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 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. ln 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 grouted into its hole and that the grout (or other filling material) has filled the entire hole, homogeneously and to capacity.

WO2015/128831 (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 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 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 CN101343876, 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.

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. 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 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. ln 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 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 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 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 5ms 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 1 A is an electrical circuit diagram representation of grout / cement;

FIGURE 1 B is a simplified electrical circuit diagram of Figure 1 A; 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 FIGURE 4F is a perspective view from above of the clip of Figure 4A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As illustrated in Figure 1 A, 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 jointly referred to as“RCL”. For simplicity and to facilitate the reading of this document, Figure 1 B presents a simplified block diagram with RCL indicating the presence of a grout-based resistor, capacitor and inductor identical to Figure 1 A. 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. 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]. 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 2C. 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 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: R _no grout = R1 + R2 + R3.

Flowever, 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+S2 ^* 1/RG) +1/(1/R3+S3 ^* 1/RG) Equation (1 ) where S1 , 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 S1 to S3 is closed (cement or grout is present in the respective exposed core section [30]) and which are open (cement or grout is not present in the respective exposed core section [30]).

For example, and with reference to Figure 2C, 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 2C, is equal to L3=8mm. Further assume that in the presence of cement or grout, the impedance of RG=0.4 x 10 ⁶ Ohm. Table 1 presents the calculation of Re according to Equation (1 ) above for all the 8 combinations of the three switches S1 to S3. Note that by choosing R1 =1 .5, R2=3 and R3=6 mega Ohm (10 ⁶ 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 (S1 to S3) are equal to 0 (all open - no cement or grout present), to a position where S1 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 S1 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 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. 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 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 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]. 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 1 A, 1 B 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] 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 5ms 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 • measuring specific properties of the RCL circuit in the presence of grout to determine grout properties and integrity.