A method for evaluating the stability of surrounding rock in steeply inclined, extra-thick coal seam mining roadways.

Abstract

This invention discloses a method for evaluating the stability of the surrounding rock in steeply inclined extra-thick coal seam mining roadways, comprising the following steps: (1) calculating the vertical depth H1 of the triangular plastic zone in the steeply inclined extra-thick coal seam; (2) calculating the vertical depth H2 of the deep plastic zone in the steeply inclined extra-thick coal seam; (3) determining the vertical depth H of the plastic zone in the steeply inclined extra-thick coal seam mining area; (4) evaluating the stability of the surrounding rock in the steeply inclined extra-thick coal seam roadway based on the relationship between the segmented vertical height h of the working face and the vertical depth H of the plastic zone, which can provide theoretical guidance for the prevention and control of rockbursts in steeply inclined extra-thick coal seam roadways. Therefore, this invention has important practical significance and significant social benefits for the safe production and personnel safety of steeply inclined extra-thick coal seam working faces, and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of coal mining and coal mine safety technology, specifically a method for evaluating the stability of the surrounding rock in steeply inclined, extra-thick coal seam mining roadways. Background Technology

[0002] In my country, steeply dipping coal seams (dipping angle 45°–90°) account for 15%–20% of the country's total coal reserves. For steeply dipping extra-thick coal seams with a true thickness ≥18m, horizontal segmented fully mechanized longwall mining has become the main mining method. This method arranges the working face along the horizontal direction of the coal thickness, dividing the coal body into several segments at a certain height. The working face roadways are named roof roadways and floor roadways based on their proximity to the roof and floor strata on both sides. With the increasing mining depth year by year, rockburst disasters in steeply dipping extra-thick coal seams occur frequently, mainly in the roadways. Therefore, evaluating the stability of the surrounding rock in roadways of steeply dipping extra-thick coal seams is essential and can provide theoretical guidance for the prevention and control of rockbursts in such roadways.

[0003] The distribution of the plastic zone in steeply dipping, extra-thick coal seams significantly impacts the stability of the surrounding rock in roadways. The relative position of the roadway to the plastic zone determines the stress state of the surrounding rock. However, existing roadway layout schemes and surrounding rock stability analyses for steeply dipping, extra-thick coal seams are primarily based on field measurements and empirical estimations. The positional relationship between the mining roadway, peak mining stress, and the plastic zone remains unclear. This often leads to rockburst accidents caused by unreasonable roadway layouts, failing to prevent roadway rockburst disasters during the mining design phase. Therefore, proposing a quantitative method for evaluating the stability of the surrounding rock in steeply dipping, extra-thick coal seams is of significant importance for safe and efficient mine production and improving overall social economic benefits. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for evaluating the stability of the surrounding rock in steeply inclined extra-thick coal seam mining roadways. This method can accurately evaluate the stability and impact hazard level of the surrounding rock in steeply inclined extra-thick coal seam mining roadways, and can provide data support for the selection of segmented vertical heights and roadway layout in steeply inclined extra-thick coal seam working faces from the perspective of impact prevention.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] This invention discloses a method for evaluating the stability of surrounding rock in steeply inclined, extra-thick coal seam mining roadways, comprising:

[0007] Step 1: Calculate the vertical depth H1 of the triangular plastic zone in the steeply dipping extra-thick coal seam;

[0008] Step 2: Calculate the vertical depth H2 of the deep plastic zone in steeply dipping, extra-thick coal seams;

[0009] Step 3: Determine the vertical depth H of the plastic zone in the steeply inclined extra-thick coal seam mining area;

[0010] Step 4: Evaluate the surrounding rock stability of steeply inclined extra-thick coal seam roadways based on the relationship between the segmented vertical height h of the working face and the vertical depth H of the plastic zone.

[0011] Furthermore, in step 1, due to the large dip angle and horizontal segmented mining method of the steeply inclined extra-thick coal seam, a triangular plastic zone of approximately right angles is formed near the upper surface of the coal body. The coal body in this area is relatively broken and has a weak bearing capacity. To calculate the vertical depth H1 of the triangular plastic zone of the steeply inclined extra-thick coal seam: first, obtain the dip angle and true thickness of the steeply inclined extra-thick coal seam; then, substitute the obtained data into the following formula:

[0012] H1 = xcosθ (0 ≤ x ≤ M)

[0013] In the formula, H1 represents the vertical depth of the triangular plastic zone of the steeply dipping extra-thick coal seam, in meters; θ represents the dip angle of the steeply dipping extra-thick coal seam, in degrees; M represents the true thickness of the steeply dipping extra-thick coal seam, in meters; and x represents the normal distance between the steeply dipping coal body and the roof strata, in meters.

[0014] Step 2: Below the triangular plastic zone of the steeply dipping, extra-thick coal seam lies the deep plastic zone, which possesses a certain bearing capacity. Calculate the vertical depth H2 of the deep plastic zone of the steeply dipping, extra-thick coal seam: First, obtain the dip angle, true thickness, top coal thickness, coal cohesion, internal friction angle, mining depth at the top surface of the coal seam, friction coefficient between the coal seam and the roof and floor, mining stress concentration factor, average volumetric force of the coal seam, average volumetric force of the overburden, lateral pressure coefficient, and average support strength of the working face supports. Then, substitute the obtained data into the following formula:

[0015]

[0016] In the formula, σ b γ represents the normal bearing strength at the interface between the triangular plastic zone and the deep plastic zone, expressed in Pa. m The average volumetric force of the coal seam is expressed in kN / m. 3 ; The average support strength of the working face support is expressed in Pa, and is given by on-site measurement; h m This indicates the thickness of the top coal layer, expressed in meters (m).

[0017] The σ obtained from Formula 2 b Substitute into the following formula three:

[0018]

[0019] In the formula, N bThe tangential bearing capacity at the interface between the triangular plastic zone and the deep plastic zone is expressed in Pa; c represents the cohesion of the coal, expressed in Pa. This represents the internal friction angle of the coal, expressed in degrees (°).

[0020] The N obtained from Formula 3 b Substitute the obtained data into the following formula four:

[0021]

[0022] In the formula, L represents the dip depth of the deep plastic zone, in meters (m); f represents the friction coefficient between the coal body and the roof and floor, in units of 1; H0 represents the mining depth at the top surface of the coal body, in meters (m); and γ represents the average volumetric force of the overburden, in kN / m³. 3 λ is the lateral pressure coefficient, with a unit of 1;

[0023] Solving Formula 4 yields the inclination depth L of the deep plastic zone. Then, substitute L into Formula 5 as follows:

[0024]

[0025] In the formula, H2 represents the vertical depth of the deep plastic zone in steeply dipping extra-thick coal seams, in meters (m).

[0026] Step 3: Determine the vertical depth H of the plastic zone in the steeply inclined extra-thick coal seam mining area: Substitute H1 and H2 obtained in Step 1 and Step 2 into the following formula six:

[0027] H = H1 + H2

[0028] In the formula, H represents the vertical depth of the plastic zone in a steeply inclined, extra-thick coal seam mining area, in meters (m).

[0029] Step 4: Evaluate the surrounding rock stability of steeply inclined extra-thick coal seam roadways based on the relationship between the segmented vertical height h of the working face and the vertical depth H of the plastic zone: Compare the vertical depth H of the plastic zone obtained in Step 3 with the segmented vertical height h of the steeply inclined coal seam working face; if h ≤ H, it indicates that the roadway is within the plastic zone of the mining area and there is no impact hazard; conversely, if h > H, it indicates that the roadway has an impact hazard.

[0030] Preferably, if H < h ≤ (H + 0.5H2), the roadway is near the peak stress zone of the dipping mining, and the roadway has a strong impact risk; if (H + 0.5H2) < h ≤ (H + 1.5H2), the roadway is in the elastic zone between the peak stress zone of the dipping mining and the original rock stress zone, and the roadway has a moderate impact risk; if h > (H + 1.5H2), the roadway is near or in the original rock stress zone, and the roadway has a weak impact risk.

[0031] Furthermore, based on the evaluation results, the working face roadways should be prioritized to be located within the plastic zone of the mining area, i.e., the non-hazardous area, during the mining design stage. If the roadways have already been arranged and are located outside the plastic zone of the mining area, corresponding pressure relief measures should be taken according to the hazard level.

[0032] Compared with existing technologies, this invention calculates the vertical depth H1 of the triangular plastic zone and the vertical depth H2 of the deep plastic zone in steeply inclined extra-thick coal seams sequentially, and then comprehensively obtains the vertical depth H of the plastic zone in the mining area of ​​steeply inclined extra-thick coal seams. The vertical height h of the segmented working face of the steeply inclined extra-thick coal seam is compared with the vertical depth H of the plastic zone in the mining area. Based on the comparison results, the impact hazard level of the surrounding rock in the roadway is determined. This provides theoretical guidance for the pre-mining anti-impact design of the working face of steeply inclined extra-thick coal seams and the targeted prevention and control of impact hazards in existing roadways, and ultimately can effectively ensure the safety of mine personnel and safe production in the mine. Attached Figure Description

[0033] Figure 1 This is a flowchart of the evaluation process of the present invention.

[0034] Figure 2 This is a schematic diagram of the layout of steeply inclined, extra-thick coal seam roadways and the distribution of the plastic zone in this invention.

[0035] In the diagram: 1. Triangular plastic zone, 2. Deep plastic zone, 3. Top slab tunnel, 4. Bottom slab tunnel. Detailed Implementation

[0036] The present invention will be further described below.

[0037] Example 1:

[0038] In a horizontally segmented mining operation of a steeply dipping, extra-thick coal seam, multiple rockburst manifestations have occurred in the No. 5 mining area, primarily located in roof roadway 3, which presents a potential rockburst hazard. Targeted depressurization measures for roof roadway 3 and optimized rockburst prevention design for subsequent working face segments are required. Figure 1 The method of the present invention shown evaluates the stability of the surrounding rock of the roof tunnel 3. The specific steps are as follows:

[0039] Step 1: It is known that the steeply dipping, extra-thick coal seam in the fifth mining area of ​​this mine has a dip angle of 60° and a true thickness of 59m; If Figure 2 As shown, the vertical depth H1 of the triangular plastic zone 1 in the steeply dipping extra-thick coal seam can be calculated:

[0040] H1=xcos60°=0.5x(0≤x≤59m)

[0041] Step 2: Given that the steeply dipping, extra-thick coal seam in the fifth mining area of ​​this mine has a dip angle of 60°, a true thickness of 59m, a top coal thickness of 22m, a coal seam cohesion of 3.6MPa, a coal seam friction angle of 34°, a mining depth of 505m at the top of the coal seam, a friction coefficient of 0.5 between the coal seam and the roof and floor, a mining-induced stress concentration factor of 2, and an average volumetric force of 14kN / m³, the following information is provided: 3 The average volumetric force of the overlying rock is 25 kN / m. 3 The lateral pressure coefficient is 1.83, and the measured average support strength of the working face support is 0.686 MPa. The normal bearing strength σ at the interface between the triangular plastic zone 1 and the deep plastic zone 2 of the steeply inclined extra-thick coal seam can be calculated. b :

[0042]

[0043] The normal bearing strength σ is calculated based on the above formula. b The diagonal bearing strength N at the interface between the triangular plastic zone 1 and the deep plastic zone 2 can be calculated. b :

[0044]

[0045] Based on the above formula, the tangential bearing strength N is obtained. b Based on the basic data of the fifth mining area, the dip depth L of the deep plastic zone 2 in the steeply dipping extra-thick coal seam can be calculated using the following formula:

[0046]

[0047] By using MATLAB software to write code to solve the above equation, the dip depth L of the deep plastic zone 2 can be obtained as 19.96m. Then, the vertical depth H2 of the deep plastic zone 2 in the steeply dipping extra-thick coal seam can be calculated:

[0048]

[0049] Step 3: Based on the vertical depth H1 of the triangular plastic zone 1 and the vertical depth H2 of the deep plastic zone 2 calculated in Steps 1 and 2, the vertical depth H of the plastic zone in the steeply dipping extra-thick coal seam mining area can be calculated:

[0050] H=H1+H2=0.5x+23(0≤x≤59m)

[0051] For Roof Lane 3, x = 0. Substituting this into the above formula, we can obtain that the depth H of the plastic zone in Roof Lane 3 is 23m.

[0052] Step 4: Given that the vertical height h of the steeply inclined coal seam working face in the fifth mining area of ​​this mine is currently 25m, compared with the calculated vertical depth H (23m) of the plastic zone in the roof roadway 3, h > H, indicating that the roof roadway 3 has a rockfall hazard; further calculations show that h satisfies:

[0053] H=23m<h=25m≤(H+0.5H2)=(23+0.5×23)=34.5m

[0054] Therefore, the surrounding rock of Roof Roadway 3 is located near the peak stress zone of a steeply dipping, extra-thick coal seam, posing a strong risk of impact. Based on the evaluation results, to prevent the strong impact hazard in the existing Roof Roadway 3, a combined pressure relief measure of deep-hole pre-splitting blasting of the roof, pressure relief blasting of the coal face, and pressure relief blasting of the bottom coal is required. For subsequent sub-faces, an optimized design for face impact prevention is needed. It is recommended that the vertical height h of each sub-face be 20m. This will appropriately reduce the vertical height of the sub-faces to within the vertical depth of the plastic zone in the mining area, ensuring that Roof Roadway 3 is in a safe zone, thereby effectively guaranteeing mine safety and personnel safety.

Claims

1. A method for evaluating the stability of surrounding rock in steeply inclined, extra-thick coal seam mining roadways, characterized in that, include: Step 1: Calculate the vertical depth H1 of the triangular plastic zone in the steeply dipping extra-thick coal seam; Step 2: Calculate the vertical depth H2 of the deep plastic zone in steeply dipping, extra-thick coal seams; Step 3: Determine the vertical depth H of the plastic zone in the steeply inclined extra-thick coal seam mining area; Step 4: Evaluate the surrounding rock stability of steeply inclined extra-thick coal seam roadways based on the relationship between the segmented vertical height h of the working face and the vertical depth H of the plastic zone. Step 1: Steeply inclined extra-thick coal seams form an approximately right-angled triangular plastic zone near the upper surface of the coal body. Calculate the vertical depth H1 of the triangular plastic zone of the steeply inclined extra-thick coal seam: First, obtain the dip angle and true thickness of the steeply inclined extra-thick coal seam; then substitute the obtained data into the following formula: H1 = xcosθ (0 ≤ x ≤ M) In the formula, H1 represents the vertical depth of the triangular plastic zone of the steeply dipping extra-thick coal seam, in meters; θ represents the dip angle of the steeply dipping extra-thick coal seam, in degrees; M represents the true thickness of the steeply dipping extra-thick coal seam, in meters; and x represents the normal distance between the steeply dipping coal body and the roof strata, in meters. Step 2: Below the triangular plastic zone of the steeply dipping extra-thick coal seam lies the deep plastic zone. Calculate the vertical depth H2 of the deep plastic zone of the steeply dipping extra-thick coal seam: First, obtain the dip angle, true thickness, top coal thickness, coal cohesion, internal friction angle, mining depth at the top surface of the coal seam, friction coefficient between the coal seam and the roof and floor, mining stress concentration factor, average volumetric force of the coal seam, average volumetric force of the overburden, lateral pressure coefficient, and average support strength of the working face supports; then substitute the obtained data into the following formula: In the formula, σ b γ represents the normal bearing strength at the interface between the triangular plastic zone and the deep plastic zone, expressed in Pa. m The average volumetric force of the coal seam is expressed in kN / m. 3 ; The average support strength of the working face support is expressed in Pa, and is given by on-site measurement; h m This indicates the thickness of the top coal layer, expressed in meters (m). The σ obtained from Formula 2 b Substitute into the following formula three: In the formula, N b The tangential bearing capacity at the interface between the triangular plastic zone and the deep plastic zone is expressed in Pa; c represents the cohesion of the coal, expressed in Pa. This represents the internal friction angle of the coal, expressed in degrees (°). The N obtained from Formula 3 b Substitute the obtained data into the following formula four: In the formula, L represents the dip depth of the deep plastic zone, in meters (m); f represents the friction coefficient between the coal body and the roof and floor, in units of 1; H0 represents the mining depth at the top surface of the coal body, in meters (m); and γ represents the average volumetric force of the overburden, in kN / m³. 3 λ is the lateral pressure coefficient, with a unit of 1; Solving Formula 4 yields the inclination depth L of the deep plastic zone. Then, substitute L into Formula 5 as follows: In the formula, H2 represents the vertical depth of the deep plastic zone in steeply dipping extra-thick coal seams, in meters (m). Step 3: Determine the vertical depth H of the plastic zone in the steeply inclined extra-thick coal seam mining area: Substitute H1 and H2 obtained in Step 1 and Step 2 into the following formula six: H = H1 + H2 In the formula, H represents the vertical depth of the plastic zone in a steeply inclined, extra-thick coal seam mining area, in meters (m). Step 4: Evaluate the surrounding rock stability of steeply inclined extra-thick coal seam roadways based on the relationship between the segmented vertical height h of the working face and the vertical depth H of the plastic zone: Compare the vertical depth H of the plastic zone obtained in Step 3 with the segmented vertical height h of the steeply inclined coal seam working face; if h ≤ H, it indicates that the roadway is within the plastic zone of the mining area and there is no impact hazard; conversely, if h > H, it indicates that the roadway has an impact hazard. If H < h ≤ (H + 0.5H2), the roadway is near the peak stress zone of the dipping mining, and the roadway has a strong impact risk; if (H + 0.5H2) < h ≤ (H + 1.5H2), the roadway is in the elastic zone between the peak stress zone of the dipping mining and the original rock stress zone, and the roadway has a moderate impact risk; if h > (H + 1.5H2), the roadway is near or in the original rock stress zone, and the roadway has a weak impact risk.

2. The method for evaluating the stability of surrounding rock in steeply inclined, extra-thick coal seam mining roadways according to claim 1, characterized in that: Based on the evaluation results, the working face roadways should be arranged in the plastic zone of the mining area, i.e., the non-hazardous area, during the mining design stage. If the roadways have been arranged and are located outside the plastic zone of the mining area, corresponding pressure relief measures should be taken according to the hazard level.

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