Method for monitoring time-space evolution law of three zones of overburden rock in stope based on distributed optical fiber

Abstract

The application discloses a method for monitoring time-space evolution law of overburden rock three zones of a stope based on distributed optical fiber, and belongs to the technical field of coal mine safety mining. The method comprises the following steps: determining required drilling parameters according to field geological conditions and damage characteristics of the overburden rock of the stope; setting drilling distribution positions, the drillings are divided into two groups, and the distribution directions of the two groups of drillings are parallel and perpendicular to the tendency of the working face; drilling according to the drilling parameters and the drilling distribution positions, and installing an optical fiber monitoring station at each drilling; grouting and sealing the drillings; monitoring by using the optical fiber monitoring station, obtaining overburden rock strain data, and analyzing the data to obtain the time-space evolution law of the overburden rock three zones with coal seam mining; compared with the prior art which is limited to detecting the development of the overburden rock three zones at a specific time and a specific point, the application can monitor the development height and development form of the overburden rock three zones on the tendency and the tendency of the working face in the process of coal seam mining, and obtain the time-space evolution law of the overburden rock three zones with coal seam mining.

Description

Technical Field

[0001] This invention belongs to the field of coal mine safety mining technology, specifically involving a method for monitoring the spatiotemporal evolution of the three overburden zones in a mining area based on distributed optical fiber. Background Technology

[0002] The migration and destruction of the overlying strata after underground coal seam mining is the root cause of a series of mine disasters and environmental problems, such as underground mine pressure manifestation, mine water inrush, and surface subsidence. Therefore, conducting research on the evolution of the three overlying strata after coal seam mining is of great guiding significance for safe and efficient coal mine production and environmental protection in mining areas.

[0003] Currently, the height of the three zones of overburden in the goaf of a working face is typically determined by drilling specialized observation boreholes on the surface and using methods such as borehole flushing fluid loss measurement or borehole television observation. The borehole flushing fluid loss measurement method uses boreholes drilled from the surface into the coal seam roof. By analyzing the flushing fluid consumption in each section and phenomena such as drill bit loss, stuck drill bit, and air leakage during drilling, the boundaries of the overburden failure zones are determined, thus obtaining the height of the three zones. The borehole television observation method involves placing a borehole sight in the borehole after drilling to directly observe the development of fractures within the borehole to determine the height of the three zones. However, to ensure mine safety, these methods require immediate sealing of the borehole after observation, thus only allowing for one-time overburden zone data collection and preventing multiple monitoring.

[0004] Existing methods still have certain shortcomings in detecting the height of the three overburden zones. They are often limited to detecting the development of the three overburden zones at a specific time and location, and cannot reveal the spatiotemporal evolution of overburden damage under mining disturbance. Therefore, the proposed method based on distributed optical fiber monitoring of the spatiotemporal evolution of the three overburden zones in the mining area has important practical significance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, a method based on distributed optical fiber for monitoring the spatiotemporal evolution of the three zones of overburden in mining areas is provided.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] The method for monitoring the spatiotemporal evolution of the three zones of overburden in a mining area based on distributed optical fiber includes the following steps:

[0008] The required borehole parameters are determined based on the on-site geological conditions and the characteristics of overlying rock damage in the mining area;

[0009] The drilling locations are set, and the drilling is divided into two groups. The distribution direction of the two groups of drilling is parallel and perpendicular to the working face.

[0010] Drilling is carried out according to the drilling parameters and the location of the boreholes, and a fiber optic monitoring station is installed at each borehole.

[0011] Grouting and sealing of the borehole;

[0012] By using fiber optic monitoring stations to monitor and obtain overburden strain data, and by analyzing the data, the spatiotemporal evolution of the three overburden zones during coal seam mining was obtained.

[0013] Furthermore, the drilling parameters include: inclination angle, hole depth, hole diameter, number of holes, and hole spacing.

[0014] Furthermore, the drilling angle is 90 degrees, the hole diameter is 50-90 mm, and the number of holes is 5.

[0015] Furthermore, three of the boreholes are equidistantly distributed along the working face dip; the other two boreholes are arranged perpendicular to the working face dip and are located on the center line of the working face dip.

[0016] Furthermore, the distance between the three boreholes, which are equidistant from each other along the working face, is one-quarter of the working face inclination length.

[0017] Furthermore, the fiber optic monitoring station includes an optical fiber, a protective box located at the top of the borehole, and a steel wire rope; the first end of the optical fiber is placed inside the protective box, the tail end of the optical fiber is fixed with a counterweight guide, and the end of the steel wire rope is also fixed to the counterweight guide.

[0018] Furthermore, the optical fiber is a metal-based cable-like strain sensing optical cable with an internal steel strand reinforcement structure.

[0019] Furthermore, a hollow grouting drill rod is installed in the borehole for grouting and sealing; the method of sealing the borehole section by section by lifting the hollow grouting drill rod is adopted. The grouting and sealing of the borehole begins when the hollow grouting drill rod is 5m above the bottom of the hole. The cement slurry outlet at the bottom of the hollow grouting drill rod is not higher than the cement slurry surface in the hole, and the sealing height of each section is not greater than 50m at one time.

[0020] Furthermore, the protective box is equipped with a single-ended distributed fiber optic strain demodulator, which is connected to an optical fiber.

[0021] Furthermore, during the data analysis process, based on the obtained fiber optic strain data, the strain change curve of the fiber optic monitoring station as coal seam mining is obtained. Combined with the on-site stratigraphic distribution characteristics, the spatiotemporal evolution law of the three overburden zones as coal seam mining is summarized.

[0022] The beneficial effects of this invention are:

[0023] 1. This invention uses ground drilling, which facilitates drilling construction and data monitoring.

[0024] 2. This invention describes an analysis method for strain data obtained from fiber optic monitoring, which facilitates accurate determination of the development height of the three overburden zones.

[0025] 3. Compared with traditional technologies that are limited to detecting the development of the three overburden zones at a specific time and location, this invention can monitor the development height and morphology of the three overburden zones on the strike and dip of the working face during coal seam mining, and obtain the spatiotemporal evolution law of the three overburden zones with coal seam mining. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram showing the location of the fiber optic monitoring stations;

[0028] Figure 2 This is a schematic diagram of a fiber optic monitoring station;

[0029] Figure 3 This is a schematic diagram showing the dip direction of the working face before the coal seam is mined to the borehole.

[0030] Figure 4 This is a schematic diagram showing the dip direction of the working face at a drilled location in a coal seam that has already been mined.

[0031] Figure 5 This is a schematic diagram showing the orientation of the working face before the coal seam is mined up to the borehole.

[0032] Figure 6 This is a schematic diagram showing the orientation of the working face at a drilled location in a coal seam that has already been mined;

[0033] Figure 7 This is a curve showing the strain variation of optical fiber during coal seam mining.

[0034] In the diagram: 1-Fiber optic monitoring system; 1101-Fiber optic monitoring station A; 1102-Fiber optic monitoring station B; 1103-Fiber optic monitoring station C; 1104-Fiber optic monitoring station D; 1105-Fiber optic monitoring station E; 1201-Protection box; 1202-Fiber optic cable; 1203-Steel wire rope; 1204-Counterweight guide head; 1205-Hollow grouting drill rod; 2-Coal seam; 3-Roadway; 4-Working face; 5-Goaf; 6-Collapse zone; 7-Fractured zone; 8-Bending subsidence zone; 9-Borehole collapse zone section; 10-Borehole fracture zone section; 11-Borehole bending subsidence zone section. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] like Figures 1 to 6 As shown, the method for monitoring the spatiotemporal evolution of the three overlying zones in a mining area based on distributed optical fiber includes the following steps:

[0037] S1, Determine drilling parameters;

[0038] Based on the on-site geological conditions and the characteristics of overlying rock failure in the mining area, the required borehole parameters are calculated and determined, including borehole inclination angle α, borehole depth L0, borehole diameter D, number of boreholes n, and borehole spacing K. n ;

[0039] Drilling inclination angle α: α = 90°, which is a vertical drilling angle;

[0040] Hole depth L0: The length of the borehole is the vertical distance from the ground surface at the location of the borehole to the top plate of the working face;

[0041] Aperture D: ranges from 50 to 90 mm;

[0042] Number of holes n: n = 5;

[0043] Hole spacing K n :like Figure 1 As shown, each borehole is equipped with an optical fiber monitoring station to form an optical fiber monitoring system 1; in this embodiment, the five boreholes are respectively equipped with: optical fiber monitoring station A1101, optical fiber monitoring station B1102, optical fiber monitoring station C1103, optical fiber monitoring station D1104 and optical fiber monitoring station E1105.

[0044] The distance between fiber optic monitoring station A1101 and fiber optic monitoring station B1102, and between fiber optic monitoring station B1102 and fiber optic monitoring station C1103 is K1, which is one-quarter of the working surface inclination length.

[0045] The distance between fiber optic monitoring station B1102 and fiber optic monitoring station D1104 is K2, which is within the range of severe influence from the pre-support pressure on the working face. This distance can be calculated from the actual site conditions combined with the following empirical formula:

[0046]

[0047] In the formula: f is the inter-layer friction coefficient, and m is the coal seam thickness. denoted as the internal friction angle, M as the stress concentration factor, γ as the unit weight of the coal and rock mass, H as the mining depth, and c as the cohesion within the coal mass.

[0048] The distance between fiber optic monitoring station B1102 and fiber optic monitoring station E1105 is K3, which represents the influence range of the working face's advanced support pressure. This range can be determined from the actual site conditions combined with the following empirical formula:

[0049]

[0050] In the formula: m is the coal seam thickness, β is the lateral pressure coefficient, and f is the interlayer friction coefficient.

[0051] S2, Determine the drilling layout area;

[0052] Fiber optic monitoring stations A1101, B1102, and C1103 are arranged parallel to the dip of the working face; fiber optic monitoring stations D1104 and E1105 are arranged perpendicular to the dip of the working face and located on the centerline of the dip; fiber optic monitoring station E1105 is 100m ahead of the working face; the monitoring results of fiber optic monitoring stations A1101, B1102, and C1103 can be jointly analyzed to determine the development height and morphology of the three overburden zones along the entire working face dip; the monitoring results of fiber optic monitoring stations B1102, D1104, and E1105 can be jointly analyzed to determine the influence of the advance support stress along the entire working face strike on the development height and morphology of the three overburden zones.

[0053] S3, Drilling operation;

[0054] Based on S1, the drilling inclination angle α, hole depth L0, hole diameter D, number of holes n, and hole spacing K are determined. n Meanwhile, based on the drilling layout area confirmed by S2, drilling was carried out vertically downward on the ground surface in sequence;

[0055] S4, Construction of fiber optic monitoring station;

[0056] like Figure 2 As shown, the fiber optic monitoring station includes an optical fiber 1202, a protective box 1201 located at the top of the borehole, and a steel wire rope 1203. A distributed fiber optic strain demodulator is installed inside the protective box 1201. The first end of the optical fiber 1202 is placed inside the protective box 1201 to avoid interference from the external environment. A counterweight guide head 1204 is fixed to the tail end of the optical fiber 1202. The end of the steel wire rope 1203 is also fixed to the counterweight guide head 1204. By lowering the steel wire rope 1023, the counterweight guide head 104 can enter the depth of the borehole to pull the optical fiber 1202 into the depth of the borehole.

[0057] It is worth mentioning that the Fiber 1202 uses a metal-based cable-like strain sensing optical cable with an internal steel strand reinforced structure, which has high tensile strength and is not easy to break.

[0058] S5, Grouting and sealing;

[0059] Hollow grouting drill rod 1205 is inserted into the borehole. Cement grout is used to plug leaks and seal the borehole using the hollow grouting drill rod 1205. The sealing method is adopted by lifting the drill rod section by section upwards. Grouting and sealing of the borehole begins when the hollow grouting drill rod 1205 is inserted to a depth of 5m above the bottom of the hole. The cement grout outlet at the bottom of the hollow grouting drill rod 1205 is not higher than the cement grout surface in the hole. The sealing height of each section at one time is not greater than 50m, which is conducive to the coupling of optical fiber and rock strata and optimizes the monitoring effect.

[0060] S6, Data Monitoring;

[0061] The distributed fiber optic strain demodulator is a single-ended type, capable of single-ended testing and suitable for complex environment detection. The fiber optic cable inside protection box 1201 is connected to the distributed fiber optic strain demodulator to demodulate the sensing signal and acquire overburden strain data. After the fiber optic monitoring station is deployed, the first fiber optic monitoring begins, and the acquired data serves as initial data for comparison with subsequent monitoring data. When the working face has not reached the location of fiber optic monitoring station E1105, the detection frequency is 2-3 times / week. When the working face approaches the location of fiber optic monitoring station E1105, the data acquisition frequency is increased to 1 time / day. When the working face approaches the location of fiber optic monitoring station D1104, the data acquisition frequency is increased to 3-4 times / day, until the fiber optic monitoring data inside fiber optic monitoring station B1102 reaches stability.

[0062] S7, Results Analysis;

[0063] The fiber optic strain monitoring data analysis method is as follows:

[0064] ①For the pre-support stress, as the working face gradually approaches the borehole opening, the strain value of the optical fiber gradually increases, and the reaction overburden is continuously affected by the pre-support pressure. After the working face crosses the borehole opening, the local stratigraphic compressive strain gradually transforms into tensile strain and continues to increase.

[0065] ② Regarding the height of the collapse zone, when the working face pushes past the borehole, the overburden of the roof collapses irregularly, which will cause the optical fiber at this location to deform beyond the limit and break. There will be no monitoring data from this break point to the end of the optical fiber. By comparing with the initial data, the length of this section of the optical fiber without monitoring can be obtained. This length corresponds to the collapse zone in the three overburden zones.

[0066] ③ Regarding the height of the fracture zone, when the optical fiber has a large peak strain curve, the rock strata at the peak of the optical fiber are in a state of separation or horizontal shear failure. The rock strata on both sides of the peak belong to different integral rock blocks under different motion states. That is, the length of the section where the optical fiber has a large strain peak corresponds to the fracture zone in the three zones of the overburden.

[0067] ④ For the curved and sunken zone, when the strain of the optical fiber does not change much, it indicates that the rock stratum where the optical fiber is located is in an overall deformation state under the action of external force. That is, this length of the optical fiber corresponds to the curved and sunken zone in the three zones of the overburden.

[0068] Based on the obtained fiber optic strain data, the strain change curve of the fiber optic monitoring station during coal seam mining was obtained. Combined with the on-site stratigraphic distribution characteristics, the spatiotemporal evolution law of the three overburden zones during coal seam mining was summarized.

[0069] like Figure 7 The figure shows the strain variation curve of the optical fiber during coal seam mining. Using the strain data analysis method obtained from optical fiber monitoring as described in this invention, the development height of the three overburden zones can be accurately determined. ① For the pre-support stress, the strain value of the optical fiber gradually increases, indicating that under the influence of the pre-support stress, the local compressive strain gradually transforms into tensile strain and continues to increase, indicating that the working face crosses the borehole opening; ② For the caving zone height, comparing the three curves, it can be seen that after the working face pushes past the borehole, the length of the curve in the vertical axis direction becomes shorter (no data is available at the point of optical fiber breakage). This length is the caving zone height, which is 20m; ③ For the fracture zone height, comparing the three curves, the length of the segment with the larger strain peak corresponds to the fracture zone height, which is 320m; ④ For the bending subsidence zone, the length of the segment with small strain and gentle change corresponds to the bending subsidence zone height, which is 260m.

[0070] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0071] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for monitoring the spatiotemporal evolution of the three overlying zones in a mining area based on distributed optical fiber, characterized in that, Includes the following steps: The required borehole parameters are determined based on the on-site geological conditions and the characteristics of overlying rock damage in the mining area; The drilling locations are set, and the drilling is divided into two groups. The distribution direction of the two groups of drilling is parallel and perpendicular to the working face. Drilling is carried out according to the drilling parameters and the location of the boreholes, and a fiber optic monitoring station is installed at each borehole. Grouting and sealing of the borehole; By using fiber optic monitoring stations to monitor and obtain overburden strain data, and by analyzing the data, the spatiotemporal evolution of the three overburden zones during coal seam mining was obtained. The drilling parameters include: inclination angle, hole depth, hole diameter, number of holes, and hole spacing; The drilling angle is 90 degrees, the hole diameter is 50~90mm, and the number of holes is 5; Three of the boreholes are equidistant from each other along the dip of the working face; the other two boreholes are arranged perpendicular to the dip of the working face and are located on the center line of the dip of the working face. The distance between three boreholes that are equidistant from each other along the working face is one-quarter of the working face dip length; Fiber optic monitoring stations A, B, and C are installed at three boreholes equidistant from the working face; fiber optic monitoring stations D and E are installed at two other boreholes perpendicular to the working face. The distance between fiber optic monitoring station B and fiber optic monitoring station D is K2: In the formula: Here, m is the inter-layer friction coefficient, and m is the coal seam thickness. It is the internal friction angle. The stress concentration factor is... For the bulk density of coal and rock mass, For deeper mining, For the cohesive force within the coal; The distance between fiber optic monitoring station B and fiber optic monitoring station E is K3: In the formula, This is the lateral pressure coefficient.

2. The method for monitoring the spatiotemporal evolution of the three overlying zones in a mining area based on distributed optical fiber monitoring according to claim 1, characterized in that, The fiber optic monitoring station includes an optical fiber, a protective box located at the top of the borehole, and a steel wire rope; the first end of the optical fiber is placed inside the protective box, the tail end of the optical fiber is fixed with a counterweight guide, and the end of the steel wire rope is also fixed to the counterweight guide.

3. The method for monitoring the spatiotemporal evolution of the three overlying zones in a mining area based on distributed optical fiber monitoring according to claim 2, characterized in that, The optical fiber is a metal-based cable-like strain sensing optical cable with an internal steel strand reinforcement structure.

4. The method for monitoring the spatiotemporal evolution of the three overburden zones in a mining area based on distributed optical fiber monitoring according to claim 1, characterized in that, Hollow grouting drill rods are installed in the borehole for grouting and sealing. The method of sealing the borehole section by section is adopted by lifting the hollow grouting drill rod. Grouting and sealing begin when the hollow grouting drill rod is 5m above the bottom of the hole. The cement slurry outlet at the bottom of the hollow grouting drill rod is not higher than the cement slurry surface in the hole. The sealing height of each section at one time is not greater than 50m.

5. The method for monitoring the spatiotemporal evolution of the three overlying zones in a mining area based on distributed optical fiber monitoring according to claim 2, characterized in that, The protective box is equipped with a single-ended distributed fiber optic strain demodulator, which is connected to an optical fiber.

6. The method for monitoring the spatiotemporal evolution of the three overlying zones in a mining area based on distributed optical fiber monitoring according to claim 1, characterized in that, During the data analysis process, based on the obtained fiber optic strain data, the strain change curve of the fiber optic monitoring station as coal seam mining is obtained. Combined with the on-site stratigraphic distribution characteristics, the spatiotemporal evolution law of the three overburden zones as coal seam mining is summarized.

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