A sensor system and method for determining the strength of shotcrete in underground development headings

Abstract

A sensor unit (30) for use in determining the strength of a shotcrete slurry that has been applied to a substrate. The sensor unit (30) includes a printed circuit board on which there is mounted a temperature sensor (31) that is capable of measuring the temperature of shotcrete and which is operably connected to a central processing unit for storing sensor data that is received from the temperature sensor (31). The sensor unit (30) also includes a BLE module (32) which is mounted on the printed circuit board and operably connected to the central processing unit and wherein the BLE module may be used for wireless transmission of sensor data. The temperature sensor (31), central processing unit and BLE module (32) are powered by a battery (33) that is mounted on the printed circuit board and operably connected to each of these devices.

Description

[0001] "A SENSOR SYSTEM AND METHOD FOR DETERMINING THE STRENGTH OF SHOTCRETE IN UNDERGROUND DEVELOPMENT HEADINGS"

[0002] This invention relates to both a sensor system and a method of determining the strength of shotcrete in underground development headings .

[0003] This invention has particular but bot exclusive but not exclusive application to both a sensor system and a method of determining the strength of shotcrete in underground development headings . However, it will be appreciated that the sensor system and the method may be used in other applications where shotcrete is utilised for lining purposes .

[0004] Mining operations are essential for the extraction of valuable minerals and resources from the earth . To maintain productivity and ensure the safety of mining personnel , the structural integrity of mine walls is paramount . As mines deepen and expand, creating new tunnels becomes necessary to access additional resources . These new tunnels require stable and durable construction to prevent collapse and other structural failures .

[0005] Traditionally, various materials and methods have been used to line the walls of mines , but shotcrete has emerged as a preferred solution due to its ease of application and ef fectiveness in reinforcing mine walls . Shotcrete , a mixture of cement , sand, and aggregates combined with water and often admixtures , and applied through a high-pressure hose , provides immediate support and can be applied to irregular surfaces , making it particularly suitable for the rough and uneven walls of underground mines . The inclusion of steel or synthetic fibres in the shotcrete mix can further enhance its strength and durability, making it ideal for demanding mining applications . However, the curing time of shotcrete , which is crucial for it to achieve its full strength and stability, presents a signi ficant challenge . The curing time can vary based on several factors , including the speci fic ingredients used in the mixture ( including the type and dosage of admixtures and the inclusion of fibres ) and environmental conditions within the mine . The curing time is not precisely measured but rather estimated based on typical ingredient formulations , environment conditions and experience of the user . This often leads to curing times that are longer than is required by providing a margin of error to ensure that the shotcrete is suf ficiently cured .

[0006] Any downtime during mining operations , such as the time allowed for shotcrete to cure , directly impacts productivity . The longer the shotcrete is allowed to cure , the longer the mine tunnel remains inaccessible, delaying subsequent mining activities . This downtime can lead to substantial economic losses , making it imperative to accurately determine when the shotcrete has suf ficient strength to minimise delays while ensuring the safety and stability of mine structures , including wall linings .

[0007] It is an obj ect of the present invention to provide a sensor system and a method of determining the strength of shotcrete in underground development headings that will alleviate at least some of the problems associated with the prior art and which will be reliable and efficient in use .

[0008] With the foregoing and other obj ects in view, this invention in one aspect relates to a sensor unit for use in determining the strength of a shotcrete slurry that has been applied to a substrate , said sensor unit being embedded in said shotcrete slurry, said sensor unit including : a casing; at least one sensor located within said casing for sensing one or more physical properties of the shotcrete slurry to produce sensor data ; a transmitter located within said casing for transmitting said sensor data, and a power source located within said housing and operatively connected to said at least one sensor and said transmitter for powering said at least one sensor and said transmitter .

[0009] Shotcrete is typically applied to a substrate in the form of a slurry that is pumped through a noz zle . Where the sensor units are added to the shotcrete slurry prior to the application of the shotcrete slurry to the substrate using a delivery system that includes a noz zle , preferably the sensor unit is of a si ze and shape that is suitable for passage through the noz zle .

[0010] Preferably the casing has suf ficient impact toughness and abrasion resistance so as not to be damaged during the process of either mixing the shotcrete slurry and / or the application of the shotcrete slurry to the substrate . Preferably the casing is also waterproof and resistant to the alkaline environment of shotcrete .

[0011] In one embodiment , the casing may be made from a robust polymeric material .

[0012] In one embodiment , the casing maybe adapted to encapsulate the internal components of the sensor unit and may be formed around the internal components during manufacture of the sensor unit . Alternatively, the casing may include an opening that will allow for internal components of the sensor unit , such as the sensor, transmitter and power source , to pass therethrough during assembly of the sensor unit .

[0013] In order to protect the internal components from impact damage during the process of mixing the shotcrete slurry and / or the application of the shotcrete slurry to a substrate , the internal components of the sensor unit may be encapsulated within a protective material that is contained within the casing . For example , the internal components o f the sensor unit , having been operatively located within the casing, may be encapsulated within a suitable epoxy resin which itsel f may be poured into the casing via the opening and wherein the epoxy resin may be used to fill al l voids in the casing and thereby close the opening .

[0014] In those embodiments where portions of the protective material that is used to encapsulate the internal components of the sensor unit will in use be exposed to the shotcrete slurry, preferably the protective material is waterproof and resistant to the alkaline environment of shotcrete .

[0015] The casing may have an external shape that is adapted to optimise the ability of the sensor unit to pass through a shotcrete noz zle while also minimi zing the likelihood that the sensor unit will become clogged in the noz zle . For example , the casing may be spherical or may include a hemispherical shaped end portion . However, in the preferred embodiment the casing resembles a cube and wherein the casing may include rounded corners .

[0016] Further, where the shape of the casing resembles a cube , and having regard for currently available delivery systems that are used to spray shotcrete on a substrate , preferably the maximum length of the side of the cube shaped casing is approximately 25 mm .

[0017] The sensor or sensors may each be capable of measuring one or more physical characteristics of the shotcrete . These physical characteristics may include temperature and electrical resistivity . For resistivity sensing, the sensor unit may include two electrodes located on the outside of the casing which are adapted to measure the changing electrical resistivity of the curing shotcrete .

[0018] The transmitter may be adapted to transmit data to an external device . For this purpose , the transmitter may utilise any suitable wireless RF communication technique such as , Bluetooth, Zigbee , LoRaWAN or any other forms of communication which are suitable for underground environments , ensuring robust signal transmission from within the cured shotcrete to a gateway .

[0019] The power source may be an active power source , such as a battery, and may have a pre-set operational li fespan . Alternatively, the power source may be a passive power source such as an induction coil . I f the power source is an active power source , the power source may be activated prior to the sensor unit being located within the shotcrete slurry and wherein the sensor unit may include visual means , such as an LED that is operatively connected to the power source , that is capable of indicating the operational status of the power source , such as on or of f . Further, the sensor unit may be configured to enter a low-power state when not actively transmitting data so as to conserve energy .

[0020] In another aspect , this invention relates to a method of determining the strength of shotcrete comprising the steps of : mixing a multiplicity of sensor units into a shotcrete slurry, wherein the sensor units are of the type described above ; spraying the mixture of shotcrete slurry and sensor units onto a substrate to form a lining; utilising one or more of the sensor units to measure one or more physical characteristics of the shotcrete to create sensor data ; transmitting the sensor data to an external device ; and analysing the sensor data to determine the strength of the shotcrete .

[0021] In still yet another aspect , this invention relates to a method of determining the strength of shotcrete comprising the steps of : spraying a shotcrete slurry onto a substrate to form a lining; embedding a multiplicity of sensor units of the type described above into the shotcrete slurry that has been applied to the substrate ; utilising one or more of the sensor units to measure one or more physical characteristics of the shotcrete to create sensor data ; transmitting the sensor data to an external device ; and analysing the sensor data to determine the strength of the shotcrete .

[0022] In one embodiment the sensor units may be adapted to measure temperature and / or electrical resistivity and wherein the maturity method for curing estimations based upon temperature and / or changes in electrical resistivity may be used to analyse the sensor data and to determine current estimated strength and / or predicted time to reach target strength . The shotcrete slurry may be a dry-mix slurry or a wet-mix slurry .

[0023] The mixture of shotcrete slurry and sensor units may be sprayed onto a surface in the same manner that shotcrete is normally sprayed onto a substrate . The shotcrete slurry and the associated sensor units may be pneumatically proj ected onto a substrate .

[0024] Alternatively, the sensor units may be embedded in the shotcrete once it has been sprayed onto a surface .

[0025] Regardless of which method is used, preferably the sensor units are distributed throughout the shotcrete slurry such that it is possible to obtain representative data on the curing process throughout the structure .

[0026] Where the shotcrete is a dry-mix slurry, water may be added to the dry-mix when the dry-mix is passed through a noz zle . When the shotcrete is a wet-mix slurry, water is included in the wetmix slurry when the wet-mix slurry is mixed .

[0027] The sensor data may be transmitted using an existing telecommunication network adj acent to where the shotcrete is located, such as a mine-wide WI FI or a dedicated LoRaWAN network optimised for underground communication . This telecommunication network may transmit the sensor data to an external device located remotely to where the shotcrete is located, or to a local device underground . Alternatively, this telecommunication network may transmit the sensor data to an external device located adj acent to the desired surface .

[0028] The sensor data may be transmitted directly to the external device via a direct wireless link such as Bluetooth or a low- power wide-area network ( LPWAN) technology . The external device may be handheld, such as a tablet or a rugged smartphone , or a fixed computer workstation . Further, the external device may be used to provide power to the sensor unit i f the sensor unit has a passive power source , for example , through inductive charging .

[0029] The external device may include software capable of analysing the sensor data to determine the strength of the shotcrete using the maturity method for curing estimations from temperature and / or the changing electrical resistivity . The software may allow manual inputs into the software to be based on the ingredients of the shotcrete to assist in determining the strength of the shotcrete . The external device may allow inputs into the software based on environmental conditions to assist in determining the strength of the shotcrete . The environmental conditions may be manually inputted into the software or may be inputted using environmental sensors that automatically trans fer environmental data .

[0030] The software may calculate the likely time the shotcrete may achieve a desired cure strength us ing the maturity method and / or resistivity correlation . The software may present this information as an estimated time to reach a target strength ( e . g . , in MPa ) required for safe access or further operational activities .

[0031] The external device may include a visual display unit . The visual display unit may display the results of the software calculation, including current estimated strength, predicted time to reach target strength, and historical curing data . The display may also provide alerts i f the curing process deviates from expected parameters . The method may include the further step of determining when it is safe to continue work within the area adj acent to where the shotcrete was deposited based on the measurements , in at least some part , obtained from the sensor units and the analysis using the maturity method and / or resistivity changes .

[0032] In order that the invention may be more easily understood and put into a practical ef fect , reference will now be made to the accompanying drawings wherein :

[0033] FIG . 1 is a schematic representation of a mine site which includes an underground mine ;

[0034] FIG . 2 is a schematic representation of a heading development of the underground mine illustrating in Figure 1 , and

[0035] FIG . 3 is a perspective view of a sensor unit , that has been constructed in accordance with the present invention .

[0036] Figure 1 is a schematic representation of a typical underground mine 10 which includes a ramp or s loping tunnel 11 that extends generally vertically deep under the ground and wherein the ramp 11 may be used to provide access for vehicles and other equipment to a plurality of vertically interconnected, generally hori zontally orientated, heading developments or tunnels 12 that may be used to gain access to an ore body 13 .

[0037] Figure 1 also shows an agitator 14 that includes a mixing drum 15 that is mounted on the rear of a vehicle 16 and wherein the mixing drum is capable of rotational movement about its longitudinal axis relative to the vehicle .

[0038] The vehicle 16 is typically used to transport a shotcrete slurry to the heading development 12 and wherein the continuous rotation of the mixing drum 15 ensures that the cement , sand, aggregate and water are thoroughly blended, resulting in a predictable and reliable shotcrete .

[0039] Figure 2 is a schematic view of a typical heading development 12 as shown in figure 1 , including a vehicle 16 containing a load of shotcrete 17 to be used to line an exposed substrate or rock wall 18 .

[0040] Figure 2 also shows spraying means 19 that is mounted on the rear of a second vehicle 20 . The spraying means 19 includes a noz zle 21 and a hopper 22 having an inlet through which shotcrete may be received from the agitator 14 and an outlet that is fluidly connected to the noz zle by a hose 22 . The spraying means 19 may be used to spray shotcrete 17 on the substrate 18 .

[0041] Figure 3 shows a sensor unit 30 that includes a printed circuit board on which there is mounted a temperature sensor 31 that is capable of measuring the temperature of shotcrete and which is operably connected to a central processing unit for storing sensor data that is received from the temperature sensor 31 .

[0042] The sensor unit also includes a BLE module 32 which is mounted on the printed circuit board and operably connected to the central processing unit and wherein the BLE module may be used for wireless transmission of sensor data .

[0043] The temperature sensor 31 , central processing unit and BLE module 32 are powered by a battery 33 that is mounted on the printed circuit board and operably connected to each of these devices .

[0044] The supply of Power to temperature sensor 31 , central processing unit and BLE module 32 is selectively controlled by a reed sensor 34 that may be used to selectively turn the sensor unit on or of f .

[0045] The sensor unit also includes an LED 35 which is operably connected to the battery 33 and wherein use actuation of the LED may be used as a visual signal that the sensor unit has been turned on .

[0046] The sensor unit 30 is preferably surrounded by a casing, not shown, that is typically made from a robust polymeric material , designed for durability and resistance to the shotcrete environment .

[0047] In use Shotcrete may be applied to reinforce underground structures of the mine site , such as wall s in heading developments 12 . A multiplicity of sensor units 30 are preferably mixed into the shotcrete slurry prior to application .

[0048] The temperature sensor 31 is used to measure the temperature of the shotcrete . This sensor data is typically processed by the central processing unit ( CPU) and stored in memory within the sensor unit , ready for transmission .

[0049] The BLE module 32 is electrical ly connected to transmit the sensor data obtained by the temperature sensor 31 . The sensor data is typically transmitted to an external device (not shown in these figures , but conceptually present as a computer or handheld device ) via a mine telecommunications network, which can utilise technologies like WI FI , Bluetooth, or LoRaWAN, depending on the underground environment .

[0050] The battery 33 is used to power the components within the sensor unit . This battery is typically able to power the temperature sensor 31 and the BLE module 32 for a duration exceeding the typical shotcrete curing time , for example , 24 to 48 hours .

[0051] In use , each battery 33 of each sensor unit 30 is switched on prior to the sensor unit 30 being located within shotcrete . An external magnet (not shown) is used to activate the reed switch 34 . The LED 35 indicates when the battery 33 is turned on and is providing power to the components . After activation, the sensor units 30 are located within the shotcrete slurry, which is mixed using an agitator 14 . The casing protects the internal components from being damaged during the mixing process . The shotcrete slurry with associated sensors is then transported to the desired application site .

[0052] For wall lining applications , the shotcrete slurry is sprayed onto the walls using known pneumatic delivery techniques 19 . As shown in FIG . 2 , shotcrete 17 is shot from a spray noz zle 21 onto the walls within a heading development 12 .

[0053] Once the shotcrete is placed, the temperature sensor 31 measures the temperature of the shotcrete . This sensor data is transmitted wirelessly to a remote external device , such as a computer or a handheld device , via the mine telecommunications network .

[0054] Software located on the external device is used to analyse the sensor data and calculate the curing time and strength development of the shotcrete using the maturity method . In order to calculate the curing time , the type and amount of ingredients ( including cement type , admixtures , and fibres i f used) are inputted into the software . The calculated curing time and shotcrete strength determined by the maturity method are then displayed on the computer screen or the handheld device ' s display . This information is used to determine when the shotcrete has achieved suf ficient strength, indicating it is safe to continue work in the area adj acent to where the shotcrete was deposited . The software may provide a visual indication, such as a color-coded system, to indicate the current strength status relative to the required strength for safe operation .

[0055] The BLE module 32 may be replaced or augmented by other wireless communication protocols like LoRaWAN to wirelessly transmit the sensor data to the handheld external device or a gateway connected to a network, depending on the range and power ef ficiency requirements .

[0056] Utilising a handheld external device that is located locally can provide immediate details to a worker who is located adj acent shotcrete site . They can determine when the site is safe to access and physically mark the site as such using appropriate signage , based on the real-time strength data provided by the system .

[0057] The method of determining the strength of shotcrete makes mining more ef ficient . Mine ore can be accessed earlier and the shotcrete strength can be determined with greater accuracy . This enables sites to be accessed earlier than they otherwise would have under traditional methods .

[0058] While the foregoing description has been given by way of example of the invention, it will be understood that the invention may be embodied in many other forms and all such forms are deemed to fall within the broad scope and ambit of the invention as hereinbefore defined in the appended claims .

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS :1 . A sensor unit for use in determining the strength of a shotcrete slurry that has been applied to a substrate , said sensor unit being embedded in said shotcrete slurry, said sensor unit including : a casing; at least one sensor located within said casing for sensing one or more physical properties of the shotcrete slurry to produce sensor data ; a transmitter located within said casing for transmitting said sensor data, and a power source located within said housing and operatively connected to said at least one sensor and said transmitter for powering said at least one sensor and said transmitter .2 . A sensor unit as claimed in claim 1 , wherein said casing is robust , waterproof and resistant to the alkaline environment of shotcrete .3 . A sensor as claimed in claim 2 wherein said casing includes an opening that will allow for internal components of the sensor unit , such as said sensor, transmitter and power source , to pass therethrough during assembly of the sensor unit .4 . A sensor unit as claimed in claim 3 , wherein said internal components of the sensor unit are encapsulated within a protective material that is contained within said casing .5 . A sensor unit as claimed in claim 4 , wherein said protective material is an epoxy resin that is poured into said casing via said opening and wherein said epoxy resin is used to fill all voids in said casing and to close said opening .6 . A sensor unit as claimed in any one of claims 1 to 5 , wherein said casing generally resembles the shape of a cube .7 . A sensor unit as claimed in any one of the preceding claims wherein said sensor is adapted to measure temperature .8 . A sensor unit as claimed in any one of claims 1 to 6 , wherein said sensor is adapted to measure electrical resistivity and wherein the sensor unit includes two electrodes located on the outside of said casing .9 . A sensor unit as claimed in any one of the preceding claims , wherein said transmitter utilises wireless RF communication techniques .10 . A sensor unit as claimed in any one of claims 1 to 9 , wherein said power source is an active power source .11 . A sensor unit as claimed in any one of claims 1 to 9 , wherein said power source is a passive power source .12 . A method of determining the strength of shotcrete comprising the steps of : mixing a multiplicity of sensor units into a shotcrete slurry, wherein the sensor units are of the type as claimed in any one of claims 1 to 11 ; spraying the mixture of shotcrete slurry and sensor units onto a substrate to form a lining; utilising one or more of the sensor units to measure one or more physical characteristics of the shotcrete to create sensor data ; transmitting the sensor data to an external device ; andanalysing the sensor data to determine the strength of the shotcrete .13 . A method of determining the strength of shotcrete comprising the steps of : spraying a shotcrete slurry onto a substrate to form a lining; embedding a multiplicity of sensor units of the type defined in any one of claims 1 to 11 above into the shotcrete slurry that has been applied to the substrate ; utilising one or more of the sensor units to measure one or more physical characteristics of the shotcrete to create sensor data ; transmitting the sensor data to an external device ; and analysing the sensor data to determine the strength of the shotcrete .

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