CN114595544B - A comprehensive safety evaluation method for buried pipelines in goafs of coal mines - Google Patents

Abstract

The invention discloses a comprehensive safety evaluation method for a buried pipeline in a coal mine goaf, which relates to the field of oil and gas transmission and comprises the steps of obtaining a surface subsidence displacement curve of the goaf; dividing a goaf surface displacement early warning interval according to the surface subsidence displacement curve; acquiring a pipeline dynamic stress curve, and dividing a pipeline dynamic early warning interval; and comprehensively evaluating the buried pipeline in the goaf to obtain a comprehensive evaluation grade by combining the displacement early warning interval of the surface of the goaf and the dynamic early warning interval of the pipeline. The invention provides a comprehensive safety evaluation method for a buried pipeline in a coal mine goaf, which aims to solve the problem that the comprehensive safety evaluation of the buried pipeline penetrating through the coal mine goaf is difficult in the prior art, realize the comprehensive evaluation of the dynamic risk of the buried pipeline penetrating through the coal mine goaf, provide a complete model for actual prediction and early warning and provide a guidance basis for engineering evaluation.

Description

A comprehensive safety evaluation method for buried pipelines in coal mine goaf

technical field

The invention relates to the field of oil and gas transportation, in particular to a comprehensive safety evaluation method for buried pipelines in goafs of coal mines.

Background technique

With the massive mining of coal resources, the formation range of gobs has gradually increased. As a result, the impact on many buildings and structures on the ground continues to increase. Oil and natural gas are one of the main energy sources, and their long-distance oil and gas pipelines are known as the national economic artery as the largest transportation carrier. Oil and gas pipelines will inevitably pass through many complex regions during transportation, and will encounter many geological disasters. As one of the more typical disasters, coal mine goaf subsidence, oil and gas pipelines will inevitably pass through coal mine goafs during long-distance transportation. area, causing huge damage to oil and gas pipelines.

Taking the West-East Gas Pipeline laying area as an example, the first-line project of the West-East Gas Pipeline passes through 9 provinces, and the route passes through about 76 coal mining goafs, of which 8 major goafs are located in Shanxi and Ningxia. In the province, the total length of pipeline sections affected by coal mine goafs is about 388 kilometers. Oil and gas pipelines passing through coal mine goafs will not only affect the mining of underground coal resources, but also seriously affect the transportation performance of oil and gas pipelines.

For gobs in coal mines, excessive mining is very likely to cause secondary geological disasters such as surface cracking or even collapse. When the oil and gas pipeline passes through the goaf, due to the subsidence of the surface, the pipeline is mainly bent and pulled. If it passes through the goaf, the rapid subsidence area may cause the pipeline to hang or even break. However, in the prior art, there is no specific and comprehensive safety evaluation standard for the critical failure of oil and gas pipelines passing through gobs in coal mines.

Contents of the invention

The invention provides a comprehensive safety evaluation method for buried pipelines in goafs in coal mines, to solve the problem in the prior art that it is difficult to conduct comprehensive safety evaluations for buried pipelines passing through goafs in coal mines, and to realize comprehensive evaluation of goafs in coal mines The purpose of providing a complete model for actual prediction and early warning, and providing a guiding basis for engineering evaluation.

The present invention realizes through following technical scheme:

A comprehensive safety evaluation method for buried pipelines in goafs of coal mines, including:

Obtain the surface subsidence displacement curve of the goaf; divide the early warning interval of the goaf surface displacement according to the surface subsidence displacement curve;

Obtain the pipeline dynamic stress curve and divide the pipeline dynamic early warning interval;

Combined with the goaf surface displacement early warning interval and the pipeline dynamic early warning interval, the buried pipeline in the goaf is comprehensively evaluated, and the comprehensive evaluation grade is obtained.

Aiming at the problem in the prior art that it is difficult to perform comprehensive safety evaluation on buried pipelines passing through goafs in coal mines, the present invention proposes a comprehensive safety evaluation method for buried pipelines in goafs in coal mines. The inventors of this case found in the research process that the subsidence and deformation of the ground surface is a gradual bottom-up influence process formed by the gradual mining of underground coal seams. The subsidence of the ground surface directly affects the safe operation of buried pipelines in this area, while The prior art completely ignores the existence of this factor. To this end, this method first obtains the surface subsidence displacement curve of the goaf, and then divides the early warning interval of the goaf surface displacement according to the obtained surface subsidence displacement curve; after that, obtains the pipeline dynamic stress curve, and divides the pipeline based on the stress failure criterion Dynamic early-warning interval; finally, combined with the obtained goaf surface displacement early-warning interval and pipeline dynamic early-warning interval, the comprehensive evaluation of goaf-buried pipeline is carried out. It can be seen that this application combines the subsidence displacement of the goaf surface and the dynamic stress of the buried pipeline passing through the goaf, and establishes a comprehensive evaluation method suitable for the buried pipeline in the coal mine goaf, which fills the existing The gap in technology can comprehensively evaluate the dynamic safety risks of buried pipelines passing through coal mine goafs, provide a complete model for actual prediction and early warning, and provide guidance for engineering evaluation.

Further, the method for obtaining the surface subsidence displacement curve of the goaf includes:

Set the calculation point to calculate the maximum subsidence value of the goaf surface;

The dynamic subsidence equation is obtained based on the segmented Knothe time function, and the surface subsidence displacement curve is drawn according to the dynamic subsidence equation.

The Knothe time function model conforms to the creep theory, and it is believed that the subsidence velocity at the moment of surface subsidence is the final subsidence value of the surface, which is proportional to the difference between the dynamic subsidence values at this moment. The piecewise Knothe time function is an improvement to the original Knothe time function, and its predicted surface subsidence is more accurate and has smaller errors. This scheme is based on the combination of the segmented Knothe time function and the maximum subsidence value to obtain the equation expression of the surface subsidence and subsidence, and then the surface subsidence displacement curve can be drawn.

In addition, those skilled in the art should understand that the Knothe time function is a general term in this field, and there is no standard Chinese translation.

Further, the maximum subsidence value of the goaf surface is calculated by the following formula: W _m = hq cos ψ ;

In the formula, W _m is the maximum subsidence value; h is the thickness of the coal seam; q is the subsidence coefficient; ψ is the inclination angle of the coal seam;

The dynamic sinking equation is:

In the formula, W ( t ) is the dynamic subsidence value _of the maximum subsidence point; t is the time; c is the time coefficient; τ is the moment when the maximum subsidence velocity appears at the surface point; , Ф ₂ ( t ) is the piecewise Knothe time function; e is the natural logarithm.

Further, the method for obtaining the dynamic stress curve of the pipeline includes:

Set the calculation point to calculate the maximum subsidence value of the goaf surface;

Calculate the radius of influence of the goaf on the coal seam, and use the edge of the radius of influence as the sinking starting point of the pipeline deformation;

Calculate the bending moment of the pipeline at the sinking starting point;

Calculate the dynamic stress σ ₁ of the pipeline according to the maximum subsidence value, the radius of influence, and the bending moment of the pipeline at the starting point of subsidence;

Calculate the stress σ ₀ of the pipeline due to internal pressure;

Calculate the ultimate stress σ of the pipeline: σ=σ ₁ + σ ₀ ;

Draw the pipeline dynamic stress curve according to the ultimate stress σ .

The dynamic stress curve of the pipeline can reflect the stress and strain of the buried pipeline when it passes through the goaf of the coal mine. The dynamic stress curve of this scheme is based on the dynamic stress σ ₁ of the pipeline. On this basis, the stress on the pipeline due to internal pressure is considered In this case, the sum of the two is used as the final stress to draw the pipeline dynamic stress curve. Compared with the conventional way of directly using dynamic stress as the basis of stress analysis, it has more practical engineering application value. Certainly, the dynamic stress therein can be obtained by those skilled in the art according to the existing stress analysis means, and will not be repeated here.

Further, the maximum subsidence value of the goaf surface is calculated by the following formula: W _m = hq cos ψ ; where W _m is the maximum subsidence value; h is the thickness of the coal seam; q is the subsidence coefficient; ψ is coal seam inclination;

The influence radius is calculated by the following formula: r = H /tan α ; where r is the influence radius, H is the coal seam mining depth, and α is the mining influence angle;

If the buried pipeline belongs to the pipe-soil collaborative deformation in the goaf, the bending moment of the pipeline at the starting point of subsidence is calculated by the following formula:

，k为弹性地基系数；In the formula, M _A is the bending moment of the pipeline at the sinking starting point, W ( l ₁ , γ ) is the sinking value of the maximum sinking point of the pipeline, L is the distance from the sinking starting point to the calculation point, and EI is the bending moment of the pipeline stiffness, λ is the set coefficient, and

, k is the coefficient of elastic foundation;

If the buried pipeline belongs to the pipe-soil non-cooperative deformation in the goaf, the bending moment of the pipeline at the starting point of subsidence is calculated by the following formula:

，k为弹性地基系数；In the formula, M _A is the bending moment of the pipeline at the sinking starting point, EI is the bending stiffness of the pipeline, y _D is the sinking value of the end of the dark suspended area, x _D is the distance from the sinking starting point to the end of the dark suspended area, i is the surface slope corresponding to the end of the dark suspended area, λ is the setting coefficient, and

, k is the coefficient of elastic foundation;

The stress σ ₀ suffered by the pipeline due to internal pressure is calculated by the following formula: σ ₀ = PD /2 S ; where P is the internal pressure of the pipeline, D is the outer diameter of the pipeline, and S is the wall thickness of the pipeline.

Among them, the pipe-soil synergistic deformation refers to the situation that the buried pipeline deforms together with the soil during the small surface change at the initial stage of mining when the ground surface changes little;

Pipe-soil non-coordinated deformation means that with the continuous mining, the land subsidence increases continuously. When the deformation of the soil below the pipeline is greater than the deformation of the pipeline, the deformation of the pipeline and the soil is manifested at the point of maximum subsidence between the pipeline and the soil. The body is separated, and a local dark suspended state under the pipe appears, which is called pipe-soil non-cooperative deformation. In the pipe-soil non-cooperative deformation stage, the pipe in the dark overhang area bears the weight of the pipe and the weight of the soil from above. For the pipe-soil part without dark overhang, the closer the support force of the soil below the pipe is to the edge of the goaf, the greater the support force for the pipe. As the mining continues, the mining area becomes larger and larger, and the dark overhang area formed becomes larger and larger. When the formed dark overhang area is large enough, the soil above the pipeline will be broken due to the subsidence of the surrounding soil. Therefore, pipe-soil non-cooperative deformation is a more complicated mechanical model, but it is also an actual situation that is more likely to be encountered in engineering sites.

In the process of calculating the bending moment, this scheme considers the two situations that the buried pipeline belongs to the pipe-soil synergistic deformation or the pipe-soil non-synergistic deformation in the goaf, and puts forward the respective applicable bending moment calculation formulas , significantly improving the accuracy and precision of subsequent dynamic stress calculations.

Further, the division method of the early warning interval of surface displacement in the goaf includes:

According to the surface subsidence displacement curve, draw the tangent angle change diagram of the displacement curve;

In the tangent angle change diagram of the displacement curve, find two critical time points when the tangent angle is equal to 45°, which are marked as T ₁ and T ₂ , where T ₁ < T ₂ ;

Divide the early warning interval of surface displacement in the goaf:

If the time t satisfies t< T ₁ , it is classified as primary warning;

If the time t satisfies T ₁ ≤ t < T ₂ , it is classified as an intermediate warning;

If the time t satisfies T ₂ ≤t, it is classified as advanced warning.

This program introduces the tangent angle of the displacement curve to carry out scientific and reasonable early warning interval division for the displacement change of the surface.

The inventors of this case found out during a large amount of research that the surface deformation of the goaf is divided into three processes: the initial period of surface subsidence, the active period and the recession period, and the speed is a process from slow to fast and then slow. Therefore, when the tangent angle formed by the surface change rate per unit time is less than 45°, it can be defined as the initial period of surface subsidence, that is, the initial deformation stage; when the tangent angle formed by the surface change rate per unit time is greater than 45°, it is defined as the active period of surface displacement, namely Surface accelerated deformation stage; after the accelerated deformation stage, when the tangent angle formed by the surface change rate per unit time is less than 45°, it can be defined as the surface displacement decay period, that is, the deceleration deformation stage.

Therefore, this scheme adopts two critical time points T ₁ and T ₂ when the tangent angle of the displacement curve is equal to 45° in the change diagram of the tangent angle of the displacement curve are used as the critical points for the division of the early warning interval of the surface displacement of the goaf. Among them, those skilled in the art should understand that the risk levels of primary early warning, intermediate early warning, and advanced early warning increase sequentially.

When t < T ₁ , the mining area of the underground coal mine is not large, and the stress redistribution area of the rock formation is not large, resulting in slow movement of the rock formation, and it takes a long time for the rock formation to reach the state of stress rebalance, so that the displacement of the surface also moves slowly. At this stage, the ground surface has just begun to move and deform, and the movement rate is not large, so it has little effect on the change of the mechanical behavior of the pipeline, and the threat of the goaf process to the pipeline is small. At this time, the pipeline is in the initial deformation stage with the slow deformation of the ground surface. . Therefore, at this stage, the pipeline and the goaf surface are less dangerous, so the early warning interval of the goaf surface displacement is divided into primary early warning.

When T ₁ ≤ t < T ₂ , the mining area of the coal mine reaches a certain scale, resulting in a large area of rock movement. Due to the large goaf area, the original stress damage range of the rock layer is wide, and the overlying rock layer needs a larger area for stress restoration. Balanced, the rock formations move faster at this time. Due to the fast surface deformation and large deformation displacement at this stage, the mechanical behavior of the pipeline will change greatly at this stage, and the gradual mining of the goaf will pose a huge threat to the pipeline. Therefore, the early warning interval of surface displacement in the goaf at this stage is divided into intermediate early warning.

When T ₂ ≤ t, the coal mining is basically over. Since the area mined before that has gone through the movement of the active period of the strata, only a small amount of stratum displacement is required to achieve the rebalance of stratum stress at this stage, and the The rate of change of displacement is slow. However, due to the partial displacement of the ground surface at this stage, and this partial displacement determines whether the pipeline is damaged at some point, the goaf has subsidence, and the geology is complex and changeable, which increases the stress and strain of the pipeline and increases the risk of the pipeline. Therefore, the early warning interval of surface displacement in the goaf at this stage is divided into advanced early warning.

Further, the division method of pipeline dynamic early warning interval includes:

If the time t satisfies t< T ₁ , it is classified as a first-level early warning;

If the time t satisfies T ₁ ≤ t < T ₃ , it is classified as a second-level early warning;

If the time t satisfies T ₃ ≤t< T ₄ , it is divided into three levels of early warning;

If the time t satisfies T ₄ ≤ t, it is divided into four levels of early warning;

Among them, T3 is the critical time point of the third-level early warning, and T4 _is the critical time point of the _fourth -level early warning; the risk levels of the first-level early warning, the second-level early warning, the third-level early warning, and the fourth-level early warning increase sequentially.

T ₄ is calculated by the following formula:

，k为弹性地基系数；Ф(T ₄)为自变量取T ₄时的Knothe时间函数；σ _屈为管道屈服应力；In the formula, D is the outer diameter of the pipeline, MA is the bending moment of the pipeline at the starting point of subsidence, _I is the moment of inertia of the pipeline, L is the distance from the starting point of subsidence to the calculation point, λ is the setting coefficient, and

, k is the elastic foundation coefficient; Ф ( T ₄ ) is the Knothe time function when the independent variable is T ₄ ; σyield is the _yield stress of the pipeline;

Calculate T ₃ by the following formula: T ₃ = T ₄ - T'; where T' is the total time required for pipeline maintenance.

The total time required for the maintenance of the pipeline is calculated by the following formula: T'=t ₁ + t ₂ + t ₃ ; where t ₁ is the length of emergency mobilization, t ₂ is the time required for personnel to arrive at the disaster site, and t ₃ is the maintenance start until completion time.

The buried oil and gas pipeline passing through the goaf is affected by the coal seam's gradual goafing, and its pipeline will also deform at different speeds with the movement of the ground surface. The purpose of dividing the pipeline dynamic warning interval is to quantitatively evaluate the deformation caused coming security risks.

When the pipeline passes through the goaf in normal operation, the stress and strain of the pipeline and the displacement of the pipeline are in the slow deformation stage, and the pipeline dynamic warning interval is divided into a first-level warning;

When T ₁ ≤ t < T ₃ , the stress and strain on the pipeline suddenly start to accelerate or the stress and strain on a certain section of the pipeline suddenly change, that is, after T ₁ , the dynamic warning interval of the pipeline enters the second-level early warning. The stress and strain of the pipeline change rapidly, so it is necessary to pay attention to the maximum stress change law in the pipeline in real time, and to start preparations for emergency response.

When T ₃ ≤ t < T ₄ , it means that the goaf continues to sink after the pipeline dynamic warning interval passes through the second-level warning stage, making the pipeline approaching the yield limit, and the surface deformation of the goaf may still be in an active period. That is, the deformation rate of the pipeline is still relatively fast, and the impact on the pipeline is relatively large, so the warning level is upgraded to a third-level warning. At this time, in order to be able to make timely emergency response mobilization, departure, arrival, construction, maintenance and other series of work before the pipeline yields, and considering factors such as complex geology and inconvenient actions in some coal mine working areas, it is necessary to ensure that the pipeline reaches the red warning. Complete maintenance work.

The time limit between the second-level early warning and the third-level early warning is T ₃ . It depends on the level of natural road conditions and the expected severity of failure.

When T ₄ ≤t, the maximum stress on the pipeline will soon reach the yield limit, and if the pipeline stress continues to increase, serious safety accidents such as pipeline damage may occur. Therefore, it is necessary to complete the pipeline repair and maintenance work before the pipeline reaches the yield limit to ensure the safe operation of the pipeline. Considering that if the pipeline is about to reach the yield limit, the coal mine goaf is still in an active period, and the surface deformation is still in a state of accelerated deformation, that is, the stress change of the pipeline will quickly reach the yield limit. Therefore, take the pipeline stress reaching 90% yield limit as the fourth-level early warning time point, which should be the end time point of emergency response maintenance work, and T ₄ is calculated by the following formula:

Among them, Ф ( T ₄ ) is the Knothe time function when the independent variable is T ₄ ; those skilled in the art should understand that if the piecewise _Knothe time function is used, then according to which segment time T4 belongs to, the corresponding The formula will do.

Furthermore, the methods for comprehensive evaluation of buried pipelines in gobs include:

If the pipeline dynamic early warning interval belongs to the four-level early warning, the comprehensive evaluation level is catastrophic level;

If the pipeline dynamic early warning interval belongs to the third-level early warning, the comprehensive evaluation level is the warning level;

If the pipeline dynamic early warning interval belongs to the second-level early warning, the comprehensive evaluation level is the warning level;

If the pipeline dynamic early warning interval belongs to the first-level early warning, and the surface displacement early warning interval of the goaf is the primary early warning, the comprehensive evaluation level is the attention level;

If the pipeline dynamic early warning interval belongs to the first-level early warning, and the goaf surface displacement early warning interval is the intermediate early warning or high-level early warning, the comprehensive evaluation level is the warning level.

Since there is no mature model for comprehensive early warning of buried pipelines passing through coal mine goafs in the prior art, this application considers that in actual engineering, the stress and strain of pipelines will not be affected by the mining of goafs under ideal conditions. The pipeline may cause a sudden change in the mechanical behavior of the pipeline due to local shear or other behaviors. Therefore, this application uses the pipeline dynamic warning interval model based on the pipeline mechanical behavior as the main early warning and forecast index to represent the early warning of the ground displacement of the goaf in the landmark settlement. The interval model is used as an auxiliary early warning and forecast index, and the two are combined to obtain a comprehensive model that can effectively evaluate the safety level of oil and gas pipelines in goaf areas.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

1. A comprehensive safety evaluation method for buried pipelines in goafs of coal mines according to the present invention combines the surface subsidence displacement of goafs and the dynamic stress of buried pipelines passing through goafs, and establishes a method suitable for goafs in coal mines. The comprehensive evaluation method of buried pipelines in the area fills the gaps in the existing technology, and can comprehensively evaluate the dynamic safety risks of buried pipelines passing through coal mine goafs, provide a complete model for actual prediction and early warning, and provide guidance for engineering evaluation. .

2. The present invention provides a comprehensive safety evaluation method for buried pipelines in goafs in coal mines, which fully considers the effect of surface subsidence and displacement of goafs on buried oil and gas pipelines, and has practical engineering application value.

3. A comprehensive safety evaluation method for buried pipelines in goafs of coal mines according to the present invention considers the stress conditions of pipelines due to internal pressure, and uses the combination of internal pressure and dynamic stress as the final stress to draw pipeline dynamic stress curves, which is more practical. engineering application value.

4. A comprehensive safety evaluation method for buried pipelines in goafs of coal mines according to the present invention. In the process of calculating bending moments, it is considered that buried pipelines in goafs belong to two types of pipe-soil synergistic deformation or pipe-soil non-cooperative deformation. According to the situation, the applicable bending moment calculation formulas are proposed respectively, which significantly improves the calculation accuracy and precision of dynamic stress.

5. A comprehensive safety evaluation method for buried pipelines in goafs of coal mines according to the present invention adopts two critical time points when the tangent angles of the displacement curves are equal to 45° in the change diagram of the tangent angles of the displacement curves as the critical points for the division of early warning intervals of surface displacements in goafs. Points, the division of the early warning interval of surface displacement in the goaf is realized.

6. The present invention provides a comprehensive safety evaluation method for buried pipelines in goafs in coal mines, through the setting and calculation of multiple critical time points, the division of pipeline dynamic early warning intervals is realized.

7. The present invention is a comprehensive safety evaluation method for buried pipelines in goafs in coal mines. The pipeline dynamic early warning interval model based on pipeline mechanical behavior is used as the main early warning and forecast index to represent the goaf surface displacement early warning interval model of landmark settlement As an auxiliary early warning and forecast index, combining the two, a comprehensive model that can effectively evaluate the safety level of oil and gas pipelines in goaf areas is obtained.

Description of drawings

The drawings described here are used to provide a further understanding of the embodiments of the present invention, constitute a part of the application, and do not limit the embodiments of the present invention. In the attached picture:

Fig. 1 is the schematic flow chart of the specific embodiment of the present invention;

Fig. 2 is the surface subsidence displacement curve in the specific embodiment of the present invention;

Fig. 3 is a graph showing the variation of the tangent angle of the displacement curve in a specific embodiment of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the examples and accompanying drawings. As a limitation of the present invention. In the description of this application, it is to be understood that the terms "front", "rear", "left", "right", "upper", "lower", "vertical", "horizontal", "high", The orientation or positional relationship indicated by "low", "inner", "outer" and so on is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying the referred device Or elements must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the scope of protection of the present application.

Example 1:

As shown in Figure 1, a comprehensive safety evaluation method for buried pipelines in gobs in coal mines includes:

Obtain the surface subsidence displacement curve of the goaf; divide the early warning interval of the goaf surface displacement according to the surface subsidence displacement curve;

Obtain the pipeline dynamic stress curve and divide the pipeline dynamic early warning interval;

Combined with the goaf surface displacement early warning interval and the pipeline dynamic early warning interval, the buried pipeline in the goaf is comprehensively evaluated, and the comprehensive evaluation grade is obtained.

Among them, the method to obtain the surface subsidence displacement curve of the goaf is:

Set the calculation point to calculate the maximum subsidence value of the goaf surface; in this embodiment, the calculation point is preferably set at the maximum displacement of the pipeline.

The dynamic subsidence equation is obtained based on the segmented Knothe time function, and the surface subsidence displacement curve is drawn according to the dynamic subsidence equation.

The segmented Knothe time function in the present embodiment is expressed as:

where Ф ( t ) represents the Knothe time function; Ф ₁ ( t ) and Ф ₂ ( t ) are the piecewise Knothe time functions; t is the time; c is the time coefficient; ; T is the total time of sinking; e is the natural logarithm.

Among them, the maximum subsidence value of the goaf surface is calculated by the following formula: W _m = hq cos ψ ;

In the formula, W _m is the maximum subsidence value; h is the thickness of the coal seam; q is the subsidence coefficient; ψ is the inclination angle of the coal seam;

The dynamic sinking equation is expressed as:

In the formula, W ( t ) is the dynamic subsidence value _of the maximum subsidence point; t is the time; c is the time coefficient; τ is the moment when the maximum subsidence velocity appears at the surface point; , Ф ₂ ( t ) is the piecewise Knothe time function; e is the natural logarithm.

Among them, the methods for obtaining the dynamic stress curve of the pipeline include:

Set the calculation point to calculate the maximum subsidence value of the goaf surface;

Calculate the radius of influence of the goaf on the coal seam, and use the edge of the radius of influence as the sinking starting point of the pipeline deformation;

Calculate the bending moment of the pipeline at the sinking starting point;

Calculate the dynamic stress σ ₁ of the pipeline according to the maximum subsidence value, the radius of influence, and the bending moment of the pipeline at the starting point of subsidence;

Calculate the stress σ ₀ of the pipeline due to internal pressure;

Calculate the ultimate stress σ of the pipeline: σ=σ ₁ + σ ₀ ;

The ultimate stress σ draws the dynamic stress curve of the pipe.

Among them, the maximum subsidence value of the goaf surface is calculated by the following formula: W _m = hq cos ψ ;

In the formula, W _m is the maximum subsidence value; h is the thickness of the coal seam; q is the subsidence coefficient; ψ is the inclination angle of the coal seam;

The influence radius is calculated by the following formula: r = H /tan α ; where r is the influence radius, H is the coal seam mining depth, and α is the mining influence angle;

If the buried pipeline belongs to the pipe-soil collaborative deformation in the goaf, the bending moment of the pipeline at the starting point of subsidence is calculated by the following formula:

，k为弹性地基系数；In the formula, M _A is the bending moment of the pipeline at the sinking starting point, W ( l ₁ , γ ) is the sinking value of the maximum sinking point of the pipeline, L is the distance from the sinking starting point to the calculation point, and EI is the bending moment of the pipeline stiffness, λ is a coefficient, and

, k is the coefficient of elastic foundation;

If the buried pipeline belongs to the pipe-soil non-cooperative deformation in the goaf, the bending moment of the pipeline at the starting point of subsidence is calculated by the following formula:

，k为弹性地基系数；In the formula, M _A is the bending moment of the pipeline at the sinking starting point, EI is the bending stiffness of the pipeline, y _D is the sinking value of the end of the dark suspended area, x _D is the distance from the sinking starting point to the end of the dark suspended area, i is the surface slope corresponding to the end of the dark suspended area, λ is the setting coefficient, and

, k is the coefficient of elastic foundation;

The stress σ ₀ suffered by the pipeline due to internal pressure is calculated by the following formula: σ ₀ = PD /2 S ; where P is the internal pressure of the pipeline, D is the outer diameter of the pipeline, and S is the wall thickness of the pipeline.

Example 2:

A comprehensive safety evaluation method for buried pipelines in goafs of coal mines, on the basis of Embodiment 1:

(1) First, divide the early warning interval of surface displacement in the goaf:

According to the surface subsidence displacement curve, draw the tangent angle change diagram of the displacement curve;

In the tangent angle change diagram of the displacement curve, find two critical time points when the tangent angle is equal to 45°, which are marked as T ₁ and T ₂ , where T ₁ < T ₂ ;

Divide the early warning interval of surface displacement in the goaf:

If the time t satisfies t< T ₁ , it is classified as primary warning;

If the time t satisfies T ₁ ≤ t < T ₂ , it is classified as an intermediate warning;

If the time t satisfies T ₂ ≤t, it is classified as advanced warning.

(2) Re-dividing the pipeline dynamic early warning interval:

If the time t satisfies t< T ₁ , it is classified as a first-level early warning;

If the time t satisfies T ₁ ≤ t < T ₃ , it is classified as a second-level early warning;

If the time t satisfies T ₃ ≤t< T ₄ , it is divided into three levels of early warning;

If the time t satisfies T ₄ ≤ t, it is divided into four levels of early warning;

Among them, T3 is the critical time point of the third-level early warning, and T4 _is the critical time point of the _fourth -level early warning; the risk levels of the first-level early warning, the second-level early warning, the third-level early warning, and the fourth-level early warning increase sequentially.

Among them, T ₄ is calculated by the following formula:

，k为弹性地基系数；Ф(T ₄)为自变量取T ₄时的Knothe时间函数；σ _屈为管道屈服应力；In the formula, D is the outer diameter of the pipeline, MA is the bending moment of the pipeline at the starting point of subsidence, _I is the moment of inertia of the pipeline, L is the distance from the starting point of subsidence to the calculation point, λ is the setting coefficient, and

, k is the elastic foundation coefficient; Ф ( T ₄ ) is the Knothe time function when the independent variable is T ₄ ; σyield is the _yield stress of the pipeline;

Calculate T ₃ by the following formula: T ₃ = T ₄ - T'; where T' is the total time required for pipeline maintenance.

The total time required for pipeline maintenance is calculated by the following formula: T'=t ₁ + t ₂ + t ₃ ; where t ₁ is the length of emergency mobilization, t ₂ is the time required for personnel to arrive at the disaster site, and t ₃ is the time for maintenance to be completed duration.

(3) Finally, make a comprehensive evaluation of the buried pipeline in the goaf:

If the pipeline dynamic early warning interval belongs to the four-level early warning, the comprehensive evaluation level is catastrophic level;

If the pipeline dynamic early warning interval belongs to the third-level early warning, the comprehensive evaluation level is the warning level;

If the pipeline dynamic early warning interval belongs to the second-level early warning, the comprehensive evaluation level is the warning level;

If the pipeline dynamic early warning interval belongs to the first-level early warning, and the surface displacement early warning interval of the goaf is the primary early warning, the comprehensive evaluation level is the attention level;

If the pipeline dynamic early warning interval belongs to the first-level early warning, and the goaf surface displacement early warning interval is the intermediate early warning or high-level early warning, the comprehensive evaluation level is the warning level.

In this embodiment, a coal mine goaf is taken as an example for calculation and evaluation.

The oil and gas pipeline passing through the goaf of the coal mine is made of X80 pipe, with an outer diameter of 1024mm, a wall thickness of 18mm, and a design internal pressure of 10MPa. The inclination angle of the coal mining face is 4°-6°, the mining strike size is 571m, the width is 164m, the average mining depth is 260m, and the average mining thickness is 7.5m. Fully mechanized top-coal caving mining is adopted, and the roof management method is the total caving method. The influence propagation angle of mining subsidence is 86.2°, the tangent value of the main influence angle in the strike direction is 1.9, the average tangent value of the main influence angle in the inclined direction is 2.1, the subsidence coefficient is 0.79, and the horizontal movement coefficient is 0.35. Observation stations are arranged at 29 points along the mining direction.

The maximum subsidence value of the goaf surface is calculated to be -5.925m; the bending moment M _A at the starting point of the subsidence is -8272.2N·m; c =0.037; the total subsidence time T =364d; τ =0.5 T =182d ; r =136.84m; L =422.34m; k =4500N/m ³ ; E= 2.1×10 ¹¹ pa; I = 0.0037m ⁴ ; λ= _0.0347 ;

The dynamic stress σ ₁ of the pipeline is:

The dynamic subsidence equation of the ground surface is:

According to the dynamic surface subsidence equation, the surface subsidence displacement curve is drawn, as shown in Figure 2.

Draw the dynamic stress curve of the pipeline through the final stress formula of the pipeline σ=σ ₁ + σ ₀ .

According to Fig. 2, draw the tangent angle change diagram of the displacement curve, as shown in Fig. 3, T ₁ =74d, T ₂ =301d can be obtained.

According to the repair mobilization time of the oil and gas transportation company corresponding to the pipeline, the emergency mobilization time is t ₁ = 1d, the time required for personnel to arrive at the disaster site is t ₂ = 2d, and the time for maintenance to be completed is t ₃ = 7d, so the pipeline maintenance requires The total duration is T' = 10d.

The yield stress of the oil and gas pipeline passing through the goaf is 550MPa, and the time to reach the yield point can be obtained from the pipeline dynamic stress curve as 249d. Calculated to get T ₄ = 202d, T ₃ = 192d.

Through the above calculation, the comprehensive evaluation model of this embodiment can be obtained:

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the scope of the present invention. Protection scope, within the spirit and principles of the present invention, any modification, equivalent replacement, improvement, etc., shall be included in the protection scope of the present invention.

It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is a relationship between these entities or operations. any such actual relationship or order exists between them. Furthermore, the term "comprises", "comprising", or any other variation thereof, is intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus comprising a set of elements includes not only those elements, but also includes elements not expressly listed. Other elements mentioned above, or also include elements inherent in such process, method, article or equipment. In addition, the term "connection" used herein may be directly connected or indirectly connected via other components unless otherwise specified.

Claims (5)

1. A comprehensive safety evaluation method for buried pipelines in goafs of coal mines, characterized in that it comprises: Obtain the surface subsidence displacement curve of the goaf; divide the early warning interval of the goaf surface displacement according to the surface subsidence displacement curve; Obtain the pipeline dynamic stress curve and divide the pipeline dynamic early warning interval; Combined with the goaf surface displacement early warning interval and the pipeline dynamic early warning interval, the buried pipeline in the goaf is comprehensively evaluated, and the comprehensive evaluation grade is obtained; The division method of the early warning interval of surface displacement in the goaf includes: According to the surface subsidence displacement curve, draw the tangent angle change diagram of the displacement curve; In the tangent angle change graph of the displacement curve, find two critical time points when the tangent angle is equal to 45°, which are marked as T ₁ and T ₂ , where T ₁ <T ₂ ; Divide the early warning interval of surface displacement in the goaf: If the time t satisfies t<T ₁ , it is classified as primary warning; If the time t satisfies T ₁ ≤ t < T ₂ , it is classified as an intermediate warning; If the time t satisfies T ₂ ≤t, it is classified as advanced warning; The division method of pipeline dynamic early warning interval includes: If the time t satisfies t<T ₁ , it is classified as a first-level early warning; If the time t satisfies T ₁ ≤ t < T ₃ , it is classified as a second-level early warning; If the time t satisfies T ₃ ≤t<T ₄ , it is divided into three levels of early warning; If the time t satisfies T ₄ ≤ t, it is divided into four levels of early warning; Wherein, T3 is the critical time point of the _third -level early warning, and T4 is the critical time point of the _fourth -level early warning; the risk levels of the first-level early warning, the second-level early warning, the third-level early warning, and the fourth-level early warning are sequentially increased; T ₄ is calculated by the following formula:

In the formula, D is the outer diameter of the pipeline, M _A is the bending moment of the pipeline at the starting point of subsidence, I is the moment of inertia of the pipeline, L is the distance from the starting point of subsidence to the calculation point, λ is the setting coefficient, and

k is the elastic foundation coefficient; Ф(T ₄ ) is the Knothe time function when the independent variable is T ₄ ; σyield is the _yield stress of the pipeline; EI is the bending stiffness of the pipeline; Calculate T ₃ by the following formula: T ₃ =T ₄ -T'; where T' is the total time required for pipeline maintenance; The total time required for the maintenance of the pipeline is calculated by the following formula: T'=t ₁ +t ₂ +t ₃ ; where t ₁ is the length of emergency mobilization, t ₂ is the time required for personnel to arrive at the disaster site, and t ₃ is the maintenance start duration until completion; Methods for comprehensive evaluation of buried pipelines in gobs include: If the pipeline dynamic early warning interval belongs to the four-level early warning, the comprehensive evaluation level is catastrophic level; If the pipeline dynamic early warning interval belongs to the third-level early warning, the comprehensive evaluation level is the warning level; If the pipeline dynamic early warning interval belongs to the second-level early warning, the comprehensive evaluation level is the warning level; If the pipeline dynamic early warning interval belongs to the first-level early warning, and the surface displacement early warning interval of the goaf is the primary early warning, the comprehensive evaluation level is the attention level; If the pipeline dynamic early warning interval belongs to the first-level early warning, and the goaf surface displacement early warning interval is the intermediate early warning or high-level early warning, the comprehensive evaluation level is the warning level. 2. the comprehensive safety evaluation method of a kind of coal mine goaf buried pipeline according to claim 1, is characterized in that, the method for obtaining the surface subsidence displacement curve of goaf comprises: Set the calculation point to calculate the maximum subsidence value of the goaf surface; The dynamic subsidence equation is obtained based on the segmented Knothe time function, and the surface subsidence displacement curve is drawn according to the dynamic subsidence equation. 3. The comprehensive safety evaluation method of a buried pipeline in a coal mine goaf according to claim 2, wherein the maximum subsidence value of the goaf surface is calculated by the following formula: W _m = hqcosψ; where, W _m is the maximum subsidence value; h is the thickness of the coal seam; q is the subsidence coefficient; ψ is the inclination angle of the coal seam; The dynamic sinking equation is:

In the formula, W( _t ) is the dynamic subsidence value of the maximum subsidence point; t is time; c is the time coefficient; τ is the moment when the surface point has the maximum subsidence velocity; , Ф ₂ (t) is the piecewise Knothe time function; e is the natural logarithm. 4. the comprehensive safety evaluation method of a kind of coal mine goaf buried pipeline according to claim 1, is characterized in that, the method for obtaining pipeline dynamic stress curve comprises: Set the calculation point to calculate the maximum subsidence value of the goaf surface; Calculate the radius of influence of the goaf on the coal seam, and use the edge of the radius of influence as the sinking starting point of the pipeline deformation; Calculate the bending moment of the pipeline at the sinking starting point; Calculate the dynamic stress σ ₁ of the pipeline according to the maximum subsidence value, the radius of influence, and the bending moment of the pipeline at the starting point of subsidence; Calculate the stress σ ₀ of the pipeline due to internal pressure; Calculate the final stress σ of the pipeline: σ=σ ₁ +σ ₀ ; Draw the pipeline dynamic stress curve according to the ultimate stress σ. 5. the comprehensive safety evaluation method of a kind of coal mine goaf buried pipeline according to claim 4, is characterized in that, The maximum subsidence value of the goaf surface is calculated by the following formula: W _m = hqcosψ; where W _m is the maximum subsidence value; h is the thickness of the coal seam; q is the subsidence coefficient; ψ is the inclination angle of the coal seam; The influence radius is calculated by the following formula: r=H/tanα; in the formula, r is the influence radius, H is the coal seam mining depth, and α is the mining influence angle; If the buried pipeline belongs to the pipe-soil collaborative deformation in the goaf, the bending moment of the pipeline at the starting point of subsidence is calculated by the following formula:

In the formula, M _A is the bending moment of the pipeline at the starting point of sinking, W(l ₁ ,γ) is the sinking value of the maximum sinking point of the pipeline, L is the distance from the starting point of the pipeline sinking to the calculation point, and EI is the Bending stiffness, λ is the setting coefficient, and

k is the coefficient of elastic foundation; If the buried pipeline belongs to the pipe-soil non-cooperative deformation in the goaf, the bending moment of the pipeline at the starting point of subsidence is calculated by the following formula:

In the formula, M _A is the bending moment of the pipeline at the sinking starting point, EI is the bending stiffness of the pipeline, y _D is the sinking value of the end of the dark suspended area, x _D is the distance from the sinking starting point to the end of the dark suspended area, i is the surface slope corresponding to the end of the dark suspended area, λ is the setting coefficient, and

k is the coefficient of elastic foundation; The stress σ ₀ of the pipeline due to internal pressure is calculated by the following formula: σ ₀ =PD/2S; where P is the internal pressure of the pipeline, D is the outer diameter of the pipeline, and S is the wall thickness of the pipeline.

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