An in-situ monitoring system and evaluation method for the stability of ore pillars

Abstract

The present invention discloses an in-situ monitoring system for the stability of ore pillars, which includes three parts: a roof grouting and anchoring mechanism, a roof settlement and weighting monitoring mechanism, and a circumferential deformation monitoring mechanism of ore pillars. The system realizes the effective fixation of the upper structure on the ore body roof through the internally provided inflating, grouting, and exhaust pipelines and the series-connected alarm circuit. Further, through the comprehensive cooperation of multi-sensors, jacks, and monitoring lines, the real-time measurement of the stress change amount and the self-deterioration deformation amount of the ore pillars is realized, laying a foundation for the stability evaluation of the ore pillars. Based on this system, the present invention also provides an in-situ evaluation method for the stability of ore pillars. According to the deformation-time curve and stress-time curve of the ore pillars, the stable state of the ore pillars is divided into four levels: extremely high, high, medium, and low risks, realizing the multi-index comprehensive classification and characterization of the stability of the ore pillars, and providing reference and guidance for the differential treatment of the gob ore pillar group and avoiding the occurrence of gob collapse accidents.

Description

Technical Field

[0001] The present invention relates to the technical field of underground mine disaster risk monitoring and assessment, and particularly to an in-situ monitoring system and assessment method for pillar stability. Background Art

[0002] As one of the main methods for underground mine exploitation, the open stoping method has been widely used in underground mine exploitation in the past few decades, resulting in a large number of goafs with astonishing quantity and huge area left behind. Through the evolution of time and complex geological environment, these remaining goafs have gradually become unstable factors inducing major and extremely serious mine accidents, posing a serious safety threat to the ecological restoration of the mining area and the normal production and life of nearby residents.

[0003] As the main bearing structure in the goaf, the stability of the pillar largely determines the stability of the goaf. However, restricted by the complex geological conditions of the goaf and the deterioration and rheological effects of the pillar, the current monitoring and assessment methods for pillar stability mainly focus on aspects such as pillar stress monitoring, surface subsidence measurement, and theoretical analysis, having problems such as single evaluation index, obtaining non-in-situ parameters, and ignoring the geological differences of different mining areas. There is still a lack of an in-situ monitoring system and assessment method for pillar stability based on the influence of multiple factors. In fact, the instability and failure of the pillar are affected by double disaster-causing factors, namely the roof weighting (external factor) and its own deterioration and deformation (internal factor). Therefore, it is necessary to break through the limitations of traditional single monitoring and evaluation indexes, regard the roof-pillar-floor as a complete system, comprehensively consider the influence of multiple disaster-causing factors on pillar stability, and realize the in-situ real-time monitoring and comprehensive assessment of pillar stability.

[0004] In view of this, to solve the above problems, the present invention provides an in-situ monitoring system and assessment method for pillar stability. Summary of the Invention

[0005] The present invention provides an in-situ monitoring system and assessment method for pillar stability, aiming to realize the in-situ real-time monitoring and comprehensive grading characterization of pillar stability through the in-situ monitoring system for pillar stability, so as to help ground personnel quickly and accurately master the deterioration state of the pillar, guide ground personnel to take differential treatment measures for the pillars with collapse risks in the underground goaf, and timely eliminate the hidden dangers of goaf collapse.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is:

[0007] An in-situ monitoring system for the stability of ore pillars, characterized in that the system consists of three parts: a roof grouting and anchoring mechanism, a roof settlement and weighting monitoring mechanism, and a circumferential deformation monitoring mechanism of ore pillars; the roof grouting and anchoring mechanism includes a cylindrical grouting pipe body, an annular sealing airbag, and an automatic grout stop valve; a Y-shaped grouting pipeline, an airbag inflation pipeline, and an air exhaust pipeline are arranged inside the grouting pipe body, and the automatic grout stop valve is installed at the center of the top of the grouting pipe body, and a series-connected alarm line and an air exhaust pipeline are connected below it; the roof settlement and weighting monitoring mechanism is connected below the roof grouting and anchoring mechanism, and includes a roof displacement and weighting detection structure, a power supply, a mechanical jack, and a bearing bottom plate. The mechanical jack is fixed at the center of the bearing bottom plate, and a spirit level is embedded on the bearing bottom plate. The roof displacement and weighting detection structure consists of a micro laser distance measuring sensor, an elastic pressure sensor, a limit kit, and a T-shaped force transmission rod. The micro laser distance measuring sensor and the elastic pressure sensor are installed in the groove at the lower end of the cylindrical grouting pipe. One end of the T-shaped force transmission rod passes through the limit kit and is connected to the elastic pressure sensor, and the other end with a stud is connected to the mechanical jack fixed on the bearing bottom plate. The limit kit is connected to the groove at the lower end of the grouting pipe by threads, and its internal structure matches that of the T-shaped force transmission rod. Thus, when the roof settles, the limit kit can sink together with the grouting pipe, so that the limit kit can move along the T-shaped force transmission rod; the circumferential deformation monitoring mechanism of ore pillars includes a measuring line box, a measuring line length monitoring sensor, a circumferential deformation monitoring line, and a measuring line anchor; the measuring line box is installed below the grouting pipe body and close to one side of the bottom end of the pipe body. The circumferential deformation monitoring line is stored inside the measuring line box through a wire wheel. The measuring line length monitoring sensor is installed inside the grouting pipe body, connected to the power supply, and connected to the external measuring line box. The measuring line anchor is an independent component arranged on the goaf floor for fixing the monitoring line during the monitoring process.

[0008] Furthermore, a conical opening is provided at the top end of the grouting pipe body, and spaced-apart opening isolation gaskets are arranged in a circumferential circle along the outside of the opening.

[0009] Furthermore, the automatic grout stop valve consists of an arc-shaped pressure-bearing gasket, a micro spring, a waterproof and breathable membrane, and a connecting rod with a V-shaped head. The micro spring and the waterproof and breathable membrane are respectively installed between the arc-shaped pressure-bearing gasket and the conical groove at the top end of the grouting pipe body, wherein the waterproof and breathable membrane is located outside the micro spring. The connecting rod is arranged along the central axis of the micro spring, one end is connected to the arc-shaped pressure-bearing gasket, and the other end with a V-shaped head is located in the first hollow chamber inside the grouting pipe body when there is no overlying pressure above, and automatically enters the lower second hollow chamber and is fixed when the limit pressure of the pressure-bearing gasket is reached.

[0010] Further, during the grouting process, the waterproof and breathable membrane allows air to flow freely while blocking the grout from entering the lower pipeline; an air exhaust pipeline is provided below the second hollow chamber, and the air in the upper closed space in the borehole enters the exhaust channel through the waterproof and breathable membrane and is discharged from the exhaust holes on the grouting pipe.

[0011] Further, the series-connected alarm circuit consists of a wire, an indicator light with a power source, and an electrode groove below the second hollow chamber. The electrode groove is directly opposite to the central axis of the connecting rod, and a conductor is also installed below the V-shaped head of the connecting rod. When the V-shaped head completely enters the second hollow chamber, the conductor enters the electrode groove accordingly, and the alarm circuit below is connected, and the indicator light on the grouting pipe body lights up to indicate that the grouting is completed.

[0012] Further, a groove is circumferentially provided on the grouting pipe body near the bottom end side, and the annular sealing airbag is located in the groove and is connected to the airbag inflation pipeline inside the grouting pipe body. The grouting holes of the Y-shaped grouting pipeline, the exhaust holes of the air exhaust pipeline, the inflation holes of the airbag inflation pipeline, the indicator lights of the alarm circuit, and the measuring line box are all located below the annular sealing airbag, and only the two slurry outlet holes of the Y-shaped grouting pipeline are located above the annular sealing airbag.

[0013] Further, the elastic pressure sensor, the limit kit, the T-shaped force transmission rod, the mechanical jack, and the bearing bottom plate are all located on the central axis of the grouting pipe body. The micro laser ranging sensor is arranged in the installation hole on one side inside the groove at the lower end of the grouting pipe body, and the emitted laser shoots at the end of the T-shaped force transmission rod. The elastic pressure sensor is arranged in the central installation hole inside the groove at the lower end of the grouting pipe body.

[0014] Further, the measuring line anchor consists of an upper pipe body with a vertical diversion channel opened in the center and a lower conical head with a V-shaped diversion channel opened inside. The vertical diversion channel is connected to the V-shaped diversion channel at the junction of the conical head and the upper pipe body, and the V-shaped diversion channel communicates with the outside, and the two channel outlets are arranged on the conical surface.

[0015] The present invention also provides a method for in-situ evaluation of the stability of ore pillars, which is realized by using the above-mentioned in-situ monitoring system for the stability of ore pillars, and includes the following steps:

[0016] 1) Measure the initial vertical ground stress near the ore pillar, calculate the strength of the ore pillar according to the formula, and evaluate the initial stability of the ore pillar;

[0017] 2) Drill a hole at the junction of the top end of the ore pillar to be measured and the ore body roof, and construct a groove at the bottom of the ore pillar borehole, and clean the residual rock debris in the whole hole in advance;

[0018] 3) Place the in-situ monitoring system for pillar stability into the borehole, adjust the height through a mechanical jack to ensure that the annular sealing airbag is inside the roof borehole and other structures below the airbag are outside the roof borehole;

[0019] 4) Use the spirit level on the pressure-bearing floor to level the overall position of the system, and fix the grouting pipe body and the pressure-bearing floor respectively by grouting in the hole;

[0020] 5) After the slurry solidifies, reciprocally pull the handle of the mechanical jack to apply pressure until the pressure detected by the elastic pressure sensor is equal to the vertical stress of the rock mass measured in step 1);

[0021] 6) Pull out the monitoring wire in the cable box, arrange it downward along the circumference of the pillar closely against the pillar, and fix it on the goaf floor through the wire anchor nails;

[0022] 7) Turn on the laser distance measuring sensor and the wire length monitoring sensor, record the initial values of the sensors, and start the long-term monitoring mode;

[0023] 8) Real-time evaluate the stability of the pillar according to the changes of the stress-time curve and the circumferential deformation-time curve, and comprehensively classify the pillar stability into four levels: extremely high risk, high risk, medium risk and low risk.

[0024] Further, the specific operation of using grouting to fix the system components is as follows: Inflate the airbag through the inflation hole to seal the upper space in the hole. Subsequently, grout into the sealed space in the hole through the grouting hole until the indicator light comes on and stop grouting, and wait for the slurry to solidify. Then, grout into the groove at the bottom of the pillar borehole to fix the pressure-bearing floor.

[0025] Further, the basis for classifying the pillar stability is as follows: When both the stress-time curve and the circumferential deformation-time curve fluctuate near the initial value, it is determined that the stability of the pillar at this time is low risk; When one of the two curves fluctuates near the initial value and the other shows an upward trend (below the instability threshold), it is determined that the stability of the pillar at this time is medium risk; When one of the two curves exceeds the instability threshold and the other curve does not exceed the instability threshold or both curves show an upward trend (below the instability threshold), it is determined that the stability of the pillar at this time is high risk; When both curves exceed the instability threshold, it is determined that the stability of the pillar at this time is extremely high risk.

[0026] Beneficial effects

[0027] The in-situ monitoring system and evaluation method for pillar stability proposed by the present invention have the following three main outstanding advantages:

[0028] (1) The solution proposed by the present invention realizes the long-term monitoring of the stability of ore pillars under in-situ conditions in the goaf, breaking through the limitations of the traditional non-in-situ method of monitoring the collapse risk of the goaf through surface subsidence;

[0029] (2) Regarding the roof-ore pillar-floor as a complete system, it realizes the real-time measurement of three important parameters, namely the roof settlement amount, stress change amount, and ore pillar deformation amount. The monitoring results not only lay a foundation for the stability evaluation of the corresponding ore pillar to be measured, but also provide a reference for the stability evolution evaluation of the ore pillar group system with the ore pillar as the support unit in the surrounding area;

[0030] (3) An in-situ evaluation method for the stability of ore pillars is proposed. According to the data collected by the in-situ monitoring system for the stability of ore pillars, comprehensively considering the internal and external dual disaster-causing factors of the self-deterioration of the ore pillar and the change of roof weighting, it realizes the multi-index classification of the stability of the ore pillar, and solves the problem of ignoring the internal / external dual disaster-causing factors existing in a single evaluation index. Description of the Drawings

[0031] Figure 1 It is the external view schematic diagram of the in-situ monitoring system for the stability of ore pillars described in Embodiment 1 of the present invention;

[0032] Figure 2 It is the internal core structure and partial enlarged detail schematic diagram of the in-situ monitoring system for the stability of ore pillars described in Embodiment 1 of the present invention;

[0033] Figure 3 It is the on-site application schematic diagram of the in-situ monitoring system for the stability of ore pillars described in Embodiment 2 of the present invention;

[0034] Figure 4 It is the risk grading schematic diagram of the in-situ evaluation method for the stability of ore pillars described in Embodiment 2 of the present invention.

[0035] The marks and corresponding names in the drawings are as follows:

[0036] 1. Grouting pipe body; 101. Circumferential isolation gasket; A. Automatic grout stop valve; 201. Vent hole; 202. Vent passage; 203. Second hollow chamber; 204. First hollow chamber; 205. Link activity passage; 3. Indicator light with power supply; 301. Wire; 302. Electrode groove; 401. Grouting hole; 402. Y-shaped grouting passage; 403. Grout outlet hole; 5. Annular sealing airbag; 501. Inflation hole; 502. Inflation passage; 6. Cable box; 601. Monitoring cable; 7. Cable length monitoring sensor; 8. Power supply circuit; 9. Power supply; B. Roof displacement and abutment pressure detection structure; 10. T-shaped force transfer rod; 11. Mechanical jack; 111. Jack piston rod; 112. Jack handle; 12. Bearing bottom plate; 121. Spirit level; 131. Arc-shaped bearing gasket; 132. Micro spring; 133. Link; 134. Waterproof and breathable membrane; 135. Conductor; 14. Micro laser distance measuring sensor; 15. Elastic pressure sensor; 161. Mounting hole; 162. Lower end groove; 17. Limit kit; C. Cable anchor; 18. Upper pipe body; 181. Vertical diversion passage; 19. Lower conical head; 191. V-shaped diversion passage; 20. Grout; 21. Ore body roof; 211. Roof drilling hole; 22. Ore pillar; 221. Drilling groove; 23. Goaf floor. Detailed implementation manners

[0037] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] Here, it should also be noted that in order to avoid obscuring the present invention due to unnecessary details, only the structures and processing steps closely related to the solution of the present invention are shown in the drawings, while other details less related to the present invention are omitted.

[0039] Embodiment 1

[0040] Such as Figures 1 to 3As shown in the figure, Embodiment 1 of the present invention provides an in-situ monitoring system for the stability of ore pillars, which consists of three parts: a roof grouting and anchoring mechanism, a roof settlement and abutment pressure monitoring mechanism, and a circumferential deformation monitoring mechanism for ore pillars. The roof grouting and anchoring mechanism includes a cylindrical grouting pipe body 1, an annular sealing airbag 5, and an automatic grout stop valve A. The grouting pipe body 1 is internally provided with a Y-shaped grouting pipeline (including a grouting hole 401 opened on the grouting pipe body 1, an internal Y-shaped grouting channel 402, and two slurry outlets 403 opened on the grouting pipe body 1), an airbag inflation pipeline (including an inflation hole 501 opened on the grouting pipe body 1 and an internal inflation channel 502), and an air exhaust pipeline (including an exhaust hole 201 opened on the grouting pipe body 1 and an internal exhaust channel 202). The automatic grout stop valve A is installed at the center of the top of the grouting pipe body 1, and a series-connected alarm line and an air exhaust pipeline are connected below it. The roof settlement and abutment pressure monitoring mechanism is connected below the roof grouting and anchoring mechanism, and includes a roof displacement and abutment pressure detection structure B, a power supply 9, a mechanical jack 11, and a bearing bottom plate 12. The mechanical jack 11 is fixed at the center of the bearing bottom plate 12, and a spirit level 121 is embedded on the bearing bottom plate 12. The roof displacement and abutment pressure detection structure B consists of a micro laser distance measuring sensor 14, an elastic pressure sensor 15, a limit kit 17, and a T-shaped force transmission rod 10. The micro laser distance measuring sensor 14 is arranged in an installation hole 161 on one side in a groove 162 at the lower end of the grouting pipe, the elastic pressure sensor 15 is arranged in a central installation hole in the groove 162 at the lower end of the grouting pipe, one end of the T-shaped force transmission rod 10 passes through the limit kit and is connected to the elastic pressure sensor 15, and the other end with a stud is connected to a piston rod 111 with a threaded hole on the mechanical jack 11. The limit kit 17 is connected to the groove 162 at the lower end of the grouting pipe by threads, and its internal structure matches that of the T-shaped force transmission rod 10, so that when the roof 21 settles, the limit kit 17 can sink together with the grouting pipe, and the limit kit 17 can move along the T-shaped force transmission rod 10. The circumferential deformation monitoring mechanism for ore pillars includes a measuring wire box 6, a measuring wire length monitoring sensor 7, a circumferential deformation monitoring wire 601, and a measuring wire anchor C. The measuring wire box 6 is installed below the grouting pipe body 1 and close to one side of the bottom end of the pipe body. The circumferential deformation monitoring wire 601 is stored inside the measuring wire box 6 through a wire wheel (not shown). The measuring wire length monitoring sensor 7 is installed inside the grouting pipe body 1, connected to the power supply 9, and connected to the external measuring wire box 6. The measuring wire anchor C is an independent component arranged on the goaf floor 23 for fixing the monitoring wire 601 during the monitoring process.

[0041] Furthermore, a conical opening is provided at the top end of the grouting pipe body 1, and spacer gaskets 101 with spaced openings are arranged in a circumferential circle along the outside of the opening.

[0042] Furthermore, the automatic grout stop valve A is composed of an arc-shaped pressure-bearing gasket 131, a micro spring 132, a connecting rod 133 with a V-shaped head, and a waterproof breathable membrane 134. The micro spring 132 and the waterproof breathable membrane 134 are respectively installed between the arc-shaped pressure-bearing gasket 131 and the conical groove at the top of the grouting tube body 1, wherein the waterproof breathable membrane 134 is located outside the micro spring 132. The connecting rod 133 is arranged along the central axis of the micro spring 132, one end of which is connected to the arc-shaped pressure-bearing gasket 131, and the other end with a V-shaped head is located in the first hollow chamber 204 in the grouting tube body 1 when there is no pressure from above, and automatically enters the second hollow chamber 203 below and is fixed when subjected to the limit pressure of the pressure-bearing gasket 131.

[0043] Furthermore, the waterproof and breathable membrane 134 allows air to flow freely during the grouting process and blocks the slurry 20 from entering the lower pipeline; an air exhaust pipeline is opened below the second hollow chamber 203, and the air in the upper enclosed space in the drilled hole enters the exhaust channel 202 from the waterproof and breathable membrane 134 and is discharged from the exhaust hole 201 on the grouting pipe.

[0044] Furthermore, the series alarm circuit is composed of a conductor 301, an indicator light 3 with a power supply, and an electrode groove 302 located below the second hollow chamber 203. The electrode groove 302 is directly opposite to the central axis of the connecting rod 133. A conductor 135 is also installed below the V-shaped head of the connecting rod 133. When the V-shaped head of the connecting rod 133 completely enters the second hollow chamber 203, the conductor 135 enters the electrode groove 302, the alarm circuit below is connected, and the indicator light 3 on the grouting pipe body 1 lights up, indicating that the grouting is completed.

[0045] Furthermore, the grouting pipe body 1 is circumferentially provided with a groove on one side near the bottom end, the annular sealing airbag 5 is located in the groove and is connected to the airbag inflation pipeline inside the grouting pipe body, the grouting hole 401 of the Y-shaped grouting pipeline, the exhaust hole 201 of the air exhaust pipeline, the inflation hole 501 of the airbag inflation pipeline, the indicator light 3 of the alarm circuit and the measuring line box 6 are all located below the annular sealing airbag 5, and only the two slurry outlet holes 403 of the Y-shaped grouting pipeline are located above the annular sealing airbag 5.

[0046] Furthermore, the elastic pressure sensor 15, the limit kit 17, the T-shaped force transmission rod 10, the mechanical jack 11 and the pressure-bearing base plate 12 are all located on the central axis of the grouting pipe body 1, and the micro laser ranging sensor 14 is arranged in a mounting hole 161 on one side inside the groove at the lower end of the grouting pipe body, and the emitted laser is projected onto the end of the T-shaped force transmission rod 10.

[0047] Furthermore, the survey line anchor C is composed of an upper pipe body 18 with a vertical diversion channel 181 opened at the center and a lower conical head 19 with a V-shaped diversion channel 191 opened inside. The vertical diversion channel 181 is connected to the V-shaped diversion channel 191 at the junction of the conical head 19 and the upper pipe body 18. The V-shaped diversion channel 191 is communicated with the outside, and the two channel outlets are arranged on the conical surface.

[0048] Specifically, the working process of this application is as follows: During the installation of the in-situ monitoring system for pillar stability, first level the whole system through the spirit level 121 on the pressure-bearing bottom plate 12, and then use the annular sealing airbag 5 to position and seal the upper structure of the system inside the borehole 211, creating conditions for grouting. The grout 20 is injected from the grouting hole 401, flows out from the grout outlet 403 through the Y-shaped grouting channel 402, and gradually fills the enclosed borehole space. During the grouting process, the function of the waterproof and breathable membrane 134 is to allow air to circulate freely while blocking the grout 20 from entering the lower pipeline. Therefore, the air in the upper enclosed space in the borehole 211 enters the exhaust channel 202 through the waterproof and breathable membrane 134 and is discharged from the exhaust hole 201, thus ensuring the complete filling of the enclosed space in the borehole with the grout 20. When the enclosed space in the borehole is filled with the grout 20, the pressure above the arc-shaped pressure-bearing gasket 131 continuously increases, causing the micro spring 132 to be compressed. When the compression limit is reached, the connecting rod 133 is pushed from the first hollow chamber 204 into the second hollow chamber 203, and the conductor 135 installed at the top of the connecting rod 133 enters the electrode groove 302, and the series alarm circuit is connected, and the indicator light 3 on the grouting pipe body 1 lights up, indicating that the grouting is completed. After that, grout is injected into the groove 221 at the bottom of the borehole 211 to complete the fixation of the pressure-bearing bottom plate 12 on the pillar 22. In addition, by injecting grout into the upper pipe body 18 of the survey line anchor C, the grout 20 is diverted from the vertical diversion channel 181 through the V-shaped diversion channel 191 and flows into the gap between the survey line anchor C and the rock mass of the goaf floor 23. After filling and solidifying, the purpose of firmly fixing the survey line anchor C is achieved, realizing the stable binding of the monitoring line 601 on the goaf floor 23.

[0049] The principle of evaluating the stability of the ore pillar in this application is as follows: During the monitoring process of the system, the grouting pipe body 1 and the ore body roof 21 form an integral whole. The grouting pipe body 1 descends as the ore body roof 21 subsides. The elastic pressure sensor 15 undergoes elastic deformation and monitors the change in the roof stress. The micro laser ranging sensor 14 measures the deformation of the elastic pressure sensor 15 in real time and further converts it into the subsidence of the ore body roof 21. As time goes by and the external environment changes, when the ore pillar 22 undergoes deterioration deformation, ore stripping will occur on the side wall of the ore pillar 22, resulting in a change in the length of the monitoring line 601. The line length monitoring sensor 7 located inside the grouting pipe body 1 records the change in the length of the monitoring line 601 in real time, thereby obtaining the deformation-time curve of the ore pillar 22. Finally, the stability of the ore pillar is evaluated by recording and comprehensively analyzing the stress-time curve and deformation-time curve of the ore pillar.

[0050] Embodiment 2

[0051] Embodiment 2 of the present invention provides an in-situ evaluation method for the stability of an ore pillar, as Figure 4 shown, which is implemented by using the in-situ monitoring system for the stability of the ore pillar in Embodiment 1, and includes the following steps:

[0052] 1) Measure the initial vertical ground stress near the ore pillar 22, record the initial vertical stress as σ0, calculate the strength of the ore pillar 22 according to the formula, and evaluate the initial stability of the ore pillar 22;

[0053] 2) Construct a drill hole 211 at the junction of the top of the ore pillar 22 to be measured and the ore body roof 21, and construct a groove 221 at the bottom of the drill hole 211, and clean the residual rock debris inside the entire drill hole 211 in advance;

[0054] 3) Place the in-situ monitoring system for the stability of the ore pillar into the drill hole 211, adjust the height through the mechanical jack 11 to ensure that the annular sealing airbag 5 is inside the roof drill hole 211, and other structures below the airbag 5 are outside the roof drill hole 211;

[0055] 4) Use the spirit level 121 on the pressure-bearing bottom plate 12 to level the overall position of the system, and fix the grouting pipe body 1 and the pressure-bearing bottom plate 12 respectively by in-hole grouting;

[0056] 5) After the slurry 20 solidifies, reciprocally pull the handle 112 of the mechanical jack 11 to apply pressure until the pressure detected by the elastic pressure sensor 15 is equal to the rock mass vertical stress σ0 measured in step 1);

[0057] 6) Pull out the monitoring line 601 in the wire box 6, arrange it circumferentially downward around the ore pillar 22 and closely attach it to the ore pillar 22, and fix it on the goaf floor 23 through the wire anchor C;

[0058] 7) Turn on the laser ranging sensor 14 and the measuring line length monitoring sensor 7, record the initial values of the sensors, and start the long-term monitoring mode;

[0059] 8) Evaluate the stability of the ore pillar 22 in real time according to the changes of the stress-time curve and the circumferential deformation-time curve, and comprehensively classify the stability of the ore pillar into four levels: extremely high risk, high risk, medium risk, and low risk.

[0060] Furthermore, the following principles can be referred to for selecting the strength calculation formula of the ore pillar 22:

[0061] ① When there is uniaxial compressive strength (σ p ) data of the unit cube specimen taken from the ore pillar 22, the strength calculation formula of the ore pillar 22 (S p ) can be selected as:

[0062]

[0063] In the formula, S p is the strength of the ore pillar (MPa); w is the width of the ore pillar (m); h is the height of the ore pillar (m); n is the ore pillar shape factor. When the width-height ratio w / h ≥ 5, n takes 1.4, and when w / h < 5, n takes 1.0; σ p is the uniaxial compressive strength (MPa) of the cube specimen taken from the ore pillar.

[0064] ② When there is no uniaxial compressive strength (σ p ) data of the unit cube specimen taken from the ore pillar 22, the strength calculation formula of the ore pillar 22 (S p ) can be selected as:

[0065]

[0066] It should be noted that due to the irregularity and randomness of the ore pillar contour shape, the width of the ore pillar can be replaced by the equivalent width calculated by the hydraulic radius:

[0067]

[0068] In the formula, A p is the cross-sectional area of the ore pillar (m 2 ); C p is the cross-sectional perimeter of the ore pillar (m).

[0069] Furthermore, according to the ore pillar instability theory, that is, when the stress of the roof rock layer borne by the ore pillar exceeds the strength limit of the ore pillar, the ore pillar becomes unstable. Therefore, the calculated ore pillar strength S p is used as the stress threshold for the instability of the ore pillar 22.

[0070] Furthermore, the overall radial deformation of the ore pillar 22 caused by its own deterioration can be monitored by the measuring line length monitoring sensor 7. Since the local deterioration deformation of the ore pillar 22 over time is random, it is difficult to calculate the threshold value of its deterioration deformation theoretically. Therefore, this value is recommended to be determined comprehensively based on a large number of on-site measured data and the geological environment conditions of the goaf.

[0071] Furthermore, as Figure 4 shown, when classifying the stability of the ore pillar by comprehensively considering the roof weighting monitoring situation (ore pillar stress-time curve) and the self-deterioration deformation situation of the ore pillar (ore pillar deformation amount-time curve), the classification principle is as follows: when both the stress-time curve and the circumferential deformation amount-time curve fluctuate near the initial value, the stability of the ore pillar at this time is determined to be of low risk; when one of the two curves fluctuates near the initial value and the other shows an upward trend (below the instability threshold), the stability of the ore pillar at this time is determined to be of medium risk; when one of the two curves exceeds the instability threshold and the other curve does not exceed the instability threshold or both curves show an upward trend (below the instability threshold), the stability of the ore pillar at this time is determined to be of high risk; when both curves exceed the instability threshold, the stability of the ore pillar at this time is determined to be of extremely high risk. According to the stability classification of different ore pillars and comprehensively considering the overall distribution of the stability of the ore pillars in the goaf, differential treatment measures can be taken for the ore pillar group in the goaf, so as to avoid the occurrence of goaf collapse disasters in a timely manner.

[0072] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Any equivalent structure or equivalent transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be included in the patent protection scope of the present invention by the same token.

Claims

1. An in-situ monitoring system for pillar stability, characterized in that, The system consists of three parts: a roof grouting and anchoring mechanism, a roof settlement and abutment pressure monitoring mechanism, and a pillar circumferential deformation monitoring mechanism; the roof grouting and anchoring mechanism includes a cylindrical grouting pipe body, an annular sealing airbag, and an automatic grout stop valve. A Y-shaped grouting pipeline, an airbag inflation pipeline, and an air exhaust pipeline are provided inside the cylindrical grouting pipe body. The automatic grout stop valve is installed at the center of the top of the cylindrical grouting pipe body, and a series-connected alarm circuit and an air exhaust pipeline are connected below it; the roof settlement and abutment pressure monitoring mechanism is connected below the roof grouting and anchoring mechanism and includes a roof displacement and abutment pressure detection structure, a power supply, a mechanical jack, and a bearing bottom plate. The mechanical jack is fixed at the center of the bearing bottom plate, and a spirit level is embedded in the bearing bottom plate. The roof displacement and abutment pressure detection structure consists of a micro laser distance measuring sensor, an elastic pressure sensor, a limit kit, and a T-shaped force transmission rod. The micro laser distance measuring sensor and the elastic pressure sensor are installed in the lower groove of the cylindrical grouting pipe body. One end of the T-shaped force transmission rod passes through the limit kit and is connected to the elastic pressure sensor, and the other end with a stud is connected to the mechanical jack fixed on the bearing bottom plate. The limit kit is connected to the lower groove of the cylindrical grouting pipe body by threads, and its internal structure matches that of the T-shaped force transmission rod; the pillar circumferential deformation monitoring mechanism includes a measuring line box, a measuring line length monitoring sensor, a circumferential deformation monitoring line, and a measuring line anchor. The measuring line box is installed on one side near the bottom end of the cylindrical grouting pipe body. The circumferential deformation monitoring line is stored inside the measuring line box through a wire wheel. The measuring line length monitoring sensor is installed inside the cylindrical grouting pipe body, connected to the power supply, and connected to the external measuring line box. The measuring line anchor is an independent component arranged on the goaf floor for fixing the circumferential deformation monitoring line during the monitoring process.

2. The in-situ monitoring system for pillar stability according to claim 1, characterized in that, A conical opening is provided at the top end of the cylindrical grouting pipe body, and spacer gaskets with spaced openings are arranged in a circle along the circumferential direction of the pipe body outside the opening.

3. The in-situ monitoring system for pillar stability according to claim 1, characterized in that, The automatic grout stop valve consists of an arc-shaped pressure-bearing gasket, a micro spring, a waterproof and breathable membrane, and a connecting rod with a V-shaped head. The micro spring and the waterproof and breathable membrane are respectively installed between the arc-shaped pressure-bearing gasket and the conical groove at the top of the cylindrical grouting pipe body. Among them, the waterproof and breathable membrane is located outside the micro spring. The connecting rod is arranged along the central axis of the micro spring, one end is connected to the arc-shaped pressure-bearing gasket, and the other end with a V-shaped head is located in the first hollow chamber inside the cylindrical grouting pipe body when there is no overlying pressure above, and automatically enters the lower second hollow chamber and is fixed when the ultimate pressure of the pressure-bearing gasket is reached.

4. The in-situ monitoring system for pillar stability according to claim 3, wherein The waterproof and breathable membrane allows air to flow freely during the grouting process and blocks the grout from entering the lower pipeline; an air exhaust pipeline is provided below the second hollow chamber. The air in the upper closed space in the borehole enters the exhaust passage from the waterproof and breathable membrane and is discharged from the exhaust hole on the cylindrical grouting pipe body.

5. The in-situ monitoring system for pillar stability according to claim 1, characterized in that, The series alarm circuit consists of a wire, an indicator light with a power supply and an electrode groove located below the second hollow chamber; the electrode groove is directly opposite to the central axis of the connecting rod, and a conductor is also installed below the V-shaped head of the connecting rod. When the V-shaped head completely enters the second hollow chamber, the conductor enters the electrode groove, the alarm circuit below is connected, and the indicator light on the cylindrical grouting pipe body lights up, indicating that the grouting is completed.

6. The in-situ monitoring system for the stability of ore pillars according to claim 1, characterized in that, A groove is circumferentially arranged on one side near the bottom end of the cylindrical grouting pipe body. The annular sealing airbag is located in the circumferentially arranged groove and is connected with the airbag inflation pipeline inside the cylindrical grouting pipe body. The grouting holes of the Y-shaped grouting pipeline, the exhaust holes of the air exhaust pipeline, the inflation holes of the airbag inflation pipeline, the indicator lights of the alarm circuit and the measuring line box are all located below the annular sealing airbag. Only the two grouting holes of the Y-shaped grouting pipeline are located above the annular sealing airbag.

7. The in-situ monitoring system for pillar stability according to claim 1, characterized in that, The survey line anchor consists of an upper tube body with a vertical diversion channel in the center and a lower conical head with a V-shaped diversion channel inside. The vertical diversion channel and the V-shaped diversion channel are connected at the junction of the conical head and the upper tube body. The V-shaped diversion channel is connected to the outside world, and two channel outlets are arranged on the cone surface.

8. A method for in-situ assessment of the stability of ore pillars, which is implemented by using the in-situ monitoring system for the stability of ore pillars according to any one of claims 1-7, characterized in that, The following steps are involved: 1) Measure the initial vertical ground stress near the pillar, calculate the pillar strength according to the formula, and evaluate the initial stability of the pillar; 2) Drill a hole at the junction of the top of the pillar to be tested and the roof of the ore body, and construct a groove at the bottom of the pillar hole to clean up the residual rock cuttings in the entire borehole in advance; 3) Place the pillar stability in-situ monitoring system into the borehole, and adjust the height using a mechanical jack to ensure that the annular sealing airbag is located inside the roof borehole and other structures below the airbag are located outside the roof borehole; 4) Use the level bubble on the pressure bottom plate to level the overall position of the system, and fix the cylindrical grouting pipe body and the pressure bottom plate by grouting into the borehole and the groove at the bottom of the borehole; 5) After the slurry solidifies, the handle of the mechanical jack is reciprocated to apply pressure until the pressure detected by the elastic pressure sensor is equal to the vertical stress of the rock mass measured in step 1); 6) Pull out the circumferential deformation monitoring line in the measuring line box, arrange it around the pillar downward and close to the pillar, and fix it on the floor of the goaf with the measuring line anchors; 7) Turn on the micro laser ranging sensor and line length monitoring sensor, record the initial value of the sensor, and start the long-term monitoring mode; 8) The stability of the pillars is evaluated in real time based on the changes in the stress-time curve and the circumferential deformation-time curve, and the pillar stability is comprehensively divided into four levels: extremely high risk, high risk, medium risk and low risk.

9. The in-situ evaluation method for pillar stability according to claim 8, wherein The specific operation of using grouting to fix the system components is as follows: inflate the airbag through the inflation hole to seal the upper space in the borehole, then inject grout into the enclosed space in the borehole through the grouting hole until the indicator light comes on and stop grouting, wait for the slurry to solidify, and then inject grout into the groove at the bottom of the pillar borehole to fix the pressure base plate.

10. The in-situ evaluation method for pillar stability according to claim 8, characterized in that, The basis for classifying the stability of ore pillars is as follows: When both the stress-time curve and the circumferential deformation-time curve fluctuate near the initial value, the stability of the ore pillar at this time is determined to be of low risk; when one of the two curves fluctuates near the initial value and the other shows an upward trend but is lower than the instability threshold, the stability of the ore pillar at this time is determined to be of medium risk; when one of the two curves exceeds the instability threshold and the other curve does not exceed the instability threshold, or both curves show an upward trend but are lower than the instability threshold, the stability of the ore pillar at this time is determined to be of high risk; when both curves exceed the instability threshold, the stability of the ore pillar at this time is determined to be of extremely high risk.

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