A method for evaluating and determining a working face stopping distance based on a coal seam roadway protection

Abstract

The application provides a working face stopping mining distance evaluation and determination method based on coal seam large roadway protection, relates to the underground safety evaluation and mining design field of coal mines, and comprises the following steps: step one: according to the distribution characteristics and laws of the space structure transfer stress of the upper strata and the self-weight stress of the overburden strata, the relationship between the supporting stress p of an arbitrary position of the interval coal pillar between the stopping working face and the coal seam large roadway and the distance between the stopping working face is calculated; step two: the interval coal pillar is regarded as a "large coal pillar" and has typical "large coal pillar" characteristics, and the relationship between the bearing strength R of the arbitrary position of the interval coal pillar and the distance between the stopping working face and / or the roadway coal wall is obtained according to the typical "large coal pillar" characteristics; step three: stopping distance safety evaluation; the scheme provided by the application can quantitatively evaluate the surrounding rock stability of the coal seam large roadway under different stopping distance conditions, and the relatively reasonable stopping distance is determined accordingly, which can guide the stopping design engineering in the working face final mining stage.

Description

Technical Field

[0001] This invention relates to the field of underground safety assessment and mining design in coal mines, and in particular to a method for assessing and determining the stopping distance of working faces based on the protection of coal seam main roadways. Background Technology

[0002] The vast majority of my country's coal resources are mined underground. To achieve effective mining and sustained production, coal mining enterprises often adopt a panel layout centered on "working faces + main roadways." This involves pre-planning main roadways around the coal seam to be mined for various functions such as pedestrian access, transportation, and ventilation. Working faces for coal recovery are then designed around these main roadways. To minimize damage to the surrounding rock caused by working face mining, a certain width of stopping distance is required between the working faces and the main roadways. Generally, main roadways serve a specific mining area, multiple mining areas, or even the entire mine, and have a relatively long service life. They are a prerequisite for ensuring safe production and stable coal output, thus requiring high overall safety and stability. However, with rapid national industrial development and improved living standards, the dependence on coal resources has not fundamentally changed. Furthermore, due to the continuous depletion of shallow and easily mined coal resources, coal mining enterprises are increasingly adopting the main roadway layout to achieve rapid production and reduce mining operations. Compared with the layout of rock strata roadways, the roadway excavation target of coal seam roadways is the coal seam. Due to the low strength of the coal seam, the biggest advantage is that it can be excavated quickly and can produce coal in the mining area and working face in a short period of time. The biggest disadvantage is that the surrounding rock stability of coal seam roadways is worse than that of rock strata roadways. In the later stage, it is easily affected by mining disturbances, which can lead to deformation and damage, making it difficult to determine the stopping distance of the working face.

[0003] Currently, at the national and coal industry levels, there is no well-established standardized and regulated method for "safety assessment and quantitative determination of the stopping distance for working faces protecting coal seam main roadways." Therefore, when encountering coal seam main roadways during underground mining, there is no mature technical system for reference. Instead, the method mainly relies on analogies with similar projects and adjacent working faces in the mine, leading to results that are somewhat empirical. If the experience of the reference objects is insufficient or the matching is unreasonable, it may cause two problems: excessive stopping distance, resulting in certain coal resource losses; or insufficient stopping distance, causing continuous deformation or damage to the coal seam main roadway. Both of these situations may have adverse consequences for coal mining enterprises. Currently, scholars have conducted research and practice on the movement of overlying strata, stress transfer laws, and instability and stability control of surrounding rock in the tailing stage of working faces. However, there are no reports on methods for safety assessment and quantitative determination of the stopping distance for working faces protecting coal seam main roadways. This issue has received continuous attention from safety departments, production units, and researchers. Safety assessment and optimization design of coal seam main roadways under special conditions such as rockbursts are explicitly required. Therefore, there is an urgent need for a method to assess and determine the working face shutdown distance based on coal seam main roadway protection to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to provide a method for evaluating and determining the stopping distance of a working face based on the protection of the main roadway of a coal seam, so as to solve the problems existing in the prior art, quantitatively evaluate the stability of the surrounding rock of the main roadway of the coal seam under different stopping distance conditions, and determine a relatively reasonable stopping distance accordingly, which can guide the stopping design engineering of the final stage of the working face.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] This invention provides a method for assessing and determining the stopping distance of a working face based on coal seam main roadway protection, including:

[0007] Step 1: Based on the distribution characteristics and laws of stress transfer in the overlying strata during mining and the self-weight stress of the overlying strata, calculate the relationship between the supporting stress p at any position of the coal pillar between the mining stop face and the main roadway of the coal seam and the distance between the mining stop face.

[0008] Step 2: Treat the coal pillar between the stopped working face and the main coal seam roadway as a "large coal pillar" with typical "large coal pillar" characteristics. Based on the typical "large coal pillar" characteristics, determine the relationship between the bearing strength R at any position of the coal pillar between the stopped working face and the main coal seam roadway and the distance between the stopped working face and / or the coal wall of the roadway.

[0009] Step 3: Safety assessment of the distance to stop mining;

[0010] Calculate the working face stoppage boundary support stress p at the boundary between the elastic zone and the original rock stress zone of the surrounding rock in the coal seam main roadway, and the bearing capacity R of the coal seam main roadway. Compare p and R:

[0011] p > R indicates that the main roadway of the coal seam is unsafe;

[0012] p < R indicates the safety of the main roadway in the coal seam;

[0013] When p and R are equal, it indicates that the main roadway of the coal seam is at the critical point between unsafe and safe.

[0014] Preferably, in step three, the coefficient ω = R / p is used to characterize the safety of the coal seam main roadway. The larger ω is, the higher the safety of the coal seam main roadway. ω > 1.0 indicates safety, and ω < 1.0 indicates unsafety. The critical condition for safety or unsafety of the coal seam main roadway is ω = R / p = 1.0.

[0015] Preferably, it also includes step four: quantitative determination of the stopping distance;

[0016] Based on the critical condition for safety or unsafety of the main roadway in the coal seam, ω = R / p = 1.0, the ultimate safety condition for the main roadway in the coal seam, ω = R, is obtained. max / p x＝D-a-b The stopping distance under the condition of 1.0 is determined, and a reasonable stopping distance is quantitatively determined based on the actual solution.

[0017] Where, p x＝D-a-b This refers to the supporting stress at the boundary between the elastic zone and the original rock stress zone.

[0018] Preferably, in step one: with the mining direction of the working face as the abscissa x, the height direction of the working face as the ordinate y, and the bottom boundary of the stopped working face as the origin o; the expression for the relationship between the coal seam support stress p and x is obtained as follows:

[0019]

[0020] Based on the curve distribution characteristics of p, the peak value of the support stress p is obtained.

[0021] Where H is the average mining depth of the working face, α and β are the overburden movement angle and the overburden contact angle, respectively, and γ is the average unit weight of the overburden;

[0022] Taking the bottom boundary of the main roadway or the closed working face as the origin o, the direction extending towards the "large coal pillar" as the abscissa x, and the coal seam height direction as the ordinate y, the expression for the bearing capacity R at any location in the coal seam in relation to x is obtained as follows:

[0023]

[0024] In the formula: [σ c[ ] represents the uniaxial compressive strength of the coal seam. η is used to approximate the confining pressure parameter in different regions of the main roadway of the coal seam. η varies with the confining pressure state. At the point where η0 = 0 in the coal wall of the roadway, and at the boundary between the elastic and plastic zones, η is... min =1, the boundary position η between the elastic zone and the original rock stress zone max =N, where the value of N is related to the uniaxial compressive strength of the coal seam; the higher the strength, the smaller the value. Generally, N is taken as 3 to 5. The widths of the fractured-plastic zone and elastic zone of the surrounding rock in the main roadway of the coal seam are respectively... t is the roadway height, and δ is the roadway coal wall lateral pressure coefficient. Let be the internal friction angle of the coal, c be the cohesion of the coal, and k be the stress concentration factor of the surrounding rock in the roadway. This is the coefficient of friction between the roof and floor of the roadway and the coal seam. It is the internal friction angle between the roof and floor of the roadway and the coal seam.

[0025] Preferably, due to the different distribution characteristics of the support stress p at the working face stop mining boundary at the boundary of the elastic zone and the original rock stress zone under different working conditions, the bearing strength R of the coal seam roadway is different, which leads to the coefficient ω=R / p characterizing the safety of the coal seam roadway having multiple possible situations.

[0026] The methods and steps for quantitatively determining the stopping distance are discussed in the following categories:

[0027] (1) If Dab>Hcotα, the support stress at the working face stop-mining boundary at the boundary of elastic zone-original rock stress zone is γH;

[0028] 1) If γH≥N[σ c If the coal seam main roadway is not properly constructed, it needs to be reinforced or a rock stratum main roadway layout should be adopted.

[0029] 2) If γH < N[σ] c The working face stopping distance D can be further reduced according to the following analysis;

[0030] (2) If 0.5Hcotα<Dab≤Hcotα, the peak value of the support stress at the stop-mining boundary of the working face is...

[0031] 1) If This indicates that the maximum bearing capacity of the coal seam main roadway is always greater than the peak value of the supporting stress. At this time, any position meets the stop mining distance. We only need to find the coal seam main roadway position that best meets the conditions.

[0032] 2) If This indicates that the maximum bearing capacity of the main roadway in the coal seam is less than the peak bearing stress. Analysis In extreme cases, the result of D has one and only one value, which is the reasonable working face stopping distance under the condition of coal seam main roadway.

[0033] (3) If 0 < Dab ≤ 0.5Hcotα, then the peak value of the support stress at the stop-mining boundary of the working face is...

[0034] 1) If This indicates that the maximum bearing capacity of the coal seam main roadway is always greater than the peak value of the supporting stress. At this time, any position meets the stop mining distance. We only need to find the coal seam main roadway position that best meets the conditions.

[0035] 2) If This indicates that the maximum bearing capacity of the main roadway in the coal seam is less than the peak bearing stress. At this point, the boundary between the elastic zone and the original rock stress zone in the main roadway spatially "passes through" the peak bearing stress, i.e., Dab = 0.5Hcotα, before it "arrives" in the region near the working face (0 < Dab ≤ 0.5Hcotα). Therefore, considering... The result of D under extreme conditions contradicts the zoning assumption, namely, there is no reasonable working face stopping distance under the condition of no coal seam main roadway. At this time, the design needs to be reconsidered, and the stopping distance needs to be "increased" and re-quantified according to the above steps (1), (2), and (3).

[0036] Preferably, considering that the main roadway of the coal seam is located in the "pressure boosting zone" and satisfies 0.5Hcotα<Dab≤Hcotα, the bearing capacity R curve of the main roadway of the coal seam is plotted.

[0037] If x = Dab, p x＝D-a-b >N[σ c If the working face stop distance D is not designed properly, then according to... Analysis suggests that the reasonable working face stopping distance D needs to be increased;

[0038] If x = Dab And p x＝D-a-b <N[σ c If the working face stopping distance D is designed to meet safety requirements, it can also be done according to... It can further determine the stopping distance D under extreme conditions.

[0039] The present invention achieves the following technical effects compared to the prior art:

[0040] The method for evaluating and determining the stopping distance of a working face based on the protection of the main roadway provided by this invention can quantitatively evaluate the stability of the surrounding rock of the main roadway under different stopping distances, and determine a relatively reasonable stopping distance accordingly, which can guide the stopping design engineering of the final stage of the working face. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 A schematic diagram of the mining coal seam, main coal seam roadway, stop line, and inter-coal pillar;

[0043] Figure 2 for Figure 1 A cross-sectional schematic diagram;

[0044] Figure 3 An analytical model for calculating support stress;

[0045] Figure 4 An analytical model for calculating the bearing capacity of coal seam roadways;

[0046] Figure 5 A schematic diagram illustrating the influence of different support stress curves on the stopping distance D;

[0047] Figure 6 This is a schematic diagram illustrating the stopping distance of the underground working face and the damage of the main roadway in the application example;

[0048] Figure 7 A diagram illustrating the application and analysis of the actual stopping distance at the working face;

[0049] In the picture:

[0050] 1- Bearing strength curve of the coal pillar at the working face when mining is suspended;

[0051] 2- Support stress curve (peak value) at the working face stoppage boundary;

[0052] 2'- Support stress curve at the working face cessation boundary (low peak value);

[0053] 3-Stop mining line; 4-Main coal seam roadway; 5-Interval coal pillar; 6-Working face roadway. Detailed Implementation

[0054] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] The purpose of this invention is to provide a method for evaluating and determining the stopping distance of a working face based on the protection of the main roadway of a coal seam, so as to solve the problems existing in the prior art, quantitatively evaluate the stability of the surrounding rock of the main roadway of the coal seam under different stopping distance conditions, and determine a relatively reasonable stopping distance accordingly, which can guide the stopping design engineering of the final stage of the working face.

[0056] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0057] This invention provides a method for assessing and determining the stopping distance of a working face based on coal seam main roadway protection, including:

[0058] Step 1: Based on the distribution characteristics and laws of stress transfer in the overlying strata during mining and the self-weight stress of the overlying strata, calculate the relationship between the supporting stress p at any position of the coal pillar between the mining stop face and the main roadway of the coal seam and the distance between the mining stop face.

[0059] Step 2: Treat the coal pillar between the stopped working face and the main coal seam roadway as a "large coal pillar" with typical "large coal pillar" characteristics. Based on the typical "large coal pillar" characteristics, determine the relationship between the bearing strength R at any position of the coal pillar between the stopped working face and the main coal seam roadway and the distance between the stopped working face and / or the coal wall of the roadway.

[0060] Step 3: Safety assessment of the distance to stop mining;

[0061] Calculate the working face stoppage boundary support stress p at the boundary between the elastic zone and the original rock stress zone of the surrounding rock in the coal seam main roadway, and the bearing capacity R of the coal seam main roadway. Compare p and R:

[0062] p > R indicates that the main roadway of the coal seam is unsafe;

[0063] p < R indicates the safety of the main roadway in the coal seam;

[0064] When p and R are equal, it indicates that the main roadway of the coal seam is at the critical point between unsafe and safe.

[0065] Coal seam main roadway surrounding rock: The coal and rock mass surrounding the main roadway; in this patent, it mainly refers to the coal body surrounding the roadway. The specific analysis process and implementation method are as follows:

[0066] 1. Distance between working faces and mining stoppages, considering coal seam main roadway protection

[0067] like Figure 1The diagram shown illustrates a simplified plan view of the mining area, depicting the horizontal relationship between the working face and the main coal seam roadway. Based on relevant requirements and actual needs, the working face is pushed forward to a designated stop-mining position before being withdrawn; this position is called the stop-mining line. Due to factors such as coal seam conditions and mining disturbances, a key technical parameter needs to be determined: the reasonable working face stop-mining distance D. To protect the main coal seam roadway while avoiding resource waste, a reasonable working face stop-mining distance D can ensure the stability of the main coal seam roadway while minimizing coal resource loss (reducing the stop-mining distance), achieving an integrated "economic-technical" approach.

[0068] Will Figure 1 A profile analysis was conducted along the mining direction of the working face to obtain... Figure 2 As the working face advances, the local overburden space structure near the working face takes on an inverted triangular shape (this part of the rock strata is "temporarily stable" and moves with the advancement of the working face). The rock mass in front of the inverted triangle shape does not show significant mining damage, while the rock strata behind the inverted triangle shape undergo fracturing from bottom to top, gradually forming a rock-touch effect. The outline of the inverted triangle shape is mainly formed by the overburden movement line and the overburden-rock-touch line. The overburden movement line is the boundary between the stable rock mass in front of the working face and the local overburden space structure near the working face, while the overburden-rock-touch line is the boundary between the local overburden space structure near the working face and the stable fractured rock strata behind the goaf. Because the overburden space structure near the working face is in a "hinged" structure with the surrounding rock, the load on the overburden space structure can form a stress transfer effect. This stress is roughly distributed according to the trend of "0 at the stope boundary - increase - peak value - decrease - original rock stress - remain stable," i.e. Figure 2 The support stress curve shown is roughly divided into a decompression zone, a pressure-increasing zone, and a original rock stress zone according to the comparison with the original rock stress. H is the average mining depth of the working face, and the overburden movement angle and the overburden contact angle are α and β, respectively. ①, ②, and ③ are possible locations of the main roadway in the coal seam.

[0069] Based on the relationship between the location of the main coal seam roadway and the support stress curve, the following classifications can be made:

[0070] (1) The main roadway of the coal seam is located in the original rock stress zone (the location of the main roadway of the coal seam is ①). The main roadway of the coal seam is the longest distance from the stop line. The external stress borne by the main roadway of the coal seam is the original rock stress. It is least affected by mining disturbance, but the resource loss is the greatest.

[0071] (2) The main roadway of the coal seam is located in the pressure-boosting zone (location ② of the main roadway of the coal seam). The distance between the main roadway of the coal seam and the stop line is relatively large. The external stress borne by the main roadway of the coal seam is the high stress or even peak stress of the pressure-boosting zone. It is relatively affected by mining disturbance, but the resource loss is relatively small.

[0072] (3) The main roadway of the coal seam is located in the pressure relief zone (location ③ of the main roadway of the coal seam). The distance between the main roadway of the coal seam and the stop line is relatively small. The external stress borne by the main roadway of the coal seam is the peak stress. It is relatively most affected by mining disturbance (as the working face is pushed forward and the support stress curve moves forward, the main roadway of the coal seam can only "come" to the pressure relief zone near the working face by "passing through" the support peak stress. Therefore, it needs to be analyzed according to the peak stress). However, the resource loss is relatively small.

[0073] 2. Calculation of support stress curve at the working face stoppage boundary

[0074] Using the mining direction of the working face as the abscissa (x), the height direction of the working face as the ordinate (y), the boundary of the working face or the stop-mining location as the origin (o), and the inverted triangle shape representing the outline boundary of the overlying rock space structure near the working face, an analytical model for the support stress curve at the stop-mining boundary of the working face is established, such as... Figure 3 As shown, half of the load from the "unit" formed by the rock strata within the overburden space structure is transferred to the back goaf contact rock strata, and half is transferred to the front rock mass (this part forms the bearing stress curve). Therefore, based on the load source that forms the bearing stress, it can be obtained that the bearing stress p is caused by the overburden self-weight stress σ. g With half of the overburden space structure transferred stress σ Δ The superimposed composition, taking the average unit weight of the overlying rock as γ, yields the bearing stress p expressed as:

[0075] p = σ g +σ Δ (1)

[0076] Where, σ g σ Δ Further, based on the distribution characteristics and patterns of the overburden's self-weight stress and the stress transferred by the overburden's spatial structure, the corresponding expression is:

[0077]

[0078]

[0079] Substituting equations (2) and (3) into equation (1), we can further obtain the expression for the support stress p.

[0080]

[0081] Based on the curve distribution characteristics of p, the peak value of the support stress p is obtained.

[0082] 3. Calculation of bearing capacity curve of main roadway in coal seam

[0083] The actual stopping distance D of a typical working face is greater than 20-30m. This means the stopping distance between the working face boundary or stopping line and the main coal seam roadway is a typical "large coal pillar" characteristic, exhibiting a complete distribution of fractured-plastic zone, elastic zone, and original rock stress zone. Due to the different confining pressure states of the coal body in different areas, from the stopping boundary or roadway coal wall to the deep original rock stress zone, the coal body gradually transitions from a free-floating state to a triaxial confining pressure state. Considering that the uniaxial compressive strength of the coal body is approximately linearly related to the confining pressure state, the expression for the bearing capacity curve R of the surrounding rock in the main coal seam roadway is obtained:

[0084]

[0085] In the formula: [σ c [ ] represents the uniaxial compressive strength of the coal seam. η is used to approximate the confining pressure parameters in different regions of the main roadway. Generally, η varies with the confining pressure state. At the roadway coal wall, η0 = 0, and at the boundary between elastic and plasticity, η... min =1, the boundary position η between the elastic zone and the original rock stress zone max =N (the value is related to the uniaxial compressive strength of the coal body; the greater the strength, the smaller the value; generally, N = 3 to 5 is taken), the widths of the fractured-plastic zone and elastic zone of the surrounding rock in the main roadway of the coal seam are respectively t is the roadway height, δ is the roadway coal wall lateral pressure coefficient, φ is the internal friction angle of the coal body, c is the coal body cohesion, k is the roadway surrounding rock stress concentration coefficient, f = tanφ' is the friction coefficient between the roadway roof and floor and the coal seam, and φ' is the internal friction angle between the roadway roof and floor and the coal seam.

[0086] It can be observed that the bearing capacity R of the coal seam main roadway reaches its maximum value at the boundary between the elastic zone and the original rock stress zone of the surrounding rock. max =N[σ c ].

[0087] 4. Methods for Safety Assessment and Quantitative Determination of Mining Stop Distance in Coal Seam Main Roadways

[0088] 4.1 Safety Assessment of Coal Seam Main Roadways

[0089] The safety and instability risk of coal seam roadways are jointly controlled by "external" and "internal" factors. From a stress perspective, under static stress conditions, the support stress p at the working face stoppage boundary is an "external" factor, while the bearing capacity R of the coal seam roadway is an "internal" factor. At the boundary between the elastic zone and the original rock stress zone of the surrounding rock in the coal seam roadway, if the support stress p at the working face stoppage boundary is higher than the bearing capacity R of the corresponding area, the coal seam roadway has the mechanical conditions to become unstable and unsafe. Therefore, the criterion for the safety of the coal seam roadway is p < R. If the coefficient ω = R / p is used to characterize the safety of the coal seam roadway, the larger ω is, the higher the safety of the coal seam roadway, and ω > 1.0 indicates safety, ω < 1.0 indicates unsafety. The critical condition for the safety (or unsafety) of the coal seam roadway is ω = R / p = 1.0.

[0090] Therefore, the above ideas and methods can be used to assess the safety and stability of coal seam main roadways and the reasonableness of the stopping distance, and provide a reference for determining a reasonable stopping distance.

[0091] 4.2 Quantitative Determination of Mining Stop Distance

[0092] Due to the different distribution characteristics of the support stress p at the working face stoppage boundary at the elastic zone-original rock stress zone boundary under different working conditions, the bearing capacity R of the coal seam main roadway varies, leading to multiple possible values ​​for the coefficient ω = R / p, which characterizes the safety of the coal seam main roadway. Furthermore, based on the critical condition of safety (or unsafety) of the coal seam main roadway, ω = R / p = 1.0, and the maximum bearing capacity R at the elastic zone-original rock stress zone boundary (i.e., x = Dab) of the surrounding rock in the coal seam main roadway... max =N[σ c (At this point, the bearing strength R reaches its maximum value), and the support stress p x＝D-a-b (At this time, the support stress p is based on the result of x = Dab in equation (2), and the ultimate safety condition ω = R in the main roadway of the coal seam is analyzed. max / p x＝D-a-b The stopping distance is determined when the value is 1.0, and a reasonable stopping distance is quantitatively determined based on the actual solution.

[0093] The methods and steps for quantitatively determining the stopping distance are further categorized and discussed below:

[0094] (1) If Dab>Hcotα, the support stress at the working face stoppage boundary at the boundary of the elastic zone-original rock stress zone is γH.

[0095] 1) If γH≥N[σ] c If the coal seam main roadway is not properly constructed, it needs to be reinforced or a rock stratum main roadway layout should be adopted.

[0096] 2) If γH < N[σ] cThe working face stopping distance D can be further reduced according to the following analysis;

[0097] (2) If 0.5Hcotα<Dab≤Hcotα, the peak value of the support stress at the stop-mining boundary of the working face is...

[0098] 1) If This indicates that the maximum bearing capacity of the coal seam main roadway is always greater than the peak value of the supporting stress. At this time, any position meets the stop mining distance. We only need to find the coal seam main roadway position that best meets the conditions.

[0099] 2) If This indicates that the maximum bearing capacity of the main roadway in the coal seam is less than the peak bearing stress. Analysis The result of D under extreme conditions (there is one and only one value) is the reasonable working face stopping distance under the conditions of the main roadway of the coal seam.

[0100] (3) If 0 < Dab ≤ 0.5Hcotα, then the peak value of the support stress at the stop-mining boundary of the working face is...

[0101] 1) If This indicates that the maximum bearing capacity of the coal seam main roadway is always greater than the peak value of the supporting stress. At this time, any position meets the stop mining distance. We only need to find the coal seam main roadway position that best meets the conditions.

[0102] 2) If This indicates that the maximum bearing capacity of the main roadway in the coal seam is less than the peak bearing stress. At this point, the boundary between the elastic zone and the original rock stress zone in the main roadway spatially "passes through" the peak bearing stress (i.e., Dab = 0.5Hcotα) to "arrive" in the region near the working face (0 < Dab ≤ 0.5Hcotα). Therefore, considering... In the extreme case, the result of D (which contradicts the zoning assumption) indicates that there is no reasonable working face stopping distance under the condition that there is no main roadway in the coal seam. At this time, the design needs to be reconsidered, and the stopping distance needs to be "increased" and re-quantified according to the steps (1), (2), and (3) above.

[0103] Further explanation of the application, such as... Figure 5 As shown, considering that the main coal seam roadway is located in the "pressure boosting zone" and satisfies 0.5Hcotα<Dab≤Hcotα, the bearing capacity R curve of the main coal seam roadway is as follows. Figure 5 Curve 1. If the support stress curve is as shown... Figure 5 For curve 2, when x = Dab, p x＝D-a-b >N[σ c If the working face stop distance D is not designed properly, then according to... Analysis suggests that the reasonable working face stopping distance D needs to be increased. If the support stress p curve is as follows... Figure 5 The 2' curve, when x = Dab, And p x＝D-a-b <N[σ c If the working face stopping distance D is designed to meet safety requirements, it can also be done according to... It can further determine the stopping distance D under extreme conditions.

[0104] 5. Application and Analysis

[0105] In a deep mine, the 8006 working face was initially mined, with the main coal seam being mined at a depth H = 650m. The nearest main roadway to the working face is the No. 1 dedicated return airway in the 80 mining area, which adopts a coal roadway layout. The coal seam main roadway and the working face's stop-mining line are not parallel; the stop-mining distance is smaller on the haulage roadway side and larger on the return airway side. According to engineering analogy, the actual underground stop-mining distance D = 55-100m. During the final stop-mining period, local deformation or damage occurred in the No. 1 dedicated return airway in the 80 mining area ahead of the working face. Due to the unreasonable stop-mining distance and varying degrees of impact, the safety of the No. 1 dedicated return airway in the 80 mining area was affected in a "zonal" manner. The deformed and damaged areas were mainly located near the haulage roadway side, with a stop-mining distance of 55-75m from the working face's stop-mining line. Meanwhile, the main roadway within the range of 75-100m from the working face's stop-mining line remained relatively stable. Figure 6 As shown.

[0106] Verification analysis was conducted based on the proposed model and method. The uniaxial compressive strength [σ] of coal seam 3 in the working face was determined. c =11MPa, the height of the No.1 dedicated return airway in mining area 80 is t=3m, the side pressure coefficient of the coal wall in the roadway is δ=0.6, and the internal friction angle of the coal body is... The coal seam cohesion c = 0.87 MPa, the stress concentration factor of the surrounding rock in the roadway k = 1.8, and the internal friction angle between the roadway roof and floor and the coal seam... The coefficient of friction between the roadway roof and floor and the coal seam The overburden movement angle α = 80° and the overburden contact angle β = 65° at the working face are given. The confining pressure parameter η is located at the boundary between the elastic zone and the original rock stress zone. max =N=3.5. Based on this, the width of the fractured-plastic zone in the main roadway of the coal seam in the 8006 working face is a=5~6m, the width of the elastic zone is b=7~8m, a+b=12~14m (average 13m), and the peak support stress at the stop-mining boundary is p. x＝57 = 42.7 MPa, maximum bearing capacity R of coal seam main roadway max =38.5MPa.

[0107] The bearing stress curve p at the working face stoppage boundary and the maximum bearing strength R of the coal seam main roadway max Distribution as Figure 7 As shown. From Figure 7It can be concluded that when the stopping distance of the 8006 working face is D = 55-75m and Dab = 42-62m, the No. 1 dedicated return airway in the 80 mining area is located at the boundary between the elastic zone and the original rock stress zone. The supporting stress at the working face stopping boundary is p = 30.8-40.4MPa > 38.5MPa, and the roadway is assessed as "unsafe". This is consistent with the deformation and damage of the main roadway in the coal seam in the area 55-75m away from the stopping line of the working face. When the stopping distance of the 8006 working face is D = 75-100m and Dab = 62-87m, the No. 1 dedicated return airway in the 80 mining area is located at the boundary between the elastic zone and the original rock stress zone. The supporting stress at the working face stopping boundary is p = 28.8-40.4MPa, and most of them are less than 38.5MPa. The roadway is assessed as "safe", which is consistent with the relative stability of the main roadway in the range of 75-100m away from the stopping line of the working face.

[0108] The peak value of the support stress p at the stop-mining boundary of the 8006 working face is p x＝57 =42.7MPa is greater than the maximum bearing capacity R of the main roadway of the coal seam. max =38.5MPa, the No. 1 dedicated return airway in mining area 80 cannot "cross" the peak support stress area of ​​the working face stoppage boundary at the boundary of the elastic zone and the original rock stress zone. Under the condition that 55 < D - 13 ≤ 114, according to Under extreme conditions, the relatively reasonable stopping distance D = 80m for the 8006 working face was quantitatively determined. Considering other factors such as the surrounding rock support of the main roadway, this is basically consistent with the actual situation that the No. 1 dedicated return airway of the 80 mining area has different characteristics of "unsafe" and "safe" at a stopping distance of 75m from the stopping line of the 8006 working face.

[0109] This invention uses specific examples to illustrate the principles and implementation methods of the invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the invention.

Claims

1. A method for assessing and determining the stopping distance of a working face based on coal seam main roadway protection, characterized in that: include: Step 1: Based on the distribution characteristics and laws of stress transfer in the overlying strata during mining and the self-weight stress of the overlying strata, calculate the relationship between the supporting stress p at any position of the coal pillar between the mining stop face and the main roadway of the coal seam and the distance between the mining stop face. Step 2: Treat the spacer coal pillar as a "large coal pillar," possessing typical characteristics of a "large coal pillar." Calculate the bearing capacity at any location within the spacer coal pillar based on these typical characteristics. R Relationship between the distance to the working face and / or the coal wall of the roadway; Step 3: Safety assessment of the distance to stop mining; Determine the working face stoppage support stress at the boundary between the elastic zone and the original rock stress zone of the surrounding rock in the main roadway of the coal seam. p and the bearing capacity of the main roadway of the coal seam R ,contrast p and R : p Greater than R A main roadway in a coal seam indicates an unsafe condition. p Less than R Characterizes the safety of coal seam main roadways; p and R Equal values ​​indicate that the main roadway of the coal seam is at the critical point between unsafe and safe conditions. In step three, coefficients are used The value of ω represents the safety of a coal seam main roadway. A larger ω indicates higher safety, with ω > 1.0 indicating safety and ω < 1.0 indicating unsafety. The critical condition for a coal seam main roadway to be considered safe or unsafe is... =1.0; It also includes step four: quantitative determination of the stopping distance; Based on the critical conditions for safety or unsafety in coal seam roadways =1.0, the ultimate safety condition of the main roadway of the coal seam is obtained. The stopping distance is determined when the value is 1.0, and a reasonable stopping distance is quantitatively determined based on the actual solution. in, p x=D-a-b This refers to the supporting stress at the boundary between the elastic zone and the original rock stress zone. In step one: the direction of the working face mining is used as the horizontal axis. x The vertical axis is the height of the working face. y The bottom boundary of the stopped working face is the origin of the coordinate system. o ; Determine the coal seam support stress p and x The expression between them is: according to p The curve distribution characteristics are used to obtain the support stress. p peak ; in H This represents the average mining depth of the working face. α , β These are the overburden movement angle and the overburden contact angle, respectively. γ This represents the average unit weight of the overlying strata. The origin of the coordinate system is the bottom boundary of the main roadway or the closed working face. o， Using the direction extending towards the "large coal pillar" as the horizontal axis x The vertical axis represents the height of the coal seam. y To obtain the bearing capacity at any location in the coal seam. R and x The expression between them is: In the formula: [ σ c [ ] represents the uniaxial compressive strength of the coal body, using η Approximate representations of confining pressure parameters in different regions of the coal seam main roadway. η It changes with the confining pressure, in the coal wall of the roadway η 0=0, the boundary between the elastic and plastic zones. η min =1, Location of the boundary between the elastic zone and the original rock stress zone η max = N , N The value of is related to the uniaxial compressive strength of the coal; the greater the strength, the smaller the value. Generally, it is taken as . N =3~5, the widths of the fractured-plastic zone and elastic zone of the surrounding rock in the main roadway of the coal seam are respectively , , t The height of the tunnel, This refers to the side pressure coefficient of the coal face in the roadway. The internal friction angle of the coal. c For coal body cohesion, k This is the stress concentration factor of the surrounding rock in the tunnel. f =tan ' is the coefficient of friction between the roof and floor of the roadway and the coal seam. ' is the internal friction angle between the roof and floor of the roadway and the coal seam.

2. The method for assessing and determining the stopping distance of a working face based on coal seam main roadway protection according to claim 1, characterized in that: Due to different working conditions, the support stress at the working face stoppage boundary at the boundary of the elastic zone and the original rock stress zone varies. p Different distribution characteristics result in varying bearing capacity of main roadways in coal seams. R Differences exist, leading to variations in the coefficients characterizing the safety of coal seam roadways. There could be several possibilities; The methods and steps for quantitatively determining the stopping distance are discussed in the following categories: (1) If D - a - b > H cot α At this point, at the boundary between the elastic zone and the original rock stress zone, the working face stops mining at the support stress. For γH ; 1) If γH ≥ N [ σ c If the coal seam main roadway is not properly constructed, it needs to be reinforced or a rock stratum main roadway layout should be adopted. 2) If γH < N [ σ c Distance from the working face to stop mining D The scope can be further narrowed down using the following analysis; (2) If 0.5 H cot α < D - a - b ≤ H cot α At this point, the peak value of the support stress at the boundary of the working face where mining has stopped. ; 1) If ≤ N [ σ c This indicates that the maximum bearing capacity of the coal seam main roadway is always greater than the peak value of the supporting stress. At this time, any position meets the stop mining distance. We only need to find the coal seam main roadway position that best meets the conditions. 2) If > N [ σ c This indicates that the maximum bearing capacity of the main roadway in the coal seam is less than the peak bearing stress. Analysis = N [ σ c In extreme cases D As a result, D The result has one and only one value, which is the reasonable working face stopping distance under the condition of coal seam main roadway; (3) If 0 < D - a - b ≤0.5 H cot α At this point, the peak value of the support stress at the boundary of the working face where mining has stopped. ; 1) If ≤ N [ σ c This indicates that the maximum bearing capacity of the coal seam main roadway is always greater than the peak value of the supporting stress. At this time, any position meets the stop mining distance. We only need to find the coal seam main roadway position that best meets the conditions. 2) If > N [ σ c This indicates that the maximum bearing capacity of the coal seam main roadway is less than the peak bearing stress. At this time, the boundary between the elastic zone and the original rock stress zone of the coal seam main roadway spatially "passes through" the peak bearing stress, i.e. D - a - b =0.5 H cot α Only then can one "arrive" in the area near the working face. 0 < D - a - b ≤0.5 H cot α Therefore, consider = N [ σ c In extreme cases D The result is that this contradicts the zoning assumption, namely, that there is no reasonable working face stopping distance under the condition of no coal seam main roadway. At this time, the design needs to be reconsidered, and the stopping distance needs to be "increased" and re-quantified according to the above steps (1), (2), and (3).

3. The method for assessing and determining the stopping distance of a working face based on coal seam main roadway protection according to claim 1, characterized in that: Considering that the main roadway of the coal seam is located in the "pressure boosting zone" and satisfies 0.5 H cot α < D - a - b ≤ H cot α Draw the bearing capacity of the main roadway of the coal seam. R curve; like x = D - a - b hour, p x=D-a-b > N [ σ c The working face stopping distance is [missing information]. D The design is unreasonable, according to = N [ σ c Analysis shows that the reasonable stopping distance for the working face is... D Need to be added; like x = D - a - b hour, > N [ σ c ]and p x=D-a-b < N [ σ c The working face stopping distance is [missing information]. D The design meets safety requirements and can be carried out in accordance with = N [ σ c This allows for further determination of the stopping distance under extreme conditions. D .

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