Early warning method for primary fracture of upper roof based on internal strain of overlying strata

Abstract

The invention provides an early warning method for primary fracture of an upper roof based on internal strain of overlying strata, and the method comprises the steps: continuously monitoring the strain of the upper roof, and comparing the strain with the limit deflection of a rock stratum of the upper roof; the accumulated deformation of the upper roof can be obtained by performing integral calculation on the strata strain in the upper roof range, and when the accumulated deformation exceeds 80% of the limit deflection of the upper roof, early warning can be performed in advance. The early warning method is simple, early warning can be carried out on primary fracture of the upper roof in advance, and good guiding significance is achieved for working face strong mine pressure prevention and control.

Description

Technical Field

[0001] The invention relates to the technical field of mine safety prevention and control, and in particular to an old roof initial breakage early warning method based on internal strain of overburden rock. Background Art

[0002] After coal seam mining, goaf will be formed. As the working face moves forward from the cut, the immediate roof will first collapse. The immediate roof is usually soft rock, and the collapse has little effect on the stress of the working face support. The old roof is usually stronger and has a larger overhang range. When the overhang range reaches a certain limit, the old roof will break. The initial break of the old roof usually causes an increase in the stress on the working face support, that is, the initial pressure on the working face. When the initial pressure is strong, it is easy to cause safety accidents. If the timing of the initial break of the old roof can be warned, accidents can be prevented in advance.

[0003] In order to understand the pressure situation of the working face, the support resistance of the working face is monitored in real time, and the initial pressure step distance of the working face can be obtained according to the change law of the support resistance. However, this method is usually a post-analysis and lacks a certain early warning function.

[0004] This method arranges ground boreholes in front of the cutting face, and deploys distributed optical cables inside the ground boreholes to monitor the internal deformation of the overburden. Through the strain monitoring inside the overburden of the ground monitoring borehole, the deformation of the old roof is timely grasped and compared with the ultimate deflection of the old roof (i.e., the first break), in order to achieve early warning of the first break of the old roof. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention aims to provide an early warning method for the initial break of the old roof based on the internal strain of the overburden rock.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] An early warning method for the initial break of the old roof based on internal strain of the overburden rock comprises the following steps:

[0008] S1 Arrange a coring ground borehole at a certain distance L m in front of the cutting eye of the working face, and the drilling depth to the top interface of the coal seam is H m;

[0009] S2 pushes the drill rod to lay the distributed optical cable into the borehole. The depth of the distributed optical cable is consistent with the depth of the borehole. After the distributed optical cable is laid, cement slurry is used to seal the entire borehole to ensure that the distributed optical cable is coupled with the wall and surrounding rock of the upward borehole.

[0010] S3 After the coal seam is mined, as the relative distance between the borehole and the working face gradually decreases, the distributed optical cable inside the borehole will be affected by the mining and produce corresponding strain deformation;

[0011] S4 integrates the strain generated by the distributed optical cable within the old top range of the borehole to obtain its total deformation ΔD;

[0012] S5 As the working face continues to move forward, the exposed range of the old roof continues to increase and bends. When the deflection of the old roof exceeds its limit deflection ω 老顶 The first break will occur when

[0013] S6 When the deformation of the old top ΔD is greater than the limit deflection ω of the old top 老顶 80% of them can provide early warning.

[0014] Furthermore, the specific process of step S1 in the present invention is as follows:

[0015] S1.1 Since the core is taken from the borehole, all the rock layers inside the borehole can be catalogued in a columnar manner, so that the lithology and thickness of each rock layer can be obtained. i , where the thickness of the old top is h 老顶 ;

[0016] S1.2 Perform mechanical tests on the cores of each rock layer to obtain the bulk density γ of each rock layer. i , tensile strength R Ti , elastic modulus E i , where the bulk density of the old top is γ 老顶 , tensile strength is R T老顶 , elastic modulus is E 老顶 ;

[0017] S1.3 With the mechanical parameters of each rock layer, all the key layers in the entire borehole can be obtained by applying the key layer identification theory. The first key layer close to the coal seam can be considered as the old roof.

[0018] S1.4 is a certain distance Lm from the front of the cutting eye of the working face. This distance is the limit span L of the old top. 老顶 Half of the theoretical where q 老顶 =γ 老顶 h 老顶 .

[0019] Furthermore, the specific process of step S4 in the present invention is as follows:

[0020] S4.1 Use an optical fiber demodulator on the ground to monitor the strain inside the borehole. After monitoring, the continuous strain distribution of the entire distributed optical cable can be obtained. The scale coordinates of the distributed optical cable from the hole mouth to the hole bottom are 0m to Hm;

[0021] S4.2 Select to integrate the strain within the old top range to obtain the cumulative deformation within the rock layer. Among them, h1 and h2 represent the scale coordinates of the distributed optical cable within the range of the old top, h1 is the scale coordinate of the old top top interface, and h2 is the scale coordinate of the old top bottom top interface. Since the scale increases gradually from the hole mouth to the hole bottom, h1 is smaller than h2. ε(h) is the strain of each measuring point of the distributed optical cable within the range of the old top;

[0022] S4.3 When collecting data on distributed optical cables, due to the limitation of the accuracy of the optical fiber demodulation instrument, data is usually collected at a certain collection interval Δh. If n is an integer, the acquisition coordinates within the old top range are h1, h1+Δh, h1+2Δh, +…, h1+(n-1)Δh, h2, and the cumulative deformation can be obtained according to the following formula during specific calculation:

[0023]

[0024] Obviously, the smaller the acquisition interval Δh is, the more accurate the calculated cumulative deformation is.

[0025] S4.4 When the old top is bent, the scale coordinates h1 and h2 of the old top will also change, but the change can be ignored compared with the initial values ​​of h1 and h2. For the convenience of calculation, the scale coordinates h1 and h2 are kept unchanged in actual calculation.

[0026] Furthermore, the specific process of step S5 in the present invention is as follows:

[0027] S5.1 The deflection of the old top will be greatest at the middle of its ultimate span, i.e., where the borehole passes through;

[0028] S5.2 Ultimate deflection of old top ω 老顶 It can be obtained through theoretical calculation first, and its theoretical calculation formula is:

[0029]

[0030] Among them, I 老顶 is the moment of inertia of the old top, which can be obtained through the theoretical formula:

[0031]

[0032] Among them, in the above formula, 控顶 The top control distance refers to the distance of the top control of the working surface support, which is determined by the model parameters of the working surface support and is usually a fixed constant.

[0033] The beneficial effects of the present invention are:

[0034] 1. The method of the present invention can realize the deformation monitoring of the entire old top rock layer in the vertical direction, and the data is more comprehensive than the monitoring data of the underground inclined hole.

[0035] 2. The method of the present invention can obtain continuous strain data of the entire old roof rock layer, and the deformation calculation of the old roof is more accurate.

[0036] 3. The identification method of the present invention is simple and can provide early warning of the initial pressure on the working face caused by the initial breakage of the old roof, thereby providing important data support for on-site safety prevention. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the distribution of overburden strata and arrangement of drilling holes on the working face in an embodiment of the present invention;

[0038] Figure 2 It is a schematic diagram of the overhanging length of the old roof reaching the limit span in an embodiment of the present invention;

[0039] Figure 3 It is a schematic diagram of the deflection when the exposed length of the old roof reaches the limit span in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with the accompanying drawings. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to this embodiment.

[0041] Example

[0042] like Figures 1 to 3 As shown, the present invention provides an early warning method for the initial break of the old roof based on the internal strain of the overburden rock, and the method comprises the following steps:

[0043] S1 arranges a coring ground borehole at a certain distance L m in front of the cutting eye of the working face, and the drilling depth to the top interface of the coal seam is H m:

[0044] S1.1 Since the core is taken from the borehole, all the rock layers inside the borehole can be catalogued in a columnar manner, so that the lithology and thickness of each rock layer can be obtained. i , where the thickness of the old top is h 老顶 ;

[0045] S1.2 Perform mechanical tests on the cores of each rock layer to obtain the bulk density γ of each rock layer. i , tensile strength R Ti , elastic modulus E i , where the bulk density of the old top is γ 老顶 , tensile strength is R T老顶 , elastic modulus is E 老顶 ;

[0046] S1.3 With the mechanical parameters of each rock layer, all the key layers in the entire borehole can be obtained by applying the key layer identification theory. The first key layer close to the coal seam can be considered as the old roof.

[0047] S1.4 The drilling hole is a certain distance Lm from the front of the cutting eye of the working face. This distance is the limit span L of the old top. 老顶 Half of the theoretical where q 老顶 =γ 老顶 h 老顶 .

[0048] S2 pushes the drill rod to lay the distributed optical cable into the borehole. The depth of the distributed optical cable is consistent with the depth of the borehole. After the distributed optical cable is laid, cement slurry is used to seal the entire borehole to ensure that the distributed optical cable is coupled with the wall and surrounding rock of the upward borehole.

[0049] S3 After the coal seam is mined, as the relative distance between the borehole and the working face gradually decreases, the distributed optical cable inside the borehole will be affected by the mining and produce corresponding strain deformation;

[0050] S4 integrates the strain generated by the distributed optical cable within the old top range of the borehole to obtain its total deformation ΔD:

[0051] S4.1 Use an optical fiber demodulator on the ground to monitor the strain inside the borehole. After monitoring, the continuous strain distribution of the entire distributed optical cable can be obtained. The scale coordinates of the distributed optical cable from the hole mouth to the hole bottom are 0m to Hm;

[0052] S4.2 Select to integrate the strain within the old top range to obtain the cumulative deformation within the rock layer. Among them, h1 and h2 represent the scale coordinates of the distributed optical cable within the range of the old top, h1 is the scale coordinate of the old top top interface, and h2 is the scale coordinate of the old top bottom top interface. Since the scale increases gradually from the hole mouth to the hole bottom, h1 is smaller than h2. ε(h) is the strain of each measuring point of the distributed optical cable within the range of the old top;

[0053] S4.3 When collecting data on distributed optical cables, due to the limitation of the accuracy of the optical fiber demodulation instrument, data is usually collected at a certain collection interval Δh. If n is an integer, the acquisition coordinates within the old top range are h1, h1+Δh, h1+2Δh, +…, h1+(n-1)Δh, h2, and the cumulative deformation can be obtained according to the formula in the specific calculation:

[0054]

[0055] Obviously, the smaller the acquisition interval Δh is, the more accurate the calculated cumulative deformation is.

[0056] S4.4 When the old top is bent, the scale coordinates h1 and h2 of the old top will also change, but the change can be ignored compared with the initial values ​​of h1 and h2. For the convenience of calculation, the scale coordinates h1 and h2 are kept unchanged in actual calculation.

[0057] S5 As the working face continues to move forward, the exposed range of the old roof continues to increase and bends. When the deflection of the old roof exceeds its limit deflection ω 老顶 The first break will occur when:

[0058] S5.1 The deflection of the old top will be greatest at the middle of its ultimate span, i.e., where the borehole passes through;

[0059] S5.2 Ultimate deflection of old top ω 老顶 It can be obtained through theoretical calculation first, and its theoretical calculation formula is:

[0060]

[0061] Among them, I 老顶 is the moment of inertia of the old top, which can be obtained through the theoretical formula:

[0062]

[0063] Among them, in the above formula, 控顶 The top control distance refers to the distance of the top control of the working surface support, which is determined by the model parameters of the working surface support and is usually a fixed constant.

[0064] S6 When the deformation of the old top ΔD is greater than the limit deflection ω of the old top 老顶 80% of them can provide early warning.

[0065] The method of the present invention can realize the deformation monitoring of the entire old roof rock layer in the vertical direction, which is more comprehensive than the data monitored by the underground inclined hole. The method can obtain the continuous strain data of the entire old roof rock layer, and the deformation calculation of the old roof is more accurate. The discrimination method of the present invention is simple, and can realize the initial pressure warning of the working face caused by the initial break of the old roof, thereby providing important data support for safety prevention on site.

[0066] For those skilled in the art, various corresponding changes and modifications can be made according to the above technical solutions and concepts, and all of these changes and modifications should be included in the protection scope of the claims of the present invention.

Claims

1. A method for early warning of the initial breakage of the old roof based on internal strain of the overburden rock, characterized in that: The method comprises the following steps: S1 Arrange a coring ground borehole at a certain distance L m in front of the cutting eye of the working face, and the drilling depth to the top interface of the coal seam is H m; S2 pushes the drill rod to lay the distributed optical cable into the borehole. The depth of the distributed optical cable is consistent with the depth of the borehole. After the distributed optical cable is laid, cement slurry is used to seal the entire borehole to ensure that the distributed optical cable is coupled with the wall and surrounding rock of the upward borehole. S3 After the coal seam is mined, as the relative distance between the borehole and the working face gradually decreases, the distributed optical cable inside the borehole will be affected by the mining and produce corresponding strain deformation; S4 integrates the strain generated by the distributed optical cable within the old top range of the borehole to obtain its total deformation ΔD; S5 As the working face continues to move forward, the exposed range of the old roof continues to increase and bends. When the deflection of the old roof exceeds its limit deflection ω 老顶 The first break will occur when S6 When the deformation of the old top ΔD is greater than the limit deflection ω of the old top 老顶 80% of them can provide early warning.

2. The method for early warning of the initial breakage of the old roof based on internal strain of the overburden rock according to claim 1 is characterized in that: The step S1 comprises: S1.1 Since the core is taken from the borehole, all the rock layers inside the borehole can be catalogued in a columnar manner, so that the lithology and thickness of each rock layer can be obtained. i , where the thickness of the old top is h 老顶 ; S1.2 Perform mechanical tests on the cores of each rock layer to obtain the bulk density γ of each rock layer i , tensile strength R Ti , elastic modulus E i ; The bulk density of the old top is γ 老顶 , tensile strength is R T老顶 , elastic modulus is E 老顶 ; S1.3 Use the key layer discrimination theory to obtain all the key layers inside the entire borehole, among which the first key layer close to the coal seam is the old roof; S1.4 is a certain distance Lm from the front of the cutting eye of the working face. This distance is the limit span L of the old top. 老顶 Half of the theoretical where q 老顶 =γ 老顶 h 老顶 .

3. The method for early warning of the initial breakage of the old roof based on internal strain of the overburden rock according to claim 1 is characterized in that: The step S4 comprises: S4.1 Use an optical fiber demodulator on the ground to monitor the strain inside the borehole. After monitoring, the continuous strain distribution of the entire distributed optical cable can be obtained. The scale coordinates of the distributed optical cable from the hole mouth to the hole bottom are 0m to Hm; S4.2 Select to integrate the strain within the old roof range to obtain the cumulative deformation within the rock layer Among them, h1 and h2 represent the scale coordinates of the distributed optical cable within the range of the old top, h1 is the scale coordinate of the old top top interface, and h2 is the scale coordinate of the old top bottom top interface. Since the scale increases gradually from the hole mouth to the hole bottom, h1 is smaller than h2. ε(h) is the strain of each measuring point of the distributed optical cable within the range of the old top; S4.3 When collecting data on distributed optical cables, due to the limitation of the accuracy of the optical fiber demodulation instrument, data is collected at a certain collection interval Δh. The number of collection intervals within the old top range is n is an integer; and the acquisition coordinates within the old top range are h1, h1+Δh, h1+2Δh, +…, h1+(n-1)Δh, h2. When the cumulative deformation is calculated specifically, it is calculated according to the formula: Among them, when the collection interval Δh is smaller, the calculated cumulative deformation is more accurate.

4. The method for early warning of the initial breakage of the old roof based on internal strain of the overburden rock according to claim 1 is characterized in that: The step S5 comprises: S5.1 The deflection of the old top will be greatest at the middle of its ultimate span, i.e., where the borehole passes through; S5.2 Ultimate deflection of old top ω 老顶 Obtained through the following calculation formula: Among them, I 老顶 is the moment of inertia of the old top, obtained by the following formula: Among them, l 控顶 The top control distance refers to the distance of the top control of the working surface support, which is determined by the model parameters of the working surface support and is usually a fixed constant.

Images