Small coal pillar gob-side roadway surrounding rock stability control method

Abstract

The invention relates to the technical field of coal mine roadway surrounding rock reinforcement, in particular to a small coal pillar gob-side roadway surrounding rock stability control method which comprises the following steps: establishing four immediate roof fracture mechanical models; calculating correlation among direct roof shearing force, bending moment and deflection; judging the type of the mechanical model to which the small coal pillar gob-side roadway belongs; calculating a mathematical relationship between the maximum value of direct roof deflection and the supporting force of the small coal pillar; carrying out primary loading on a plurality of rock samples, coal samples and a plurality of groups of grouting reinforcement material consolidation samples, and carrying out secondary loading on a grouting coupling test body by adopting an orthogonal test; obtaining an optimal grouting reinforcement material, consolidation time and an injection rate; establishing a gob-side roadway small coal pillar grouting reinforcement numerical model through FLAC3D, and simulating the gob-side roadway small coal pillar grouting reinforcement numerical model; an optimal grouting layout scheme is obtained through a simulated annealing algorithm; determining an optimal grouting reinforcement scheme; test and simulation are combined, support reinforcement parameters are scientifically evaluated, the stability of the surrounding rock of the small coal pillar gob-side roadway is effectively controlled, the method is simple, and the cost is low.

Description

Technical Field

[0001] The invention relates to the technical field of coal mine tunnel surrounding rock reinforcement, and in particular to a method for controlling the stability of surrounding rock in a tunnel along a small coal pillar. Background Art

[0002] Coal is the main energy source and important chemical raw material in my country, and the basis of my country's energy production and consumption. The exploitation of coal resources is inseparable from the service of tunnels. The stability and maintenance quality of underground tunnels as passages of coal mine production systems directly affect whether the mine can achieve safe and efficient production. The western region will be the key area for China's coal industry production in the future. The geological conditions in the northwest region mainly present the following characteristics: the topsoil layer is mostly sedimentary sand layer; the bedrock layer is mostly mudstone layer, sand layer, and mud-sandstone interlayer rock mass. The tunnels along the goaf with small coal pillars are affected by the disturbance of mining, and the deformation of the surrounding rock is one of the main problems that plague coal mine production and construction in my country and even in the world, which puts forward higher requirements on coal mining equipment and technology; the tunnels along the goaf with small coal pillars often experience large deformation of the surrounding rock, roof collapse, floor bulging and spalling and other engineering disasters due to the looseness and instability of the small coal pillars, which directly affect the safe and efficient mining of coal; and the remaining small coal pillars generally cannot be recovered, which greatly wastes coal resources. Digging tunnels in the high gravity area of ​​the remaining small coal pillars is prone to impact ground pressure accidents, coal seam gas outbursts and gas explosions. At the same time, the ventilation of the goaf caused by the force damage of the small coal pillars reserved for protecting the tunnel is also prone to cause gas and fire accidents.

[0003] In the prior art, when retaining a tunnel, the original tunnel roof is generally supported in advance by a combination of anchors, nets, cables and spraying. However, due to the complex conditions in the western mining areas, the rock strata of the composite roof are complex, and improper support measures are prone to delamination or roof collapse. In addition, the deformation of different rock strata during mining is inconsistent, which can easily lead to tunnel deformation. Traditional support methods are difficult to meet the requirements of tunnel stability under the conditions of the roof, and the overall strength of the surrounding rock is low, which is greatly disturbed by mining, and the spatial structure of the overburden collapse caused by mining at adjacent working faces is complex. All of the above problems pose a serious threat to the safety and stability of the tunnel.

[0004] The present invention proposes a method for controlling the stability of surrounding rock in tunnels along goafs with small coal pillars. By combining theoretical analysis, indoor rock mechanics experiments, numerical calculations and other methods, a deformation grouting reinforcement scheme for surrounding rock in tunnels along goafs with small coal pillars is obtained, which is of great significance to the development of grouting reinforcement technology for surrounding rock in tunnels along goafs with small coal pillars and the safe and efficient mining of coal mines. Summary of the invention

[0005] The purpose of the present invention is to provide a method for controlling the stability of surrounding rock in a roadway along a small coal pillar, so as to solve the problems raised in the above-mentioned background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for controlling the stability of surrounding rock in a small coal pillar gob-side roadway comprises the following steps:

[0008] Step S1: four types of fracture structures are divided according to the positions of the fracture lines between the basic roof rock blocks, and four types of direct roof mechanical models of small coal pillars along the goaf are established accordingly;

[0009] Step S2: According to the four mechanical models, the correlation between the shear force, bending moment and deflection of the top is calculated respectively through the static equilibrium conditions of the top;

[0010] Step S3: using the borehole optical camera method and the roof separation monitoring method to monitor the surrounding rock of the gob-side roadway with small coal pillars, obtain the environmental parameters of the gob-side roadway, determine the type of mechanical model to which the gob-side roadway with small coal pillars belongs, and calculate the support load of rock blocks and coal walls;

[0011] Step S4: inputting the environmental parameters of the gob-side tunnel and the loads imposed on the immediate roof by the coal wall and coal pillar into the corresponding mechanical model, and calculating the mathematical relationship between the maximum deflection of the immediate roof and the supporting load of the small coal pillar;

[0012] Step S5: obtaining multiple groups of initial complete rock samples of the roof of the gob-side tunnel and initial complete coal samples of the side tunnel of the small coal pillar, making consolidation samples of grouting reinforcement materials, conducting a loading test and obtaining the corresponding mechanical properties and related parameters; and conducting a secondary loading test on the post-destruction grouting coupling reinforcement test body using an orthogonal test method;

[0013] Step S6: Obtain test results to obtain the grouting reinforcement materials, grouting reinforcement material consolidation time and grouting reinforcement material injection rate in the optimal small coal pillar grouting reinforcement scheme;

[0014] Step S7: using FLAC3D corresponding to the numerical model of grouting reinforcement of small coal pillars in gob-side tunnels, calculating and simulating the deformation data of surrounding rock in gob-side tunnels without grouting, and making statistics;

[0015] Step S8: using simulated annealing algorithm to obtain the optimal grouting layout scheme, obtain the grouting hole positions and determine the row spacing between grouting holes, calculate and count the deformation data of the surrounding rock of the gob-side tunnel after simulated grouting reinforcement;

[0016] Step S9: Analyze the stress, strain and plastic zone development and evolution characteristics of the gob-side tunnel and small coal pillars before and after grouting to determine the optimal grouting reinforcement scheme.

[0017] Preferably, the four mechanical models are established based on the position of the basic top fracture line and the relative position between the roadway and the solid coal wall. The four mechanical models include the basic top fracture line located on the inner side of the solid coal wall, the basic top fracture line located above the roadway, the basic top fracture line located above or outside the small coal pillar and the basic top does not constitute a structure.

[0018] Preferably, the environmental parameters include the length of the immediate roof hanging roof, the thickness of the immediate roof, the elastic modulus E of the immediate roof, the buried depth of the gob-side tunnel, the width of the gob-side tunnel, the length of the small coal pillar and the length of the coal wall.

[0019] Preferably, the secondary loading test on the post-destruction grouting coupled reinforcement test body using the orthogonal test method comprises the following steps: determining three key factors, grouting reinforcement material, consolidation time and grouting amount, as relevant parameters of the selected key factors.

[0020] Preferably, step S5 comprises the following steps:

[0021] Multiple groups of grouting reinforcement material consolidation specimens were made, and multiple primary loading tests were carried out on multiple groups of initial intact rock samples of gob-side tunnel roofs, initial intact coal samples of small coal pillar side tunnels, and grouting reinforcement material consolidation specimens according to the small coal pillar support load conditions. For each group of broken rock samples and damaged coal samples after uniaxial compression, the corresponding grouting reinforcement materials were used to couple different consolidation times to obtain the post-peak broken rock sample coupled grouting reinforcement test bodies and the post-peak broken coal sample coupled grouting reinforcement test bodies after primary loading. The relevant parameters were adjusted according to the orthogonal test table, and secondary loading tests were carried out respectively.

[0022] Preferably, the orthogonal test is arranged as 9 tests, including three factors and four parameters for each factor. The generated orthogonal test table has 9 rows and 3 columns, each row is a test, each column is a different factor, and each test takes different parameters for each factor.

[0023] Preferably, the step S8 comprises the following steps:

[0024] Step S81: Select the spacing layout parameter between grouting as the design variable, set the objective function value as the total deformation of the upper section working face after mining, randomly obtain a spacing layout parameter between grouting as the initial solution T0, and simulate to obtain the initial objective function F(T0);

[0025] Step S82: generating a new grouting spacing layout parameter Tk+1 in the neighborhood of the current grouting spacing layout parameter Tk;

[0026] Step S83: Evaluate the grouting reinforcement effect of the new grouting spacing arrangement parameter Tk+1 and calculate the new objective function value F(Tk+1);

[0027] Step S84: accepting the new grouting spacing layout parameter Tk+1 according to the Metropolis criterion;

[0028] Step S85: according to the exponential cooling strategy, i.e., reducing in the order of Tk+2=α*Tk+1, where α is the cooling coefficient, and 0<α<1, k is the number of iterations, and k>1;

[0029] Step S86: Repeat steps S82 to S85 until k reaches the set number of iterations.

[0030] Preferably, the step S83 comprises the following steps:

[0031] The obtained optimal grouting reinforcement material and its corresponding optimal consolidation time and grouting injection rate, and the obtained new grouting spacing layout parameters are input into the established grouting reinforcement numerical model, and the deformation data statistics of the surrounding rock of the goaf tunnel after grouting are obtained. Without changing other parameters, the strength of the goaf tunnel before and after grouting is compared with the deformation data statistics of the surrounding rock of the goaf tunnel before grouting, so as to evaluate the strength recovery effect of the goaf tunnel.

[0032] Preferably, the set probability P=exp(-Δf / Tk), the current grouting spacing layout parameter objective function value is F(Tk), and Δf is the difference between the new grouting spacing layout parameter F(Tk+1) and the current grouting spacing layout parameter objective function value F(Tk).

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention provides a method for controlling the stability of surrounding rock in gob-side tunnels with small coal pillars, analyzes and establishes a direct roof mechanical model of gob-side tunnels with small coal pillars, studies the intrinsic factors of instability and deformation of surrounding rock in gob-side tunnels with small coal pillars, and uses FLAC3D to establish a numerical model for grouting reinforcement of small coal pillars in gob-side tunnels. Based on the coupled reinforcement strength characteristics of crushed surrounding rock obtained after coupling of rock samples, coal samples, grouting reinforcement materials and their crushing, the optimal grouting reinforcement scheme is determined, and the control effect is evaluated using the stress, strain and plastic zone changes of the surrounding rock as evaluation indicators. Finally, the deformation control of surrounding rock in gob-side tunnels with small and medium coal pillars in western mining areas and the optimization of grouting reinforcement parameters are obtained, which has positive social and economic benefits and great technical significance for safe and efficient coal mining.

[0035] The present invention provides a method for controlling the stability of surrounding rock in gob-side tunnels with small coal pillars. The method determines the relevant mechanical properties of the field geology through a test of the coupled reinforcement strength characteristics of the broken surrounding rock, and uses conventional support materials in the test to determine the optimal grouting reinforcement material and grouting reinforcement time, thereby reducing the waste of grouting reinforcement materials and saving support costs. The method can also optimize the support and grouting reinforcement parameters according to the actual geological conditions of the engineering site, thereby realizing the practical application of one policy for each mine.

[0036] The present invention provides a method for controlling the stability of surrounding rock in goaf-side tunnels with small coal pillars. The method uses a simulated annealing algorithm to analyze the stability of surrounding rock in goaf tunnels under the action of grouting reinforcement of small coal pillars with different grouting amounts, scientifically evaluates support and reinforcement parameters, and effectively controls the stability of surrounding rock in goaf-side tunnels with small coal pillars. The method is simple and low-cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic flow chart of a method for controlling surrounding rock stability in a roadway along a small coal pillar according to an embodiment of the present invention;

[0038] Figure 2 It is a schematic diagram of the consolidation uniaxial compression test process of rock samples, coal samples and different grouting reinforcement materials according to an embodiment of the present invention;

[0039] Figure 3 This is a schematic diagram of the overlying rock strata structure of a small coal pillar gob-side roadway according to an embodiment of the present invention;

[0040] Figure 4 It is a schematic diagram of the direct roof mechanical model of a small coal pillar gob-side roadway according to an embodiment of the present invention;

[0041] Figure 5 This is a schematic diagram of the structure of a numerical calculation model for grouting reinforcement of small coal pillars in gob-side tunnels according to an embodiment of the present invention;

[0042] Figure 6 This is a cross-sectional view of the return air lane support of an embodiment of the present invention;

[0043] Figure 7 This is a plan view of the support of the return airway according to an embodiment of the present invention;

[0044] Figure 8 A schematic cross-sectional view of the grouting scheme arrangement according to an embodiment of the present invention;

[0045] Fig. 9 It is a schematic plan view of the grouting scheme arrangement according to an embodiment of the present invention;

[0046] Fig.10 This is a schematic diagram of the anchor cable structure according to an embodiment of the present invention;

[0047] Fig.11 This is a relationship diagram between the maximum value of the direct roof deflection and the small coal pillar support load according to an embodiment of the present invention. DETAILED DESCRIPTION

[0048] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] In the following description of the invention, it should be noted that the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating directions or positional relationships, are based on directions or positional relationships shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific direction or be constructed and operated in a specific direction. The term "connection" only indicates the connection between devices and has no special meaning.

[0050] In addition, the technical fields and installation methods involved in the embodiments of the present invention described below can be combined with each other as long as there is no conflict between them.

[0051] Specific implementation: Please refer to Figure 1 and Figure 2 A method for controlling the stability of surrounding rock in a roadway along a small coal pillar includes the following steps:

[0052] Step S1: Four types of fracture structures are divided according to the positions of the fracture lines between the basic roof rock blocks, and four types of direct roof mechanical models of small coal pillar gob-side tunnels are established accordingly.

[0053] Specifically, Figure 3 As shown in the figure, according to the basic roof, roadway, coal wall C, small coal pillar D and the position of the basic roof fault line, it is divided into four types of fracture structures. After the basic roof is broken, rock blocks A and rock blocks B are formed on both sides. The overlying rock stratum structure model of the small coal pillar along the goaf roadway is established, corresponding to Figure 3 In the four mechanical models (a), (b), (c) and (d), the lengths of rock block A, rock block B, coal wall C and small coal pillar D are represented by l A , l B , l C With l D , the width of the gob-side tunnel is represented as l, and the length of the direct roof under study is represented as L.

[0054] Specifically, Figure 3 In (a), l A ≤l C , indicating that the basic top fracture line is located inside the solid coal wall C; in (b), l C <l A ≤l+l C , indicating that the basic top fracture line is located above the roadway; in (c), l+l C <l A <L, indicating that the basic top fracture line is located above or outside the small coal pillar; in (d), l A ≥L, indicating that the basic top is not sufficient to form a structure.

[0055] Step S2: According to the four mechanical models, the correlation between the shear force of the direct top, the bending moment of the direct top and the deflection of the direct top is calculated respectively through the static equilibrium condition of the direct top.

[0056] Among them, according to the force relationship between the direct roof, coal wall C, small coal pillar D and basic roof, the direct roof mechanical model is constructed as follows: Figure 4 As shown, q A ,q B (x), q C With q D (x) represents the loads applied to the immediate roof by rock block A, rock block B, coal wall C and small coal pillar D respectively. The deformation amounts of rock block B and small coal pillar at different positions are different. According to Hooke's law, the loads applied by rock block B and small coal pillar are uneven. They are expressed as functions about the horizontal axis x respectively.

[0057] Specifically, the static equilibrium conditions of the direct roof are used to calculate the parameter expressions of the shear force, bending moment and deflection of the direct roof, so as to judge the stability of the direct roof of the small coal pillar along the gob:

[0058] (1) When the mechanical model is that the basic top fracture line is located inside the solid coal wall, the deflection of the gob-side tunnel and the small coal pillar roof satisfies the following relationship respectively.

[0059]

[0060] Where E represents the elastic modulus, I represents the interface moment of inertia, and ω represents the deflection.

[0061] (2) When the mechanical model is that the basic top fracture line is located above the roadway, the deflection of the roadway along the gob and the small coal pillar roof satisfies the following relationship respectively

[0062]

[0063] (3) When the mechanical model is that the basic roof fracture line is located above or outside the small coal pillar, the deflection of the gob-side tunnel and the roof of the small coal pillar satisfies the following relationship respectively.

[0064]

[0065] (4) The mechanical model is that the basic roof does not constitute a structure, and the deflection of the gob-side tunnel and the small coal pillar roof satisfies the following relationship respectively

[0066]

[0067] Step S3: Use borehole optical photography and roof separation monitoring methods to monitor the surrounding rock of the small coal pillar roadway along the goaf, obtain the environmental parameters of the roadway along the goaf, determine the type of mechanical model of the small coal pillar roadway along the goaf, and calculate the support load of the rock block and coal wall.

[0068] Specifically, the borehole optical camera method is used to observe the tunnel surrounding rock to obtain geological information such as deformation and cracks of the tunnel surrounding rock. The roof delamination monitoring method is used to monitor the delamination of the tunnel roof in real time to obtain the environmental parameters of the tunnel along the goaf; the environmental parameters include the buried depth of the tunnel along the goaf, the width of the tunnel along the goaf l, the length of the direct roof hanging top, the thickness of the direct roof, the elastic modulus E of the direct roof, the length l of the rock block A A , length of rock block B l B , Coal wall C length l C , small coal pillar D length l D The length of the direct roof hanging roof refers to the length of the small coal pillar D protruding from the direct roof extending to the goaf, which is determined by the width of the goaf roadway l, the length of the coal wall C l C , small coal pillar D length l D The length of the direct roof L is obtained by summing the length of the direct roof and the length of the suspended roof of the direct roof. According to the environmental parameters and the basic roof length, the type of mechanical model of the small coal pillar gob-side roadway can be determined. Combined with the roadway surrounding rock stress monitoring data, the stress distribution of the roadway surrounding rock is analyzed. According to the roadway support structure load monitoring data and the roadway surrounding rock stress monitoring data, the load q applied by the rock block A and the coal wall C to the direct roof is calculated. A ,q D .

[0069] Step S4: Input the environmental parameters of the gob-side tunnel and the loads applied by rock blocks and coal walls to the immediate roof into the corresponding mechanical model, and calculate the mathematical relationship between the maximum deflection of the immediate roof and the supporting load of the small coal pillar.

[0070] This embodiment takes the roof rock structure where the basic roof does not constitute a structure as an example and calculates the load q acting on the direct roof by the small coal pillar D (x) is considered as a uniformly distributed load q D :

[0071] At this time, the static condition for the stability of the roof is

[0072] F Oy +q C l C +q D l D -q A L=0

[0073]

[0074] Among them, F Oy With M O They respectively represent the vertical force and bending moment borne by the coal wall C.

[0075] available

[0076] F Oy =q A Lq Cl C -q D l D

[0077]

[0078] At this time, when 0<x≤l C When the direct top deflection satisfies

[0079]

[0080] From the initial condition of the cantilever beam

[0081]

[0082] ω x＝0 =0

[0083] It can be obtained that E1=0, F1=0.

[0084] Through the above calculation, we can get

[0085]

[0086] At this time, we can obtain x = l C The rotation angle and deflection at

[0087]

[0088] At this time when l C <x≤l+l C When the deflection of the top of the roadway meets

[0089]

[0090] When x = l C When

[0091]

[0092] From this we can get

[0093]

[0094] From this, the relationship between the rotation angle and deflection of the roof deformation of the small coal pillar along the goaf can be obtained:

[0095]

[0096] make Then there exists x=x0(0<x0≤l C ), so that If the direct top deflection satisfies

[0097] ω max =ωx＝x0

[0098] Since E, I, x0, q A ,q C , l A , l B , l C , l D , l and L are constants, so we can get

[0099]

[0100] At this time, the maximum value of the direct roof deflection and the small coal pillar support load q can be obtained D The following relationship is satisfied

[0101] ω max =aq D +b (a, b are both constants)

[0102] in

[0103]

[0104] According to the geological conditions of the example mine, the thickness of the immediate roof is H = 17.01m, the elastic modulus is E = 4.61GPa, and when the basic roof does not constitute a structure, l A =L, take l C =10m, tunnel width l = 5.4m, small coal pillar l D =6.0m; Assuming that the direct roof on the goaf side is 5m long, the length of the direct roof studied is L = l + l C +l D +5=26.4m, the tunnel depth is 309.4m, then q A ≈q C =7.5MPa, so the moment of inertia is obtained 10m<x0≤15.4m; Substituting the data, we can get a<0, b>0, so we can get a linear function of the maximum subsidence of the direct roof and the supporting force of the small coal pillar, which is monotonically decreasing, as follows: Fig.11 As shown in the figure, the deformation of the direct roof is closely related to the supporting strength of the small coal pillar. Therefore, grouting reinforcement measures can be taken to restore and improve the strength of the broken small coal pillar.

[0105] Specifically, the relationship between the maximum value of the direct roof deflection and the small coal pillar support load is shown in Fig.11 , where the maximum deflection corresponding to the maximum sinking critical value of the safe production roof is ω3, and the corresponding small coal pillar support load is q D2 ,q D4 is the supporting load of the small coal pillar before crushing, and the corresponding maximum deflection of the roof is ω1; q D1 is the supporting load of the coal pillar after crushing, and the corresponding maximum deflection of the roof is ω4; qD3 The supporting load after grouting reinforcement of the broken small coal pillar corresponds to the maximum deflection of the roof of ω2.

[0106] Furthermore, the critical value of the maximum subsidence of the roof for safe production needs to be determined in combination with the actual engineering situation and the relevant data obtained in step S3.

[0107] When the upper section working face is mined to form a goaf, the internal structure of the small coal pillar is destroyed and its supporting performance is changed from q D4 Reduce to q D1 , the corresponding maximum roof deformation increases from ω1 to ω4. At this time, the roof deformation seriously exceeds the critical value of the maximum roof deformation for safe production, that is, the maximum value allowed for roof separation within the safety range. Therefore, the strength of the coal pillar must be improved. Generally, grouting reinforcement measures are taken to restore the strength of the broken small coal pillars. After grouting reinforcement, the supporting load of the coal pillar after strength recovery is q D1 Increase to q D3 , where q D2 <q D3 <q D4 The maximum deflection of the roof is also reduced from ω4 to ω2, and its deformation is less than the maximum deformation of the surrounding rock for safe production, meeting the normal production requirements.

[0108] The obtained relevant parameters are respectively substituted into the corresponding formulas of the mechanical model of the goaf-side tunnel obtained in step S3, and the mathematical relationship between the maximum value of the direct roof deflection and the small coal pillar support load is calculated, and the maximum deflection of the corresponding roof after the broken small coal pillar is grouting reinforced and the small coal pillar support force data are obtained, so that the strength and stability of the small coal pillar after the broken grouting reinforcement, and the maximum deflection of the corresponding roof of the small coal pillar after the broken grouting reinforcement are lower than the maximum deflection of the roof corresponding to the maximum sinking critical value of the safe production roof, so as to meet the safety production needs.

[0109] Step S5: Obtain multiple groups of initial complete rock samples of the roof of the gob-side tunnel and initial complete coal samples of the side tunnel of the small coal pillar, make consolidation samples of grouting reinforcement materials, conduct a loading test and obtain their corresponding mechanical properties and related parameters; use the orthogonal test method to conduct a secondary loading test on the post-destruction grouting coupling reinforcement test body.

[0110] Specifically, rock samples of the roof of the gob-side tunnel and coal samples of small coal pillars are collected on-site, and multiple rock sample test bodies and coal sample test bodies are made. The compressive load is adjusted according to the obtained small coal pillar support load conditions. A loading test is carried out on the multiple rock sample test bodies and coal sample test bodies respectively to obtain the mechanical properties and related parameters of the rock and coal samples.

[0111] Among them, the setting of the compressive load can be carried out by combining gradual load change with setting the maximum load. First, a gradually changing load is used to observe the deformation process of the rock sample or coal sample or grouting reinforcement material consolidation sample, and then the load is maintained for a period of time after reaching the preset maximum load to observe the damage of the rock sample or coal sample or grouting reinforcement material consolidation sample. This method can more comprehensively understand the mechanical properties of coal samples, and determine key mechanical parameters such as compressive strength of rock samples or coal samples or grouting reinforcement material consolidation samples; the mechanical properties and related parameters of rock samples, coal samples and various grouting reinforcement material consolidation test bodies include compressive strength, elastic modulus, Poisson's ratio, strain and deformation, etc.

[0112] Furthermore, cement slurry grouting reinforcement materials that are commonly used in mine tunnel surrounding rock grouting reinforcement projects in the prior art are selected, and the grouting reinforcement material consolidation samples are mixed according to a water-cement ratio of 1:2, and additives are added at 8% of the material to obtain a variety of grouting reinforcement material consolidation test bodies. The compressive load is adjusted to make it the same as the above test, and a loading test is carried out to obtain the mechanical properties and related parameters of the various grouting reinforcement material consolidation test bodies.

[0113] For each group of broken rock samples and damaged coal samples after the first loading test, the corresponding grouting reinforcement materials were used for coupling with different consolidation times to obtain the coupled grouting reinforcement test bodies of the broken rock samples after the peak and the broken coal samples after the peak after the first loading. Secondary loading tests were carried out according to the supporting load conditions of the small coal pillars.

[0114] Specifically, broken rock samples and broken coal samples are collected after a primary loading test, and cemented with different grouting reinforcement materials respectively, and multiple post-peak broken rock sample coupled grouting reinforcement test bodies and multiple post-peak broken coal sample coupled grouting reinforcement test bodies are prepared at different consolidation times; the obtained post-peak broken rock sample coupled grouting reinforcement test bodies and post-peak broken coal sample coupled grouting reinforcement test bodies are subjected to a secondary loading test, and both the primary loading test and the secondary loading test are uniaxial compression tests.

[0115] Furthermore, this embodiment adopts the orthogonal test design method to conduct the secondary loading test, and by selecting some representative points for the test, the number of tests is greatly reduced, and the required test materials and time costs are reduced. At the same time, it can clarify the influence of various factors on the test results, and provide a basis for optimizing the test conditions.

[0116] At least three factors are selected as key factors from the factors that affect the compressive strength of the grouting coupling test body. In this embodiment, three key factors are selected, namely, grouting reinforcement material, coupling material consolidation time and grouting injection rate.

[0117] Parameters are set for the selected key factors, and an orthogonal experimental table is generated according to the selected factors and their parameters. Each key factor takes n values, and the orthogonal test scheme is determined according to the three key factors and the n values ​​of each factor. In this embodiment, n is 4, and 9 groups of orthogonal test schemes are determined; a secondary loading test is carried out based on the test parameters corresponding to the orthogonal test scheme to obtain the corresponding mechanical properties and related parameters under different parameter combinations, and the primary and secondary order of each factor affecting the compressive strength is determined according to the test results, and the optimal solution for grouting reinforcement to improve the compressive strength of small coal pillars is designed.

[0118] Among them, grouting reinforcement materials include high-performance cement-based grouting materials, ordinary cement grouting materials, fly ash cement grouting materials and silicate cement grouting materials. The consolidation time of coupling materials is set to 3 days, 7 days, 14 days and 28 days respectively, and the injection rates are selected as 20%, 25%, 30% and 35% respectively.

[0119] Step S6: Obtain test results to obtain the grouting reinforcement materials, grouting reinforcement material consolidation time and grouting reinforcement material injection rate in the optimal small coal pillar grouting reinforcement scheme.

[0120] Step S7: using FLAC3D corresponding to the numerical model of small coal pillar grouting reinforcement in gob-side tunnels, calculate and simulate the deformation data of surrounding rock in gob-side tunnels without grouting and make statistics.

[0121] Specifically, the FLAC 3D A numerical model of grouting reinforcement of small coal pillars in gob-side tunnels with a length × width × height = 280m × 60m × 60m was established. The simulated return air tunnel was a coal tunnel with a burial depth of 309.4m. A fixed load of 7.5MPa was applied to the top of the entire model. The upper section of the return air tunnel was the working face being mined, with a 6m protective small coal pillar left in between. According to the grouting reinforcement design plan and the diffusion law of the grouting slurry, a grouting reinforcement area was established on the side of the small coal pillar tunnel. The specific numerical calculation simulation is as follows: Figure 5 shown.

[0122] In the above tunnel model, support reinforcement is set up. The support scheme is shown in Figure 6 and Figure 7 , computational simulation is carried out without grouting to obtain the stress, strain and plastic zone development and evolution characteristics of the empty tunnel and small coal pillar at the grouting front.

[0123] Step S8: Use simulated annealing algorithm to obtain the optimal grouting layout plan, obtain the grouting hole position and determine the row spacing between grouting holes, calculate and count the deformation data of the surrounding rock of the gob-side tunnel after simulated grouting reinforcement.

[0124] Step S81: select the grouting spacing arrangement parameter that affects the stress and deformation of the small coal pillar as the design variable, set the objective function value as the total deformation after the upper section working face is mined, randomly obtain a grouting spacing arrangement parameter as the initial solution T0, and simulate to obtain the initial objective function F(T0);

[0125] Furthermore, the diffusion radius of the grouting hole can be preliminarily determined based on the crushing of the small coal pillar and relevant grouting experience, usually ranging from 1 to 3 meters; according to the process requirements of the grouting reinforcement materials and the actual situation, the constraint conditions and objective function values ​​for optimizing the grouting reinforcement effect are determined;

[0126] Specifically, a solution is randomly generated as the current grouting spacing layout parameter. In this embodiment, the cooling strategy can be set to use exponential cooling, which can usually be expressed as T k+1 =α*T k , where α is the temperature drop coefficient, and 0<α<1, T is the current temperature, k is the number of iterations, and k>1; the objective function value is set to the total deformation after mining of the upper section working face, and the algorithm termination condition k is set to reach the set number of iterations, etc.; a larger grouting spacing layout parameter is randomly obtained as the initial solution T0, and the initial objective function value F(T0) is simulated to obtain.

[0127] Step S82: Setting the spacing parameter T in the current grouting room k A new grouting spacing layout parameter T is generated in the neighborhood of k+1 ;

[0128] Step S83: Setting the parameters T for the new grouting spacing k+1 Evaluate the grouting reinforcement effect and calculate the new objective function value F(T k+1 );

[0129] The optimal grouting reinforcement material and its corresponding optimal consolidation time and grouting reinforcement material injection rate obtained in step S6 are used to obtain the new grouting spacing layout parameter T k+1 Input the grouting reinforcement numerical model established in step S7, without changing other parameters, obtain the deformation statistics of the surrounding rock of the tunnel along the goaf after grouting, and compare the strength of the tunnel along the goaf before and after grouting with the deformation statistics of the surrounding rock of the tunnel along the goaf obtained in step S7 to evaluate the strength recovery effect of the tunnel along the goaf.

[0130] Step S84: According to the Metropolis criterion, accept the new grouting spacing layout parameter T k+1 ;

[0131] If the new objective function value F(T k+1 ) is less than the current objective function value F(T k ), then directly accept the new grouting spacing layout parameter T k+1; If the new objective function value F(T k+1 ) is greater than the current objective function value F(T k ), then the new grouting spacing layout parameter T is accepted with the set probability P k+1 ;

[0132] Where P = exp(-Δf / T), Δf is the new objective function value F(T k+1 ) and the current objective function value F(T k ) difference.

[0133] Step S85: According to the cooling strategy, T k+2 =α*T k+1 The order continues to decrease.

[0134] Step S86: Repeat steps S82 to S85 until k reaches the set number of iterations.

[0135] After the algorithm terminates, the optimal solution obtained is the optimal grouting spacing layout parameters.

[0136] Step S9: Analyze the stress, strain and plastic zone development and evolution characteristics of the gob-side tunnel and small coal pillars before and after grouting to determine the optimal grouting reinforcement scheme.

[0137] This embodiment discloses one group of simulation test results (see Table 1) to illustrate that grouting reinforcement improves the strength of the goaf-side tunnel. In the simulation comparison verification of this group of slurries, the deformation data analysis of the tunnel surrounding rock before and after grouting reinforcement shows that grouting reinforcement reduces the plastic zone of the tunnel to 1.2m, and an elastic zone of 2.00 to 3.00m appears in the center of the entire small coal pillar; the reinforced support effect makes the stress values ​​of the two sides of the support body approach continuously, making the stress distribution of the tunnel surrounding rock more balanced, and grouting reinforcement plays a role in maintaining the stability of the tunnel. It can be verified that the grouting-related parameters obtained by deep learning model simulation have a good effect on coal sample reinforcement.

[0138] Table 1 Statistics of deformation data of tunnel surrounding rock before and after grouting reinforcement

[0139]

[0140]

[0141] Obtain the optimal value of the spacing between grouting holes obtained in step S8, and determine the grouting reinforcement scheme according to the optimal grouting reinforcement material, the consolidation time of the grouting reinforcement material, and the injection rate of the grouting reinforcement material obtained in step S7; the optimal grouting reinforcement scheme disclosed in this embodiment is: the optimal grouting reinforcement material is a high-performance cement-based grouting material, the optimal grouting reinforcement material consolidation time is 14 days, the grouting reinforcement material injection rate is 25%, the grouting hole spacing is 3.0m, the spacing between the bottom row of grouting anchor rods and the middle row of grouting anchor cables is 400mm, and the spacing between the middle row of grouting anchor cables and the top row of grouting anchor cables is 800mm.

[0142] In this embodiment, on the basis of combined support by anchor, net, cable and spraying, a grouting reinforcement process is further performed, wherein the combined support by anchor, net, cable and spraying includes the following steps:

[0143] During tunnel excavation, the full section is used Threaded steel anchor rods, each threaded steel anchor rod is filled with 2 sections of MSK2370 resin rolls, the anchoring force is not less than 190kN (28.5MPa), the pre-tightening torque of the threaded steel anchor rod is not less than 250N·m, the tray specification is 150×150×10mm disc tray, the row spacing is 800×1000mm; 2 single-point anchor cables are set in alternate rows at the top of the tunnel, the specific structure of the anchor cable is shown in Fig.10 , the spacing between two anchor cables is 1600×2000mm; three rows of anchor cable beams are arranged in a "five-flower" pattern, with a spacing of 2000×1600mm; the top anchor cable specifications are Steel strands, each anchor cable is filled with 2.5 sections of MSK2370 resin rolls, the tray specification is 300×300×16mm, the anchor cable beam is made of 11# mining steel with L=2400mm, and the eye distance is 2000mm;

[0144] Two single-point anchor cables are installed in alternate rows on the side of the roadway for mining, and arranged in the same row with the threaded steel anchor rods, with a spacing of 1600×2000mm. Steel strand, each anchor cable is filled with 2 sections of MSK2370 resin anchoring agent, and the lower anchor cable is Steel strands, each anchor cable is filled with 2 sections of MSK3535 resin anchoring agent;

[0145] Three rows of anchor cable beams are set up along the side of the small coal pillar in the tunnel in a "five-flower" step-by-step arrangement. The first and second rows of anchor cables are both Steel strands, each anchor cable is filled with 2 sections of MSK3535 resin anchoring agent; the third row of anchor cables uses 21.8×5500mm steel strands, each anchor cable is filled with 2 sections of MSK2370 resin anchoring agent;

[0146] An oblique single-point anchor cable is installed between every two rows of support in the side shoulder of the small coal pillar in the tunnel. Steel strands, each anchor cable is filled with 2.5 sections of MSK2370 resin anchoring agent, and all anchor cables (except the foot) in the watering section are changed to full anchor shear devices, which include anchors and matching steel strands. Steel pipes, grout plugs, bolts (screw plugs); the anchoring force of the side anchor cable of the full-anchor shear device shall not be less than 200kN (24MPa), and the anchoring force of the top anchor cable shall not be less than 300kN (38MPa).

[0147] During the tunnel excavation process, double-layer meshes are hung at the two shoulder sockets (one layer of diamond mesh and one layer of steel mesh, with the diamond mesh on the inner layer), and the length of the diamond mesh is 2m; a metal mesh made of Φ6.5mm round steel is hung on the entire section of the tunnel, and the steel belt is Φ16×6480×80-800-9 round steel belt; the entire section is hung with a hooked steel mesh welded with Φ6.5mm round steel, length × width: 3000×1000mm, 80mm of exposed hook, mesh specification 100×100mm; the top and side meshes are connected by hooking, and two strands of 14# lead wire are used to connect the network at intervals of 100mm, with no less than three twists; Φ16×6480×80-800-9 round steel belt is used on the top, and threaded steel anchor rods and anchor cables are arranged with the steel belt.

[0148] The floor thickness is 200mm, the concrete strength grade is C25, the shotcrete thickness is 100mm, the concrete strength is C20, and the tunnel ditch is arranged on the left side of the excavation direction. The support structure in this embodiment is the existing technology. The specific support structure is shown in the following figure. Figure 6 and Figure 7 .

[0149] On the basis of the above-mentioned combined support, grouting reinforcement is carried out again. A grouting reinforcement area is established on the side of the small coal pillar roadway. A total of 3 rows of drill holes are arranged on the side of the small coal pillar. The upper row is 5.1m grouting anchor cable holes with a hole depth of 4.8m, 1.6m from the top, 3.0m spacing, 32° elevation, and a hole body of about 1.4m in the roof rock layer to prevent the displacement of the small coal pillar. The lower row is grouting anchor holes, about 0.4m away from the bottom plate, anchored into the bottom plate at a depression angle of 15°, with a spacing of 3.0m. The middle row is 5.1m grouting anchor cables, arranged between the upper row of grouting anchor cables, about 0.8m away from the bottom plate, with an elevation angle of 18° and a spacing of 3.0m. The middle row of grouting anchor cables can be lengthened and combined with the original support body anchoring on the goaf side; its specific grouting reinforcement scheme is as follows: Figure 8 and Fig. 9 shown.

[0150] Among them, grouting anchor construction Drill and install 2 sections of 3535 resin medicine rolls. Wrap the hole mouth with cotton yarn to stop the slurry during installation. Install the tray with the slurry stop plug. Install the 2 sections of rods (2.4m) in front of the grouting anchor hole. Drill holes, construct 032mm holes in the inner section (2.4-4.8m), install a section of 2370 resin roll in each hole, and when constructing the grouting anchor, first insert a 0.7m long 16mm aluminum-plastic tube as the grouting pipe into the grouting anchor hole, and expose 0.2m of the aluminum-plastic tube. Seal the hole with the stirred resin roll, and then install the anchor tray of the grouting anchor. When grouting, install a connector in the aluminum-plastic pipe hole, and connect it to the grouting pipeline through the connector.

[0151] The grouting branch pipes are arranged according to the positions of the reserved grouting holes. Each grouting branch pipe is equipped with a control gate valve. The grouting reinforcement material uses high-performance cement-based grouting material. The grouting order is to grout one by one from bottom to top. The grouting pressure is controlled at 2-4MPa. When the pressure reaches 4MPa, the grouting is continued for 5 minutes at a stable pressure. If the grouting pressure is less than 4MPa (2-4MPa), the grouting time can be adjusted to 5-10min. When local leakage occurs during the grouting process, stop the grouting in time and grout again after 10-15min. After grouting, wait for the slurry to initially solidify, then remove the grouting device and seal the hole in time. The overall grouting reinforcement time is maintained at 14 days, and the injection rate during the grouting process is maintained at 25%.

[0152] The present invention provides a method for controlling the stability of surrounding rock in gob-side tunnels with small coal pillars, analyzes and establishes a direct roof mechanical model of gob-side tunnels with small coal pillars, studies the intrinsic factors of instability and deformation of surrounding rock in gob-side tunnels with small coal pillars, and uses FLAC3D to establish a numerical model for grouting reinforcement of small coal pillars in gob-side tunnels. Based on the coupled reinforcement strength characteristics of crushed surrounding rock obtained after coupling of rock samples, coal samples, grouting reinforcement materials and their crushing, the optimal grouting reinforcement scheme is determined, and the control effect is evaluated using the stress, strain and plastic zone changes of the surrounding rock as evaluation indicators. Finally, the deformation control of surrounding rock in gob-side tunnels with small and medium coal pillars in western mining areas and the optimization of grouting reinforcement parameters are obtained, which has positive social and economic benefits and great technical significance for safe and efficient coal mining.

[0153] The present invention provides a method for controlling the stability of surrounding rock in gob-side tunnels with small coal pillars. The method determines the relevant mechanical properties of the field geology through a test of the coupled reinforcement strength characteristics of the broken surrounding rock, and uses conventional support materials in the test to determine the optimal grouting reinforcement material and grouting reinforcement time, thereby reducing the waste of grouting reinforcement materials and saving support costs. The method can also optimize the support and grouting reinforcement parameters according to the actual geological conditions of the engineering site, thereby realizing the practical application of one policy for each mine.

[0154] The present invention provides a method for controlling the stability of surrounding rock in goaf-side tunnels with small coal pillars. The method uses a simulated annealing algorithm to analyze the stability of surrounding rock in goaf tunnels under the action of grouting reinforcement of small coal pillars with different grouting amounts, scientifically evaluates support and reinforcement parameters, and effectively controls the stability of surrounding rock in goaf-side tunnels with small coal pillars. The method is simple and low-cost.

Claims

1. A method for controlling the stability of surrounding rock in a small coal pillar gob-side roadway, characterized in that: The steps include: Step S1: four types of fracture structures are divided according to the positions of the fracture lines between the basic roof rock blocks, and four types of direct roof mechanical models of small coal pillars along the gob are established accordingly; Step S2: According to the four mechanical models, the correlation between the shear force, bending moment and deflection of the top is calculated respectively through the static equilibrium conditions of the top; Step S3: using the borehole optical camera method and the roof separation monitoring method to monitor the surrounding rock of the gob-side roadway with small coal pillars, obtain the environmental parameters of the gob-side roadway, determine the type of mechanical model to which the gob-side roadway with small coal pillars belongs, and calculate the support load of rock blocks and coal walls; Step S4: inputting the environmental parameters of the gob-side tunnel and the loads applied by the coal wall and coal pillars to the immediate roof into the corresponding mechanical model, and calculating the mathematical relationship between the maximum deflection of the immediate roof and the supporting load of the small coal pillars; Step S5: obtaining multiple groups of initial complete rock samples of the roof of the gob-side tunnel and initial complete coal samples of the side tunnel of the small coal pillar, making consolidation samples of grouting reinforcement materials, conducting a loading test and obtaining the corresponding mechanical properties and related parameters; and conducting a secondary loading test on the post-destruction grouting coupling reinforcement test body using an orthogonal test method; Step S6: Obtain test results to obtain the grouting reinforcement materials, grouting reinforcement material consolidation time and grouting reinforcement material injection rate in the optimal small coal pillar grouting reinforcement scheme; Step S7: using FLAC3D corresponding to the numerical model of grouting reinforcement of small coal pillars in gob-side tunnels, calculating and simulating the deformation data of surrounding rock in gob-side tunnels without grouting, and making statistics; Step S8: using simulated annealing algorithm to obtain the optimal grouting layout scheme, obtain the grouting hole positions and determine the row spacing between grouting holes, calculate and count the deformation data of the surrounding rock of the gob-side tunnel after simulated grouting reinforcement; Step S9: Analyze the stress, strain and plastic zone development and evolution characteristics of the gob-side tunnel and small coal pillars before and after grouting to determine the optimal grouting reinforcement scheme.

2. The method for controlling surrounding rock stability of a small coal pillar gob-side roadway according to claim 1, characterized in that: The four mechanical models are established based on the position of the basic top fracture line and the relative position between the roadway and the solid coal wall. The four mechanical models include the basic top fracture line located on the inner side of the solid coal wall, the basic top fracture line located above the roadway, the basic top fracture line located above or outside the small coal pillar and the basic top does not constitute a structure.

3. The method for controlling the surrounding rock stability of a small coal pillar gob-side roadway according to claim 1, characterized in that: The environmental parameters include the length of the immediate roof hanging roof, the thickness of the immediate roof, the elastic modulus E of the immediate roof, the buried depth of the gob-side tunnel, the width of the gob-side tunnel, the length of the small coal pillar and the length of the coal wall.

4. The method for controlling surrounding rock stability of a small coal pillar gob-side roadway according to claim 1, characterized in that: The secondary loading test of the post-destruction grouting coupling reinforcement test body using the orthogonal test method includes the following steps: determining three key factors, grouting reinforcement material, consolidation time, and grouting amount, as relevant parameters of the selected key factors.

5. The method for controlling the surrounding rock stability of a small coal pillar gob-side roadway according to claim 4 is characterized in that: The step S5 comprises the following steps: Multiple groups of grouting reinforcement material consolidation specimens were made, and multiple primary loading tests were carried out on multiple groups of initial intact rock samples of gob-side tunnel roofs, initial intact coal samples of small coal pillar side tunnels, and grouting reinforcement material consolidation specimens according to the small coal pillar support load conditions. For each group of broken rock samples and damaged coal samples after uniaxial compression, the corresponding grouting reinforcement materials were used to couple different consolidation times to obtain the post-peak broken rock sample coupled grouting reinforcement test bodies and the post-peak broken coal sample coupled grouting reinforcement test bodies after primary loading. The relevant parameters were adjusted according to the orthogonal test table, and secondary loading tests were carried out respectively.

6. A method for controlling surrounding rock stability of a small coal pillar gob-side roadway according to claim 5, characterized in that: The orthogonal test is arranged as 9 tests, including three factors and four parameters for each factor. The generated orthogonal test table has 9 rows and 3 columns, each row is a test, each column is a different factor, and each test takes different parameters for each factor.

7. The method for controlling surrounding rock stability of a small coal pillar gob-side roadway according to claim 1, characterized in that: The step S8 comprises the following steps: Step S81: Select the spacing layout parameter between grouting as the design variable, set the objective function value as the total deformation of the upper section working face after mining, randomly obtain a spacing layout parameter between grouting as the initial solution T0, and simulate to obtain the initial objective function F(T0); Step S82: Setting the spacing parameter T in the current grouting room k The neighborhood generates a new grouting spacing layout parameter T k+1 ; Step S83: Setting the parameters T for the new grouting spacing k+1 Evaluate the grouting reinforcement effect and calculate the new objective function value F(T k+1 ); Step S84: Accept the new grouting spacing layout parameter T according to the Metropolis criterion k+1 ; Step S85: According to the exponential cooling strategy, i.e. T k+2 =α*T k+1 The order of decrease is, where α is the temperature reduction coefficient, and 0<α<1, k is the number of iterations, and k>1; Step S86: Repeat steps S82 to S85 until k reaches the set number of iterations.

8. The method for controlling surrounding rock stability of a small coal pillar gob-side roadway according to claim 1, characterized in that: The step S83 comprises the following steps: The obtained optimal grouting reinforcement material and its corresponding optimal consolidation time and grouting injection rate, and the obtained new grouting spacing layout parameters are input into the established grouting reinforcement numerical model, and the deformation data statistics of the surrounding rock of the goaf tunnel after grouting are obtained. Without changing other parameters, the strength of the goaf tunnel before and after grouting is compared with the deformation data statistics of the surrounding rock of the goaf tunnel before grouting, so as to evaluate the strength recovery effect of the goaf tunnel.

9. The method for controlling the surrounding rock stability of a small coal pillar gob-side roadway according to claim 7, characterized in that: The set probability P = exp(-Δf / T k ), the current grouting spacing layout parameter objective function value is F(T k ), Δf is the new grouting spacing layout parameter F(T k+1 ) and the objective function value F(T k ) difference.

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