A method for supporting the surrounding rock of a top coal roadway in a thick coal seam with soft upper and hard lower hollows

Abstract

The application discloses a kind of upper soft lower hard hollow thick coal seam roof coal roadway surrounding rock supporting method, it is related to coal mine roadway supporting technical field.The method includes: based on the hard coal solidity coefficient in stratum feature and soft coal thickness, required hard coal sublayer thickness is quantitatively calculated, actively selected high-strength hard coal sublayer as immediate roof, to provide solid bearing base for anchor cable support.Advance detection cavity is carried out by geological radar, and according to the size and horizon of cavity, grouting parameters are determined and advance accurate grouting modification is implemented, and hidden cavity is converted into measurable and controllable object.Shallow-middle-deep three-level coupling bearing structure is constructed by short, medium and long ladder anchor cable, and support parameters are determined in combination with suspension theory.Section shrinkage and roof separation amount are monitored in real time during tunneling by laying monitoring station, and quantitative evaluation standard is established, if deformation is out of limit, then start reinforcement support and optimize subsequent parameters, form closed-loop control of real-time monitoring-quantitative evaluation-feedback optimization, ensure long-term stability of roadway.

Description

Technical Field

[0001] This invention relates to the field of coal mine roadway support technology, and in particular to a method for supporting the surrounding rock of a thick coal seam with soft upper and hard lower layers and containing cavities. Background Technology

[0002] In the mining of thick coal seams with a soft upper layer and a hard lower layer, high-gas mines often employ measures such as hydraulic perforation to reduce the gas content of the coal seam. These measures can create hidden cavities of a certain size in the upper soft coal seam, damaging the integrity of the surrounding rock and significantly reducing its bearing capacity. Thick coal seams are often mined using fully mechanized longwall mining. To facilitate the layout of the longwall face and the mining process, the longwall roadways often employ roof-supporting tunneling, that is, retaining a certain amount of coal seam as the immediate roof for support. When the top coal is soft coal, it leads to poor roof integrity and insufficient self-supporting capacity, making it prone to roof delamination, fragmentation, and even collapse under tunneling disturbances. When the thickness of the supporting top coal is large, the required thickness of soft coal also increases. In order to anchor the anchor cables in the deep stable rock strata, the length of the anchor cables increases significantly, resulting in a delayed support effect, difficulty in effectively controlling the initial deformation of the roof, and a significant increase in cost. When the hydraulic perforation in the top coal leaves large voids, it leads to a serious weakening of the roof structure, making it difficult for the anchor cables to be anchored in the stable rock strata, which can easily cause the overall support to fail and induce roof collapse accidents.

[0003] Current technologies lack a method for calculating the required thickness of hard coal to support the roof based on the thickness of soft coal in the roof. Furthermore, existing technologies neither clearly define how to detect cavities left by hydraulic drilling in advance, nor specify the threshold size of cavities that need to be addressed, nor provide corresponding treatment measures. After tunnel excavation, the roof is prone to non-uniform deformation and even collapse accidents due to the combined effects of excavation disturbance and soft coal and cavity defects in the roof. Summary of the Invention

[0004] The purpose of this invention is to provide a method for supporting the surrounding rock of a thick coal seam with soft upper and hard lower layers and cavities, aiming to solve or improve at least one of the above-mentioned technical problems.

[0005] To achieve the above objectives, the present invention provides the following solution: A method for supporting the surrounding rock of a thick coal seam with soft upper and hard lower layers and containing cavities in a coal roadway includes: Geological exploration is used to obtain the stratigraphic characteristics of the mine. The required thickness of the hard coal layer is calculated based on the hard coal firmness coefficient in the stratigraphic characteristics and the thickness of the soft coal. Before tunneling, advance detection of cavities is conducted to obtain their dimensions; When the cavity size exceeds the preset cavity threshold, tunneling is stopped, and grouting parameters are determined based on the thickness of the roof coal seam and the cavity size. Pre-grouting modification is carried out based on grouting parameters, and voids are detected and inspected to ensure that the void size is smaller than the void threshold. After grouting is completed, the support parameters when the safety factor exceeds the safety threshold are determined based on the roadway roof coal support conditions, cavity size, physical and mechanical properties of the surrounding rock, and suspension theory. The required thickness of the hard coal layer to support the top coal layer is found by moving downwards along the roof and used as the direct roof for top coal tunneling. Construction is carried out according to the support parameters to form a support bearing structure. Multiple monitoring stations were set up during the tunnel excavation process to monitor the deformation and delamination of the surrounding rock in real time. Once the tunnel excavation has stabilized, calculate the tunnel cross-sectional shrinkage rate. Separation layer Based on the criteria for qualified support, determine whether the support effect is qualified; If the support effect is not up to standard, secondary reinforcement support for the surrounding rock of the roadway shall be carried out, the cause of exceeding the limit shall be analyzed, and the support parameters of the subsequent roadway section shall be optimized according to the cause of exceeding the limit until the roadway meets the support qualification conditions.

[0006] Further, stratigraphic characteristics include: the location, thickness, integrity, and mechanical properties of the basic roof, soft coal, and hard coal layers.

[0007] Furthermore, the required thickness of the hard coal stratification is expressed as follows: In the formula, To achieve the required thickness of the hard coal stratification, when hour, ; This is the proportionality coefficient; The thickness of soft coal.

[0008] Furthermore, the proportionality coefficient When the hardness coefficient of hard coal hour, ;when Hard coal soundness coefficient hour, When the hardness coefficient of hard coal When >1.4, .

[0009] Furthermore, the void threshold is 1.0m.

[0010] Furthermore, the grouting parameters include: grouting borehole depth, grouting material ratio, grouting pressure, grouting volume per hole, and grouting time; The grouting borehole depth is expressed as: In the formula, This refers to the depth of the grouting borehole. The horizontal depth of the cavity; The vertical depth of the cavity; The grouting material is a cement-water glass two-component grout with a water-cement ratio of 0.7:1, a water glass content of 5% to 8% of the cement mass, and a final grouting pressure of 3 MPa. The grouting volume per hole is determined based on the cavity volume, the degree of development of surrounding rock fissures, and the grout absorption rate of the coal body, and the expression is: In the formula, This refers to the grouting volume per hole; The volume of the cavity; To increase the volume of fractures in the surrounding rock; The filling coefficient; This is the crack loss coefficient; The grouting time is determined based on the grouting volume per hole and the grouting flow rate, expressed as follows: In the formula, Q represents the grouting time; Q represents the grouting volume per hole. This refers to the grouting flow rate.

[0011] Furthermore, the support parameters include the length, spacing, and preload of short, medium, and long anchor cables; The expression for the anchor cable length is: In the formula, , , These refer to the lengths of the short, medium, and long anchor cables for the top slab, respectively. To support the thickness of the top coal; The required thickness of the hard coal stratification; The thickness of soft coal.

[0012] Furthermore, the required thickness of the hard coal layer is located along the roof and used as the direct roof for roof coal tunneling, including: When the thickness of the hard coal in the roof is less than the required thickness of the hard coal to support it, the bottom-breaking tunneling method is adopted, and the bottom-breaking depth is the difference between the required thickness of the hard coal to support it and the actual thickness of the roof coal. If the bottom-breaking still cannot meet the required thickness of the hard coal to support it, the bottom of the soft coal is reinforced by grouting in advance.

[0013] Furthermore, the criteria for support qualification include: shrinkage rate. Separation layer .

[0014] Furthermore, secondary reinforcement support includes at least one of the following measures: installing additional anchor cables, grouting reinforcement, or adjusting the support parameters of subsequent roadway sections.

[0015] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects: This invention discloses a method for supporting the surrounding rock of a thick coal seam with soft upper and hard lower layers and cavities. This method differs from conventional methods of supporting soft coal or blindly determining the thickness of supporting hard coal. Based on the thickness and mechanical strength of the soft and hard coal in the roof, this invention quantitatively calculates the required thickness of supporting hard coal and actively selects the layer of hard coal with higher strength as the direct roof, providing a solid and reliable bearing foundation for subsequent anchor cable support, and suppressing the delamination and fragmentation deformation of soft coal from the source.

[0016] This invention clarifies the threshold for handling cavities, achieves advanced detection through ground-penetrating radar, determines grouting parameters based on the actual size and stratum of the cavity, and performs advanced and precise grouting, transforming hidden cavities from "unknown hidden dangers" into "measurable, controllable, and eliminable" management objects, significantly reducing the risk of roof collapse.

[0017] This invention employs short, medium, and long tiered anchor cables to form a shallow-medium-deep three-level coupled bearing structure. By deploying monitoring stations to monitor the cross-sectional shrinkage rate f and the roof delamination amount l in real time, it establishes the support qualification conditions (f≤10%, l<5cm). When the deformation exceeds the limit, it initiates reinforcement support and support parameter optimization, forming a closed loop of "real-time monitoring-quantitative evaluation-feedback optimization" to ensure the long-term stability of the roadway. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic flowchart of the method of the present invention; Figure 2 This is a schematic diagram of the pre-grouting in this embodiment; Figure 3 This is a schematic diagram of the arrangement of the support system on the cross section of the roadway in this embodiment; Figure 4 This is a schematic diagram of the plan layout of the tiered anchor cable-channel steel composite structure in this embodiment. Detailed Implementation

[0020] 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.

[0021] The purpose of this invention is to provide a method for supporting the surrounding rock of a thick coal seam with soft upper and hard lower layers and cavities, aiming to solve or improve at least one of the above-mentioned technical problems.

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] like Figure 1 As shown, the present invention provides a method for supporting the surrounding rock of a thick coal seam with soft upper and hard lower layers and cavities, comprising: Step 1: Obtain the stratigraphic characteristics of the mine through geological exploration; Among them, the stratigraphic characteristics include the stratigraphic position, thickness, integrity and mechanical properties of the basic roof, soft coal and hard coal layers; Step 2: Based on the hard coal firmness coefficient in the stratigraphic characteristics and the thickness of the soft coal, calculate the required thickness of the hard coal layer. The expression is as follows: In the formula, To achieve the required thickness of the hard coal stratification, when hour, ; This is the proportionality coefficient; For soft coal thickness; Among them, the proportionality coefficient When the hardness coefficient of hard coal hour, ;when Hard coal soundness coefficient hour, When the hardness coefficient of hard coal When >1.4, ; Step 3: Before tunneling, conduct advance detection of cavities to obtain their dimensions; In this embodiment, ground-penetrating radar or acoustic detectors are used to detect cavities. The detection range is greater than 10m.

[0024] Step 4: When the cavity size exceeds the preset cavity threshold, stop tunneling and determine the grouting parameters based on the roof coal seam thickness and cavity size, including: The grouting parameters include: grouting borehole depth, grouting material mix ratio, grouting pressure, grouting volume per borehole, and grouting time. The void threshold is 1.0m.

[0025] The grouting borehole depth is expressed as: In the formula, This refers to the depth of the grouting borehole. The horizontal depth of the cavity; The vertical depth of the cavity.

[0026] The grouting material is a cement-water glass two-component grout with a water-cement ratio of 0.7:1 and a water glass content of 5% to 8% of the cement mass. The final grouting pressure is 3 MPa.

[0027] The grouting volume per hole is determined based on the cavity volume, the degree of development of surrounding rock fissures, and the grout absorption rate of the coal body, and is expressed as follows: In the formula, This refers to the grouting volume per hole; The volume of the cavity; To increase the volume of fractures in the surrounding rock; The filling factor is 1.1 to 1.3 in this embodiment; The crack loss coefficient is taken as 0.2~0.5 in this embodiment.

[0028] In practical applications, the preferred grouting volume per hole is 500~2000L.

[0029] The grouting time is determined based on the grouting volume per hole and the grouting flow rate, expressed as follows: In the formula, Q represents the grouting time; Q represents the grouting volume per hole. This refers to the grouting flow rate.

[0030] In practical applications, the grouting time is preferably 5 to 10 minutes.

[0031] Grouting is stopped when the grout return at the orifice is stable and the grouting pressure does not decrease for 1 minute.

[0032] Step 5: Perform advanced grouting modification according to the grouting parameters, and detect and inspect the cavities to ensure that the cavity size is smaller than the cavity threshold. Step 6: After grouting is completed, based on the conditions of the coal seam in the roadway, the size of the cavity, the physical and mechanical properties of the surrounding rock, and in conjunction with the suspension theory, determine the support parameters when the safety factor exceeds the safety threshold. The safety threshold is 2; the support parameters include the length, spacing and preload of short anchor cables, medium and long anchor cables and long anchor cables. The expression for the anchor cable length is: In the formula, , , These refer to the lengths of the short, medium, and long anchor cables for the top slab, respectively. To support the thickness of the top coal; The required thickness of the hard coal stratification; For soft coal thickness; The spacing between anchor cables is determined based on the tunnel span, surrounding rock stability, and anchor cable control range. When the surrounding rock stability is poor or the degree of cavity development is high, the spacing between anchor cables is reduced. In this embodiment, the spacing between short anchor cables is 800~1000mm, and the spacing between medium-length and long anchor cables is 900~2000mm. The anchor cable preload is determined based on the top plate load and the anchor cable design bearing capacity; when the degree of top plate breakage increases, the anchor cable preload is increased; in this embodiment, the preload of short anchor cables is 150~250kN, and the preload of medium and long anchor cables is 250~350kN. The stability of the support system is checked based on the suspension theory. When the safety factor is greater than the safety threshold, the support parameters are determined to meet the support requirements.

[0033] Step 7: Find the required thickness of the hard coal layer along the top plate and use it as the direct roof for top coal tunneling. Then, construct the support structure according to the support parameters. The load-bearing structure is configured with shallow, middle and deep couplings based on the length of the anchor cables.

[0034] In this embodiment, when the thickness of the hard coal in the roof is less than the required thickness of the hard coal to support it, the bottom-breaking tunneling method is adopted. The bottom-breaking depth is the difference between the required thickness of the hard coal to support it and the actual thickness of the roof coal, so as to ensure that the roof retains enough hard coal layers. If the bottom-breaking still cannot meet the required thickness of the hard coal to support it, the bottom of the soft coal is pre-grouted to strengthen it and improve the strength of the soft coal.

[0035] Step 8: During the tunnel excavation process, multiple monitoring stations are set up to monitor the deformation and delamination of the surrounding rock in real time.

[0036] Monitoring stations are set up every 30-50 meters.

[0037] Step 9: After the tunnel excavation has stabilized, calculate the tunnel cross-sectional contraction rate. Separation layer Based on the criteria for qualified support, the effectiveness of the support is determined, including: Measure the initial cross-sectional area S0 and the stable cross-sectional area S1 of the roadway; Calculate the reduction of area The expression is: In the formula, The tunnel cross-sectional shrinkage rate; This represents the initial cross-sectional area of ​​the tunnel. The cross-sectional area of ​​the roadway after it has stabilized; Delamination amount This calculation is based on data from continuous monitoring of the roadway using a roof separation instrument, and is a well-known existing technology in this field.

[0038] If shrinkage rate Separation layer If the support is satisfactory, the support effect is deemed acceptable; otherwise, the support effect is deemed unacceptable.

[0039] Step 10: If the support effect is unqualified, secondary reinforcement support for the surrounding rock of the roadway shall be carried out, and the support parameters for subsequent roadway sections shall be optimized according to the cause of the exceeding limit. Specifically, this includes: Based on the monitoring results, identify the areas where the surrounding rock exceeds the limit, and obtain the amount of roof delamination, roadway shrinkage rate, cavity development, and anchor cable stress state in the areas where the limit is exceeded; When the amount of delamination of the top slab exceeds the limit and the anchor cable is not under sufficient stress, additional anchor cables are installed for reinforcement support. When cavities expand or surrounding rock fissures develop severely, grouting reinforcement is used for strengthening and support. When the overall deformation of the surrounding rock is large, reinforcement support is carried out by reducing the spacing between anchor cables and increasing the preload. Construction is carried out according to the determined secondary reinforcement support method. The reinforcement area is continuously monitored in real time, and the monitoring and optimization process is repeated until the roadway meets the support qualification conditions.

[0040] To verify the beneficial effects of the present invention, the present invention will be described below in conjunction with the conditions of the 1609 transport roadway of a certain mine.

[0041] The No. 1609 transport roadway in this mine is buried at a depth of approximately 500m, with an average coal seam thickness of H=7.2m. It exhibits a soft-over-hard characteristic: the upper 0-3.0m consists of soft, broken coal (f=0.4-0.6), while the lower 3-7.0m consists of hard coal (f=1.1-1.3). Hydraulic perforations left over from gas control projects exist in the soft coal seams of the roof. Ground-penetrating radar indicates that the diameter of these cavities ranges from 0.5 to 2.0m, with some areas exceeding 1.0m in diameter.

[0042] The implementation steps are as follows: S1: Geological feature survey: Roof core sampling was conducted at the designed location of the roadway to determine the thickness of soft coal (h_soft = 2.0m) and the obvious stratification of hard coal. A columnar section of the roof strata was obtained, in which the thickness of hard coal (f ≈ 1.3m) was determined.

[0043] S2: Determination of the thickness of the hard coal: Take the proportionality coefficient k=0.6, and calculate the thickness of the hard coal hhard=0.6×2.0=1.2m.

[0044] S3: Advanced cavity detection: Using ground-penetrating radar to conduct advanced detection on the roof in front of the working face, with a detection range of L=15m, a cavity with a diameter of about 1.5m was found in the soft coal area 5.0m above the working face.

[0045] S4: Determination of Pre-grouting Parameters: If a cavity diameter R = 1.5m ≥ 1.0m is found, excavation should be stopped immediately. The horizontal depth of the cavity L_water = 5.0m, the vertical depth L_vertical = 3.2m, and the diameter R = 1.5m. Calculate the grouting borehole depth H_hole = ... = The diameter of the hole is approximately 7.2m, the hole spacing is 700mm, the final grouting pressure is 3.0MPa, and the grouting volume and time per hole are determined according to the site conditions.

[0046] like Figure 2 As shown, S5: Advanced grouting and grouting effect inspection: Cement-water glass dual-liquid grout (water-cement ratio 0.7:1, water glass content 6%) was used. Grouting boreholes were drilled and grouting was performed in front of the working face. After grouting, ground-penetrating radar inspection showed that the cavities were basically filled by the grout, the fractured area was effectively cemented, and the effect was good. The diameter of the residual cavity was re-measured to be R<1.0m.

[0047] like Figure 3 As shown, S6: Roadway support parameters are determined: the diameter of the pre-detected cavity is small, and the grouting effect is satisfactory. Based on the top coal support conditions, cavity size, surrounding rock characteristics, and combined with suspension theory, a safety factor K=2.0 is taken, and the parameters for the tiered anchor cable support are given: Short anchor cable: diameter 21.8mm, length 4.2m, spacing 850×900mm, preload 200kN; Medium-length anchor cable: diameter 21.8mm, length 7.2m, spacing 900×1800mm, preload 300kN; Long anchor cable: diameter 21.8mm, length 10.2m, spacing 900×1800mm, preload 300kN.

[0048] like Figure 4 As shown, S7: Hard coal seam tunneling and support: Based on the hard coal thickness determined in S2, a layer of hard coal with a thickness of approximately 1.2m is selected downwards along the top of the coal seam as the direct roof, and tunneling is carried out using the hard coal seam support. After tunneling, tiered anchor cables are constructed according to the parameters determined in S6, and the short anchor cables are connected by 16# channel steel to form a cooperative load-bearing beam structure.

[0049] S8: Real-time monitoring of tunnel deformation and delamination: During tunnel excavation, a monitoring station is set up every 40m, equipped with a roof delamination meter and a total station.

[0050] S9: Evaluation of support effect: After continuous monitoring for one month, the cross-sectional shrinkage rate f = 6.5% ≤ 10% and the delamination l = 1.2cm < 5cm were calculated.

[0051] S10: Dynamic feedback optimization of support parameters: The surrounding rock control effect is good, and no secondary reinforcement support is required.

[0052] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0053] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for supporting the surrounding rock of a thick coal seam with soft upper and hard lower layers and containing cavities in a coal roadway, characterized in that, include: Geological exploration is used to obtain the stratigraphic characteristics of the mine. The required thickness of the hard coal layer is calculated based on the hard coal firmness coefficient in the stratigraphic characteristics and the thickness of the soft coal. Before tunneling, advance detection of cavities is conducted to obtain their dimensions; When the cavity size exceeds the preset cavity threshold, tunneling is stopped, and grouting parameters are determined based on the thickness of the roof coal seam and the cavity size. Pre-grouting modification is carried out based on grouting parameters, and voids are detected and inspected to ensure that the void size is smaller than the void threshold. After grouting is completed, the support parameters when the safety factor exceeds the safety threshold are determined based on the roadway roof coal support conditions, cavity size, physical and mechanical properties of the surrounding rock, and suspension theory. The required thickness of the hard coal layer to support the top coal layer is found by moving downwards along the roof and used as the direct roof for top coal tunneling. Construction is carried out according to the support parameters to form a support bearing structure. Multiple monitoring stations were set up during the tunnel excavation process to monitor the deformation and delamination of the surrounding rock in real time. Once the tunnel excavation has stabilized, calculate the tunnel cross-sectional shrinkage rate. and separation layer Based on the criteria for qualified support, determine whether the support effect is qualified; If the support effect is not up to standard, secondary reinforcement support for the surrounding rock of the roadway shall be carried out, the cause of exceeding the limit shall be analyzed, and the support parameters of the subsequent roadway section shall be optimized according to the cause of exceeding the limit until the roadway meets the support qualification conditions.

2. The method for supporting the surrounding rock of a thick coal seam with soft upper and hard lower layers and cavities according to claim 1, characterized in that, The stratigraphic features include: the stratigraphic position, thickness, integrity, and mechanical properties of the main roof, soft coal, and hard coal layers.

3. The method for supporting the surrounding rock of a thick coal seam with soft upper and hard lower layers and cavities according to claim 1, characterized in that, The required thickness of the hard coal layer is expressed as follows: In the formula, To achieve the required thickness of the hard coal stratification, when hour, ; This is the proportionality coefficient; The thickness of soft coal.

4. The method for supporting the surrounding rock of a thick coal seam with soft upper and hard lower layers and cavities according to claim 3, characterized in that, The proportionality coefficient When the hardness coefficient of hard coal hour, ;when Hard coal soundness coefficient hour, ; When the hard coal firmness coefficient When >1.4, .

5. The method for supporting the surrounding rock of a thick coal seam with soft upper and hard lower layers and cavities according to claim 1, characterized in that, The void threshold is 1.0m.

6. The method for supporting the surrounding rock of a thick coal seam with soft upper and hard lower layers and cavities according to claim 1, characterized in that, The grouting parameters include: grouting borehole depth, grouting material ratio, grouting pressure, grouting volume per hole, and grouting time; The grouting borehole depth is expressed as: In the formula, This refers to the depth of the grouting borehole. The horizontal depth of the cavity; The vertical depth of the cavity; The grouting material is a cement-water glass two-component grout with a water-cement ratio of 0.7:1, a water glass content of 5% to 8% of the cement mass, and a final grouting pressure of 3 MPa. The grouting volume per hole is determined based on the cavity volume, the degree of development of surrounding rock fissures, and the grout absorption rate of the coal body, and the expression is: In the formula, This refers to the grouting volume per hole; The volume of the cavity; To increase the volume of fractures in the surrounding rock; The filling coefficient; This is the crack loss coefficient; The grouting time is determined based on the grouting volume per hole and the grouting flow rate, expressed as follows: In the formula, Q represents the grouting time; Q represents the grouting volume per hole. This refers to the grouting flow rate.

7. The method for supporting the surrounding rock of a thick coal seam with soft upper and hard lower layers and cavities according to claim 1, characterized in that, The support parameters include the length, spacing, and preload of short anchor cables, medium-length anchor cables, and long anchor cables; The expression for the anchor cable length is: In the formula, , , These refer to the lengths of the short, medium, and long anchor cables for the top slab, respectively. To support the thickness of the top coal; The required thickness of the hard coal stratification; The thickness of soft coal.

8. The method for supporting the surrounding rock of a thick coal seam with soft upper and hard lower layers and cavities according to claim 1, characterized in that, The process of finding the required thickness of the hard coal layer along the roof as the direct roof for roof coal tunneling includes: When the thickness of the hard coal in the roof is less than the required thickness of the hard coal to support it, the bottom-breaking tunneling method is adopted, and the bottom-breaking depth is the difference between the required thickness of the hard coal to support it and the actual thickness of the roof coal. If the bottom-breaking still cannot meet the required thickness of the hard coal to support it, the bottom of the soft coal is reinforced by grouting in advance.

9. A method for supporting the surrounding rock of a thick coal seam with soft upper and hard lower layers and cavities, as described in claim 1, is characterized in that... The conditions for qualified support include: shrinkage rate. Separation layer .

10. A method for supporting the surrounding rock of a thick coal seam with soft upper and hard lower layers and containing cavities, as described in claim 1, characterized in that... The secondary reinforcement support includes at least one of the following measures: installing additional anchor cables, grouting reinforcement, or adjusting the support parameters of subsequent roadway sections.

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