Impact hazard assessment method based on the relationship between the thickness of hard thick rock layer and coal seam

Abstract

The present invention discloses an impact hazard assessment method based on the relationship between the thickness of hard thick rock layers and coal seams. The method comprises the following steps: firstly, the geological data above the coal seam to be evaluated are collected to determine the distribution of each rock layer above the coal seam and the mechanical properties of each rock layer; then, the hard thick rock layers that meet the conditions are selected, and the thickness of each hard thick rock layer and the distance between their lower boundaries and the upper boundary of the coal seam are recorded; then, according to the relationship between the thickness of the hard thick rock layer above the coal seam and the distance between the lower boundary of the hard thick rock layer and the upper boundary of the coal seam, it is found that there is a corresponding influence on the impact ground pressure of the coal seam according to the research of the applicant; after the value is divided, the discrimination standard is determined; after the selected hard thick rock layers are processed by the discrimination standard respectively, the corresponding hazard index of each hard thick rock layer is obtained; finally, the maximum value among the hazard indexes corresponding to each hard thick rock layer is selected and determined as the final hazard index; and the intensity of the impact ground pressure hazard caused by the coal seam roof to the coal seam is determined according to the final hazard index.

Description

Technical Field

[0001] This invention relates to a method for assessing impact hazard based on the relationship between the thickness of hard, thick rock strata and coal seams, belonging to the field of coal mine safety monitoring technology. Background Art

[0002] With the increasing depth of coal mining, the threat of rockburst disasters in mines has significantly increased. Rockburst hazard assessment and prediction are crucial for preventing and controlling these disasters. Currently, coal mining regulations stipulate that mines prone to rockbursts must undergo regional and local hazard predictions. Regional and local predictions can be based on geological and mining technology conditions, with the comprehensive index method being the preferred approach to determine rockburst hazard. The comprehensive index method for rockburst hazard assessment was first proposed in Poland and further developed and improved by industry scholars. It is now widely used in rockburst hazard assessments of mines (including roadways, working faces, and permanent chambers). However, over more than a decade of application has revealed that the comprehensive index method considers some factors somewhat one-sidedly, and the division of index intervals lacks scientific basis when predicting specific coal seams. For example, the third geological factor concerning the impact of hard, thick rock strata on coal seams only considers the influence of the distance between the hard, thick rock strata and the coal seam within the fracture zone or a range of 100m. It does not comprehensively consider the influence of rock strata at greater distances, the influence of changes in rock strata thickness on the coal seam, or the coupled influence of thickness and distance changes. An unreasonable value for one indicator may lead to an unreasonable overall evaluation result. Therefore, it is necessary to propose a new method for assessing rock hazard, one that fully considers the influence of changes in rock strata thickness between the hard, thick rock strata and the coal seam, as well as the coupled influence of thickness and distance changes on the coal seam, when assessing rock hazard in coal seams. This would effectively improve the accuracy of rock hazard assessment and is one of the research directions in this industry. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a shock hazard assessment method based on the relationship between the thickness of hard, thick rock strata and the coal seam thickness. When assessing the shock hazard of deep coal seams, this method fully considers the influence of changes in the thickness of the rock strata between the hard, thick rock strata and the coal seam on the coal seam, as well as the coupling effect of thickness and distance changes on the coal seam, thereby effectively improving the accuracy of the shock hazard assessment.

[0004] To achieve the above objectives, the technical solution adopted by this invention is: a method for assessing impact hazard based on the relationship between hard, thick rock strata and coal seam thickness, the specific steps of which are as follows:

[0005] A. Collect geological data above the coal seam area to be evaluated, and determine the distribution and mechanical properties of each rock layer above the coal seam based on the geological data;

[0006] B. Based on the conditions of each rock layer above the coal seam determined in step A, select rock layers with a single layer thickness greater than or equal to 10m and a uniaxial compressive strength greater than or equal to 60MPa under natural moisture content conditions as hard and thick rock layers. Record the thickness M of each selected hard and thick rock layer and calculate the distance d between the lower boundary of each hard and thick rock layer and the upper boundary of the coal seam.

[0007] C. Substitute the thickness M of each hard, thick rock layer selected in step B and its distance d from the coal seam into the following discrimination criteria. The specific discrimination criteria are as follows:

[0008] If M-0.9d≤10, then the danger index of this hard, thick rock layer is determined to be 0;

[0009] If M-0.9d>10 and M-1.35d≤15, then the danger index of this hard, thick rock layer is determined to be 1;

[0010] If M-1.35d>15 and M-1.8d≤20, then the danger index of this hard, thick rock layer is determined to be 2;

[0011] If M-1.8d>20, then the danger index of this hard, thick rock layer is determined to be 3;

[0012] The danger index corresponding to each hard, thick rock layer is determined according to the above discrimination criteria.

[0013] The principle behind the above-mentioned discrimination criteria is as follows: The applicant's research found that the relationship between the thickness of the hard and thick rock layer above the coal seam (i.e., the hard and thick rock layer refers to the overlying rock layer with a single layer thickness greater than 10m and a uniaxial compressive strength greater than 60MPa under natural moisture conditions) and the distance between the lower boundary of the hard and thick rock layer and the upper boundary of the coal seam has a corresponding impact on the rockburst of the coal seam. The greater the thickness of the hard and thick rock layer and the closer it is to the coal seam, the greater the impact on the rockburst, and vice versa. Based on this research finding, the discrimination criteria were derived.

[0014] D. Select the maximum value from the hazard indices corresponding to each hard, thick rock layer determined in step C, and determine it as the hazard index w. If the hazard index w is 0, it indicates that the overlying rock layer has no impact on the rock pressure of the coal seam; if w is 1, it indicates that the impact on the rock pressure of the coal seam is weak; if w is 2, it indicates that the impact on the rock pressure of the coal seam is moderate; if w is 3, it indicates that the impact on the rock pressure of the coal seam is strong; thus completing the rock pressure evaluation process of the coal seam.

[0015] Furthermore, the geological data in step A includes geological borehole columnar sections and rock mechanics test results, wherein the geological borehole columnar sections are used to determine the distribution of various rock strata above the coal seam, and the rock mechanics test results are used to determine the mechanical properties of each rock strata.

[0016] Furthermore, the coal seam to be evaluated in step A exceeds 300m in depth. In coal seams deeper than 300m, it is more likely that a hard, thick coal seam greater than 100m above it will appear, making the method of this invention even more advantageous.

[0017] This invention first collects geological data above the coal seam to determine the distribution and mechanical properties of each rock stratum above the coal seam. Then, it selects suitable hard, thick rock strata and records the thickness of each hard, thick rock stratum and the distance between its lower boundary and the upper boundary of the coal seam. Next, based on the applicant's research finding a relationship between the thickness of the hard, thick rock strata above the coal seam and the distance between the lower boundary of the hard, thick rock strata and the upper boundary of the coal seam, it determines the impact on the rockburst of the coal seam. After value division, a discrimination standard is determined. The selected hard, thick rock strata are processed according to the discrimination standard to obtain the corresponding hazard index for each hard, thick rock strata. Finally, the maximum value among the hazard indices corresponding to each hard, thick rock strata is selected as the most critical hazard index. The final hazard index is used to determine the rockburst intensity of the coal seam based on the final hazard coefficient. Compared with the prior art, which only considers the influence of the distance between the coal seam and the hard, thick rock layer within the fracture zone or within 100m, this invention considers the influence of all hard, thick rock layers above the coal seam on the rockburst. It combines the influence of the thickness of the hard rock layer, the distance from the coal seam, and the coupling effect of thickness and distance changes on the coal seam to derive a discrimination criterion. Finally, after processing with the discrimination criterion, the rockburst influence intensity on the coal seam is obtained. The actual verification through specific embodiments shows that this invention has higher accuracy in evaluating the rockburst of coal seams with hard, thick coal layers above them and can effectively predict the rockburst situation of this type of coal seam better. Attached Figure Description

[0018] Figure 1 This is a value division diagram of the discrimination criteria in this invention. Detailed Implementation

[0019] The present invention will be further described below.

[0020] Example: A coal seam mine with a depth exceeding 1000m is a rockburst mine. It is affected by a 700m thick conglomerate layer located 300m above the coal seam, resulting in a high risk of rockbursts and frequent rockburst events. According to existing rockburst assessment methods, only the distance between the coal seam and a hard, thick rock layer (with a uniaxial compressive strength greater than 60MPa and a single layer thickness greater than or equal to 10m under natural water-bearing conditions) within the fracture zone above the coal seam or within 100m is considered. When the distance is greater than 100m, the index is set to 0, indicating no impact on rockburst. The final rockburst assessment result is "no impact," which is inconsistent with the actual situation. Therefore, the method of this invention is used for rockburst assessment. The specific steps are as follows:

[0021] A. Collect geological data above the coal seam area to be evaluated. The geological data includes geological drill hole histograms and rock mechanics test results. The geological drill hole histograms are used to determine the distribution of various rock layers above the coal seam. Based on the rock mechanics test results in the geological data, it is determined that the uniaxial compressive strength of the siltstone layer, fine-grained sandstone layer, medium-grained sandstone layer, and conglomerate layer in the overlying rock layer of the coal seam is greater than 60 MPa.

[0022] B. Based on the rock formations above the coal seam determined in step A, select rock formations with a single layer thickness greater than or equal to 10 m and a uniaxial compressive strength greater than or equal to 60 MPa under natural moisture conditions as hard and thick rock formations. That is, rock formations No. 2, No. 7, and No. 11 in Table 1 are hard and thick rock formations. Record the thickness M of each selected hard and thick rock formation, and calculate the distance d between the lower boundary of each hard and thick rock formation and the upper boundary of the coal seam, ultimately forming Table 1.

[0023] C. Substitute the thickness M of each hard, thick rock layer selected in step B and its distance d from the coal seam into the following discrimination criteria. The specific results are shown in Table 2. The specific discrimination criteria are as follows:

[0024] If M-0.9d≤10, then the danger index of this hard, thick rock layer is determined to be 0;

[0025] If M-0.9d>10 and M-1.35d≤15, then the danger index of this hard, thick rock layer is determined to be 1;

[0026] If M-1.35d>15 and M-1.8d≤20, then the danger index of this hard, thick rock layer is determined to be 2;

[0027] If M-1.8d>20, then the danger index of this hard, thick rock layer is determined to be 3;

[0028] As shown in Table 2, according to the above discrimination criteria, the danger index of No. 2 hard thick rock layer is determined to be 3, the danger index of No. 7 hard thick rock layer is 0, and the danger index of No. 11 hard thick rock layer is 0.

[0029] The principle of determining the above-mentioned discrimination criteria is as follows: the applicant has found that the relationship between the thickness of the hard and thick rock layer above the coal seam (i.e., the hard and thick rock layer refers to the overlying rock layer with a single layer thickness greater than 10m and a uniaxial compressive strength greater than 60MPa under natural water content conditions) and the distance between the lower boundary of the hard and thick rock layer and the upper boundary of the coal seam has a corresponding impact on the rock burst pressure of the coal seam. The greater the thickness of the hard and thick rock layer and the closer it is to the coal seam, the greater the impact on the rock burst pressure, and vice versa. Based on this research finding, the specific value division process of the discrimination criteria is as follows:

[0030] like Figure 1As shown, the following trend control points are first selected: (0, 10), (20, 20), (40, 40), (60, 70), (80, 120), and (100, 200). Then, the area division control points are selected: (100, 100) and (100, 150). Based on these six trend control points, a trend line representing the change of two parameters is drawn. The area below the arc-shaped trend line represents the region with less impact from rock bursts, while the area above it represents the region with greater impact. To facilitate calculation and division of different index intervals, the area covered by the arc needs to be divided into four parts, each corresponding to one of the four indices. If an upward shift is used to classify the hazard index using different arc-shaped trend lines, the thickness of the rock layer corresponding to the shifted trend line will increase dramatically. For example, if the trend line is shifted upwards by 10m along the longitudinal axis, the thickness of the rock layer at a distance of 100m will increase dramatically, significantly exceeding a reasonable range. Therefore, this invention uses a straight line method for area division.

[0031] The principle of the straight line method is as follows: Draw an approximate slope line from the point (0, 10) to the area division control point (100, 100), which gives the line 1 between the two points: M = 0.9d + 10. This line is extended to intersect the horizontal axis at (-100 / 9, 0). Then connect the point (-100 / 9, 0) and the area division control point (100, 150) to get the line 2 between the two points: M = 1.35d + 15. Then connect the point (-100 / 9, 0) and the point (100, 200) to get the line 3 between the two points: M = 1.8d + 20. At the same time, the intercepts of the three lines with the vertical axis are 10m, 15m, and 20m, respectively.

[0032] The four regions divided by the three straight lines are defined as different risk indices, and the inequalities for determining the indices are given respectively, thus completing the specific value division process of the discrimination criteria.

[0033] D. Select the maximum value from the hazard indices corresponding to each hard, thick rock layer determined in step C, and determine it as the hazard index w, i.e., w = max{w2 = 3; w7 = 0; w 11 =0}=3, it can be judged that the hard and thick rock layer has a strong impact on the rock burst pressure of the coal seam; this evaluation result is consistent with the on-site rock burst risk level, which shows that the accuracy of the rock burst pressure evaluation of this type of coal seam is better in the present invention.

[0034] Table 1. Evaluation of the distribution of overlying strata of the coal seam

[0035]

[0036]

[0037] Table 2 Danger index of various hard and thick rock formations

[0038] Layer number Lithology Rock stratum thickness M (m) Distance from coal seam d(m) Risk Index Remark 2 conglomerate 773.92 282.32 3 <![CDATA[W2]]> 7 siltstone 20.00 160.87 0 <![CDATA[W7]]> 11 medium-grained sandstone 20.60 115.27 0 <![CDATA[W 11 ]]>

[0039] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for assessing impact risk based on the relationship between the thickness of hard thick rock strata and coal seams, characterized in that: The specific steps are: A. Collect geological data above the coal seam area currently required for evaluation, and determine the distribution of each rock layer above the coal seam and the mechanical properties of each rock layer based on the geological data; B. According to the conditions of the rock layers above the coal seam determined in step A, select the rock layers with a single layer thickness greater than or equal to 10m and a uniaxial compressive strength greater than or equal to 60MPa under natural water content conditions as hard and thick rock layers, record the thickness M of each selected hard and thick rock layer, and calculate the distance d between the lower boundary of each hard and thick rock layer and the upper boundary of the coal seam; C. The thickness M of each hard and thick rock layer selected in step B and the distance d between the hard and thick rock layer and the coal seam are respectively introduced into the following discrimination criteria. The specific discrimination criteria are: If M-0.9d≤10, the danger index of the hard and thick rock formation is determined to be 0; If M-0.9d>10 and M-1.35d≤15, the danger index of the hard and thick rock formation is determined to be 1; If M-1.35d>15 and M-1.8d≤20, the danger index of the hard and thick rock layer is determined to be 2; If M-1.8d>20, the danger index of the hard and thick rock layer is determined to be 3; According to the above-mentioned criteria, the corresponding danger index of each hard and thick rock layer is determined respectively; D. Select the maximum value from the danger indexes corresponding to the various hard and thick rock layers determined in step C, and determine it as the danger index w. If the danger index w is 0, it means that the overlying rock layer of the coal seam has no effect on the rock burst pressure of the coal seam; if w is 1, it means that the rock burst pressure on the coal seam has a weak impact; if w is 2, it means that the rock burst pressure on the coal seam has a medium impact; if w is 3, it means that the rock burst pressure on the coal seam has a strong impact, thereby completing the rock burst pressure evaluation process of the coal seam.

2. The impact risk assessment method based on the relationship between the thickness of hard thick rock layer and coal seam according to claim 1 is characterized in that: The geological data in step A include geological drilling column charts and rock mechanics test results, wherein the geological drilling column charts are used to determine the distribution of various rock layers above the coal seam, and the rock mechanics test results are used to determine the mechanical properties of each rock layer.

3. The impact risk assessment method based on the relationship between the thickness of hard thick rock layer and coal seam according to claim 1 is characterized in that: The depth of the coal seam required to be evaluated in step A is more than 300m.

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