Chain type instability prevention and control method for coal pillar group-roof system

Abstract

The invention belongs to the technical field of coal mine room and pillar mining, and particularly relates to a chain type instability prevention and control method for a coal pillar group-roof system. Comprising the following steps: determining a coal pillar which can cause instability of a coal pillar group-roof system, and calculating the lowest strength of a filling body wall of the coal pillar; determining the width of the filling wall according to the minimum strength of the filling body wall; and a filling wall is constructed on the peripheral side of the coal pillar to reinforce the coal pillar, and the height of the filling wall is equal to that of the coal pillar. Aiming at the problem of instability (chain type instability) of the coal pillar group-roof system in the room type goaf, the invention provides a scheme for reinforcing the filling wall constructed on the peripheral side of the coal pillar which can cause instability of the coal pillar group-roof system, and provides a calculation method for determining the width and the strength of the filling body wall, so that grouting materials can be configured in a targeted manner. Lateral bearing pressure can be provided for the coal pillar by arranging the filling body wall, so that the coal pillar recovers a three-way stress state, the ultimate bearing strength of the coal pillar is improved, and meanwhile, the filling body wall blocks the influence of an external physical environment on the coal pillar.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mine room-pillar mining, and in particular relates to a method for preventing and controlling chain instability of a coal pillar group-roof system. Background Art

[0002] After the formation of the room-type goaf, a large number of residual coal pillars exist densely to form a coal pillar group. The coal pillar group and the roof constitute a coal pillar group-roof system. The stability of the residual coal pillar group and the roof is the decisive factor for the overall stability of the goaf. Within a certain period of time, the coal pillar can effectively support the roof of the goaf without losing stability. Except for the weak pseudo-roof that falls, the rest of the roof does not break and collapse. However, over time, under the influence of many factors, the surface of the coal pillar gradually peels off, the limited bearing width of the coal pillar continues to decrease, and eventually it becomes unstable and damaged, breaking the stable equilibrium stress state in the overburden above it, and then causing a large-scale roof collapse. During this period, a series of disasters such as rock burst, water and sand burst, coal and gas outbursts may be triggered, threatening the safe mining of horizontal adjacent and overlying or underlying coal seams. In addition, the instability of the coal pillar will cause surface subsidence and damage the surface ecological environment of the mining area.

[0003] Under the concept of green mining in coal mines, the prevention and control of instability of coal pillars in goafs caused by instability and destruction of coal pillars in goafs has become an urgent problem to be solved. This can not only effectively prevent disasters in goafs and ensure the healthy development of the ecological environment in mining areas, but also provide support for re-entering goafs to recover remaining coal pillars as technology and equipment develop. Summary of the invention

[0004] The purpose of the present invention is to provide a chain instability prevention and control method for a coal pillar group-roof system, which is used to solve the problem that coal pillar instability causes roof instability, which in turn causes goaf disasters and damage to the ecological environment of the mining area.

[0005] In order to achieve the above-mentioned invention object, the present invention adopts the following technical solutions:

[0006] The chain instability prevention and control method of the coal pillar group-roof system includes the following steps:

[0007] Step 1: Determine the coal pillar that will cause the coal pillar group-roof system to become unstable, calculate the minimum strength of the filling wall of the coal pillar, and meet the following conditions

[0008]

[0009] In the formula, σ pc is the ultimate compressive strength of the backfill wall under triaxial stress, x1 and x2 represent the starting and ending coordinates of the original coal pillar in the length direction, y1 and y2 represent the starting and ending coordinates of the original coal pillar in the width direction, l px is the original length of the coal pillar, l pyis the original width of the coal pillar, l pb h is the spalling size of the coal pillar, p Refers to the height of the coal pillar, E p is the elastic modulus of the coal pillar, l fx is the distance between coal pillars in the length direction, l fy is the distance between the coal pillars in the width direction, ω is the deflection of the roof at the coal pillars; c is the cohesion of the coal pillars; is the internal friction angle of the coal pillar; μ c is the Poisson’s ratio of the filling wall;

[0010] Step 2: Determine the width of the filling wall based on the minimum strength of the filling wall, and meet the following conditions

[0011]

[0012] In the formula, x c is the width of the filling wall, d is the mining disturbance factor, is the internal friction angle of the filling wall, c pc is the cohesion of the filling wall, β is the lateral pressure coefficient at the interface between the yield zone and the elastic core zone of the filling wall;

[0013] Step 3: The construction width around the coal pillar is not less than x c The coal pillar is reinforced by a filling wall, and the height of the filling wall is equal to the height of the coal pillar.

[0014] Preferably, in the first step, the ultimate compressive strength of the filling body wall under a three-dimensional stress state is greater than the supporting pressure of the filling body wall on the top plate.

[0015] Preferably, in the second step, it is assumed that the coal pillar does not exert lateral constraints on the backfill wall, and the height of the backfill wall is equal to the height of the coal pillar.

[0016] Preferably, in the third step, a filling borehole of suitable size is drilled from the ground or underground, and based on the minimum strength of the filling body wall determined in the first step, suitable filling materials are configured, and a filling pump is used to perform grouting reinforcement on one side of the coal pillar through the filling borehole.

[0017] Preferably, in the third step, a grouting borehole of a suitable size is drilled from the ground or underground, grouting reinforcement materials are arranged, and a grouting pump is used to perform grouting reinforcement on the inside of the coal pillar through the grouting borehole.

[0018] Beneficial technical effects: 1. The present invention aims at the problem of instability (chain instability) of coal pillar group-roof system in room-type goaf, and proposes a plan to construct backfill walls to reinforce the coal pillars that may cause instability of the coal pillar group-roof system. It also provides a calculation method for determining the width and strength of the backfill wall, so that grouting materials can be configured in a targeted manner.

[0019] 2. In the present invention, for coal pillars that may cause instability of the coal pillar group-roof system, after injecting grouting reinforcement materials into the coal pillars, high-strength extrusion force and bonding force can be provided to the internal crack weak surfaces of the coal pillars, thereby achieving the effect of repairing the damaged and broken areas, and at the same time, further damage to the existing damaged weak surfaces caused by load disturbance can be significantly reduced; by setting up a filling body wall, lateral support pressure can be provided to the coal pillars, so that the coal pillars can be restored to a three-dimensional stress state, the ultimate bearing strength of the coal pillars is improved, and at the same time, the filling body wall blocks the influence of the external physical environment on the coal pillars. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of coal pillar reinforcement for backfill wall;

[0021] In the figure: 1-coal pillar; 2-backfill wall; 3-roof; 4-bottom plate. DETAILED DESCRIPTION

[0022] The specific implementation of the present invention will be described below in conjunction with the accompanying drawings.

[0023] like Figure 1 As shown, the present invention proposes a chain instability prevention and control method for a coal pillar group-roof system, comprising the following steps:

[0024] Step 1: Determine the coal pillar 1 that will cause partial or complete instability (including chain instability) of the coal pillar group-roof system, and determine the minimum strength of the backfill wall 2 of the coal pillar 1 according to the coal rock mass parameters; to ensure the stability of the backfill wall 2, the ultimate compressive strength of the backfill wall 2 under the three-way stress state, that is, the uniaxial compressive strength should be greater than the supporting pressure of the backfill wall 2 on the roof 3. At this time:

[0025]

[0026] In the formula, σ pc is the ultimate compressive strength of the filling wall under triaxial stress, MPa; σ′ pc is the bearing pressure of the filling wall on the roof, MPa; σ p is the load on the coal pillar when it is only affected by the overlying rock strata, MPa; c is the cohesion of the coal pillar, MPa; is the internal friction angle of the coal pillar, °; μ c is the Poisson’s ratio of the filling wall;

[0027] Considering the spalling of coal on the surface of coal pillar 1, the load on coal pillar 1 when it is only affected by the overlying strata is:

[0028]

[0029] Wherein, x1+lpb and x2-lpb represent the horizontal coordinate range of the effective bearing length of the coal pillar (the starting and ending coordinates of the coal pillar in the length direction), x1 and x2 represent the horizontal coordinate range of the original length of the coal pillar (the starting and ending coordinates of the coal pillar in the length direction); y1+lpb and y2-lpb represent the vertical coordinate range of the effective bearing width of the coal pillar (the starting and ending coordinates of the coal pillar in the width direction); y1 and y2 represent the vertical coordinate range of the original width of the coal pillar (the starting and ending coordinates of the coal pillar in the width direction); l px is the original length of the coal pillar (x2-x1), m; l py is the original width of the coal pillar (y2-y1), m; l pb h is the spalling size of the coal pillar; p is the height of the coal pillar, m; E p is the elastic modulus of the coal pillar, GPa; l fx is the length of the coal room (the distance between the coal pillars in the length direction), m; l fy is the width of the coal room (the distance between the coal pillars in the width direction), m; ω is the deflection of the roof at the coal pillar, m;

[0030] The load σ when the coal pillar is only subjected to the overlying rock strata p The strength σ of the filling wall 2 to ensure the stability of the coal pillar can be obtained as pc Should meet:

[0031]

[0032] Step 2: Determine the minimum width of the filling wall according to the minimum strength of the filling wall;

[0033] Assuming that the coal pillar 1 does not produce lateral constraints on the backfill wall 2, that is, the lateral constraints of the backfill wall 2 are 0, the yield zone width of the backfill wall is:

[0034]

[0035] In the formula, x yc is the yield zone width of the filling wall, m; h p Refers to the height of the coal pillar, m; d is the mining disturbance factor, generally 1.5 to 3.0; is the internal friction angle of the filling wall, °; c pc is the cohesion of the filling wall, MPa; β is the lateral pressure coefficient at the interface between the yield zone and the elastic core zone of the filling wall;

[0036] Assuming that the backfill wall is completely connected to the top, that is, the height of the backfill wall 2 is equal to the height of the coal pillar 1, according to the limit equilibrium theory, in order to ensure the stability of the backfill wall 2, the width of the backfill wall 2 should meet the following requirements:

[0037] x≥2x+2h

[0038] cycp

[0039] In the formula, x c is the width of the filling wall, m;

[0040] According to the yield zone width x of the filling wall 2 yc , and finally the width of the filling wall is obtained c The following conditions should be met:

[0041]

[0042] Step 3: According to the calculation results, the construction width around the coal pillar is not less than x c The coal pillar is reinforced by a filling wall, and the height of the filling wall 2 is equal to the height of the coal pillar 1;

[0043] Specifically, a grouting borehole of a suitable size is drilled from the ground or underground, grouting reinforcement materials are configured, and a grouting pump is used to perform grouting reinforcement on the inside of the coal pillar 1 through the grouting borehole to improve the inherent strength of the coal pillar 1; a filling borehole of a suitable size is drilled from the ground or underground, and based on the minimum strength of the filling body wall 2 determined in the first step, suitable filling materials are configured, and a filling pump is used to perform grouting reinforcement on the side of the coal pillar 1 through the filling borehole to form a lateral constraint on the coal pillar 1.

[0044] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of methods under the inspiration of the present invention. Any technical solution that is the same or similar to that of the present application falls within the protection scope of the present invention.

Claims

1. A chain instability prevention and control method for a coal pillar group-roof system, characterized in that: The steps include: Step 1: Determine the coal pillar that will cause the coal pillar group-roof system to become unstable, calculate the minimum strength of the filling wall of the coal pillar, and meet the following conditions In the formula, σ pc is the ultimate compressive strength of the backfill wall under triaxial stress, x1 and x2 represent the starting and ending coordinates of the original coal pillar in the length direction, y1 and y2 represent the starting and ending coordinates of the original coal pillar in the width direction, l px is the original length of the coal pillar, l py is the original width of the coal pillar, l pb h is the spalling size of the coal pillar, p Refers to the height of the coal pillar, E p is the elastic modulus of the coal pillar, l fx is the distance between coal pillars in the length direction, l fy is the distance between the coal pillars in the width direction, ω is the deflection of the roof at the coal pillars; c is the cohesion of the coal pillars; is the internal friction angle of the coal pillar; μ c is the Poisson's ratio of the filling wall; Step 2: Determine the width of the filling wall based on the minimum strength of the filling wall, and meet the following conditions In the formula, x c is the width of the filling wall, d is the mining disturbance factor, is the internal friction angle of the filling wall, c pc is the cohesion of the filling wall, β is the lateral pressure coefficient at the interface between the yield zone and the elastic core zone of the filling wall; Step 3: The construction width around the coal pillar is not less than x c The coal pillar is reinforced by a filling wall, and the height of the filling wall is equal to the height of the coal pillar.

2. The method for preventing and controlling chain instability of the coal pillar group-roof system according to claim 1 is characterized in that: In the first step, the ultimate compressive strength of the filling wall under the three-dimensional stress state is greater than the supporting pressure of the filling wall on the top plate.

3. The method for preventing and controlling chain instability of the coal pillar group-roof system according to claim 1 is characterized in that: In the second step, it is assumed that the coal pillar does not exert lateral constraints on the backfill wall, and the height of the backfill wall is equal to the height of the coal pillar.

4. The method for preventing and controlling chain instability of a coal pillar group-roof system according to any one of claims 1 to 3, characterized in that: In the third step, a filling borehole of suitable size is drilled from the ground or underground, and based on the minimum strength of the filling body wall determined in the first step, suitable filling materials are configured, and a filling pump is used to perform grouting reinforcement on the sides of the coal pillar through the filling borehole.

5. The method for preventing and controlling chain instability of the coal pillar group-roof system according to claim 4 is characterized in that: In the third step, a grouting borehole of suitable size is drilled from the ground or underground, grouting reinforcement materials are configured, and a grouting pump is used to grout the inside of the coal pillar through the grouting borehole.

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