Prediction and prevention of impacts on isolated island working faces before mining, taking into account both overall and local impacts

Abstract

The present invention relates to a mining method for predicting and controlling the impact of an isolated working face before mining, which takes into account both the overall and local aspects, and belongs to the technical field of safe mining and disaster prevention and control in coal mines. It solves the technical problems that the spatial structure and pressure distribution of the overburden of the existing isolated working face before mining is unclear, there is no clear prediction theory and method for the impact type of the isolated working face, and there is no targeted prevention and control measures for the isolated working face before mining. The solution is: a mining method for predicting and controlling the impact of an isolated working face before mining, which takes into account both the overall and local aspects, comprises the following steps: 1) clarifying the support stress of the isolated working face; 2) clarifying the bearing strength of the isolated working face; 3) clarifying the overall stability coefficient and the local stability coefficient of the isolated working face; 4) clarifying the impact type of the isolated working face; 5) clarifying the prevention and control mining measures. Compared with the prior art, the present invention has the advantages of clarifying the relationship between the support stress and the bearing strength of the isolated working face, clarifying the impact prediction method of the impact type of the isolated working face, and proposing targeted prevention and control measures for the isolated working face.

Description

Technical Field

[0001] The present invention belongs to the technical field of safe mining and disaster prevention and control in coal mines, and specifically relates to a mining method for predicting and preventing impacts of an isolated island working face before mining, taking both overall and local factors into consideration. Background Art

[0002] Due to the gradual depletion of shallow coal resources in China and the increased intensity of deep coal resource mining, in order to maintain a stable balance in the supply of coal resources, many mines are faced with the problem of disaster prevention and control in isolated working faces. However, due to the complex and changeable spatial structure of the overburden rock in the isolated working face, the spatial structure of the overburden rock is prone to instability during excavation and mining, thereby inducing mine earthquakes and even coal-rock rock burst accidents, which seriously threaten the lives of underground workers and the safety benefits of coal mines. Rock burst is the continuous accumulation of elastic energy of rocks and coal seams during tunnel excavation or mining. When the elastic energy accumulates to a certain extent and exceeds the bearing capacity of rocks and coal seams, the surrounding rock of the tunnel will be damaged and unstable.

[0003] However, most of the existing isolated working faces are mined on both sides, with deep mining and thick coal seams. Before mining, the isolated working face and the surrounding mining environment form a "goaf-coal pillar-goaf" overburden spatial structure, which leads to the transfer of overburden load and redistribution of surrounding rock stress in the goaf area of ​​the working face, affecting the type and degree of danger of rock bursts on the working face. Moreover, there is no mature prediction theory and method for the type of rock bursts on the existing isolated working faces, whether it is an overall or local impact of the isolated working faces, which brings certain difficulties to anti-burst research and technical implementation. In addition, the anti-burst measures for the isolated working faces before mining have not been implemented in a targeted manner in combination with the "overall-local" type and characteristics, and the primary and secondary distinctions and parameter changes of the prevention and control measures have not been clarified, which often results in relatively poor application effects, and rock burst accidents still occur even after pressure relief measures are taken. Summary of the invention

[0004] In order to overcome the shortcomings of the existing technology and solve the technical problems such as the unclear spatial structure and pressure distribution of the overburden of the existing isolated island working face before mining, the lack of clear prediction theory and method for the impact type of the isolated island working face, and the lack of targeted prevention and control measures for the isolated island working face before mining, the present invention provides a mining method for impact prediction and prevention and control of the isolated island working face before mining that takes into account both the overall and local aspects.

[0005] The present invention is achieved through the following technical solutions.

[0006] The present invention provides a mining method for impact prediction and prevention and control of an isolated island working face before mining, taking into account both overall and local impacts, wherein the left side of the isolated island working face is a first goaf area, and the right side of the isolated island working face is a second goaf area, comprising the following steps:

[0007] 1) Clarify the support stress of the isolated working face:

[0008] Based on the spatial structure of the overburden formed by the isolated working face and the mining environment, an estimation model for the support stress of the isolated working face is established. According to the estimation model for the support stress of the isolated working face, the relationship between the support stress of any point on the isolated working face and the distance from the first goaf and the total support stress of the isolated working face are obtained.

[0009] The expression of the relationship between the support stress at any point on the isolated working surface and the distance to the first goaf is as follows:

[0010] According to the island working face support stress estimation model, the support stress at any point on the island working face is obtained as σ x =σ q +Δσ1+Δσ2, where σ x is the support stress at any point on the island working surface, σ q is the self-weight stress of the overburden above any point on the isolated working face, Δσ1 is the stress transferred from the first goaf to any point on the isolated working face, and Δσ2 is the stress transferred from the second goaf to any point on the isolated working face;

[0011] Will

[0012]

[0013] Substitute σ x =σ q +Δσ1+Δσ2, where γ is the average bulk density of the overburden above any point on the isolated working face, x is the distance between any point on the isolated working face and the first goaf, Δσ is the maximum value of the stress increment generated by the key layer of the overburden above the first goaf on the isolated working face, β is the stratum movement angle, H is the coal seam burial depth, and L is the width of the isolated working face;

[0014] The maximum value of the stress increment Δσ generated by the overlying key layer of the first goaf on the isolated island working surface is based on Calculate, where γ is the average bulk density of the overburden above any point on the isolated working face, l is the width of the first goaf, d1 is the length of the rock contacting the lowest rock layer, d2 is the length of the rock contacting the surface subsidence basin, H is the depth of the coal seam, h is the height of the first goaf, and β is the rock layer movement angle;

[0015] The relationship between the support stress at any point on the isolated working face and the distance from the first goaf is expressed as follows: where σ x is the support stress at any point of the isolated working face, γ is the average bulk density of the overburden stratum above any point of the isolated working face, x is the distance between any point of the isolated working face and the first goaf, Δσ is the maximum value of the stress increment generated by the key layer of the overburden stratum above the first goaf on the isolated working face, β is the stratum movement angle, H is the buried depth of the coal seam, and L is the width of the isolated working face;

[0016] 2) Clarify the bearing strength of the isolated working surface:

[0017] Based on theoretical knowledge, the relationship between the bearing strength of any point on the isolated working face and the distance from the first goaf and the total bearing strength of the isolated working face are obtained;

[0018] The relationship between the bearing strength of the isolated working face and the distance from the first goaf is:

[0019] Where R x is the bearing strength of the isolated working face, λ is the confining pressure coefficient of the coal body in different areas, when the coal body is in an empty state, λ=0, when the coal body is at the elastic-plastic boundary position, λ min =1, when the coal body is at the boundary between the elastic zone and the original rock stress zone, λ max = k; σ c is the uniaxial compressive strength of coal; x p is the width of the plastic zone, x e is the width of the elastic zone;

[0020] Where m is the thickness of the coal seam, n is the stress concentration coefficient of the surrounding rock of the tunnel, and δ is the side pressure coefficient of the coal wall of the tunnel. is the internal friction angle of the coal body, c is the cohesion of the coal body, γ is the average bulk density of the overlying strata at any point on the isolated island working face, and H is the buried depth of the coal seam;

[0021] Where m is the thickness of the coal seam, n is the stress concentration coefficient of the surrounding rock of the tunnel, δ is the side pressure coefficient of the coal wall of the tunnel, and f is the friction coefficient between the bottom plate of the coal seam and the rock layer;

[0022] 3) Clarify the overall stability coefficient and local stability coefficient of the isolated island working face:

[0023] The overall stability coefficient of the isolated working face is obtained based on the total support stress of the isolated working face and the total bearing strength of the isolated working face; the local stability coefficient of the isolated working face is obtained based on the support stress at any point of the isolated working face and the bearing strength at any point of the isolated working face;

[0024] 4) Clarify the impact type of the isolated working face:

[0025] The impact type of the isolated working face is obtained based on the overall stability coefficient of the isolated working face and the local stability coefficient of the isolated working face;

[0026] 5) Clarify the prevention and control measures for mining:

[0027] Establish different countermeasures based on the impact type of the isolated working face.

[0028] Furthermore, the width of the first goaf is equal to the width of the second goaf.

[0029] Further, the total support stress of the island working surface in step 3) is the integration of the support stress at any point on the island working surface over the width of the island working surface, that is,

[0030]

[0031] Where σ is the total support stress of the island working face;

[0032] The total bearing strength of the island working surface is the integral of the bearing strength at any point on the island working surface over the width of the island working surface.

[0033]

[0034] Where R is the total bearing strength of the island working surface.

[0035] Furthermore, the overall stability coefficient of the isolated working surface is

[0036] Where I is the overall stability coefficient of the isolated working face. If I < 1, the isolated working face is stable as a whole. If I > 1, the isolated working face is unstable as a whole.

[0037] The local stability coefficient J of the isolated working surface is: If J < 1, the island working surface is locally stable; if J > 1, the island working surface is locally unstable.

[0038] Furthermore, in the step 4), the impact types of the isolated working face include a first impact type, a second impact type, a third impact type and a fourth impact type, wherein the first impact type is overall stable A1+locally stable B1, with no impact risk; the second impact type is overall stable A1+locally unstable B2, with a local impact risk; the third impact type is overall unstable A2+locally stable B1, with an overall impact risk; the fourth impact type is overall unstable A2+locally unstable B2, with a high impact risk.

[0039] Furthermore, if it is the first impact type, the isolated working face is a mineable working face; if it is the second impact type or the third impact type, the isolated working face is a mineable working face after taking measures; if it is the fourth impact type, the isolated working face is an unmineable working face.

[0040] Furthermore, if it is the first impact type, A1+B1, the isolated working face should be monitored more during excavation and mining, and attention should be paid to the changes in the support stress at any point of the isolated working face and the total support stress of the isolated working face;

[0041] If it is the second impact type, A1+B2 type, when 1≤J<1.2, coal body pressure relief is used to locally relieve the coal body of the isolated working face; when 1.2≤J<1.5, pressure relief is carried out by increasing the borehole diameter and reducing the borehole spacing; if J≥1.5, pressure relief is carried out by combining coal body pressure relief with roof pre-cracking;

[0042] If it is the third impact type, A2+B1 type, when 1≤I<1.2, the roof pre-splitting is used to control the roof of the isolated working face; when 1.2≤I<1.5, the pressure relief is carried out by reducing the spacing between blasting holes and increasing the charge density; if I≥1.5, the pressure relief is carried out by combining coal body pressure relief with roof pre-splitting;

[0043] If it is the fourth impact type, A2+B2, it is not recommended to mine the isolated working face.

[0044] The beneficial effects achieved by the present invention are as follows: the present invention proposes the spatial structure of the overburden of the mined-out on both sides of the isolated working face and establishes a support stress estimation model for the isolated working face, and combines the specific conditions of the isolated working face to obtain the support stress at any point of the isolated working face, the total support stress of the isolated working face, the bearing strength at any point of the isolated working face and the total bearing strength of the isolated working face, establishes the relationship between the support stress and the bearing strength of the isolated working face, and finds an impact prediction method and mechanical criterion for the isolated working face before mining that takes into account both the overall and local aspects; proposes four types of impacts on the isolated working face, and from the perspective of safe mining and impact prevention and control, divides the isolated working face into three categories: mineable working face, mineable working face after taking measures and unmineable working face, and proposes corresponding targeted measures.

[0045] Compared with the prior art, the present invention has the advantages of clarifying the relationship between the supporting stress and the bearing strength of the isolated working face, clarifying the impact prediction method of the isolated working face impact type, and proposing targeted prevention and control measures for the isolated working face. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a flowchart of the present invention;

[0047] Figure 2 It is a schematic diagram of the spatial structure of the overburden rock of the isolated island working face in the present invention;

[0048] Figure 3 It is a schematic diagram of the support stress curve at any point on the isolated island working surface in the present invention;

[0049] Figure 4 It is a diagram of the stress state of coal bodies in different areas of the isolated working face in the present invention;

[0050] Figure 5 It is a schematic diagram of the bearing strength curve of any point on the isolated island working surface in the present invention;

[0051] Figure 6 is the island working surface σ in the embodiment of the present invention x -R x -x relationship curve graph;

[0052] Figure 7 is the σ of the first impact type in the present invention x -R x -x relationship curve graph;

[0053] Figure 8 is the σ of the second impact type in the present invention x -R x -x relationship curve graph;

[0054] Fig. 9 is the σ of the third impact type in the present invention x -R x -x relationship curve graph;

[0055] Fig.10 is the σ of the fourth impact type in the present invention x -R x -x relationship curve graph;

[0056] Fig.11 It is a schematic diagram of drilling pressure relief in the present invention;

[0057] Fig.12 It is a schematic diagram of the roof before blasting in the present invention;

[0058] Fig.13 It is a schematic diagram of the roof after blasting in the present invention;

[0059] Fig.14 It is a schematic diagram of combined pressure relief of coal body and roof cracking in the present invention;

[0060] Fig.15 It is a numerical calculation model of an isolated island working surface in an embodiment of the present invention;

[0061] Fig.16 This is a stress cloud diagram of the support before the pressure relief of the isolated island working face in the embodiment of the present invention;

[0062] Fig.17 is a support stress cloud diagram after pressure relief on an isolated island working face in an embodiment of the present invention;

[0063] Fig.18 is a vertical stress curve diagram of an island working surface in an embodiment of the present invention;

[0064] Fig.19 Schematic diagram of the position of the pressure relief measuring point of the drilling hole on the isolated working face in the embodiment of the present invention;

[0065] Fig. 20is a stress variation curve diagram of measuring point 1 of an isolated working surface in an embodiment of the present invention;

[0066] Fig.21 is a stress variation curve diagram of measuring point 2 of the isolated working surface in an embodiment of the present invention;

[0067] Fig. 22 This is an impact warning diagram before pressure relief on an isolated island working face in an embodiment of the present invention;

[0068] Fig.23 It is an impact warning diagram after pressure relief on the isolated island working face in an embodiment of the present invention. DETAILED DESCRIPTION

[0069] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0070] like Figures 1 to 23 As shown, the left side of the isolated working face is the first goaf, and the right side of the isolated working face is the second goaf. The width of the first goaf is equal to the width of the second goaf, so as to ensure that the stress of the overburden key layer above the first goaf is transferred to the coal body of the isolated working face in an isosceles triangle distribution; in this embodiment, the width L of the isolated working face is 295m, the width l of the first goaf or the width l of the second goaf is 450m, the buried depth of the coal seam H is 605m, the height h of the first goaf is 120m, the length d1 of the lowest rock layer to touch the gangue is 280m, the length d2 of the gangue to touch the surface sinking basin is 470m, and the average bulk density γ of the overburden layer above any point of the isolated working face is 25kN / m 3 , the rock movement angle β is taken as 87°, according to the actual situation η is 1.0∽1.5, the uniaxial compressive strength of the coal body σ c is 11.0MPa, the coal seam thickness m is 5.5m, the tunnel surrounding rock stress concentration coefficient n is 1.5, the tunnel coal wall side pressure coefficient δ is 0.6, and the internal friction angle of the coal body is The angle of the coal body is 35.6°, the cohesion of the coal body c is 0.9MPa, the friction coefficient between the coal seam floor and the rock layer f is 0.2, and k is 4.5. The pre-mining isolated island working face takes into account the overall and local impact prediction and prevention and control mining methods, such as Figure 1 As shown, the following steps are included:

[0071] 1) Clarify the support stress of the isolated working face:

[0072] Based on the spatial structure of the overburden formed by the isolated working face and the mining environment, a support stress estimation model for the isolated working face is established. Figure 2 , according to the island working face support stress estimation model, the relationship expression between the support stress of any point on the island working face and the distance from the first goaf and the total support stress of the island working face are obtained;

[0073] According to the island working face support stress estimation model, the support stress at any point on the island working face is obtained as σ x =σ q +Δσ1+Δσ2, where σ x is the support stress at any point on the island working surface, σ q is the self-weight stress of the overburden above any point on the isolated working face, Δσ1 is the stress transferred from the first goaf to any point on the isolated working face, and Δσ2 is the stress transferred from the second goaf to any point on the isolated working face;

[0074] Will

[0075]

[0076] Substitute σ x =σ q +Δσ1+Δσ2, where γ is the average bulk density of the overburden above any point on the isolated working face, x is the distance between any point on the isolated working face and the first goaf, Δσ is the maximum value of the stress increment generated by the key layer of the overburden above the first goaf on the isolated working face, β is the stratum movement angle, H is the coal seam burial depth, and L is the width of the isolated working face;

[0077] The maximum value of the stress increment Δσ generated by the overlying key layer of the first goaf on the isolated island working surface is based on Calculate, where γ is the average bulk density of the overburden above any point on the isolated working face, l is the width of the first goaf, d1 is the length of the rock contacting the lowest rock layer, d2 is the length of the rock contacting the surface subsidence basin, H is the depth of the coal seam, h is the height of the first goaf, and β is the rock layer movement angle;

[0078] Therefore, the relationship between the support stress at any point on the isolated working face and the distance from the first goaf is expressed as follows: where σ x is the support stress at any point of the isolated working face, γ is the average bulk density of the overburden above any point of the isolated working face, x is the distance between any point of the isolated working face and the first goaf, Δσ is the maximum value of the stress increment generated by the key layer of the overburden above the first goaf on the isolated working face, β is the rock movement angle, H is the buried depth of the coal seam, and L is the width of the isolated working face, which can be obtained from Figure 3 You can intuitively see the schematic diagram of the support stress curve at any point on the island working surface.

[0079] Substituting the specific values ​​of this embodiment into

[0080]

[0081] 2) Clarify the bearing strength of the isolated working surface:

[0082] Based on theoretical knowledge, the relationship between the bearing strength of any point on the isolated working face and the distance from the first goaf and the total bearing strength of the isolated working face are obtained;

[0083] The stress states in different areas of the isolated working face are different, including unidirectional stress, bidirectional stress and tridirectional stress, see Figure 4 The bearing strength of the isolated working face is approximately linearly related to the confining pressure, so the relationship between the bearing strength of the isolated working face and the distance from the first goaf is:

[0084] Can be obtained from Figure 5 The changing trend and magnitude of the bearing strength can be intuitively seen in the figure, where R x is the bearing strength of the isolated working face, λ is the confining pressure coefficient of the coal body in different areas, when the coal body is in an empty state, λ=0, when the coal body is at the elastic-plastic boundary position, λ min =1, when the coal body is at the boundary between the elastic zone and the original rock stress zone, λ max =k, the value of k is related to the uniaxial compressive strength of the coal body. The greater the strength, the smaller k; σ c is the uniaxial compressive strength of coal; x p is the width of the plastic zone, x e is the width of the elastic zone;

[0085] Where m is the thickness of the coal seam, n is the stress concentration coefficient of the surrounding rock of the tunnel, and δ is the side pressure coefficient of the coal wall of the tunnel. is the internal friction angle of the coal body, c is the cohesion of the coal body, γ is the average bulk density of the overlying strata at any point on the isolated island working face, and H is the buried depth of the coal seam;

[0086] Where m is the thickness of the coal seam, n is the stress concentration coefficient of the tunnel surrounding rock, δ is the side pressure coefficient of the tunnel coal wall, and f is the friction coefficient between the coal seam floor and the rock layer; Substituting the data in this embodiment, we get According to the support stress σ at any point on the island working surface in this embodiment x The bearing strength of any point on the isolated working face and the distance x from the first goaf can be plotted as Figure 6, it can be seen that the bearing strength of the isolated working face in this embodiment is roughly trapezoidal in distribution, and it shows an upward trend at 0∽15.0m on both sides of the isolated working face, and reaches its maximum bearing strength of 30.0MPa at x=15.0m; and it can also be seen that the support stress and bearing strength of the isolated working face in this embodiment are symmetrically distributed. At x=0∽15.0m, the slope of the bearing strength curve of the working face is greater than the slope of the supporting stress curve, and the bearing strength curve remains unchanged after reaching a peak value of 30.0MPa at x=15.0m, while the supporting stress still maintains an upward trend at x=15.0∽30.0m and reaches a peak value of 31.1MPa at x=30.0m. After the supporting stress locally exceeds the bearing strength, it begins to decrease, and finally decreases to 15.1MPa and stabilizes.

[0087] 3) Clarify the overall stability coefficient and local stability coefficient of the isolated island working face:

[0088] The overall stability coefficient of the isolated working face is obtained based on the total support stress of the isolated working face and the total bearing strength of the isolated working face; the local stability coefficient of the isolated working face is obtained based on the support stress at any point of the isolated working face and the bearing strength at any point of the isolated working face;

[0089] The total support stress of the island working surface is the integration of the support stress at any point on the island working surface over the width of the island working surface.

[0090]

[0091] Where σ is the total support stress of the island working face;

[0092] The total bearing strength of the island working surface is the integral of the bearing strength at any point on the island working surface over the width of the island working surface.

[0093]

[0094] Where R is the total bearing strength of the island working surface.

[0095] The overall stability coefficient of the isolated working face is:

[0096] Where I is the overall stability coefficient of the isolated working surface. If I < 1, the isolated working surface is stable as a whole. If I > 1, the isolated working surface is unstable as a whole. Substituting the data in this embodiment, we can get Thus, the overall stability coefficient of the isolated island working surface in this embodiment is less than 1, and the isolated island working surface in this embodiment is overall stable;

[0097] The local stability coefficient J of the isolated working surface is: If J < 1, the island working surface is locally stable; if J > 1, the island working surface is locally unstable; Substituting the data in this embodiment, we can get Thus, it is obtained that the local stability coefficient of the isolated island working surface in this embodiment is greater than 1, and the isolated island working surface is locally unstable;

[0098] 4) Clarify the impact type of the isolated working face:

[0099] The impact type of the isolated working face is obtained based on the overall stability coefficient of the isolated working face and the local stability coefficient of the isolated working face;

[0100] The impact types of the isolated working face include the first impact type, the second impact type, the third impact type and the fourth impact type. The first impact type is overall stability A1 + local stability B1, with no impact risk. Figure 7 σ x -R x -x relationship curve; the second shock type is overall stability A1 + local instability B2, there is a risk of local shock, you can refer to Figure 8 σ x -R x -x relationship curve; the third impact type is overall instability A2 + local stability B1, there is an overall impact risk, you can refer to Fig. 9 σ x -R x -x relationship curve; the fourth impact type is overall instability A2 + local instability B2, the impact risk is large, you can refer to Fig.10 σ x -R x -x relationship curve graph;

[0101] In this embodiment, the overall stability coefficient of the isolated island working face is less than 1, which means it is overall stable, and the local stability coefficient is greater than 1, which means it is locally unstable and has a local impact risk;

[0102] 5) Clarify the prevention and control measures for mining:

[0103] Establish different countermeasures based on the impact type of the isolated working face.

[0104] If it is the first impact type, the isolated working face is a mineable working face; if it is the second impact type or the third impact type, the isolated working face is a mineable working face after taking measures; if it is the fourth impact type, the isolated working face is an unmineable working face, and from step 4), it is obtained that the isolated working face in this implementation is a mineable working face after taking measures;

[0105] If it is the first impact type, A1+B1, the isolated working face should be monitored more during excavation and mining, and attention should be paid to the changes in the support stress at any point of the isolated working face and the total support stress of the isolated working face;

[0106] If it is the second impact type, A1+B2 type, when 1≤J<1.2, coal body pressure relief is used to locally relieve the coal body of the isolated working face. Commonly used pressure relief methods include drilling pressure relief and hydraulic cavitation. Drilling pressure relief can cause structural damage to the coal body, thereby achieving the effect of local pressure relief; when 1.2≤J<1.5, pressure relief is carried out by increasing the borehole diameter and reducing the borehole spacing. The larger the borehole diameter, the larger the pressure relief area formed, and the more obvious the pressure relief effect will be. The smaller the borehole spacing, the easier it is to form through cracks between the holes, and the better the pressure relief effect; if J≥1.5, pressure relief is carried out by combining coal body pressure relief with roof pre-cracking.

[0107] Take drilling pressure relief as an example. Fig.11 As shown, L b is the drilling depth, R b is the drilling diameter, d b D is the drilling distance, x is the distance between drilling and working surface, d x is the distance between the borehole and the base plate, k' is the hazard correction coefficient of the pressure relief borehole spacing, which is related to the drilling dust removal; d3 is the diameter of the pressure relief drilling drill bit; K is the deformation modulus index, K = λ1 / E; λ1 is the softening modulus after the peak value of the stress-strain curve; E is the elastic modulus before the peak value of the stress-strain curve. The specific parameters of the drilling pressure relief can be seen from Table 1.

[0108] Table 1 Specific parameters of drilling pressure relief

[0109]

[0110] If it is the third impact type, A2+B1 type, when 1≤I<1.2, the roof pre-splitting is used to control the roof of the isolated working face. Common methods include roof blasting, hydraulic fracturing, etc.; when 1.2≤I<1.5, the pressure relief is carried out by reducing the spacing between blast holes and increasing the charge density. After the explosion of explosives, the rock mass within a certain range around the blast hole is strongly compressed and crushed to form a compressed crushing zone, and radial radial cracks and annular tangential cracks are formed in the crushing zone and the crack zone, interrupting or weakening the transmission of radial and tangential stresses in the surrounding rock, reducing the stress of the surrounding rock and the energy accumulation of the roof rock layer, and the overall pressure relief effect is good; if I≥1.5, the coal body pressure relief and roof pre-splitting are combined for pressure relief. You can refer to Fig.14 ;

[0111] Take roof blasting as an example. Fig.12 and Fig.13 As shown, θ is the blast hole inclination angle, L sis the drilling depth, L f is the sealing section, L d The charging section, where the drilling opening and final hole positions are determined based on site conditions, key layer positions, blasting rock layers, etc. The opening position should be arranged near the shoulder of the tunnel. The specific parameters of the roof blasting can be seen from Table 2, where h s is the height difference between the drilling opening position and the final hole position, l s It is the horizontal distance between the drilling position and the final hole position.

[0112] Table 2 Specific parameters of roof blasting

[0113]

[0114] If it is the fourth impact type, A2+B2, this type of isolated working face has a strong impact hazard and is prone to accidents. It is not recommended to mine the isolated working face.

[0115] This embodiment belongs to the second impact type. J<1.5, the width of the coal pillars on both sides of the isolated working face in this embodiment is set to 10m, and the drilling pressure relief is carried out by increasing the borehole diameter and reducing the borehole spacing, wherein the borehole diameter is 120mm, the borehole depth is 15m, and the hole spacing is 2.0m∽3.0m. For areas with higher impact risk, the hole spacing is 2.0m, and the borehole is 1.0m away from the bottom plate. A numerical calculation model is established according to actual geological conditions, such as Fig.15 . The model has a total of 119,400 grids and 1,231,200 nodes. The upper boundary of the model is a stress boundary, and a vertical load is applied to simulate the weight of the overlying rock strata. The horizontal direction is a sliding and stress boundary. The side of the model restricts horizontal movement, and the bottom restricts vertical movement. The simulated depth is 605.0 m. Based on the relationship between the actual burial depth of the coal seam and the height of the model, a vertical equivalent load of 13.5 MPa needs to be applied to the upper surface of the model. The model adopts the Moore-Coulomb constitutive model as a whole. After the ground stress is balanced, the coal seams on both sides of the working face are excavated and then the coal seams are decompressed by drilling. The support stress cloud map before decompression, the support stress cloud map after decompression and the vertical stress curve are obtained, as shown in the figure. Fig.16 , 17 As shown in Figures 18, it can be clearly seen that the vertical stress of the isolated working face in this embodiment first increases, then decreases and finally stabilizes from the coal wall to the deep coal body, and the stress concentration is mainly at about 30m on both sides of the working face, with the stress peak reaching 30.6MPa. After the implementation of the drilling pressure relief measures, the stress peak is reduced and obviously transferred to the deep working face, and the stress concentration is alleviated.

[0116] In order to verify the decompression effect of drilling holes in the isolated working face in this embodiment, two groups of measuring points are set in the isolated working face, which are 10m and 15m away from the coal wall respectively. Measuring point 1 is composed of stress gauges I and II, and measuring point 2 is composed of stress gauges III and IV. Fig.19 You can see the distribution of measurement points. Fig. 20 and 21 It can be seen that the relative vertical stress of the coal body at measuring point 1, 10m away from the coal wall, was about 8.0MPa before drilling unloading. After drilling unloading, the relative vertical stress at measuring point 1 gradually decreased to about 6.5MPa, which was about 19% lower than the original relative vertical stress. At the same time, the relative vertical stress of the coal body at measuring point 2, 15m away from the coal wall, remained basically unchanged before unloading, but showed an upward trend after unloading.

[0117] from Fig. 22 and 23 It can also be seen that during the excavation process, the impact warning of the isolated working face in this embodiment appeared, and the drilling pressure relief measures were effective. There was no shrinkage of the tunnel section, subsidence of the roof, or damage to the anchor rods, and the warning was lifted.

[0118] This embodiment applies the overall and local impact prediction and prevention and control mining method of the present invention, clarifies the impact type of this embodiment, and uses drilling pressure relief to locally relieve pressure on the isolated working face, with significant results. It ensures the safe excavation of the isolated working face in this embodiment and improves the economic benefits of the coal mine to a certain extent.

[0119] The above describes in detail the implementation modes of the present invention in conjunction with the accompanying drawings, but the present invention is not limited to the above implementation modes. The implementation modes can still be changed within the knowledge scope of ordinary technicians in the field. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A mining method for predicting and preventing impacts of an isolated island working face before mining that takes into account both the overall and local impacts, wherein the left side of the isolated island working face is the first goaf area, and the right side of the isolated island working face is the second goaf area, and the method is characterized in that: The following steps are involved: 1) Clarify the support stress of the isolated working surface: Based on the spatial structure of the overburden formed by the isolated working face and the mining environment, an estimation model for the support stress of the isolated working face is established. According to the estimation model for the support stress of the isolated working face, the relationship between the support stress of any point on the isolated working face and the distance from the first goaf and the total support stress of the isolated working face are obtained. The expression steps for the relationship between the support stress at any point on the isolated working surface and the distance to the first goaf are as follows: According to the island working face support stress estimation model, the support stress at any point on the island working face is obtained as σ x =σ q +Δσ1+Δσ2, where σ x is the support stress at any point on the island working surface, σ q is the self-weight stress of the overburden above any point on the isolated working face, Δσ1 is the stress transferred from the first goaf to any point on the isolated working face, and Δσ2 is the stress transferred from the second goaf to any point on the isolated working face; Substitute σ x =σ q +Δσ1+Δσ2, where γ is the average bulk density of the overburden above any point on the isolated working face, x is the distance between any point on the isolated working face and the first goaf, Δσ is the maximum value of the stress increment generated by the key layer of the overburden above the first goaf on the isolated working face, β is the stratum movement angle, H is the coal seam burial depth, and L is the width of the isolated working face; The maximum value of the stress increment Δσ generated by the overlying key layer of the first goaf on the isolated island working surface is based on Calculate, where γ is the average bulk density of the overburden above any point on the isolated working face, l is the width of the first goaf, d1 is the length of the rock contacting the lowest rock layer, d2 is the length of the rock contacting the surface subsidence basin, H is the depth of the coal seam, h is the height of the first goaf, and β is the rock layer movement angle; The relationship between the support stress at any point on the isolated working face and the distance from the first goaf is expressed as follows: The support stress at any point of the island working face, γ is the average bulk density of the overburden above any point of the island working face, x is the distance between any point of the island working face and the first goaf, Δσ is the maximum value of the stress increment generated by the key layer of the overburden above the first goaf on the island working face, β is the rock movement angle, H is the buried depth of the coal seam, and L is the width of the island working face; 2) Clarify the bearing strength of the isolated working surface: Based on theoretical knowledge, the relationship between the bearing strength of any point on the isolated working face and the distance from the first goaf and the total bearing strength of the isolated working face are obtained; The relationship between the bearing strength of the isolated working face and the distance from the first goaf is: Where R x is the bearing strength of the isolated working face, λ is the confining pressure coefficient of the coal body in different areas, when the coal body is in an empty state, λ=0, when the coal body is at the elastic-plastic boundary position, λ min =1, when the coal body is at the boundary between the elastic zone and the original rock stress zone, λ max = k; σ c is the uniaxial compressive strength of coal; x p is the width of the plastic zone, x e is the width of the elastic zone; Where m is the thickness of the coal seam, n is the stress concentration coefficient of the surrounding rock of the tunnel, and δ is the side pressure coefficient of the coal wall of the tunnel. is the internal friction angle of the coal body, c is the cohesion of the coal body, γ is the average bulk density of the overlying strata at any point on the isolated island working face, and H is the buried depth of the coal seam; Where m is the thickness of the coal seam, n is the stress concentration coefficient of the tunnel surrounding rock, δ is the side pressure coefficient of the tunnel coal wall, and f is the friction coefficient between the coal seam floor and the rock layer. 3) Clarify the overall stability coefficient and local stability coefficient of the isolated island working face: The overall stability coefficient of the isolated working face is obtained based on the total support stress of the isolated working face and the total bearing strength of the isolated working face; the local stability coefficient of the isolated working face is obtained based on the support stress at any point of the isolated working face and the bearing strength at any point of the isolated working face; 4) Clarify the impact type of the isolated working face: The impact type of the isolated working face is obtained based on the overall stability coefficient of the isolated working face and the local stability coefficient of the isolated working face; 5) Clarify the prevention and control measures for mining: Establish different countermeasures based on the impact type of the isolated working face.

2. The method for predicting and preventing impacts of isolated island working faces before mining according to claim 1, characterized in that: The width of the first goaf is equal to the width of the second goaf.

3. The method for predicting and preventing impacts of isolated island working faces before mining according to claim 2 is characterized in that: The total support stress of the island working surface in step 3) is the integration of the support stress at any point on the island working surface over the width of the island working surface. Where σ is the total support stress of the island working face; The total bearing strength of the island working surface is the integral of the bearing strength at any point on the island working surface over the width of the island working surface. Where R is the total bearing strength of the island working surface.

4. The method for predicting and preventing impacts of isolated island working faces before mining according to claim 3 is characterized in that: The overall stability coefficient of the isolated working face is: Where I is the overall stability coefficient of the isolated working face. If I < 1, the isolated working face is stable as a whole. If I > 1, the isolated working face is unstable as a whole. The local stability coefficient J of the isolated working surface is: If J < 1, the island working surface is locally stable; if J > 1, the island working surface is locally unstable.

5. The method for predicting and preventing impacts of isolated island working faces before mining according to claim 4 is characterized in that: In the step 4), the impact types of the isolated working face include the first impact type, the second impact type, the third impact type and the fourth impact type. The first impact type is overall stability A1+local stability B1, and there is no impact risk; the second impact type is overall stability A1+local instability B2, and there is a local impact risk; the third impact type is overall instability A2+local stability B1, and there is an overall impact risk; the fourth impact type is overall instability A2+local instability B2, and there is a high impact risk.

6. The method for predicting and preventing impacts of isolated island working faces before mining according to claim 5 is characterized in that: If it is the first impact type, the isolated island working face is a mineable working face; if it is the second impact type or the third impact type, the isolated island working face is a mineable working face after taking measures; if it is the fourth impact type, the isolated island working face is an unmineable working face.

7. The method for predicting and preventing impacts of isolated island working faces before mining according to claim 6 is characterized in that: If it is the first impact type, A1+B1, the isolated working face should be monitored more during excavation and mining, and attention should be paid to the changes in the support stress at any point of the isolated working face and the total support stress of the isolated working face; If it is the second impact type, A1+B2 type, when 1≤J<1.2, coal body pressure relief is used to locally relieve the coal body of the isolated working face; when 1.2≤J<1.5, pressure relief is carried out by increasing the borehole diameter and reducing the borehole spacing; if J≥1.5, pressure relief is carried out by combining coal body pressure relief with roof pre-cracking; If it is the third impact type, A2+B1 type, when 1≤I<1.2, the roof pre-splitting is used to control the roof of the isolated working face; when 1.2≤I<1.5, the pressure relief is carried out by reducing the spacing between blasting holes and increasing the charge density; if I≥1.5, the pressure relief is carried out by combining coal body pressure relief with roof pre-splitting; If it is the fourth impact type, A2+B2, it is not recommended to mine the isolated working face.

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