Supporting method for improving stability and safety of narrow coal pillar

Abstract

The invention discloses a supporting method for improving the stability and safety of a narrow coal pillar, and relates to the technical field of coal pillar anchoring. Comprising the steps that in a first working face haulage roadway, horizontal through holes are drilled in supporting coal pillars in the direction perpendicular to the haulage roadway; according to the thickness of the supporting coal pillar, a yielding noose and a constant-resistance noose are cut out in advance; the pretreated yielding nooses and constant-resistance nooses are alternately arranged in drill holes according to the designed row pitch to form a cross supporting structure; a first constant-resistance main anchor cable section and a first yielding main anchor cable section are sequentially installed on the side of a first working face haulage roadway; after the air return roadway of the second working face is tunneled to the corresponding drill hole, the extending parts of the yielding noose and the constant-resistance noose are cut off, and a second constant-resistance main anchor cable section and a second yielding main anchor cable section which correspond to each other are sequentially installed; and on the air return roadway side of the second working face, tensioning pre-tightening force is applied to the constant-resistance noose and the yielding noose, the meshing effect of the side wall of the coal pillar is enhanced, and the overall deformation resistance of the coal pillar is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of coal pillar anchoring, and specifically relates to a support method for improving the stability and safety of narrow coal pillars. Background Art

[0002] During the mining process of deep mines, with the continuous increase in mining depth and the continuous increase in mining intensity, the stress of roadway surrounding rock shows a significant growth trend, which is particularly prominent under the condition of double roadway layout. Specifically, the support coal pillar bears complex lateral pressure and roof pressure simultaneously, making the control of surrounding rock face a severe challenge. The existing support technologies mainly have the following key problems:

[0003] 1. With the increase in mining depth, the stress of surrounding rock increases significantly, and the traditional bolt support generally shows the phenomenon of anchoring failure under high-pressure environments. The typical manifestations are deformation problems such as roadway rib spalling and floor heave, which seriously affect the stability of the roadway.

[0004] 2. Under the condition of double roadway layout, the composite stress state borne by the support coal pillar is more complex, and the existing support methods are difficult to form an effective lateral constraint system, resulting in insufficient bearing capacity of the coal pillar and an increased risk of overall instability.

[0005] 3. The traditional bolt support has inherent defects such as limited anchoring force and poor deformation adaptability, and is prone to bolt fracture or overall outward movement under large deformation conditions of the surrounding rock; although the existing cable bolt support has a large anchoring force, it lacks the characteristics of constant resistance and large deformation, and is difficult to adapt to the deep high-stress environment.

[0006] 4. The current design mostly adopts a single roadway independent support mode, lacking overall consideration of double roadway collaborative support, and it is difficult to form an effective mechanical connection on both sides of the coal pillar, resulting in poor support effect.

[0007] 5. Under complex geological conditions such as soft roof and developed joint fissures, the existing support system is difficult to effectively control the deformation of the surrounding rock, resulting in a large amount of roadway repair work and high maintenance costs. Summary of the Invention

[0008] The purpose of the present invention is to provide a support method for improving the stability and safety of narrow coal pillars, which can adapt to the deep high-stress environment and complex geological conditions, and achieve the effect of double roadway collaborative support, providing reliable technical support for the safe and efficient mining of deep mines.

[0009] To achieve the above purpose, the technical solution of the present application is: a support method for improving the stability and safety of narrow coal pillars, including:

[0010] Step 1: In the first working face transportation roadway, drill a horizontal through hole along the direction perpendicular to the transportation roadway on the support coal pillar, penetrating to the side of the second working face return airway;

[0011] Step 2: According to the thickness of the support coal pillar, pre-cut the yielding cable and constant-resistance cable to ensure that their lengths can completely cover the boreholes and leave enough truncation margin;

[0012] Step 3: Alternately arrange the pre-treated yielding cable and constant-resistance cable in the boreholes according to the designed row spacing to form a cross-support structure, and ensure that the exposed ends of the yielding cable and constant-resistance cable on the side of the first working face transportation roadway extend, and the anchoring ends extend to the side of the second working face return airway;

[0013] Step 4: On the side of the first working face transportation roadway, sequentially install the first constant-resistance main anchor cable section, and then apply a tensile pre-tightening force to the constant-resistance cable;

[0014] Step 5: On the side of the first working face transportation roadway, sequentially install the first yielding main anchor cable section, and then apply a tensile pre-tightening force to the yielding cable;

[0015] Step 6: After the second working face return airway is driven to the corresponding borehole, cut off the extended parts of the yielding cable and constant-resistance cable on the side of the second working face return airway, and sequentially install the corresponding second constant-resistance main anchor cable section and second yielding main anchor cable section to ensure the coordinated force of the anchor cables on both sides;

[0016] Step 7: On the side of the second working face return airway, apply a tensile pre-tightening force to the constant-resistance cable to make it reach the constant-resistance range to provide continuous high-resistance support; then apply a tensile pre-tightening force to the yielding cable to relieve the deformation stress of the coal pillar by using its yielding characteristics;

[0017] Through the coordinated action of the constant-resistance trays and yielding trays on both sides, the biting effect of the coal pillar sidewall is enhanced, and the overall anti-deformation ability of the coal pillar is improved.

[0018] As a preferred embodiment of the present invention, the yielding cable and constant-resistance cable are arranged in columns on the support coal pillar; the constant-resistance cables are equally spaced on the odd-numbered columns, and the yielding cables are equally spaced on the even-numbered columns.

[0019] As a preferred embodiment of the present invention, the yielding cable and constant-resistance cable arranged crosswise horizontally are equally spaced.

[0020] As a preferred implementation manner provided in this embodiment, the vertical stress on the support coal pillar is obtained in the following way:

[0021] First, obtain the stress of the overlying strata (original in-situ stress) on the support coal pillar:

[0022] σ 原始 =γ·H 埋深

[0023] In the formula: γ is the average unit weight of the overlying strata; H 埋深 is the burial depth of the coal seam (m);

[0024] Then, obtain the additional stress caused by mining (stress concentration coefficient M):

[0025] Δσ 采动 = M×σ 原始

[0026] The total vertical stress is:

[0027] σ = σ 原始 +Δσ 采动

[0028] As a preferred implementation provided in this embodiment, compare the total vertical stress σ with the uniaxial compressive strength σ c (MPa) of the coal body:

[0029] If σ≥σ c , the coal pillar has entered the plastic deformation stage, and it is necessary to further obtain the elastic and plastic compression amounts;

[0030] If σ<σ c , the coal pillar is still in an elastic stable state.

[0031] As a preferred implementation provided in this embodiment, the method for obtaining the elastic compression amount is:

[0032]

[0033] In the formula: ΔL e is the elastic compression amount (Mpa); H is the height of the coal pillar (m); E is the elastic modulus of the coal body (Mpa).

[0034] The plastic compression amount ΔL p is obtained as follows:

[0035] ΔL p = ε p ·H

[0036] In the formula: H is the height of the coal body (m); ε p is the plastic strain (Mpa); the plastic strain ε p (empirical formula) is:

[0037]

[0038] In the formula: ε p is the plastic strain (Mpa); C is the plastic parameter; m is the mining concentration coefficient.

[0039] Therefore, the total compression amount:

[0040] ΔL 总 = ΔL e +ΔL p

[0041] As a preferred embodiment provided in this embodiment, the total compression amount is corrected for the size effect (aspect ratio H / W):

[0042] ΔL 修正 = β × ΔL 总

[0043] Then, the time effect is corrected:

[0044] ΔL 长期 = ΔL 修正 + ΔL 蠕变

[0045] Among them, β is the correction coefficient, and ΔL 蠕变 is obtained through creep tests.

[0046] As a preferred embodiment provided in this embodiment, the safety factor N should satisfy:

[0047] Δ 锚索 > N × ΔL 长期

[0048] The determination method for the spacing between adjacent constant-resistance large-deformation anchor cables and pressure-relieving anchor cables in each column is as follows:

[0049]

[0050] In the formula: L is the length of the constant-resistance cable and the pressure-relieving anchor cable; Δ 锚索 is the deformation amount of the anchor cable.

[0051] As a preferred embodiment provided in this embodiment, the row spacing S2 between two adjacent rows of pressure-relieving cables and constant-resistance cables is:

[0052]

[0053] In the formula: n2 is the number of pressure-relieving cables or constant-resistance cables in each row; h is the height of the transportation roadway or the return airway; γ is the average unit weight of the overlying strata; Qs is the lateral pressure value; Ku is the influence coefficient of the advanced abutment pressure on the transportation roadway or the influence coefficient after the first mining disturbance of the return airway; α is the coal seam dip angle; is the internal friction angle of the coal body.

[0054] As a preferred solution of the present invention, the first pressure-relieving main anchor cable section and the second pressure-relieving main anchor cable section both include a pressure-relieving lock, a pressure-relieving device, and a pressure-relieving tray connected in sequence. The two ends of the pressure-relieving cable pass through the corresponding pressure-relieving tray, pressure-relieving device, and pressure-relieving lock in sequence;

[0055] The first constant-resistance main anchor cable section and the second constant-resistance main anchor cable section both include a constant-resistance lock, a constant-resistance tray, and a constant-resistance rod connected in sequence. The two ends of the constant-resistance cable pass through the corresponding constant-resistance rod, constant-resistance tray, and constant-resistance lock in sequence.

[0056] Due to the adoption of the above technical solutions, the present invention can achieve the following technical effects:

[0057] 1. Through the design of bidirectional through-going anchor cables, mechanical linkage is formed on both sides of the coal pillar, transforming the traditional two-way stress state into a three-way constraint system; the odd and even number series cross-arrangement of yielding cables and constant-resistance cables constructs a spatial three-dimensional support network, significantly enhancing the shear and compressive resistance of the coal pillar; the two-side tension pre-tightening technology ensures uniform stress distribution and avoids the stress concentration phenomenon caused by single-side support.

[0058] 2. The constant-resistance cables provide continuous high-strength support, and the yielding cables achieve controllable deformation; the constant-resistance - yielding combination forms a complementary mechanism of "rigid support + flexible yielding", which can both control deformation and absorb energy.

[0059] 3. Based on the calculation of vertical stress, the support parameters are dynamically adjusted, and the yielding amount is quantitatively controlled. The size effect correction and time effect correction achieve the stress regulation throughout the life cycle.

[0060] 4. The spacing and design enable the scientific quantification of support parameters. Considering geological parameters such as coal seam dip angle and internal friction angle, it ensures adaptability under complex conditions and improves the support accuracy.

[0061] 5. Compared with the traditional 20 - 30m wide coal pillar, this method can achieve stable support for a 5 - 8m narrow coal pillar, significantly improving the coal recovery rate, reducing the roadway repair rate, and lowering the comprehensive cost.

[0062] The present invention organically combines mechanical calculation, dynamic support, and spatial structure optimization, solves the contradiction system of "high stress - large deformation - weak support" in deep mining, and provides a systematic solution for the safe and efficient mining of narrow coal pillars. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0064] Figure 1 is the structural schematic diagram of each working face in actual work;

[0065] Figure 2 is the structural schematic diagram of the constant-resistance large-deformation anchor cable;

[0066] Figure 3 is the structural schematic diagram of the yielding device anchor cable;

[0067] Figure 4 is the plan view of the bidirectional through-going anchor cables for the narrow coal pillar under the double-heading layout;

[0068] Figure 5 It is the elevation view of two-way through-anchored cables with a narrow coal pillar under double-gallery layout;

[0069] Figure 6 It is the schematic diagram of the cross arrangement of constant-resistance large-deformation cables and pressure-relieving cables;

[0070] Explanation of the numbers in the figure: 1: Return airway; 2: Coal pillar; 3: Haulage roadway; 4: Constant-resistance large-deformation cable; 5: Pressure-relieving cable; 6: Constant-resistance locking device; 7: Constant-resistance tray; 8: Constant-resistance rod; 9: Constant-resistance cable; 10: Pressure-relieving locking device; 11: Pressure-relieving device; 12: Pressure-relieving tray; 13: Pressure-relieving cable; 14: First working face; 15: Second working face. Specific implementation manners

[0071] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application clearer and more understandable, the following further details this application in combination with the attached drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit this application.

[0072] It should be noted that when an element is referred to as "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0073] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of this application, "a plurality of" means two or more unless otherwise specifically defined. "Several" means one or more unless otherwise specifically defined.

[0074] In the description of this application, it should be understood that the orientation or positional relationship indicated by the terms "center", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the attached drawings, and is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the indicated device or element must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to this application.

[0075] In the description of this application, it should be noted that unless otherwise clearly specified and limited, the terms "installation", "connection", and "linkage" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0076] Embodiment 1

[0077] Please refer to Figure 1-6 , this embodiment provides a support system for implementing the above method, including a number of reinforcement units for two-way cooperative anchoring of the support coal pillar between the first working face transportation roadway (current mining face) and the second working face return airway (to-be-mined face). The reinforcement unit adopts a support structure in which a constant-resistance large-deformation anchor cable (NPR anchor cable) and a yielding-pressure anchor cable are cross-combined. Among them: the constant-resistance large-deformation anchor cable adapts to the plastic deformation of the coal pillar through its continuous high resistance and large-deformation characteristics; the yielding-pressure anchor cable relieves stress concentration and prevents the anchor cable from breaking prematurely through a controllable yielding mechanism; the two work together to build a three-dimensional stress balance system inside the coal pillar and improve the overall stability.

[0078] In this embodiment, the yielding-pressure anchor cable includes: the yielding-pressure main anchor cable section (located on the roadway side) has a yielding-pressure lock, a yielding-pressure device, and a yielding-pressure tray; the yielding-pressure cable (penetrating the coal pillar) passes through the corresponding yielding-pressure trays, yielding-pressure devices, and yielding-pressure locks at both ends in sequence to form a slidable yielding-pressure structure.

[0079] The constant-resistance large-deformation anchor cable (NPR anchor cable) includes: the constant-resistance main anchor cable section (located on the roadway side) has a constant-resistance lock, a constant-resistance tray, and a constant-resistance rod; the constant-resistance cable (penetrating the coal pillar) passes through the corresponding constant-resistance rods, constant-resistance trays, and constant-resistance locks at both ends in sequence to provide high constant resistance and large-deformation ability.

[0080] In this embodiment, a number of through holes are drilled in the support coal pillar; the yielding-pressure main anchor cable section is respectively fixed on the side of the first working face transportation roadway and the side of the second working face return airway through the yielding-pressure lock, and the yielding-pressure tray fits the surface of the coal pillar; the constant-resistance main anchor cable section is respectively fixed on the side of the first working face transportation roadway and the side of the second working face return airway through the constant-resistance lock, and the constant-resistance tray fits the surface of the coal pillar to form a through-hole reinforcement structure.

[0081] In this embodiment, the constant-resistance large-deformation anchor cable and the yielding-pressure anchor cable are arranged in a columnar cross pattern: the constant-resistance large-deformation anchor cables are arranged at equal intervals in odd-numbered columns; the yielding-pressure anchor cables are arranged at equal intervals in even-numbered columns; horizontally, the two types of anchor cables are staggered and equally spaced to form a three-dimensional support network, enabling the coal pillar to change from two-way stress to three-way stress.

[0082] The effect of this embodiment is that by using the through-going anchor cable and combining the yielding anchor cable and the NPR constant-resistance large-deformation anchor cable for cross-support technology, the efficient reinforcement of the coal pillar is realized. By optimizing the spatial layout of the anchor cables, a three-dimensional support network with two-way crossing in the vertical and horizontal directions is constructed, so that the stress state of the coal pillar is improved from the traditional two-way stress to three-way stress, thus effectively inhibiting the deformation and failure of the coal pillar. Compared with the traditional double-heading technology that requires a coal pillar with a width of 20 - 30 m, through the synergistic effect of the yielding anchor cable and the NPR constant-resistance large-deformation anchor cable, the present invention significantly improves the compressive bearing capacity of the coal pillar while greatly reducing the size of the reserved coal pillar. This innovation not only enhances the stability of the narrow coal pillar, but also significantly improves the coal recovery rate, reduces resource waste, and has important engineering application value.

[0083] Example 2

[0084] This embodiment provides a support method for improving the stability and safety of narrow coal pillars, which is implemented based on the system described in Example 1, and specifically includes:

[0085] Step 1: Borehole construction

[0086] In the first working face transportation roadway, along the direction perpendicular to the transportation roadway, horizontal through-holes are drilled on the supporting coal pillar, penetrating to the side of the second working face return airway. During borehole construction, it is necessary to ensure that the axis is straight, and the allowable deviation ≤ 2%.

[0087] Step 2: Pretreatment of anchor cables

[0088] According to the thickness of the supporting coal pillar, appropriate lengths of yielding strands and constant-resistance strands are pre-cut to ensure that their lengths can completely cover the borehole and leave enough truncation margin.

[0089] Step 3: Installation of anchor cables

[0090] The pretreated yielding strands and constant-resistance strands are alternately arranged in the borehole to form a cross-support structure, and it is ensured that the exposed ends of the yielding strands and constant-resistance strands on the side of the first working face transportation roadway extend out, and the anchoring ends extend to the side of the second working face return airway.

[0091] Step 4: Reinforcement and tensioning of constant-resistance strands

[0092] On the side of the first working face transportation roadway, the first constant-resistance main anchor cable section is installed in sequence, and then a tensile pre-tightening force is applied to the constant-resistance strands.

[0093] Step 6: Reinforcement and tensioning of yielding strands

[0094] On the side of the first working face transportation roadway, the first yielding main anchor cable section is installed in sequence, and then a tensile pre-tightening force is applied to the yielding strands to ensure that they are tightly engaged with the side wall of the coal pillar;

[0095] Step 7: Installation of the main cable section on the return airway side of the second working face

[0096] After the return airway of the second working face is driven to the corresponding borehole, cut off the extended parts of the yielding cable and the constant-resistance cable on the return airway side of the second working face, and sequentially install the corresponding second constant-resistance main cable section and the second yielding main cable section to ensure the coordinated force of the cables on both sides.

[0097] Step 8: Cable tensioning and coal pillar reinforcement

[0098] On the return airway side of the second working face, apply a tension preload to the constant-resistance cable to make it reach the constant-resistance range (200 - 250 kN) to provide continuous high-resistance support; then apply a tension preload (150 - 250 kN) to the yielding cable and utilize its yielding characteristic to relieve the deformation stress of the coal pillar;

[0099] After applying the tension preload, the constant-resistance trays and the yielding trays on both sides are closely attached to the surface of the supporting coal pillar. Through the coordinated action of the trays on both sides, the biting effect of the coal pillar sidewall is enhanced, and the overall deformation resistance of the coal pillar is improved.

[0100] As a preferred implementation provided in this embodiment, the method for obtaining the vertical stress on the supporting coal pillar is as follows:

[0101] First, obtain the stress of the overlying strata of the supporting coal pillar (original in-situ stress):

[0102] σ 原始 = γ·H 埋深

[0103] Where: γ is the average unit weight of the overlying strata; H 埋深 is the burial depth of the coal seam (m);

[0104] Then, obtain the mining-induced additional stress (stress concentration factor M):

[0105] Δσ 采动 = M×σ 原始

[0106] The total vertical stress is:

[0107] σ = σ 原始 +Δσ 采动

[0108] As a preferred implementation provided in this embodiment, compare the total vertical stress σ with the uniaxial compressive strength σ c (MPa) of the coal body:

[0109] If σ ≥ σ c , the coal pillar has entered the plastic deformation stage, and it is necessary to further calculate the elastic and plastic compression amounts;

[0110] If σ < σc , the coal pillar is still in an elastic stable state.

[0111] As a preferred implementation provided in this embodiment, the method for obtaining the elastic compression amount is:

[0112]

[0113] In the formula: ΔL e is the elastic compression amount (Mpa); H is the height of the coal pillar (m); E is the elastic modulus of the coal body (Mpa).

[0114] The plastic compression amount ΔL p The obtaining method is:

[0115] ΔL p = ε p ·H

[0116] In the formula: H is the height of the coal body (m); ε p is the plastic strain (Mpa); the plastic strain ε p (empirical formula) is:

[0117]

[0118] In the formula: ε p is the plastic strain (Mpa); C is the plastic parameter; m is the mining concentration coefficient.

[0119] Therefore, the total compression amount:

[0120] ΔL 总 = ΔL e + ΔL p

[0121] As a preferred implementation provided in this embodiment, size effect (height-width ratio H / W) correction is performed on the total compression amount:

[0122] ΔL 修正 = β × ΔL 总

[0123] Then time effect correction is performed:

[0124] ΔL 长期 = ΔL 修正 + ΔL 蠕变

[0125] Among them, β is the correction coefficient, and ΔL 蠕变 is obtained through creep tests.

[0126] As a preferred implementation provided in this embodiment, the safety factor is taken as N, and it is required to satisfy:

[0127] Δ 锚索 > N × ΔL长期

[0128] In this embodiment, the design requirements are as follows: the total yielding amount of the constant-resistance large-deformation anchor cable and the pressure-relieving anchor cable ≥ 100 cm; under the double-gallery layout, the yielding amount on each side ≥ 50 cm (to ensure the long-term stability of the coal pillar).

[0129] Anchoring force standard: single-rope pre-tightening force of the constant-resistance cable: 200 - 250 kN; single-rope pre-tightening force of the pressure-relieving cable: 150 - 250 kN.

[0130] The determination method of the spacing between adjacent constant-resistance large-deformation anchor cables and pressure-relieving anchor cables in each row is as follows:

[0131]

[0132] In the formula: L is the length of the constant-resistance cable and the pressure-relieving anchor cable.

[0133] The row spacing S2 between adjacent rows of pressure-relieving cables and constant-resistance cables is:

[0134]

[0135] In the formula: n2 is the number of pressure-relieving cables or constant-resistance cables in each row; h is the height of the transportation roadway or the return airway; γ is the average unit weight of the overlying strata; Qs is the lateral pressure value; Ku is the influence coefficient of the advanced abutment pressure on the transportation roadway or the influence coefficient after the first mining disturbance of the return airway; α is the dip angle of the coal seam; is the internal friction angle of the coal body.

[0136] This support method enables the supported coal pillar to change from two-way stress to three-way stress through the cross layout and step-by-step tensioning of the bidirectional through-going anchor cables, effectively improving its stability and bearing capacity. At the same time, the coordinated support of the constant-resistance large-deformation anchor cable and the pressure-relieving anchor cable is adopted, which not only adapts to the large deformation of the surrounding rock but also avoids the breakage of the anchor cable caused by stress concentration, ensuring the long-term stability of the narrow coal pillar during the mining process.

[0137] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A support method for improving the stability and safety of narrow coal pillars, characterized in that, Including: Step 1: In the first working face transportation roadway, drill a horizontal through-hole along the direction perpendicular to the transportation roadway on the support coal pillar, penetrating to the side of the second working face return airway; Step 2: According to the thickness of the support coal pillar, pre-cut yielding cables and constant resistance cables to ensure that their lengths can completely cover the borehole and leave enough truncation margin; Step 3: Alternately arrange the pre-treated yielding cables and constant resistance cables in the borehole according to the designed row spacing to form a cross-support structure, and ensure that the exposed ends of the yielding cables and constant resistance cables on the side of the first working face transportation roadway protrude, and the anchoring ends extend to the side of the second working face return airway; Step 4: On the side of the first working face transportation roadway, successively install the first constant resistance main anchor cable section, and then apply a tensile pre-tightening force to the constant resistance cable; Step 5: On the side of the first working face transportation roadway, successively install the first yielding main anchor cable section, and then apply a tensile pre-tightening force to the yielding cable; Step 6: After the second working face return airway is driven to the corresponding borehole, cut off the protruding parts of the yielding cable and constant resistance cable on the side of the second working face return airway, and successively install the corresponding second constant resistance main anchor cable section and second yielding main anchor cable section to ensure that the anchor cables on both sides are stressed synergistically; Step 7: On the side of the second working face return airway, apply a tensile pre-tightening force to the constant resistance cable to make it reach the constant resistance range to provide continuous high resistance support; then apply a tensile pre-tightening force to the yielding cable to relieve the deformation stress of the coal pillar by using its yielding characteristics.

2. The support method for improving the stability and safety of narrow coal pillars according to claim 1, characterized in that, The yielding cables and constant resistance cables are arranged in columns on the support coal pillar; constant resistance cables are equally spaced on odd-numbered columns, and yielding cables are equally spaced on even-numbered columns.

3. The support method for improving the stability and safety of narrow coal pillars according to claim 1 or 2, characterized in that, The yielding cables and constant resistance cables that cross each other horizontally are equally spaced.

4. The support method for improving the stability and safety of a narrow coal pillar according to claim 1, characterized in that, The vertical stress on the support coal pillar is obtained as follows: First, obtain the overlying strata stress (original in-situ stress) of the support coal pillar: σ 原始 = γ·H 埋深 where: γ is the average unit weight of the overlying strata; H 埋深 is the burial depth of the coal seam (m); Then, obtain the mining-induced additional stress (stress concentration coefficient M): Δσ 采动 = M × σ 原始 The total vertical stress is: σ = σ 原始 + Δσ 采动。 5. The support method for improving the stability and safety of narrow coal pillars according to claim 4, characterized in that, Compare the total vertical stress σ with the uniaxial compressive strength σ of the coal body c Comparison: If σ≥σ c , the coal pillar has entered the plastic deformation stage, and it is necessary to further obtain the elastic and plastic compression amounts; If σ < σ c , the coal pillar remains in an elastic stable state.

6. The support method for improving the stability and safety of a narrow coal pillar according to claim 5, characterized in that The elastic compression amount is obtained as follows: Where: ΔL e is the elastic compression (Mpa); H is the height of the coal pillar (m); E is the elastic modulus of the coal body (Mpa). Plastic compression amount ΔL p The acquisition method is as follows: ΔL p = ε p ·H Where: H is the height of the coal body (m); ε p is the plastic strain (Mpa); the plastic strain ε p (empirical formula) is: where: ε p is the plastic strain (Mpa); C is the plastic parameter; m is the mining-induced concentration coefficient. Therefore, the total compression amount: ΔL 总 = ΔL e + ΔL p 。 7. The support method for improving the stability and safety of narrow coal pillars according to claim 6, characterized in that, Perform size effect (height-width ratio H / W) correction on the total compression amount: ΔL 修正 = β × ΔL 总 Then perform time effect correction: ΔL 长期 = ΔL 修正 + ΔL 蠕变 where β is the correction coefficient, and ΔL 蠕变 is obtained through a creep test.

8. The support method for improving the stability and safety of a narrow coal pillar according to claim 7, wherein The safety factor N should satisfy: Δ 锚索 > N × ΔL 长期 The determination method of the spacing between adjacent constant resistance large deformation anchor cables and yielding pressure anchor cables in each column is as follows: Where: L is the length of the constant-resistance cable and the pressure-relief cable; Δ 锚索 is the deformation of the cable.

9. The support method for improving the stability and safety of narrow coal pillars according to claim 8, characterized in that The row spacing S2 between adjacent two columns of yielding cables and constant resistance cables is: Where: n2 is the number of yielding cables or constant resistance cables per column; h is the height of the haulage roadway or the return airway; γ is the average unit weight of the overlying strata; Qs is the lateral pressure value; Ku is the influence coefficient of the advanced abutment pressure on the haulage roadway or the influence coefficient after the first mining disturbance of the return airway; α is the dip angle of the coal seam; is the angle of internal friction in the coal.

10. The support method for improving the stability and safety of narrow coal pillars according to claim 1, characterized in that, The first yielding main anchor cable section and the second yielding main anchor cable section both include connected yielding locks, yielding pressure devices, and yielding trays. The two ends of the yielding cable pass through the corresponding yielding trays, yielding pressure devices, and yielding locks in sequence; The first constant resistance main anchor cable section and the second constant resistance main anchor cable section both include connected constant resistance locks, constant resistance trays, and constant resistance rods. The two ends of the constant resistance cable pass through the corresponding constant resistance rods, constant resistance trays, and constant resistance locks in sequence.

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