Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS AND METHOD FOR TESTING INSTALLATION OF A REINFORCING
ANCHOR
INTRODUCTION
The invention relates to an apparatus and method for testing the structural
installation
integrity of a reinforcing anchor which is installed within a host body and
filled with a
grout material, just before or after inserting the anchor into the host body.
BACKGROUND TO THE INVENTION
For purposes of this specification and to facilitate a reading of the
document, all
references to "grout" and "grout material" should be interpreted to include
and extend to
cement, concrete, epoxy resin, mortar, plaster, putty and the like high-
strength
reinforcing substances used to secure an anchor in place within a hole in a
host body.
Similarly, all references to "anchor" should be interpreted to include and
extend to rock
bolts, roof bolts, tendons, cables and cable anchors, dowels (such as re-bar),
bars, pins,
rods and the like anchors that are grouted or otherwise secured in place
within a hole by
means of a reinforcing substance. The invention claimed herein is not limited
to the
mining industry and is also used in civil engineering applications.
Rock anchors are used in civil engineering and mining structures to counteract
uplift
forces acting on foundations and post-tension existing concrete structures or
rock
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strata. Rock anchors are generally made of high tensile steel, and they are
typically
anchored in sound rock by means of high strength cementitious grouting for
foundations, walls and roofs, and through holes drilled into or through a
structure for
post-tensioning applications. For most applications, rock anchors are
tensioned to a
force higher than what is necessary to resist the foundation uplift force.
When no
tensioning is applied to the rock anchors, they are called rock bolts. Both
rock anchors
and rock bolts are eventually grouted in place for their full length. Some of
the more
common uses for rock anchors and bolts are to provide tiebacks for bridges; to
increase
stability of walls, slopes and dams; to secure walls and roofs in mines and
tunnels; or to
secure structures against forces from wind or vibrating machinery. Various
apparatus
and methods exist to secure the anchor within its hole in the host body and to
grout-fill
the hole, all of which go beyond the scope of the present invention. The
anchor is
typically positioned such that its trailing end extends from the hole.
Large-scale, high-capacity, permanent rock anchors generally provide a fixed
anchor or
tendon bond length, a free tendon length, a stressable (and preferably re-
stressable)
anchor head, and corrosion protection. Obviously, in terms of their scale,
purposes,
rock engineering design and detailed design and installation, these large rock
anchors
can differ significantly from the rock bolts, cable bolts and rock socketed
piles used
widely in surface and underground construction and mining. However, these
elements
all have some features in common that allow data, understandings and elements
of
design approaches to be transferred from one application to another.
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In addition to providing resistance and stabilising forces, grouted post-
tensioned
anchors themselves must be able to resist the four principal modes of applied
tension-
induced failure, namely steel tendon tensile failure, grout¨tendon interface
failure, rock¨
grout interface failure, and shear or uplift failure within the surrounding
rock mass.
Actual capacities will depend on strength of the tendon, strength of the rock,
grout
strength, and quality of the installation.
In order to achieve these vital desired
reinforcing outcomes, it is of utmost importance to have an accurate, robust
and
affordable means to test and measure grout strength and integrity of the
anchor
installation after it is filled with grout, to ensure that each rock anchor is
securely
to grouted into its hole and that the grout (or other filling material) has
filled the entire hole,
homogeneously and to capacity.
W02015/128831 (Barnard, A J) provides one such prior art solution for testing
grout
around a rock anchor which is grouted into a drill hole. Barnard provides
inserting a first
and second conductor within a grouted drill hole, with the first conductor
being insulated
but having an exposed contact which is secured in spaced apart relationship to
the
second conductor within the body of grout material. The conductors extend to
outside
of the drill hole. After the hole is filled, direct electrical current (DC) is
applied through
the conductors and resistivity is measured between the first and second
conductors.
Barnard proposes an open circuit before grout-filling, with no current flowing
between
the first and second conductors prior to filling, because there is an air gap
between
them. After grout filling, a grout bridge is created between the first and
second
conductors that creates an electrical resistance between the conductors, which
can be
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measured, for example, by a common multi-meter, to confirm the presence of
grout at
the desired positions between the conductors.
There are a number of shortcomings associated with Barnard. Firstly, measuring
only
the resistivity of wet or moist grout is not an accurate reflection of
structural integrity,
since it does not take into account the capacitive and inductive reactance of
grout, and
results in unstable readings which cannot be repeated or verified. Capacitive
reactance
and inductive reactance are measures of the grout's opposition to alternating
current
(AC), and together with resistance, are collectively referred to as impedance.
Like
resistance, impedance is measured in ohms, but impedance reactance is more
complex
than resistance, because its value depends on the frequency (f) of the
electrical signal
passing through the grout as well. Both capacitive and inductive reactance are
dependent upon the frequency of an applied current.
Secondly, Barnard's system is limited in that a single conductor can only
measure
resistivity at one position between the two conductors. Multiple conductors
are required
at multiple installation positions along the length of the anchor to measure
resistivity at
multiple sensing positions throughout the length of the hole. It is not
possible to attach
more than one sensor to the same electrically conductive channel.
Thirdly, Barnard's open circuit installation is further limited in that it
cannot measure
integrity of the system before grout is injected so as to guarantee accuracy
of a
resistivity reading after grout is injected. Barnard's open circuit before
grout-filling
means that the system cannot detect broken wires or wires where the cores are
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accidentally exposed due to damage before or after installation. In other
words, if a
resistivity reading cannot be measured before grouting the installation,
Barnard cannot
advise whether such failure is the result of Barnard's open circuit design or
the result of
a broken conductor and/or sensor. Therefore, it is impossible to check the
integrity of
Barnard's system once it is installed and before grouting.
Measurement of the resistance of grout and the frequency domain analysis in
general is
not new, as is evident from 0N101343876, US2010315103, US5608323, GB2349224
and DE4243878. However, the prior art generally focusses on resistivity
measurements
and not impedance of the grout. Grout has resistive, capacitive and
inductive
properties, which depend on moisture content, and which are collectively
referred to as
impedance.
For applications in, for example, mines, a grout measuring system needs to be
robust,
.. simple and very inexpensive to be commercially viable, while simultaneously
not
compromising on reliability and accuracy in readings. It is an object of the
present
invention to provide an apparatus and method that will provide reliable,
repeatable and
accurate readings, and that will overcome, or at least minimise, the
disadvantages
associated with prior art solutions.
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SUMMARY OF THE INVENTION
For purposes of this invention, any reference to a resistor or resistors
should be
interpreted to include and extend to a capacitor or capacitors, which can be
used either
together with, or alternatively to, the resistor(s).
According to a first aspect of the invention there is provided an apparatus
for testing
structural installation integrity of a reinforcing anchor which is installed
within a host
body and filled with a grout material, the apparatus comprising ¨
a first and second conductor which are insertable into a drill hole within the
host
body, wherein the first and second conductors are connected to each other
before the
hole is filled with the grout material, to form a continuous conductive path;
and
either at least one resistor with a measurable resistance value or at least
one
capacitor with a measurable capacitance value arranged intermediate the first
and
second conductors so as to create a closed electrical circuit when current is
applied to
the conductors both before and after the hole is filled with grout material,
and wherein
the measurable resistance value or the measurable capacitance value changes to
a
different measurable impedance value when the resistor or the capacitor is
encased in
the grout material.
The apparatus is installed within the host body just before or after inserting
the anchor
into the host body.
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The apparatus may include multiple resistors arranged in series along the same
electrically conductive path so as to provide measurable impedance values at
different
positions within the drill hole both before and after the hole is filled with
grout material.
The resistors may be characterised therein that they each have a different
resistance
value such that a change in each resistance value is indicative of which
resistor is
encased within the grout material. Alternatively, the apparatus may include
multiple
capacitors arranged in series along the same electrically conductive path,
wherein each
capacitor has a different capacitance value such that a change in each
capacitance
value is indicative of which capacitor is encased within the grout material.
Yet further
alternatively, the apparatus may include a combination of resistors and
capacitors
arranged in series along the same electrically conductive path.
Both conductors may terminate at their free ends in exposed electrical
contacts which
are spaced apart from each other and which extend to a position outside of the
drill
hole.
According to one embodiment of the invention, each of the first and second
conductors
may comprise a continuous conducting core and a surrounding electrical
insulation
around the core. In another embodiment of the invention, the second conductor
may be
provided by an elongate body of the reinforcing anchor.
In one embodiment of the invention, the first and second conductors are
created by
looping a single elongate, continuous conductor with a flexible conducting
core so as to
create two substantially parallel and abutting conductor legs that both extend
for
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substantially the length of the drill hole, and with each conductor leg
terminating at its
free end in an exposed electrical contact. In this looped configuration, the
conductor is
inserted into the drill hole substantially parallel to, but spaced apart from,
the anchor
within the body of grout material.
In this looped embodiment, the resistors and/or capacitors are connected in
series to
and at various positions along the length of the first conductor leg. The
first conductor
leg may include at least one exposed core section where the insulation is
removed to
expose the conducting core, with a resistor or a capacitor being connected to
the first
conductor leg at the exposed core section such that it is bordered on either
side thereof
by a section of exposed conducting core. In a preferred form of the invention,
the first
conductor leg includes multiple exposed core sections in series for
accommodating
multiple resistors and/or capacitors such that each resistor and/or capacitor
in series is
bordered on either side thereof by a section of exposed conducting core.
In another embodiment of the invention, where the second conductor is provided
by the
reinforcing anchor, the first conductor comprises an elongate conductor that
extends for
substantially the length of the drill hole, with the first conductor
terminating at each of its
opposite free ends in an exposed electrical contact. In this configuration,
the first
conductor is inserted into the drill hole and connected to the anchor through
an
intermediate electrical connector, with the anchor terminating at its trailing
free end in an
exposed electrical contact, such that a continuous electrical flow path is
created
between the first conductor and the anchor.
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In this embodiment, the resistors and/or capacitors are connected in series to
and at
various positions along the length of the first conductor. The first conductor
may include
at least one exposed core section where the insulation is removed to expose
the
conducting core, with a resistor or capacitor being connected to the first
conductor at
the exposed core section such that it is bordered on either side thereof by a
section of
exposed conducting core. In a preferred form of the invention, the first
conductor
includes multiple exposed core sections in series for accommodating multiple
resistors
and/or capacitors such that each resistor and/or capacitor in series is
bordered on either
side thereof by a section of exposed conducting core.
According to a yet a further embodiment of the invention, the apparatus
includes at least
one electrically insulated hollow tube which is co-axially securable to a body
of the
anchor and which includes at least one conductors-receiving aperture extending
through a sidewall of the tube; and at least one electrically insulated
resistor-carrying
clip which engages the tube and which houses at least one resistor or
capacitor, the clip
including a conductors-exit hole which is aligned with the conductors-
receiving aperture
of the tube, the arrangement being such that the two conductors which extend
from
either side of the resistor pass through the conductors-exit hole of the clip
and the
conductors-receiving aperture into the hollow tube. The conductors may
terminate at
their free ends in exposed core contacts which extend to a position outside of
the tube.
The tube may be an elongate tube which includes a number of conductors-
receiving
apertures arranged along the length of the tube so as to accommodate and
cooperate
with an equal number of clips. Alternatively, the apparatus may provide a
number of
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spaced-apart collar-type tubes connected coaxially to the anchor, with each
tube
cooperating with a different clip.
In this embodiment of the invention, the two conductors each may include a
flexible
conducting core which is insulated by electrical insulation and terminating at
their free
ends in exposed contacts which extend to a position outside of the tube, while
at their
opposite ends the two conductors terminate in exposed core sections where the
insulation is removed. The resistor or capacitor may include two resistor /
capacitor
legs extending from opposite ends of the resistor or capacitor; and each of
the exposed
core sections of the conductors may be soldered to one of the two resistor /
capacitor
legs respectively, so as that the resistor or capacitor is bordered on either
side thereof
by a section of exposed conducting core. The resistor-carrying clip may be
configured
such that the resistor or capacitor, exposed core sections and resistor /
capacitor legs
are at least partially encased in grout material when the drill hole is
filled.
A number of resistors and/or capacitors may be arranged in series by
connecting a
number of resistor-carrying clips in series to the anchor through one or a
number of
tubes, and connecting a first conductor of one resistor or capacitor to a
second
conductor of a neighbouring resistor or capacitor, so as to create a closed
electrical
circuit when current is applied to the conductors both before and after the
hole is filled
with grout material.
In the absence of cement or grout within the drill hole, the impedance of the
closed
electrical circuit between the exposed core contacts is the sum of the
resistors and/or
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conductors in series, but after the drill hole is filled with grout material
and exposed core
sections are encased, the grout material creates a closed electrical circuit
parallel to
each of the resistors or capacitors.
.. The apparatus further may include a grout detector measuring device for
measuring
frequency parameters of an applied current between the conductors, including
impedance, capacitance and inductance - impedance.
According to a second aspect of the invention, there is provided a method for
testing
structural installation integrity of a reinforcing anchor which is installed
in a drill hole
within a host body, both before and after the drill hole is filled with grout
material, the
method comprising the steps of ¨
providing an apparatus as disclosed herein before;
testing for an open circuit and specific resistance of the resistors or
specific
capacitance of the capacitors through an applied current before the hole is
filled with
grout material to verify integrity of the apparatus and eliminate broken or
faulty
apparatus; and
measuring one or more frequency domain parameters of impedance,
capacitance and/or inductance of an applied alternating current (AC) after the
hole is
filled to determine grout properties and post-filling installation integrity.
The method may provide measuring capacitance of the grout material through an
applied alternating current (AC) or voltage after the hole is filled to ensure
that all
cavities within the drill hole are filled with grout material. Alternatively,
the method may
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provide measuring capacitance charging time until the capacitors are fully
charged
through an applied current or voltage across the core contacts.
The method may provide measuring impedance of the grout material by measuring
impedance of a parallel circuit created between a resistor and the grout
material
between the exposed core sections. This is done by applying a sinusoidal wave
form or
a wave form of known frequency, or a series of pulses, to the exposed core
sections
and measuring voltage drop across it. The impedance is then calculated.
The method may include the step of varying frequency, pulse width and voltages
of the
applied alternating current (AC) for best results with specific grouts. The
method
specifically may provide for varying frequency between 50Hz and 300kHz and
using a
pulse width of 5m5 to 20ms.
BRIEF DESCRIPTION OF THE DRAWINGS
Without limiting the scope thereof or wishing to be bound thereto the
invention will now
further be described and exemplified with reference to the accompanying
drawings and
non-limiting examples in which -
TABLE 1 is a table containing calculated impedance (Re) values for various
switch
(S) combinations;
FIGURE 1A is an electrical circuit diagram representation of grout / cement;
FIGURE 1B is a simplified electrical circuit diagram of Figure 1A;
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FIGURE 2A is a sectional side elevation of a testing apparatus installation
according to
a first embodiment of the invention;
FIGURE 2B is a plan view from above of the installation of Figure 2A;
FIGURE 2C is an enlarged view of an exposed core section of the first
embodiment,
illustrated as "C" in Figure 2A;
FIGURE 2D is a circuit diagram representing an exposed core section according
to the
first embodiment;
FIGURE 2E is the simplified circuit diagram of Figure 2D;
FIGURE 3A is a sectional side elevation of a testing apparatus installation
according to
a second embodiment of the invention;
FIGURE 3B is a plan view from above of the embodiment of Figure 3A;
FIGURE 3C is an enlarged view of an exposed core section of the second
embodiment, illustrated as "C" in Figure 3A;
FIGURE 3D is a circuit diagram representing an exposed core section according
to the
second embodiment;
FIGURE 4A is a perspective view from a first angle of rotation of an
electrically
insulated resistor-carrying clip and tube arrangement according to a third
embodiment of the invention;
FIGURE 4B is a perspective view from a second angle of rotation of the clip
and tube
of Figure 4A;
FIGURE 4C is a sectional side elevation of the clip and tube of Figures 4A and
4B;
FIGURE 4D illustrates the configuration between the conductors and resistor of
the
third embodiment;
FIGURE 4E is a plan view from below of the clip of Figure 4A; and
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FIGURE 4F is a perspective view from above of the clip of Figure 4A.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As illustrated in Figure 1A, when analysing the behaviour of grout between two
conductors [7] and [8], the grout can be modelled as a capacitor [2] with
capacitance
CG in units of Farad (F); in series with an inductor [3] in units of Henry (H)
with
inductance LG; while the capacitor [2] and inductor [3] are jointly in
parallel with resistor
[1] with resistance RG in Ohm. Resistance (R), capacitance (C) and inductance
(L) are
io jointly referred to as "RCL". For simplicity and to facilitate the
reading of this document,
Figure 1B presents a simplified block diagram with RCL indicating the presence
of a
grout-based resistor, capacitor and inductor identical to Figure 1A. RCL has
an
impedance which may be measured in Ohm.
When a direct current (DC) / voltage is applied across conductors [7] and [8],
the
capacitor will initially act as a closed circuit and begin to charge. After a
certain time
passed (Tc), the capacitor will be fully charged and will now act as an open
circuit at
which point the circuit will simplify to a resistor [1] in series only. If the
inductance of the
inductor [3] is very low, the inductor can be simplified as a closed circuit.
However, when applying an alternating current (AC) / voltage across conductors
[7] and
[8], the response will be one of continued charge and discharge in the
capacitor [2] with
an opposite charging and discharging in the inductor [3]. Consequently, the
frequency
response can be measured and the values of RG, CG, LG can be calculated.
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Therefore, in order to detect the presence of grout between two conductors [7]
and [8],
where the grout is modelled as the RCL circuit of Figure 1, the following AC
methods
are available:
= measuring the resistance between conductors [7] and [8];
= measuring the capacitance between conductors [7] and [8];
= measuring the inductance between conductors [7] and [8];
= measuring the charging time (proportional to capacitance CG) when a DC
current/voltage is applied to conductors [7] and [8];
= Measuring the impedance value of (RG + LG) // LG by using the frequency
response at conductors [7] and [8] when a current/voltage is applied at
conductors [7] and [8].
First embodiment of the invention (Figures 2A ¨ 2E)
Figure 2A represents the first embodiment of the invention. An apparatus
according to
the invention is generally designated by reference numeral [16]. The apparatus
[16] is
used to test the structural integrity of a reinforcing anchor [14], such as a
tendon, roof
anchor or roof bolt, which is installed within a host body [10], such as rock
strata, and
filled with grout before or after installation. Generally, a hole [12] is
drilled into the host
.. body [10] and both the anchor [14] and the apparatus [16] are secured
within the hole
[12]. The remaining drill hole [12] surrounding the anchor [14] and apparatus
[16] is
progressively filled by pumping grout or cement into it after installation of
the anchor [14]
and apparatus [16].
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The apparatus [16] comprises an elongate, continuous insulated conductor [20]
having
a conducting core [22] and a surrounding electrical insulation [24] around the
core [22].
The conductor terminates at its opposite free ends in two exposed core
contacts [26;
28]. The conductor [20] is looped before insertion into the hole [12] to
effectively define
two parallel and abutting conductor legs [20.1; 20.2], with the first
conductor leg [20.1]
terminating at its free end in core contact [26], and with the second
conductor leg [20.2]
terminating at its free end in core contact [28]. In its looped configuration,
the conductor
[20] extends substantially for the length of the anchor [14], substantially
parallel to, but
spaced apart from, the anchor [14]. Those in the industry will appreciate that
the anchor
[14] typically extends through a faceplate (not shown), which abuts a face of
the host
body wall [10] to close off the hole [12]. The looped conductor [20] is
inserted into the
hole [12] such that the two conductor legs [20.1; 20.2] similarly extend
through the
faceplate, such that the free contacts [26; 28] are accessible from outside of
the drill
hole [12] after installation of the anchor [14].
The apparatus [16] further comprises a series of intermittent exposed core
sections [30]
arranged along the length of the first conductor leg [20.1], where the
insulation [24] is
removed to expose the conducting core [22]. Each exposed core section [30]
includes
a resistor (R) which is bordered on either side thereof by a section [40] of
exposed
conducting core [22], as best illustrated in Figure 20. In the illustrated
embodiment, the
apparatus [16] includes three exposed core sections [30] with three resistors
(R1, R2
and R3) arranged within the three exposed core sections [30]. The apparatus
[16] is
positioned such that the sections [40] of exposed conducting core [22] within
the
exposed core sections [30] never come into contact with the anchor [14]. This
is
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achieved either through thick insulation [24], or by means of an electrically
isolated clip
illustrated in Figures 4A to 4F and discussed below.
In the absence of cement or grout within the drill hole [12], the resultant
impedance of
.. the electrical circuit between exposed core contacts [26; 28] will simply
be the sum of
the three resistors (R1, R2, R3) in series ¨ in other words: Rno grout = R1 +
R2 + R3.
However, after the drill hole [12] is filled with cement or grout and exposed
core sections
[30] are encased, the cement or grout creates an electrical circuit parallel
to each of the
resistors (R1, R2, R3). Figure 2D presents this electrical circuit around the
second
exposed core section [30], therefore parallel to resistor R2. This electrical
circuit also
includes a switch S2 for modelling purposes to serve as a parameter to
indicate cement
or grout presence when the switch S2 is closed. When S2 is open, it means that
no
cement or grout is present about the exposed core section [30]. If a
current/voltage is
applied with S2 closed, the equivalent impedance (Re) between core contacts
[26; 28]
can be calculated as:
Re =1/(1/R1+S1*1/RG) + 1/(1/R2+52*1/RG) +1/(1/R3+531/RG)
Equation (1)
where Si, S2 and S3 represent the three switches and have a value of 1 if
cement or
grout is present and a value of 0 if cement or grout is not present. The
following system
will demonstrate that by choosing different values for R1 to R3 the resistance
measurement can differentiate in the sense to indicate which switches Si to S3
is
closed (cement or grout is present in the respective exposed core section
[30]) and
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which are open (cement or grout is not present in the respective exposed core
section
[30]).
For example, and with reference to Figure 20, assume the section [40] of
exposed
conducting core [22] has a length L1 at the bottom of the resistor, and L2 at
the top of
the resistor (R2), and that L1=L2=10mm. The resistor length of R1 to R3, which
is
indicated by L3 in Figure 20, is equal to L3=8mm. Further assume that in the
presence
of cement or grout, the impedance of RG=0.4 x 106 Ohm. Table 1 presents the
calculation of Re according to Equation (1) above for all the 8 combinations
of the three
switches Si to S3. Note that by choosing R1=1.5, R2=3 and R3=6 mega Ohm (106
Ohm), the 8 combinations each provide distinct impedance values of Re.
Therefore, during the process when cement or grout is pumped into the drill
hole [12]
the impedance can be monitored to follow the filling process from a condition
when all
switches (Si to S3) are equal to 0 (all open ¨ no cement or grout present), to
a position
where Si is closed, then to a position where S2 is also closed, and then to a
position
where S3 is also closed. The closing of switches Si to S3 can be followed by
the
corresponding impedance change according to Table 1 to ensure complete filling
of the
entire drill hole [12]. When air bubbles or incomplete filling takes place,
the resultant
open switch can be pin-pointed by looking at and matching the corresponding
resistance in Table 1.
A measuring system can be calibrated to compensate for wet cement or grout
(which is
being pumped into the cavities [18]), as well as cured (hardened) cement or
grout, in
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order to do continuous measurements even after the installation stage so as to
ensure
that no cavities or air bubbles exist in either the wet or cured cement or
grout. The
values of R1, R2, R3, L1 and L2 can be optimised to result in the most
effective
measurement. It will be appreciated that Table 1 only serves as an example to
demonstrate the principle of the invention. This invention is not limited to
resistors R1 to
R3, as these resistors can be replaced by capacitors R1 to R3 with the same
effect.
Prior to grout injection the known capacitance in series can be measured.
The continuous insulated conductor [20] of the first embodiment may be
manufactured
from insulated common twin core wire where the wires are already insulated and
attached next to each other. The exposed core sections [30] can simply be cut
into one
wire and the appropriate resistors (R1 ¨ R3) soldered in.
Capacitance related measurements
In the same manner as explained above, the capacitance can be measured to
ensure
all cavities [18] are filled with cement or grout. Alternatively, the
capacitance charging
time can be measured until the capacitors are fully charged by applying a
direct or wave
of known frequency current (DC) / voltage across core contacts [26; 28].
Alternating current (AC)
When applying an alternating current (AC) / voltage across core contacts [26;
28], a
frequency domain response can be measured and shown to change as the
grout/cement dries.
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Second embodiment of the invention (Figures 3A to 3D)
The second embodiment of the invention is presented in Figures 3A to 3D. In
this
embodiment, the apparatus [16] comprises an elongate, continuous insulated
conductor
[20] having a conducting core [22] and a surrounding electrical insulation
[24] around
the core [22]. The conductor [20] is no longer looped and terminates in two
opposing
ends. The trailing free end extends through the faceplate (not shown) and
terminates in
an exposed core contact [26]. The opposite end of the conductor [20]
terminates in an
exposed core contact [50], which is connected to the anchor [14] through a
steel
connector [60]. A second contact [28] is connected to and extends from the
anchor
[14], such that the anchor [14] effectively replaces the second conductor leg
[20.2] of
Figure 2A.
Figure 3D presents the circuit diagram created around each of the exposed core
sections [30] for the second embodiment. An RCL circuit is created parallel to
each R1
to R3 resistor, as well as between the L1 length and the anchor [14], and
between the
L2 length and the anchor [14]. Non-conductive spacers or clips may be employed
to
locate the L1 and L2 lengths at a fixed distance from the anchor [14] to
maintain a
stable and consistent RG, CG and LG. The solution to the resultant equivalent
resistance between the first and second contacts [26; 28] is a more
complicated
solution, but the measurement effect on the first and second contacts [26; 28]
of this
embodiment is the same as for the first embodiment.
Note that this invention is not limited to three exposed core sections [30],
but one or
more may be employed. The invention is not limited to roof bolts or anchors
but may be
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used to detect the presence of any initial liquid conductive substance at
multiple
locations by employing two measuring contacts. Presence detection may be
during
progressive injection or pumping of the substance during installation, as well
as
measurement or detection post installation or when cured to a solid state. All
embodiments in this invention provides an integrity test, by measuring the
resistance,
before cement or grout is injected, in order for this impedance to be compared
to the
known resistance when all or some switches (S) are closed after gout is
injected.
Third embodiment of the invention (Figures 4A ¨ 4F)
A third embodiment of the invention is illustrated in Figures 4A to 4F and
includes a
resistor [41], an electrically insulated clip [43], an electrically insulated
tube [45] and
conductors [47].
The clip [43], as can most clearly be seen in Figures 4E and 4F, includes a
rectangular
.. body [49] with a top face [51] and two opposite side faces [55]. A semi-
circular cut-out
[53] extends through the body [49] and is bordered by two curved arms [57; 59]
in such
a manner that a radial exit distance L4 is smaller than diameter D1 of cut-out
[53]. This
configuration makes it possible for the clip [43] to be clipped onto the tube
[45] with the
tube [45] being accommodated within the cut-out [53].
Top face [51] also includes a rectangular hole [61] with rounded internal
corners and
circumferentially bordering cut-out [53]. Rectangular hole [61] extends
through body
[49] and runs over into conductors-exit hole [63], which terminates in cut-out
[53]. Top
face [51] also includes two rectangular corner cut-outs [65] (refer Figure
4B), creating
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faces [67] including slotted holes [69], terminating in face [71]. Face [71]
includes a drill
hole [73] extending to and linking hole [61] and [69] while terminating in
bottom face
[75]. Extending from one of slotted holes [69] to the other slotted hole [69],
extends a
circular drill hole [79] perpendicular to side faces [55], which in a radial
direction extends
to face [75] in such a manner that an exit distance L5 is smaller than
diameter D2 of
circular drill hole [79], creating a finger structure [81].
The clip [43] may be manufactured from a flexible material like plastic which
creates a
spring loaded finger structure [81] which can locate a cylindrical object in
drill hole [79],
as well as allowing for the sideways spring loaded clip-on of a cylindrical
object in
circular cut-out [53].
Referring to Figure 4D, the two conductors [47] include two flexible
conducting cores
[83; 84], each insulated by electrical insulation [85] and terminating at
their free ends in
exposed contacts [83; 84], while at their other end the conductors [47] are
split apart to
form two branches [87; 89]. Each branch [87; 89] has an exposed core section
[91; 93]
where the insulation [85] is removed. Each branch [87; 89] is soldered to a
leg [95; 97]
of the resistor [41] respectively to create exposed core sections [99; 101].
The
conductors [47] are bent between sections [99] and [101] to the exposed
contacts [83;
84] in order to create a conductive path as described below.
The tube [45], is typically a standard PVC tube with a radial conductors-
receiving hole
[103] drilled through its sidewall. The tube [45] may be located around an
anchor [14].
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In the assembled third embodiment of the invention the resistor [41] is
located in circular
drill hole [79] with its soldered legs [95; 97] extending through slotted
holes [69]. Clip
[43] is clipped onto tube [45] at such a position that conductors-receiving
hole [103] is
adjacent to conductors-exit hole [63]. From its soldered cores [91; 93]
conductors [47]
come together and extend through hole [61], through conductors-exit hole [63]
and
through conductors-receiving hole [103] into hollow tube [45] to exit the tube
[45] at one
end. The tube [45] may be of variable length and conductors [47] may be of
extended
length to extend beyond the drill hole such that a grout detector measuring
device
(discussed below) can be connected to exposed contacts [83; 84].
During operation of the third embodiment, exposed core sections [99; 101],
together
with resistor [41], create a circuit similar to that explained in Figures 1A,
1B and 2D with
the RCL circuit established between core sections [99] and [101], resistor
[41] replacing
R2 and the presence of grout between the exposed core sections [99; 101]
representing
a closed switch S2.
Measuring device
The grout detector measuring device is configured to read three channels
representing
three third embodiment devices, represented by three colours (e.g. coded red,
green
and blue). The three third embodiment devices may be present around the same
anchor [14] at different locations along the length of the anchor. The three
third
embodiment devices may also share a common electrical wire connected to one of
the
exposed conducting cores [83; 84].
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The grout detector measuring device may display results and record the results
in its
memory. The results are downloadable, using a Grout Detector Application, into
an
Excel formatted file. The device has in-built self-diagnostics, including
checking its
battery level. The battery is rechargeable via a port on the side of the
device.
Measuring method
Measurement of the impedance of the grout is achieved by measuring the
impedance of
a parallel circuit created between the resistor [41] and the grout material
between the
exposed core sections [99; 101] ("the target"). Grout impedance is non-linear
and may
be simulated by a dynamic combination of resistive, capacitive and inductive
components. A wave form or a series of pulses are applied to the target and
the
voltage drop across it is read. The process is repeated at least three times
or more,
and the final result is presented as an average of all the readings. During
development
it was found that the reading results are stable and repeatable. A range of
frequencies
and duty cycles of the wave or pulses with various width are used, depending
on the
grout properties. For example, frequencies between 50Hz and 300kHz and pulse
width
of 5m5 to 20ms have been used. Results are read at the crest of the input
signal.
In general, operation of the measuring device specifically, amongst others,
includes the
following functions:
= testing for an open grout circuit in the absence of grout which would
indicate a
broken or faulty wire or circuit;
= testing for specific resistance of the resistors in the absence of grout
to further
ensure integrity of the apparatus; and
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= measuring specific properties of the RCL circuit in the presence of grout
to
determine grout properties and integrity.
