A method and system for evaluating overburden stability in mining of a shallowly buried coal seam in a valley terrain

Abstract

The present application belongs to the technical field of coal mining stratum stability determination and stratum control, discloses a kind of gully topography shallow buried coal seam mining overburden stability evaluation method and system, the method is based on the column of borehole near working face to obtain the stratum distribution characteristics of working face, based on rock mechanics experiment to obtain the basic mechanics parameters of overburden stratum of working face;Based on basic mechanics parameters and stratum distribution, key layer is discriminated, and basic information of thickness differentiation key block is obtained according to column of borehole in different regions simultaneously;Establish the stability mechanics model of thickness differentiation key block in different regions, and list the statics equilibrium equation according to the stress condition in different regions.The present application comprehensively considers the continuity process of thickness differentiation key layer in different regions under the action of different loads, makes up the stability results of key layer without considering thickness differentiation and the separate research of uphill mining and downhill mining in working face in existing theory, so that the calculation result is more in line with engineering actual effect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of strata stability determination and strata control in coal mining, and particularly relates to a method and system for evaluating the stability of overburden strata in shallow coal seam mining in a valley topography. BACKGROUND

[0002] The mining damage and ecological environment problems caused by coal mining are related to strata movement, and clarifying the evolution characteristics of the overburden bearing structure is one of the methods to improve the strata control effect. The surface of the valley strata is irregular, and when the surface valley development depth is large, the loose layer and part of the bedrock are easily eroded and present a missing state, that is, a thickness differentiation strata is generated. Compared with the conventional shallow coal seam mining under the horizontal surface, the morphological evolution and bearing structure characteristics of the overburden strata in the shallow coal seam under the valley topography are more complex, and are more likely to cause problems such as dynamic load mining pressure, mining cracks and surface subsidence. In the process of coal mining, the key layer as the strata bearing structure plays a control role on the movement of the overburden strata, so studying the stability characteristics of the thickness differentiation key layer in the shallow coal seam in the valley topography is the key to preventing and controlling the dynamic disaster and ecological environment problem in the coal mine. The existing strata structure stability only analyzes the uniform thickness key layer, and only studies the uphill mining and downhill mining of the working face, without considering the whole process of the working face mining in the valley topography. Therefore, it is necessary to propose a method for evaluating the stability of the overburden strata in the shallow coal seam in the valley topography, to establish a stability mechanical model of the thickness differentiation key block in different regions according to the geological and mining conditions, and to realize the stability evaluation of the thickness differentiation strata structure in the shallow coal seam mining based on the statics equilibrium equation. SUMMARY

[0003] To overcome the problems in the related art, the present application provides a method and system for evaluating the stability of the overburden strata in the shallow coal seam in the valley topography, and the technical solution is as follows:

[0004] The present application is implemented as follows: the method for evaluating the stability of the overburden strata in the shallow coal seam in the valley topography comprises the following steps:

[0005] S1, based on the coal mine geological data, the position, depth and angle of the drill hole are determined, the rock core is collected and recorded during the drilling core process, the original data is standardized, and the drill hole columnar section is drawn to obtain the strata distribution characteristics of the working face, and the basic mechanical parameters of the rock core, such as the compressive strength, elastic modulus, cohesion and internal friction angle, are obtained based on the rock mechanics experiment;

[0006] S2, based on the basic mechanical parameters, strata distribution and strength and stiffness conditions, the key layer is distinguished, and the basic information of the key layer is obtained according to the drill hole columnar section in different regions;

[0007] S3, a stability mechanical model of the thickness differentiation key block in different regions is established, and the statics equilibrium equation is listed according to the load distribution in different regions;

[0008] S4, according to the calculation results of the mechanical equilibrium equation, combined with the key layer theory, the thickness differentiation key block rotation instability and sliding instability criteria of different regions are obtained.

[0009] In step S1, the original data is standardized, and a borehole column chart is drawn, including: determining the stratification limit and corresponding thickness of different rock layers, and determining the mineral composition of each rock layer; drilling and coring on the surface or underground in the coal mining area to save the obtained samples, and determining the mechanical parameters by uniaxial compression, uniaxial tension and triaxial compression experiments to obtain the basic mechanical parameters of each rock layer.

[0010] In step S2, the key layer basic information is obtained according to the borehole column of different regions, including:

[0011] There are rock layers in the overburden rock of the stope, , respectively, the load of the and rock layers on the first rock layer; respectively, the breaking distance of the and rock layers, according to the stiffness criterion and strength criterion for identifying key layers, if , the key layer is the main key layer; if , the key layer is a sub-key layer; according to the geological profile of the key layer in different regions, the basic information of the key block and the load distribution form are obtained.

[0012] In step S3, a thickness differentiation key block stability mechanical model of different regions is established, including:

[0013] A coordinate system is established with the left vertex of the thickness differentiation key block I as the origin, and the force condition of the thickness differentiation key block structure is determined, the lengths of the thickness differentiation key block I and the thickness differentiation key block II are , the thicknesses are , the subsidence amounts are , and the rotation angles are ; the contact surface height of the left lower corner extrusion of the thickness differentiation key block I is , the contact surface height of the right upper corner extrusion of the thickness differentiation key block II is , the horizontal thrust of both ends of extrusion is , the hinge points of both ends are taken as the center positions of the contact surface height, and are defined as hinge points , and the corresponding shear forces are ; the breaking degree of the thickness differentiation key block I is , the breaking degree of the thickness differentiation key block II is , and the support force of the lower part of the thickness differentiation key block II Equal to the upper load, the application location is taken at the midpoint of the thickness differentiation key block II, and the relevant parameter relationships are:

[0014] ;

[0015] The overlying load of the key block for thickness differentiation during trench mining is:

[0016] ;

[0017] In the formula, These are the functional expressions for the load distribution of the thickness-differentiated key blocks under the condition of trench mining at the working face. Let be the horizontal distance from any point on the two thickness-differentiated key blocks to the origin of the coordinate system. The horizontal distance from the origin of the coordinate system to the point where the overlying load on the critical block of thickness differentiation is 0. The peak load above the critical block I for thickness differentiation during trench mining. The peak load above the critical block II for thickness differentiation during trench mining.

[0018] Furthermore, in the structural mechanics model of the thickness differentiation key block in the trench mining, based on the moment balance and vertical static equilibrium at points A and C of the thickness differentiation key block structure... ;in, The point is the midpoint of the contact end at the extrusion point of the critical thickness differentiation block I and critical thickness differentiation block II. The static equilibrium equation of the critical thickness differentiation block is obtained as follows:

[0019] ;

[0020] By combining the static equilibrium equations of the thickness-differentiated key block, the shear force can be obtained. and horizontal thrust The expression is:

[0021] ;

[0022] In the formula, These represent the subsidence amounts of key blocks I and II, respectively, which are the thickness differentiation key blocks. It is a horizontal thrust.

[0023] Furthermore, the structural mechanical model of the key block with thickness differentiation in the mining section shows the overburden load distribution as follows:

[0024] ;

[0025] In the formula, This represents the peak value of the mining load at the working face.

[0026] In the structural mechanics model of the thickness differentiation key block in shallow coal seam over-peak mining, according to the torque balance at points A and C of the thickness differentiation key block and the static balance in the vertical direction wherein, is the midpoint of the contact end of the extrusion of the thickness differentiation key block I and the thickness differentiation key block II, the static balance equation of the thickness differentiation key block in over-peak mining is obtained as

[0027] ;

[0028] The expressions of the shear force and the horizontal thrust are obtained by simultaneously solving the static balance equation of the thickness differentiation key block in over-gully mining as

[0029] ;

[0030] According to the structural evolution characteristics of overburden rock in shallow coal seam mining under the action of gully erosion, when there is a loose layer arch above the working face, the overburden load of the thickness differentiation key block presents a quadratic function load distribution, and the load distribution form is

[0031] ;

[0032] wherein, are undetermined parameters, indicating that the load distribution form is a quadratic function distribution form when the working face is over the loose layer arch, are the total lengths of the thickness differentiation key block I and the thickness differentiation key block II in over-loose layer arch mining, respectively.

[0033] Further, in the structural mechanics model of the thickness differentiation key block in shallow coal seam over-loose layer arch mining, according to the torque balance at points A and C of the thickness differentiation key block and the static balance in the vertical direction , is the midpoint of the contact end of the extrusion of the thickness differentiation key block I and the thickness differentiation key block II, the static balance equation of the thickness differentiation key block is obtained as

[0034] ;

[0035] The expressions of the shear force and the horizontal thrust are obtained by simultaneously solving the three expressions in the static balance equation of the thickness differentiation key block in over-loose layer arch mining, and the calculation result is

[0036] ;

[0037] wherein, are undetermined parameters, indicating that the load distribution form is a quadratic function distribution form when the working face is over the loose layer arch.

[0038] In step S4, according to the calculation results of the mechanical equilibrium equation, combined with the key layer theory, the thickness differentiation key block rotation instability and sliding instability criteria of different regions are obtained, including:

[0039] According to the key layer theory controlled by the rock stratum, if the key block does not occur sliding instability, it satisfies , Take 0.3; if the key block does not occur rotation deformation instability, it satisfies , Indicates the extrusion strength of the rock mass at the corner end, Take 0.3; the expression of the key block sliding instability and rotation deformation instability criterion is:

[0040] ;

[0041] ;

[0042] In the formula, Indicates the friction coefficient between the rock mass, Indicates the extrusion strength of the rock mass at the corner end, Indicates the contact surface height at the extrusion of both ends.

[0043] Further, for over-gully mining, according to the expression of the sliding instability and rotation deformation instability criterion of the thickness differentiation key block of over-peak mining, the sliding instability and rotation deformation instability criterion thereof is:

[0044] ;

[0045] For over-peak mining, according to the expression of the sliding instability and rotation deformation instability criterion of the thickness differentiation key block of over-peak mining, the sliding instability and rotation deformation instability criterion thereof is:

[0046] ;

[0047] For the working face mining with loose layer arch, according to the expression of the sliding instability and rotation deformation instability criterion of the thickness differentiation key block of over-loose layer arch mining, the sliding instability and rotation deformation instability criterion thereof is:

[0048] ;

[0049] Another purpose of the present application is to provide a gully terrain shallow buried coal seam mining overburden stability evaluation system, which is used for regulating and controlling the gully terrain shallow buried coal seam mining overburden stability evaluation method, and the system comprises:

[0050] The working face stratum distribution feature extraction module is used for obtaining the stratum distribution features of the overburden rock of the working face based on the borehole column, determining the delimitation and corresponding thickness of different rock layers, and determining the mineral composition of each rock layer.

[0051] The working face overburden rock basic mechanical parameter acquisition module is used for obtaining the samples by drilling and coring on the surface of the coal mining area or the underground construction ground, performing uniaxial compression, uniaxial tension and triaxial compression experiments on the obtained samples to determine the mechanical parameters, and obtaining the basic mechanical parameters of each rock layer.

[0052] The key layer discrimination module is used for discriminating the key layer based on the key layer theory and the stiffness and strength criteria through a key layer discrimination software, obtaining the basic information of the key layer position and thickness in the overburden rock of the working face, and obtaining the basic information of the key block according to the borehole column of different regions.

[0053] The thickness differentiation key block rotation instability and sliding instability evaluation module is used for establishing the stability mechanical model of the thickness differentiation key block in different regions, listing the statics equilibrium equation according to the load distribution in different regions, and obtaining the rotation instability and sliding instability criteria of the thickness differentiation key block in different regions according to the calculation results of the mechanical equilibrium equation and the key layer theory.

[0054] In combination with all the technical solutions described above, the present application has the following beneficial effects:

[0055] Firstly, the present application obtains the stratum distribution features of the overburden rock of the working face by collecting the boreholes near the working face, obtains the basic mechanical parameters of the rock through rock mechanics experiments, discriminates the key layer position according to the key layer position discrimination condition based on the key layer theory analysis, obtains the basic information of the thickness differentiation key layer, establishes the stability mechanical model of the thickness differentiation key layer in different regions, obtains the rotation instability and sliding instability criteria of the thickness differentiation key layer in different regions, and determines the stress peak value and stress influence range of the coal and rock strata subjected to mining stress.

[0056] Secondly, the present application establishes the system for determining the sliding instability and rotation deformation instability criteria of the overburden rock in different regions of the shallow coal seam passing through the valley topography, obtains the rotation deformation instability and sliding instability criteria of the thickness differentiation key layer in different regions, and provides a theoretical reference for determining the stability of the overburden rock.

[0057] Thirdly, the shallow coal seam over the different regions of the valley topography strata sliding instability and rotation deformation instability criterion determination method and system provided by the application can analyze the mine pressure distribution characteristics according to the thickness differentiation key layer morphology and other information, predict the strength, step distance and roof subsidence of the pressure and other characteristics; on the other hand, the load applied on the support when the thickness differentiation key layer is unstable is the core basis for the selection of the working face hydraulic support and the design of the rated working resistance. The stability analysis can estimate the maximum value and dynamic change of the instability load, guide the scientific selection, avoid excessive prevention and control, and reduce the prevention and control cost. The thickness differentiation key layer stability analysis is currently mainly through the method of theoretical analysis, and the existing theory only considers one situation, and idealizes the key block according to the equal thickness and length, and the result deviates from the engineering practice. The application comprehensively considers the stability distribution characteristics of the thickness differentiation key layer in different lengths and widths and under different loads in different regions, and makes up for the idealization and large difference of the existing theoretical analysis.

[0058] Fourthly, the form evolution and bearing structure characteristics of the shallow coal seam over the valley topography are relatively complex, which is more likely to cause problems such as dynamic load mine pressure, mining cracks and surface subsidence, and therefore, it is necessary to determine the stability characteristics of the overburden rock structure in different regions of the shallow coal seam over the valley topography, which is the basis for preventing and controlling disasters. The existing rock structure stability only analyzes the uniform thickness key layer, and only studies the uphill mining and downhill mining of the working face, without considering the whole process of the working face mining in the valley topography. Therefore, it is necessary to propose a kind of overburden rock stability evaluation method for the shallow coal seam mining in the valley topography, establish a stability mechanical model of the thickness differentiation key block under different loads according to the geological and mining conditions, and realize the stability evaluation of the thickness differentiation rock structure in the shallow coal seam mining based on the statics equilibrium equation.

[0059] Fifthly, the shallow coal seam over the different regions of the valley topography strata sliding instability and rotation deformation instability criterion determination method and system can realize the discrimination of the instability type of the thickness differentiation key block. On the one hand, the application discriminates according to the different geological conditions in different regions of the shallow coal seam, and can more accurately identify the most likely instability type and its critical condition at different positions. The dominant control factors of different regions and different instability modes are determined, which provides a theoretical basis for targeted prevention and control. On the other hand, the working face and roadway layout can be optimized according to the prediction of the criterion, and the support selection is reasonable, and more targeted safety technical measures and emergency plans are developed, thereby reducing the probability of accidents. The existing rock structure stability only analyzes the uniform thickness key layer, and only studies the uphill mining and downhill mining of the working face, without considering the whole process of the working face mining in the valley topography. Therefore, it is necessary to propose a kind of overburden rock stability evaluation method for the shallow coal seam mining in the valley topography, establish a stability mechanical model of the thickness differentiation key block under different loads according to the geological and mining conditions, and realize the stability evaluation of the thickness differentiation rock structure in the shallow coal seam mining based on the statics equilibrium equation. BRIEF DESCRIPTION OF DRAWINGS

[0060] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and serve to explain the principles of the present disclosure, in which:

[0061] Figure 1 is a flow chart of a method for evaluating the stability of overburden strata in shallowly buried coal seams in valley topography provided by an embodiment of the present application;

[0062] Figure 2 is a mechanical model diagram of the stability of a thickness-differentiated key block during over-gully mining provided by an embodiment of the present application;

[0063] Figure 3 is a mechanical model diagram of the stability of a thickness-differentiated key block during over-peak mining provided by an embodiment of the present application;

[0064] Figure 4 is a mechanical model diagram of the stability of a thickness-differentiated key block during over-peak mining provided by an embodiment of the present application;

[0065] Figure 5 is a mechanical model diagram of the stability of a thickness-differentiated key block during over-gully mining provided by an embodiment of the present application;

[0066] Figure 6 is a mechanical model diagram of the stability of a thickness-differentiated key block during over-gully mining provided by an embodiment of the present application;

[0067] Figure 7 is a mechanical model diagram of the stability of a thickness-differentiated key block during over-peak mining provided by an embodiment of the present application;

[0068] Figure 8 is a mechanical model diagram of the stability of a thickness-differentiated key block during over-peak mining provided by an embodiment of the present application;

[0069] Figure 9 is a mechanical model diagram of the stability of a thickness-differentiated key block during over-peak mining provided by an embodiment of the present application;

[0070] Figure 10 is a mechanical model diagram of the stability of a thickness-differentiated key block during over-peak mining provided by an embodiment of the present application;

[0071] Figure 11 is a valley 1 overburden strata configuration diagram provided by the present application;

[0072] Figure 12 is a valley 2 overburden strata configuration diagram provided by the present application;

[0073] Figure 13 is a valley 3 overburden strata configuration diagram provided by the present application;

[0074] Figure 14ZK5907 drilling columnar chart of a working face provided by the present application; DETAILED DESCRIPTION

[0075] In order to make the above objectives, characteristics and advantages of the present application more apparent, obvious and easy to understand, the specific embodiments of the present application are described in detail below with reference to the drawings. In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the concept of the present application, so the present application is not limited to the specific implementations disclosed below.

[0076] The mining damage and ecological environment problems caused by coal mining are related to the movement of rock strata. Clarifying the evolution characteristics of the overburden bearing structure is one of the methods to improve the control effect of rock strata. The existing rock strata structure stability only analyzes the uniform thickness key layer, and only studies the uphill mining and downhill mining of the working face, without considering the whole process of the working face mining in the valley terrain. Therefore, it is necessary to propose an overburden stability evaluation method for shallow coal seam mining in valley terrain. According to the geological and mining conditions, a stability mechanical model of key block with different load thickness differentiation is established, and based on the static equilibrium equation, the stability evaluation of rock strata structure with thickness differentiation in shallow coal seam mining is realized.

[0077] The mining damage and ecological environment problems caused by coal mining are related to the movement of rock strata. Clarifying the evolution characteristics of the overburden bearing structure is one of the methods to improve the control effect of rock strata. The existing rock strata structure stability only analyzes the uniform thickness key layer, and only studies the uphill mining and downhill mining of the working face, without considering the whole process of the working face mining in the valley terrain. Therefore, it is necessary to propose an overburden stability evaluation method for shallow coal seam mining in valley terrain. According to the geological and mining conditions, a stability mechanical model of key block with different load thickness differentiation is established, and based on the static equilibrium equation, the stability evaluation of rock strata structure with thickness differentiation in shallow coal seam mining is realized.

[0078] The mining damage and ecological environment problems caused by coal mining are related to the movement of rock strata. Clarifying the evolution characteristics of the overburden bearing structure is one of the methods to improve the control effect of rock strata. The existing rock strata structure stability only analyzes the uniform thickness key layer, and only studies the uphill mining and downhill mining of the working face, without considering the whole process of the working face mining in the valley terrain. Therefore, it is necessary to propose an overburden stability evaluation method for shallow coal seam mining in valley terrain. According to the geological and mining conditions, a stability mechanical model of key block with different load thickness differentiation is established, and based on the static equilibrium equation, the stability evaluation of rock strata structure with thickness differentiation in shallow coal seam mining is realized.

[0079] The innovation of the present application is that the present application establishes a statics model of different regional different load distribution thickness differentiation key blocks based on different regional geological conditions of shallow coal seam mining, and obtains key block sliding instability and restacking instability criterion of different regions of shallow coal seam.

[0080] As shown in Embodiment 1, Figure 1 The valley terrain shallow coal seam mining overburden stability evaluation method provided by the embodiment of the present application comprises the following steps:

[0081] S1, based on coal mine geological data, the position, depth and angle of the drill hole are determined, the rock core is collected and recorded during the drilling core process, the original data is standardized, and the drill hole columnar graph is drawn to obtain the stratum distribution characteristics of the working face, and the basic mechanical parameters of the taken rock core, such as compressive strength, elastic modulus, cohesion and internal friction angle, are obtained based on rock mechanics experiment;

[0082] S2, based on the basic mechanical parameters, stratum distribution and strength and stiffness conditions, the key layer is distinguished, and the basic information of the key layer is obtained according to the drill hole columnar graph of different regions;

[0083] S3, a stability mechanics model of different regional thickness differentiation key blocks is established, and statics equilibrium equations are listed according to different regional different load distribution;

[0084] S4, according to the calculation results of the mechanics equilibrium equation, the key layer theory is combined to obtain the rotation instability and sliding instability criterion of different regional thickness differentiation key blocks.

[0085] During the mining of shallow coal seam under valley topography, the working face exists over-gully mining and over-peak mining phenomenon; according to the spatial form evolution characteristics of overburden strata of shallow coal seam mining under valley topography, the main key layer is taken as the research object, and based on the masonry beam structure mechanics model, the thickness differentiation key block structure mechanics model of mining masonry beam structure under over-gully mining, over-peak mining and loose layer arch is established as shown in Figure 2 、 Figure 3 and Figure 4 .

[0086] The present application establishes a coordinate system with the left vertex of thickness differentiation key block I as the origin, and determines the stress condition of thickness differentiation key block structure, the length of thickness differentiation key block I and thickness differentiation key block II is , the thickness is , the subsidence is , the rotation angle is , (in the masonry beam structure mechanics model, the left vertex of thickness differentiation key block is taken as the reference); the contact surface height of the extrusion at the lower left corner of thickness differentiation key block I is , the contact surface height of the extrusion at the upper right corner of thickness differentiation key block II is , and the horizontal thrust at both ends of the extrusion is (See Figure 2 The hinge points at both ends are defined as the center positions of the contact surface height. The corresponding shear forces are respectively The fracture degree of the key block I with thickness differentiation is: The fracture degree of the thickness differentiation key block II is Support force at the bottom of the thickness-differentiated key block II It is approximately equal to the upper load, and its position can be approximately taken at the midpoint of the thickness differentiation key block II. The relevant parameter relationship is shown in formula (1).

[0087] (1)

[0088] The overburden load of the key block for thickness differentiation during trench mining is given by formula (2):

[0089] (2)

[0090] In the structural mechanics model of the thickness differentiation key block in shallow coal seam cross-ditch mining, this invention is based on the thickness differentiation key block structure. At the point of torque equilibrium and vertical static equilibrium, i.e. ,in, The point is the midpoint of the contact end of the extrusion point of the thickness differentiation key block I and the thickness differentiation key block II, and equation (3) is obtained:

[0091] (3)

[0092] Shear force can be obtained through calculation. and horizontal thrust T The expression is obtained as equation (4):

[0093] (4)

[0094] Based on the critical layer theory of rock strata control, this invention aims to prevent critical blocks from slipping and becoming unstable, which requires the following conditions to be met. , A value of 0.3 is generally acceptable; to prevent the critical block from undergoing transformation and instability, the following condition must be met. , This indicates the compressive strength of the rock block at its corners. Generally, 0.3 can be taken; the expression for the criteria of slippage instability and rotational deformation instability of the thickness differentiation key block is shown in equation (5).

[0095] (5)

[0096] The structural mechanics model of the key block structure with thickness differentiation in shallow coal seam over-peak mining provided in this embodiment of the invention is as follows: Figure 3As shown, the load distribution thereon is shown as formula (6).

[0097] (6)

[0098] According to the moment balance and vertical statics balance of the thickness differentiation key block structure A and C in overburden mining, namely As shown in formula (7):

[0099] (7)

[0100] Through calculation, the expressions of shear force and horizontal thrust are obtained, and the calculation results are shown as formula (8):

[0101] (8)

[0102] According to the key layer theory of rock stratum control, if the key block does not slide and lose stability, it should satisfy , Generally, 0.3 is acceptable; in order to make the key block not to rotate and deform and lose stability, it should satisfy , represents the extrusion strength of the rock mass at the corner end, Generally, 0.3 is acceptable; the expression of the sliding instability and the rotary deformation instability criterion of the thickness differentiation key block in overburden mining is shown as formula (9).

[0103] (9)

[0104] When the overburden loose layer on the key layer reaches a certain thickness, the overburden load of the thickness differentiation key block presents a quadratic function load distribution (see Figure 4 ), which is shown as formula (10);

[0105] (10)

[0106] According to the moment balance and vertical statics balance of the thickness differentiation key block structure A and C in overburden mining, namely As shown in formula (11):

[0107] (11)

[0108] Through calculation, the expressions of shear force and horizontal thrust are obtained, and the calculation results are shown as formula (12):

[0109] (12)

[0110] According to the key stratum theory of stratum control, the key block does not slide and lose stability, and the following conditions should be met , Generally, 0.3 is preferred; to make the key block not rotate and deform and lose stability, the following conditions should be met , represents the extrusion strength of the rock mass at the corner end, Generally, 0.3 is preferred; the expression of the over-loose layer arch mining thickness differentiation key block sliding instability and rotation deformation instability criterion is shown in formula (13);

[0111] (13)

[0112] In Example 2, the overburden stability evaluation system for mining in a shallow buried coal seam in a valley terrain provided by the present application comprises:

[0113] A working face stratum distribution feature extraction module is used to obtain the stratum distribution features of the overburden rock of the working face based on the borehole column, to clearly define the layering boundaries and corresponding thicknesses of different strata, and to clearly define the mineral composition of each stratum.

[0114] A working face overburden stratum basic mechanical parameter acquisition module is used to save the obtained samples by drilling and coring on the surface or underground construction ground in the coal mining area, to determine the mechanical parameters by uniaxial compression, uniaxial tensile and triaxial compression experiments, and to obtain the basic mechanical parameters of each stratum.

[0115] A key stratum discrimination module is used to discriminate the key stratum based on the stiffness and strength criteria through key stratum discrimination software according to the key stratum theory, to obtain the basic information of the key stratum position and thickness in the overburden stratum of the working face, and to obtain the basic information of the thickness differentiation key block according to the borehole column in different regions.

[0116] A thickness differentiation key block rotation instability and sliding instability evaluation module is used to establish a stability mechanical model of the thickness differentiation key block in different regions, to list the statics equilibrium equations according to the different load distributions in different regions; to obtain the rotation instability and sliding instability criteria of the thickness differentiation key block in different regions according to the calculation results of the mechanical equilibrium equations, combined with the key stratum theory.

[0117] To further prove the positive effect of the above-mentioned Example 6, the present application based on the above technical solution is as follows.

[0118] 1. The difference between the calculation results of the thickness differentiation key block and the traditional key block is analyzed by theoretical comparison. Taking a certain mine in Ordos as an example, according to the measured results of the borehole, the load transfer under the condition of working face over valley mining q 1=1.95MPa, q 2=1.15MPa, h 1=25m, h 2=30m, L2=50m, i 2=0.6, x 0= L 1+0.2 L 2, into formula (4), (5), get its working face shallow seam over the ditch mining thickness differentiation key block stress component and instability law as shown in Figure 5 , Figure 6 shown. Dotted part of h 1= h 2=30m stress curve of uniform thickness key block. Working face over the peak mining load transfer q 0=2.15MPa, h 1=25m, h 2=30m, L 2=50m, i 2=0.6, x 0= L 1+0.2 L 2, into formula (8), (9), get its working face shallow seam over the peak mining thickness differentiation key block stress component and instability law as shown in Figure 7 , Figure 8 shown. Dotted part of h 1= h 2=30m stress curve of uniform thickness key block. Working face over the loose layer arch mining its overlying load stress curve as shown in formula (11), h 1=25m, h 2=30m, L 2=50m, i 2=0.6, x 0= L 1+0.2 L 2, into formula (12), (13), get its working face shallow seam over the ditch mining thickness differentiation key block stress component and instability law as shown in Figure 9 , Figure 10 shown. Dotted part of h 1= h 2=30m stress curve of uniform thickness key block. According to Figure 5 、 Figure 7 , Figure 9 display, overall, to make the key block does not occur sliding instability, with the key block corner θ increases, its fracture degree i also gradually increases, at the same corner, the greater the thickness difference after two thickness differentiation key block, its fracture degree iThe larger the thickness difference, meaning the smaller the difference in critical layer thickness under the same conditions, the less likely slippage instability will occur. The calculation results of this invention show a lower likelihood of slippage instability compared to traditional uniform-thickness critical block calculations. It also clarifies the relationship between thickness difference and the ease of slippage instability. Based on... Figure 6 、 Figure 8 , Figure 10 The diagram shows that, overall, to prevent the critical block from undergoing rotational deformation and instability, the angle of rotation of the critical block must be adjusted accordingly. θ The increase of its fracture strength i The thickness difference gradually increases, and when the corners are the same, the greater the thickness difference after the two thickness-differentiated key blocks, the greater the fracture strength. i The larger the thickness difference, meaning the smaller the difference in critical layer thickness under the same conditions, the easier it is for rollover deformation instability to occur. The calculation results of this invention are less prone to slippage instability than traditional calculations for uniform-thickness critical blocks. It also clarifies the relationship between thickness difference and the ease of rollover deformation instability.

[0119] 2. A numerical simulation model with a length of 1600m and a width of 350m was established using numerical simulation software. Based on the key layer theory, the key layers in the model were divided into longitudinal joints, and soft rocks were divided into horizontal and longitudinal joints. Thiessen polygons were used to simulate Quaternary aeolian sand. An elastoplastic model was adopted for the rock strata contact surfaces in the numerical model, and the constitutive relation conformed to the Mohr-Coulomb strength criterion. Horizontal displacement constraints were applied to the left and right boundaries of the model, and vertical displacement constraints were applied to the bottom of the model. The working face was divided into three mining stages along the advance direction: Valley 1, Valley 2, and Valley 3. The advance length of each mining stage was 500m, and the mining step distance was 20m. Displacement and stress monitoring points were arranged in each key layer. To reduce the boundary effect during model mining, 30m coal pillars were left on both the left and right boundaries of the model. To reduce the mutual influence between mining sections, 20m coal pillars were left between mining sections. The mechanical parameters of each rock stratum are shown in Table 1. The evolution of the key blocks with different thicknesses of the main key layers in different regions is shown in Table 1. Figure 11-13 As shown, the key blocks of different thicknesses in different regions did not show obvious slippage or instability; only some of them rotated.

[0120] Table 1. Rock strata mechanical parameters in the numerical model

[0121]

[0122] 3. The columnar borehole ZK5907 in a certain working face of a certain mine is as follows: Figure 14 As shown, the thickness of the main key layer was determined to be 45.97m based on the key layer identification. The mining in this area is an over-peak mining operation. The overlying load was obtained based on the geological and mining conditions. q 0 = 2.15 MPa, the lengths of thickness differentiation key block I and thickness differentiation key block II. l 1. l 2 are 75m and 50m respectively, with thicknesses of respectivelyh 1、 h 2 respectively 25m, 30m, the amount of subsidence is respectively W 1、 W 2 respectively 5.45m, 1.09m, the angle of rotation is respectively θ 1、 θ 2 respectively 5°, 1.25°, the degree of rupture is i 1、 i 2 respectively 0.33, 0.60, a 1、 a 2 respectively 9.78m, 14.45m, x 0 is 72.5m, according to formula (9) is obtained under this condition, prone to sliding instability is not prone to rotation deformation instability.

[0123] 4. A certain working face ZK6131 borehole columnar key layer in a certain mine is discriminated to obtain the main key layer thickness of 25.50m, the working face in this area is mined as crossing ditch mining, and the overburden load is obtained based on the geological and mining conditions q 1=1.85MPa, q 2=1.15MPa the length of the thickness differentiation key block I and the thickness differentiation key block II l 1、 l 2 respectively 70m, 50m, the thickness is respectively h 1、 h 2 respectively 25m, 30m, the amount of subsidence is respectively W 1、 W 2 respectively 3.66m, 0.65m, the angle of rotation is respectively θ 1、 θ θ 2 respectively 5°, 1.25°, the degree of rupture is i 1、 i 2 respectively 0.57, 0.66, a 1、 a 2 respectively 10.67m, 14.67m, x 0 is 80m, according to formula (11) is obtained under this condition, prone to rotation deformation instability is not prone to sliding instability.

[0124] The above describes only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited to this, any skilled person in the art within the technical range disclosed by the present application, any modification, equivalent replacement and improvement within the spirit and principle of the present application, etc. should be covered within the protection scope of the present application.

Claims

1. A method for evaluating the stability of overburden rock in the mining of a shallowly buried coal seam in a valley terrain, characterized in that, The method comprises the following steps: S1, based on coal mine geological data, determining the drilling position, depth and angle, collecting and recording the core in the drilling coring process, standardizing the original data, drawing a drilling columnar section, obtaining the stratum distribution characteristics of the working face, and obtaining the basic mechanical parameters of the taken core, such as compressive strength, elastic modulus, cohesion and internal friction angle, based on rock mechanics experiments; S2, based on the basic mechanical parameters, stratum distribution and strength and stiffness conditions, performing key layer discrimination, and obtaining key layer basic information according to the drilling columnar sections of different regions; S3, establishing a key block stability mechanics model of different regional thickness differentiation, and listing statics balance equations according to different load distributions in different regions; S4, obtaining key block rotary instability and sliding instability criteria of different regional thickness differentiation according to the calculation results of the mechanics balance equations and in combination with the key layer theory; In step S3, the key block stability mechanics model of different regional thickness differentiation is established, including: A coordinate system is established with the left top point of the thickness differentiation key block I as the origin, and the force conditions of the thickness differentiation key block structure are determined. The length of the thickness differentiation key block I and the thickness differentiation key block II is l1 and l2, respectively, the thickness is h1 and h2, respectively, the subsidence is W1 and W2, respectively, and the rotation angle is θ1 and θ2, respectively. The contact surface height of the left lower corner extrusion of the thickness differentiation key block I is a1, the contact surface height of the right upper corner extrusion of the thickness differentiation key block II is a2, the horizontal thrust of the two ends is T, the hinge points are located at the center of the contact surface height, and are defined as hinge points A and B, respectively, and the corresponding shear force is Q A , Q B ; the fracture degree of the thickness differentiation key block I is i1, the fracture degree of the thickness differentiation key block II is i2, and the support force R1 of the lower part of the thickness differentiation key block II is equal to the upper load, and the action position is located at the midpoint of the thickness differentiation key block II. The relevant parameter relationship is: The overburden load of the thickness differentiation key block in the over-gully mining is: In the formula, Q1(x), Q2(x) are function expressions of the load distribution form of the working face thickness differentiation key block, x is the horizontal distance of any point on the thickness differentiation key block to the coordinate origin, x0 is the horizontal distance from the thickness differentiation key block overburden load to the coordinate origin, q1 is the peak load above the thickness differentiation key block I under the over-gully mining, and q2 is the peak load above the thickness differentiation key block II under the over-gully mining; The overburden load distribution of the thickness differentiation key block structure mechanics model in the over-peak mining is: In the formula, q0 is the peak load of the working face over-peak mining; According to the overburden structure evolution characteristics of the shallow coal seam mining under the gully erosion, when there is a loose layer arch above the working face, the overburden load of the thickness differentiation key block presents a quadratic function load distribution, and the load distribution form is: In the formula, e, f, g are undetermined parameters, and l1+l2 is the total length of the thickness differentiation key block I and the thickness differentiation key block II in the over-loose layer arch mining.

2. The method according to claim 1, characterized in that, In step S1, the original data is standardized, and the drilling columnar section is drawn, including: determining the delimitation and corresponding thickness of different rock layers, determining the mineral composition of each rock layer, drilling and coring on the surface or underground construction ground in the coal mining area, saving the obtained sample, performing uniaxial compression, uniaxial tension and triaxial compression experiments to determine the mechanical parameters, and obtaining the basic mechanical parameters of each rock layer.

3. The method according to claim 1, characterized in that, In step S2, the key layer basic information is obtained according to the drilling columnar sections of different regions, including: There are k layers of rock in the overburden rock of the mining field, q1|n+1 and q1|n are the load of the n+1 and n layers of rock on the first layer of rock respectively; l n+1 ,l n are the breaking distance of the n+1 and n layers of rock respectively, according to the stiffness criterion and the strength criterion for identifying the key layer, if n=k, the key layer is the main key layer; if n<k, the key layer is the sub-key layer; according to the geological profile of the key layer in different regions, the basic information of the key block and the load distribution form are obtained.

4. The method according to claim 1, characterized in that, In the structural mechanics model of the thickness differentiation key block in over-gutter mining, according to the torque balance at the structures A and C of the thickness differentiation key block and the vertical statics balance, the following equations are obtained: ∑M A =0, ∑M C =0, ∑M Y =0; wherein, the C point is the midpoint of the contact end at the extrusion of the thickness differentiation key block I and the thickness differentiation key block II, and the statics balance equation of the thickness differentiation key block in over-gutter mining is obtained as follows: By combining the key block static equilibrium equation with the thickness differentiation, the expressions of shear force Q A , B and horizontal thrust T are obtained as In the formula, w1, w2 are the subsidence amounts of the thickness differentiation key block I and the key block II respectively, and T is the horizontal thrust.

5. The method according to claim 1, characterized in that, In the structural mechanics model of the thickness differentiation key block in shallow seam over-peak mining, according to the torque balance and vertical statics balance of the thickness differentiation key block A and C in over-peak mining, the statics balance equation of the thickness differentiation key block in over-peak mining is obtained as follows: ∑M A =0, ∑M C =0, ∑M Y =0, wherein, C is the midpoint of the contact end of the thickness differentiation key block I and the thickness differentiation key block II extrusion, and the statics balance equation of the thickness differentiation key block in over-peak mining is obtained as follows: By combining the peak over exploitation thickness differentiation key block static equilibrium equation, the expression of shear force Q A , B and horizontal thrust T is:

6. The method according to claim 5, characterized in that, In the key block structure mechanics model of the thickness differentiation key block in shallow seam over-soft layer arch mining, according to the torque balance of the thickness differentiation key block structure A and C and the vertical statics balance ∑M A =0, ∑M C =0, ∑M Y =0, C point is the midpoint of the contact end of the thickness differentiation key block I and the thickness differentiation key block II extrusion, and the statics balance equation of the thickness differentiation key block in shallow seam over-soft layer arch mining is obtained as follows: The three expressions in the static equilibrium equation of the key block with different thickness of the overlying loose layer and the mining arch are solved simultaneously A , B The expressions of shear force Q and horizontal thrust T are obtained, and the calculation results are as follows: In the formula, e, f, g are undetermined parameters, and the load distribution form of the working face over-loose layer arch mining is a quadratic function distribution form.

7. The method according to claim 6, characterized in that, In step S4, the key block rotary instability and sliding instability criteria of different regional thickness differentiation are obtained according to the calculation results of the mechanics balance equations and in combination with the key layer theory, including: According to the key stratum theory of rock stratum control, if the key block does not slide and lose stability, it satisfies Take 0.3; if the key block does not rotate and deform and lose stability, it satisfies T≤αησ C ,ησ C Indicates the extrusion strength of the rock mass at the corner end, and η is 0.3; the expression of the key block sliding and losing stability and the rotation and deformation and losing stability criterion is: wherein represents the friction coefficient between the rock masses, ησ C represents the compressive strength of the rock mass at the corner end, and α represents the contact surface height at the two end compressions.

8. The method according to claim 7, characterized in that, For over-gully mining, according to the expression of the sliding instability and rotary deformation instability criteria of the over-gully mining thickness differentiation key block, the criteria for sliding instability and rotary deformation instability are: In the formula, w1, w2 are the subsidence amounts of the thickness differentiation key block I and the key block II respectively, and T is the horizontal thrust. For over-peak mining, according to the expression of the key block sliding instability and the rotation deformation instability criterion of the over-peak mining thickness differentiation, the sliding instability and the rotation deformation instability criterion of the key block are obtained as: For over-peak mining, according to the expression of the key block sliding instability and the rotation deformation instability criterion of the over-peak mining thickness differentiation, the sliding instability and the rotation deformation instability criterion of the key block are obtained as:

9. A system for evaluating the stability of overburden in mining a shallowly buried coal seam in a valley terrain, characterized in that, The system is used for regulating and controlling the overburden stability evaluation method of the valley topography shallow seam mining according to any one of claims 1-8, and the system comprises: The working face stratum distribution feature extraction module is used for obtaining the stratum distribution features of the overburden strata of the working face based on the borehole column, determining the different rock stratum layering boundaries and corresponding thicknesses, and determining the mineral compositions of each rock stratum. The working face overburden stratum basic mechanical parameter acquisition module is used for saving the core samples obtained by drilling the surface or underground construction ground of the coal mining area, performing uniaxial compression, uniaxial tension and triaxial compression experiments on the obtained samples to determine the mechanical parameters, and obtaining the basic mechanical parameters of each rock stratum. The key layer discrimination module is used for discriminating the key layer based on the key layer theory and the stiffness and strength criteria through the key layer discrimination software, obtaining the basic information of the key layer position and thickness in the overburden strata of the working face, and obtaining the basic information of the key block according to the borehole column of different regions. The thickness differentiation key block rotation instability and sliding instability evaluation module is used for establishing the stability mechanical model of the thickness differentiation key block in different regions, listing the statics equilibrium equation according to the different load distributions in different regions, and obtaining the rotation instability and sliding instability criterion of the thickness differentiation key block in different regions according to the calculation results of the mechanical equilibrium equation and in combination with the key layer theory.

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