Rakoilumalli luotiin loggausten, kartoituksen, latauspotentiaalin ja reikägeofysiikan avulla.
Reikägeofysiikassa havaittiin neljä fysikaalisesti anomaalista vyöhykettä kuprikan alta. Näistä kolme liittyi ensisijaisesti intensiivisesti rakoilleeseen gneissiin ja yksi gneissin poikkeuksellisen korkeaan kiillepitoisuuteen.
Olkiluodon kivilajit jaotellaan kartoituksessa ja mallinnuksessa gneisseihin ja syväki- viin. Todellisuudessa Olkiluodon kivet ovat kaikki enemmän tai vähemmän migmatiit- teja. Parhaillaan ollaan luomassa alueen migmatiittirakenneluokittelua, joten tähänkin työhön otettiin mukaan myös kuprikan migmatiittien tarkastelu. Kuprikasta löytyneet rakenteet olivat suurimmaksi osaksi eriasteisia schlieren -rakenteita. Kuprikan alueelta löydettiin myös homofaaninen rakenne, suonirakenne sekä metateksiittisen ja diatek- siittisen migmatiitin raja.
Mallinnuksen lisäksi työssä haluttiin keskittyä käytetyn datan ja luotujen mallien laatutarkasteluun sekä niiden käytettävyyden arviointiin. Mallinnuksen aikana löydettiin kuprikan alta myös intensiivisesti rakoillut haarniskarakosetti, joka viittaa mahdolli- suuteen, että kuprikan alla kulkee hauraan ruhjevyöhykkeen (bfz-265) jatke. Näiden rakenteiden yhdistäminen tarvitsee kuitenkin vielä lisätutkimuksia.
Asiasanat: Olkiluoto, ONKALO, ydinjätteen loppusijoitus, Surpac, 3D-mallinnus, rakennegeologia, geofysiikka, kalliomekaniikka, POSE-koe, takaisinlaskenta, litologia, foliaatio, rakoilu, anomalia, migmatiitti, laatutarkastelu, bfz-265.
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CONTENTS
1. INTRODUCTION ...... 3 2. REGIONAL GEOLOGY ...... 5 2.1. Geology of southern Finland ...... 5 2.1.1. Tectonic Evolution ...... 7 2.2 Geology of Satakunta Area ...... 8 2.3 Geology of Olkiluoto Island ...... 11 2.3.1 Lithological Classification used in Geological Mapping ...... 11 2.3.2 Migmatite Classification ...... 11 2.3.3 Deformation and Metamorphism ...... 14 3. THIRD INVESTIGATION NICHE ...... 17 3.1 Excavation History ...... 17 3.2 POSE Experiment ...... 19 4. DATA AND METHODS ...... 23 4.1 Geological Methods ...... 23 4.1.1 Drill Core Loggings ...... 23 4.1.2 Geological Mapping of the Niche and Experiment Holes ...... 24 4.2 Geophysical Methods ...... 27 4.2.1 Ground Penetrating Radar ...... 27 4.2.2 Mise-á-la-Masse Surveys ...... 30 4.2.3 Drill Hole Geophysics ...... 33 4.3 3D-modeling Methods ...... 35 5. RESULTS ...... 37 5.1 Lithological Model ...... 37 5.1.1 Modeled mica bands ...... 43 5.2 Foliation Model ...... 44 5.3 Fracture Model ...... 47 5.4 Physical Rock Property Model ...... 48 5.5 Modeling Files ...... 49 5.6 Migmatite Structures in the Investigation Niche ...... 49 6. DISCUSSION ...... 55 6.1 Applicability and Representativeness of the Data and Methods ...... 55 6.2 Representativeness of the Model ...... 56 6.3 Correlation with the Site Model ...... 57 7. SUMMARY AND CONCLUSIONS ...... 61 8. ACKNOWLEDGEMENTS ...... 65 9. REFERENCES ...... 67 APPENDIX 1. APPENDIX 2. APPENDIX 3. APPENDIX 4. APPENDIX 5. APPENDIX 6. APPENDIX 7. APPENDIX 8. 2
3
1. INTRODUCTION
Posiva Oy is responsible for implementing the final disposal programme for spent nuclear fuel of its owners Teollisuuden Voima Oy and Fortum Power & Heat. Spent nuclear fuel is planned to be disposed at a depth of 400-450 meters in crystalline bedrock on the Olkiluoto site. Posiva submitted an application for a construction license for the disposal facility at the end of 2012 and the active phase of final disposal is scheduled to begin at 2022. This Master of Science Thesis is part of Posiva's site studies for the characterization of the bedrock. The aim of this Thesis is to create geological 3D model of the third investigation niche based on geological and geophysical data.
Posiva has an ongoing rock mechanical POSE (Posiva's Olkiluoto Spalling Experiment) experiment; the goals of the experiment are to settle in situ stress conditions and spalling strength of the bedrock as well as to "act as a Prediction–Outcome exercise" (Johansson et al 2013). However the results of the POSE experiment were complicated due to heterogenous lithology. For that reason, the rock mechanical back analysis cannot be completed without a detailed geological model. In the future this model will be in a key role in determining if geological features such as lithology, foliation or fracturing have an effect on the mechanical properties of the bedrock.
Versatile geological and geophysical data were used in the modeling. Systematic geological mapping was carried out in the POSE niche and in the three experiment holes. 97 drill cores were drilled and investigated from the niche. Also diverse geophysical data related to the POSE experiment and EDZ (Excavation Damage Zone) studies within the niche were available for use. These data comprise ground penetrating radar, mise-à-la-masse and drill hole geophysics. The model itself was created with Geovia Surpac 3D modeling software.
During the work, four separate models will be created: lithological model, foliation model, fracture model and physical rock property model. Lithology is modeled as solids, foliation and fracturing as a discs and physically anomalous features as zones. Apart from the modeling, the migmatite structures of investigation niche 3 will also be studied with the assistance of Aulis Kärki at the University of Oulu.
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2. REGIONAL GEOLOGY
2.1. Geology of southern Finland
The bedrock of southern Finland can be divided into five separate terrains. These are Savo belt (SB), Central Finland Granitoid Complex (CFGC), Tampere belt (TB), Häme belt (HB) and Uusimaa belt (UB) (Figure 1) (Vaasjoki et al. 2005). Savo belt locates at the area, where Arcaean and Fennoskandian shields face. Tampere belt and Central Finland Granitoid Complex form most of the central Finland and Häme and Uusimaa belts form most of the southern Finland.
According to Vaasjoki et al. (2005), dominant rock types of the Savo belt are mica gneisses, which contain volcanic rocks, graphite schists, black schists, and carbonate rocks as interlayers. Magmatic rocks are 1.92 Ga gneissic tonalites and 1.89-1.88 Ga granitoids (Vaasjoki et al. 2005). Savo belt (SB) is characterized by several shear zones (Vaasjoki et al. 2005).
Central Finland Granitoid Complex (CFGC) consists mainly of 1.89-1.88 Ga synkinematic tonalites, granodiorites and granites as well as 1.88-1.86 Ga postkinematic quartz monzonites and granites (Vaasjoki et al. 2005). According to Vaasjoki et al. (2005), minor areas of the complex consist of subvolcanic intermediate rocks, mafic igneous rocks and remnants of supracrustal belts.
According to Vaasjoki et al. (2005), Tampere belt (TB) consists of 1.90-1.89 Ga intermediate and felsic volcanic rocks as well as turbiditic mica schists with conglomerate interlayers. Also mafic volcanic rocks occur. The youngest rocks are 1.88 Ga granitoids which crosscuts the supracrustal rocks (Vaasjoki et al. 2005).
Häme belt (HB) is characterized by volcanic rocks. According to Vaasjoki et al. (2005), only at the western parts of the belt some metasedimentary rocks occur. Main igneous rock types are 1.88 Ga granitoids and 1.84-1.82 Ga granites which crosscuts the supracrustal rocks (Vaasjoki et al. 2005).
Uusimaa belt (UB) is sedimentary dominated belt that contains mica schists and gneisses with carbonate rock interlayers. According to Vaasjoki et al. (2005), also felsic sedimentary rocks of volcanic origin are typical to the Uusimaa belt. The composition of volcanic rocks varies usually from mafic to intermediate but in western parts of the belt volcanism is bimodal (Vaasjoki et al. 2005). Similarly to Häme belt, igneous rocks are 1.88 Ga granitoids and 1.84-1.82 Ga granites which crosscuts the supracrustal rocks (Vaasjoki et al. 2005). 6
Figure 1. The geological setting of the Fennoscandian area (Lehtinen et al. 2005).
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2.1.1. Tectonic Evolution
Fennnoscandian Shield has formed between 2.06 - 1.77 Ga during the five orogenies: Lapland-Kola orogen, Lapland-Savo orogen, Fennian orogeny, Svecobaltic orogeny and Nordic orogeny (Lahtinen et al. 2005) (Figure 2). According to Lahtinen et al. (2005), these orogenies partly overlap in time and space. Even though, before the active stage of orogenies started, Arcean craton started to break up. Multiple rifting of the craton occurred at 2.5-2.1 Ga. The location of the breakup followed the present western margin of the Karelian craton and created marginal basins along the edge.
Lapland-Kola orogen was most active at 1.94-1.91 Ga ago. The orogen started by subduction related magmatism at Inari area and Tersk terrain (Lahtinen et al. 2005). According to Lahtinen et al. (2005), at 1.93 Ga subduction was active towards the southwest under the Lapland-Kola area and back-arc basin formed. Back-arc basins were shortened because of Kola craton collided to Karelian craton at 1.93-1.91 Ga (Lahtinen et al. 2005). The accretion of Tersk terrain occurred at ca. 1.91 Ga. The orogenic collapse of the Lapland-Kola orogen occurred at 1.88-1.87 Ga and this caused thinning of the crust (Lahtinen et al. 2005).
Collision of the Lapland-Savo orogeny started 1.92 Ga ago when Kittilä allocton emplaced and at the same time the Savo belt accreted to the Keitele microcontinent (Lahtinen et al. 2005). According to Lahtinen et al. (2005), continent-continent collision of Karelia craton and Keitele microcontinent in Finland and Norrbotten microcontinent in Sweden occurred at 1.92-1-89 Ga. Bothnian microcontinent collided to Norbotten and Keitele 1.90 Ga (Lahtinen et al. 2005). This collision caused magmatism which formed Knaften arc at 1.90 Ga (Lahtinen et al. 2005).
Between Lapland-Savo and Fennian orogenies, "the accretion of Keitele microcontinent and Karelia craton resulted in a subduction reversal" which caused the extension at the southern edge of Keitele microcontinent (Lahtinen et al. 2005). According to Lahtinen et al. (2005), in Sweden, the docking of Bothnia and Norrbotten led to a subduction switch-over. This caused a new subduction zone under either oceanic crust or Bothnia microcontinent at 1.89-1.87 Ga (Lahtinen et al. 2005).
During the Fennian orogeny (1.89-1.85 Ga) the tectonic events differ in time across the Gulf of Bothnia from Finland to Sweden because the fault system separated Keitele and Bothnia microcontinents (Lahtinen et al. 2005). According to Lahtinen et al. (2005), oceanic plate subducted towards south and this caused the combination of Tavastia island arc and Bergslagen microcontinent (Lahtinen et al. 2005). After that, Tavastian island arc collided to Keitele microcontinent 1.89 Ga ago. The major collisional stage is associated with voluminous continental growth in current area of Central Finland (Lahtinen et al. 2005).
Lapland-Savo orogeny attempted to collapse simultaneously with the collisional stage of Fennian orogeny (Lahtinen et al. 2005). According to Lahtinen et al. (2005), this caused related magmatism at central Finland's area. At the end of Fennian orogeny, subduction reversal occurred at the southern margin of the shield. Also the boundaries between Karelia-Keitele and Keitele-Tavastian stabilized at the time between Fennian orogeny and Svecobaltic orogeny (Lahtinen et al. 2005). 8
Svecobaltic orogeny occurred at 1.84-1.80 Ga when Sarmatia continent collided obliquely to the southern parts of Fennoscandian continent (Lahtinen et al. 2005). According to Lahtinen et al. (2005), this collision caused migmatization, thrusting and folding in the southern Finland. The cyclic nature of events caused the complicated stacking structure to the bedrock of southern Finland (Lahtinen et al. 2005). In the southwestern parts of Fennoscandia, Andean-type magmatic stage occurred (ca. 1830 Ma) associated with the collision (Lahtinen et al. 2005).
Nordic orogeny occurred at 1.82-1.79 Ga ago and the presently exposes as Transcandinavian Igneous Belt (TIB) (Figure 1) (Lahtinen et al. 2005). According to Lahtinen et al. (2005), the orogeny is proposed as continent-continent collision, possibly between Fennoscandia and Amazonia. The main effects of the collision can be seen at the central parts of the Fennoscandian Shield, currently locating in Sweden and Norway (Lahtinen et al. 2005).
Figure 2. Tectonic evolution of Fennoscandia.
2.2 Geology of Satakunta Area
The supracrustal rocks of Satakunta formed during the evolution described in Chapter 2.1.1 (Paulamäki 2009). In Satakunta area these rock types forms a belt of pelitic migmatites (PEMB) at southwest and a belt of psammitic migmatites (PSMB) at northeast (Paulamäki 2002).
Metamorphism in Satakunta area took place in 750-800°C and 5-6 kb and ductile deformation and migmatitization are connected to close to the peak of metamorphism (Korhonen et al. 2010). In Figure 3, the rocks of Olkiluoto island are marked as mica schists and mica gneisses.
After orogenies, rapakivi magmatism of southern Finland took place at 1.65-1.55 Ga. During this stage, the Laitila rapakivi batholith and the Eurajoki stock were intruded 1.58 Ga (Vaasjoki 1996). 9
Jotnian sedimentary rocks deposited ca. 1.4-1.3 Ga ago (Korhonen et al. 2010). The Satakunta sandstone deposited to the graben structure (Korhonen et al. 1993, Korja &Salonen 1995). According to Korhonen et al. (1993), the depositional setting of the Satakunta sandstone is comparable with fluvial delta. The exact deposition period cannot be defined, but it is supposed, that deposition took place between rapakivi magmatism and diabase magmatism.
Postjotnian olivine diabase veins and sills are the youngest rocks (1270-1250 Ma) in the Satakunta area (Korhonen et al. 2010). These veins are usually north-south trending (Suominen 1991, Veräjämäki 1998) and the sills are gently dipping or horizontal. 10
the black square (Posiva Oy 2011).
. Lithology of the Satakunta area. Olkiluoto Island is marked with
Figure 3 11
2.3 Geology of Olkiluoto Island
2.3.1 Lithological Classification used in Geological Mapping
In geological mapping, the rocks of Olkiluoto are firstly classified as variably migmatized high-grade metamorphic rocks and magmatic rocks (Posiva Oy 2011) and rocks are further classified according to the BGS (British Geological Survey) standards (Mattila 2006). According to Mattila (2006) the types of metamorphic gneisses are stromatic gneiss (SGN), veined gneiss (VGN), diatexitic gneiss (DGN), mica gneiss (MGN), quartz gneiss (QGN), mafic gneiss (MFGN) and tonalitic-granodioritic gneiss (TGG). The magmatic rocks are pegmatite granite (PGR), K-feldspar porphyry (KFP) and diabase (MDB) (Mattila 2006). A closer classification of the gneisses is shown in Figure 4. This classification is used in tunnel mapping and drill core logging.
Figure 4. Classification of the gneisses in Olkiluoto (Aaltonen et al. 2010).
2.3.2 Migmatite Classification
The rocks in Olkiluoto can also be divided by the state of migmatitization. Migmatites are mixtures, consisting of metamorphic looking and igneous looking rock components (Kärki 2014). In literature, there are several different definitions for the term migmatite and as examples the definitions of Sederholm (1907) and Mehnert (1968) are mentioned here. According to Sederholm (1907) migmatite is "a mixture of two genetically different constituents of which one is of a more intrusive type than the other". Examples of these rocks are gneissic granites, which show structures characteristic to the partial melting (Sederholm 1907). According to Mehnert (1968) migmatite is "megascopically composite rock consisting of two or more petrographically different parts. One is a country rock in a more or less metamorphic state and the other is pegmatitic, aplitic, granitic or generally plutonic appearance" (Mehnert 1968). In any case, whatever the 12
definition is, migmatites are "closely associated with high-grade metamorphism but equally with magmatic prosesses" (Kärki 2014).
Migmatites of Olkiluoto are formed in high temperature in prograde or/and retrograde metamorphism where partial melting or anatexis occurs in pre-existing rocks (Kärki et al. 2006). Migmatized rocks can be divided into paleosome and neosome. Paleosome is a remnant of source rock and neosome consists of melanosome and leucosome (Kärki 2014). According to Sawyer (2008), three different leucosome types can be identified: in situ leucosome, in-source leucosome and leucocratic dikes.
The intensity of migmatitization divides rocks into two main types: metatexites and diatexites (Figure 5). In metatexites, several discrete components can be detected and the rock is overall heterogenous (Kärki 2014). According to Kärki (2014), paleosome is identifiable and pre-migmatitization structures, for example layering and foliation, are identifiable. The neosome content is usually something between 20-30% but it can vary. Diatexites are more intensively melted rocks, where paleosome and pre-structures are not always detectable (Kärki 2014). According to Kärki (2014), neosome forms a major part of diatexites and the appearance of neosome varies. For that reason diatexites are difficult to classify. A more specific classification of migmatites is based on visible factors and "variables describing the properties of the neosome and paleosome" (Engström 2014).
Figure 5. The classification of migmatites of the Olkiluoto island (Kärki 2014).
Migmatites of Olkiluoto can be divided into ten different classes based on their structures. These structures are dike-structure, net-structure, breccia-structure, patch- structure, layer-structure, vein-structure, schollen structure, schlieren structure, nebulitic 13
structure and homophanous structure (Figure 6) (Kärki 2014). Kärki (2014) described the terms as: I) Dike structure occurs as parallel or sub-parallel leucosome dikes cross- cutting the paleosome. II) Net structure is more complex dike system and dikes are oriented in at least to two or more directions. III) Breccia structure occurs when rather sharp paleosome blocks are surrounded by a moderate amount of leucosome. IV) Patch structure is the lowest grade of migmatite, where melting has not progressed further and leucosome occurs as patches. V) Layer structure occurs when leucosome is parallel with foliation. Stromatic gneisses are examples of these layer structure migmatites. VI) Vein structure occurs when leucosomes are "pipe-like" veins. VII) In schollen structure paleosome exist as roundish blocks and leucosome surrounds them completely. VIII) Schlieren or flame structure consists of flame shaped paleosome and narrow and longish blocks of mafic restite. IX) Nebulitic structure occurs in high-grade migmatites, where the pre-existing rocks are scarcely distinguishable from the neosome mass. X) Homophanous structure is "dominated by non-segregated neosome and mesosome" (Kärki 2014).
Figure 6. Examples of common migmatite structures in Olkiluoto: 1. dike-structure, 2. net-structure, 3. breccia structure, 4. patch structure, 5. stromatic (layer-) structure, 6. vein structure, 7. schollen structure, 8. schlieren structure, 9. nebulitic structure, 10. homophanous structure (Kärki 2014).
Even though migmatite structures are described in Olkiluoto as ten separate classes, they actually form a transitional series according to the state of migmatitization (Kärki 14
2014). For example as the degree of migmatitization increases, dike structure gradually transforms into net structure or breccia structure and ultimately to schollen structure.
2.3.3 Deformation and Metamorphism
The metasedimentary rocks of Olkiluoto island metamorphosed in upper amphibolite facies, at the temperature of 650-700°C and at the pressure of 4-5 kb (Aaltonen et al. 2010) and they deformed ductilely in four stages (D1-D4) (Engström 2014).
The oldest visible structures are primary lithological lamination S0 and slightly segregated schistosity S1 (Engström 2014). The deformation phases D2, D3 and D4 can be separated from each other. During the D2, the pervasive east-west oriented S2 foliation was formed (Engström 2014). According to Engström (2014), also the migmatization was intense during the D2.
The D3 phase deformed primary structures and secondary patterns that were formed earlier. Migmatites formed F3 folds and ductile shear zones, parallel with the S3 axial planes, were formed. Also dextral shearing occurred in S2 structures and thrust faults were formed (Engström 2014). Engström (2014) continues that also earlier S2 foliation rotated mostly parallel to F3 axial surfaces during the D3. Migmatitization continued through the D3 and neosome veins and patches were formed.
During the D4 stage, axial planes of F4 folds and foliation rotated to NNE-SSW (Engström 2014). Small scale, S4 oriented dextral shears are also associated with this deformation phase. D4-deformation was most intense at eastern part of the island (Engström 2014). According to Engström (2014), the pinitization of the cordierites and the formation of a migmatites, which contains quartz and k-feldspar porphyroblast, are associated with this deformation phase.
In addition to ductile deformation, some semi-brittle and brittle structures also exist. Faulting types in Olkiluoto are thrust faults and strike-slip faults (Aaltonen et al. 2010). According to Aaltonen et al (2010), thrust faults are typically south-east dipping and strike-slip faults are north-east to south-west striking.
There are also three main fracture directions in Olkiluoto. According to Posiva Oy (2011), most of the fractures are gently (0-40°) dipping to the S or SSE. In addition two steeply-dipping N-S and E-W striking fracture clusters are observed (Posiva Oy 2011). The lithological map of Olkiluoto is shown in Figure 7.
In post D4-stage the rocks continued to cool, but some features, connected to lowering temperature can be identified from the rocks of Olkiluoto island. Low temperature (100- 300°C) hydrothermal fluids, related to the rapakivi magmatism in the Satakunta area (Haapala 1977), caused some alterations, specifically connected to the structures of brittle deformation. The most typical hydrothermal alterations in Olkiluoto are sulphidization and kaolinization. In sulphidization, the alteration product is generally pyrite (Aaltonen et al. 2010). According to Aaltonen et al. (2010), there is also illitization which can be seen in altered leucosomes and in several thrust faults. 15
is marked on the map with black square (Posiva Oy 2011).
Figure 7. Lithology of Olkiluoto Island. The location ONKALO
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3. THIRD INVESTIGATION NICHE
3.1 Excavation History
The third investigation niche is located in ONKALO tunnel chainage level 3620 at -345 meters below the surface (Posiva Oy 2011) (Figure 8).
Figure 8. The location of the investigation niche 3 in ONKALO.
The niche was excavated from June 2009 to November 2009 and it was originally used for EDZ (Excavation damage zone) studies and sometimes referred to as the EDZ tunnel (Hurmerinta et al. 2010). Excavation with explosives causes a damage zone in the surrounding rock (Figure 9), creating possible hydraulic connections. This damage extends a maximum of 30-40 cm outside the tunnel profile in ONKALO.
The studying of these zones is therefore critical for tunnel constructing and long term safety (Mustonen et al. 2010, Tsang et al. 2005). Even though, the main goal of the EDZ studies is to develop an excavation technique that minimizes the damage (Tsang et al. 2005). The ground penetrating radar has produced reliable results in Olkiluoto and it is therefore the most used method in EDZ studies (Mustonen et al. 2010). For example in a study by Cal and Kaisers (2005), microseismics and acoustic emission was used to create a numerical model. 18
Figure 9. Approximated excavation damage zone shown with a dash line around the tunnel profile.
The niche was excavated by using different blasting techniques to minimize EDZ and the target of first phase of the EDZ study was to control the excavation (Mustonen et al. 2010). According to Mustonen et al. (2010), the second phase of the study mostly concentrated on geophysical testing. During phase 2, seismic testing (Hurmerinta et al. 2010), drill hole geophysics, flow log and ground penetrating radar measurements (Mustonen et al. 2010) were carried out. The EDZ-field, which nowadays is located in investigation niche 3, is actually probably one of the most investigated areas in the world.
Planning of Posiva's Olkiluoto Spalling Experiment started in 2008 and continued till 2009. The decision was to execute the test in the EDZ tunnel, but the tunnel was too narrow for the experiment (Johansson et al 2013). Because of this, an extension of the niche was excavated between January and March in 2010 (Johansson et al. 2010) (Figure 10). The POSE experiment is explained in more detail in Chapter 3.2. 19
Figure 10. The layout differences in investigation niche 3 between the present (left) and before the extension (right).
3.2 POSE Experiment
After the extension of the niche, preparations for POSE (Posiva's Olkiluoto Spalling Experiment) started in 2010. The experiment was divided into phase 1, 2 and 3. The target of the first and second phases was to determine the spalling strength of the veined gneiss, confirm the in situ stress conditions at -345 m and to "act as a Prediction– Outcome exercise" (Johansson et al. 2014).
The first phase was to drill two nearly full scale deposition test holes, which are called experiment holes 1 and 2 (ONK-EH1 and ONK-EH2) (Johansson et al. 2014). Johansson et al. (2014) continues that a 90 cm thick rock pillar was left between the 20
experiment holes. The first phase is therefore also referred to as the Pillar test. The layout of ONK-EH 1 and 2 is shown in Figure 11. The aim was to focus the high stresses to the pillar and cause spalling and damage into the pillar (Johansson et al. 2014).
Figure 11. The layout of investigation niche 3 and experiment holes 1 and 2.
The second phase of the POSE experiment was heating of the rock mass near the pillar. Heating increases the stress state in the pillar and spalling should occur. According to Johansson et al. (2014), two heaters were installed at the north end of the pillar and two at the south end. During heating, ONK-EH2 was filled with sand (Johansson et al. 2014). Heating continued for two months in the spring of 2011.
The results of phases 1 and 2 were quite unexpected and did not produced spalling at the pillar as expected. Rock mass in Olkiluoto doesn't behave in brittle manner as previously tested in Mine-by-experiment in AECL's (Atomic Energy of Canada Limited) Underground Research Laboratory (URL) in Canada and in the ASPE- experiment in ÄSPÖ HRL (Hard Rock Laboratory) in Sweden (Johansson et al 2013, Martino et al. 2004). In AECL's experiment, the experimental tunnel was excavated parallel with the principal stress (σ1/max) and the spalling damage appeared in σmin direction as is shown in Figures 12a and 12b (Martin et al. 1996). 21
Figures 12a and 12b. Damage in the experimental hole in AECL's spalling experiment.
In ÄSPÖ's Hard Rock Laboratory, the spalling experiment was executed between 2002- 2006 (Andersson 2007). The experiment setup (pillar test) was the same as the one later used in the POSE experiment. The damaging "took place close to the centre of the pillar where the tangential stress was highest" (Figure 13) (Andersson 2007). In Olkiluoto only minor spalling could be seen in the pegmatite granite and the veined gneiss was damaged irregularly (Johansson et al. 2010). According to these results, the failure criteria are in Olkiluoto controlled by the heterogeneity and anisotropy of the rock.
Figure 13. Spalling in ÄSPÖ experiment (Andersson 2007).
The third phase was executed in experiment hole 3 (ONK-EH3) (Figure 14). The hole was heated from inside to associate thermal expansion around the experimental hole (Valli et al. 2011, Valli et al. 2012). According to Valli et al. (2012), the three primary goals of third phase were: "establishing the in situ spalling/damage strength of Olkiluoto pegmatite granite, establishing the state of in situ stress at the -345 m depth level and act as a Prediction–Outcome (P–O) exercise". 22
Figure 14. The layout of investigation niche 3 and experiment hole 3.
Mechanical calculations of the POSE experiment were carried out with 3DEC program. 3DEC (3 Dimensional Distinct Element Code) is a "three dimensional numerical program based on the distinct element method for discontinuum modeling" (Itasca Consulting Group Inc. 2013). Because of that, the program is suitable for jointed and faulted bedrock. According to the predictions, suitable heating was determined to be 3 weeks with 400W per heater and then 9 more weeks with 800W per heater (Valli et al. 2012). 12 weeks of heating with eight heaters caused damages in the veined gneiss but not in the pegmatite granite. In the future the heating test will be repeated using eight heaters located around experiment hole 3. The final interpretations of the POSE experiment will be carried out using a rock mechanical back-analysis at the next phase (Valli et al. 2012). The geological model created as a part of this Master of Science Thesis will be used in the back-analysis.
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4. DATA AND METHODS
4.1 Geological Methods
4.1.1 Drill Core Loggings
A total of 97 drill cores were drilled around the investigation niche. ONK-SH1-49 and SH151-152 are so called short holes that have been drilled from the EDZ-field (Mustonen et al. 2010). ONK-PP199 and ONK-PP200 are long pilot holes that have been drilled before the excavation (Hurmerinta et al. 2010). According to Hurmerinta et al. (2010) ONK-PP202-205 and ONK-PP207-209 are pilot holes for the EDZ investigation field. ONK-PP224-225 were also drilled from the tunnel towards the investigation niche and ONK-PP226 was drilled under the niche (Toropainen 2010). The rest of the drill cores (ONK-PP223, ONK-PP253-261, ONK-PP268-272, ONK- PP340-347, ONK-PP398-405 and ONK-PP410-413) are more or less vertical and run downwards from the floor of the niche. The drilling layout is shown in Figure 15.
Figure 15. The drill core layout in and around the investigation niche 3.
The drill cores were drilled during the years 2009-2013. All the cores were logged according to the drill core logging sheet presented in Appendix 1. Most of the loggings were carried out by Vesa Toropainen from Suomen Malmi Oy (SMOY) but the loggings of drill cores ONK-PP398-405 were carried out as a part of this Thesis during the summer of 2013. Lithological description, fracturing, foliation, Q-class, fracture frequency, RQD, fracture zones and core loss, weathering degree, core dicing and zone intersections are defined during drill core logging (Appendix 1) (Toropainen 2008). The Q-class and RQD are rock mechanical indices that provide information about the quality of the rock.
RQD (rock quality designation index) number designates the sum of over 10 cm core sticks in 1 m distance (Deere et al. 1988). The index was created in 1967 by Deere, Hendron, Patton and Cording. RQD gives a value between 0-100 and it is calculated using the following formula: