A monitoring system and method for a pillar-roof support system

Abstract

The application discloses a kind of based on distributed optical fiber composite multidirectional stress grid's pillar-roof system stability monitoring method, including multidirectional stress grid for bearing structural load and sharing load and distributed optical fiber sensor for monitoring pillar-pillar system rock mass inside and distributed optical fiber sensor embedded in multidirectional stress grid.Accesses underground mine safety refuge "six big system" network, data transmission to ground dispatch center records and analysis, realizes pillar-roof system instability early warning.The pillar-roof system stability monitoring method of the application realizes the pillar-roof system instability early warning of systematized perception network, suitable for internal and external collaborative monitoring of arbitrary pillar shape under the complex environment of mine, with three-dimensional visual high-precision reliable monitoring effect, low application cost and convenient construction operation, it is a low-cost, systematized, high-precision, toughness reliable, suitable for the supporting and monitoring method of complex shape of pillar.

Description

Technical Field

[0001] This invention relates to a method for stability control and monitoring of the pillar-roof system left over from underground mining operations, specifically a method for stability control and monitoring of the pillar-roof system based on a distributed fiber optic sensor composite multi-directional stress grid. Background Technology

[0002] Underground mining requires numerous pillars for support. These pillars, together with the adjacent roof, form a collaborative support system to ensure safe mining operations. From small drilling chambers within the stope to large goaf areas, the pillar-roof system is essential for maintaining stability during the mining process. However, statistics show that half of underground mine accidents stem from the instability and failure of the pillar-roof support system, a problem particularly pronounced in deep, high-stress mines. Currently, microseismic monitoring technology is primarily used for pillars or roofs surrounding large goaf areas. However, this technology employs point-distributed internal monitoring, meaning that boreholes are drilled at multiple designated locations, with one sensor installed in each hole. The remaining space is then filled with concrete to fix the sensors to the surrounding rock mass, facilitating microseismic monitoring.

[0003] The drawbacks of the above monitoring methods are: 1. Sensors are only individually deployed inside the rock mass, making it impossible to promptly report the fracturing and sliding behavior of the pillars or roof, and failing to provide early warnings of the initial surface behavior of the rock mass where damage occurs. 2. The limited number of boreholes results in a small monitoring area. If key monitoring points are not monitored, data deviations may increase, reducing the reliability of the data. The data is also highly susceptible to noise, requiring manual analysis and processing, often leading to misjudgments and difficulty in providing effective early warnings. 3. In hazardous mining areas, the number of boreholes must be minimized, making it difficult to balance monitoring accuracy and operational safety. 4. Installation and systematic application costs are high.

[0004] Therefore, there is still a lack of a systematic, high-precision, reliable, low-cost, and pillar-roof flexible monitoring method applicable to complex pillar shapes, which is of great significance and application value for safe mining in underground mines.

[0005] In recent years, with the development of computer and communication technologies, fiber optic sensor monitoring and distributed fiber optic monitoring have been rapidly promoted and applied. For example, patent CN106092304A provides a distributed fiber optic sensor system for monitoring blasting vibrations, which arranges sensors in an array on an aluminum plate to monitor the short-duration waveform curves of blasting vibrations; patent CN113932944A provides a system and method for monitoring displacement, strain, and temperature inside soil, which uses a double-layer geogrid with fiber optic sensors bound to its outer surface and buried at a certain depth inside the soil to achieve long-term monitoring and early warning of geological disasters such as landslides; patent CN114017121A provides a real-time monitoring system and early warning method for rockburst based on strain field, which drills a row of parallel blast holes in the coal seam, installs metal sleeves with built-in fiber optic sensors in the holes and connects them in series to achieve rockburst strain monitoring and early warning.

[0006] The above monitoring methods have the following drawbacks:

[0007] 1. The monitoring method of a single array of optical fibers (gratings) or attaching optical fibers (gratings) sensors to the outside of an array of geogrids aims to achieve the array arrangement of sensors and can only utilize the shape of the "well" shaped geogrid. Since the above method describes the need to use the planar and three-dimensional structure of the geogrid to enhance the friction strength and anti-sliding ability between the geogrid and the soil (see paragraph 26 of CN113932944), it is not deformable. Therefore, the above grating arrangement cannot utilize the inherent load-bearing capacity of the geogrid.

[0008] 2. Existing microseismic monitoring can only achieve multi-point monitoring within the rock mass. Even when drilling parallel holes, fiber optic sensors replace traditional internal point source sensors, and internal monitoring is achieved through casing, thus only internal monitoring is performed. Currently, there is no technology for monitoring the external rock mass surface. This is mainly due to the fact that surface monitoring sensors must not only fit closely to the geometry of the pillars and roof to monitor surface data, but also require the support material to have sufficient load-bearing capacity to ensure the stability of the surface rock mass. Although flexible distributed optical fibers have been applied to monitoring scenarios such as blasting vibrations, the measurement data is not affected by the load-bearing capacity of the flexible distribution during the monitoring process. That is, the measurement data and results do not utilize the flexibility of the distribution, and the monitored data and the resulting experimental purpose are different, thus offering no technological inspiration. Pillars or roofs are engineering conditions with inherent stability requirements, so analogy is not applicable. Furthermore, in some existing technologies, single internal or external monitoring methods cannot systematically reflect the surface damage, spalling process, and internal stress changes of the pillar system, failing to achieve real-time dynamic collaborative monitoring of internal and external components. This often leads to delayed forecasts in current early warning systems.

[0009] 3. Both traditional microseismic monitoring systems and proposed fiber-optic-related monitoring systems require separate, complete systems, including sensors, independent data lines, data storage and analysis hardware and software platforms, and data early warning platforms. This independent construction approach is suitable for simple, short-distance engineering scenarios. However, when applied to underground mines, especially where mining depths increasingly exceed 1000m, traditional microseismic monitoring systems require long-distance lines in vertical shafts and roadways to achieve surface control, early warning, and scheduling of pillar-roof stability. Furthermore, the maintenance of these long-distance lines is complex and time-consuming. Maintenance in critical shafts not only requires stopping the normal operation of equipment such as shaft cages but also involves dangerous work for personnel. As a result, although independent lines have been installed in mines, their application rate is low due to the disruption of normal production during maintenance, leading to a persistently high rate of accidents caused by pillar-roof instability. Therefore, independently constructing microseismic systems in deep mines presents problems such as high cost, difficult maintenance, and short operating time.

[0010] Therefore, there is an urgent need for a new method applicable to the stability control and monitoring of large-scale pillar systems in mines, and to achieve real-time dynamic collaborative monitoring both internally and externally. Summary of the Invention

[0011] The purpose of this invention is to provide a low-cost, systematic, high-precision, resilient, and reliable flexible support and monitoring method suitable for complex pillar shapes in order to achieve stable control and monitoring and early warning of the pillar-roof support system during safe underground mining.

[0012] This invention is achieved using the following monitoring technology:

[0013] A monitoring system for a mine pillar-roof support system includes a mine safety monitoring substation, connecting optical cables, and flexible distributed optical fiber sensors. The system is characterized by further including a flexible multi-directional stress grid and prestressed anchor bolts.

[0014] The flexible multi-directional stress grid is laid on the surface of the mine pillar and / or the wall surface of the roof plate supported by the mine pillar; the flexible multi-directional stress grid includes multiple intersecting hollow ribs, the ribs are flexible, the ribs include transverse ribs, longitudinal ribs and diagonal ribs, the transverse ribs, longitudinal ribs and diagonal ribs are hollowly interconnected at the intersection, and flexible distributed optical fiber sensors are installed in the transverse ribs, longitudinal ribs and diagonal ribs, and the flexible distributed optical fiber sensors in the ribs are connected to the mine safety monitoring substation through the grid sensor optical cable bus;

[0015] The prestressed anchor is installed inside the pillar and / or the roof; symmetrical flexible distributed fiber optic sensors are arranged along the axis on the inner side of the prestressed anchor to ensure that the flexible distributed fiber optic sensors change synchronously with the axial stress of the anchor. The flexible distributed fiber optic sensors in the prestressed anchor are connected to the mine safety monitoring substation through connecting optical cables.

[0016] The mine safety monitoring substation simultaneously collects monitoring data from the flexible multi-directional stress grid and prestressed anchor bolts, and transmits the data to the surface dispatch platform for early warning of the stability of the pillar-roof support system.

[0017] When the local surface dispatch platform determines that the following formula is true, it will issue an early warning for the pillar-roof support system:

[0018]

[0019]

[0020] Where: ε i The strain value at a single point of the flexible multi-directional stress grid is obtained through... Perform calculations; λ B The center wavelength of the flexible multi-directional stress grid; Δλ B The change in the center wavelength of the flexible multi-directional stress grid; Λ is the thermal expansion coefficient of the optical fiber; Λ is the period of the Bragg grating. The thermo-optic coefficient of the optical fiber; n is the effective elastic-optical coefficient of the optical fiber; eff The effective refractive index of the fiber core is given by E; ΔT is the temperature change; E is the effective refractive index of the fiber core. B S represents the Young's modulus of the corresponding optical fiber material. 外 The correction factor for strain when laying optical fibers on the rock surface; P0 is the preload after fiber installation; N is the number of fiber segment measuring points selected for calculating strain at a certain location; δ d The dynamic tensile strength of the rock mass at the location of the pillar-roof support system is defined as the dynamic tensile strength of the rock mass. The instability and failure of the rock mass are determined by the stress on the rock mass exceeding its dynamic tensile strength. Furthermore, the smallest repeating unit of the flexible multi-directional stress grid is a triangle formed by transverse ribs, longitudinal ribs, and diagonal ribs.

[0021] Furthermore, before each optical fiber reaches the mine safety monitoring substation, a temperature compensation component is attached to the outside of the optical fiber. The temperature compensation component is fitted on the outside of the optical fiber to correct and monitor microseismic data.

[0022] Furthermore, the multi-directional stress grid is also fixed to the wall surface of the pillar and roof using prestressed anchor rods. One end of the prestressed anchor rod is inserted into the wall through the grid unit, and the other end of the prestressed anchor rod is connected to an end plate to fix the grid to the wall surface.

[0023] Furthermore, the parameters monitored by the mine safety monitoring substation include one or more of the following: displacement, velocity, acceleration, stress, strain, and temperature inside the mine pillar and / or roof and on the wall surface; the mine safety monitoring substation includes an optical fiber modem, CPU, memory, optical fiber data output port, power supply, and indicator light module.

[0024] Furthermore, by using fiber optic data output ports, the pillar-roof monitoring substation is connected to the monitoring substations of the "six major systems" for mine safety and disaster prevention and the fiber optic ring network, and the data is transmitted to the surface dispatch platform.

[0025] Furthermore, the surface dispatching platform synchronously analyzes measured data of the surface and interior of the pillars and / or roof, and provides three-dimensional visualization and early warning of the stability of the pillar-roof support system.

[0026] Furthermore, the connecting optical cable is a 12-core optical fiber cable, and each connecting optical cable connects to 6 prestressed anchor rods, thereby enabling simultaneous monitoring of the data of 6 adjacent prestressed anchor rods.

[0027] Furthermore, the grid material is hollow Cr2MoV alloy steel, with longitudinal and transverse ribs having a diameter of 5 to 6 mm, diagonal ribs having a diameter of 3.5 to 4 mm, and the hollow diameter of each rib being 1.5 to 2 mm. The rib length of the grid unit is 6 to 10 cm. Furthermore, a flexible distributed optical fiber sensor is composited inside the transverse ribs of the multi-directional stress grid. A horizontal composite optical fiber sensor rib is independently set every 3 to 5 rib lines, and a diagonal composite optical fiber sensor rib is arranged every 2 to 4 diagonal rib lines (two diagonal directions). The optical fiber inside a single grid assembly is concentrated at one end through the longitudinal ribs to the middle of the grid assembly as the main interface for the grid sensor optical cable bus.

[0028] On the other hand, the present invention utilizes the monitoring system of the aforementioned pillar-roof support system for monitoring, and provides a monitoring method for the pillar-roof support system, comprising the following steps:

[0029] S1: Lay flexible multi-directional stress grids on the surface of the pillar and / or the wall surface of the roof supported by the pillar; S2: Set prestressed anchors inside the pillar and / or inside the roof.

[0030] S3: The mine safety monitoring substation simultaneously collects monitoring data from the flexible multi-directional stress grid and the prestressed anchor bolt, and transmits the data to the surface dispatch platform.

[0031] S4: When the surface dispatch platform determines that the following formula is true, it will issue an early warning for the pillar-roof support system:

[0032]

[0033]

[0034] Where: ε i The strain value at a single point of the flexible multi-directional stress grid is obtained through... Perform calculations; λ B The center wavelength of the flexible multi-directional stress grid; Δλ B The change in the center wavelength of the flexible multi-directional stress grid; Λ is the thermal expansion coefficient of the optical fiber; Λ is the period of the Bragg grating. The thermo-optic coefficient of the optical fiber; n is the effective elastic-optical coefficient of the optical fiber; eff The effective refractive index of the fiber core is given by E; ΔT is the temperature change; E is the effective refractive index of the fiber core. B S represents the Young's modulus of the corresponding optical fiber material. 外 The correction factor for strain when laying optical fibers on the rock surface; P0 is the preload after fiber installation; N is the number of fiber segment measuring points selected for calculating strain at a certain location; δ d It is the dynamic tensile strength of the rock mass at the location of the pillar-roof support system. The instability and failure of the rock mass is based on the stress on the rock mass exceeding the dynamic tensile strength of the rock mass.

[0035] The present invention has the following beneficial effects:

[0036] (1) Stability control of the pillar-roof system

[0037] This invention employs prestressed anchor bolts and a mine-reinforced "rice"-shaped hollow grid to achieve coordinated internal and external control. Designed to meet the complex geometric requirements of the mine pillar-roof structure, the flexible alloy steel grid is fully fitted to the surface of the rock mass, overcoming the limitations of existing steel anchor mesh support methods that struggle to adapt to complex geometric shapes of the pillar and roof. For loads transmitted to the grid from any location within the pillar or roof rock mass, the "rice"-shaped multi-directional stress grid design ensures that the load is evenly distributed radially across the entire grid assembly. The Cr2MoV alloy steel material boasts a tensile strength approaching 1 GPa, representing a 200-300 MPa increase compared to traditional steel or support materials, effectively preventing collapse and instability of the surface rock mass within the pillar system. Simultaneously, the hollow grid and prestressed anchor bolts fully adhere to the rock surface and borehole walls, providing support components and space for the installation of fragile and easily damaged distributed optical fibers.

[0038] (2) A systematic sensing network was implemented for coordinated monitoring and instability early warning of the pillar-roof system inside and outside the mine pillar-roof system.

[0039] This invention employs coordinated monitoring of the interior and surface of the pillar-roof rock mass, combining multi-point linear distributed sensors to monitor parameters such as rock mass displacement and strain. Coupled with a fiber optic temperature compensation device, it forms a spatial sensing network for the pillar-roof system and integrates with the six essential safety and disaster mitigation systems required in mines. This effectively addresses the shortcomings of traditional point-based microseismic systems, such as small radiation area, poor representativeness, and the limitation of drilling installations only within the surrounding rock. It enables effective early warning and assessment of instability in underground mine pillar-roof systems. Furthermore, the fiber optic sensors in the grid abandon the traditional linear arrangement, instead "dividing the eggs in multiple baskets," with independent sensors placed every 2-5 ribs. This avoids the situation where, in a linear arrangement, all sensors before a break in the fiber optic cable become unusable.

[0040] (3) Low-cost application and safe and rapid construction technology

[0041] The distributed fiber optic sensors used in this invention have advantages such as fast installation, short construction period, and low construction cost. Even if a small number of sensors are damaged, the remaining sensors can still transmit optical signals and data in one direction. For dangerous goaf areas, poles and ropes can be thrown to the other side of the goaf for installation, making construction safe and convenient. The distributed fiber optic monitoring cable is connected to the dual-ring fiber optic network of the six essential safety and disaster prevention systems in the mine through the monitoring substation. The cost of setting up long-distance dedicated lines in deep shafts is very high, and the economic investment accounts for more than half of the system construction cost. Moreover, the subsequent maintenance and repair of the lines require the shutdown of the normal operation of all facilities in the shaft. Therefore, connecting to the dual-ring fiber optic network that must be set up for the six systems not only avoids the cost of building a separate monitoring system, but also reduces the system construction cost by at least 50%. Furthermore, the dual-ring system (i.e., one set uses the fiber optic network and one set is a backup line) can greatly reduce the annual maintenance and repair costs of the simple transmission lines of traditional microseismic systems.

[0042] (4) Applicable to surface flexibility monitoring of any pillar shape in complex mining environments

[0043] This invention employs distributed fiber optic sensors. Based on the flexible surface characteristics of fiber optic sensors, and considering the harsh and complex monitoring environment of underground mines, which is characterized by humidity, high temperature, uneven surrounding rock surfaces, and susceptibility to damage from other construction activities, a small-volume (fiber core diameter is generally 8μm to 10μm) flexible distributed fiber optic sensor is combined with a hollow alloy steel grid and placed on the surface of the mine pillar. This allows for in-situ monitoring of deformation and damage to the surface of the mine pillar rock mass, overcoming the current predicament of underground mines where only micro-seismic monitoring inside the mine pillar is available, while surface monitoring of the mine pillar is lacking.

[0044] (5) High-precision and reliable distributed monitoring

[0045] The present invention adopts a distributed optical fiber monitoring method to synchronously monitor parameters such as displacement, velocity, acceleration, strain, and stress, and uses adjacent sensors distributed along the optical fiber as references for each other, enabling the display of the optical fiber sensors in the form of three-dimensional visualization graphics. That is, the end user can view the specific location where microseismic events occur in three dimensions through the GUI interface and capture the three-dimensional evolution dynamic process of the instability and failure of the ore pillar-roof. Compared with the traditional single-parameter (acceleration / velocity) point-type microseismic monitoring, it provides high-precision feedback and evaluation of the stability of the ore pillar-roof rock mass. At the same time, the optical fiber sensor has good apparent toughness, and the monitoring signal is transmitted through a laser light source, avoiding the phenomenon that traditional sensors are easily disturbed by other construction disturbances and noise. The monitoring system has high reliability, a large amount of effective data, and good stability.

[0046] In summary, the present invention is a flexible distributed optical fiber ore pillar-roof system stability control and monitoring method that is internally and externally coordinated, based on a systematic perception network, suitable for complex surrounding rock environments in mines, highly accurate and reliable, and has low input costs and maintenance expenses.

[0047] The application scenario of the present invention is extensive. In underground mine mining, a large number of ore pillars need to be left as supports. The ore pillar and the adjacent roof form a cooperative support system to ensure the safe mining operation in the mining area. From the small rock drilling chambers in the stope to the large goafs, the ore pillar-roof system is required to maintain its stability during the mining process.

[0048] The following further describes the present invention in conjunction with the drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 . Sensor layout diagram of the ore pillar-roof system

[0050] Figure 2 . Schematic diagram of the "meter" - shaped grille and its composite optical fiber sensor

[0051] Figure 3 . Connection diagram of the monitoring sub-station and the "six major systems" of the mine

[0052] Reference numerals in the figures: 1 - Drilled blast hole with built-in anchor bolt and optical fiber sensor, 2 - Roof rock mass, 3 - Ore pillar, 4 - Flexible multi-directional stress grille with flexible deformation sensor attached inside, 5 - Anchor bolt and built-in optical fiber sensor in the blast hole, 6 - Floor rock mass, 7 - Connecting optical fiber cable, 8 - Mine safety monitoring sub-station, 9 - Data transmission sub-station in the six major systems, 10 - Surface monitoring equipment, 11 - Gigabit switch, 12 - Data acquisition and storage server, 13 - Data analysis platform, 14 - User terminal, 15 - Optical fiber cable interface DETAILED DESCRIPTION OF THE EMBODIMENTS

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0054] Example 1

[0055] This invention provides a stability control and monitoring system and method for a pillar-roof system based on a distributed optical fiber composite multi-directional stress grid. According to the shape of the supporting pillars and the upper roof supported by the pillars in deep mines, a hollow alloy steel flexible multi-directional stress grid 4 is laid, and combined with prestressed anchor bolts 5 inside the boreholes to control the stability of the pillar rock surface and roof. The grid ribs have 3-core distributed optical fiber sensors built into them, and 2-core optical fiber sensors are attached to the inner surface of the prestressed anchor bolts. Both the surface-laid optical fiber sensors and the internal optical fiber sensors are connected to optical cable interfaces to achieve coordinated monitoring of internal and external optical fiber sensors. The optical cable is connected to the "six major systems" of mine safety and disaster prevention through a mine safety monitoring substation, thereby transmitting the monitoring data to the surface dispatch platform to realize parameter analysis and early warning of the pillar system.

[0056] In some embodiments, the pillar-roof system includes adjacent pillars and roofs of upper and lower chambers within the stope, and also includes adjacent supporting pillars and upper roofs of goaf areas.

[0057] In some embodiments, for the stable control of the pillar-roof system, a multi-directional stress grid for mines is laid on the surface of the pillar-roof. The grid adopts a "rice" - shaped grid. The minimum repeating unit of the grid is a triangle formed by the transverse ribs, longitudinal ribs, and diagonal ribs of the grid. The grid material is hollow Cr2MoV alloy steel. The diameters of the longitudinal ribs and transverse ribs of the grid are 5 - 6 mm. In some embodiments, the diameters of both the longitudinal ribs and transverse ribs are 5, 5.5, or 6 mm. In some embodiments, the diameters of the longitudinal ribs and transverse ribs are 5 and 6 mm respectively; the diameter of the diagonal rib is 3.5 - 4 mm, such as 3.5, 3.8, 4 mm; the hollow diameter of each rib is 1.5 - 2 mm. In some embodiments, it is 1.8, 1.5, 2 mm; the length of the rib of the grid unit is 6 - 10 cm, that is, the length and width of the grid unit are 6 - 10 cm. In some embodiments, the length and width are both 6, 8, or 10 cm, or the length and width are 6 and 8 cm respectively, or the length and width are 7 and 10 cm respectively. According to the space limitation in the underground mine and the convenience of transportation and personnel installation, a grid assembly includes multiple cells. The total width of a grid assembly is 2.0 - 2.5 m. In some embodiments, it is 2.0 m, 2.2 m, or 2.5 m. The grid assembly is in the form of a reel package. The length of the grid assembly is determined according to the requirements of the mine project, and the high tensile strength of the grid is effectively utilized to avoid the slip instability of the rock mass on the surface of the pillar and roof.

[0058] In some embodiments, a flexible distributed fiber optic sensor is compounded inside the transverse rib of the multi-directional stress grid. A horizontal composite fiber optic sensor rib line is independently set every 3, 4, or 5 rib lines, and a diagonal composite fiber optic sensor rib line is arranged every 2, 3, or 4 diagonal rib lines (in two diagonal directions). The optical fibers inside a grid assembly are concentrated at the middle of a grid assembly through the longitudinal rib at one end as the grid sensor optical cable bus, realizing the dynamic and full - fitting monitoring of the movement parameters of the surface layer of the pillar - roof rock mass.

[0059] In some embodiments, for the internal monitoring of the pillar - roof system, a prestressed anchor rod is installed in each borehole. Two symmetric flexible distributed fiber optic sensors are arranged along the axis inside the prestressed anchor rod to ensure that the fiber optic sensor changes synchronously with the axial stress of the anchor rod and to improve the reliability of the monitoring process. The prestressed anchor rods are connected by connecting optical cables for boreholes. The connecting optical cables for boreholes are 12 - core fiber optic cables. Each connecting optical cable for boreholes connects 6 prestressed anchor rods, so that the data inside 6 adjacent prestressed anchor rods can be monitored simultaneously.

[0060] In some embodiments, due to the high - temperature environment in deep mines, which may cause the monitoring data of fiber optic sensors to be distorted, a temperature compensation component needs to be connected outside each optical fiber before reaching the optical cable interface of the mine safety monitoring sub - station. The diameter of the temperature compensation component is slightly larger than the diameter of the optical fiber and is sleeved outside the optical fiber. The length of the temperature compensation component is 1 - 3 cm to realize the correction of the monitored micro - seismic data.

[0061] Example 2

[0062] See Figure 1-3 As shown in the diagram, the sensor layout of the pillar-roof system illustrates the specific processing method for monitoring the stability of this system according to the present invention. Four fiber optic sensors are deployed at fixed intervals from bottom to top along the supporting pillars in the deep mine. Two rows of four fiber optic sensors are also deployed at fixed intervals along the roof rock of the roadway separating the two pillars. A multi-directional stress grid containing flexible deformation sensors is installed on the outer surface of the pillars. After the sensors are deployed, they are connected to a fiber optic demodulator via connecting cables. The demodulator converts the optical signals into data, which is then transmitted to a data transmission substation and connected to surface monitoring equipment. Through comprehensive online monitoring of internal and external sensors, real-time early warning and stability evaluation of the underground mine pillar-roof system are achieved. In the actual deployment of sensors in the pillar-roof system, the sensor layout can be specifically designed according to the actual dimensions of the pillars and roof.

[0063] In some embodiments, the pillar-roof system includes pillars and roofs surrounding the upper and lower chambers inside the stope, as well as supporting pillars and upper roofs surrounding the goaf.

[0064] In some embodiments, a multi-directional stress grid for mining is laid on the surface of the pillar-roof plate. The grid adopts a "rice" shaped mesh, and the grid material is internally reinforced. The diameter of the longitudinal and transverse ribs of the grid is 5-6 mm, the diameter of the oblique ribs is 2.5-4 mm, and the length of the grid unit ribs is 6-10 cm. According to the space constraints of the underground mine, the width of a single grid component is 2.0-2.5 m, effectively utilizing the high tensile strength performance of the grid.

[0065] Flexible distributed fiber optic sensors are integrated within the transverse ribs of a multi-directional stress grid. One composite fiber optic sensor is independently installed every 3-5 ribs, with the internal fiber optic cable diameter 2mm smaller than the diameter of each rib. The fiber optic cable within each grid is concentrated at one end via longitudinal ribs to serve as the sensor's main interface, enabling dynamic, fully integrated monitoring of surface motion parameters of the pillar-roof rock mass. The multi-directional stress grid is deployed on the outer surface of the pillar and its edges are fixed with anchor bolts to ensure close contact with the pillar's outer surface. This enhances the pillar's load-bearing capacity and monitors its stability. The close contact with the pillar surface is crucial for utilizing the back-Brillouin principle. If the pillar surface deforms due to temperature or stress disturbances, the flexible deformation sensor on the surface will simultaneously deform. By utilizing the back-Brillouin principle, the dynamic response waveform under displacement deformation and dynamic loads can be monitored.

[0066] In some embodiments, the internal monitoring of the pillar-roof system utilizes space left by drilled blast holes for sensor placement. Two symmetrical flexible distributed fiber optic sensors are arranged along the axis inside each prestressed anchor bolt to ensure the sensors synchronize with the axial stress of the anchor bolt and the reliability of the monitoring process. The fiber optic cable outside the borehole contains 12 cores, simultaneously monitoring data from six adjacent boreholes. Simultaneously, linear distributed flexible deformation sensors are obliquely arranged in the drilled blast holes at the roof, thus fixing them along the borehole wall. Figure 1 As shown in the diagram, the sensors deployed at the top slab are arranged obliquely. This arrangement allows for the monitoring of both horizontal disturbances and vertical settlement, thereby enabling the monitoring of displacement and strain curves.

[0067] In some embodiments, the multi-directional stress grid is fixed to the wall surface of the pillar and / or roof using prestressed anchor bolts. One end of the prestressed anchor bolt is inserted into the wall through the grid unit, and the other end of the prestressed anchor bolt is connected to an end plate to fix the grid to the wall surface. That is, during the internal drilling process, the prestressed anchor bolt is inserted into the grid unit in a "nail" manner, and the grid assembly is fixed by the end plate, realizing the combined and coordinated monitoring of parameters such as displacement, stress, and temperature inside and outside the pillar-roof rock mass.

[0068] In some embodiments, the interface of each grid sensor fiber optic bus conforms to the 64-core fiber optic interface standard. Both the grid sensor fiber optic bus used for external monitoring and the 12-core connecting fiber optic cable used for internal monitoring are connected to the mine safety monitoring substation to achieve synchronous data acquisition, recording, and transmission, and to collaboratively monitor parameters such as displacement, velocity, acceleration, stress, strain, and temperature within the rock pillar-roof structure. The monitoring substation includes modules such as a fiber optic modem, CPU, memory, fiber optic data output port, power supply, and indicator lights.

[0069] Using fiber optic data output ports, the pillar-roof monitoring substation is connected to the monitoring substations of the "six major systems" for mine safety and disaster prevention and the fiber optic ring network, and the data is transmitted to the surface dispatch platform.

[0070] The underground pillar-roof system monitoring network connects the terminal server to the surface data acquisition and processing server, records curves of displacement deformation, stress and temperature changes, and synchronously analyzes measured data on the surface and inside of the pillar-roof rock mass, providing three-dimensional visualization for early warning and evaluation of the stability of the deep-well pillar-roof system.

[0071] The following formula is used as the basis for judging whether the system has an early warning:

[0072]

[0073]

[0074] Where: ε iThe strain value at a single point of the flexible multi-directional stress grid is obtained through... Perform calculations; λ B The center wavelength of the flexible multi-directional stress grid; Δλ B The change in the center wavelength of the flexible multi-directional stress grid; Λ is the thermal expansion coefficient of the optical fiber; Λ is the period of the Bragg grating. The thermo-optic coefficient of the optical fiber; n is the effective elastic-optical coefficient of the optical fiber; eff The effective refractive index of the fiber core is given by E; ΔT is the temperature change; E is the effective refractive index of the fiber core. B S represents the Young's modulus of the corresponding optical fiber material. 外 The correction factor for strain when laying optical fibers on the rock surface; P0 is the preload after fiber installation; N is the number of fiber segment measuring points selected for calculating strain at a certain location; δ d It is the dynamic tensile strength of the rock mass at the location of the pillar-roof support system. The instability and failure of the rock mass is based on the stress on the rock mass exceeding the dynamic tensile strength of the rock mass.

[0075] Using data from internal and external monitoring, the strain and stress values ​​of the pillar-roof system are calculated using the following formula. The N value is selected as 20 based on the small-distance distribution characteristics of the fiber optic grating monitoring points; that is, the average of the data from 20 adjacent monitoring points is used as the calculated rock mass stress value for that area. Based on the on-site fiber optic installation and usage, the center wavelength λ of the fiber optic grating can be determined. B The change in the center wavelength of the fiber grating is Δλ, which is 1550.116 nm. B Because the optical fibers at various internal and external measuring points change with strain and temperature, the following formula is used as the basis for judging whether the system is experiencing an early warning:

[0076]

[0077]

[0078] Where: ε i The strain value at a single point of the flexible multi-directional stress grid is obtained through... Perform calculations; λ B The center wavelength of the flexible multi-directional stress grid; Δλ B The change in the center wavelength of the flexible multi-directional stress grid; Λ is the thermal expansion coefficient of the optical fiber; Λ is the period of the Bragg grating. The thermo-optic coefficient of the optical fiber; n is the effective elastic-optical coefficient of the optical fiber; eff The effective refractive index of the fiber core is given by E; ΔT is the temperature change; E is the effective refractive index of the fiber core. B S represents the Young's modulus of the corresponding optical fiber material. 外The correction factor for the strain of the fiber optic cable laid on the rock surface is determined based on the monitored lithology and installation conditions; P0 is the pre-tension force after the fiber optic cable is installed; 20 is the number of fiber optic segment measuring points selected for calculating the strain at a certain location.

[0079] In some embodiments, 20 monitoring points are selected at both the inner and outer optical fibers to monitor the change in the center wavelength of the fiber grating at each of the 20 monitoring points. When the temperature in the fiber increases from an initial temperature of 25°C to 27.5°C, the effective refractive index of the fiber changes due to the increased temperature, resulting in a change in the center wavelength of the fiber grating. By collecting the detected center wavelengths of the inner and outer fiber gratings, the change in the center wavelength of the fiber grating inside the outer grating is obtained. Change in center wavelength of fiber optic grating attached inside the anchor bolt Then substitute it into the formula In the sensor parameters used, the optical fiber's thermal expansion coefficient α = 24.3 pm / ℃, the optical fiber's thermo-optical coefficient ξ = 28.9 pm / ℃, and the optical fiber's effective elastic-optical coefficient ρ e =0.8. The strain values ​​of individual fiber optic gratings at each measuring point, both internal and external, were obtained through calculation.

[0080]

[0081] After calculating the single-point strain value of the fiber optic grating at each measuring point using the formula, the single-point strain value of the fiber optic grating is then substituted into the formula. Since silica constitutes a large proportion of the optical fiber material, the Young's modulus of the optical fiber is taken as 72.6 GPa, based on the Young's modulus of silica. A correction factor of 0.75 is used for the strain of the optical fiber laid on the rock mass surface. The stress on the rock mass is calculated to be δ = 150.05 MPa using the formula. The dynamic tensile strength δ of the monitored rock mass is then obtained experimentally. d The stress ranges from 120 to 180 MPa. The criterion for rock mass instability and failure is whether the stress on the rock mass exceeds its maximum dynamic tensile strength. Therefore, the stress on the rock mass is δ = 150.05 MPa. d The stress between these values ​​did not exceed the maximum dynamic tensile strength, so no warning was triggered. However, if the stress on the rock mass exceeded the maximum dynamic tensile strength, a warning would be triggered.

[0082] The above specific embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A monitoring system of a pillar-roof support system, comprising a mine safety monitoring substation, a connecting optical cable, characterized in that, Also include flexible multidirectional stress grid and prestressed anchor rod; The flexible multidirectional stress grid is laid on the surface of the pillar and / or the wall surface of the roof supported by the pillar; the flexible multidirectional stress grid comprises a plurality of intersecting hollow ribs, the ribs are flexible, the ribs comprise horizontal ribs, vertical ribs and inclined ribs, the horizontal ribs, the vertical ribs and the inclined ribs are internally hollow and communicated with each other at the intersection, the horizontal ribs, the vertical ribs and the inclined ribs are provided with flexible distributed optical fiber sensors, and the flexible distributed optical fiber sensors in the ribs are connected with the mine safety monitoring substation through a grid sensor optical cable bus; The prestressed anchor rod is arranged in the interior of the pillar and / or the interior of the roof; the flexible distributed optical fiber sensors are symmetrically arranged on the inner side of the prestressed anchor rod along the axis, so that the flexible distributed optical fiber sensors change synchronously with the axial stress of the anchor rod; the flexible distributed optical fiber sensors in the prestressed anchor rod are connected to the mine safety monitoring substation through a connecting optical cable; The mine safety monitoring substation simultaneously collects monitoring data in the flexible multidirectional stress grid and the prestressed anchor rod, and transmits the data to the ground dispatching platform for early warning of the stability of the pillar-roof support system.

2. The monitoring system according to claim 1, wherein the local surface dispatching platform determines that the pillar-roof support system issues a warning when the following formula is established: In the formula: is the strain value of the flexible multidirectional stress grid single point, which is calculated by ; respectively refer to the strain value of the i measuring point of the fiber Bragg grating in the external grid and the strain value of the j measuring point of the fiber Bragg grating attached inside the anchor rod; is the central wavelength of the flexible multidirectional stress grid; is the central wavelength change of the flexible multidirectional stress grid; is the thermal expansion coefficient of the optical fiber; is the Bragg grating period; is the thermo-optic coefficient of the optical fiber; is the effective elasto-optic coefficient of the optical fiber; is the effective refractive index of the optical fiber core region; is the temperature change; is the corresponding Young's modulus of the optical fiber material; is the correction coefficient of the optical fiber strain laid on the rock mass surface; is the pre-tension after the installation of the optical fiber; is the number of measuring points of the optical fiber segment selected for calculating the strain at a certain position; is the dynamic tensile strength of the rock mass where the pillar-roof support system is located, and the instability and failure of the rock mass is subject to the criterion that the stress on the rock mass exceeds the dynamic tensile strength of the rock mass.

3. The monitoring system according to claim 2, wherein each optical fiber is fitted with a temperature compensation component outside the optical fiber before reaching the mine safety monitoring substation, and the temperature compensation component is sleeved on the optical fiber to correct the monitored microseismic data.

4. The monitoring system according to claim 3, wherein the parameters monitored by the mine safety monitoring substation include one or more of the internal and wall surface displacement, speed, acceleration, stress, strain and temperature of the pillar and / or the roof; and the mine safety monitoring substation comprises an optical fiber modem module, a CPU, a memory, an optical fiber data output port, a power supply and an indicator light module.

5. The monitoring system according to claim 1, wherein the fixation of the multidirectional stress grid on the wall surface of the pillar and the roof is also achieved by using the prestressed anchor rod, one end of the prestressed anchor rod is inserted into the wall through the grid unit, and the other end of the prestressed anchor rod is connected with an end plate to fix the grid on the wall surface.

6. The monitoring system according to claim 5, wherein the smallest repeating unit of the flexible multidirectional stress grid is a triangle surrounded by the horizontal ribs, the vertical ribs and the inclined ribs.

7. The monitoring system according to claim 1, wherein the mine pillar-roof monitoring substation is connected to the mine safety and risk monitoring substation and the optical fiber ring network of the "six major systems" of the mine safety and risk monitoring system through the optical fiber data output port, and the data is transmitted to the ground dispatching platform.

8. The monitoring system according to claim 1, wherein the connecting optical cable is a 12-core optical fiber cable, and each connecting optical cable is connected with six prestressed anchor rods, so that the data of the six adjacent prestressed anchor rods can be simultaneously monitored.

9. The monitoring system according to claim 1, wherein the grating material is hollow Cr2MoV alloy steel, the grating longitudinal ribs and transverse ribs have a diameter of 5-6 mm, the inclined ribs have a diameter of 3.5-4 mm, the hollow diameter of each rib is 1.5-2 mm, and the length of the grating unit rib is 6-10 cm; the multi-directional stress grating transverse ribs are internally provided with a flexible distributed optical fiber sensor, a horizontal composite optical fiber sensor rib is arranged every 3-5 ribs, an inclined composite optical fiber sensor rib is arranged every 2-4 inclined ribs, and the optical fiber in a single grating assembly is concentrated at one end of the longitudinal rib to the middle of the grating assembly as a grating sensor optical cable bus total interface.

10. A monitoring method using the monitoring system of the pillar-roof support system according to any one of claims 1-9, comprising the following steps: S1: laying the flexible multi-directional stress grating on the surface of the pillar and / or the wall surface of the roof supported by the pillar; S2: arranging the pre-stressed anchor rod in the interior of the pillar and / or the interior of the roof; S3: simultaneously collecting the monitoring data in the flexible multi-directional stress grating and the pre-stressed anchor rod by using the mine safety monitoring substation, and transmitting the data to the ground dispatching platform. ​ ​ ​ S4: The surface scheduling platform determines that the following formula is true, and determines that the pillar-roof support system issues a warning: In the formula: is the strain value of the flexible multidirectional stress grid single point, which is calculated by ; respectively refer to the strain value of the i measurement point of the optical fiber Bragg grating in the external grid and the strain value of the j measurement point of the optical fiber Bragg grating attached inside the anchor rod; is the central wavelength of the flexible multidirectional stress grid; is the central wavelength change of the flexible multidirectional stress grid; is the thermal expansion coefficient of the optical fiber; is the Bragg grating period; is the thermo-optic coefficient of the optical fiber; is the effective elasto-optic coefficient of the optical fiber; is the effective refractive index of the optical fiber core region; is the temperature change; is the corresponding optical fiber material Young's modulus; is the correction coefficient of the optical fiber strain laid on the rock mass surface; is the pre-tension after the optical fiber is installed; is the number of optical fiber segment measurement points selected for calculating the strain at a certain position; is the dynamic tensile strength of the rock mass where the pillar-roof support system is located, and the instability and failure of the rock mass is subject to the criterion that the stress on the rock mass exceeds the dynamic tensile strength of the rock mass.

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