Investigation Ahead of the Tunnel Face by Use of a Measurement-While-Drilling System at ...

76 Pages·2010·3.3 MB·English

by  Valli Jouni

Working Report 2010-05
Investigation Ahead of the Tunnel Face by
Use of a Measurement-While-Drilling System
at Olkiluoto, Finland
Jouni Valli
January 2010
POSIVA OY
Olkiluoto
FI-27160 EURAJOKI, FINLAND
Tel [phone]
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Working Report 2010-05
Investigation Ahead of the Tunnel Face by
Use of a Measurement-While-Drilling System
at Olkiluoto, Finland
Jouni Valli
Posiva Oy
January 2010
Base maps: ©National Land Survey, permission 41/MML/10
Working Reports contain information on work in progress
or pending completion.
The conclusions and viewpoints presented in the report
are those of author(s) and do not necessarily
coincide with those of Posiva.
Investigation Ahead of the Tunnel Face by Use of a Measurement-While-
Drilling System at Olkiluoto, Finland
ABSTRACT
This study focuses on the Measurement-While-Drilling (MWD) -system and its uses
within the scope of the ONKALO-project in Olkiluoto.
The MWD-system is based on monitoring while drilling wherein nine parameters are
logged at predetermined measurement intervals. This thesis investigated two inferred
parameters produced by a program developed by Atlas Copco AB; hardness and
fracturing. Due to the numerical nature of the data correlation to geological conditions
was attempted through the use of rock mechanical measurements. The following four
rock mechanical tests were used: the Schmidt-hammer, Uniaxial Compressive Strength,
Point Load Strength and Indirect Tensile Strength (Brazilian test).
MWD-data did not exhibit satisfactory correlations, neither with the Schmidt-hammer
test results, the uniaxial compressive strength test results nor with the point load results.
A moderate correlation was apparent with indirect tensile strength test results. Visual
observations confirmed the results: MWD can detect pegmatites from gneisses in
Olkiluoto.
The limits of the MWD-system were determined to be significant in Olkiluoto as the
bedrock of Olkiluoto is heterogeneous both in mineralogy as well as with regards to its
rock mechanical properties. The MWD-system has been proven to function under
geologically simple/homogeneous conditions where the rock properties of different
lithologies are clearly different. Drilling Rate Index tests are possibly the most reliable
method of establishing a correlation between MWD data and rock properties.
Further research should focus on the use of the MWD-system in a geologically simple
environment with a logging interval that is as frequent as possible. In addition, Drilling
Rate Index tests should be performed for each rock type and, when possible, samples
should be obtained from as close as possible to MWD-holes.
Keywords: measurement-while-drilling, drillhole, borehole, hardness, Schmidt,
uniaxial, tensile, strength.
Porauksenaikaisen mittausjärjestelmän käyttö tunnelin perästä tehtävässä
kallioperän tunnustelussa, ONKALO, Olkiluoto
TIIVISTELMÄ
Tässä tutkielmassa käsitellään Measurement-While-Drilling (MWD) -järjestelmää ja
sen soveltuvuutta Olkiluodossa ONKALO-projektin puitteisiin.
MWD-järjestelmä perustuu porauksen aikaiseen seurantaan jossa tallennetaan yhdeksän
parametria määrätyin tallennusvälein. Tutkielmassa tutkittiin Atlas Copcon kehittämän
ohjelman tuottamia laskennallisia parametreja; lujuus ja rakoilu. Datan numeerisesta
luonteesta johtuen korrelointi geologisiin olosuhteisiin pyrittiin tekemään kallio-
mekaanisten mittausten avulla. Käytettyjä kalliomekaanisia tutkimusmenetelmiä oli
neljä: Schmidt-vasara, yksiaksiaalinen puristusmurtolujuus, pistekuormitus ja epäsuora
vetolujuus (brazilian test).
MWD-data ei korreloinut Schmidt-vasara -tulosten, yksiaksiaalisen puristusmurto-
lujuuden eikä pistekuormituslujuuden kanssa riittävän hyvin. Kohtalainen korrelaatio oli
havaittavaissa epäsuoran vetolujuuden kanssa. Visuaaliset havainnot vahvistivat tulok-
set: MWD kykenee Olkiluodon olosuhteissa havaitsemaan pegmaatiset alueet gneis-
seistä.
MWD-järjestelmän rajoitteet todettiin suuriksi sillä Olkiluodon kallioperä on sekä
mineralogiselta koostumukseltaan että kalliomekaanisilta ominaisuuksiltaan hetero-
geeninen. MWD-järjestelmä on osoittautunut toimivaksi geologisesti yksinkertaisissa/
homogeenisissa olosuhteissa missä eri kivilajien ominaisuudet ovat selvästi erilaisia.
Porattavuusmääritelmien tekeminen tarjoaa todennäköisesti luotettavimman keinon
tarkistaa korrelaatio MWD-järjestelmän ja kiven ominaisuuksien välillä.
Jatkotutkimuksia varten suositellaan MWD-järjestelmän käyttöä mahdollisimman
tiheällä tallennusvälillä geologisesti yksinkertaisessa ympäristössä. Lisäksi porattavuus-
määritykset pitäisi tehdä jokaiselle kivilajille ja, mikäli mahdollista, näytteet pitäisi
saada mahdollisimman läheltä toteutuneita MWD-reikiä.
Avainsanat: measurement-while-drilling, drillhole, borehole, hardness, Schmidt,
uniaxial, tensile, strength.
1

TABLE OF CONTENTS
ABSTRACT
TIIVISTELMÄ

1 INTRODUCTION ................................................................................................... 3
2 POSIVA SITE DESCRIPTION ............................................................................... 5
2.1 Posiva Oy and the ONKALO-project ............................................................... 5
2.2 Regional Geology of Olkiluoto and the surrounding area ................................ 6
2.3 Geology of the ONKALO-site .......................................................................... 7
2.4 ONKALO general mineralogy and rock properties ........................................ 12
3 MATERIAL AND METHODS................................................................................ 21
3.1 Fundamentals of bedrock drilling .................................................................. 21
3.1.1 Drilling Procedure .................................................................................. 21
3.1.2 Drilling Equipment ................................................................................. 22
3.2 Measurement-while-drilling ........................................................................... 23
3.2.1 MWD background .................................................................................. 23
3.2.2 MWD benefits and restrictions ............................................................... 24
3.2.3 MWD Parameters logged by AC Boomer E3-C30 .................................. 25
3.2.4 Atlas Copco MWD interpretation ............................................................ 26
3.3 Rock mechanical testing methods for rock strength ...................................... 26
3.3.1 Schmidt Hammer: theory and application .............................................. 26
3.3.2 Point-Load Strength: theory and application .......................................... 29
3.3.3 Indirect Brazilian Tensile Strength testing: theory and application.......... 31
3.3.4 Uniaxial Compressive Strength testing: theory and application .............. 32
3.4 Programs used data interpretation/management .......................................... 32
3.4.1 Surpac ................................................................................................... 32
3.4.2 Realworks Survey .................................................................................. 33
3.4.3 Tunnel Manager .................................................................................... 33
3.4.4 Microsoft Access/Microsoft Excel ........................................................... 34
4 RESULTS ............................................................................................................ 35
4.1 Schmidt test results ...................................................................................... 35
4.2 Pointload test results .................................................................................... 44
4.3 Indirect Brazilian Tensile Strength ................................................................ 46
4.4 Uniaxial compressive strength testing ........................................................... 47
4.5 Measurement-while-drilling ........................................................................... 49
4.6 3-D Digital Terrain Model (DTM) ................................................................... 50
5 DISCUSSION & CONCLUSIONS ........................................................................ 51
2

5.1 Schmidt Hammer conclusions ...................................................................... 51
5.2 Point-Load Test conclusions ......................................................................... 54
5.3 Indirect Brazilian Tensile Strength test conclusions ...................................... 54
5.4 Uniaxial Compressive Strength test conclusions ........................................... 55
5.5 MWD data conclusions ................................................................................. 55
REFERENCES ........................................................................................................... 59
APPENDICES............................................................................................................. 63
Appendix 1 .............................................................................................................. 63
Appendix 2 .............................................................................................................. 65
3

1 INTRODUCTION
Measurement-while-drilling (MWD) is a technique that allows for rock mass
characterisation during drilling with the aid of drill performance parameters. The
technique itself is old -Schlumberger first introduced downhole electrical logging to the
oil industry in 1911 which has since been extensively developed with the addition of
other features and in is in frequent use throughout the oil industry at present day (Segui
and Higgins 2002). Since the 1970's the technology has been extended to the mining
industry (Segui and Higgins 2002) and has now been tested as a rock mechanical
application in this study. Primarily this method is not aimed at rendering visual
geological interpretations obsolete but to increase the efficiency of underground (in this
particular case, tunnel) construction, as characterisation of rock strength ahead of
quarrying allows for modification of blasting plans as well as quarrying schedules. The
technique has been successfully used in distinguishing rock from fluid (in the oil
industry) as well as waste rock from ore (in the mining industry). All of the calculated
parameters developed from base parameters are fundamentally dependent on
penetration rate as it has been shown there are strong correlations between penetration
rate and rock strength.
Prior studies in this field have involved a number of different techniques for the
interpretation of raw drilling data; the focus of this study is on the use of an existing
method, developed by Atlas Copco. The parameter used throughout this study is
hardness which is a calculated result of an algorithm run on raw drilling data.
The objective of this study is to identify the uses of the MWD-system in the geological
circumstances that exist in Olkiluoto, Finland, and more specifically in the ONKALO
tunnel, where stress-strain situations are very different to those nearer the surface. This
encompasses correlation of MWD-hardness to measured rock strength and identification
of weaker structures within the bedrock ahead of the tunnel face as well as a possible
result of reduced blast fragmentation through optimisation of blasting.
4
5

2 POSIVA SITE DESCRIPTION
2.1 Posiva Oy and the ONKALO-project
With four nuclear power plants in operation in Finland and a fifth under construction
nuclear waste disposal requirements had to be fulfilled in accordance with the Finnish
Nuclear Energy Act which states that all nuclear waste produced in Finland must be
treated, stored and disposed of within Finnish borders and that no nuclear waste from
other countries can be imported into Finland (Posiva Oy 2008a). This responsibility lies
with the power companies operating the reactors in question and they must dispose of
their own waste accordingly as well as decommission any reactors used safely once
their usable lifespan has been exhausted.
In this particular case, Teollisuuden Voima Oyj and Fortum Power and Heat Oy
established a joint venture company, Posiva Oy, in 1995 to ensure the safe disposal of
all waste generated from their power plants. Posiva Oy is responsible for all of the
research related to the final disposal as well as design and implementation of disposal
logistics.
The final disposal site (in Olkiluoto, Finland) for spent nuclear fuel produced by TVO
Oyj and Fortum Power and Heat Oy was selected in 1999 by Posiva and therefore
proposed as the site for the repository. This proposal was then ratified in 2001 by the
Parliament and after preliminary site characterization research was completed,
construction of the underground rock characterization facility ONKALO began in 2004.
ONKALO consists of one access tunnel and three shafts of which two are ventilation
shafts and one is a personnel shaft. ONKALO will extend to the final disposal depth of -
420 m and is vital for the application for the construction license of the actual repository
as it provides a wealth of research data and will naturally function as the primary access
tunnel to the repository. The planned layout is displayed in figure 1. The current
schedule has final disposal beginning in 2020 with the repository being sealed in the
22nd century (Posiva Oy 2008a).
6

Figure 1. ONKALO underground rock characterisation facility layout as of 2009.

Posiva's final disposal plans are based on the KBS-3 concept (originally developed by
Swedish Nuclear Fuel and Waste Management Co) which makes use of a multiple-
barrier principle. These barriers include a final disposal canister, a bentonite barrier and
the bedrock itself in order to minimise any risk to the isolation of the nuclear waste
(Posiva Oy 2008a). Development of these release barriers continues alongside research
involving several branches of science to produce 3-dimensional models such as a
geological model, a hydrogeological and hydrogeochemical model as well as a rock
mechanical model. These are then to be integrated to produce a comprehensive rock
model for the final disposal area.

2.2 Regional Geology of Olkiluoto and the surrounding area
Located in a bedrock area that covers approximately 800 million years of Precambrian
geological history the island of Olkiluoto is approximately 10 km2 in size. Protoliths of
the migmatised high-grade metamorphic mica gneisses found at Olkiluoto were mainly
supracrustal, metasedimentary and metavolcanic rocks deformed and metamorphosed
during the Palaeoproterozoic Svecofennian orogeny ca. 1900-1800 Ma. Plutonic rocks
such as trondhjemites, tonalites, granodiorites, coarse-grained granites and pegmatites
intrude the supracrustal rocks (Paulamäki 2009).