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Report 2008:P3 ISSN 1653-5006
Swedish Blasting Research CentreMejerivägen 1, SE-117 43
Stockholm
Luleå University of TechnologySE-971 87 Luleå www.ltu.se
Application of time domain reflectometry (TDR) for block and
sublevel caving mines – State-of-the-art and preliminary laboratory
shear tests
Användning av tidsdomän reflektrometri (TDR) för block-och
skivrasgruvor – dagsläget i industrin och en första serie
labbskjuvförsök
Matthias Wimmer, SwebrecFinn Ouchterlony, Swebrec
Universitetstryckeriet, L
uleå
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Swebrec Report 2008:P3
Application of time domain reflectometry (TDR) for block and
sublevel caving mines - State-of-the-art and preliminary laboratory
shear tests
Användning av tidsdomän reflektrometri (TDR) för block- och
skivrasgruvor - dagsläget i industrin och en första serie
labbskjuvförsök
Matthias Wimmer, Swebrec
Finn Ouchterlony, Swebrec
Luleå April 2008, revised May 2, 2008
Swebrec - Swedish Blasting Research Centre
Luleå University of Technology
Department of Civil and Environmental Engineering • Division of
Rock Engineering
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Application of TDR for block and sublevel caving mines Swebrec
Report 2008:P3
SUMMARY
The objective of the present report is to summarize the
state-of-the-art of the application of time
domain reflectometry (TDR) with regard to its application to
block and sublevel caving mines.
A second objective is to report on preliminary laboratory shear
tests in which a grouted cable was
exposed to a controlled shear movement in a plane inclined
relative to the cable.
TDR is an essential part of successful cave management for block
caving mines. It is used to verify
cave initiation, the subsequent progress of the caving zone and
the effect of caving on rock mass
fracturing. This enables operators to adjust production to the
caving rate and allows remedial action to
encourage caving to be implemented if stagnant or delayed areas
exist within the cave. Continuous
TDR monitoring also supports the identification of caving
mechanisms such as gravity, stress, or
structure controlled caving. In contrast, monitoring initiation
and caving by using TDR in sublevel
caving mines is limited to few applications.
The TDR tests are part of a test program named “full-scale
in-situ burden instrumentation test”
(FIBIT). The tests focus on the verification of the blast
function in the upper part of the ring and
comprise the drilling of boreholes from the longitudinal drifts
in the footwall. These boreholes pass
through the interfaces of the intact pillar and the succeeding
blast rings.
In the TDR measurements of the FIBIT project, coaxial cables
will be grouted into several of these
boreholes and long-term monitored. This monitoring determines
the actual burden and verifies that the
planned breakage was complete and if overbreak occurred. In
addition, the TDR system could be
useful in monitoring displacements and thus blast related damage
behind the actual blasted ring in
order to verify the initial situation as well as functionality
of charge columns in the next pre-charged
rings. The laboratory tests focus on this and the following
factors:
Correlation between TDR reflection magnitude and shear
displacement,
Effect of different shear angles and failure modes,
Influence of cable length (attenuation and resolution),
Influence of upstream cable deformations (different sizes and
positions).
As an extension of the present study, field tests preceding the
FIBIT tests are planned in the Kiruna
mine to verify the laboratory findings. Another purpose of these
tests is to see whether the blast
induced dynamic failure of a coaxial cable could be
distinguished from a geologically induced one.
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Application of TDR for block and sublevel caving mines Swebrec
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SAMMANFATTNING
Syftet med denna rapport är först att ge dagsöverblick av hur
tidsdomän reflektrometri (TDR) används
i block- och skivrasgruvor. Det andra syftet är att rapportera
en första serie med laboratorieförsök där
en ingjuten koaxialkabel utsatts för styrd skjuvrörelse i ett
plan snett kabeln.
TDR utgör en viktig metod för att kontrollera rasets utbredning
i en blockrasgruva. Den används för
att verifiera att raset börjar, hur raset utvecklas liksom hur
raset påverkar bergmassans uppsprickning.
Detta gör det möjligt för gruvan att anpassa produktionen till
rasutbredningshastigheten och att
tillgripa åtgärder som skyndar på raset om man träffar på
områden där raset stagnerat eller dess
hastighet avtagit En kontinuerlig TDR-mätning kan också hjälpa
till att identifiera rasmekanismen som
varande främst tyngdkrafts-, spännings- eller strukturdriven.
Däremot har TDR bara använts i ett fåtal
fall för att studera initieringen av raset och dess senare
utveckling i skivrasgruvor.
De laboratorieförsök med TDR som rapporteras utgör en del av ett
försöksprogram med namnet ”full-
scale in-situ burden instrumentation test” (FIBIT). De är
inriktade mot att verifiera rassalvans funktion
i den övre delen av skivraskransen och i dem ingår borrning av
mäthål genom den kvarstående
malmpelaren in i skivraskransar från en fältort i liggväggen
I TDR-mätningarna i FIBIT-försöken kommer koaxialkablar att
gjutas in i flera av borrhålen och
övervakas under en längre tid. Huvudintresset inriktas mot att
bestämma kransytans läge och att
bestämma om lossbrytningen blivit fullständig samt om någon
bakåtbrytning skett. Dessutom kan
TDR-mätningarna visa sig användbara för att detektera
förskjutningar och sprängskador bakom
skivras-kransarna. På så sätt kan de sprängtekniska
förutsättningarna för laddningarna i nästa
förvägsladdad skivraskrans bestämmas. De redovisade
laboratorieförsöken har inriktats mot frågor av
vikt för FIBIT-försöken enligt följande:
Sambandet mellan den reflekterade TDR-signalens amplitud och
skjuvrörelsens storlek
Inverkan av olika skjuvvinklar mot kabelriktningen vid skjuvning
med drag eller tryck
Kabellängdens inverkan på signaldämpning och upplösning
Inverkan av klämpunkter uppströms ett skjuvplan
Som en fortsättning innan FIBIT-försöken planeras försök i
Kiruna-gruvan där labbresultaten om
möjligt verifieras. Dessutom skall undersökas om ett
spränginducerat dynamiskt kabelbrott kan
särskiljas från ett mer statiskt, geologiskt inducerat
brott.
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Application of TDR for block and sublevel caving mines Swebrec
Report 2008:P3
Contents
1 INTRODUCTION
.....................................................................................................
1
2 MONITORING MOVEMENTS NEAR CAVING STOPES
........................................ 2
3 EXPERIMENTAL WORK
........................................................................................
5
3.1 Objectives
................................................................................................................................
5
3.2 Test procedure
.........................................................................................................................
6
3.3 Description of TDR system
.....................................................................................................
9
3.4 Discussion of results
..............................................................................................................
10
3.4.1 Characteristic waveform signatures
......................................................................................
10
3.4.2 Evaluation of reflection coefficients
.....................................................................................
11
3.4.3 Influence of distance on a single shear
reflection..................................................................
14
3.4.4 Effects of upstream cable deformations
................................................................................
15
4 CONCLUSIONS AND RECOMMENDATIONS
......................................................18
5 ACKNOWLEDGEMENTS
......................................................................................21
6 REFERENCES
.......................................................................................................22
7 APPENDICES
........................................................................................................26
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Application of TDR for block and sublevel caving mines Swebrec
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APPENDICES
Appendix 1. Drawings of steel pipes for shear tests at different
angles. ............................................... 26
Appendix 2. Documented data for all tests.
..........................................................................................
28
Appendix 3. Images of shear faces for all tests.
....................................................................................
32
FIGURES
Figure 1. 3D view of TDR cables located around DOZ (Deep Ore
Zone) block cave (Szwedzicki et al.,
2004).
..................................................................................................................................
3
Figure 2. Transverse section of SLC rings showing installation
of TDR cables (Krekula 2004). .......... 4
Figure 3. Conceptual test layout for the instrumentation of the
burden of blasted SLC rings (not to
scale).
..................................................................................................................................
5
Figure 4. Test set-up for laboratory shear tests at Complab,
LTU. .........................................................
7
Figure 5. Crimps in mm, cable type P3 750 JCA.
...................................................................................
8
Figure 6. Crimps in mm, cable type CA 519 J.
.......................................................................................
8
Figure 7. Distinction of different shear failure modes.
...........................................................................
8
Figure 8. Testing machine, sample III-C-30deg loaded, Complab,
LTU. ............................................... 9
Figure 9. Example of characteristic waveform signatures,
II-S-0deg. ..................................................
10
Figure 10. Reflection coefficient versus shear displacement, 40
m distance, without crimps upstream.
..........................................................................................................................................
12
Figure 11. Comparison of width-to-magnitude ratios.
..........................................................................
13
Figure 12. Reflection coefficient versus position, III-C-0deg.
..............................................................
14
Figure 13. Reflection coefficient versus position, III-C-45deg.
............................................................ 14
Figure 14. Reflection coefficient versus shear displacement,
I-S-45deg, without upstream crimp. ..... 15
Figure 15. Reflection coefficient “small” crimp (1) / no crimp,
40m distance. .................................... 17
Figure 16. Reflection coefficient “medium” crimp (1) / no crimp,
40m distance. ................................ 17
Figure 17. Reflection coefficient “large” crimp (1) / no crimp,
40m distance. ..................................... 17
Figure 18. Suggested, improved design of a shearing apparatus.
.......................................................... 20
TABLES
Table 1. Properties of used smooth and corrugated coaxial
cables. ........................................................
7
Table 2. Mixture for used mortar.
...........................................................................................................
7
Table 3. Level of noise for different tests.
.............................................................................................
11
Table 4. Influence of upstream crimps with respect to position.
........................................................... 16
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Application of TDR for block and sublevel caving mines Swebrec
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1 INTRODUCTION
The concept of time domain reflectometry (TDR) was initially
developed and used as a measurement
technique to locate and evaluate discontinuities in coaxial
transmission lines by observing reflected
waveforms (Moffitt, 1964). The concept was first extended to the
measurement of material properties
such as soil moisture in which coaxial cables have been embedded
(Topp et al., 1980). TDR has also
been applied to monitor progressive, localized rock mass
movements and failure (Wade & Conroy,
1980; Panek & Tesch, 1981; O`Connor & Dowding, 1984) as
well as soil deformations (Dowding &
Pierce, 1994; Dussud, 2002).
Rock mass movements deform coaxial cables grouted into
boreholes, which produces localized
deformations. This changes the cable capacitance which in turn
causes reflections of injected pulses,
whose waveform depends on the nature of the change. It has
always been of particular interest to
determine a quantitative measure of the magnitude and type of
the rock mass deformation, both
empirically and numerically (Su, 1987; Dowding et al., 1989;
Aimone-Martin & Francke, 1997;
Bordas, 1998).
Regarding the operating principles of TDR it can basically be
viewed as a remote and real-time
sensing electrical measurement technique in which a fast
rise-time step voltage pulse is emitted out to
be reflected by any kind of deformation along the coaxial cable.
By assuming a constant pulse
propagation velocity (vp), the distance to the detected
deformation is proportional to the elapsed time
between initiation of the voltage pulse and the arrival of the
returned pulse. The magnitude of the
reflection coefficient ρ defines the impedance change (severity
due to the deformation) as the ratio of
the reflected voltage Vr to the incident voltage Vi. The shape
of the reflection, i.e. the waveform
signature, defines the type of cable deformation.
An extended review on TDR technology and in particular its
application to geomechanics is provided
by O`Connor & Dowding (1999).
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2 MONITORING MOVEMENTS NEAR CAVING STOPES
To maintain a successful caving operation in terms of production
and safety understanding of rock
mass behavior under caving conditions is necessary. Hence
regular monitoring, which provides
information on cave initiation, propagation and caving rate is
essential for actual production
management. Furthermore this supports and allows correct
decision-making to avoid operational risks
that can alter the continuity of the production process.
Optimization of the current design makes the
mine cost-effective during the later stage of mine life.
Monitoring becomes even more vital today as
several operations mining deep low-grade but massive orebodies
are being opened, in which stresses
normally become greater and rock masses may be more competent
than in previous operations.
Four general types of measurement methods (Brown, 2003) are
commonly used to monitor the
initiation and development of caving, namely a) measurements in
open holes, b) cavity monitoring
systems, c) microseismic systems and d) time domain
reflectometry (TDR). In practice, most of these
methods are often used in combination and they complement one
another. Progress was made in
estimating the shape of the cave back by using gravity
measurements at El Teniente mine (Gaete et al.,
2007). The following review focuses on the application of
TDR.
TDR was widely used for monitoring cave progression and
concomitant phenomena among others in
DOZ (Rachmad & Sulaeman, 2002; Szwedzicki et al., 2004), El
Teniente (Rojas et al., 2000; De
Nicola Escobar & Fishwick, 2000), Henderson (Stewart et al.,
1984; Rech & Watson, 1994), Kiruna
(Henry & Dahnér-Lindqvist, 2000; Krekula, 2004), Northparkes
(La Rosa & Chen, 1997), Palabora
(Bartlett, 2008), Ridgeway (Trifu et al., 2002) and San Manuel
(Panek & Tesch, 1981) mines.
One of the earliest applications of TDR in monitoring rock mass
deformation in caving mines was
accomplished by Panek and Tesch (1981). Several experiments were
conducted in which coaxial
cables were installed both in boreholes drilled into the walls
and roofs as well as laid out on the floor
of a drift against the rib, covered by mortar. These cables were
used to detect the outward progress of
cracking around a separate mining block as it was undercut and
caved on the level below. Although
changes in TDR waveforms were documented, the correlation
between rock mass response and cable
deformation was limited to locate major rock fractures, which
developed as the caving progressed
(O`Connor & Wade, 1994). The location of visible fractures
observed in the grout allowed comparison
of the aperture and shear displacement with TDR reflections
received along the cable.
Following these first trials, TDR measurements were more widely
used to verify the cave initiation
process and to serve as a long-term data source on cave growth
for determination of the production
schedule. This was mainly done by periodically monitoring the
progress of breakage on singular
coaxial cables grouted into former exploration boreholes
(Stewart et al., 1984; Rech & Watson, 1994).
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Great efforts were made to advance the monitoring of cave growth
by using TDR as numerous TDR
cables (e.g. DOZ, Northparkes and Palabora mines) were installed
in a fan like manner from several
stations to cover a large area, see Figure 1. This allows,
besides the verification of cave initiation, an
accurate determination of the actual 3-D shape of the caving
zone, i.e. horizontal and vertical
propagation as well as the effects of caving on rock mass
fracturing (Szwedzicki et al., 2004).
Figure 1. 3D view of TDR cables located around DOZ (Deep Ore
Zone) block cave (Szwedzicki et al., 2004).
Adequate knowledge about the shape of the cave front is an
essential part of cave management and
enables one to adjust production in relevant areas to increase
or slow down caving (La Rosa & Chen,
1997). Thereby waste dilution at an early stage deriving either
from the sides of the orebody or the
surface caused by chimney caving can be mitigated. Furthermore,
if stagnant or delayed areas exist
within the cave, remedial actions such as boundary weakening or
extending the undercut can be
implemented to encourage caving. TDR by itself, even if combined
with production data, cannot
provide accurate enough information on the development of an air
gap, i.e. the distance between the
solid cave back and the loose caved rock. However, the actual
air gap might simply be monitored in
open holes with the “cable and plug method” (Julin, 1992) or
“geophone-type detector with whiskers”
(Chen 2000) or more advanced methods with cavity monitoring
systems (Stewart et al., 1984; De
Nicola Escobar & Fishwick Tapia, 2000).
Continuous and thus fully automatic TDR monitoring also aids
definition of caving mechanisms such
as gravity-, stress-, or structure controlled caving (La Rosa
& Chen, 1997).
Monitoring initiation and caving by using TDR with respect to
sublevel caving (SLC) mines is limited
to a few applications (Trifu et al., 2002; Henry &
Dahnér-Lindqvist, 2000).
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Application of TDR for block and sublevel caving mines Swebrec
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There was an investigation on the effect of blasting and mucking
on rock mass fracturing behind
blasted SLC rings at the Kiruna mine (Krekula, 2004). TDR cables
have been installed parallel with
the rings and measurements have been performed directly after
blasting and at different stages of
mucking the material, see Figure 2.
Figure 2. Transverse section of SLC rings showing installation
of TDR cables (Krekula 2004).
Possible displacements could be combined with the locally
observed joint planes by combining
magnitudes as well as positions of rock displacements at a
specific time. The promising results have
shown that the top and central part of the subsequent rings is
the part most affected by blast damage
and movements while mucking. Shear movements considerably
decreased in number and magnitude
with increased distance to the actual brow. It could also be
shown that the intersecting of several waste
lenses of quartz porphyry has caused major, detectable
movements. The position of displacements in
the subsequent rings coincides well with the assumed shape and
development of the Isolated
Movement Zone (Larsson, 1998). However, the extent of
back-breakage caused by blasting to the
subsequent ring could not be studied with this layout of the
cable installation.
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Application of TDR for block and sublevel caving mines Swebrec
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3 EXPERIMENTAL WORK
3.1 Objectives
The implementation of TDR is part of a test program named
“full-scale in-situ burden instrumentation
test” (FIBIT) as part of the doctoral thesis “Improved breakage
and flow in sublevel caving” which is
being carried out at the LKAB mine in Kiruna, Sweden.
The complete test program focuses on the following:
Verification of actual burden (TDR, part 1)
Study of deformations behind the blasted ring (TDR, part 2)
Measurement of the propagation of breakage inside the burden
(fast-sampling TDR)
Study of burden movement and compaction of caving masses
(different sensor systems)
All tests will be monitored by new and proven measuring methods
so that a relevant judgment of the
results can be made and a better conceptual flow model can be
built up.
The conceptual layout of the test program is outlined in Figure
3. The tests focus on the verification of
the blast function in the upper part of the ring and comprise
the drilling of boreholes from the
longitudinal drifts in the footwall. These boreholes pass
through the interfaces of the intact pillar and
the succeeding blast rings.
Figure 3. Conceptual test layout for the instrumentation of the
burden of blasted SLC rings (not to scale).
Concerning TDR measurements as part of this project, coaxial
cables will be grouted into several of
these boreholes and long-term monitored. The main interest lies
in determining the actual burden and
verifying if the planned breakage has been completed and if
back-breakage has occurred. This process
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Application of TDR for block and sublevel caving mines Swebrec
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of blasting in a confined situation is entirely inaccessible to
direct observation. In addition, the TDR
system is useful in monitoring deformations and thus
blast-related damage behind the actual blasted
ring to verify the initial situation as well as the
functionality of charge columns in the next pre-charged
rings.
The laboratory tests focus on this and the following
relationships and factors are:
Correlation between TDR reflection magnitude and shear
displacement,
Effect of different shear angles and failure modes,
Influence of cable length (attenuation and resolution),
Influence of upstream deformations (different sizes and
positions).
Preliminary field tests are planned to verify the laboratory
findings as well as if the blast induced
dynamic failure of a coaxial cable (tensile failure) could be
distinguished from a geologically induced
one (shear failure).
3.2 Test procedure
The tests described in the following were carried out within 2
campaigns (I and II) at Complab at
Luleå University of Technology (LTU) and comprise totally 9
cable samples.
To study the influence of the shear angle on the TDR response,
steel pipes (ST 52.0) with a length of
1.5 m and cut at three different angles (0, 30 and 45 deg) at
half-length have been prepared. The
diameter of the pipes, Ø 127 × 6.3 mm, has been adjusted to the
standard dimension of boreholes that
are drilled in Kiruna. To enable the griping of the sample by
the servo-controlled dynamic testing
machine (Dartec, 600 kN capacity) precisely aligned steel plates
have been welded to the pipes. To
facilitate the mounting of the sample in the machine the pipe
halves have been dot welded. Drawings
of the pipes are shown in Appendix 1. Two coaxial cable types,
i.e. smooth Al- and corrugated Cu –
outer conductor (P3 750 JCA“S” and CA 519 J “C”), with different
mechanical and electrical
properties (see Table 1) were tested. They have almost the same
outer dimensions, Ø 21.08 and 20.10
mm respectively. Both cable types had an impedance of 75
ohm.
The cables have been centrically grouted into the pipe. To
increase the bond between cable and
concrete the plastic jacket of the cable has been roughened. The
concrete was mixed according to the
standard recipe used by KGS (LKAB`s contractor for concrete),
see Table 2. The curing time was at
least 28 days (DIN 1164).
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Application of TDR for block and sublevel caving mines Swebrec
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Table 1. Properties of used smooth and corrugated coaxial
cables.
Table 2. Mixture for used mortar.
Figure 4 shows the complete test assembly. The cable ends have
been prepared with suitable cable
preparation tools and then interconnected using suitable splice
connectors as well as reducers with low
return loss and high shielding efficiency. If the splice
connectors are well screwed together no
influence on the signal is detected.
Figure 4. Test set-up for laboratory shear tests at Complab,
LTU.
type OD type ID OD OD
- mm - mm mm mm mm N N/m pf/mOhm
s% nom Ohms/km
P3750JCA Al-Cu 4,24 Al 17,2 19 21,1 203 3002 3,86 50 ± 3 75 ± 2
87 2,55
CA519J Cu 3,90 Cu 16,70 17,20 20,10 145 1606 5,37 50 ± 3 75 ± 2
88 4,22
* CommScope; both cables ahave a micro-cellular foam
polyethylene dielectric and polyethylene jacket
Attenuation @68°F [dB/100m] versus frequency, see corresponding
data sheets at: www.commscope.com
conductor
inner outerjacket
imped
ance
min
ben
din
g
radiu
s
velo
city o
f
pro
pag
ation
capacitan
ce
vendor id
Electrical characteristicsm
ax D
C lo
op
resistance
@68°F
Properties of coaxial cablesMechanical
characteristics
max
pullin
g
tensio
n
weig
ht
Contents Specification / trade name mass- %
sand 0-8 mm 72,61
cement CEMII/A-LL 42.5R, Maxit 17,66
water - 8,48
silica sand Grade 920-D, Elkem Microsilika 1,18
plasticizer Glenium 51, BASF 0,07
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Application of TDR for block and sublevel caving mines Swebrec
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In order to study the effect of upstream deformations on signals
reflected downstream, crimps with
different sizes (campaign I and II) and positions (campaign I)
have been simulated. The crimps have
been made in a controlled and repeatable way and are shown in
Figure 5 and Figure 6. The depth of
the crimp is set by adjusting the separation of the squeezing
grips in a bench vice. The length of the
crimps is determined by the grip’s rounded width (half of a
steel rod with Ø = 40 mm).
Figure 5. Crimps in mm, cable type P3 750 JCA. Figure 6. Crimps
in mm, cable type CA 519 J.
In campaign I the attenuation as a function of cable lengths
(30, 40 and 50 m) was also studied. The
frequent changing of cables according to the set-up chosen
required the use of special low-resistance
cable connectors. In campaign II the effect of the actual
shearing mode was studied, see Figure 7. The
shearing was then associated with tension acting on the cable
whereas for campaign I the cable was
being compressed while sheared off. According to this the shear
angle could also be linked to the
actual shearing mode if the angle was defined between the centre
line of the pipe and the shear plane
at the sliding, with the sign depending on the direction of
movement (downward or upward).
Figure 7. Distinction of different shear failure modes.
The following three tests have been affected by hydraulic system
problems: I-S-0deg (at 6 mm; stop at
14 mm shearing), II-S-30deg (0 - 10 mm shearing deformation not
captured) and II-S-45deg (19 - 20
mm shearing deformation not captured, slipping of machine
grips). Here S refers to the cable type P3
750 JCA with smooth Al outer conductor and C to cable type CA
519 J with a corrugated Cu outer
conductor.
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Application of TDR for block and sublevel caving mines Swebrec
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Figure 8 shows the testing made at Complab, LTU. Appendix 2
contains the documentation of all tests
carried out.
Figure 8. Testing machine, sample III-C-30deg loaded, Complab,
LTU.
3.3 Description of TDR system
The Campbell Scientific`s TDR100 time domain reflectometry
system consisting of the TDR100
reflectometer, the SDMX50 coaxial multiplexer as well as the
PCTDR software were used in these
tests. The system had the following features (TDR100 – manual,
2001):
Pulse generator output: 250 mV
Output impedance: 50 ohms ± 1 %
Time response of combined pulse generator and sampling circuit:
300 ps
Pulse generator aberrations: ± 5 % within first 10 ns, ± 0.5 ns
after 10 ns
Pulse length: 10 ms
Timing resolution: 12.2 ps
Waveform sampling: 20 to 2048 waveform values over chosen
length
Distance (vp = 1)
o Range: 2 to 2100 m (i.e. 0 to 7 ms)
o Resolution: 1.8 mm (i.e. 6.1 ps)
Waveform averaging: 1 - 128
The reflectometer was highly sensitive to electrostatic
discharge since no transient protector is present.
The pulser should thus not be used without an appropriate
protector or solely in combination with the
multiplexer. In addition to this the pulser should be grounded
in a proper way.
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Application of TDR for block and sublevel caving mines Swebrec
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3.4 Discussion of results
3.4.1 Characteristic waveform signatures
Figure 9 shows typical composite characteristic waveform
signatures, in which the reflection
coefficient ρ is plotted versus the cable length. Totally 2048
waveform values have been sampled over
a length of 60 m and averaging 4 values at a given distance
before collecting values at the next
distance increment.
For a short distance in the beginning the influence of the
multiplexer as well as the patch cable (RG
59) was noticeable. Afterwards the signal was stable with ρ
around 0.2 and could be explained by the
mismatch of the TDR pulser with 50 ohm output impedance
connected to a 75 ohm cable which
created a nominal Reflection Coefficient Rc = (Z1 + Z2) / (Z1 +
Z2) = (75 - 50) / (75 + 50) = 0.2.
To identify amplitude minima within the signal it was necessary
to refer to the actual Rc (=offset),
which was averaged from the waveform values 500 to 1000.
Figure 9. Example of characteristic waveform signatures,
II-S-0deg.
As can be seen from the graph, the crimp of size 12.2 mm
upstream of the actual shearing, then results
in a relative ρ of 0.063. The subsequent actual shearing, in the
present example 22 mm, is clearly
visible at a distance of 40 m yielding a ρ of 0.138. Exceeding
the maximum shear displacement for the
chosen cable type and set-up typically results at first in a
short circuit (27 mm, present case). Further
displacement will then finally shear off the cable completely,
being observed as open circuit (35 mm).
The open end should normally look like a 100 % mismatch and it
is thus interesting to actually have
had a Rc > 1. A possible explanation might be that – because
of the relatively short length of the cable
– one might get a reflected signal from the mismatch which could
add back in phase with the original
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 10 20 30 40 50 60
Cable length, m
Ref
lect
ion
coef
fici
ent
ρ, -
II-S-0deg, crimp 12.2mm(1), def = 22mm
II-S-0deg, crimp 12.2mm(1), def = 27mm
II-S-0deg, crimp 12.2mm(1), def = 35mm
Multiplexer,
patch cable
Crimp 12.2 mm,
position (1)
def = 27 mm
Open circuit
Short circuit
75 ohm coaxial cable
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11
Application of TDR for block and sublevel caving mines Swebrec
Report 2008:P3
signal from the TDR as this could add around 10 % (20 reflected
back then 20 % reflected forward)
back into the equation thus giving an apparent Rc of 1.1.
Comparing the two different cable types, smooth Al- versus
corrugated Cu- outer conductor, and with
regard to the noise level, it could be concluded that there was
practically no difference between the
two types. Table 3 summarizes the calculated standard deviation
from the reflection coefficients for
both cable types. The noise level was typically around 1 mρ. The
evaluation thus considered reflection
coefficients > 5 mρ as being significantly above the noise
level.
Table 3. Level of noise for different tests.
test id ρ stdev def steps
I-S-0deg 0.1899 0.00078 7
I-S-30deg 0.1992 0.00070 5
I-S-45deg 0.1996 0.00109 9
II-S-0deg 0.1927 0.00122 27
II-S-30deg 0.1922 0.00117 30
II-S-45deg 0.1923 0.00110 64
II-C-0deg 0.1879 0.00100 22
II-C-30deg 0.1878 0.00102 24
II-C-45deg 0.1881 0.00090 40
Note:
Reflection coefficients averaged from waveform values
500-1000, 40 m cables, without crimps upstream.
3.4.2 Evaluation of reflection coefficients
Figure 10 plots the reflection coefficient magnitude ρ versus
the amount of shearing for all tests done.
It should be noted that test II-S-45deg should be excluded since
the conductor began to slide facilitated
by the adhesive film between the outer conductor and the plastic
jacket. This caused the cable only to
be stretched within the shear zone (after 45 mm shearing).
At first view a distinct separation between the curves is
obvious. The relationship between ρ and
shearing is certainly not linear. Especially in the beginning
the amplitude/shearing ratio is strongly
reduced and the TDR system was therefore less sensitive. This
supports recent findings by Singer et al.
(2006) and Krekula (2004), but is in contrast to those found
earlier by Dowding et al. (1989). It is
assumed that the sensitivity for a small shear displacement is
dependent on the cable type and
dimension and also on the response of the actual measurement
instrument.
The separation of curves can be related to the different shear
angles and thus also the larger effective
cross section of the cable being involved in the shear process.
In fact, the larger the shear angle the
smaller is the reflection coefficient at a given step of
deformation. This circumstance that the
reflection coefficient might be different when the cable is not
sheared perpendicular to its centre line
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Application of TDR for block and sublevel caving mines Swebrec
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has not been mentioned in previous studies (Dowding et al.,
1989; Pierce et al., 1994; Aimone-Martin
& Francke, 1997). However, oblique shearing is likely to
occur in field measurements.
Figure 10. Reflection coefficient versus shear displacement, 40
m distance, without crimps upstream. 1
It is important to stress that the deformation mode affected by
the shear zone width (i.e. gap between
pipe halves) could also have an essential effect on the TDR
signal. Localized shearing causes a
distinct, large increase in the reflection amplitude, whereas a
longitudinal extension of the cable
produces only a small but increasingly wide reflection with
little increase in amplitude (Su, 1987;
Dowding et al., 1988). It thus becomes essential to verify to
what extent this circumstance influenced
testing. One reason is that with shear angles 30 and 45° and
larger shear displacement it was not
possible to control the shear zone width. In addition to the
mode of grout fracturing (giving an ill-
defined shear plane) the rotation of the grips due to the
eccentric load (Appendix 1) caused a certain
separation of the pipe halves. The actual gap widths are
documented in Appendix 2 and images of the
shear planes for each test are shown in Appendix 3. This
separation effect is the most plausible
explanation that shears larger than the actual cable dimensions
could occur.
O`Connor & Dowding (1999) suggested that the “width to
magnitude” ratio of the reflection
coefficient could be used to verify the actual shearing
mechanism and failure of the cable since
bending of the cable through large shear zone should give
greater ratios that localized shear within
small gaps.
1 Annotation: I-S-0deg, problems at 6 mm; I-S-0deg &
II-S-45deg, cables not sheared off; see
Appendix 2.
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Application of TDR for block and sublevel caving mines Swebrec
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Figure 11 shows the width to magnitude ratios for the tests
carried out. There is no tendency towards
larger ratios with increasing shear angle. Nor is there any
observable increase in the ratios as the tests
near completion at larger shear displacements. It can be thus
concluded that the decreased sensitivity
(ρ/mm) for increased shear angles (Figure 10) is mainly
attributable to an effect by the angle itself.
The shape of the reflection coefficient curves does not contain
any information about the shear angle.
For instance, an increased shifting of the peak values with
progressing shearing which resulted in a
more systematic skewing of the curves is not noticeable, see the
comparison in Figure 12 and Figure
13. The only observation might be that the minima of the
reflection coefficient curves are not that
precisely positioned at the shearing plane for shear angles >
0 deg.
Figure 11. Comparison of width-to-magnitude ratios.2
2 Box and whisker plot showing mean (white bar), average
(red-white rhomb), 1
st and 3
rd quartiles
(gray boxes), whiskers (perpendicular line segments; as far as
the farthest point within 1.5 inter-
quartile ranges below the 1st or above the 3rd
quartile) and outliers.
0
2
4
6
8
10
12
14
I-S-0deg I-S-30deg I-S-45deg II-S-0deg II-S-30deg II-S-45deg
II-C-0deg II-C-30deg II-C-45deg
Test id
Wid
th-t
o-m
ag
nit
ud
e ra
tio
, m
/-
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Application of TDR for block and sublevel caving mines Swebrec
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Figure 12. Reflection coefficient versus position,
III-C-0deg.
Figure 13. Reflection coefficient versus position,
III-C-45deg.
Comparing the two different cables used with each other it can
be observed that the corrugated Cu-
cable is considerably more sensitive (mρ/mm) than the
smooth-walled Al-cable. On the other hand,
this also implies that the displacement limit before the cable
is finally sheared off is substantially
lowered. Both cable types show a minimum shearing displacement
limit before any movement can be
detected of around 5 mm.
Part of this test program was used to verify if differences in
the actual shearing mode are detectable
(see chapter 2.2). For this purpose the curves for the test I-S
(shear + compression) and II-S (shear +
tension) should be directly compared in Figure 10. Test I-S-0deg
had machinery problems at 6 mm
and for both tests I-S-0deg and II-S-45deg the cable could not
be sheared off completely (Appendix
2). Despite this, a preliminary interpretation is that the
curves for different shearing modes are quite
congruent with each other. Noticeable though is that a test in
which shear was associated with tension
could take remarkably larger shear displacements than a test
associated with compression (II-S-30deg
compared to I-S-30deg). In this respect, there are no observable
differences in the width-to-magnitude
ratio of the tests in campaign I (shear + compression) and in
campaign II (shear + tension), see Figure
11.
3.4.3 Influence of distance on a single shear reflection
Figure 14 shows the decrease in magnitude of the reflection
coefficient curves with increasing cable
length. For example, shearing the 21.1 mm smooth-walled aluminum
cable by 20 mm produces a
reflection coefficient of 36 mρ at a distance of 30 m, 31 mρ at
40 m and only 27 mρ at 50 m. Around
10 - 15 % attenuation in the reflection coefficient can thus be
anticipated per 10 m of cable length,
progressively increasing with larger shear displacements.
The decrease occurs rapidly and the minimum shear displacement
needed to detect a 1 mρ change in
the waveform magnitude increases with distance from the TDR
instrument. This reduction in
reflection magnitude results from an attenuation of the signal
along the cable as well as a signal
0.0
0.1
0.1
0.2
0.2
0.3
43.2 43.4 43.6 43.8 44.0 44.2 44.4 44.6-0.1
0.0
0.1
0.1
0.2
0.2
0.3
43.2 43.4 43.6 43.8 44.0 44.2 44.4 44.6
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Application of TDR for block and sublevel caving mines Swebrec
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dispersion, i.e. increase in rise time (Su, 1987). This
dispersion also has a major influence on the
resolution (Taflove, 1995), i.e. smallest distance between two
local cable deformities that can be
resolved before the discontinuities appear as one. Besides this,
the resolution is dictated by the
specified timing capabilities of the TDR instrument (see chapter
3.3). An important factor is also the
increasing width of the reflected signal amplitude with
progressive shear displacement on the cable.
This would in the end have a bearing on the possibility to
identify narrowly spaced deformities.
Figure 14. Reflection coefficient versus shear displacement,
I-S-45deg, without upstream crimp.
Within one and the same test at constant cable length, but with
different deformities the position of the
minima of the reflection coefficient always occurred within ± 3
cm. This resolution could probably be
increased if, unlike the present case, only a certain cable
length of interest (e.g. a few metres behind
the burden) is surveyed for any deformities with the available
waveform sampling rate (2048
waveform values over chosen length).
3.4.4 Effects of upstream cable deformations
Figure 15, Figure 16 and Figure 17 show the ratio of reflection
coefficient amplitudes with upstream
deformations of different sizes (ρsmall, ρmedium and ρlarge) to
amplitudes without any upstream crimps
(ρ0). All upstream crimps are located 2 m (position 1 in Figure
3) ahead of the actual deformation at 40
m cable length.
The effect of upstream crimps on signals reflected downstream is
minimal. A clear effect is not visible
until the upstream deformity is very large as for the crimp made
on the smooth-walled Al- cable with a
reduction in diameter of 15.2 mm, i.e. down 72 % from the actual
cable dimension. In this case the
cable is almost short-circuited, but a highly resistant bond is
still left between the inner conductor and
the dielectric, see Figure 5 and Figure 6. Concerning the
corrugated Cu-cable for which the upstream
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16
Application of TDR for block and sublevel caving mines Swebrec
Report 2008:P3
crimp is reducing the cable dimension by 62 %, only a slight
decrease in the reflection coefficient
amplitude is obtained.
The recent findings are consistent with those by Pierce et al.
(1994), which have also shown that even
multiple deformities upstream have a marginal effect. The
application of artificial crimps as “location
markers” to enhance the position accuracy of TDR measurements
for the identification of actual
deformities could thus be worth consideration. “Small” crimps
that cause a reflection coefficient
amplitude of about 20 - 25 mρ are easily discernible from noise
along the cable and do not affect the
signal reflected from downstream shear displacements. However,
the number of crimps should be
minimized to reduce the energy loss that occurs as the pulse
passes through these multiple deformities.
If the location of interest is relatively well identified, a
single crimp may be placed near this location
and its position accurately measured to reduce the errors
deriving from cable and borehole
misalignment.
The influence of upstream crimps with respect to the position
relative to the downstream shear
displacement was investigated in campaign I. Table 4 compares
the amplitudes of ρ for an upstream
crimp at position 1 to one at position 2, i.e. 2 m and 5 m in
front of the downstream shearing (see also
Figure 4).
Table 4. Influence of upstream crimps with respect to
position.
test id ρsmall (1) / ρsmall (2) ρmedium (1) / ρmedium (2)
average stdev data average stdev data
I-S-0deg, 30m 1.001 0.011 5 1.101 0.178 6
I-S-30deg, 30m 1.095 0.182 4 0.960 0.088 4
I-S-45deg, 30m 1.050 0.069 6 0.971 0.081 6
I-S-0deg, 40m 1.008 0.049 5 1.081 0.149 5
I-S-30deg, 40m 0.979 0.050 3 0.936 0.051 3
I-S-45deg, 40m 1.009 0.076 5 0.989 0.041 4
I-S-0deg, 50m 1.002 0.046 5 0.953 0.061 5
I-S-30deg, 50m 1.032 0.041 3 0.965 0.023 3
I-S-45deg, 50m 0.950 0.081 6 0.975 0.085 6
Note: Reflection coefficients from > 0.005 considered
It is therefore concluded that the exact position of the crimp
is irrelevant and does not affect the
amplitude of the later reflected signal. The minimum distance
relationship needed to resolve multiple
deformities is still valid though (see chapter 3.4.3).
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Application of TDR for block and sublevel caving mines Swebrec
Report 2008:P3
Figure 15. Reflection coefficient “small” crimp (1) / no crimp,
40m distance.
Figure 16. Reflection coefficient “medium” crimp (1) / no crimp,
40m distance.
Figure 17. Reflection coefficient “large” crimp (1) / no crimp,
40m distance.
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
I-S-0deg I-S-30deg I-S-45deg II-S-0deg II-S-30deg II-S-45deg
II-C-0deg II-C-30deg II-C-45deg
Tests: "small" crimp (1) / no crimp @ 40m
Ref
lect
ion
coef
fici
ent
ρsm
all/ρ
0, -
0.6
0.8
1.0
1.2
1.4
1.6
1.8
I-S-0deg I-S-30deg I-S-45deg II-S-0deg II-S-30deg II-S-45deg
II-C-0deg II-C-30deg II-C-45deg
Tests: "medium" crimp (1) / no crimp @ 40m
Ref
lect
ion
co
effi
cien
t ρ
med
ium
/ρ0,
-
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
II-S-0deg II-S-30deg II-S-45deg II-C-0deg II-C-30deg
II-C-45deg
Tests: "large" crimp (1) / no crimp @ 40m
Ref
lect
ion
co
effi
cien
t ρ
larg
e/ρ
0,
-
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Application of TDR for block and sublevel caving mines Swebrec
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4 CONCLUSIONS AND RECOMMENDATIONS
The following conclusions may be drawn:
There exists a non-linear relationship between the reflection
coefficient and the actual shear
displacement. Especially in the beginning the reflection
amplitude to shear displacement ratio
is quite small and the TDR system is therefore insensitive. It
may be assumed that the
sensitivity at small deformities is dependent on the cable
dimension and on the response of
the measurement device.
The position of the reflection coefficient versus shear
displacement curves depends on the
shear angles involved. The larger the shear angle, the smaller
the reflection coefficient is for a
given amount of displacement. This dependence of the reflection
coefficient on the shearing
angle has not been reported in previous studies. Oblique
shearing probably occurs more
frequently than perpendicular shearing in the field. A
connection line between the shearing-
off points on the curves for different shear angles may have
some practical interest but these
loci were not investigated here.
The actual set-up could not avoid the development of a gap in
the shear zone with
progressing shear displacement. The importance of this effect
has been verified by
determining the width of reflection coefficients to magnitude
ratio. It may be assumed that
localized shearing causes a narrow and large increase in the
reflection amplitude whereas
extension produces only a minor but increasingly wide reflection
with little increase in
amplitude. Analyzing the actual data does not show any tendency
to greater width to
magnitude ratios with increased shear angles. Nor is there an
increase in the ratio when it
comes to larger deformations. It can thus be concluded that the
decreased sensitivity (ρ/mm)
for increased shear angles is mainly attributable to an effect
of the angle itself.
The shape of the reflection coefficient curve does not reveal
any information about the shear
angle.
Different signal responses to the actual shear failure mode
(down- or upslip, i.e. shear
associated with compression or tension) may exist. If so, they
can – at least within this test
series – not be clearly identified.
Cable length has a significant and quantifiable effect on TDR
reflections. Around 10-15%
attenuation in the reflection coefficient can be expected per 10
m cable extension,
progressively increasing with larger shear displacement.
This signal dispersion due to longer cables also affects the
overall resolution since the width
of the reflected signal will also increase. Besides this, the
width increases with progressive
shear displacement on the cable, which finally will also
influence the possibility to resolve
narrowly spaced cable deformities.
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19
Application of TDR for block and sublevel caving mines Swebrec
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A clear effect of upstream crimps on downstream deformities is
not readily identifiable
unless the upstream deformation is very large. Thus artificial
crimps (in the range of 10 - 25
mρ) should be considered to enhance the position accuracy of TDR
measurements for the
identification of natural shearing displacements.
The exact position of an upstream crimp is irrelevant and does
not affect the amplitude of the
signal reflected downstream. However, deformities situated too
close to each other cannot be
individually resolved.
Comparing the two different cables used with each other one can
observe that the corrugated
Cu- cable is considerably more sensitive (mρ/mm) than the
smooth-walled Al- cable. On the
other hand this also means that the displacement range before
the cable is finally sheared off
is correspondingly smaller. Both cable types need a minimum
shear displacement before any
movement of around 5 mm can be detected. The level of noise is
around 1 mρ for both cable
types. In a single case (II-S-45deg, cable type P3 750 JCA), the
conductor began to slide
facilitated by the adhesive film between the outer conductor and
the plastic jacket. This
caused an unwanted stretching of the cable within the shear
zone.
The actual set-up has been effective in the sense that the
concrete embedded the coaxial
cables and prevented a slippage of the cable. No such slippage
could be detected. However,
the separation of the pipe halves and widening gap at the shear
zone, with a bending of the
cable through this zone could not be avoided.
The most important outcome of the present test program is that
the monitoring of the reflection
coefficient with progressive shear displacement (i.e. monitoring
time) contains information about the
shear angle of the actual rock movement. If this information is
combined with that from a borehole
imager a-priori to the cable installation a 3D model with
respect to the caving propagation or blast
damaging zone behind SLC rings could be constructed.
The correlation between different shear angles and TDR response
found in the present test campaigns
is definitely worth further study. A continuation of laboratory
tests should then focus on this and
eliminate all other possible interference effects. The cables
should then be mounted between two rigid
guide plates, see Figure 18. Steel rings fastened to the outside
of the cables on both sides would keep
the cable in position and avoid any lengthwise extension of the
cable. Easily interchangeable steel
plates with different angles drilled for the insertion of cables
would be prepared. In addition the effect
of shear failure associated both with tension and compression
could be simulated.
As an extension of the present study, preliminary field tests
are planned in the Kiruna mine in block
12, level 691, to verify the laboratory findings. Another
purpose of these field tests is to see whether
the blast-induced dynamic failure of a coaxial cable could be
distinguished from a geologically
induced failure.
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20
Application of TDR for block and sublevel caving mines Swebrec
Report 2008:P3
Figure 18. Suggested, improved design of a shearing
apparatus.
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Application of TDR for block and sublevel caving mines Swebrec
Report 2008:P3
5 ACKNOWLEDGEMENTS
Hjalmar Lundbohm Research Centre (HLRC) of Luleå University of
Technology, endowed by LKAB,
is thanked for the continuing support within the PhD project
“Improved breakage and flow in sublevel
caving”.
The present report also serves as project work for the course
“Block Caving Principles” at the
University of the Witwatersrand, South Africa. I thank HLRC for
financial support which enabled me
to attend this course.
I also thank colleagues at Complab, LTU for their invaluable
practical support as well as for
discussions concerning the actual test set-up and results.
CommScope Europe and Corning Cablecon are thanked for the
generous provision of coaxial cables
and connectors as well as tools. I also thank Richard Harris and
Johan Holmberg, both of CommScope
Europe, for most valuable discussions.
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North American Rock Mechanics Symposium (pp. 189-193). Toronto,
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7 APPENDICES
Appendix 1. Drawings of steel pipes for shear tests at different
angles.
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Appendix 2. Documented data for all tests.
Test I-S-0, date 15-16.11.2007
Shear angle 0 deg (+-90deg), cable P3 750 JCA
displ gap load remarks
mm mm kN -
0 - 0.24 - 2 - 11 - 4 - 4 - 6 - 1 6.4mm (30m) / 15.2mm (40+50m,
not used files) 8 - 4 new fixation in the machine
10 - 3 - 12 - 4 - 14 - 5 machinery problems, stop
Test I-S-30, date 04.12.2007
Shear angle 30 deg (-120deg), cable P3 750 JCA
displ gap load remarks
mm mm kN -
0 0 3.8 - 5 2.5 6 101kN max
10 3.2 7.4 - 15 3.6 14 - 20 3.8 12 - 25 3.8 16.4 short
circuit
Test I-S-45, date 22.11.2007
Shear angle 45 deg (-135deg), cable P3 750 JCA
displ gap load remarks
mm mm kN -
0 0 6 - 2 2.7 11 - 4 4.3 11.5 - 6 5.6-5.9 10.1 - 8 6.1-6.4 14.2
-
12 6.8-6.9 12.3 - 16 7.5-7.8 12.7 - 20 7.8-8 12.4 - 25 8.4 11.6
- 29 8.9-9.1 30 geometrical limits + cable break outside pipe
(excessive bending),
open circuit at that position Test II-S-0, date 11.01.2008
Shear angle 0 deg (+-90deg), cable P3 750 JCA
displ gap load remarks
mm mm kN -
0-4 - - - 5 4.2 - - 6 - - - 7 4.9 - - 8 - - - 9 4.9 - -
10-12 - - - 13 5-6 - -
14-15 - - - 16 - - = file 17 (overwritten) 17 5.5-6.6 - -
18-20 - - - 21 6-7 - -
22-25 - - -
26 7-8.5 - short circuit, open circuit (cut cable) at 35mm
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Test II-S-30, date 18.01.2008
Shear angle 30 deg (+60deg), P3 750 JCA
displ gap load remarks
mm mm kN -
11.2 4.2-5.3 - machinery problems 12.2-13.2 - - -
14.2 5-5.5 - - 15.2-16.2 - - -
17.2 5.1-6.1 - - 18.2-21.2 - - -
22.2 5.5-6.5 - - 23.2-25.2 - - -
26.2 - - slipping of plastic jacket 27.2-31.2 - - -
32.2 5.6-7 - - 33.2-38.2 - - -
39.2 - - unstable signal 40.2 - - - 41.2 6-7.3 - short circuit
43.2 - - short circuit 51.2 - - unstable signal, short-open
circuit
Test II-S-45, date 21.01.2008
Shear angle 45 deg (+45deg), cable P3 750 JCA
displ gap load remarks
mm mm kN -
0 2.5-7.5 - - 1-2 - - - 3 2-8 - -
4-6 - - - 7 3.5-9.8 - -
8-10 - - - 11 5.8-12.5 - -
12-15 - - - 16 6-12 - -
17-20 - - - 21 6-12 - -
22-25 - - - 26 6-12 - -
27-29 - - - 30 6-12 - -
31-35 - - - 36 6-12 - -
37-42 - - - 43 6-12 - -
44-49 - - - 50 - - file 50.3 (15.2mm) missing 51 - - - 52 - -
file 52-3 (15.2mm) missing
53-59 - - - 60 4-10 - - 63 4-10 - - 66 - - - 69 - - -
72 - - relative slide between outer Al-conductor and plastic
jacket; no cable cut (break),
no short circuit
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Test II-C-0, date 28.01.2008
Shear angle 0 deg (+-90deg), cable CA 519 J
displ gap load remarks
mm mm kN -
0 - - intact concrete 1 - - 37.8kN max
2-4 - -
5 1.5-2.5 - -
6-8 - - -
6-8 - - - 9 3-2 - - 10 - 11-12 -
11-13 - - - 14 2.5-3.5 - = file 15 (overwritten) 15 - - - 16
2.8-3.8 - -
17-20 - - - 21 4-5 - - 22 - - open circuit
Test II-C-30, date 31.01.2008
Shear angle 30 deg (+60deg), cable CA 519 J
displ gap load remarks
mm mm kN -
0 - - - 1 - 48.7 68.3kN max (welding point!) 2 - 19.6 - 3 - - -
4 - 20.5 - 5 3-3.8 - -
6-8 - - - 9 3.7-4.4 - -
10-12 - - - 13 4-5 - -
14-15 - - - 16 - 22 - 17 4.8-5.5 - -
18-20 - - - 21 5.2-5.8 - - 22 - - - 23 - - snap at 23.5mm 24
5.9-6.2 - open circuit
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Test II-C-45, date 01.02.2008
Shear angle 45 deg (+45deg), cable CA 519 J
displ gap load remarks
mm mm kN -
0 - - - 1 0.8 38.5 - 2 1.6-1.9 15.8 47.6kN max 3 - 25.9
remaining load: friction in the concrete 4 3.3-3.5 16 - 5 - 15.3 -
6 - 15 - 7 - - - 8 5.7-5.9 - - 9 - - file 9.1 (8.5mm),9.2 (10.5mm),
9.3 (12.5mm) missing
10 - - file 10.0 (0mm) missing 11-12 - - -
13 9.5-9.5 - - 14-16 - - -
17 12.5-12.9 - - 18 - - - 19 - - missing files (slipping of
machine) 20 - - missing files (slipping of machine)
21.4 14-15.5 - - 22-23 - - -
24 16.5-17.8 - - 25-28 - - -
29 21.5-23.5 - - 32 - - - 35 25.3-26.8 - - 38 - - -
41 - - cable only pulled in the gap
51 - - short circuit 103 - - open circuit
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Appendix 3. Images of shear faces for all tests.
I-S and II-S series denote tests on cable type P3 750 JCA, II-C
series on cable type CA 519 J
I-S-0deg
II-S-0deg
I-S-30deg
II-S-30deg
I-S-45deg
II-S-45deg
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III-C-0deg
III-C-30deg
III-C-45deg
-
Report 2007:1 ISSN 1653-5006
Swedish Blasting Research CentreMejerivägen 1, SE-117 43
Stockholm
Luleå University of TechnologySE-971 87 Luleå www.ltu.se
An experimental investigation of blastability
Experimentell bestämning av sprängbarhet
Matthias Wimmer, Swebrec
Universitetstryckeriet, L
uleå