Method for determining support load of coal seam overburden structure under concentrated load of shallow buried crossing coal pillar

Abstract

The present application relates to coal seam mining technical field, specifically to shallow buried coal seam group cross coal pillar concentrated load under coal seam overburden structure support load determination method. Analysis section coal pillar concentrated eccentric load under sub key layer II bearing structure, construct rock structure mechanics model; Through similar simulation experiment analysis section coal pillar both sides disturbance bearing structure; Based on the section coal pillar both sides disturbance bearing structure determines interlayer rock layer breakage bearing structure load characteristics; Combined with section coal pillar both sides disturbance bearing structure and interlayer rock layer breakage bearing structure load characteristics determine structure support resistance; The structure support resistance is the structure support load. The present application is based on cross coal pillar mining test, gives the lower coal seam mining upper coal pillar load distribution form and interlayer rock layer breakage bearing structure characteristics, and establishes cross coal pillar mining mechanics calculation model, thereby determines shallow buried coal seam group cross coal pillar mining under coal seam overburden structure support load.

Description

Technical Field

[0001] This invention relates to the field of coal seam mining technology, specifically to a method for determining the load on a coal seam overburden structure support under concentrated load across a shallow-buried coal pillar. Background Technology

[0002] With the high-intensity mining of shallow-buried, thin-bedrock, and thick-loose coal seams in the Yushenfu mining area, the coal seams in this area have gradually transformed into medium-deep, multi-layered bedrock and thick-loose body conditions. To address these coal seam characteristics, in-depth research on coal seam group mining has been initiated. Coal seam group mining leads to the formation of coal pillar groups in mining areas, prompting the emergence of cross-coal pillar mining patterns in lower coal seams. After coal seam mining, numerous section coal pillars are left between working faces to protect the stability of roadways and overlying strata, causing stress concentration in the coal pillars and increasing the difficulty of cross-coal pillar mining in lower coal seams. The root cause lies in the combined effect of the overlying load distribution characteristics of the section coal pillars and the bearing capacity characteristics of the inter-layer rock strata in the lower coal seam. Therefore, the impact of upper coal pillars in coal seam group mining on lower coal seam mining should be attributed to the distribution characteristics of upper coal seam pillar loads and the bearing capacity characteristics of the inter-layer rock strata in lower coal seam mining.

[0003] Currently, scholars from various countries have conducted extensive research on the reasonable offset and stress distribution characteristics of coal pillars. They mainly study the load on coal pillars based on the fracture morphology of the overlying bearing strata and the thickness of the loose layer, and have obtained the load and stress distribution laws of coal pillars under various geological conditions. By combining the elastic-plastic properties of coal pillars and the creep characteristics of rocks, they have constructed a variety of comprehensive evaluation models for stress distribution and coal pillar stability. Due to the unique geological conditions of shallow coal seams, the stability of coal pillars in certain sections is insufficient. The bearing structure of the fractured overburden strata is prone to instability, leading to a vicious cycle of declining coal pillar stability. Regarding the study of overburden load on the upper part of the coal pillar, scholars have decomposed the overburden structure into various geometric combinations based on the geometric unit weight, starting from the geometric morphology of the fractured overburden. This method has, to some extent, obtained the overburden load of the coal pillar under stable conditions. However, during cross-coal pillar mining, the overburden is not subjected to uniformly distributed loads but rather to stress concentration and eccentric loads. In this case, a study method for concentrated coal pillar loads that conforms to the on-site production conditions should be adopted to obtain the distribution characteristics of the overburden load during cross-coal pillar mining of the lower coal seam.

[0004] Regarding the issue of the load-bearing structure of interlayer rock strata under shallow coal seam conditions, most studies mainly consider the energy dissipation during interlayer rock strata fracture, the thickness of the fractured rock strata required to fill the coal seam mining space, and the impact of mining height on interlayer rock strata. At the same time, some scholars have studied the interlayer rock strata fracture process, mainly from the aspects of upper rock strata load, fracture propagation, fixed beam structure and simply supported beam structure, and obtained some qualitative conclusions about the fractured blocks of interlayer rock strata. After the interlayer rock strata fracture in the lower coal seam mining, it still has a certain load-bearing capacity and plays a supporting role for the overlying load with different load-bearing characteristics. However, for the mining of shallow coal seam groups across coal pillars, considering only the uniformly distributed concentrated load of the upper coal pillar or the interlayer rock strata fracture load in the lower coal seam mining has limitations. It may lead to a sudden change in the load-bearing capacity of the interlayer rock strata, causing accidents such as the collapse of the working face in the lower coal seam mining. Summary of the Invention

[0005] To address the problem in existing technologies that only consider uniformly distributed concentrated loads on the upper coal pillar or the fracture loads of inter-layer rock strata during mining of the lower coal seam, this invention provides a method for determining the load on the overburden structure support of a coal seam under concentrated loads across a coal pillar in shallow-buried coal seams. This method includes: analyzing the bearing structure of the subcritical layer II under concentrated eccentric loads on the coal pillar section, and constructing a rock strata structure mechanical model; analyzing the disturbance bearing structure on both sides of the coal pillar section through similar simulation experiments; determining the load characteristics of the inter-layer rock strata fracture bearing structure based on the disturbance bearing structure on both sides of the coal pillar section; and determining the support resistance of the structural support by combining the disturbance bearing structure on both sides of the coal pillar section and the load characteristics of the inter-layer rock strata fracture bearing structure. The support resistance of the structural support is the load of the structural support. Based on cross-coal pillar mining experiments, this invention presents the load distribution pattern of the upper coal pillar and the characteristics of the inter-layer rock strata fracture bearing structure during mining of the lower coal seam, and establishes a mechanical calculation model for cross-coal pillar mining, thereby determining the load on the overburden structure support of the coal seam under cross-coal pillar mining in shallow-buried coal seam groups.

[0006] This invention adopts the following technical solution: a method for determining the load on a coal seam overburden structure support under concentrated load across a shallowly buried coal pillar, comprising:

[0007] The subcritical layer II bearing structure under concentrated eccentric load of coal pillar in the analysis section was analyzed, and a rock structure mechanical model was constructed.

[0008] The disturbance bearing structure on both sides of the coal pillar in the section was analyzed through similar simulation experiments. The disturbance bearing structure on both sides of the coal pillar in the section includes: the force of the articulated rock beam structure disturbed throughout the entire life cycle of the main critical layer, the force of the hysteresis fracture step rock beam structure disturbed throughout the entire life cycle of the subcritical layer I, the force of the rock stratum structure disturbed during the half life cycle of the main critical layer, the force of the step rock beam structure disturbed during the half life cycle of the subcritical layer I, and the direct roof force of the coal body in the section coal pillar.

[0009] Based on the disturbance bearing structure on both sides of the coal pillar in the section, the load characteristics of the interlayer rock strata fracture bearing structure are determined; the load characteristics of the interlayer rock strata fracture bearing structure include: the force of the subcritical layer II type step rock beam structure and the force of the subcritical layer II hinged rock beam structure.

[0010] The support resistance of the structural support is determined by combining the load characteristics of the disturbance bearing structure on both sides of the coal pillar and the load characteristics of the fracture bearing structure of the interlayer rock strata; the support resistance of the structural support is the load of the structural support.

[0011] Furthermore, the expression for the force acting on the subcritical layer type II stepped rock beam structure is as follows:

[0012] R XT1 =(P YZ +R Z1 +R R1 +P M )·K GM +P XT1 +P XT

[0013] Among them, P YZ For transferring loads to the inverted trapezoidal rock pillar area overlying the coal pillar in the section; R Z1 and R R1 These represent the load-bearing structural forces on both sides of the coal pillar section; P M P is the self-weight load of the coal pillar in the section; XT1 The load is the self-weight load of the lower load layer; P XT K represents the self-weight load of the critical block EXT in subcritical layer II. GM This is the load transfer coefficient of the coal pillar in the section.

[0014] Furthermore, the calculation method for the load transferred by the inverted trapezoidal rock pillar zone overlying the coal pillar section is as follows:

[0015]

[0016] Among them, L m The width of the coal pillar in the section; β is the sum of the thicknesses of the overlying rock and soil layers of the coal pillar section; β is the average fracture angle of the rock strata; γ is the average unit weight of the overlying rock and soil layers, b m b is the width of the fracture zone of the coal pillar in the section. z This refers to the width of the fracture zone in the coal pillar section.

[0017] Furthermore, the expression for the force acting on the subcritical layer II articulated rock beam structure is as follows:

[0018]

[0019] Among them, P YZ For transferring loads to the inverted trapezoidal rock pillar area overlying the coal pillar in the section; R R1P represents the load-bearing structural force on the right side of the coal pillar section. M P is the self-weight load of the coal pillar in the section. XJ1 For the subcritical layer II articulated rock beam structure, the load layer self-weight load, P XJ The load is the self-weight load of the hinged rock beam in the subcritical layer II.

[0020] Furthermore, the support resistance of the structural support is determined by combining the load characteristics of the disturbance bearing structures on both sides of the coal pillar and the fracture bearing structures of the interlayer rock strata, including:

[0021] The support resistance of the structural support includes the first support resistance under the action of the subcritical layer II type stepped rock beam structure, and the second support resistance under the action of the subcritical layer II hinged rock beam structure.

[0022] The calculation method for the first support resistance is as follows: R T =(R XT1 +P XT2 )K;

[0023] Among them, R XT1 For the subcritical layer, type II stepped rock beam structure, the force P XT2 The force is the direct roof force of the lower coal seam under the action of the Class II bench rock beam structure in the subcritical layer, and K is the dynamic load coefficient of the support.

[0024] The calculation method for the second support resistance is as follows: R J =(R XJ1 +P XJ2 )K;

[0025] Among them, R XJ1 For the force acting on the hinged rock beam structure of subcritical layer II, P XJ2 K represents the direct roof force of the lower coal seam under the action of the hinged rock beam structure of the subcritical layer II, and K is the dynamic load coefficient of the support.

[0026] Furthermore, the specific force exerted on the main critical layer's full life-cycle disturbance articulated rock beam structure is as follows:

[0027] Including loess loose layer load P Z3 The force P of the key block in the main key layer ZJ and the force P in the delayed failure zone of the main critical layer Z5 The expression is:

[0028]

[0029] Among them, i Z2 The block size of the key block to the left of the master key layer, θ ZJ The rotation angle of the key block on the left side of the main key layer hinged rock beam structure;

[0030] In the formula, the load P of the loose loess layerZ3 For: P Z3 =(L Z1 +h 10 cotβ ZJ )·γ 10 h 10 K G Among them, L Z1 The fracture length of the key block on the left side of the main key layer, h 10 For the thickness of the loose layer, β ZJ The fracture angle of the rock strata in the key hinged rock beam structure, γ 10 K represents the average bulk density of the loose layer. G The load transfer coefficient of the loess layer;

[0031] The force P of the key block in the primary key layer ZJ For: P ZJ =L Z1 γ9h9; where L Z1 The fracture length of the key block on the left side of the main key layer, γ9 is the average unit weight of the main key layer, and h9 is the thickness of the main key layer.

[0032] Force P in the hysteresis zone of the main critical layer Z5 for:

[0033]

[0034] Among them, γ9 is the average bulk density of the main critical layer, h9 is the thickness of the main critical layer, and β ZJ The fracture angle of the rock strata in the key hinged rock beam structure, b Z θ represents the dip length of the fracture structure acting on the coal pillar in the hysteresis fracture zone, i.e., the width of the fracture zone in the coal pillar section. ZJ The rotation angle of the key block of the hinged rock beam structure in the main key layer.

[0035] Furthermore, the specific force acting on the subcritical layer I full life cycle disturbance hysteresis fracture step rock beam structure is as follows:

[0036] Including the load transfer W of the hinged rock beam structure in the main key layer Z2 The force load P acting on the subcritical layer I critical block by the upper load layer Z2 The self-weight load P of the critical block in subcritical layer I ZT The upper load layer acts on the subcritical layer I with the delayed fracture block load P Z4 cosθ ZT and the hysteretic fracture block load P of subcritical layer I Z6 The expression is:

[0037] R ZT =W Z2 +P Z4 cosθ ZT+P ZT +P Z6

[0038] W Z2 =R ZJ +P Z2

[0039] Where, θ ZT The rotation angle of the key block of the subcritical layer I step rock beam structure, R ZJ The forces acting on the articulated rock beam structure during the entire life cycle disturbance of the main critical layer, P Z4 The force acting in the hysteresis fracture zone of the upper load layer;

[0040] In the formula, P is the self-weight load of the critical block in subcritical layer I. ZT For: P ZT =h7γ7L Z2 Where h7 is the thickness of subcritical layer I, γ7 is the average bulk density of subcritical layer I, and L Z2 The fracture length of the critical block on the left side of subcritical layer I;

[0041] The force P in the hysteresis fracture zone of the upper load layer Z4 For: P Z4 =h8γ8b Z Where h8 is the thickness of the upper load layer, γ8 is the average unit weight of the upper load layer, and b Z It is the inclination length of the fracture structure in the hysteresis fracture zone acting on the coal pillar, i.e., the width of the fracture zone in the coal pillar section;

[0042] The force load P acting on the subcritical layer I critical block by the upper load layer Z2 For: P Z2 =L Z2 γ8h8; where L Z2 h8 is the fracture length of the critical block on the left side of the subcritical layer I, h8 is the thickness of the upper load layer, and γ8 is the average unit weight of the upper load layer.

[0043] Subcritical layer I hysteresis fracture block load P Z6 for:

[0044]

[0045] Where γ7 is the average bulk density of subcritical layer I, h7 is the thickness of subcritical layer I, and β ZT The fracture angle of the subcritical layer I, the step-beam structure, is θ. ZT For the critical block rotation angle of the subcritical layer I step rock beam structure, b Z It is the directional length of the fracture structure in the hysteresis fracture zone acting on the coal pillar, i.e., the width of the fracture zone in the coal pillar section.

[0046] Furthermore, the specific force exerted by the semi-life-cycle disturbance of the rock strata in the main key layer is as follows:

[0047] A determination formula for the bearing capacity of the main critical layer is constructed based on the rotational subsidence of the articulated rock beam structure of the main critical layer during the mining of the lower coal seam.

[0048] The main critical layer bearing structure is determined based on the value of the main critical layer bearing structure determination formula.

[0049] When the value of the main key layer bearing structure determination formula is less than or equal to zero, the main key layer hinged rock beam structure becomes unstable and fails, and has no bearing effect on the overlying load.

[0050] When the value of the main critical layer bearing structure determination formula is greater than zero, the main critical layer maintains a hinged rock beam structure and has a bearing effect on the overlying load. At this time, the half-life-cycle disturbance rock stratum structure force of the main critical layer is expressed as:

[0051]

[0052] Among them, i R2 The block size of the key block to the right of the master key layer, θ RJ The rotation angle of the right critical block of the key layer hinged rock beam structure, P R3 For the load of the loose loess layer, P RJ The force of the key block on the right side of the main key layer, P R5 The force acting on the delayed failure zone of the main critical layer.

[0053] Furthermore, the specific forces acting on the subcritical layer I semi-life-cycle disturbed stepped rock beam structure are as follows:

[0054] Including the load transferred by the main key layer rock beam structure W R2 The force load P acting on the right critical block of subcritical layer I from the upper load layer R2 The load P acting on the key layer I hysteresis fracture block by the upper load layer R4 cosθ RT Subcritical layer I delayed fracture block load P R6 And the self-weight load P of the critical block on the right side of subcritical layer I. RT The expression is:

[0055] R RT =W R2 +P R4 cosθ RT +P RT +P R6

[0056] W R2 =R RJ +P R2

[0057] Where, θ RTFor the critical block rotation angle of the subcritical layer I step rock beam structure, P R4 This refers to the force acting in the hysteresis fracture zone of the upper load layer.

[0058] Furthermore, the direct jacking force of the coal pillar in the aforementioned section is specifically as follows:

[0059] This includes the direct jacking force on the left side of the coal column and the direct jacking force on the right side of the coal column.

[0060] The direct jacking force on the left side of the coal pillar in the section is: R Z1 =W Z1 +P Z1 Among them, W Z1 =R ZT ;

[0061] The direct jacking force on the right side of the coal pillar in the section is: R R1 =W R1 +P R1 Among them, W R1 =R RT ;

[0062] In the formula, P Z1 To control the self-weight load of the left side direct jacking of the cantilever beam in the upper coal seam, P R1 The coal seam controls the direct self-weight load of the right side of the cantilever beam.

[0063] The beneficial effects of this invention are as follows: This invention obtains the bearing structure of the fractured rock strata in cross-coal pillar mining through physical similarity simulation experiments, establishes a mechanical calculation model of the bearing structure in cross-coal pillar mining using theoretical derivation and calculation methods, and analyzes the fractured rock strata structure and support load of the lower coal seam under the condition of cross-coal pillar mining in shallow buried coal seams. Combining the load characteristics of the disturbance bearing structure on both sides of the coal pillar section and the fractured rock strata bearing structure between layers, this invention provides a scientific and effective research method and theoretical calculation formula to solve the problem of sudden increase in support load in the lower coal seam working face, improves the limitations of the traditional empirical estimation method of support load, and realizes the accuracy and reliability of the theoretical budget of support load, thus realizing the research process from experiment to theory. Attached Figure Description

[0064] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0065] Figure 1 This is a schematic diagram of the method for determining the load of a coal seam overburden structure support under concentrated load across a shallow coal pillar, according to an embodiment of the present invention.

[0066] Figure 2 This is a schematic diagram of a physical simulation experiment according to an embodiment of the present invention;

[0067] Figure 3 This is a schematic diagram of a section coal pillar overburden fracture structure according to an embodiment of the present invention;

[0068] Figure 4 This is a schematic diagram of a stepped rock beam structure for cross-coal pillar mining between strata according to an embodiment of the present invention;

[0069] Figure 5 This is a schematic diagram of a hinged rock beam structure for cross-coal pillar mining between rock strata according to an embodiment of the present invention;

[0070] Figure 6 This is a schematic diagram illustrating the rock strata fracture characteristics in shallow-buried cross-coal pillar mining according to an embodiment of the present invention; wherein, Figure 6 (a) is a schematic diagram of the fracture structure characteristics of a stepped rock beam. Figure 6 (b) is a schematic diagram of the fracture structure characteristics of the articulated rock beam;

[0071] Figure 7 This is a schematic diagram of a mechanical calculation model for rock strata structure in shallow-buried cross-coal pillar mining according to an embodiment of the present invention; wherein, Figure 7 (a) is a mechanical model of a stepped rock beam structure. Figure 7 (b) is the mechanical model of the hinged rock beam structure;

[0072] Figure 8 This is a schematic diagram of a mechanical calculation model for a key layer full life cycle disturbance articulated rock beam according to an embodiment of the present invention;

[0073] Figure 9 This is a schematic diagram of a mechanical calculation model for a subcritical layer I full life cycle disturbance hysteresis fracture step rock beam according to an embodiment of the present invention;

[0074] Figure 10 This is a schematic diagram of a direct top-mechanical calculation model for a full life-cycle disturbance according to an embodiment of the present invention;

[0075] Figure 11 This is a schematic diagram of a main critical layer half-lifetime disturbance dynamics calculation model according to an embodiment of the present invention;

[0076] Figure 12 This is a schematic diagram of a mechanical calculation model for a subcritical layer I semi-life cycle disturbance hysteresis fracture step rock beam according to an embodiment of the present invention;

[0077] Figure 13 This is a schematic diagram of a direct top-mechanical calculation model for a half-life-cycle disturbance according to an embodiment of the present invention;

[0078] Figure 14This is a schematic diagram of a mechanical calculation model for a subcritical layer type II stepped rock beam according to an embodiment of the present invention;

[0079] Figure 15 This is a schematic diagram of a mechanical calculation model for a subcritical layer II articulated rock beam according to an embodiment of the present invention;

[0080] Figure 16 This is a schematic diagram of a mechanical calculation model of the overlying strata structure of a section coal pillar according to an embodiment of the present invention. Detailed Implementation

[0081] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0082] A schematic diagram of the method for determining the load of a coal seam overburden structure support under concentrated load across a shallow coal pillar according to an embodiment of the present invention is shown below. Figure 1 As shown, it includes:

[0083] The subcritical layer II bearing structure under concentrated eccentric load of coal pillar in the analysis section was analyzed, and a rock structure mechanical model was constructed.

[0084] The disturbance bearing structure on both sides of the coal pillar in the section was analyzed through similar simulation experiments. The disturbance bearing structure on both sides of the coal pillar in the section includes: the force of the articulated rock beam structure disturbed throughout the entire life cycle of the main critical layer, the force of the hysteresis fracture step rock beam structure disturbed throughout the entire life cycle of the subcritical layer I, the force of the rock stratum structure disturbed during the half life cycle of the main critical layer, the force of the step rock beam structure disturbed during the half life cycle of the subcritical layer I, and the direct roof force of the coal body in the section coal pillar.

[0085] Based on the disturbance bearing structure on both sides of the coal pillar in the section, the load characteristics of the interlayer rock strata fracture bearing structure are determined; the load characteristics of the interlayer rock strata fracture bearing structure include: the force of the subcritical layer II type step rock beam structure and the force of the subcritical layer II hinged rock beam structure.

[0086] The support resistance of the structural support is determined by combining the load characteristics of the disturbance bearing structure on both sides of the coal pillar and the load characteristics of the fracture bearing structure of the interlayer rock strata; the support resistance of the structural support is the load of the structural support.

[0087] This invention is based on the mining of shallow coal seams. It employs similarity simulation experiments to study the load distribution characteristics of the coal pillar in cross-pillar mining and the fracture characteristics of the inter-layer rock bearing structure. The project uses the mining of shallow coal seams in northern Shaanxi as the engineering background. In this mining area, the main coal seams are generally 3 to 4 layers, numbered 1. -2 2-2 3 -2 and 4 -2 The coal seam has a mining thickness of 1.5-8.8m. The model selected a mining thickness of 2.95m and 3.3m. It adopts fully mechanized downward mining and the roof is managed by the caving method. It is a typical shallow buried near-horizontal coal seam group mining.

[0088] The embodiments of the present invention take the mining area 1 as an example. -2 Coal and 2 -2 Coal seam (1 in this invention) -2 The coal seam is also called the upper coal seam, 2 -2 Taking the lower coal seam as the focus of the study, in 1 -2 The coal seam is divided into two working faces, left and right, with a 20m section coal pillar between the working faces. When 1 -2 After the coal seam is mined out, for 2 -2 Coal seam mining, with 2 -2 The coal seam intake and exhaust pillar processes are the main focus of this study. 1 -2 The upper part of the coal seam contains two key layers: a subcritical layer I located 12m from the coal seam and a main critical layer located 37m from the coal seam. -2 A subcritical layer II, 16m thick, is distributed between the coal seams, 4m away from the coal seam, and a load layer of 15.5m is located above it.

[0089] Based on the coal and rock mechanics characteristics of the Longhua Coal Mine in northern Shaanxi and the geological conditions of the study area, the similarity geometric constant is selected as k. l =1 / 100; the similarity constant for coal seam mining time is selected as k. t =1 / 10; the bulk density similarity constant is chosen as k. c =1.56; the stress similarity constant is chosen as K. σ =156, Model length × width × height = 300cm × 20cm × 155.5cm, The height in this study is 110cm, and the coal (rock) mechanical parameters are shown in Table 1:

[0090] Table 1. Schematic diagram of the main mechanical properties of each material

[0091]

[0092] This embodiment further constructs an auxiliary model based on the original physical similarity model to provide supplementary research for cross-coal pillar mining. The auxiliary model is 60cm high, and equivalent loads are applied to the unconstructed portion. Since the load layer in the upper 15.5m of the subcritical layer II has weak bearing capacity and mainly serves as the load-bearing body, and to better study the fracture bearing structure, the height of this load layer is reduced, and equivalent loads are applied to the upper part of the model. The main materials of the physical similarity model are river sand, fly ash, gypsum, and whiting powder, with mica powder used as the model layering material. Cameras and computers are used as experimental recording tools to establish a physical similarity simulation experimental platform for cross-coal pillar mining of shallow buried coal seams. The physical simulation test diagram is shown below. Figure 2 As shown.

[0093] Physical similarity simulation experiments show that after coal seam mining, an approximately symmetrical rock strata fracture structure will form on both sides of the coal pillar in the section. An inverted trapezoidal fractured rock pillar area will form above the coal pillar. Due to the presence of two key layers in the overlying coal seam, through the mining of the left and right working faces of the section coal pillar, it was found that the sub-key layer first fractures along a rock strata fracture angle of about 65° to form a stepped rock beam structure. The anterior stress support point of the stepped rock beam structure is located in the upper rock strata of the coal pillar, and the posterior stress support point is located on the upper part of the collapsed and compacted rock block. At this time, the front and rear stress support points are located at the top of the coal pillar. The stepped rock beam structure between support points plays a major load-bearing role for the overburden. Difficult-to-heal transverse and longitudinal fissures form in the overburden between the support points before and after the rock beam, creating a permanent fracture zone. As the exposed length of the overburden increases, the main critical layer above the subcritical layer begins to fracture with a certain deflection. Due to the filling and swelling properties of the lower fractured rock layers, the free movement space of the fractured main critical layer is reduced, resulting in small-scale rotational subsidence of the fractured rock mass. The rock blocks are hinged together to form a hinged rock beam structure, such as... Figure 3 As shown. At this time, the articulated rock beam structure of the main key layer and the stepped rock beam structure of the sub-key layer form a unified load-bearing body, jointly bearing the overlying load. After the physical model is left to stand still for a period of time, the inverted trapezoidal fractured rock pillar area above the section coal pillar will undergo re-failure on the side close to the rock beam structure, forming a delayed fracture zone, which will rotate to a certain extent towards the goaf side, generating a load effect on the mechanical fracture structure of the key layer and causing stress disturbance to the section coal pillar.

[0094] After the upper coal seam was mined out, a section coal pillar with inverted trapezoidal fractured rock pillars was formed, with goaf areas on both sides. When the lower coal seam mining face entered the coal pillar, micro-cracks appeared in the inter-layer rock strata, but no fracture occurred, and the section coal pillar was relatively stable. After the working face entered the coal pillar, the overlying rock behind the working face fractured at a rock strata fracture angle of 64°. The fractured rock strata were hinged to each other, and the overall pressure strength of the working face was relatively weak. The overlying rock above the section coal pillar was relatively stable. When the working face advanced to 1 / 2 the width of the section coal pillar, the direct roof completely fractured and collapsed, and the subcritical layer II fractured in layers. The section coal pillar and the inverted trapezoidal fractured rock pillar area showed a tendency to rotate back to the goaf area of ​​the lower coal seam, but the section coal pillar as a whole did not become unstable. It can be seen that the load on the section coal pillar during cross-coal pillar mining is not a uniformly distributed load, but rather the load on the section coal pillar gradually shifts from the mined area to the unmined area as the working face advances, forming a partial load phenomenon on the section coal pillar. When the coal pillar is being removed from the working face, a sudden, step-like shearing occurs between the interlayers, leading to faulting and failure. Subcritical stratum II fractures, forming a stepped-beam structure under unstable conditions, weakening its load-bearing capacity. The overburden load on the working face is primarily borne by the working face supports. The goaf behind the working face is instantly compacted, closing overburden fissures and causing instability in the section of the coal pillar, resulting in severe damage on the side of the coal pillar. Figure 4 As shown, after the coal pillar is produced at the working face, the overlying rock structure undergoes periodic fracturing and collapse, without generating concentrated load phenomena.

[0095] When the working face enters the coal pillar, the interlayer rock breaks, and the rock mass behind the working face migrates, while the rock mass in front of the working face does not migrate significantly. At this time, the stress sensor values ​​on the goaf side below the section coal pillar show a slight decrease, while the stress on the working face side shows a brief increase, with a small overall amplitude. After the working face enters half the width of the coal pillar, the immediate roof breaks and collapses first. The section coal pillar and the inverted trapezoidal broken rock pillar area undergo a slight rotation towards the goaf side. At this time, the stress sensor below the section coal pillar located behind the working face is in a decompression state. In the working face, the stress sensors ahead of the working face show a state of stress concentration. When the working face advances to 2 / 3 of the width of the coal pillar, the subcritical layer II develops longitudinal fractures that extend to the upper part of the coal pillar. The fractured and unfractured rock layers form an articulated structure, and the rotation of the overlying rock layers increases. When the working face exits the coal pillar, the interlayer rock layers do not undergo step fractures, and the coal pillar rotates again. After the working face has pushed out a certain distance of the coal pillar, the subcritical layer II fractures, forming an articulated rock beam structure with the rock mass ahead of the working face and the fractured and collapsed rock blocks behind the working face. Figure 5 As shown.

[0096] Physical simulation analysis shows that cross-coal pillar mining is not only affected by the overlying load of the coal pillar section, but also by the load of the inter-layer rock strata and the bearing effect of the fractured bearing structure. Therefore, the preliminary study of the working resistance of cross-coal pillar mining support needs to take the above forces and bearing structures as a unified research body.

[0097] Based on physical similarity simulation studies, this invention demonstrates that during the mining of upper coal seams, the immediate roof on both sides of the section coal pillar breaks and collapses first, filling the mining space. As the advancing distance of the left and right working faces increases, the upper subcritical layer I reaches its bearing limit and breaks, forming a stepped rock beam structure, which bears the upper load. As the mining space of the working face further increases, the main critical layer's bearing capacity becomes insufficient, causing it to break. Due to the swelling and fragmentation of the collapsed rock mass, the movement space of the main critical layer decreases, forming a hinged rock beam structure. At this point, the articulated rock beam structure of the main key layer and the stepped rock beam structure of the sub-key layer I form a joint bearing structure, which supports the overlying load. Due to the effect of the rock strata fracture angle, an inverted trapezoidal rock pillar area gradually increases from the lower rock pillar to the upper rock pillar in the section coal pillar. After the working face is mined and left to stand for a period of time, the inverted trapezoidal rock pillar area near the goaf will experience delayed fracture again, forming a delayed fracture area. Due to the rock strata rotation effect, the delayed fracture area rotates back to the goaf, which has a re-effect on the rock strata bearing structure on both sides of the section coal pillar.

[0098] The lower coal seam advances from the left side of the section coal pillar. After the working face advances to the section coal pillar of the upper coal seam, the mined portion below the coal pillar forms a pressure relief zone. The articulated rock beam structure and the stepped rock beam structure formed by the lagging fracture zone of the section coal pillar strata and the bearing strata of the upper coal seam exert loads on the section coal pillar, causing eccentric loading of the coal pillar. Due to the working face advance speed, the subcritical stratum II develops two types of fracture bearing structures under the concentrated eccentric load of the section coal pillar: a stepped rock beam structure under the condition of stepped shear fracture and an articulated rock beam structure under the condition of rock strata rotation fracture. Both bearing structures play a role in bearing the overlying load. The bearing capacity of the stepped rock beam structure is weaker than that of the articulated rock beam structure, and there is a possibility of frame collapse accidents. Therefore, when studying cross-coal pillar mining, it is necessary to study the load-bearing structure of the coal pillar section, and also analyze the fracture and collapse structure of the sub-critical layer II of the lower coal seam. This will allow for the calculation method of the support working resistance under different load-bearing structural conditions. Based on the fracture characteristics of the overlying strata bearing structure in cross-coal pillar mining, this invention approximates the fracture structure of the rock strata in cross-coal pillar mining of shallow-buried coal seam groups as follows: Figure 6 The diagram shown illustrates the fracture characteristics of rock strata in shallow-buried cross-coal pillar mining. Figure 6 (a) is a schematic diagram of the fracture structure characteristics of a stepped rock beam. Figure 6 (b) is a schematic diagram of the structural characteristics of the fracture of the articulated rock beam. Figure 6 The 1-1 coal seam is the upper coal seam or 1 in this invention. -2 Similarly, coal seam 2-2 is the lower coal seam or 2 in this invention. -2 Coal seam.

[0099] The load characteristics of cross-coal pillar mining are mainly divided into two parts: the inverted trapezoidal rock pillar area of ​​the overlying rock pillar generated by the mining of the upper coal seam, the bearing structure of the rock strata on both sides, and the delayed fracture zone; and the bearing body formed by the sub-key layer II of the lower coal seam mining, which is a stepped rock beam structure or a hinged rock beam structure.

[0100] This invention establishes a structural mechanical calculation model for shallow-buried cross-coal pillar mining based on the load characteristics of the coal pillar bearing structure in the upper coal seam mining section, the load characteristics of the bearing structure in the lower coal seam cross-coal pillar mining section, and the working resistance of the support. Figure 7 As shown, where, Figure 7 (a) is a mechanical model of a stepped rock beam structure. Figure 7 (b) is a mechanical model of a hinged rock beam structure. For simplicity, the subscripts Z and R are used to represent the mechanical elements on the left and right sides of the coal pillar section, respectively. To make the mechanical model more intuitive, the elements with smaller effects in the model are simplified.

[0101] Figure 7 The model parameters included are defined as follows: h1 is the mining height of the lower coal seam; h2 is the thickness of the immediate roof of the lower coal seam; h3 is the thickness of subcritical stratum II; h4 is the thickness of the lower load stratum; h5 is the mining height of the upper coal seam; h6 is the thickness of the immediate roof of the upper coal seam; h7 is the thickness of subcritical stratum I; h8 is the thickness of the upper load stratum; h9 is the thickness of the main critical stratum; h 10 The thickness of the loose layer;

[0102] P Z3 P R3 Loads are transferred from the loose layer to the main critical layer; P ZJ P RJ Main key layer B Z B R Key block self-weight load; P Z2 P R2 For the upper load layer load; P Z4 P R4 The load is transferred from the hysteresis failure zone of the upper load layer to the subcritical layer I; P ZT P RT E is a subcritical layer I stepped rock beam structure. Z E R Key block self-weight load; P Z1 P R1 To control the direct self-weight load of the cantilever beam on the upper coal seam;

[0103] P XT1 The self-weight load of the load layer under the subcritical layer Class II stepped rock beam structure; P XJ1 For the subcritical layer II articulated rock beam structure, the load layer is the self-weight load of the load layer; P XT The self-weight load of the Class II stepped rock beam in the subcritical layer; P XJ For the self-weight load of the articulated rock beam in subcritical layer II; PXJ2 The load is the self-weight of the cantilever beam directly above the lower coal seam.

[0104] L Z1 L R1 These are the key blocks B of the main key layer. Z B R Breaking length; L Z2 L R2 For subcritical layer I critical block E Z E R Breaking length; L Z3 L R3 For subcritical layer I critical block F Z F R Breaking length; L XT Key Block E of the Subcritical Layer II Step Cut-off Rock Beam Structure XT Breaking length; L XJ Key Block B of the Subcritical Layer II Hinged Rock Beam Structure XJ Breaking length;

[0105] θ ZJ θ RJ Main key layer hinged rock beam structure B Z B R Key block rotation angle; θ ZT θ RT For the subcritical layer I step rock beam structure F Z F R Key block rotation angle; θ XT E is a subcritical layer, type II stepped rock beam structure. XT Key block rotation angle; θ XJ For subcritical layer II articulated rock beam structure B XJ Key block rotation angle;

[0106] β ZJ β RJ The fracture angle of the rock strata in the key hinged rock beam structure; β ZT β RT The fracture angle of the subcritical layer I, a step-beam structure; β XT The fracture angle of the Class II step-beam structure subcritical stratum; β XJ The fracture angle of the rock strata in the subcritical layer II articulated rock beam structure.

[0107] (1) Forces on the articulated rock beam structure under disturbance throughout the entire life cycle of the main critical layer:

[0108] The stability of the main critical layer fracture structure plays a crucial role in controlling the overlying strata and loose layers. This invention, based on the coal seam mining direction, first studies the bearing structure of the strata on the left side of the coal pillar, and then studies the bearing structure on the right side of the coal pillar. Mining of the lower coal seam causes a counter-clockwise rotation of the bearing structure on the left side of the coal pillar. The support point on the goaf side first subsides, while the support point on the coal pillar side rotates without causing subsidence displacement. The key block B of the main critical layer... Z Rotate around the support point on the side of the coal pillar. For simplicity, this invention refers to the support point on the side of the coal pillar as the front support point, the support point on the side of the goaf as the rear support point, and the hinge point in the middle of the rock beam for a bench rock beam structure as the transfer support point. When the lower coal seam is pushed to the main critical layer break line, the front support point undergoes a downward displacement, at which point the critical block B... Z A stable articulated rock-beam structure is formed again. This invention refers to a stable load-bearing structure that retains the same structure after mining as a full-life-cycle disturbance load-bearing structure. Since the upper part of the main key layer is a loose loess layer lacking load-bearing characteristics, the loose layer above the main key layer is considered as a uniformly distributed load. At this time, the load in the hysteresis failure zone can be simplified to a uniformly distributed load in the loose layer. The mechanical calculation model of the articulated rock-beam in the main key layer is as follows: Figure 8 As shown.

[0109] During the mining of the upper coal seam, the main critical layer forms a hinged rock beam structure. After the lower coal seam is mined, the rear and front support points of the hinged rock beam undergo rotational subsidence. Due to the supporting effect of the rear support point, the main critical block B... Z No slippage occurred, and the articulated rock beam structure did not become unstable. Therefore, it can be seen that the critical block B is stable at this time. Z The calculation method for articulated rock beam structures still applies. Since the loose loess layer cannot form an effective load-bearing structure, it can be considered as a uniformly distributed load. Therefore, the expression for the forces acting on the articulated rock beam structure during the entire life cycle disturbance of the main critical layer is:

[0110]

[0111] Among them, i Z2 The block size of the key block to the left of the master key layer, θ ZJ The rotation angle of the key block on the left side of the main key layer hinged rock beam structure;

[0112] In the formula, the load P of the loose loess layer Z3 For: P Z3 =(L Z1 +h 10 cotβ ZJ )·γ 10 h 10 K G Among them, L Z1 The fracture length of the key block on the left side of the main key layer, h 10 For the thickness of the loose layer, β ZJThe fracture angle of the rock strata in the key hinged rock beam structure, γ 10 K represents the average bulk density of the loose layer. G The load transfer coefficient of the loess layer;

[0113] The force P of the key block in the primary key layer ZJ For: P ZJ =L Z1 γ9h9; where L Z1 The fracture length of the key block on the left side of the main key layer, γ9 is the average unit weight of the main key layer, and h9 is the thickness of the main key layer.

[0114] Because the mining of the upper coal seam causes the main key stratum to form a delayed failure zone, the force P acting on the delayed failure zone of the main key stratum is... Z5 for:

[0115]

[0116] Among them, γ9 is the average bulk density of the main critical layer, h9 is the thickness of the main critical layer, and β ZJ The fracture angle of the rock strata in the key hinged rock beam structure, b Z θ represents the dip length of the fracture structure acting on the coal pillar in the hysteresis fracture zone, i.e., the width of the fracture zone in the coal pillar section. ZJ The rotation angle of the key block of the hinged rock beam structure in the main key layer.

[0117] (2) Forces acting on the subcritical layer I during the full life cycle disturbance hysteresis failure of the stepped rock beam structure:

[0118] Under the conditions of lower coal seam mining, the key block F of subcritical seam I. Z With the fractured and collapsed rock mass and the fractured rock mass G Z Subsidence occurs preferentially, at which point the subsidence of the key block F in the lagging fractured step-beam structure increases, and the key block F... Z Still located in critical block F Z The lower part, similar to the upper coal seam mining bench rock beam structure, exhibits high stability. As the working face pushes below the section coal pillar, and the coal pillar subsides, a full life-cycle disturbance hysteresis failure bench rock beam mechanical calculation model is established, as follows: Figure 9 As shown, the forces acting on the subcritical layer I full life-cycle disturbance hysteresis failure step rock beam structure at this time include: the load W transferred by the main critical layer hinged rock beam structure. Z2 The force load P acting on the subcritical layer I critical block by the upper load layer Z2 The self-weight load P of the critical block in subcritical layer I ZT The upper load layer acts on the subcritical layer I with the delayed fracture block load P Z4 cosθ ZT and the hysteretic fracture block load P of subcritical layer I Z6 The expression is:

[0119] R ZT =W Z2 +P Z4 cosθ ZT +P ZT +P Z6

[0120] W Z2 =R ZJ +P Z2

[0121] Where, θ ZT The rotation angle of the key block of the subcritical layer I step rock beam structure, R ZJ The forces acting on the articulated rock beam structure during the entire life cycle disturbance of the main critical layer, P Z4 The force acting in the hysteresis fracture zone of the upper load layer;

[0122] In the formula, P is the self-weight load of the critical block in subcritical layer I. ZT For: P ZT =h7γ7L Z2 Where h7 is the thickness of subcritical layer I, γ7 is the average bulk density of subcritical layer I, and L Z2 The fracture length of the critical block on the left side of subcritical layer I;

[0123] The force P in the hysteresis fracture zone of the upper load layer Z4 For: P Z4 =h8γ8b Z Where h8 is the thickness of the upper load layer, γ8 is the average unit weight of the upper load layer, and b Z It is the inclination length of the fracture structure in the hysteresis fracture zone acting on the coal pillar, i.e., the width of the fracture zone in the coal pillar section;

[0124] The force load P acting on the subcritical layer I critical block by the upper load layer Z2 For: P Z2 =L Z2 γ8h8; where L Z2 h8 is the fracture length of the critical block on the left side of the subcritical layer I, h8 is the thickness of the upper load layer, and γ8 is the average unit weight of the upper load layer.

[0125] Subcritical layer I hysteresis fracture block load P Z6 for:

[0126]

[0127] Where γ7 is the average bulk density of subcritical layer I, h7 is the thickness of subcritical layer I, and β ZT The fracture angle of the subcritical layer I, the step-beam structure, is θ. ZT For the critical block rotation angle of the subcritical layer I step rock beam structure, b ZIt is the directional length of the fracture structure in the hysteresis fracture zone acting on the coal pillar, i.e., the width of the fracture zone in the coal pillar section.

[0128] In another specific embodiment, the bearing stratum of the subcritical layer I on the left side of the coal pillar, which is subjected to disturbance lag and failure of the stepped rock beam structure throughout its entire life cycle, still retains its original bearing structure. Therefore, a masonry beam calculation model can also be used. Since the rock beam structure is supported by the coal pillar at the working face boundary, the failure distance of the stepped rock beam in subcritical layer I at this time satisfies L. Z2 = (1~1.3)L Z3 The relationship is as follows. Based on the moment equilibrium condition, assuming each uniformly distributed load is a concentrated load acting on the middle of the rock mass, take ∑M... ZO =0, ∑M FZ2 =0, Based on the "SR" stability theory, the supporting force for maintaining stability of the subcritical layer I hysteresis fracture step-beam structure is:

[0129]

[0130] Among them, Q ZA Q ZB For the subcritical layer I critical block in O Z and F Z3 Shear force on the contact hinge; 0.5 is the coefficient of friction of the rock block; 0.5a is the height of the compression surface of the subcritical layer I rock structure, usually taken as 0; b m K represents the dip length of the load-bearing structure acting on the coal pillar during rock strata fracture; P6 The coefficient for the filling and expansion of the roof strata directly above the coal seam.

[0131] (3) Direct jacking force on the left side of the coal pillar in the section:

[0132] Based on the function of the coal pillar in the section, it can be seen that after the support is withdrawn after the working face is finished mining, the coal pillar still maintains its original bearing capacity, and the overburden load is supported by the coal pillar. Therefore, the load on the upper part of the coal pillar can be obtained by inverting the calculation method of the working resistance of the support. A full life cycle disturbance direct roof mechanical calculation model of this invention is as follows: Figure 10 As shown.

[0133] During the mining of the lower coal seam, the coal pillar in the section has become relatively stable and there is no mining-induced effect; therefore, the direct roof force on the left side of the coal pillar is R. Z1 =W Z1 +P Z1 Among them, W Z1 =R ZT ;

[0134] In the formula, the self-weight load P of the immediate roof strata of the coal seam Z1 For P Z1 =h6γ6(bm +b h ); where γ6 is the average unit weight of the immediate roof of coal seam 1-2, b h The width of the alleyway.

[0135] When the working face of the lower coal seam is located at 1 / 2 to 2 / 3 of the width of the section coal pillar, the coal pillar and the inverted trapezoidal fractured rock pillar area undergo slight rotation, which has no significant impact on the bearing structure of the overlying strata. When the working face exits the coal pillar, the front support point of the bearing structure of the overlying strata sinks with the rotation of the section coal pillar. After the working face exits the coal pillar, the front support point of the bearing structure of the overlying strata undergoes rapid sinking and rotation. The coal seam below the rear support point is not mined, so it cannot form an effective free movement space and basically maintains the original fracture characteristics. The bearing structure in which only the front support point changes after mining, and the rear support point does not change, is called a semi-life-cycle disturbed bearing structure. Based on the rock strata fracture characteristics, the mechanical calculation model of the semi-life-cycle disturbed articulated rock beam of the main key layer can be obtained as follows: Figure 11 As shown.

[0136] (4) The structural forces of rock strata disturbance during the half-life cycle of the main key layer:

[0137] Since the bearing structure of the main critical layer only experiences rotational subsidence at the front support point, the traditional hinged rock beam structure with its front-high-back-low hinged shape is easily altered. Therefore, to obtain the bearing structure of the main critical layer under half-life-cycle disturbance conditions, it is necessary to first determine the resulting mechanical structure. Because mining the lower coal seam easily alters the bearing structure of the overlying strata of the upper coal seam, and given that the section coal pillar, inverted trapezoidal rock pillar area, and interlayer strata migrate in the same direction during the mining of the lower coal seam, the ability of the broken strata of the upper coal seam to refill the goaf is weak and is not considered.

[0138] Based on factors such as the subsidence value of the bearing strata in the lower coal seam, the filling and swelling properties of the fractured and collapsed strata, and the mining height, this invention yields the following formula for determining the bearing structure of the main key strata: Δd RJ =d RJ -d 2-2m ;

[0139] Where, d RJ =L R1 sinθ RJ ,

[0140] In the above formula, Δd RJ The difference in rotational settlement of the articulated rock beam structure connecting the main and key layers in the mining of the upper and lower coal seams; d RJ The rotational settlement of the hinged rock beam structure in the main key layer; d 2-2m K represents the rotational settlement of the articulated rock beam structure in the main key layer of the lower coal seam mining. PXThe coefficient of strata fragmentation between the lower coal seams is given. Subcritical stratum II is the main bearing stratum of the lower coal seam. Its fractured rock mass consists of regular rock blocks, so its filling capacity is relatively weak. Therefore, the coefficient of strata fragmentation is considered to be zero.

[0141] When Δd RJ When the value is ≤0, the hinged rock beam structure of the main key layer becomes unstable and fails, and has no bearing effect on the overlying load, but only applies load as a load layer;

[0142] When Δd RJ When the value is greater than 0, the main critical layer still maintains a hinged rock beam structure and bears the overlying load. The force exerted on the rock strata structure by the main critical layer during its half-life cycle is then expressed as:

[0143]

[0144] Among them, i R2 The block size of the key block to the right of the master key layer, θ RJ The rotation angle of the right critical block of the key layer hinged rock beam structure, P R3 For the load of the loose loess layer, P RJ The force of the key block on the right side of the main key layer, P R5 The force acting on the delayed failure zone of the main critical layer.

[0145] In the formula, the load P of the loose loess layer R3 For: P R3 =(L R1 +h 10 cotβ RJ )·γ 10 h 10 K G ;

[0146] Key Block B of the Main Key Layer R Force P RJ For: P RJ =L R1 γ9h9;

[0147] There is a delayed failure zone in the main critical stratum on the right side of the coal pillar. At this time, the force P in the delayed failure zone of the main critical stratum is... R5 for:

[0148]

[0149] (5) Subcritical Layer I Half-Life Cycle Disturbance Stepped Rock Beam Structure Forces:

[0150] This invention is based on physical similarity simulation experiments, and the original key block E is obtained. R and F RThe resulting stepped rock beam structure, with a higher front and lower rear, transformed into a stepped rock beam structure under disturbance. This structure conforms to the load characteristics of stepped rock beam structures and possesses complete load-bearing capacity. Therefore, the study of subcritical layer I can be conducted based on the structural characteristics of the stepped rock beam. Furthermore, since the forces acting on the stepped rock beam structure under half-life-cycle disturbance in subcritical layer I are similar to the stress characteristics of the stepped rock beam structure on the left side of the coal pillar in the section, the mechanical calculation model for the semi-life-cycle disturbance-induced hysteresis failure of the stepped rock beam in subcritical layer I is as follows: Figure 12 As shown.

[0151] Subcritical layer I half-life-cycle disturbance hysteresis failure step rock beam structure force R RT Includes: Load transferred by the main key layer rock beam structure W R2 The force load P acting on the right critical block of subcritical layer I from the upper load layer R2 The load P acting on the key layer I hysteresis fracture block by the upper load layer R4 cosθ RT Subcritical layer I delayed fracture block load P R6 And the self-weight load P of the critical block on the right side of subcritical layer I. RT The expression is:

[0152] R RT =W R2 +P R4 cosθ RT +P RT +P R6

[0153] W R2 =R RJ +P R2

[0154] Where, θ RT For the critical block rotation angle of the subcritical layer I step rock beam structure, P R4 This refers to the force acting in the hysteresis fracture zone of the upper load layer.

[0155] In the formula, the force load P acting on the right critical block of the subcritical layer I is... R2 For: P R2 =L R2 γ8h8;

[0156] The force P in the hysteresis fracture zone of the upper load layer R4 For: P R4 =h8γ8b Z ;

[0157] Subcritical layer I hysteresis fracture block load P R6 for:

[0158]

[0159] Subcritical layer I right-side critical block E R Self-weight load P RT For: P RT =h7γ7L R2 .

[0160] In another specific embodiment, based on the moment balance condition, it is assumed that each uniformly distributed load is a concentrated load acting on the middle part of the rock mass, and ∑M is taken as... RO =0, ∑M FR2 =0, Based on the "SR" stability theory, the supporting force R that maintains the stability of the subcritical layer I hysteresis fracture step rock beam structure can be obtained. RT for:

[0161]

[0162] Among them, Q RA Q RB For the subcritical layer I critical block in O R and F R3 Shear force on the contact hinge.

[0163] (6) Direct jacking force on the right side of the coal pillar in the section:

[0164] Because the stress characteristics of the immediate roof strata on the right side of the coal pillar are similar to those on the left side of the coal pillar, the semi-life-cycle disturbance immediate roof mechanical calculation model is as follows: Figure 13 As shown.

[0165] The direct jacking force on the right side of the coal pillar in the section is: R R1 =W R1 +P R1 Among them, W R1 =R RT ;

[0166] In the formula, the self-weight load P of the directly overhead strata of the upper coal seam R1 For: P R1 =h6γ6(b m +b h ).

[0167] This invention further determines the bearing structure characteristics of the sub-critical stratum II in lower coal seam mining. First, it analyzes the forces acting on the sub-critical stratum II-type bench rock beam structure in lower coal seam mining. An embodiment of this invention provides a mechanical calculation model for the sub-critical stratum II-type bench rock beam as follows: Figure 14 As shown, during the process of the lower coal seam working face entering the section coal pillar, no obvious fracture was observed in subcritical layer II. Only the direct roof of the lower coal seam fell during mining. After the working face exited the section coal pillar for 1.34m, subcritical layer II experienced shearing and fracture of critical block E. XT With key block D XT and FXT The mechanical structure formed by the support points is approximately a stepped rock beam, referred to here as a stepped rock beam structure. In this case, the rock beam structure cannot satisfy the mechanical equilibrium condition and requires support from the working face support. The support force provided by the support is considered as P. XTC When the coal seam is pushed to the subcritical stratum II bench shear point, the strata undergo overall shearing. When this type of stratum fracture occurs, the working resistance of the support increases suddenly, which has a significant impact on the mining face. At this time, the force of the bench-like rock beam structure formed by the subcritical stratum II includes: the load P transferred from the inverted trapezoidal rock pillar area overlying the section coal pillar. YZ The load-bearing structural force R on both sides of the coal pillar section Z1 and R R1 ; Self-weight load P of the coal pillar section M ; Lower load layer self-weight load P XT1 And the self-weight load P of the subcritical layer II critical block EXT XT The expression is:

[0168] R XT1 =(P YZ +R Z1 +R R1 +P M )·K GM +P XT1 +P XT

[0169] Among them, K GM This is the load transfer coefficient of the coal pillar in the section.

[0170] In the formula, the load P transferred by the inverted trapezoidal rock pillar area overlying the coal pillar section is... YZ for:

[0171]

[0172] Among them, L m The width of the coal pillar in the section; β is the sum of the thicknesses of the overlying rock and soil layers of the coal pillar section; β is the average fracture angle of the rock strata; γ is the average unit weight of the overlying rock and soil layers, b m b is the width of the fracture zone of the coal pillar in the section. z This refers to the width of the fracture zone in the coal pillar section.

[0173] Section coal pillar self-weight load P M For: P M =γ5h5L m ; where γ5 is the bulk density of the upper coal seam.

[0174] Lower load layer self-weight load P XT1 For: P XT1 =γ4h4(L XT +h4cotβ XT), where γ4 is the unit weight of the lower load layer.

[0175] Subcritical layer II critical block E XT Self-weight load P XT for:

[0176] Due to the subcritical layer II critical block E XT The collapse was primarily caused by step-like shearing, resulting in severe damage to the immediate roof of the lower coal seam. Based on the collapse characteristics of the immediate roof, it is assumed that all the rock strata behind the support have collapsed. Therefore, the force P exerted by the immediate roof of the lower coal seam is... XT2 for:

[0177] P XT2 =γ2h2L K

[0178] Where γ2 is the direct roof density of the lower coal seam; L K The control length for the lower coal seam mining is taken as 5.7m.

[0179] To ensure the maximum working resistance required for cross-coal pillar mining faces in the lower coal seam, the dynamic load factors of the supports during production must be considered. Therefore, the working resistance R of the supports under the action of the Class II bench rock beam structure in the subcritical layer of the lower coal seam is determined. T for:

[0180] R T =(R XT1 +P XT2 )K

[0181] Among them, R XT1 For the subcritical layer, type II stepped rock beam structure, the force P XT2 The force is the direct roof force of the lower coal seam under the action of the Class II step rock beam structure of the subcritical layer. K is the dynamic load coefficient of the support, which can be taken as 1.1 based on field measurements and experiments.

[0182] The fracture forms of the subcritical stratum II in lower coal seam mining are mainly divided into two types: bench-like rock beam structure and hinged rock beam structure. This invention further analyzes the hinged rock beam structure. Through physical similarity simulation tests and field drilling exploration, it is shown that reasonably controlling the working face advance speed can effectively eliminate bench shedding. When the subcritical stratum II fractures and forms a hinged rock beam structure during cross-coal pillar mining, the key block B... XJ Rear support point F XJ2 Located at half the dip length of the section coal pillar, the section coal pillar and the inverted trapezoidal rock pillar area above it form a distinct rotation, with the rotation angle corresponding to the critical block B. XJ rotation angle θ XJ Same. At this time, the front support point F XJ1 Located directly above the lower coal seam, key block A XJ B XJ and CXJ A complete articulated rock beam structure is formed, and its stress characteristics are as follows: Figure 15 The mechanical calculation model of the hinged rock beam in subcritical layer II is shown.

[0183] Due to the critical block B of the hinged rock beam structure in subcritical layer II XJ The rear support point is located in the middle of the coal pillar section, and the load-bearing structural force on the left side of the coal pillar section mainly acts on the critical block C. XJ For key block B XJ The generated force is relatively small, and will not be discussed in detail here. At this time, the force R of the articulated rock beam structure formed by the subcritical layer II is relatively small. XJ1 This mainly includes: the load transferred by the inverted trapezoidal rock pillar area overlying the coal pillar in the section. YZ The load-bearing structural force R on the right side of the coal pillar section R1 ; Self-weight load P of the coal pillar section M Subcritical layer II articulated rock beam structure under load layer self-weight load P XJ1 Subcritical layer II articulated rock beam self-weight load P XJ The expression for the forces acting on the articulated rock beam structure in subcritical layer II is:

[0184]

[0185] Among them, P YZ For transferring loads to the inverted trapezoidal rock pillar area overlying the coal pillar in the section; R R1 P represents the load-bearing structural force on the right side of the coal pillar section. M P is the self-weight load of the coal pillar in the section. XJ1 For the subcritical layer II articulated rock beam structure, the load layer self-weight load, P XJ The load is the self-weight load of the hinged rock beam in the subcritical layer II.

[0186] Since the section coal pillar above the subcritical layer II rock beam structure and the overlying inverted trapezoidal rock pillar area transmit the same load, this invention will not elaborate further here.

[0187] In the formula, the self-weight load P of the load layer under the key layer II hinged rock beam structure is... XJ1 For: P XJ1 =γ4h4(L XJ +h4cotβ XT ).

[0188] Subcritical layer II articulated rock beam self-weight load P XJ For: P XJ =γ3h3L XJ .

[0189] The direct roof force P of the lower coal seam under the action of the hinged rock beam structure of the subcritical layer II XJ2 For: P XJ2 =γ2h2LK b XZ .

[0190] The required support resistance R for maintaining the stability of the articulated rock beam structure in the subcritical layer II of the lower coal seam mining. J for:

[0191] R J =(R XJ1 +P XJ2 )K

[0192] Among them, R XJ1 For the force acting on the hinged rock beam structure of subcritical layer II, P XJ2 K represents the direct roof force of the lower coal seam under the action of the hinged rock beam structure of the subcritical layer II, and K is the dynamic load coefficient of the support.

[0193] In cross-pillar mining, the coal pillar section plays a crucial role as the stress transfer unit between the upper and lower coal seams. The stability and failure characteristics of the coal pillar section are inextricably linked to the bearing structure of the upper coal seam. The dynamic disturbance structure of the lower coal seam is considered at the width b of the coal pillar's inclination contact. m and b z Inverting to the width of the fracture zone and the width of the fissure zone in the coal pillar section, this invention, in order to simplify the mechanical analysis process, considers the upper load-bearing structure of the coal pillar section as a combination of a cantilever beam and an "inverted trapezoidal" rock pillar group structure, thus obtaining the following... Figure 16 The mechanical calculation model of the overlying strata structure of the coal pillar shown is presented.

[0194] Based on the mechanical equilibrium relationship, mechanical calculations are performed on the coal pillar section. The unit weight of the soil and rock layer above the coal pillar is taken as the average unit weight γ for calculation. The structural mechanical calculation model of the overlying strata of the coal pillar section can be obtained: R Z1 +R R1 +R YZ -PL m =0; After the upper coal seam is mined, the coal pillar in the section is disturbed, resulting in concentrated stress; during the mining of the lower coal seam, the coal pillar in the section is prone to instability, leading to an increase in the width of the plastic zone of the coal pillar. At this time, the upper load P of the coal pillar in the section is: P = k q γH; where k q H represents the stress concentration factor of the coal pillar in the section after disturbance during mining of the lower coal seam; H represents the burial depth of the coal pillar in the section.

[0195] Because the overlying strata of the coal pillar will inevitably rotate due to mining disturbance, a fracture zone will form at the coal wall of the coal pillar. The width b of the fracture zone of the coal pillar can be obtained according to the stress balance calculation equation. m for:

[0196]

[0197] Where λ is the lateral pressure coefficient of the coal column in the section; c is the cohesion of the coal body; The internal friction angle of the coal; p z The strength of the coal pillar support in the section.

[0198] Based on the research object and the coal and rock mass mechanical parameters of the Yushenfu mining area, the embodiments of this invention take the following values: lateral pressure coefficient of the coal pillar λ = 0.7; stress concentration factor of the coal body k = 3.2; coal cohesion c = 1.18 MPa; and internal friction angle of the coal body. The support strength of the coal pillar section, PZ, is 0.08 MPa, from which the width b of the fracture zone of the coal pillar section can be calculated. m =2.05m; Substituting this value into the structural mechanics calculation model of the overlying strata of the coal pillar, the width b of the fracture zone of the coal pillar can be obtained. z This invention uses MATLAB numerical calculation software to solve for b. z =2.14m.

[0199] Meanwhile, based on the geometric relationship of the structural mechanical calculation model of the overlying strata of the coal pillar section, the elastic zone b of the coal pillar section can be obtained. t The expression is: b t =L m -2(b m +b Z ), b m and b z Substituting the value into the equation, we can obtain its value.

[0200] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for determining the load on a coal seam overburden structure support under concentrated load across a shallow coal pillar, characterized in that, include: The subcritical layer II bearing structure under concentrated eccentric load of coal pillar in the analysis section was analyzed, and a rock structure mechanical model was constructed. The disturbance bearing structure on both sides of the coal pillar in the section was analyzed through similar simulation experiments; The disturbance bearing structures on both sides of the coal pillar in the section include: the force of the articulated rock beam structure during the full life cycle disturbance of the main critical layer, the force of the delayed fracture step rock beam structure during the full life cycle disturbance of the subcritical layer I, the force of the rock stratum structure during the half life cycle disturbance of the main critical layer, the force of the step rock beam structure during the half life cycle disturbance of the subcritical layer I, and the direct roof force of the coal body in the section coal pillar. Based on the disturbance bearing structure on both sides of the coal pillar in the section, the load characteristics of the interlayer rock strata fracture bearing structure are determined; the load characteristics of the interlayer rock strata fracture bearing structure include: the force of the subcritical layer II type step rock beam structure and the force of the subcritical layer II hinged rock beam structure. The support resistance of the structural support is determined by combining the load characteristics of the disturbance bearing structure on both sides of the coal pillar section and the load characteristics of the fracture bearing structure of the interlayer rock strata; the support resistance of the structural support is the structural support load. The expression for the force acting on the subcritical layer type II stepped rock beam structure is as follows: ； in, To transfer loads to the inverted trapezoidal rock pillar area overlying the coal pillar section; and These represent the load-bearing structural forces on both sides of the coal pillar in the section; The load is the self-weight of the coal pillar in the section; The load is the self-weight of the lower load layer; The self-weight load of the critical block EXT in subcritical layer II. The load transfer coefficient of the coal pillar section; The calculation method for the load transferred by the inverted trapezoidal rock pillar area overlying the coal pillar section is as follows: ； in, The width of the coal pillar in the section; It is the sum of the thicknesses of the overlying rock and soil layers on the coal pillar of the section; The average fracture angle of the rock strata; This represents the average unit weight of the overlying soil and rock layer. The width of the fracture zone of the coal pillar in the section. The width of the fracture zone in the coal pillar section; The expression for the force acting on the articulated rock beam structure of the subcritical layer II is as follows: ； in, To transfer loads to the inverted trapezoidal rock pillar area overlying the coal pillar section; This indicates the load-bearing structural force on the right side of the coal pillar section; The load is the self-weight of the coal pillar in the section. The load is the self-weight load of the lower load layer of the subcritical layer II articulated rock beam structure. The self-weight load of the articulated rock beam in subcritical layer II; The determination of the support resistance of the structural support by combining the load characteristics of the disturbance bearing structures on both sides of the coal pillar section and the fracture bearing structures of the interlayer rock strata includes: The support resistance of the structural support includes the first support resistance under the action of the subcritical layer II type stepped rock beam structure, and the second support resistance under the action of the subcritical layer II hinged rock beam structure. The calculation method for the first support resistance is as follows: ; in, The force acting on the subcritical layer, type II stepped rock beam structure, The force is the direct roof force of the lower coal seam under the action of the Class II bench rock beam structure in the subcritical layer, and K is the dynamic load coefficient of the support. The calculation method for the second support resistance is as follows: ; in, The force acting on the hinged rock beam structure of the subcritical layer II. K represents the direct roof force of the lower coal seam under the action of the hinged rock beam structure of the subcritical layer II, and K is the dynamic load coefficient of the support.

2. The method for determining the load of a coal seam overburden structure support under concentrated load across a shallow coal pillar as described in claim 1, characterized in that: The specific forces acting on the articulated rock beam structure during the full life cycle disturbance of the main key layer are as follows: Including loess loose layer load The forces acting on the key blocks of the main key layer and the forces acting in the delayed failure zone of the main critical layer The expression is: ； in, The block size of the key block to the left of the primary key layer. The rotation angle of the key block on the left side of the main key layer hinged rock beam structure; In the formula, the load of the loose loess layer for: ;in, The fracture length of the critical block on the left side of the primary critical layer. For the thickness of the loose layer, The fracture angle of the rock strata in the hinged rock beam structure of the main key layer. The average bulk density of the loose layer The load transfer coefficient of the loess layer; Key Block Actions in the Primary Key Layer for: ;in, The fracture length of the critical block on the left side of the primary critical layer. The average density of the primary critical layer. The thickness of the main critical layer; Force in the delayed failure zone of the main critical layer for: ； in, The average density of the primary critical layer. The thickness of the main critical layer. The fracture angle of the rock strata in the hinged rock beam structure of the main key layer. It is the directional length of the fracture structure in the hysteresis fracture zone acting on the coal pillar, i.e., the width of the fracture zone in the coal pillar section.

3. The method for determining the load of a coal seam overburden structure support under concentrated load across a shallow coal pillar as described in claim 2, characterized in that: The specific forces acting on the subcritical layer I full life-cycle disturbance hysteresis failure step rock beam structure are as follows: Including the load transfer of the main key layer articulated rock beam structure The force load of the upper load layer acting on the subcritical layer I critical block The self-weight load of the critical block in subcritical layer I The upper load layer acts on the subcritical layer I with the delayed fracture block load. and the hysteresis load of subcritical layer I The expression is: ； ； in, The rotation angle of the key block of the subcritical layer I step rock beam structure. The forces acting on the articulated rock beam structure during the entire life cycle of the main critical layer disturbance. The force acting in the hysteresis fracture zone of the upper load layer; In the formula, the self-weight load of the critical block in subcritical layer I. for: ;in, The thickness of subcritical layer I. The average bulk density of the subcritical layer I. The fracture length of the critical block on the left side of subcritical layer I; Upper load layer hysteresis fracture zone force for: ;in, The thickness of the upper load layer, This represents the average unit weight of the upper load layer. It is the inclination length of the fracture structure in the hysteresis fracture zone acting on the coal pillar, i.e., the width of the fracture zone in the coal pillar section; Forces and loads acting on the subcritical layer I critical block from the upper load layer for: ;in, The fracture length of the critical block on the left side of subcritical layer I. The thickness of the upper load layer, This represents the average unit weight of the upper load layer; Subcritical layer I hysteresis fracture block load for: ； in, The average bulk density of the subcritical layer I. The thickness of subcritical layer I. The fracture angle of the subcritical layer I step-beam structure rock strata is... The rotation angle of the key block of the subcritical layer I step rock beam structure. It is the directional length of the fracture structure in the hysteresis fracture zone acting on the coal pillar, i.e., the width of the fracture zone in the coal pillar section.

4. The method for determining the load of a coal seam overburden structure support under concentrated load across a shallow coal pillar as described in claim 3, characterized in that: The specific forces acting on the rock strata structure during the half-life cycle of the main key layer are: A determination formula for the bearing capacity of the main critical layer is constructed based on the rotational subsidence of the articulated rock beam structure of the main critical layer during the mining of the lower coal seam. The main critical layer bearing structure is determined based on the value of the main critical layer bearing structure determination formula. When the value of the main key layer bearing structure determination formula is less than or equal to zero, the main key layer hinged rock beam structure becomes unstable and fails, and has no bearing effect on the overlying load. When the value of the main critical layer bearing structure determination formula is greater than zero, the main critical layer maintains a hinged rock beam structure and has a bearing effect on the overlying load. At this time, the half-life-cycle disturbance rock stratum structure force of the main critical layer is expressed as: ； in, The block size of the key block to the right of the primary key layer. The rotation angle of the key block on the right side of the hinged rock beam structure of the main key layer. For the load of the loose loess layer, The force acting on the key block on the right side of the main key layer. The force acting on the delayed failure zone of the main critical layer.

5. The method for determining the load of a coal seam overburden structure support under concentrated load across a shallow coal pillar as described in claim 4, characterized in that: The specific forces acting on the subcritical layer I semi-life cycle disturbed stepped rock beam structure are as follows: Including the load transfer of the main key layer rock beam structure The load applied by the upper load layer to the critical block on the right side of subcritical layer I. The load of the upper load layer acting on the key layer I hysteresis fracture block Subcritical layer I delayed fracture block load and the self-weight load of the critical block on the right side of subcritical layer I. The expression is: ； ； in, The rotation angle of the key block of the subcritical layer I step rock beam structure. This refers to the force acting in the hysteresis fracture zone of the upper load layer.

6. The method for determining the load of a coal seam overburden structure support under concentrated load across a shallow coal pillar as described in claim 5, characterized in that: The direct jacking force of the coal pillar in the aforementioned section is specifically: This includes the direct jacking force on the left side of the coal column and the direct jacking force on the right side of the coal column. The direct jacking force on the left side of the coal pillar in the aforementioned section is: ,in, ; The direct jacking force on the right side of the coal pillar in the section is: ,in, ; In the formula, To control the self-weight load of the left side of the cantilever beam in the upper coal seam. The coal seam controls the direct self-weight load of the right side of the cantilever beam.

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