Mont Terri Project · ANDRA BGR CRIEPI ENRESA GRS HSK IRSN JAEA NAGRA OBAYASHI SCK•CEN SWISSTOPO Mont Terri Project TECHNICAL REPORT 2007-06 December 2007 Ventilation Test (VE)

ANDRA BGR CRIEPI ENRESA GRS HSK IRSNJAEA NAGRA OBAYASHI SCK•CEN SWISSTOPO

Mont Terri Project

TECHNICAL REPORT 2007-06 December 2007

Ventilation Test (VE) Experiment: Final activity report

on high resolution seismic investigations within the VE-Experiment

NF-PRO

Contract Number: FI6W-CT-2003-02389

K. Schuster

BGR, Germany

Mont Terri Project, TR 2007-06

Distribution: Standard distribution: ANDRA (J. Delay) BGR (H. J. Alheid) CRIEPI (K. Kiho) ENRESA (J. Astudillo) GRS (T. Rothfuchs) HSK (E. Frank) IRSN (J.-M. Matray) JAEA (N. Shigeta) Nagra (M. Hugi) Obayashi (H. Kawamura, T. Tanaka) SCK CEN (G. Volckaert) SWISSTOPO (P. Bossart and P. Hayoz) GI AG (Ch. Nussbaum) Additional distribution: Every organisation & contractor takes care of their own distribution.

Final activity report

on high resolution seismic investigations within the VE-Experiment

Author: Kristof Schuster

Date of issue of this report: December 19, 2007

Start date of task: 01/05/2005 Task duration: 32 Months

NF PRO RTD C4 WP 4.3 EDZ short term evolution

(Contract Number: FI6W-CT-2003-02389)

BGR Final activity report on high resolution seismic investigations within the VE-Experiment 2/37

[NF PRO] Final Activity Report Dissemination level: PU Date of issue of this report: 19/12/2007

1 Name and signature of the person responsible for drafting the deliverable 2 Name and signature of the reviewer (member of applicable Work Package) 3 Name and signature of the Work Package Leader 4 Name of the RTDC Leader. The RTDC Leader is informed on the availability of the deliverable

and verifies whether the introduction, formulation of objectives, interfaces to other project activities and conclusions are sufficiently clear to allow integration of the deliverable into the overall work programme of NF-PRO.

Name Date Signature for approval

Author1: Kristof Schuster

Verified by2: Hans-Joachim Alheid

Approved by3: Juan Carlos Mayor

Verified by RTD Leader

Jean-Francois Aranyossy

Project co-funded by the European Commission under the Euratom Research and Training Programme on Nuclear Energy within the Sixth Framework Programme (2002-2006)

Dissemination Level PU Public RE Restricted to a group specified by the partners of the [NF PRO] CO Confidential, only for partners of the [NF PRO] project



DISTRIBUTION LIST

Name Number of copies Comments



Organisation: Federal Institute for Geosciences and Natural Resources (BGR), Hannover, Germany, Section B2.2

Location: RL Mont Terri, Switzerland, Microtunnel, VE-Experiment

Task: Investigation of the Excavation Damaged/disturbed Zone (EDZ/EdZ) Several measurements

Method: Small scale seismic refraction and seismic borehole measurements Tools: High resolution seismic refraction equipment with 9 sources and 47 receivers distributed along two profiles

High resolution seismic borehole measurements (interval velocity and crosshole measurements) Borehole camera

Date: 10 campaigns between May 2005 and November 2007 Measurement & Installation Team: Friedhelm Schulte, Torsten Tietz, Wilfried Stille & Kristof Schuster Borehole camera analyses: Torsten Tietz Data Processing, Interpretation and Reporting: Kristof Schuster



TABLE OF CONTENTS

1 SUMMARY ...................................................................................................................... 6 2 INTRODUCTION............................................................................................................. 7 3 HIGH RESOLUTION SEISMIC MEASUREMENTS ........................................................ 8

3.1 Seismic refraction experiment ................................................................................... 9 3.1.1 Profile layout and instrumentation ....................................................................... 10 3.1.2 Results of first measurements............................................................................. 12 3.1.3 Comparison of data from different measurement campaigns ............................. 14 3.1.4 Finite difference ray tracing ................................................................................. 17 3.1.5 Conclusions from seismic refraction measurements........................................... 25

3.2 Borehole measurements ......................................................................................... 25 3.2.1 Borehole camera inspection................................................................................ 27 3.2.2 Interval velocity measurements........................................................................... 28 3.2.3 Conclusions from interval velocity measurements .............................................. 30 3.2.4 Cross hole measurements .................................................................................. 31 3.2.5 Conclusions from cross hole measurements ...................................................... 33

4 COMPARISON BETWEEN RESULTS FROM VE- AND EB-EXPERIMENT ................ 33 5 OVERALL CONCLUSIONS........................................................................................... 35 6 REFERENCES.............................................................................................................. 37



1 SUMMARY

Within the framework of the Ventilation-Experiment, which aims at the evaluation of the de- and resaturation of hard clay under in-situ conditions, small scale high resolution seismic measurements were performed in the Rock Laboratory Mont Terri, Switzerland. With the help of these seismic investigations mainly the excavation damaged or disturbed zone (EDZ/EdZ) should be detected and characterised with time.

Beside a long term seismic refraction experiment, as a non-invasive method, borehole based interval velocity and cross hole measurements were performed. The seismic refraction measurements along two profiles, 1.45 m (parallel to bedding) and 1.25 m (perpendicular to bedding) long, were performed between May 2005 and November 2007. Three 1 m long boreholes were drilled in October 2006. Measurements in and between these boreholes were performed just after the drilling and in July 2007, where also a borehole camera recording was done.

Concerning the determination of the extent of the EDZ/EdZ results from all three methods are in good accordance. According to the seismic refraction data (May 2005 – July 2005) the extent of the EDZ/EdZ ranges between 5 cm and 20 cm. The borehole based results, achieved in October 2006 and July 2007, yield 10 cm - 25 cm (interval velocity measurements) and 20 cm from the cross hole measurements. This range for the extent of the EDZ/EdZ can be seen at the same time as a measure of the variability along the covered area and to a certain extent of the uncertainty for the determination.

Seismic refraction data from November 2005 till November 2007 could not be used for the determination of the extent of the EDZ/EdZ due to an increase in signal attenuation. Only in November 2007 and slightly already in July 2007 the signal attenuation became weaker, but the first arrival phases were not sufficiently good developed for a quantitative analysis. Therefore only a qualitative interpretation was done.

The extent of EDZ/EdZ seems to vary only a few with ongoing time whereas changes in the attenuation of the seismic signals point to changes of rock properties mainly in the upper few centimetres of the tunnel wall. This can be explained with loosening and later as a slight consolidation of the tunnel wall.

All results point to a pronounced seismic anisotropy of the Opalinus Clay which is caused mainly by the bedding.

The interval velocity methods gave hints for the existence of cracks in the ranges between 30 – 50 cm and 65 – 80 cm from the tunnel wall.

Remarkable is that results from all three methods show similarities with results found during a geophysical investigation of the EB-Niche in 2001.



2 INTRODUCTION

The Ventilation-Experiment (VE-Exp.) performed at the Mont Terri Rock Laboratory, Switzerland aims at the evaluation of the de- and resaturation of hard clay under in-situ conditions [1]. The thereby caused changes of rock properties may have an impact on the design of repositories. A flow of well controlled dry and humid air throughout a 10 m long section of a non-lined horizontal microtunnel (excavated with the raise-boring technique) with a diameter of 1.2 m is used to generate appropriate conditions in the Opalinus Clay of the RL Mont Terri. Figure 1 shows the northern part of the Mont Terri RL. The location of the VE test section is indicated. For a comparison between seismic results from the VE-Experiment with results from the EB-Experiment which was performed in June 2001 also the location of the EB-niche is marked. The VE phase I Experiment has been carried out between December 2001 and May 2004. The successive VE phase II Experiment is part of the integrated project NF-PRO [2]. BGR (Federal Institute for Geosciences and Natural Resources, Germany) participates in the project since autumn 2004.

With the help of high resolution small scale seismic refraction measurements along two profiles installed on the side wall of the test section the extent of the excavation damaged/disturbed zone (EDZ/EdZ) was determined as well as changes in the EDZ/EdZ with time were detected. Measurements were performed eight times between May 2005 and October 2006 during the desaturation phase and two times during the resaturation phase in July and November 2007.

In October 2006 three 1 m long boreholes of 86 mm in diameter were drilled in the vicinity of the profiles in order to obtain supplemental information on seismic parameters. In October 2006 and July 2007 seismic interval velocity and cross hole measurements as well as borehole camera recordings were conducted in these boreholes. Borehole camera recordings were performed in July 2007.

The following photograph (see Figure 2) gives an impression of the situation at the selected site in the test section several weeks before the seismic array was installed.

Figure 1: Northern part of the location map of the Mont Terri Rock Laboratory, Switzerland. VE: Ventilation Experiment test section. EB: Engineered Barrier Experiment niche.



The location of the refraction profiles and the boreholes used for seismic interval and cross hole measurements are shown in Figure 3.

3 HIGH RESOLUTION SEISMIC MEASUREMENTS

Several seismic parameters change significantly in rock with progressive failure. Thus, high resolution seismic methods can help to analyse changes in rock properties in the EDZ/EdZ around underground openings.

According to our experiences made within the EB-Experiment [3] the seismic refraction method was chosen as a non-invasive geophysical tool to characterise the vicinity of the test section in the micro-tunnel. The wall stayed mainly unaffected by the installation of the seismic refraction profiles.

Figure 2: Inspection and site-selection for the seismic refraction profiles in the VE test section.

Figure 3: Seismic refraction profiles (red and blue lines) in the test section. The three boreholes are located close to the crossing point of both profiles. Labels indicate locations of other geotechnical sensors and installations.



In October 2006 three 1 m long boreholes could be drilled close to the refraction profiles. In and between these boreholes seismic interval velocity and cross hole measurements were performed in order to support the processing and confirm results from the non-invasive seismic refraction measurements.

From the registered seismic wave field several seismic parameters like seismic P- and S-wave velocity, apparent frequencies and dynamic pseudo elastic parameters are extracted for the characterisation of the rock mass.

The frequency content of the received seismic refraction signals lies between 3 and 15 kHz. For the borehole based cross hole measurements the frequency content of the signals lie in the same range, whereas for the interval velocity signals the frequencies range from 25 to 40 kHz. The resulting seismic wave lengths allow in combination with a narrow spaced deployment of the seismic sensors (typical 5 to 10 cm) a high spatial resolution.

Because the total range of the signal frequency content for all three methods span from 3 to 40 kHz we are using in this report the words seismic method or seismic signal instead of differentiating between seismic and ultrasonic methods or signals.

All three mentioned seismic methods proofed to be good tools for the characterisation of the EDZ/EdZ. We made many appropriate experiences in different international rock laboratories. The difference between the excavation damaged and disturbed zone around a tunnel was defined in the EDZ CLUSTER workshop, 2003 [4]. A clear differentiation between both stages of the excavation affected zone (damaged and disturbed) is difficult, especially with a limited amount of data. Furthermore, the situation become more complex in an anisotropic rock which is additionally, at least partly, interspersed with stratigraphic and/or lithological inhomogeneities. So we will use in general the abbreviation EDZ/EdZ.

Results from the three applied seismic methods are discussed in the following separately. In Section 5 results from all methods will be compiled.

3.1 Seismic refraction experiment

The equipment and installation material for the seismic refraction measurements within the framework of the Ventilation-Experiment consists mainly of two parts. Seismic sources, receivers and cables are fixed permanently and stay in place for the total duration of the VE-Experiment. Frequency generator, power amplifier, preamplifiers and digital oscilloscopes have to be connected each time a measurement will be performed. Figure 4 shows the principal of the layout.



Test Section Micro Tunnel

Temporary installation

pre-amplifier& peizo

power supply DSO3 x 16 channels

wave-generator

(Access tunnel)

poweramplifier

PC control

220 V power supplyneeded

no external power supply needed

220 V power supplyneeded

Fixed installation

Input signal line

output signal line

Seismic profiles

Temporary installation

MI NicheForwardDoor

(Air Lock)

∗ ∗∗

∗ ∗∗

∗∗

∗

3.1.1 Profile layout and instrumentation In order to cope with the anisotropy of the Opalinus Clay two profiles, 1.25 m and 1.45 m long, were chosen which are perpendicular orientated to each other. One profile is orientated parallel to the bedding planes whereas the other one runs perpendicular to the bedding planes. The centre of the crossing profiles is located approx. 3 m away from the forward door of the test section (see Figure 3). The determining factors for the choice of this location were the relative good condition of the wall and the fact that the area was mainly free of other sensors or installations. The design of the profiles and the installation plan was discussed with all project partners. Taking logistical as well as the subsurface conditions of the test section into account, the ENE site of the wall was chosen for the installation.

Figure 5 shows the layout of the profiles in more detail. Along each profile 23 piezoelectric transducers as seismic receivers and five transducers as seismic sources are active. The receivers as well as the emitters are distributed nearly equidistantly along the profiles. The location of the nine source transducers allows to receive simultaneously seismic signals along an in-line profile (classical refraction profile) and an off-line profile (broadside -shooting).

Figure 4: Principal layout of the seismic refraction experiment in the VE test section.



profile P2(perpend. to bedding)

Receiver positionShot position

profile P1(parallel to bedding)

16

7

1718

S1

S2

S3

S4

S5

S6

S7

S8

46

3411

33

24

28

29

39

40

23

12

S9

47

In-line

off-line

The length of the sub profile P1 (parallel to bedding plane) is 1.45 m and the length of the sub profile P2 (perpendicular to bedding plane) is 1.25 m. The spacing between the piezoelectric receiver transducers varies between 6 and 7 cm whereas the spacing between the emitting peizos varies between 25 and 40 cm.

As seismic sources (emitters) piezoelectric transducers from PCB, type: 712A01 were used. As receivers small piezoelectric transducers (PCB, type M352C67) were fixed as described above.

As a consequence of the de- and resaturation during the total duration of the experiment we expect changes at the surface of the micro tunnel wall. Therefore it was necessary to fix the piezoelectric transducers properly to the rock in order to guarantee a good coupling between piezoelectric transducers and the wall over the total duration of the experiment. Figure 6 shows a sketch of the fixation. It was necessary to drill small and short holes (20-25 mm deep, diameter: 4 mm) in the side wall for the receiver fixation. Small screw anchors (aluminium) were stuck into the small holes (see Figure 6, left side). Then the receiver piezos were screwed into the screw anchors.

Due to the greater weight and due to the fact that the emitter piezos are vibrating slightly during the measurements, they had to be fixed much stronger to the rock. The screw anchors (30-40 mm deep, diameter: 6 mm) were placed approximately 150 mm outside the profile lines (see Figure 6, right side).

Figure 5: Seismic array consisting of two linear profiles in the test section.



Receiver - PiezoL =12 mmdiam. = 10 mmweight = 2 gr

screw anchoraluminiumL = 20 mmdiam. = 4 mm

screw anchoraluminiumL = 40 mmdiam. = 6 mm

Emitter - PiezoL = 30 mmdiam. = 30 mmweight = 400 gr

Opalinus Clay

test section

All thin piezo cables (output signal line) end near the seismic profiles in a cable harness of approximately 100 mm in diameter which had to go through the double doors. For the input signal line nine coaxial cables were necessary. Both cable harnesses end near the forward door (outside the test section) in the access section of the micro tunnel. Two photographs (see Figure 7 and 8) illustrate the situation in the test section during the installation and test phase and outside in the MI niche.

3.1.2 Results of first measurements Immediately after the main part of the installation was finished a test measurement was performed on the 12th of May 2005 in order to check all components of the equipment. Figure 9 shows a seismic shot section where at source point S1 (see Figure 5) seismic energy was emitted. Traces from the in-line registration (profile 1, left side) and from the off-line registration (profile 2, right side) are shown. Data were only processed moderately (subtraction of DC shift). The section is displayed trace normalised and scaled that way that S-wave energy appears as clear arrivals. The first trace shows the sine pulse which was used as the source signal and the second trace belongs to receiver position 47, outside of both profiles, which was used for test purposes. Only two traces (receiver positions 24 and 26) are disturbed, which indicates either a problem with the receiver or with the cables and/or connections.

Figure 7: Piezoelectric transducers as seismic source and receiver sensors.

Figure 8: Digital oscilloscopes for recording of high resolution seismic signals in the MI niche.

Figure 6: Fixation of seismic sensors; receivers (left side) and emitters (right side).



In Figure 10 a higher plot scaling factor was chosen in order to display also the first arrival phases (P-waves). Compared to the S-wave arrivals they are weaker and can therefore not be recognised in Figure 9. P-waves can be identified over the total length of both profiles in Figure 10. This data examples show that the quality of the recorded data is very good.

Figure 9: Seismic shot section for source point S1 (see Figure 5). The scale is customised for a good resolution of S-wave energy.

Figure 10: Seismic shot section for source point S1 (see Figure 5). The scale is customised for a good resolution of P-wave energy.



For all 9 source positions (S1 –S9, see Figure 5) an overview of the data quality is given in Figure 11. In all nine seismogram sections the S-wave onsets as pronounced signals can be recognised whereas the P-wave onsets due to the scaling can only partly be recognised as first arrival phases. In all nine sections trace 1 shows the source signal.

Figure 11: Seismic shot sections for all nine source points (S1 – S9, see Figure 5) measured during the first campaign in May 2005. The scale is customised for a good resolution of S-wave energy.

3.1.3 Comparison of data from different measurement campaigns Between May 2005 and November 2007 ten measurements were performed. The sequence and a short description of the main activities performed during that time are compiled in Table 1.

experim. date comments VE-01 12.05.2005 part 1 of the installation and test VE-02a 08.06.2005 part 2 of the installation and final adjusting VE-02b 10.06.2005 check before closure of test section, only shot pos. S3 tested VE-03 05.07.2005 final check, start of desaturation, (source: only freq. generator used,

no power amplifier) VE-04 22.11.2005 4.5 months after start of desaturation VE-05 14.03.2006 8.5 months after start of desaturation

Table 1: Sequence of seismic measurements in the VE test section.



VE-06 18.05.2006 10.5 month after start of desaturation VE-07/08 17.10.2006 15.5 months after start of desaturation, test section was opened for

1 week, drilling of 3 boreholes and first borehole based measurements

Jan. 2007 start of resaturation VE-09/10 11.07.2007 7 months after start of resaturation. Second borehole based

measurements, borehole camera recordings VE-11 28.11.2007 11 months after resaturation

In order to assure a reliable comparison of the results the same registration parameters were used (source signal amplitude, source signal frequency and pre-amplification) for all repetition measurements. Figure 12 shows sections from six measurements in the period July 2005 to November 2007 in an ensemble normalised representation. This means that the maximum amplitude value of all traces and all six campaigns are taken to normalise all other amplitudes. Additionally amplitudes are colour coded (blue: negative, white: zero, red: positive). In general we observe a decrease in signal quality with ongoing time until May 2006 (measurement VE-06, not shown here), a slight increase in October 2006 (VE-07) and a remarkable increase in July and November 2007.

An intermediate resolution was chosen in order to recognise S-wave phases as well as P-wave phases. It is very clear that coherent S-wave phases can be correlated in results from June 2005 and again in July and November 2007. They are only indicated in the plot

Figure 12: Ensemble normalised seismic shot sections for source point S1 (see Figure 5) at different stages of the experiment. The scale is customised for an intermediate resolution between P- and S-wave recognisability. P- and S-wave phases are indicated in the first plot.



for June 2005. During the desaturation phase (July 2005 – December 2006) these phases disappear nearly completely for the chosen resolution. It is a clear indication for an increased attenuation of seismic wave energy during the desaturation period. A loosening of rock, which could be a consequence of the desaturation process, leads to a higher attenuation of seismic waves. This results in a decrease of signal quality (no coherent seismic phases can be recognised).

All piezo-electric transducers were checked in October 2006 for stable fixation at the wall when the test section was accessible for one week. We found that all 47 receivers and 9 source piezo-electric transducers were very stable. Also in July 2007 we found all sensors fixed very stable. So we can relate the decrease and increase of signal quality directly to the changing properties of the rock.

For the derivation of an underground model from the seismic data good readable P-wave onsets (first arrival phases) are necessary. As can be seen in Figure 13, where traces are trace normalise displayed and scaled for a good P-wave recognition, it is only the case for measurements made in June 2005 and partly for July and November 2007 data.

More pronounced it can be seen in Figure 14. In this trace normalised sections only the in-line recordings along profile 1 (parallel to bedding) for source point 1 are displayed. The red dashed lines show roughly the visible onsets (June 2005) and the expected onsets for the other registrations. For the July and November 2007 registration very week P-wave arrivals can be anticipated in some parts. For the other periods, except May and June 2005, no clear P-wave onsets are detectible.

Figure 13: Ensemble normalised seismic shot sections for source point S1 (see Figure 5) at different stages of the experiment. The scale is customised for a good resolution of P- wave recognisability.



Because the P-wave onsets are the basis for the further processing we have to constrict for the modelling on May/June 2005 data. Furthermore there are no mayor differences between data from May and June 2005 and there is only one month between both measurements. Therefore we consider both data sets as data which describe the initial situation.

3.1.4 Finite difference ray tracing The finite difference modelling aims at the derivation of a 2D-model which explains the measured seismic refraction travel time data in terms of distribution of seismic P-wave velocities. Reduced P-wave velocities are interpreted as an indication for the existence of an EDZ/EdZ.

Before an underground model from the data can be derived the data have to be processed. The applied main steps for the processing of seismic refraction data are listed briefly in the following:

• Insert of geometry information (profile distances, positions of receivers and shot points, topography) into the seismic trace headers

• Sort and combination of sub profiles • Start time correction due to the individual trigger time delays • Plot of shot point sections • Subtraction of DC shifts • Mean filter, 8 points

Figure 14: Trace normalised seismic shot sections for source point S1 (see Figure 5) at different stages of the experiment. Only the in-line receiver data are plotted. The scale is customised for a good resolution of P- wave recognisability.



• Picking of first arrival times (P-waves) and phase correlation • Plot of travel time curves • 1-dimensional inversions for all travel time curves • Creation of a 2-dimensinal start model • Forward computation (net work ray tracing and / or Finite Differences ray

tracing) • Iterative modelling till the best fit between model travel times and measured

travel times is reached • Final (“best”) model

After traces were sorted and the in-line sections were filtered first arrival phases were correlated and first arrival times were picked. This gives a first hint of the P-wave velocity distribution in the vicinity. In Figure 15 for the in-line profile P1 (see Fig. 5) the derived apparent P-wave velocities are indicated. These results are used for the creation of a start model.

In Figure 16 for the in-line profile P1 (parallel to bedding) and for the in-line profile P2 (perpendicular to bedding) the derived apparent velocities plotted in each case for three shot positions (see Fig. 5).

Figure 15: Shot sections for source point S1 from May 2005 (see Fig. 5) with correlated first arrival phases and apparent P-wave velocities.



As expected travel time curves from the profile P1 (parallel to bedding, red curves) show higher apparent velocities (approx. 2600 m/s) than from profile P2 (perpendicular to bedding, blue curves) which are approx. 1800 m/s. For comparison we plotted additionally a travel time curve which was derived from a similar refraction measurement which was performed in 2001 in the EB-Experiment [3]. This will be discussed in Section 4.

With the help of these derived results start models for the velocity distribution along the profiles P1 and P2 can be constructed. Furthermore experiences made in a seismic refraction experiment in the EB-niche in 2001 [3] are also taken into account.

A 2-layer start model for the finite difference ray tracing forward modelling [5,6] with a very thin first layer and the second one with a steep velocity gradient was chosen. The result of the iterative modelling process is displayed in Figure 17. The parameters P-wave velocity, P-wave velocity gradient and layer interface were manually changed until a good fit between calculated and measured data were achieved. In the upper part of Figure 17 the model can be seen. The red line represents a part of the ENE wall of the VE test section where the seismic refraction profile P1 is installed. The green bended lines represent the ray paths from shot point S1 (see Fig. 5) to the receivers. For the FD-calculation the grid size of the model was 5 mm.

Figure 16: Travel time curves for different source points from in-line profiles P1 and P2 (see Fig. 5) measured in May 2005 (VE01). Dashed lines are indicating a range of apparent velocities. Mt05 indicates travel time curves derived in the EB-Experiment.



The derived P-wave velocity distribution from the centre of the profile can be seen in Figure 18. It starts at the surface of the wall with a P-wave velocity (Vp) of 2300 m/s, reaches after 2 cm 2650 m/s and increases until 3140 m/s at a depth of 16.5 cm. This is the greatest depth which can be reached with the chosen parameters and a 1.45 m long profile.

1600 2000 2400 2800 3200

Vp (m/s)

20

15

10

5

0

dept

h (c

m)

For all five shot points (S1 – S5) the ray paths and the comparison between calculated and measured travel times is plotted in Figure 19. Again, the overall match between calculated (coloured crosses) and measured data (black crosses) is good. This 2-layer

Figure 17: Result of the FD ray tracing for a 2-layer model (VEP1IN-L2A) along in-line profile P1. Rays (upper part) and travel times (lower part) calculated for source point S1 (see Figure 5) measured in May 2005 (VE01). Calculated travel times (green crosses) match well with the measured travel times (black crosses).

Figure 18: P-wave velocity–depth distribution derived from the 2-layer model described in Fig. 17.



model explains the measured data well. Nevertheless, there are also alternative models conceivable.

An alternative model which also fits the measured data well is given in Figure 20. A 3-layer model was created. The ray paths coverage and the travel times are displayed in the same way as for the 2-layer model. Except for some parts the match between calculated and measured data is sufficiently good.

Figure 19: Result of the FD ray tracing for a 2-layer model (VEP1IN-L2A) along in-line profile P1. Rays (upper part) and travel times (lower part) calculated for 5 source points S1 - S5 (see Fig. 5) measured in May 2005 (VE01). Calculated travel times (coloured crosses) match well with the measured travel times (black crosses).



The appropriate derived velocity–depth distribution for the central part of the model is shown in Figure 20. A P-wave velocity of 3100 m/s is reached at about 8 cm depth.

1600 2000 2400 2800 3200

Vp (m/s)

20

15

10

5

0

dept

h (c

m)

Several other models were studied in order to get an idea of an upper and lower boundary for the variation of parameters which still explain the measured data sufficiently. On the basis of these analyses we can conclude, that the extent of the EDZ/EdZ lies for the in-line profile (parallel to bedding) in the range 5 to 20 cm. The “best” match was

Figure 20: Result of the FD ray tracing for a 3-layer model (VEP1IN-L3A) along in-line profile P1. Rays (upper part) and travel times (lower part) calculated for 5 source points S1 - S5 (see Fig. 5) measured in May 2005 (VE01). Calculated travel times (coloured crosses) match well with the measured travel times (black crosses).




found for the velocity-depth distribution as shown in Figure 18 with a corresponding extent of the EDZ/EdZ of 16.5 cm in the central part of profile P1.

Data from the in-line profile 2 (perpendicular to bedding) were processed, analysed and modelled in the same way as it was done for profile 1 data. A 2-layer model which fits the measured data well is given in Figure 22 and the appropriate velocity-depth distribution in Figure 23. A P-wave velocity of 2035 m/s is reached at 11 cm depth.

1600 2000 2400 2800 3200

Vp (m/s)

20

15

10

5

0

dept

h (c

m)

Fig. 22: Result of the FD ray tracing for a 2-layer model (VEP2IN-L2A) along in-line profile P2. Rays (upper part) and travel times (lower part) calculated for 3 source points S6, S3 and S9 (see Fig. 5) measured in May 2005 (VE01). Calculated travel times (coloured crosses) match well with the measured travel times (black crosses).




The remarkable difference between the results from both profiles (parallel and perpendicular to bedding) is the derived P-wave velocity. Already the discussed apparent velocities showed this immense difference. From the seismic refraction data we obtain a seismic anisotropy factor of 1.5, which is very high in comparison to a detailed seismic anisotropy study which was performed in the EB-niche with cross hole measurements [2] where we found a seismic anisotropy factor of 1.2. The Vp parallel to bedding was approximately 3100 m/s and perpendicular to bedding 2600 m/s. At other locations in the RL Mont Terri we found an anisotropy factor of 1.32 (EZ-B niche) what is in good accordance with measurements on core samples from the HE-D niche [9].

According to the FD-modelling a Vp of 3100 m/s was found at depths between 10 to 20 cm which is regarded as an indication for the undisturbed rock. This is in good accordance with the above mentioned anisotropy study. Along profile P2 a Vp of 2035 m/s was found at a depth of 11 cm. This Vp deviates much from 2600 m/s which was found for the direction perpendicular to bedding in the anisotropy study. One reason could be that along profile P2 the “undisturbed rock” with a higher Vp could not be reached with the used profile layout, especially the limited length of 1.25 m could be too short.

It was intended to describe changes in the EDZ/EdZ quantitatively by analysing and modelling all data measured within the period May 2005 until November 2007. As already described in Section 3.1.2 clear P-wave first arrival phases could only be identified in data which were measured in May and June 2005. In July-2005-data and for profile P1 P-wave phases could only be identified to a profile distance of 0.9 m. The main reason is that for this measurement no power amplifier for the generation of the emitting signal could be used. The situation became worse in data from October 2005, where P-wave phases could only be identified until 0.4 m profile distance. For all subsequent measured data (March 2006 – November 2007) P-wave phases disappeared almost completely or their quality was not sufficient for a first arrival detection. In Figure 24 the identifiable first arrival times are plotted for profile P1 for two shot points.

Figure 24: Travel time curves for source point S1 (left side) and S3 (right side) from in-line profile P1 (see Fig. 5) measured at different periods of the experiment. VE01: May 05, VE02: June 05, VE03: July 05 and VE04: Oct. 05.



Because no further travel time information can be extracted from the large data volume and the available travel time data from the first four measurement periods are very limited or/and very similar a modelling would not bring new information.

3.1.5 Conclusions from seismic refraction measurements From the seismic refraction measurements we conclude so far the following:

• Decrease in signal quality, until a lack of P-wave arrivals, within the first 10 months (July 2005 – May 2006) and slight increase in October 2006 and more pronounced in July and November 2007 due to changes in wave attenuation (loosening/consolidation of rock).

• A chronological characterisation of the EDZ/EdZ development with ongoing time can only be made qualitatively.

• Extent of EDZ/EdZ parallel to bedding (profile P1): 5 – 20 cm with a P-wave velocity of 3100 m/s for the undisturbed rock (May and June 2005 data).

• Extent of EDZ/EdZ perpendicular to bedding (profile P2): at least 11 cm with a P-wave velocity of 2050 m/s for the undisturbed rock (May and June 2005 data).

• Strong seismic anisotropy.

3.2 Borehole measurements In addition to the seismic refraction profiles the drilling of three boreholes in the vicinity of the refraction profiles was proposed in order to apply seismic borehole measurements like interval velocity and cross hole measurements. Results from these measurements can support the interpretation of seismic refraction data.

The BGR borehole methods as well as their capabilities are specified in detail in [7]. The main advantage of these invasive methods is the fact that along the borehole a highly resolved distribution of seismic parameters, like P- and S-wave velocity, wave attenuation, apparent frequencies of first arrival phases and dynamic pseudo elastic parameters like Poisson’s ratio and Young’s modulus can be derived. Furthermore, with the help of borehole based methods a look behind high velocity bodies can be achieved what practically is not possible with seismic refraction methods. Because due to the seismic refraction theory the seismic wave field is refracted back to the surface if it meets a high velocity layer or body.

Three 1 m long boreholes with 86 mm in diameter were drilled in October 2006 with a HILTI hand held drilling machine. In order to avoid an orientation of the borehole axis parallel to the strike of the bedding the boreholes were drilled with an angle of about 30° to the axis of the tunnel. This results in an angle of about 40° between the borehole axis and the strike direction. Due to the hand held drilling technique the borehole wall was not as smooth as drilled with a rack based drilling machine. Figure 25 shows the location of the three boreholes in their relative position to the crossing point of the refraction profiles



P1 and P2 whereas Figure 26 gives an impression of the activities during a cross hole measurement.

The interval velocity measurements are operated with emitting frequencies of 50 kHz (ultrasonic frequencies) whereas the cross hole measurements were performed with 13.5 kHz (rather seismic frequencies). No further differentiation is made between both terms in this report.

The following Figure 27 gives an impression on the quality of the borehole walls and an explanation of the sensor orientations used for interval velocity and cross hole measurements. The 315°-orientation runs parallel to the bedding planes of the Opalinus Clay and consequently the 45°-orientation perpendicular to bedding. The borehole wall was slightly rippled. Due to this we assume a minor decrease in seismic signal quality.

Figure 25: Location of boreholes BVE-112, BVE-113 and BVE-114.

Figure 26: Cross hole measurements between boreholes BVE-114 and BVE-113.

Figure 27: Relative position of boreholes which were used for interval velocity and cross hole measurements. Along the red lines interval velocity measurements were performed (orientation of sensors at 45° and 315°, clock wise). Blue lines indicate the orientation of source piezo in one borehole and the receiver sensors in the second borehole for the cross hole measurements. Photographs are made in October 2006 several days after drilling.



For measurements in the second campaign (July 2007) the boreholes were smoothed a bit with a steel scrubber tool mounted on a hand held drilling machine. The gain in signal quality was not striking, rather a bit disappointing. But it is not clear what influence came from a possible ‘normal’ alteration of the borehole wall, because the boreholes stayed open for more than eight months.

3.2.1 Borehole camera inspection With a BGR borehole camera the wall was inspected and recorded in July 2007. This inspection allows the assessment of the expected coupling conditions between piezoelectric transducers which are pressed pneumatically against the borehole wall. Figure 28 shows the flat projection of the visual assessment in steps of 10 cm of the borehole depth and in 15° steps of the rotation angle (clock wise). The borehole walls were stable but they showed a slight waviness caused by the hand drilling. This feature is not represented in Figure 28. The visual analysis gave hints for the existence of cracks (indicated by “c”).

VE B112depth[cm]/angle[°] 0°- 30° 30°-60° 60°-90° 90°-120° 120°-150° 150°-180° 180°-210° 210°-240° 240°-270° 270°-300° 300°- 330° 330°- 360°

0 c c c c c c c c c c c c10203040 c c c c c c50 c c c c c c60708090

100110

depth[cm]/angle[° ] 0°-30° 30°-60° 60°-90° 90°-120° 120°-150° 150°-180 ° 180°-21 0° 210°-2 40° 240°-270° 270°-300° 300°-330° 330°-360°

0 c c c c c c10 c c c c c c20 c c c c c c30 2 2 2 c c c c c c 2 2 2405060708090

100110

VE B113

de pth[cm]/angle[°] 0 °-30° 30°-60° 60°-90° 90°-1 20° 1 20°-150° 150°-180 ° 180°-210° 210°-240° 240°-270° 270 °-300° 300°-330 ° 330°-3 60°

0 c c c c c c10 c c c c c c20 c c c3040 c c c c c c c c c c c c5060708090

100110

VE B114

1 intact2 sheeting,weak

3 sheeting,stronger

4 breakout,strong

5 breakout, very strongc crack

Figure 28: Results of visual borehole camera analyses.



3.2.2 Interval velocity measurements Interval velocity measurements were performed in each of the three boreholes (BVE-112, BVE-113, BVE-114) with two orientations of the sensors, at 315° (parallel to bedding) and at 45° (perpendicular to bedding). From the measurement campaign in October 2006 the appropriate raw data are compiled in Figure 29. Within the first 40 cm of the borehole the measurements were performed in steps of 3 cm and then in 5 cm steps till the end of the borehole. Channel 1 data (distance between source and receiver is 10 cm) are plotted ensemble normalised. Strongest P-wave arrivals are observed for greater depths (75 – 90 cm) in borehole BVE-113 (45°). Relative to this maximum the other P-wave amplitudes appear smaller. At some depths an apparent complete loss of signal can be observed due to very strong seismic wave attenuation. These are hints for the existence of cracks. We can not exclude that in some cases the cause could also be a very bad coupling of the sensors.

A closer analysis of the seismic processed data, a part of it can be seen in Figure 29, gives clear indications for the existence of cracks. Some of them were confirmed with the help of the borehole camera data. Due to the very weak or even complete missing signals we assume cracks at the following depths and orientations:

BVE-112-045°: 20 - 23 cm and 35 – 40 cm BVE-112-315°: 8 - 11 cm and 45 – 50 cm BVE-113-045°: 14 - 23 cm and 60 cm BVE-113-315°: 17 - 20 cm and 32 cm BVE-114-045°: 14 - 20 cm and 40 – 45 cm and 65 – 70 cm BVE-114-315°: 8 - 17 cm and 45 – 50 cm and 75 – 80 cm

Figure 27: Raw data from interval velocity measurements (channel 1, October 2006, ensemble normalised). The identifier of the six data sets can be found in each upper left corner, for example BVE-112-045-A-C1.02T means: borehole BVE112, measured at 45°, campaign Oct. 2006 (A) and channel 1 data (C1).



The signal quality of channel 2 and more pronounced for channel 3 data degrades. To a certain extent we expect such an observation due to the longer travel path of waves for channel 2 and channel 3 signals, especially within the vicinity of a tunnel. So far only data from boreholes BE-112 and BE-113 were analysed.

Some of the derived P-wave velocities are compiled in Figure 30 for the 315° orientation of sensors and in Figure 31 for the 45° orientation. Velocities were only derived from seismic traces with a very good detectable first arrival phase (quality factor QC=2). In a first step and especially for the characterisation of the borehole-EdZ these seismic velocities are calculated by assuming straight ray propagation between source and receivers, this results in a sort of apparent velocities. Only for an isotropic (and intact) rock without a borehole-EdZ these derived apparent velocities are very close to the “real” velocities of the rock.

In general a complete loss of velocity information and/or a gradual increase of velocity, until a constant plateau at greater borehole depth is reached, are indications for the existence of an EDZ/EdZ. We interpret a relatively constant velocity plateau as an indicator for an undisturbed rock.

All graphs in Figure 30 and 31 show pronounced variations without a smooth velocity plateau. A drastic drop in velocity or a complete loss of signal indicates the existence of cracks but as mentioned before also very bad coupling conditions of the sensors could lead to such a result. Velocities in borehole BVE-112 are in general higher for both sensor orientations. As expected velocities measured along 315° orientation (parallel to bedding) are higher in each borehole than along 45° orientation (perpendicular to bedding).

Figure 30: P-wave distribution derived from interval velocity measurements along boreholes BVE-112 and BVE-113 (channel 1) measured in October 2006 (A) and July 2007 (B) with a sensor orientation of 315° (parallel to bedding).



Noticeable is that some of the P-wave velocity graphs show in the general trend up to 0.5 m higher values than for greater borehole depths. Such a velocity distribution is rather uncommon. We observed a similar velocity distribution in interval velocity measurements performed in a comparable orientation (ENE sidewall) in the approx. 40 m away located EB-niche [3]. In the EB-niche we explained this distribution with possible stress redistributions and/or lithological heterogeneities (sandy layers). This will be discussed in the final Section.

3.2.3 Conclusions from interval velocity measurements From the interval velocity measurements we conclude so far the following:

• The lack of stable velocity plateaus as indications for the undisturbed rock due to the short boreholes makes it very difficult to attribute the extent of the EDZ/EdZ.

• P-wave velocity variations are very strong and can be caused by cracks and/or lithological heterogeneities. Several cracks could be confirmed with the borehole camera inspection.

• P-wave velocity distribution shows similarities with results from a former experiment in the close by located EB-niche (‘high velocity body’ 10 cm – 100 cm behind the tunnel wall).

• The extent of the EDZ/EdZ is in the range between 10 and 25 cm although we found some indications for the existence of cracks at greater depths.

• Indications for the existence of cracks outside the EDZ/EdZ in the ranges 30 – 50 cm and 65 – 80 cm were found.

• Seismic anisotropy could be confirmed.

Figure 31: P-wave distribution derived from interval velocity measurements along boreholes BVE-112 and BVE-113 (channel 1) measured in October 2006 (A) and July 2007 (B) with a sensor orientation of 45° (perpendicular to bedding).



3.2.4 Cross hole measurements Cross hole measurements were performed between the following boreholes in October 2006 as well as in July 2007 (see also Figure 27):

BVE-112 (source) and BVE-113 (receivers) – perpendicular to bedding (L=41.8 cm) BVE-112 (source) and BVE-114 (receivers) – approximately 45° to bedding (L=56.4 cm) BVE-114 (source) and BVE-113 (receivers) – parallel to bedding (L=35.1 cm)

The distances between the borehole mouths are given in brackets. The BGR borehole mini sonic probe equipment was slightly modified for these measurements. The piezoelectric source transducer in one borehole pointed directly to the three receiver transducers in the second borehole (see also Figure 27). Measurements were performed in steps of 5 cm. Up to now the data from cross hole measurements were only processed slightly. Therefore only a qualitative analysis can be done. The signal quality from all measurements is very good as can be seen in Figure 32 were all traces are displayed trace normalised. On the left hand side data from October 2006 are displayed and on the right hand side the July 2007 data. In Figure 33 the same data set is plotted but ensemble normalised in order to emphasise the relative differences in amplitude strength. Strongest amplitudes are observed between boreholes BVE-114 and BVE-113. The seismic ray paths run parallel to the bedding in this case. The highest attenuation of seismic wave energy was observed between boreholes BVE-112 and BVE-114 where ray paths run approximately under 45° to the bedding.

Figure 32: Raw data from cross hole measurements (October 2006, trace normalised). The identifier of the six data sets can be found in each upper left corner, for example BVE-112- BVE-113-A-C1.02T means: measurement between borehole BVE112 (source) and BE-113 (receivers), measured in Oct. 2006 (A) and in July 2007 (B), channel 1 data (C1).



We assume that this orientation leads to a higher scattering of seismic wave energy than in the case of a perpendicular orientation were amplitudes show an intermediate strength.

The attenuation behaviour is furthermore influenced by the distances. A longer travel paths leads to a higher attenuation. This distance effect boosts the described orientation related attenuation. The shortest distance is between BVE-114 and BVE-113 (35.1 cm, parallel to bedding) and the longest between BVE-112 and BVE-114 (56.4 cm, 45° to bedding).

The data set BVE-114-BVE-113-A-C1 (see Fig. 32, lower left) which represents data from cross hole measurements along a parallel to bedding orientation shows an explicit variation in travel times of the first arrival phases. Decreasing travel times until 0.2 m then relative constant times around 110 μs before from 0.7 m till the end of the borehole an increase can be seen. This are very clear indications for the existence of a rock mass with higher velocities between 0.25 m and 0.7 m as it was found partly in the interval velocity measurement data and in the mentioned EB-Experiment in 2001. Furthermore, low travel times and low amplitudes within the first 20 cm from the tunnel wall point to the existence of a damaged/disturbed zone.

Figure 33: Raw data from cross hole measurements (October 2006, ensemble normalised). The identifier of the six data sets can be found in each upper left corner, for example BVE-112- BVE-113-A-C1.02T means: measurement between borehole BVE112 (source) and BE-113 (receivers), measured in Oct. 2006 (A) and in July 2007 (B), channel 1 data (C1).



3.2.5 Conclusions from cross hole measurements From the cross hole measurements we conclude so far the following:

• The extent of the EDZ/EdZ is approximately 20 cm.

• Travel time distribution shows similarities with results from a former experiment in the close by located EB-niche (‘high velocity body’ 25 cm – 70 cm behind the tunnel wall).

• Seismic anisotropy could be confirmed.

4 COMPARISON BETWEEN RESULTS FROM VE- AND EB-EXPERIMENT

In June and October 2001 several seismic refraction and borehole measurements were performed in the framework of the Engineered Barrier Experiment (EB) in the EB-niche [3] at comparable orientations with the actual profiles in the VE-Experiment (ENE side wall, see Figure 1). The distance between both locations is approx. 40 m. Both are located in the shaly facies of the Opalinus Clay.

Although the differences between both excavated sections are tremendous we observe some similarities in the seismic results achieved in both experiments. The major differences are compiled in the following Table 2.

EB niche VE test section

excavation method road header raise-boring

diameter of section 2.5 m 1.2 m

age at 1st measurement 2 weeks approx. 5 years

topography of seismic profiles

horizontal, flat, 45° towards bedding

valley like shaped, parallel and perpendicular to bedding

extent of EDZ/EdZ 5 to 15 cm (side wall) 65 cm (45° inclined up wards) 50 cm (in the roof)

5 to 25 cm (approx. 25 cm below and above a horizontal line along the side wall.

The first refraction measurement was performed approx. two weeks after the excavation of the EB-niche along a 5 m long profile. The profile ran horizontally on the side wall what resulted in a 45° orientation towards the dip of the bedding planes. The derived apparent velocities are plotted in Figure 16 (named Mt05) together with data from the VE profiles parallel and perpendicular to bedding. Forceful, the EB data graph (45°) plots between

Table 2: Main features of the EB niche and the VE test section.



both extreme VE data graphs (parallel and perpendicular). The main reason for that is the pronounced seismic anisotropy caused by the bedding.

The extent of the EDZ/EdZ varied between 5 and 15 cm with P-wave velocities between 900 and 1400 m/s. P-wave velocities of the “undisturbed” rock varied between 2300 and 3000 m/s. Additionally, with the help of seismic borehole measurements the result could be confirmed. Furthermore, a detailed anisotropy study was performed.

Figure 34 shows a seismic shot section measured along the horizontal profile Mt05 in the EB niche. The red lines indicate the first arrival phases. A clear sharp bend point at 0.45 m is visible. This is a typical indication for the existence of an interface between two layers with different seismic velocities (layer 1: lower velocity EDZ/EdZ and layer 2: higher velocity intact rock). The inlay (green box in Figure 34) shows a comparable section from the VE test section (profile P1, parallel to bedding). No sharp bend point is visible in this section. The reason could be a combination of two facts: 1) a more gradual increase of velocities in the EDZ/EdZ and 2) the valley like shaped topography of the profile. But in both locations the seismically derived extent of the EDZ/EdZ at the ENE side wall is in the same surprisingly low range, namely between 5 and 20 cm (EB-Exp.) and 5 and 15 cm (VE-Exp.). In the EB-Experiment we attributed this relatively thin EDZ/EdZ to the appearance of a ‘high velocity body’ between 25 cm – 70 cm behind the tunnel wall, which was detected with several methods at the ENE wall of the EB niche.

Figure xx: Seismic shot section from refraction measurements in the EB niche and from the VE test section (inlay, green box).



As an example in Figure 35 the P-wave velocity distribution which was derived from interval velocity measurements in the EB-Experiment in June 2001 in sub-horizontal boreholes BEB-B09 and BEB-B19 are plotted. P-wave velocities between 10 and 100 cm are higher than for greater borehole depths. When we exclude a clear lithological change then this is rather unusual according to our experiences. As mentioned before we attributed this to the existence of a ‘high velocity body’ and/or to local stress redistribution.

Less pronounced we see a similar P-wave velocity distribution in some VE borehole data. In Figure 35 also P-wave velocities from borehole BE-112 with sensor orientations of 45° and 315° are plotted. In this cases the higher velocities ranges between 15 and 50 cm. Furthermore, in all graphs P-wave velocity variations can be observed caused most probably by small scale inhomogeneities.

180020002200240026002800300032003400

180020002200240026002800300032003400

Vp [m

/s]

0.0 0.5 1.0 1.5 2.0 2.5 3.0borehole depth [m]

channel 1 datacircles crosses BVE-112-045 BEB-B09-000triangles diamondsBVE-112-315 BEB-B19-000

Indications for a rock mass with higher velocities between 25 cm and 70 cm can also bee seen very clear in the cross hole data in Figure 32 (lower left sub-plot), where travel times in this depth range are lower.

5 OVERALL CONCLUSIONS

Three high resolution seismic methods were applied in order to detect and to characterise the EDZ/EdZ around the test section in the Ventilation-Experiment. Emphasise was put on a repeated characterisation of the EDZ/EdZ during the de- and resaturation phase with the help of a non-invasive seismic refraction method. Between May 2005 and November 2007 measurements were repeated ten times. In October 2006 three 1 m long boreholes were drilled near the seismic refraction array. In and between these boreholes interval velocity and cross hole measurements were performed in October 2006 and July 2007.

Figure 35: P-wave velocity distribution derived from interval velocity measurements (channel 1 data) in the EB-Experiment (BEB-B09-0° and BEB-B19-0°, crosses and diamonds) and in the VE-Experiment (BVE-112, 45° and 315°, circles and triangles).



At the beginning of the experiment the extent of the EDZ/EdZ was determined with the refraction method to be between 5 and 20 cm. Until October 2005 only a few seismic refraction data could be used due to the increasing wave attenuation. The assessed extent of the EDZ/EdZ stayed nearly constant. With ongoing time the wave attenuation became stronger. This effect can be attributed to a loosening of the rock within the first few centimetres of the tunnel wall. No extent of the EDZ/EdZ could be determined.

Only data from the last refraction measurement, during the resaturation phase in July and November 2007, show a slight increase in signal quality which can be explained with a regressive wave attenuation and consequently with a consolidation of the upper centimetres of the tunnel wall. But data are not good enough for a quantitative EDZ/EdZ extent estimation.

Results from the borehole based methods (interval velocity and cross hole measurements) are pointing to an extent of the EDZ/EdZ between 10 and 25 cm what is in good accordance with results from the seismic refraction measurements.

This gives the range of a possible variation of the extent of the EDZ/EdZ at different spots along the profiles or the boreholes and gives at the same time a measure for the uncertainty of the extent estimation.

All results point to a pronounced seismic anisotropy of the Opalinus Clay which is caused mainly by the bedding.

The seismic parameters, mainly P-wave velocities, derived with the three methods, are partly different because the wave propagation paths were different, what is an important factor considering the anisotropic properties of the Opalinus Clay. Furthermore, local small scale inhomogeneities can be a reason.

The interval velocity methods gave hints for the existence of cracks in the ranges between 30 – 50 cm and 65 – 80 cm from the tunnel wall what partly could be confirmed with the borehole camera analyses.

Remarkable is that results from all three methods show similarities with results found during a geophysical investigation of the EB-Niche in 2001 [2].



6 REFERENCES

[1] Mayor, J. C., García-Sinerez, J. L., Velasco, M., Gómez-Hernández, J., Lloret, A., Matray, J. M., Coste, F., Giraud, A., Rothfuchs, T., Marschall, P., Roesli, U. & Mayer, G. (2005a): Ventilation experiment in Opalinus Clay for the disposal of radioactive waste in underground repositories. – Publ. téc. 05-2005, Enresa, Madrid (also: Rep. Swiss Geol. Surv. 1).

[2] NF-PRO Integrated project, Annex I – Description of work, 17 November 2004. EC contract No. FI6W-CT-2003-02389.

[3] Schuster, K. and Alheid, H.-J. (2002): Engineered Barrier (EB) Experiment and Geophysical Characterisation of the Excavation Disturbed Zone (ED-C) Experiment: Seismic Investigation of the EDZ in the EB niche. Mont Terri Technical Report (TR 2002-03).

[4] European Commission CLUSTER Conference and Workshop, 2003, Luxembourg. (2003 pre-print) Impact of the excavation Disturbed (EdZ) or Damaged Zone (EDZ) on the performance of radioactive waste geological repositories. C. Davis & F. Bernier (Ed.). Luxembourg, to be published in the EUR series.

[5] ReflexW (2007): Program for the processing of seismic, acoustic or electromagnetic reflection, refraction and transmission data, Karl-Josef Sandmeier, Karlsruhe, Germany.

[6] Vidale, J. E (1988): Finite-difference calculation of travel times, Bull. Seism. Soc. Am., 78 No. 6: 2062-2076.

[7] Schuster, K. (2002): Seismic in situ Methods for the Characterisation of Excavation Damaged Zones – Final Report, Projektträger des BMBF und BMWi für Wassertechnologie und Entsorgung, Contract-No. 02E9098, 155 p.

[8] Mayor, J. C., García-Sinerez, J. L., Alonso, E. E., Alheid, H.-J. & Blümling, P. (2005b): Engineered barrier emplacement experiment in Opalinus Clay for the disposal of radioactive waste in underground repositories. – Publ. téc. 05-2005, Enresa, Madrid (also: Rep. Swiss Geol. Surv. 1).

[9] Popp, T. and Salzer, K. (2007): HE-D Experiment: Influence of bedding planes (IfG) – Final report. Mont Terri Technical Report (TR 2007-04).

Documents

Mont Terri Project · ANDRA BGR CRIEPI ENRESA GRS HSK IRSN JAEA NAGRA OBAYASHI SCK•CEN SWISSTOPO Mont Terri Project TECHNICAL REPORT 2007-06 December 2007 Ventilation Test (VE)