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Bachelor Thesis

Geological characterisation of an underground research facility in the tunnel

Author(s): Meier, Matthias

Publication Date: 2017

Permanent Link: https://doi.org/10.3929/ethz-b-000334001

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Bachelor Thesis 2017 Geological characterization of an underground research facility in the Bedretto Tunnel

Presented at the department of earth science at ETH Zurich

Institute of Geology

Supervised by

Dr. Florian Amann ETH Zurich, Scientific Manager Deep Underground Geothermal Lab, SCCER-SoE Dr. Valentin Gischig ETH Zurich, Swiss Competence Center for Energy Research SCCER-SoE Hannes Krietsch ETH Zurich, Swiss Competence Center for Energy Research SCCER-SoE

Submitted by Matthias Meier 14-924-476 30.6.2017 Abstract A geological characterization of a cavern in the Bedretto Tunnel is made to support future hydro- mechanical experiments planned by the SCCER – SoE. The main goal is to get information about the persistence of fault zones as well as to ascertain the stress field around the cavern. Based on mapping of the tunnel from Tunnel Metre (TM) 1964 to TM 2130 a 3D model and a horizontal tunnel plan are made. The mapped structures are compared with an aerial image of the ground surface above the tunnel and some measured structures from swisstopo. They show two groups of orientation and especially high persistence in the SW/NE direction. Due to high persistence, an extrapolation of mapped fault zones is made. The influence of topography on the tunnel is illustrated with 2D finite element analysis. Stress trajectories show a vertical orientation of the 휎푍 around the cavern, concluding the influence is negligible. According to the world stress map the orientation of the maximum horizontal stress 휎퐻푚푎푥 should be parallel to the tunnel axis. Based on observed spalling (i.e. stress induced brittle failure) in the tunnel a 2D finite element analysis of a cross section at TM 2035 is made to get the k-value (i.e. the ratio between the vertical stress 휎푣 and the horizontal stress 휎ℎ (perpendicular to the tunnel)). The vertical stress around the test site is 26.89 MPa, the k-value is 0.8-1, which leads to the conclusion that the horizontal stress 휎ℎ is between 21.5 - 26.89 MPa. These results show that 휎푣 > 휎ℎ and 휎퐻푚푎푥 > 휎ℎ.

Unclear is the relation between 휎퐻푚푎푥 and 휎푣. The area around the Bedretto Tunnel can be in a normal faulting regime (휎푣 > 휎퐻푚푎푥 > 휎ℎ) or a strike-slip regime (휎퐻푚푎푥 > 휎푣 > 휎ℎ). In conclusion, the existing large fault systems crossing the cavern are ideal targets of a hydro-mechanical experiment. As the stress regime is not entirely defined based on current knowledge, local stress characterization is required. One principal stress component is vertical, which is important for the design of stress characterization boreholes.

i

Contents

Abstract ...... i

1 Introduction ...... 1

1.1 Incentive...... 1

1.2 Site description...... 2

1.2.1 Geographical description ...... 2

1.2.2 Tunnel data ...... 3

1.2.3 Geological description ...... 4

2 Methods ...... 6

2.1 Tunnel mapping ...... 6

2.1.1 Mapping in the tunnel ...... 6

2.1.2 3D model ...... 7

2.1.3 Horizontal tunnel plan ...... 8

2.1.4 GIS-Data ...... 8

2.1.5 Strike comparison ...... 8

2.1.6 Extrapolation of the fault zones ...... 9

2.2 Stress characterization...... 10

2.2.1 World stress map WSM ...... 10

2.2.2 Focal mechanism ...... 11

2.2.3 Area stress information ...... 12

3 Results ...... 14

3.1 Tunnel mapping ...... 14

3.1.1 3D model ...... 14

3.1.2 Horizontal tunnel plan ...... 16

3.1.3 GIS-Data ...... 20

ii 3.1.4 Strike comparison ...... 21

3.1.5 Extrapolation of the fault zones ...... 24

3.2 Stress characterization...... 25

3.2.1 World stress map ...... 25

3.2.2 Focal mechanism ...... 27

3.2.3 Area stress information ...... 29

4 Discussion...... 33

4.1 Tunnel mapping ...... 33

4.2 Stress characterization...... 33

5 Conclusion ...... 34

iii 1 Introduction 1.1 Incentive To unlock deep geothermal resources for electricity production, the permeability in 4-5 km depth has to be significantly enhanced. Large volumes of water (i.e. 150-200 l/min) need to be circulated at rock temperature of 150-200 °C. High pressure fluid injections are typically used to increase the permeability. These fluid injections are often accompanied by induced seismic events. Unfortunately, seismic events have been felt at the earth surface and caused some minor infrastructure damage (e.g. Basel (Giardini & Deichmann, 2007)). To enable the large-scale utilization of deep geothermal energy in , the technologies to enhance permeability must be improved and validated to reduce the risk of felt induced seismic events to a minimum. The Swiss Competence Center for Energy Research – Supply of Energy (SCCER-SOE) currently performs a series of in-situ stimulation experiments, that aim a better understanding of the seismic-hydro-mechanical processes associated with high pressure fluid injections. In a first attempt a decametre-scale in-situ stimulation experiment was recently finalized at the Grimsel Test Site (GTS) with approximately 480 m overburden in crystalline rock. In a second step, a pilot stimulation is planned in the Bedretto Tunnel at approximately 1100 m depth with significantly increased flow rates and volume as compared to the GTS experiment. This experiment will be performed in 2018.

Key requirements for a successful planning of this pilot stimulation are a detailed knowledge of the rock structures (e.g. orientations and persistence), the in-situ state of stress (magnitude and orientation) and the associated slip tendency.

This thesis focuses on an in-depth analysis of the geological structures within the experimental volume for the second pilot stimulation. This includes mapping of the tunnel and the identification of fault zones and their architecture. Further, this thesis will focus on a review of stress information in the area of the Bedretto Tunnel including the world stress map, analysis of focal mechanism and stress information inferred from stress induced structures around the Bedretto Tunnel. The fact that the tunnel walls are unsupported allows a detailed analysis of both, structures that intersect the tunnel and stress induced failure.

The aim of this thesis is to support the implementation of a pilot stimulation at the Bedretto Tunnel between TM 1964 and 2130 through characterizing the rock mass in terms of its structural settings and a detailed rock mechanics analysis of stress induced fractures in vicinity of the experimental tunnel section. This includes a 3-dimensional map of the various structures, their extrapolation with distance to the tunnel and numerical back-analysis of tunnelling induced fractures.

1 1.2 Site description 1.2.1 Geographical description The Bedretto Tunnel is a 5218 m long side branch of the Furka Base Tunnel and connects the main tunnel with the Val Bedretto. It is in the Swiss Central Alps

2 Appendix

, under the Piz Rotondo and goes from Ronco in the southeast towards northwest.

The research facility will be between TM 2000 and TM 2100, in a cavern with a bigger cross section compared to the majority of the Bedretto x/y (CH1903/LV03) Dipdr Dip Tunnel. Mapping of the tunnel was performed 680'593.2, 151'314.1 108° 73° 679'851.2, 150'258.2 128° 70° 680'814.0, 150'899.1 140° 90° 680'197.3, 152'017.3 143° 90° 680'271.2, 151'654.1 150° 63° 680'499.2, 151'718.1 157° 83° 680'573.7, 149'964.2 296° 60° 680'051.0, 150'238.2 309° 53° 680'215.5, 150'127.7 316° 60° 680'940.0, 150'625.1 317° 83° 680'500.3, 152'214.3 329° 75°

Figure 1: Geographical overview of the swiss alps (swisstopo, 2017). In blue, the location of the Furka Base and the Bedretto Tunnel.

Figure 2: A detailed geological map of the area around the two tunnels. In orange, the Bedretto Tunnel (Keller & Schneider, 1982). ina section between TM 1964 and TM 2130. (Figure 2)

3 1.2.2 Tunnel data Simultaneous to the Furka Tunnel, the Bedretto Tunnel was built from 1972 to 1982 and cost nearly 12 Mio CHF. The tunnel was conventionally excavated (i.e. drill and blast excavation). and was considered as an assistance-tunnel to get a faster access to the main tunnel. Due to a too small cross section of approximately 3 m, it was not possible to use the Tunnel for a railway connection between Oberalp/ and Ronco (Sieber, 2004).

The profile in figure 4 shows high overburden of 1650 m below the Piz Rotondo (at ca. TM3100). In the section that is considered for the second pilot stimulation (i.e. TM 200 – TM 2100) the overburden varies between 1000 and 1030 m. The tunnel has a horse shoe shaped cross section. In some parts of the tunnel, rock bolts and wire mesh were used to support the zones of increased deformations.

The occurrence of fault zones is typically associated with significant water inflow. In 1982 the amount of water that was drained from the Bedretto-Tunnel was between 90-100 l/s. Significant high waterflow (57 l/s) was found within the Rotondo-Granite part of the tunnel between TM 2815 and 2850 (Keller & Schneider, 1982).

The expected rock temperature was calculated, based on the Königsberg and Thoma process (Andreae, 1958) and is under the Piz Rotondo around 37.5 °C. The calculation of the temperature gradient for the entire Gotthard-Massif was based on the observed temperature gradient in the Gotthardtunnel (0.028 °C/m). Measurements in the Bedretto-Tunnel showed an increase of rock temperature from 8 °C (TM 200) to 18 °C (TM 2300). The misfit between actual and predicted temperature might be related to strong mountain relief, glaciation and circulating porewater which suggests an temperature gradient that differs significantly from the temperature gradient found for the Gotthard-Tunnel (Keller & Schneider, 1982).

Since 1982 the Bedretto Tunnel was only used for ventilation purposes and was never fully developed. The tunnel section to the south of TM 3000 were not accessible, due to a tunnel collapse that was reconstructed in 2015. After rehabilitation works performed in 2015, the southern part, which has not been geologically and rock mechanically exactly characterized, is accessible.

The tunnel is considered as an ideal test location for a second pilot stimulation due to 1) the overburden stress, 2) the appearance of crystalline rock types, and 3) the remote location from sensitive infrastructure.

4 1.2.3 Geological description The Gotthard massif has a maximum extent of about 80 km in the WSW-ENE direction and 10 km in the N-S direction. The total surface is around 580 km2. The geological composition is mainly Pre- Variscan gneiss and Variscan granitoids. 440 Ma years ago late Ordovician granitoids intruded. They form about the half of the pre-variscan basement. The orthogneiss were tectonically be transformed during the late Caledonian deformation phase and contain a characteristic lineation (i.e. foliation planes (Huber, 2004)). The overview of the geological settings in figure 3Figure 3 was modified from Zangerl

Test site

Test site

Figure 3: Geological map of the Aar and Gotthard massif (Zangerl, Loew, & Eberhardt, 2006), provided by Dr. V. Lützenkirchen (2017) (modified) et al. (2006) and provided by Dr. V. Lützenkirchen (2017).

A more detailed geological map (Figure 2) and a geological profile (Figure 4) of the Bedretto Tunnel were made by Keller and Schneider (1982). Geologically the tunnel starts at the southeast portal in the Tremola formation with some “Hornblendegarbenschiefer”, which are dominated by biotite gneiss and mica slate. From the end of the Tremola formation towards the northwest, the tunnel is composed of the Prato formation, which involves a zone of layered amphibolite and three different gneiss. These gneiss are a layered gneiss, a light coloured mica gneiss and a mesocratic biotite gneiss. After the Prato formation, the geology of the tunnel is dominated by the Rotondo granite. The granite contains bright, uniform, rough bedded, biotite containing granite (Keller & Schneider, 1982). With a surface area of

5 nearly 25 km2, the Rotondo granite is a dome shaped intrusive body in the Gotthard massif and was emplaced during the variscan orogeny 260 Ma years ago (Labhart, 1977). The cavern for the research facility is located in the Rotondo-Granite. All mapping and measurements presented in this thesis stem from this formation.

Kissling et al. (1978) showed in a radiometric study of the Rotondo granite the petrographic and structural aspects of the Furka Base Tunnel. As a youngest structural element, the mylonite with loose, breccia granite, loam or phyllite slate material is mentioned. These often water-bearing structures were a disadvantage in tunnel construction and have a persistence up to 10 m. Due to steep orientation and a NE strike, they can be related to the young (eventually recent) shear zone at the south border of the Aar massif.

The overburden of the tunnel in the northern-most part is around 1200 m (TM 5000-5218). Stress redistributions during the construction of the tunnel caused stress concentration from TM 3000-5000 at the side wall that lead to stress fracturing (spalling) and thus slab formation, which have been studied in the past and have been interpreted in term of stress magnitude and stress orientations by Huber (2004).

Figure 4: Geological profile of the Bedretto Tunnel (Keller & Schneider, 1982). Location of the test site shown in red.

6 2 Methods 2.1 Tunnel mapping To characterize the test site, various information need to be collected to get a better overview. A detailed mapping along a nearly 200 m section (TM 1964 – TM 2130), was made with Dr. Florian Amann and Hannes Krietsch (Supervisors from SCCER-SoC, ETH Zurich), to create a 3D structural geological model and a detailed plan view of the area around the test site.

A third part of the tunnel mapping contains the mapping of structures on the surface. An aerial photo is taken to collect information of larger persistence faults.

To compare the structures from the tunnel with the one from the surface, rose diagrams and stereo plots were created.

2.1.1 Mapping in the tunnel In a classical tunnel mapping process, the cavern and adjacent parts of the tunnel were surveyed.

On the sidewalls of the tunnel the tunnel chainage was marked every 20 metres with TM 0 at the south portal in the Bedretto valley. These numbers were useful to as a reference in the cavern. To locate the structures in the tunnel we used a 60-metre-long measuring tape. The location error is estimated to be ± 1 m.

To get the dip and dip direction of the structures, a geological compass was used. Only accessible surfaces were possible to measure. The structures without a flat surface are noticed without any direction. On the roof of the tunnel, it is not manageable to get the dip of existing structures. The dip direction was estimated during data post-processing using a triangle ruler.

During the mapping of the tunnel, the most frequently occurring orientations were combined into groups (Table 1) to simplify the measurements.

Table 1: Orientation of combined fault zones

Fault zone (Störzone) Colour code Dip direction Dip

S1 Blue 270° ± 5° 82° ± 3°

S2 Light blue 85° ± 5° 72° ± 3°

S3 green 315° ± 5° 82° ± 3°

7 By knocking on the wall with a hammer, the boundary between the intact rock and the slabs is identified. In irregular repetition, the slabs break down in the upper part of the wall.

2.1.2 3D model To visualize the mapped structures, a 3D model in AutoCAD was created. A new coordinate system for the tunnel is made with origin seen in table 2. The southeast portal of the Bedretto Tunnel is defined as the origin.

Table 2: Origin of the coordinate system used for the models

Coordinate system x-coordinate y-coordinate Altitude

CH1903/LV03 681’056.345 150’083.234 1480.5367 m a.s.l.

CH1903/LV95 2’681’056.345 1’150’083.234 1480.5367 m a.s.l. WGS84 46°29′49.992″N 8°29′40.284″E 1480.5367 m a.s.l.

For the construction of the 3D model it was assumed that the tunnel is aligned with the model-y-axis. Since the tunnel axis orientation is 317°, 43° were added to each measured dip direction. The moderate slope of 1.5-1.7% of the tunnel was ignored.

At TM 2035 a cross section of the tunnel was measured (Figure 5). The horse shoe shaped profile is afterwards extruded in the third dimension. To simplify the cavern, the same cross section is taken for TM 2000-TM 2100.

Figure 5: Cross section at TM 2035, perspective from SE (created by F. Amann, 2017).

Only previously measured structures can be orientated, the other structures are not shown in the 3D model. All the measured structures are replaced by circles according to their location in the tunnel. It is

8 possible to rotate a circle in the direction of its dip and dip direction to show a 3D orientation relative to the tunnel.

Due to a bent model wall, the structures should be bent as well, but the circle radius is measured out of the mapped data. The length of a structure in the 3D model can slightly differ from the original.

2.1.3 Horizontal tunnel plan The plan view shows the tunnel in a more detailed perspective. All mapped structures and orientations were noticed from TM 1964 to TM 2130. In the parts beside the cavern, the roof is not mapped, because of too few existing structures or are invisible due to local support measures. At TM 2004 the tunnel width increases gradually from 3m to 6m. At TM 2096 the 6m wide cavern gradually reduces to 3m.

Due to the horseshoe shaped profile of the tunnel, a horizontal plan view is not completely correct. The walls of the tunnel bow on the top of the wall towards the tunnel roof. In the plan view a simplification is aplied and the structures of the walls are enlarged, when a connected structure on the roof is mapped. All not connected structures show their actual place above tunnel ground (1515 m a.s.l.)

2.1.4 GIS-Data For collecting data around the Bedretto Tunnel a GIS topographic map and an aerial view (swissimage) of the area was needed. The data analysis was made with the Arc GIS Desktop 10 Stud – Version.

After setting the start of the tunnel at the coordinates from table 2, the tunnel alignment was added to the GIS map based on its orientation. In this case, the slope of the tunnel (1.5%-1.7%) was considered.

With the use of an air view of the area around TM 2000, it was possible to collect data about the strike of aierial visible fault zones. After zooming in to a scale of 1:200, the visible structures were traced. In a second step, the strike and length of the lines were measured by triangle. Because of curved appearance structures the strike only could be estimated.

By using the topographic map, a cross section along the tunnel and perpendicular to the tunnel was established. Additionally, the exact tunnel overburden was calculated.

2.1.5 Strike comparison To show the strike of the mapped structures from the tunnel and the aerial map as well with some mapped structures from swisstopo (2017), rose diagrams were made with the online tool from Young Technology Inc..

9 A rose diagram shows a number of data with the same strike orientation in one bar. The strike of a structure is the measured dip direction plus 90°. The rose diagram is only shown in a half circle. For every structure with an orientation between 90° and 180°, 180° are added, for the structures between 180° and 270°, 180° are subtracted.

2.1.6 Extrapolation of the fault zones To get an overview of the mapped fault zones in the Bedretto Tunnel, the big fault zones are extrapolated using the coordinate system as the horizontal tunnel plan is made. The extrapolation is made to see were the mapped fault zones intersect.

10 2.2 Stress characterization The attempt in this thesis to characterize the stress state involved 1) collection of information related to the regional stress regime (e.g. world stress map), 2 the analysis of limited seismological information to invert focal mechanism, 3) collection of local stress state information through the rock mechanical analysis of tunnel break-outs or slaps, and 4) simple numerical modelling of the influence of topography on the orientation of the vertical and horizontal stress components.

2.2.1 World stress map WSM An overview of the stress orientation is given in the WSM (Heidbach & al., 2016). The WSM provides a global compilation of information on the crustal stress field. The WSM is a collaborative project between academia and industry.

With the online tool “CASMO - create a stress map online” (www.worlds-stress-map.org/casmo/, 18.6.2017), it is possible to create a stress map in a user-defined area. CASMO provides a current database released in 2016.

The stress map, shown in chapter 3.2.1, displays the orientation of the maximum horizontal compressional stress (휎퐻푚푎푥). The map provides a basic information for further stress analysis. The stress orientation around the Bedretto Tunnel was used to collect information about the regional stress orientation. The data in a distance up to 50 km were utilized.

Figure 6: Overcoring of a rock by Hydrofrac.com (1999-2003)

Due to little data around the Bedretto Tunnel the nearest stress measurement method is shortly explained. The overcoring method (Fehler! Verweisquelle konnte nicht gefunden werden.) is an in-situ stress measurement. First a circular hole is drilled into the rock. Then the rock volume around the hole is over cored. The stress on the rock disappears, because there is no connection to the remaining rock removed.

11 The rock volume gets depressurized and starts to change. The round hole takes an elliptic or oval shape. The ovality shows information about the stress. Overcoring is mostly used to get local stress information.

2.2.2 Focal mechanism Focal mechanism is a visualisation of information from seismograms. They show the direction of the slip in an earthquake and the orientation of the fault on which it occurs. Typically, focal mechanisms are displayed as beach balls. The beach ball is a projection of earthquake data on a horizontal plane of the lower spherical shell around the earthquake source. The black part of a beach ball is in compression, the white part in extension (Figure 7).

In our case, we first needed to collect earthquake information of the area around the Bedretto Tunnel. In a circuit of 10 km every earthquake measured by the Swiss Seismological Service SED was listed to collect the according data. To create a beach ball, the first arrival of the p-wave of different stations is compared. The beach ball pattern can be laid over the collected orientation data, to show stress information.

To give suitable information, the magnitude of usable earthquakes should be above 2. Stronger earthquakes can be registered by more seismographic stations. The different earthquakes should have different take off angles, otherwise it is difficult to lay a beach ball over the collected data.

Figure 7: Creation of a beach ball (www- udc.ig.utexas.edu/external/TXEQ/faq_basics.html, 2012)

12

2.2.3 Area stress information A profile along the Bedretto Tunnel and a profile perpendicular to the axis at TM 2000 are taken from the topographic GIS map. Both profiles show the topology along 4500 m. To assess the stress situation in the tunnel it is important to know the influence of the topography. The finite element analysis models of the two profiles are made with PhaseII (RS2 9.0 - Rocscience) and have the following material properties. To simplify the models, along both profiles, the material is defined as a Rotondo-Granite, with 0.00268 MN/m3 and a Poisson’s ratio of 0.3. The Poisson ratio of 0.3 is needed to get a K-value of 0.43.

퐾 = 푃표푖푠푠표푛/(1− 푃표푖푠푠표푛)

When K is 0.43, the tectonical stress is not included in the calculation. Stress trajectories are displayed to illustrate principle stress components.

In a second step, the cross section of the Bedretto Tunnel at TM 2035 (Figure 5) is taken to analyse the influence of differential stress to the tunnel. With data from the overburden of the Bedretto Tunnel, a simplified stress situation can be modelled in the 2D finite element program PhaseII (RS2 9.0 - Rocscience).

From a previous study in the Bedretto Tunnel (Huber, 2004), the differential stress, that leads to spalling, was estimated to be in the order of 50-100 MPa for the Rotondo Granite. The location and extension of observed spalls at the sidewall, mostly in the higher part of the tunnel, were compared to the spalling zone that is predicted by numerical modelling.

Near the surface, stress field can show large variability in orientation, due to heterogeneity of rocks, erosion, topography, tectonic process and gravitated processes (Martin et al., 2003). The vertical stress

휎푣 is usually calculated with the geostatic pressure:

휎푣 = 훾 ∗ 푧

3 휎푣 is the vertical stress [MPa], 훾 is the weight of the overlying rock [MN/m ] and 푧 the overburden [m].

The overburden of the tunnel was based on the topographic GIS map, mentioned in 2.1.4 GIS Data. This information was used to perform finite element analysis of stress concentrations that potentially lead to spalling around the horse shoe shaped tunnel. The model extend was 120*120m with the tunnel located in the centre of the grid. A uniform stress state (i.e. no gradient) was assumed. A linear- elastic constitutive law was utilized to estimate the magnitude and location of stress

13 concentrations around the excavation. The Rotondo-Granite is defined as an elastic material with a density of 0.026 MN/m3. (Huber, 2004)

To compare different stress situations, the ratio between horizontal stress 휎ℎ and constant vertical stress

휎푣 is typically expressed as following:

푘 = 휎ℎ/휎푣

Based on experience of Dr. Florian Amann, a k-value from 0.5 to 1.5 is taken. A higher or lower factor would be surrealistic.

14 3 Results 3.1 Tunnel mapping 3.1.1 3D model The 3D model (Figure 8) shows a simplified cavern in black, which is 100 m long (TM 2000-TM 2100), 6 m wide and 3 m high.

On both tunnel sidewalls and the roof of the tunnel, the marked faults were illustrated as circles (Figure 7). To orient each circle, the dip and dip direction of the measurable surfaces were needed. The radius of each circle shows the minimum estimated persistence of the structure. The circles in blue (S1 - 270° ± 5°/82° ± 3°), light blue (S2 - 85° ± 5°/72° ± 3°) and green (S3 - 315° ± 5°/82° ± 3°) relate to the directions from table 1. The circles in orange represent structures that do not belong to the above structure sets.

The structures of the roof are first mapped without any dip. Faults zones are defined here as zone with a high frequency of parallel and persistent brittle joints that are often associated with branching structures oblique to the dominant brittle structure set. Several of these zones have been identified and showed a width > 6m. Because of the high persistence of the faults on the roof, the structures can be related with the structures from the walls. After adjusting the faults from the roof with both sidewalls, it was possible to estimate the structure dip. The dip is mostly the same on both sides of the tunnel. The circles on the top of the tunnel have the same colour code as before mentioned. The circles in yellow represent structures that do not belong to the above structure sets.

Figure 8 shows the tunnel from different perspectives. The orientation of the tunnel is tilted 43° towards north. The first illustration shows the roof of the tunnel seen from the top. The second shows the SW side wall viewed from the same perspective. The bottom of the wall is on the left. The third illustration shows the NE tunnel wall. The bottom of the tunnel is on the right side. Due to the mirroring of the two side perspectives, the fault zones can be easier compared.

The 3D model is an optimal way to see the different structures of the tunnel. The orientation of each measurement can be visualized and fault zones can be easily detected. The highly persistent roof structures connect the two sidewalls and can be adjusted with the dip. In a general overview, it is not useful to show little mapped structures. For example, the slabs are not shown because they do not have a dip or dip direction.

An interpretation of the different structures is compiled by the horizontal tunnel plan.

15 TM 2100

NW

EB-7

EB-6

Bottom Top Top Bottom

EB-5

EB-4

EB-3

EB-2

25 m

EB-1 SE

TM 2000

Figure 8: A) roof of the tunnel mapped in AutoCAD, TM 2000-TM 2100, with the orientation (317°); B) SW sidewall, the bottom of the tunnel is turned to the left side; C) NE sidewall, the bottom of the tunnel is on the right side. The fault zones, explained in chapter 3.1.2, are noted on the right.

16 3.1.2 Horizontal tunnel plan The complete tunnel plan is presented in the appendix.

For the faults in the plan view, the orientation and colour code from table 1 is used. The S2 orientation used for mapping did not occur as often as expected and will not be mentioned in the following paragraphs. In addition to the existing colour code, the quartz is mapped in brown, offsets are in orange and all slabs in magenta. Red shows the opened tunnel. The roof is shown in the middle; on both sides, the walls are shown adjacent to the crown.

10 cm

Figure 9: A picture of a quartz band in the Rotondo-Granite taken at TM 2005.

Mainly on the roof of the tunnel, quartz bands 2-5 cm thick occur (Figure 9). Sometimes the quartz band show an offset of 30-50 cm, which can be used to show the direction of a movement.

For future experiments in the tunnel, names were assigned to the fault zones. The names were sprayed on the tunnel walls in red. The southern groups have the names SB 1-3 (Südlicher Bereich, area south of the cavern) and the groups in the cavern EB 1-7 (Experiment Bereich, area of the experiment). In figure 7 the EB-groups are illustrated in the 3D model, in figure 10 the SB and EB fault zones are shown in the plan view.

Figure 10: A simplified plan view of the Bedretto Tunnel from TM 1960 to TM 2130.

17 The same fault zones are more precisely characterized:

- SB-3: TM 1967 - T1970

In the main fault of SB-3, a fault gouge layer 1-2 cm thick can be detected. Fault gouge is formed by tectonic forces and has mostly a very small grain size.

“Fault gouge is classified as an incohesive rock (at present-day outcrop), composed <30% of large clasts (>2 mm in size) and may be non-foliated (random-fabric orientation) or foliated” - (Woodcock & Mort, 2008)

The dip of the SB-3 is very steep (85°-90°). Due to the steep dip, on the two tunnel walls different dip directions were measured. 128° and 298°; after adding ±5° error, the two sides have the same strike.

- SB-2: TM 1979 – TM 1981

The fault zone is highly shattered. Along one metre, the fault zone has a high rate of 15-20 fractures / m. In the middle of the SB-2 water-bearing fault gouge is detected.

The orientation of the SB-2 fault zone can be related to the S3 (315° ± 5°/82° ± 3°) orientation. The S3 orientation is nearly perpendicular to the tunnel orientation.

- SB-1: TM 1984 – TM 1989

The last SB mapped fault zone is on the southwest wall, along 2 m, highly water-bearing.

South of the main fault again a high rate of fractures has been detected. Along 3 m, every 10-20 cm a fault is seen. On the northeast wall, the structures are probably not only faults. Some structures are likely to be from drilling or bursting. The main fault itself is the largest of the 3 SB zones. Along 30 cm, fault gouge can be detected.

The SB-3 orientation, with a dip/dip direction of 320°/75°, can be related to the S3 orientation.

- EB-1 TM 2000 – TM 2013

The first fault zone within the experimental area has a quartz band nearly perpendicular to its own S1 (270° ± 5°/82° ± 3°) orientation. The quartz has two clearly seen sinistral offset of 10-20 cm, but not all S1 structures offset the quartz. The most weathered part of the EB-1 is an extension of the fault zone and splits the quartz in two parts without any offset.

18 The fault zone has a clearly S1 orientation on the northern side, more to the south the orientation changes to 230°/70°. Due to the different orientation, the fault zone can be detected as a synthetic branch fault. (Kim & al., 2002)

On the northeast side of the tunnel there is a group of S3 structures. Their persistence is too small to be further seen in the tunnel roof, but slickenside can be seen on them.

- EB-2 TM 2014 – TM 2022

This fault zone does not show a weathered surface and is not deformed. It offsets two quartz bands by 30 cm, which is the biggest offset mapped in the tunnel. This fault zone resembles the EB-1 sinistral. The orientation of the fault zone is a S1 direction, the quartz is parallel to the tunnel.

- EB-3 TM 2025 – TM 2036

Two fault groups, in 1 - 2 m distance, define the EB-3. One of them consists of four S1 orientated faults and has no special events. The other bigger group has 5 parallel S1 orientated faults and offsets a little quartz band sinistral. In another section of this group, there are shattered faults along 1 metre parallel to the tunnel direction. Due to the offset and the shattered part, this group can be considered as an extension fracture.

“Linkage between fault segments is mainly controlled by extension fractures approximately parallel to the local σ1 orientation, and the extension fractures are dominantly developed in the extensional quadrants of fault segments.” - Kim & al., 2002

- EB-4 TM 2038 – TM 20 48

The EB-4 again consists of two fault strings and is S1 orientated. On the further northern group, the extensional fractures described in EB-3 are mapped. In addition to the extensional fractures, on the second string structures perpendicular to the extensional fractures are observed. They could be synthetic or antithetic faults, or they show extensional fractures from another tectonic event.

- EB-5 TM 2047 – TM 2051

This is the only fault zone in the cavern with a S3 orientation. Some SB fault zones have the same orientation. Along 2 m, five parallel single faults can be detected. The faults show a clear persistence perpendicular to the tunnel axis. On the southeast side, a quartz band stops by the first contact with a fault of the zone.

19 - EB-6 TM 2074 – TM 2084

The orientation of the fault zone is again in the S1 direction and has two strings. One string is water- bearing and shattered. The other one shows again some extensional fractures perpendicular to the tunnel axis.

Between the EB-6 and the EB-7, a 20 cm sinistral offset of a fault is mapped.

- EB-7 TM 2084 – TM 2091

Main parts of the furthest fault zone in the cavern have a S1 orientation, but to the southeast of the tunnel the orientation changes to 311°/55°. The result of the different orientation can be compared with a horsetail structure (Kim & al., 2002).

Further the S1 part of the zone has bent extension fractures, parallel and perpendicular to the tunnel.

40 cm

Figure 11: Detected spalling around TM 2038. The slabs break down up to 30 cm.

Besides these fault zones, lot of spalling is detected. On both sidewalls, the upper part of the wall is often spalled and slabs are detected (Figure 11). Mostly the slabs are in the cavern on the northeast side of the tunnel. Outside of the cavern, between TM 1964 -TM 2000 and TM 2100 – TM 2130, nearly none are mapped.

20 3.1.3 GIS-Data The aerial map (Figure 12) shows the area around TM 2000. In blue, the Bedretto Tunnel is mapped in the 317° direction. In orange, every observed structure is traced. The aim is to collect the strike of the traced structures, to compare them to the data of the tunnel.

100m

Figure 12: Aerial map around the cavern (swissimage, 2017). The visible structures are traced in orange.

1000m vertical above the cavern, unfortunately a cobble field overlie the structures of the rock. As a substitute for the area above the tunnel, the ridge in southwest of the tunnel is mapped. According to no information of the dip, only the strike data of the faults is collected and shown.

There are two main orientations of faults on the ridge:

- 3° ±7°: Most of the smaller structures have a nearly northern orientated strike. In total, 22 traces with this angle have been measured. Most of them have a length between 8-20 m; the longest has a persistence of 80 m.

21 - 50° ± 10°: Within this orientation 27 faults have been measured. A third of them have a length of 10-20 m, nearly two thirds of the structures are between 20-100 m and a few have a persistence over 140 m.

Due to high persistence of the faults (10-200 m), the ridge area can be compared with the area around the cavern.

3.1.4 Strike comparison In figure 13, 14 and 15 rose diagrams of the tunnel structures, the GIS structures and swisstopo data are created. The rose-diagram shows the number of data (noticed between 15° and 30°) with the same strike orientation (in 5° segments) in one bar.

Figure 13: Strike of the mapped structures of the two side walls of the tunnel.

Figure 13 shows two groups of strikes. The first group of the tunnel structures has the strike of 7.5° ± 7.5°. This direction is perpendicular to the S1 (270° ± 5°) orientation. Six out of ten fault zones have the S1 orientation, three of them are S3 (315° ± 5°) orientated. The strike of the S3 is 45° ± 5°. Nearly the same direction has the second group in the rose diagram 40° ± 5°. Other directions can be for example from spalling.

22 Figure 14: Structures strike of the aerial image around the Bedretto Tunnel

Figure 14 shows again two groups of strikes. The two groups are the same as in chapter 3.1.3 mentioned. Once with a 3° ± 7° strike and once with 50° ± 10°.

The data collected from swisstopo are few. In a circuit of 1 km only 11 measurements were found, but they give information about the area structure orientation. They are taken from the online map: Geologische Vektordatensätze GeoCover (1:25000) (Bundesamt für Landestopografie, swisstopo 2017) and illustrated in figure 15. The used dip and dip direction can be found in the appendix with the according coordinates.

Figure 15: Strike of the measured data from swisstopo (2017) The structures around the tunnel are mostly 45° ± 10° orientated. But the distribution goes from 18° up to 67°. No northern strikes are seen in the data from swisstopo.

23 A paper of Lützenkirchen & Loew (2010) additionally shows a 50° ± 10° orientation of aerial and tunnel measured structures (Figure 16). Their measurement is taken in the further northwest part in the area around TM 4000- TM 5000.

Figure 16: Rose-diagram of structures in the further northwest part of the Bedretto Tunnel (Lützenkirchen & Loew, 2010).

The large amount of data in the Bedretto Tunnel with a S3 orientation, can be compared with the high persistence faults of the aerial map (50° ± 10°) and the structures from swisstopo (45° ± 10°). Due to high persistence of these structures and information around the tunnel area it can be, that the higher persistence structures have a S3 orientation and only small structures have a S1 dip direction. Simultaneously, the cavern has an overburden of 1000 m and it could be that the orientation of faults changes with depth.

24 3.1.5 Extrapolation of the fault zones The results gained in chapter 3.1.2, 3.1.3 and 3.1.4 justify extrapolating the fault zones of the Bedretto Tunnel. The high persistence of structures seen in the aerial map and the comparable orientation of the structures legitimates to do so.

The extrapolation (Figure 17) is based on the same coordinate system as the horizontal tunnel plan, but only the roof of the tunnel is shown in red. The fault zones S1 and S3 are still in blue and green. The SB-3 is in a darker green, because the orientation can best be related with a S3 fault zones. The dip of the S1 and S3 is very high and the structures would match in bigger distance to the cavern. This is the reason, why only a horizontal extrapolation of the structures is made.

Figure 17: Extrapolation of the fault zones in the Bedretto Tunnel

The angle between the extrapolated S1 and S3 zones is mostly between 29° and 38°. The measured maximum is 54°, but is an angle between the SB-3 fault zone and a EB fault zone. The offset mapped in EB-1, -2, -3 and between EB-6/-7 are all sinistral.

25 3.2 Stress characterization The following chapter addresses the stress characterization of the Bedretto Tunnel in a regional and local scale. With the data from the WSM it is possible to get the maximum horizontal compressional stress 휎퐻푚푎푥. The analysis of focal mechanism has not worked as expected, the chapter will not show many results. The third part of the stress characterization is on a local scale and shows the stress around the Bedretto Tunnel analysed with Phase2-models.

3.2.1 World stress map Figure 18 shows Switzerland with the information of the WSM. The maximum horizontal compressional stress 휎퐻푚푎푥 is illustrated as lines with the corresponding orientation.

Figure 18: World stress map, Heimholz Centre Potsdam (2016), in orange the location of the Bedretto Tunnel.

26 Figure 19: Legend of the world stress map (Heidbach et al., 2016) In figure 19, the different methods and qualities of data are shown.

Based on the world stress map (Figure 18), the nearest measurement has maximum horizontal

compressional stress (휎퐻푚푎푥) in the 171°/351° direction. The regional stress could be more likely compared with the other stress orientations, because as explained, the overcoring data could be local. Data from further in the north, west and south of the Bedretto Tunnel are as well collected, to gain a regional stress overview. The measurements in the north of the tunnel, near the Lake Lucerne, show an orientation of 136°/316° ± 15° and can mostly be related to a strike-slip regime. The area in the , in the west of the tunnel, shows a lot of different orientations. The Valais is one of the tectonically most active zones in Switzerland (SED, 2006) and shows two main orientations. First a 109°/289° ± 15° orientation with a normal fault regime and second a 124°/304° ± 15°, a strike-slip regime. In the south only one measurement is illustrated, the strike-slip data has an orientation of 133°/313° ± 15°.

The over regional stress shows an average orientation of the strike-slip regimes of 131°/311° ± 20°. The measurement of the Valais normal fault regime is nearly within the error range of the average orientation and the overcoring data overlaps within the two errors.

The axis of the Bedretto Tunnel has nearly the same orientation (137°/317°). For further calculation, the

maximum horizontal compressional stress 휎퐻푚푎푥 can be assumed parallel to the tunnel axis.

27 3.2.2 Focal mechanism To collect the earthquake data, the interactive map (Figure 20) of the Swiss Seismological Service is taken. All earthquakes (since 2002 and above a magnitude of 1) in the area around the Bedretto Tunnel are illustrated in circles. The size of the circles shows the magnitude of each event.

Since 2002, all earthquakes

Magnitude 1 2 3 4

Figure 20: The interactive map from the (SED, 2017). In orange the Furka Base and the Bedretto Tunnel. The nearest earthquakes to the Bedretto Tunnel are catalogued. In total 19 events since 2002 are measured and above a magnitude of 1. For a good quality of results the earthquake should have a magnitude above 2. Of the picked ones, unfortunately only two earthquakes have a magnitude above 2.

Dr. Anne Christine Obermann, Swiss Seismological Service (SED), and Dr. John Francis Clinton, Swiss Seismological Service (SED), used the program Seiscomp to create a beach ball model of one of the biggest events (Magnitude 2.1, in figure 21) near Oberwald. A data set of 23 phase picks is illustrated on the beach ball. The event was near the surface (3.8 km deep) and only measured on a few seismic stations. Due to high and similar take off angles (95°), the picks on the beach ball are near the boundary of the circle and none of them are in the middle. The beach ball lines can be laid in completely different ways. Figure 22 illustrates one of the possible ways of the beach ball model.

28 Figure 21: The red circle shows the location of the Oberwald VS event, on the right side the data of the same

event (Obermann & Clinton, 2017).

Figure 22: Beach ball model of the Oberwald event (Obermann & Clinton, 2017).

Because of too little magnitude of the events around the Bedretto Tunnel and similar expected take off angels, no further events are processed.

29 3.2.3 Area stress information To get information about the influence of the overburden, a topographic profile along the Bedretto Tunnel and a profile perpendicular to the axis at TM 2000 is created. In Phase2 models, the two profiles illustrate the vertical stress 휎푍 according to the overburden. The influence of tectonics is not regarded. The part below the maximal stage (20 MPa) has a higher stress than 20 MPa, but is shown in white to get a better differentiation around the tunnel area.

Figure 23: Topographic profile along the tunnel axis with finite element analysis calculated with Phase2. In blue, the Bedretto Tunnel.

Figure 23 shows the different vertical stress along the tunnel. At the highest point of the profile, near the Piz Rotondo, the overburden is around 1500 m. A principle stress component, illustrated as stress trajectories, is vertical around the cavern. The topography does not influence the stress orientation after TM 1500. The vertical stress enlarges, due to more overburden, but the orientation of a principle stress component stays vertical to the tunnel.

In figure 24, the perpendicular profile to the Bedretto Tunnel is shown. The overburden above TM 2035 is 1022 m (Detailed overburden information in the Appendix). Slightly left of the tunnel, the ridge mentioned in 3.1.3 is seen. This ridge influences the principle stress component, but does not change the orientation of the stress trajectories.

30 Around the tunnel the topographical profile does not change the stress orientation and can be disregarded. At a depth of 1 km the influence of the overburden is vertical to the tunnel axis.

Figure 24: Topographic profile perpendicular to the Bedretto Tunnel at TM 2000 with finite element analysis calculated with Phase2. In blue, the Bedretto Tunnel.

The second part of the area stress information is made with a finite element analysis around the cross section (Figure 5) at TM 2035. The following overburden (Table 3) is taken to calculate the vertical

stress 휎푣 on the tunnel.

Table 3: Overburden around TM 2035

Tunnel [m a.s.l.] Surface [m.a.s.l.] Overburden [m] Vertical stress [MPa]

1515.21 2538.187 1022.977 26.89488371

The vertical stress 휎푣 and the changing k-value (0.5-1.5) are used to calculate the horizontal stress 휎ℎ:

휎ℎ = 푘 ∗ 휎푣

In the appendix, the calculation of the different horizontal stresses 휎ℎ is shown. In table 4,the same cross

section is illustrated with different k-values. The differential stress is 휎퐷:

휎퐷 = 휎3−휎1

where 휎3 and 휎1 depend on the k-values. Below a k-value of 1, the 휎푣 is 휎1 and above a k-value of 1,

the 휎ℎ is 휎1.

31 Table 4: Phase2 models from the k-value from 0.5 to 1.5, the first field shows the legend to the colour code of the differential stress

k=0.5 k=0.6

k=0.7 k=0.8 k=0.9

k=1 k=1.1 k=1.2

k=1.3 k=1.4 k=1.5

32 The information about spalling, mentioned in chapter 2.2.3 and the mapped results from chapter 2.1.33.1.2, are used to compare the observed spalling with the numerical modelling. The slabs mostly break down in the upper part of the sidewall of the tunnel. Most of the slabs do not break completely through and stay on the top of the wall. Differential stress over 50 MPa leads to spalling of the Rotondo- Granite, in table 4, the differential stress over 50 MPa is shown in colours. The different k-value calculations show different results:

- k-value: 0.5 The SW side (left side) of the wall should be broken out completely, the NE side (right side) shows spalling in the upper part of the tunnel. - k-value: 0.6 Like k-0.5, but the SW side has less spalling. - k-value: 0.7 Like k-0.6, but the SW and NE sides have less spalling. - k-value: 0.8 The both sides do not break out completely. The result is near the observed result. - k-value: 0.9 Spalling is detected on both sides in the upper part of the tunnel, which is very similar to the observed results and to the model with k-1. - k-value: 1 Spalling is detected on both sides in the upper part of the tunnel, which is very similar to the observed results and to the model with k-0.9. - k-value: 1.1 The SW side (left side) of the wall should be broken out completely, the NE side (right side) shows spalling in the upper part of the tunnel. - k-value: 1.2-1.5 Compared to the observed result, the outcome of the finite element analysis is unrealistic. Both sides of the tunnel would be broken out completely.

A k-value between 0.8 and 1 shows the best results compared to the observation in the Bedretto Tunnel.

According to this information, the two stresses have the same size (k-1), the vertical stress 휎푣 can be up to 1.25 times bigger than the horizontal stresses 휎ℎ (k-0.8) or the coefficient is around 1.11. In our case this would result in a 휎푣 of 26.89 MPa and a 휎ℎ between 21.5-26.89 MPa.

33 4 Discussion 4.1 Tunnel mapping During mapping, a lot of spalling is detected. They are in the upper part of both tunnel walls. The fracture planes are mostly fresh and give an important information for further stress analysis. Additionally, ten fault zones are mapped. Three of them are in the southwest of the cavern. In the main faults of these fault zones gouge can be detected and two of them are water bearing and show a high rate of fractures. In the cavern only one of seven fault zones is water bearing and two of them are weathered. Therefor four of them show a sinistral offset. A possible local variation of structures is mentioned by Keller & Schneider, 1982.

The results from the tunnel mapping show two main orientations of fault zones. A first group perpendicular to the tunnel and a second north-south orientated one. The 휎1 orientation during the formation of these faults should be in a SW/NE direction and the 휎2 vertical. This event can date from long ago and has no further influence on the current stress orientation.

The same orientation of fault zones is visible on the aerial image. On the aerial image, the persistence of the faults perpendicular to the tunnel is much greater than the persistent of the northern oriented faults.

4.2 Stress characterization

The world stress map (3.2.1) does not show a clear orientation of the horizontal stress maximum 휎퐻푚푎푥. In the area around the Bedretto Tunnel only one measurement is made. More measurements and different methods should be made to gain information about the orientation of principle stress components.

Due to little earthquakes with a magnitude over 2 and high take off angles focal mechanism cannot be created. To improve the quality of data a more compact seismic network could be created.

The topographic overburden gives information about the orientation of one principle stress component. A finite element analysis is made to see the influence of local topography. Neglecting the influence of tectonics, the orientation of stress trajectories is vertical to the tunnel axis (i.e. one principal stress component is vertical). Additional influence of tectonics is expected to maintain the vertical orientation of one principal stress component.

Additional finite element analysis on the scale of the tunnel cross-section showed a k-value of the vertical stress 휎푣 to the horizontal stress 휎ℎ (perpendicular to the tunnel) of 0.8 to 1. The vertical stress

휎푣 must be bigger than the horizontal one to get such a result. A k-value over 1 is possible if the mapping of the cross section at TM 2035 is incomplete or biased. The orientation of 휎푉 would not change (the topographic information stays), but the ratio between the vertical and horizontal stress would change.

34 5 Conclusion The cavern at TM 2000 – TM 2100 is an interesting site for underground research facility. Both sidewalls are completely unsupported and show the Rotondo-Granite with local stress information. With an overburden around 1000 m the stress conditions of the cavern are closer to the actual depths of 4000 - 5000 m, that are interesting for geothermal exploitation. This overburden is a new dimensioning for the SCCER to do research.

By connecting different information about local structures, two important groups of fault zones can be determined with an orientation of S1 (270° ± 5°/82° ± 3°) and S3 (315° ± 5°/82° ± 3°). The observed fault zones 1) show high persistence, 2) show offsets, 3) are sometimes water bearing and 4) gouge can be detected sometimes. Tunnel mapping, GIS-aerial image survey and surface measurements of the swisstopo show all the same strike orientation of the fault zones.

A finite element analysis of the influence of the topography on the cavern, resulted in one principal stress component vertical to the cavern and corresponding to 휎푍. According to the world stress map,

휎퐻푚푎푥 is parallel to the tunnel. A second finite element analysis, showed that the vertical stress 휎푣 (26.89

MPa) is 1 – 1.25 times bigger than the horizontal stress 휎ℎ (21.5-26.89 MPa, perpendicular to the tunnel).

It can be determined, that 휎푣 > 휎ℎ and on the other hand, 휎퐻푚푎푥 > 휎ℎ. Deductive 휎ℎ has to be the smallest stress. The relation between the maximum horizontal stress 휎퐻푚푎푥 and the vertical stress 휎푣 is unsure. There are the three following options:

- 휎푣 > 휎퐻푚푎푥 > 휎ℎ - 휎퐻푚푎푥 > 휎푣 > 휎ℎ - 휎퐻푚푎푥 = 휎푣 > 휎ℎ

Figure 19 illustrates a normal faulting regime (휎푣 > 휎퐻푚푎푥 > 휎ℎ) and a strike-slip regime

(휎퐻푚푎푥 > 휎푣 > 휎ℎ). Both are likely, but according to the other data in the world stress map, this orientation mostly occurs as a strike slip regime.

The correct orientation of the two horizontal stresses 휎퐻푚푎푥 and 휎ℎ can be clarified in a stress characterization survey, for example with overcoring or hydro-fracturing.

35 Acknowledgements I would like to thank Dr. Florian Amann and Dr. Valentin Gischig for the support during the whole process of this thesis and important advices. From the beginning, they encouraged and motivated me to work on this thesis. I am very grateful Hannes Krietsch who helped me to understand the different computer programmes. He explained them sympathetic and supported me whenever needed. Simultaneously, I want to thank them for the organisation and the support during the unforgettable field work in the Bedretto Tunnel.

Furthermore, I want to thank Dr. Anne Obermann for the support to understand the focal mechanism as well as the provided results, without her and Dr. John Francis Clinton it would not have been possible for me to create this model.

Additionally, I thank Dr. Matthew Perras for organizing the field work equipment as well as a licence for the Phase2 9.0 (Rocscience).

I am very grateful to Michèle Herren for interesting discussions and support in interpretation of mapped structures. Special thanks to Meinrad Küchler, Cornelia Meier and Luzia Meier for proofreading.

Finally, I thank the Swiss Competence Center for Energy Research – Supply of Electricity for the opportunity to work on this thesis.

36 Bibliography

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Heidbach, O. et al. (2016). Stress Map of the Mediterranean and Central Europe 2016.

Huber, B. (2004). Stess-induced fractures in the deep-seated Bedretto tunnel.

Keller, F. & Schneider, T. R. (1982). Geologie und Geotechnik. Schweizer Ingenieur und Architekt, Heft 24.

Kim, Y.-S. et al. (2002). Fault damage zones. Journal of Structural Geology 26 (2004), 503- 517.

Kissling E. et al. (1978). Radiometrische Untersuchungen am Rotondogranit.

Labhart, T. (1977). Aarmassiv und Gotthardmassiv. Sammlung Geologischer Führer, Gebr. Borntraeger Berlin, 211 p.

Luetzenkirchen, V. H. (2002). Structural Geology and Hydrogeology of Brittle Fault Zones in the Central and Eastern Gotthard Massif, Switzerland.

Lützenkirchen, V. & Loew, S. (2010). Late Alpine brittle faulting in the Rotondo granite (Switzerland): deformation mechanisms and fault evolution. Swiss Geological Society 2011.

Martin, C. et al. (2003). Stress, instability and design of underground excavation. International Journal of Rock Mechanics and Mining Sciences, 40; 7-8:1027–1047.

SED (2006). Erdbeben in der Schweiz. SED.

Sieber, F. (2004). Streit ums Furkaloch - Die politische Karriere des Furkabasistunnels.

Woodcock, N. & Mort, K. (2008). Classification of fault breccias and related fault rocks. Geological Magazine, 145(3), 435-440.

37 Zangerl, C., Loew, S. & Eberhardt, E. (2006). Structure, geometry and formation of brittle discontinuities in anisotropic crystalline rocks of the Central Gotthard Massif, Switzerland. Eclogae Geologicae Helvetiae, 99(2), 271-290.

38 List of tables

Table 1: Orientation of combined fault zones ...... 6 Table 2: Origin of the coordinate system used for the models ...... 7 Table 3: Overburden around TM 2035 ...... 30 Table 4: Phase2 models from the k-value from 0.5 to 1.5, the first field shows the legend to the colour code of the differential stress...... 31

List of figures

Figure 0: Picture on the front page - picture of the south portal of the Bedretto Tunnel – Matthias Meier, 2017 Figure 1: Geographical overview of the swiss alps (swisstopo, 2017). In blue, the location of the Furka Base and the Bedretto Tunnel...... 2 Figure 2: A detailed geological map of the area around the two tunnels. In orange, the Bedretto Tunnel (Keller & Schneider, 1982)...... 2 Figure 3: Geological map of the Aar and Gotthard massif (Zangerl, Loew, & Eberhardt, 2006), provided by Dr. V. Lützenkirchen (2017) (modified) ...... 4 Figure 4: Geological profile of the Bedretto Tunnel (Keller & Schneider, 1982). Location of the test site shown in red...... 5 Figure 5: Cross section at TM 2035, perspective from SE (created by F. Amann, 2017)...... 7 Figure 6: Overcoring of a rock by Hydrofrac.com (1999-2003) ...... 10 Figure 7: Creation of a beach ball (www-udc.ig.utexas.edu/external/TXEQ/faq_basics.html, 2012) ...... 11 Figure 8: A) roof of the tunnel mapped in AutoCAD, TM 2000-TM 2100, with the orientation (317°); B) SW sidewall, the bottom of the tunnel is turned to the left side; C) NE sidewall, the bottom of the tunnel is on the right side. The fault zones, explained in chapter 3.1.2, are noted on the right...... 15 Figure 9: A picture of a quartz band in the Rotondo-Granite taken at TM 2005...... 16 Figure 10: A simplified plan view of the Bedretto Tunnel from TM 1960 to TM 2130...... 16 Figure 11: Detected spalling around TM 2038. The slabs break down up to 30 cm...... 19 Figure 12: Aerial map around the cavern (swissimage, 2017). The visible structures are traced in orange...... 20

39 Figure 13: Strike of the mapped structures of the two side walls of the tunnel...... 21 Figure 14: Structures strike of the aerial image around the Bedretto Tunnel...... 22 Figure 15: Strike of the measured data from swisstopo (2017) ...... 22 Figure 16: Rose-diagram of structures in the further northwest part of the Bedretto Tunnel (Lützenkirchen & Loew, 2010)...... 23 Figure 17: Extrapolation of the fault zones in the Bedretto Tunnel ...... 24 Figure 18: World stress map, Heimholz Centre Potsdam (2016), in orange the location of the Bedretto Tunnel...... 25 Figure 19: Legend of the world stress map (Heidbach et al., 2016)...... 26 Figure 20: The interactive map from the (SED, 2017). In orange the Furka Base and the Bedretto Tunnel...... 27 Figure 21: The red circle shows the location of the Oberwald VS event, on the right side the data of the same event (Obermann & Clinton, 2017)...... 28 Figure 22: Beach ball model of the Oberwald event (Obermann & Clinton, 2017)...... 28 Figure 23: Topographic profile along the tunnel axis with finite element analysis calculated with Phase2. In blue, the Bedretto Tunnel...... 29 Figure 24: Topographic profile perpendicular to the Bedretto Tunnel at TM 2000 with finite element analysis calculated with Phase2. In blue, the Bedretto Tunnel...... 30

40 Appendix

Geologische Vektordatensätze GeoCover (1:25000)

Bundesamt für Landestopografie swisstopo, 2017: x/y (CH1903/LV03) Dipdr Dip 680'593.2, 151'314.1 108° 73°

679'851.2, 150'258.2 128° 70°

680'814.0, 150'899.1 140° 90°

680'197.3, 152'017.3 143° 90°

680'271.2, 151'654.1 150° 63°

680'499.2, 151'718.1 157° 83°

680'573.7, 149'964.2 296° 60°

680'051.0, 150'238.2 309° 53°

680'215.5, 150'127.7 316° 60°

680'940.0, 150'625.1 317° 83°

680'500.3, 152'214.3 329° 75°

Calculation of the different horizontal stresses 휎ℎ: sv k sh s1-s3max [Mpa] [-] [Mpa] [Mpa] 26.89 0.5 13.445 13.445 26.89 0.6 16.134 10.756

26.89 0.7 18.823 8.067 26.89 0.8 21.512 5.378 26.89 0.9 24.201 2.689 26.89 1 26.89 0 26.89 1.1 29.579 2.689

26.89 1.2 32.268 5.378 26.89 1.3 34.957 8.067 26.89 1.4 37.646 10.756 26.89 1.5 40.335 13.445

41 Overburden and vertical stress information:

TM [m] Tunnel [m a.s.l.] Surfave [m a.s.l.] Overburden [m] Overburden [MPa] 0 1480.53 1480.5367 0.0067 0.000176148 500 1489.03 1784.401 295.371 7.765539887 1000 1497.53 1988.0544 490.5244 12.8962789 1500 1506.03 2351.5852 845.5552 22.23032265 2000 1514.53 2510.8933 996.3633 26.19518825 2020 1514.87 2523.8234 1008.9534 26.52619205 2040 1515.21 2538.187 1022.977 26.89488371 2060 1515.55 2546.1582 1030.6082 27.09551406 2080 1515.89 2550.3674 1034.4774 27.19723843 2100 1516.23 2552.957 1036.727 27.25638221 2500 1523.03 2634.8869 1111.8569 29.23160739 3000 1531.53 2862.894 1331.364 35.00262465

42