A method for early warning of the initial fracture of the old roof based on internal strain of the overburden rock

Abstract

The present invention provides a method for early warning of the initial failure of the old roof based on the internal strain of the overburden. This method continuously monitors the strain of the old roof and compares it with the ultimate deflection of the old roof rock strata. Integrating the strain of the rock strata within the old roof yields the cumulative deformation of the old roof. When the cumulative deformation exceeds 80% of the ultimate deflection of the old roof, an early warning is issued. This simple early warning method can provide early warning of the initial failure of the old roof, providing valuable guidance for preventing and controlling severe mining pressure at working faces.

Description

Technical Field

[0001] The present 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, a goaf is formed. As the working face advances from the cut, the immediate roof will first collapse. The immediate roof is usually soft rock, and its collapse has little impact on the stress on the working face supports. The old roof is usually stronger and has a larger overhang. When the overhang reaches a certain limit, the old roof will break. The initial failure of the old roof often causes increased stress on the working face supports, generating the initial pressure on the working face. If the initial pressure is strong, it can easily cause safety accidents. If the timing of the initial failure of the old roof can be predicted, accidents can be prevented in advance.

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

[0004] This method involves placing a ground borehole ahead of the working face cut and deploying a distributed optical cable inside the borehole to monitor deformation within the overburden. By monitoring the strain within the overburden in the ground monitoring borehole, the deformation of the old roof can be accurately measured and compared with the ultimate deflection of the old roof (i.e., initial fracture), thereby providing early warning of the initial fracture of the old roof. Summary of the Invention

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

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

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

[0008] 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;

[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 cables 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 advance, the exposed range of the old roof continues to increase and deflects. 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 ultimate 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 recorded 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 testing 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, the key layer identification theory can be used to obtain all the key layers in the entire borehole. 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 maximum 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 a fiber optic interrogator 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 perform integral calculation on the strain within the old roof range to obtain the cumulative deformation within the rock layer. Where h1 and h2 represent the scale coordinates of the distributed optical cable within the old top range, h1 is the scale coordinate of the old top-top interface, and h2 is the scale coordinate of the old top-bottom 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 old top range.

[0022] S4.3 When collecting data on distributed optical cables, due to the limitation of the accuracy of the optical fiber demodulation instrument, data collection is usually carried out 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 in sequence. The cumulative deformation can be obtained according to the following formula during specific calculation:

[0023]

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

[0025] S4.4 When the old top is deflected, the scale coordinates h1 and h2 of the old top will also change, but the amount of 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 roof will be greatest at the midpoint of its ultimate span, where the borehole passes through;

[0028] S5.2 Ultimate deflection of the old roof 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 deformation monitoring of the entire old roof rock layer in the vertical direction, and the data is more comprehensive than that of underground inclined hole monitoring.

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

[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 overburden distribution and drilling arrangement on the working face in an embodiment of the present invention;

[0038] Figure 2 Schematic diagram of the exposed length of the old roof reaching the limit span in an embodiment of the present invention;

[0039] Figure 3 This 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 a method for early warning of the initial breakage of the old roof based on the internal strain of the overburden rock, which includes 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 recorded 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 testing 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, the key layer identification theory can be used to obtain all the key layers in the entire borehole. 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 cables 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 borehole to obtain the total deformation ΔD:

[0051] S4.1 Use a fiber optic interrogator 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 perform integral calculation on the strain within the old roof range to obtain the cumulative deformation within the rock layer. Where h1 and h2 represent the scale coordinates of the distributed optical cable within the old top range, h1 is the scale coordinate of the old top-top interface, and h2 is the scale coordinate of the old top-bottom 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 old top range.

[0053] S4.3 When collecting data on distributed optical cables, due to the limitation of the accuracy of the optical fiber demodulation instrument, data collection is usually carried out 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 in sequence. The cumulative deformation can be obtained according to the formula in the specific calculation:

[0054]

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

[0056] S4.4 When the old top is deflected, the scale coordinates h1 and h2 of the old top will also change, but the amount of 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 advance, the exposed range of the old roof continues to increase and deflects. 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 roof will be greatest at the midpoint of its ultimate span, where the borehole passes through;

[0059] S5.2 Ultimate deflection of the old roof 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 ultimate deflection ω of the old top 老顶 80% of them can provide early warning.

[0065] The method of the present invention enables vertical deformation monitoring of the entire old roof stratum, providing more comprehensive data than monitoring data from underground inclined boreholes. This method can obtain continuous strain data for the entire old roof stratum, allowing for more accurate calculation of the deformation of the old roof. The method of the present invention is simple and can provide early warning of the initial pressure on the working face caused by the initial failure of the old roof, thereby providing important data support for on-site safety and prevention.

[0066] Those skilled in the art can make various corresponding changes and modifications based on the above technical solutions and concepts, and all of these changes and modifications should be included in the scope of protection 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 by: The method comprises the following steps: S1 is a certain distance in front of the cutting eye of the working surface A coring surface drill hole is arranged at the place where the core is drilled, and the drilling depth is to the top interface of the coal seam. ; S2: The distributed optical cable is laid into the borehole by pushing the drill rod. The depth of the distributed optical cable is consistent with the depth of the borehole. After the distributed optical cable is laid, the entire borehole is sealed with cement slurry to ensure that the distributed optical cable is coupled with the wall and surrounding rock of the upward borehole. S3 After coal seam mining, as the relative distance between the borehole and the working face gradually decreases, the distributed optical cables inside the borehole will be affected by mining and produce corresponding strain deformation; S4 The total deformation can be obtained by integrating the strain generated by the distributed optical cable within the old top range of the borehole. ; S5 As the working face continues to advance, the exposed area of ​​the old roof continues to increase and deflects. When the deflection of the old roof exceeds its limit deflection The first break will occur when S6 when the old top deformation Greater than the ultimate deflection of the old top 80% of the cases can provide early warning; Wherein, the step S1 includes, S1.1 Since the core is taken from the borehole, all the rock layers inside the borehole can be cataloged in a columnar manner to obtain the lithology and thickness of each rock layer. , where the thickness of the old top is ; S1.2 Conduct mechanical tests on the cores of each rock layer to obtain the bulk density of each rock layer ,tensile strength , elastic modulus ; The bulk density of the old top is , tensile strength is , the elastic modulus is ; S1.3 Using the key layer identification theory, all key layers in the entire borehole are obtained, among which the first key layer close to the coal seam is the old roof; S1.4 A certain distance from the front of the cutting eye of the working surface , this distance is the limit span of the old top Half of the theoretical ,in ; The step S5 comprises: S5.1 The deflection of the old roof will be greatest at the midpoint of its ultimate span, where the borehole passes through; S5.2 Ultimate deflection of old roof Obtained by the following calculation formula: ； in, is the moment of inertia of the old top, which is obtained by the following formula: ； in, 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.

2. The method for early warning of the initial breakage of the old roof based on internal strain of the overburden according to claim 1 is characterized in that: The step S4 comprises: S4.1 Use optical fiber demodulator to monitor the strain inside the borehole on the ground. 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 to ; S4.2 Select to perform integral calculation on the strain within the old top range to obtain the cumulative deformation within the old top range ,in 、 Represents the scale coordinates of the distributed optical cable within the old top range, is the scale coordinate of the old top interface, is the scale coordinate of the old top-bottom interface. Since the scale increases gradually from the hole mouth to the hole bottom, is less than of, The strain of each measuring point of the distributed optical cable within the old top range; S4.3 When collecting data from distributed optical cables, due to the limitation of the accuracy of the optical fiber demodulation instrument, the data should be collected at a certain interval. For data collection, the number of collection intervals within the old top range is , is an integer; and the acquisition coordinates within the old top range are When the cumulative deformation is calculated, it is calculated according to the formula: ； Among them, when the collection interval The smaller it is, the more accurate the calculated cumulative deformation is.

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