A method for supporting gob-side entry with compressible gangue brick wall in coal mines

Abstract

The present invention relates to a method for supporting goaf-retaining lanes along coal mine compressible gangue brick walls. The method starts with goaf-retaining lane technology, proposes a segmented and graded load-bearing principle for goaf-retaining lanes along coal mines, and according to the segmented and graded load-bearing principle, calculates and solves key parameters such as the single compressive strength, compressibility, and pressure borne by the supporting body of the gangue wall, constructs a compressible gangue brick wall support structure based on goaf-retaining lane technology, and proposes a new type of coal mine compressible gangue brick wall support method and preparation system. The application of the present invention can solve the following problems: on the one hand, it solves the problem of deformation of surrounding rock of goaf-retaining lanes caused by unreasonable support design ideas; on the other hand, by constructing a compressible gangue brick wall, the filling body and the surrounding rock are coordinated, so that the wall is stable and has a larger compressibility, while meeting the needs of ventilation, gas prevention and control, etc.

Description

Technical Field

[0001] The invention relates to the technical field of mining, in particular to a method for supporting a gob-side entry with a compressible gangue brick wall in a coal mine. Background Art

[0002] Coal is my country's primary energy source and plays a vital role in its economic and social development. my country's energy resources are characterized by being "rich in coal, poor in oil, and limited in natural gas." This coal-dominated energy consumption structure means that coal is my country's most reliable primary energy source, and therefore holds a crucial position in my country's primary energy structure, a position that will remain unchanged for a long time.

[0003] Gob-side entry-retention technology is a critical technique in coal mining. It was first used in the UK and Germany in the 1960s and introduced in my country in the 1970s. Using gob-side entry-retention for pillarless mining reduces the length and number of tunnels, playing a crucial role in reducing coal loss and improving the recovery and utilization of coal resources.

[0004] In recent years, my country has conducted extensive research and practice on gob-side entry retention technology, achieving considerable success and playing a positive role in practical application. Due to the different materials used for gob-side entry retention, two methods are currently used domestically and internationally: slurry masonry walls and loose waste walling. Currently, these gob-side entry retention technologies primarily include gangue belt entry retention, dense support pillars or wood piles, artificial cement wall placement, gangue bag entry retention, anhydrite fill belt entry retention, high-water-density material side filling, and chemical material filling. In addition, many coal mines are actively exploring other entry retention technologies suitable for their mines, but these also present numerous challenges.

[0005] Furthermore, due to long-term, high-intensity mining, shallow coal reserves are gradually decreasing, and most older mines are shifting to deeper production, leading to increasingly prominent environmental issues. Take coal gangue, for example. Coal mining produces large quantities of this solid waste, which is often discharged to the surface, forming gangue heaps, causing environmental pollution and the potential for geological disasters. While extensive research is underway domestically and internationally on the comprehensive utilization of gangue, due to limitations such as geographic location, gangue characteristics, and technical costs, no gangue utilization technology is currently suitable for large-scale deployment.

[0006] Gangue discharge onto the surface creates gangue heaps, resulting in significant land occupation, environmental damage, and the potential for geological disasters. Currently, the comprehensive utilization of gangue is a hot topic and a challenging issue in academia and engineering. Experts and scholars at home and abroad have conducted a series of studies on the comprehensive utilization of gangue, including applications in power generation, road paving, construction material production, chemical raw material production, agricultural production, and gangue backfill. However, these studies still fall short of meeting the enormous demand for gangue treatment.

[0007] The main problems currently existing in my country's goaf-side tunnel retention are reflected in the following aspects:

[0008] (1) The performance of composite filling materials cannot fully meet the downhole requirements.

[0009] The surrounding rock of gob-side entryways in coal mines is greatly affected by mining activities and is characterized by complex environments, multiple mining events, severe roof deformation, and severe heave caused by coal slab extrusion. The main problems with gob-side entryway technology at present are: first, the support design concept is unreasonable, and the dynamic characteristics of periodic pressure from the working face are not fully considered. The mechanism of rock stratum movement and mine pressure changes in gob-side entryways is unclear, resulting in a mismatch between the pressure and deformation of the entryway support and the roof pressure; second, the slurry wall strength is insufficient, with a small shrinkage capacity, which cannot adapt to the entryway pressure and rock stratum movement patterns; third, the deformation of the loose waste wall is too large, making support difficult. Therefore, the key to the pillarless mining technology of gob-side entryway retention lies in the "expansion, flexibility, and rigidity" properties of the entryway filling material and the "large deformation and high bearing strength" effect of the filling body.

[0010] (2) Gas problems are prominent in some areas, and problems such as sealing and deformation of filling walls cannot be effectively solved.

[0011] Traditional backfilling processes often focus on the "force source," protecting the overburden from the perspective of supporting force, but lack consideration for gas and ventilation issues. The challenge is to achieve the goal of "coordinating the pressure and deformation of the surrounding rock in the entry retaining section with the pressure and deformation of the backfill in the entry retaining section" while simultaneously meeting ventilation requirements such as gas sealing, ultimately achieving safe, economical, and reliable entry retention along the goaf. This requires considering the fundamental requirements of "digesting waste rock" to reduce production costs and environmental protection. Summary of the Invention

[0012] The present invention conducts a thorough investigation on the current status of the generation, treatment and utilization of coal gangue in representative mining areas, analyzes the treatment methods and characteristics of coal gangue in each typical mining area, studies the stress law of the retained lane, adopts advanced technology and materials, and proposes a coal mine goaf-retained lane support method suitable for local environmental conditions to solve existing technical problems.

[0013] To solve the above technical problems, the present invention provides a method for supporting gob-side entry retaining with a compressible gangue brick wall in a coal mine, comprising the following steps:

[0014] Step S1: Based on the bearing principle of gob-side entry retention, in order to ensure that the surrounding rock mine pressure and the backfill pressure in the entry retention section of deep mining gob-side entry retention are consistent with the required deformation and meet the requirements for preventing gas leakage, the gob-side entry retention support structure of the coal mine is divided into two parts: the lower part of the entry retention is the main wall, which is built with waste rock bricks and is used to support the pressure of the roof; the upper part of the entry retention is the auxiliary wall, which is used to release the pressure of the roof rock deformation and prevent gas leakage. The material required for the auxiliary wall should have high compression capacity, good sealing performance, and no cracking.

[0015] Step S2: Since the gangue brick wall only bears the force from the direct top, a pressure-yielding strategy is adopted for the old top, and the pressure of its support body, the deformation of the roadside support, and the reserved deformation are calculated;

[0016] Step S3: Calculate the key parameters of the filling body (gangue wall), including the theoretical single compressive strength, design strength, and compressibility of the filling body;

[0017] Step S4: Design and build the main wall, mainly including the following steps:

[0018] Step S41: establishing key parameters of gangue bricks and making standard gangue brick specimens;

[0019] (1) According to the concrete mix design standard, water, cement, fine aggregate gangue, and coarse aggregate gangue are selected as the raw materials for making gangue bricks, and the material ratio of gangue bricks is determined to be: water: cement: fine aggregate gangue: coarse aggregate gangue = 0.48:1:1.364:3.182 in parts by mass;

[0020] (2) Preparation and curing of standard specimens of gangue bricks; According to the relevant provisions of the Standard Test Methods for Mechanical Properties of Ordinary Concrete, the test mold type and curing days of the standard specimens of gangue bricks in this test are determined:

[0021] A. The specimen is a cube with dimensions of 100mm×10mm×100mm;

[0022] B. Take 225g of water as the benchmark, select the water-cement ratio as 0.45, the ash-gangue ratio as 0.299, and the sand ratio as 0.25, and get water: ash: sand: stone = 1:2.222:1.861:5.583. After calculation, we get: cement is 500g, fine aggregate is 418.75g, and coarse aggregate is 1256.25g;

[0023] C. Weigh the amount of water, cement, fine aggregate and coarse aggregate respectively, mix them and stir them thoroughly;

[0024] D. Evenly apply mineral oil to the inner wall of the test mold, shovel the gangue concrete obtained in step (2) into the test mold, and manually tamp it with a tamping rod;

[0025] E. Since different test ages have a great influence on the strength of gangue bricks, the ages are selected as 4 days, 7 days and 28 days, and the best age is selected according to optimization;

[0026] F. After compaction, the test molds should be placed in an environment with a temperature of 15℃ to 25℃ for 24 hours, then numbered and demolded. After demolding, the test pieces should be placed on the support with a distance of 10 to 20 mm between each other and cured for 28 days.

[0027] (3) Determination of the uniaxial compressive strength of standard specimens of gangue bricks; the uniaxial compressive strength Rc of the specimen refers to the load per unit area when the unconfined specimen is compressed and damaged under longitudinal pressure, which is called the uniaxial compressive strength of the rock, that is, the ratio of the maximum load at the time of specimen failure to the cross-sectional area perpendicular to the loading direction; the standard specimen specification is used, and the size is a regular cube of 100mm×100mm×100mm; the steps for determining the uniaxial compressive strength of the specimen are as follows:

[0028] A. Fill in the test piece dimensions (the test piece diameter should be measured in two mutually perpendicular directions at the middle of its height, and the arithmetic average should be taken) in the record sheet;

[0029] B. Select the press dial: Generally, it should meet the requirement of 0.2P<P max <0.8P,P max ——Expected maximum breaking load, unit: KN;

[0030] C, P——maximum value of press dial, unit: KN;

[0031] D. Start the press and make it in a usable state. Place the specimen in the center of the pressure plate of the press. Adjust the spherical seat so that the specimen is evenly stressed from top to bottom. Load at a speed of 0.5-1.0 MPa / s until failure.

[0032] E. Calculate the compressive strength R of the specimen USC :R USC =P / F;

[0033] Where: R USC ——specimen compressive strength, unit: MPa; P——specimen failure load, unit: N; F——specimen area, unit: mm 2 ;

[0034] Step S42: using gangue bricks to build walls;

[0035] Step S5: secondary wall parameter design and material selection;

[0036] Calculation of the height Δh of the auxiliary wall: Based on the positional relationship between the direct roof, the old roof, and the auxiliary wall, the following can be obtained from the similarity of triangles: Where SA —The settlement of the uncollapsed rock layer at the point of contact with the gangue, S A The range is 0.1h~0.5h, and the general stope is S A The range is 0.25h~0.3h, h is the mining height, unit: m; C is the movement step, unit: m; L b ——top control distance, unit: m;

[0037] The filling material of the auxiliary wall is yellow mud, loose gangue or chemical foaming material;

[0038] Step S6: For the construction process of the "main wall + auxiliary wall" in the filling process, carry out filling operation steps in stages and areas; specifically, stage by stage (zoning and grading) means that the filling body plays different roles according to the law of mine pressure, fully considering the filling process and construction reality, and zoning construction processing according to the auxiliary wall construction area, auxiliary wall construction area, and load-bearing detection area; graded filling means performing different filling operations at different stages or times, such as the filling body pressure stage (all filling work has been completed), the auxiliary wall construction stage (the roof sinks and gradually collapses, but has not yet been connected to the top), and the main wall construction stage (the working face is mined, the old roof is still in a stable state, and the main wall is built as it is mined). At the same time, it is necessary to organize the labor organization such as the cooperation of personnel in each link, and comply with relevant safety management regulations;

[0039] Step S7: Design of on-site test scheme and effect evaluation. Research is conducted on the mine pressure in gob-side entry-retaining tunnels and the patterns of rock movement during mining. Combined with the principle of segmented and graded bearing capacity, this provides a scientific basis for calculating the deformation of the side support and the reserved deformation of the entry-retaining tunnel. This also provides an accurate on-site monitoring basis for more accurate calculation of support pressure, better understanding of the timing of entry-retaining support (the time and critical locations for entry-retaining wall formation and reinforcement support installation), and wall strength design.

[0040] Furthermore, in step S2, the pressure borne by the support body is calculated as follows:

[0041] Where, Q is the weight of the cantilever beam, L is the width of the tunnel, B is the width of the wall, and R is the supporting force of the wall.

[0042] From formula (1), the wall support force can be obtained as:

[0043] Among them, the calculation formula of the cantilever beam weight can be obtained from formula (3): Q = (L + B) × M × r (3), where M is the thickness of the direct top and r is the capacity of the direct top.

[0044] Substituting formula (3) into formula (2), the support body pressure can be obtained as follows:

[0045] Furthermore, in step S2, the calculation method of the deformation amount and the reserved deformation amount of the roadside support is:

[0046] The calculation formula for the deformation of the tunnel side support is: Where, C is the width of the cantilever beam, and D is the overall subsidence of the cantilever beam, i.e., the deformation of the tunnel side support.

[0047] Taking into account the changes in roof pressure and the errors in the theoretical calculation model, for safety reasons, the reserved deformation is increased by 2 times, and the reserved deformation is twice the deformation of the tunnel side support.

[0048] Furthermore, in step S3, the theoretical single compressive strength [D] of the filling body is further calculated by the supporting body pressure formula (4) and the wall width B: [D] = R / B (6). Substituting formula (4) into formula (6), the theoretical single compressive strength calculation formula of the filling body can be obtained as follows:

[0049] Furthermore, in step S3, the compressibility of the filling body Sc is calculated according to formula (8):

[0050]

[0051] Where,

[0052] L0—the distance from the fracture line in the coal wall to the central axis of the filling body width, which is obtained by measurement;

[0053] ΔS is the maximum settlement at the point where the old roof touches the gangue. The calculation formula of ΔS is: ΔS = h1-h2(K-1)(9), where h1 is the thickness of the coal seam; h2 is the height of the immediate roof; K is the expansion coefficient of the gangue falling from the goaf, and the range of K is 1.25-1.35.

[0054] L—Last roof lateral fracture span, L calculation formula is: Where, S is the working face inclination width; d is the periodic pressure step distance;

[0055] Furthermore, in step S5, the filling material of the secondary wall is Remi Sealed No. 3 produced by MINOVA International Materials Company. Remi Sealed No. 3 has the following material characteristics:

[0056] (1) Rapid solidification, with initial setting taking only 3 minutes and reaching a final setting strength of 0.8 MPa in 18 minutes. The solidified foam can withstand the deformation of the rock formation and meet the requirements for maintaining the integrity of the roof rock formation;

[0057] (2) Rapidly develop strength, and the strength is adjustable, adopting a scheme with a final unidirectional compressive strength of 4 MPa;

[0058] (3) Long-distance pumping can reach 300m, and the construction operation is easy to master;

[0059] (4) High expansion rate, able to meet the sealing requirements;

[0060] (5) Scope of application:

[0061] a. General cavity and stent wall filling;

[0062] b. Used for backfilling of supports along goaf and sealing of small coal pillar cracks along goaf, isolating gas in goaf and preventing spontaneous combustion of coal.

[0063] Furthermore, in step S6, according to the principle of segmented and graded bearing, the construction process of the compressible gangue brick wall along the gob retaining lane is as follows:

[0064] (1) Based on the field measured data, the mine pressure law and actual geological conditions are sought to determine the filling stage and timing of the target area. Based on the "segmented and graded" bearing theory, the main wall construction area, auxiliary wall construction area and pressure-bearing area are determined;

[0065] (2) According to the above-mentioned segmentation and classification results, the corresponding filling range and process of the goaf-side tunnel are established according to the timing of the working face advancement. For example, in the first stage, the main wall is built in the main wall construction area, and in the second stage, the auxiliary wall is constructed. The third area is the state when the auxiliary wall is in effect in the previous stage. This process is continuously cycled forward (as the working face advances), and a new main wall construction area is re-established. The original main wall area becomes the auxiliary wall construction area in the next stage, and the original auxiliary wall construction area becomes the pressure-bearing area in the next stage;

[0066] (3) The specific construction process is as follows: cleaning of the foundation of the compressible gangue brick wall, laying of the main wall of the compressible gangue brick wall, and placement of steel bars; when filling the working face with gangue, using a gangue thrower to fill the goaf of the working face; filling of foaming chemical materials including: laying of high-strength fiber bags, filling of foaming chemical materials, and forming of the auxiliary wall; withdrawal of temporary support including: withdrawal of the single temporary support at the rear of the working face after the foaming material solidifies for 1 hour, withdrawal and cleaning of the foaming pipes, etc.; construction of the main and auxiliary walls in the next stage.

[0067] (4) During the entire construction process, corresponding support operations are required. The various supports before the tunnel include: advance anchor beam support, advance support, and temporary single support behind the working face.

[0068] Furthermore, in step S6, the specific construction method of the compressible gangue brick wall mainly includes the following steps:

[0069] (1) During the construction of the tunnel wall, according to the movement of the tunnel surrounding rock and the mine pressure law in the tunnel sections before and after the working face, the structure of the tunnel surrounding rock before and after the working face is divided into three main dynamic pressure stages, namely, the expansion stage of the surrounding rock damage range in front of the working face, the stage of roof fracture behind the working face, and the creep and stability stage after the tunnel side support;

[0070] (2) Analyze the support requirements at each stage in (1) and adopt different auxiliary support methods;

[0071] ① In the stage of expanding surrounding rock damage in front of the working face, advanced reinforced support is adopted. That is, within 20 meters in front of the working face, on the roof of the working face side, a strike anchor beam is installed. The specific parameters are: I-beam length 2.4m, one beam with two cables, anchor cable length 7.5m, diameter 14mm, breaking force 20 tons; the direction is inclined toward the working face, and the angle with the plumb line is 60-70 degrees;

[0072] ② For the roof fracture stage behind the working face, temporary support is adopted in the tunnel-retaining construction section. That is, within 50m behind the working face, a row of single hydraulic pillars are supported on the side of the goaf, with one beam and two pillars, and the pillars are spaced 1m apart. On the inner side of the gangue wall behind the working face, 3-5 single pillars are supported. These pillars are withdrawn and installed in sequence as the working face advances. During this stage, the dynamic pressure of the roof fracture is mainly borne by the single pillars.

[0073] ③ For the creep and stabilization stage after the roadside support, reinforced support after dynamic pressure action is adopted; after the mine pressure observation and confirmation that the rock formation movement is stable, the single hydraulic prop can be withdrawn. The general withdrawal distance is 60-80m from the working face. During this period, the single prop can be repeatedly relieved of small amounts of pressure to allow the gangue wall to slowly bear the load. Due to the great changes in the geological conditions and mining height of the coal seam along the strike, it is necessary to determine when and what kind of reinforced support after dynamic pressure action to be adopted based on the stability of the surrounding rock (determined by mine pressure observation). The auxiliary support parameters are as follows:

[0074] A. Advance reinforced support in front of the working face: an additional 2.4m long anchor beam is driven in front of the working face.

[0075] B. Temporary support for the tunnel construction section: Drive point columns with a spacing of 1m behind the working surface.

[0076] C. Reinforcement support after dynamic pressure action: determined based on mine pressure observation results.

[0077] Furthermore, in step S7, three measuring stations are set up in the gob-side entry retaining section, and pressure measuring points and displacement measuring points are installed in each measuring station. Figure 10As shown; the distance between adjacent measuring stations is 30m. The first measuring station is installed outside the range of the advance support pressure of the working face (thin and medium-thick coal seams are generally 30m in front of the working face), followed by the second and third measuring stations. When the pressure and deformation measuring points are installed, the pressure and displacement measuring points are recorded.

[0078] Furthermore, in step S7, the following contents are monitored:

[0079] (1) Pressure observation: When constructing the wall, the hydraulic pillow is installed in the main wall, and the hydraulic gauge is outside the wall. One hydraulic gauge is placed at each of the two interfaces of the filling body, with a depth of 0.75m. The purpose of observing the contact pressure of the anchor rod is to understand the growth of the anchor rod force with the deformation of the surrounding rock at different stages, so as to provide a basis for evaluating whether the support parameters are reasonable and adjusting the support design.

[0080] (2) Observation of roadway deformation law: In order to obtain the mine pressure law of the roadway retained along the gob and provide a scientific basis for the next step of improving parameters and evaluating the effect of the roadway retained, an observation section is set up every 50m to observe the movement of the roof and floor plates and the movement of the two sides;

[0081] (3) Anchor bolt and cable stress: An observation section is set up every 30m, and anchor bolt and cable stress gauges are installed to observe the stress change pattern of anchor bolts and cables, providing a scientific basis for optimizing the anchor bolt and cable support design;

[0082] (4) Wall stress and deformation: Focus on monitoring the wall deformation and internal stress variation. The deformation is measured with a steel tape measure, and the internal stress of the wall is measured with a hydraulic pillow at a depth of 0.75m.

[0083] (5) Wall sealing performance monitoring: The concentration of gas and CO in the tunnel is monitored to evaluate the sealing performance of the wall.

[0084] The method for supporting goaf-retaining lanes with a compressible gangue brick wall in a coal mine of the present invention makes full use of underground and surface gangue to fill the goaf with gangue and replace stagnant coal. It will effectively solve the problems of ground emission, pollution and land occupation of gangue, and improve the recovery rate of coal resources. It is expected to significantly reduce the output of gangue and improve the comprehensive utilization rate of coal ore, and provide reference and technical support for realizing green mining, comprehensive resource utilization, and ecological environmental protection in mining areas. The supporting structure for goaf-retaining lanes in coal mines and the method for preparing composite filling walls proposed in the present invention are a method for systematically and completely studying composite gangue wall filling goaf-retaining lanes. Compared with the existing technology, the present invention is innovative in improving the recovery rate of coal resources, goaf-retaining lanes technology, and mining technology. It is mainly in the following three aspects:

[0085] (1) The filling mechanism of goaf-side tunnel retention was studied, and a method of goaf-side tunnel retention with compressible gangue brick wall was proposed.

[0086] (2) Propose a “segmented and graded” load-bearing theory to coordinate the mine pressure. Study the deformation and load variation of the backfill in the retained lane under mining conditions, and develop a complete set of “segmented and graded” load-bearing and construction technology for the retained lane along the gob.

[0087] (3) Propose the design, performance analysis, and preparation process of compressible gangue brick walls. Model and calculate the key parameters of the gangue wall (compressive strength, compression, etc.), establish the material selection, design parameters, and construction plan of the main and secondary walls (composite walls), and design a set of composite gangue brick wall production and on-site construction processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] The specific embodiments of the present invention will be further explained below with reference to the accompanying drawings.

[0089] Figure 1 This is the overall flow chart of the system in the present invention.

[0090] Figure 2 Schematic diagram of the lower main wall and upper auxiliary wall of the new type of lane retaining wall in the present invention.

[0091] Figure 3 This is a model diagram for calculating the supporting force of the waste rock retaining roadway wall in the present invention.

[0092] Figure 4 This is a model diagram for calculating the deformation of the tunnel side support in the present invention.

[0093] Figure 5 This is the calculation diagram of the secondary wall height in the present invention.

[0094] Figure 6 This is a schematic diagram of the "segmented and graded" load-bearing and construction of the wall in the present invention.

[0095] Figure 7 This is the advance support diagram of the anchor beam in the present invention.

[0096] Figure 8 This is a temporary support cross-section diagram of the tunnel-retaining construction section in the present invention.

[0097] Figure 9(a) shows the initial installation position of the pressure measuring point (relative position to the working surface).

[0098] Figure 9(b) shows the locations of measuring points during the advancement of the working face.

[0099] Figure 9(c) shows the working surface pushed through all measuring points.

[0100] Figure 10 This is a schematic diagram of the measurement point arrangement in the tunnel retaining section of the present invention. DETAILED DESCRIPTION

[0101] Combine Figure 1The method for supporting gob-side entry retaining with a compressible gangue brick wall in a coal mine of the present invention comprises the following steps:

[0102] Step S1: According to the bearing principle of gob-side entry retention, in order to make the surrounding rock mine pressure and filling body pressure at the entry retention section of deep mining gob-side entry retention adapt to the required deformation and meet the needs of preventing gas leakage, the gob-side entry retention support structure of the coal mine is divided into two parts: the lower part of the entry retention is the main wall, which is made of gangue bricks and is used to support the pressure of the roof; the upper part of the entry retention is the auxiliary wall, which is used to release the pressure of the roof rock deformation and prevent gas leakage. The material required for the auxiliary wall should have the characteristics of high compression, good sealing, and no cracking. The new entry retention wall is as follows: Figure 2 As shown;

[0103] Step S2: Since the gangue brick wall only bears the force from the direct top, a pressure-yielding strategy is adopted for the old top, and the pressure of its support body, the deformation of the roadside support, and the reserved deformation are calculated;

[0104] Step S3: Calculate the key parameters of the filling body (gangue wall), including the theoretical single compressive strength, design strength, and compressibility of the filling body;

[0105] Step S4: Design and build the main wall, mainly including the following steps:

[0106] Step S41: establishing key parameters of gangue bricks and making standard gangue brick specimens;

[0107] (1) According to the concrete mix design standard, water, cement, fine aggregate gangue, and coarse aggregate gangue are selected as the raw materials for making gangue bricks, and the material ratio of gangue bricks is determined to be: water: cement: fine aggregate gangue: coarse aggregate gangue = 0.48:1:1.364:3.182 in parts by mass;

[0108] (2) Preparation and curing of standard specimens of gangue bricks; According to the relevant provisions of the Standard Test Methods for Mechanical Properties of Ordinary Concrete, the test mold type and curing days of the standard specimens of gangue bricks in this test are determined:

[0109] A. The specimen is a cube with dimensions of 100mm×10mm×100mm;

[0110] B. Take 225g of water as the benchmark, select the water-cement ratio as 0.45, the ash-gangue ratio as 0.299, and the sand ratio as 0.25, and get water: ash: sand: stone = 1:2.222:1.861:5.583. After calculation, we get: cement is 500g, fine aggregate is 418.75g, and coarse aggregate is 1256.25g;

[0111] C. Weigh the amount of water, cement, fine aggregate and coarse aggregate respectively, mix them and stir them thoroughly;

[0112] D. Evenly apply mineral oil to the inner wall of the test mold, shovel the gangue concrete obtained in step (2) into the test mold, and manually tamp it with a tamping rod;

[0113] E. Since different test ages have a great influence on the strength of gangue bricks, the ages are selected as 4 days, 7 days and 28 days, and the best age is selected according to optimization;

[0114] F. After compaction, the test molds should be placed in an environment with a temperature of 15℃ to 25℃ for 24 hours, then numbered and demolded. After demolding, the test pieces should be placed on the support with a distance of 10 to 20 mm between each other and cured for 28 days.

[0115] (3) Determination of the uniaxial compressive strength of standard specimens of gangue bricks; the uniaxial compressive strength Rc of the specimen refers to the load per unit area when the unconfined specimen is compressed and damaged under longitudinal pressure, which is called the uniaxial compressive strength of the rock, that is, the ratio of the maximum load at the time of specimen failure to the cross-sectional area perpendicular to the loading direction; the standard specimen specification is used, and the size is a regular cube of 100mm×100mm×100mm; the steps for determining the uniaxial compressive strength of the specimen are as follows:

[0116] A. Fill in the test piece dimensions (the test piece diameter should be measured in two mutually perpendicular directions at the middle of its height, and the arithmetic average should be taken) in the record sheet;

[0117] B. Select the press dial: Generally, it should meet the requirement of 0.2P<P max <0.8P,P max ——Expected maximum breaking load, unit: KN;

[0118] C, P——maximum value of press dial, unit: KN;

[0119] D. Start the press and make it in a usable state. Place the specimen in the center of the pressure plate of the press. Adjust the spherical seat so that the specimen is evenly stressed from top to bottom. Load at a speed of 0.5-1.0 MPa / s until failure.

[0120] E. Calculate the compressive strength R of the specimen: R = P / F;

[0121] Where: R - compressive strength of specimen, MPa; P - failure load of specimen, unit: N; F - area of ​​specimen, unit: mm 2 ;

[0122] Step S42: using gangue bricks to build walls;

[0123] Step S5: secondary wall parameter design and material selection;

[0124] Calculation of the height Δh of the auxiliary wall: Combined Figure 5According to the positional relationship between the direct roof, old roof and auxiliary wall, we can get the following from the similarity of triangles: Where S A —The settlement of the uncollapsed rock layer at the point of contact with the gangue, S A The range is 0.1h~0.5h, and the general stope is S A The range is 0.25h~0.3h, h is the mining height, unit: m; C is the movement step, unit: m; L b ——top control distance, unit: m;

[0125] The filling material of the auxiliary wall is yellow mud, loose gangue or chemical foaming material;

[0126] Step S6: For the construction process of the "main wall + auxiliary wall" in the filling process, carry out filling operation steps in stages and areas; specifically, stage by stage (zoning and grading) means that the filling body plays different roles according to the law of mine pressure, fully considering the filling process and construction reality, and zoning construction processing according to the auxiliary wall construction area, auxiliary wall construction area, and load-bearing detection area; graded filling means performing different filling operations at different stages or times, such as the filling body pressure stage (all filling work has been completed), the auxiliary wall construction stage (the roof sinks and gradually collapses, but has not yet been connected to the top), and the main wall construction stage (the working face is mined, the old roof is still in a stable state, and the main wall is built as it is mined). At the same time, it is necessary to organize the labor organization such as the cooperation of personnel in each link, and comply with relevant safety management regulations;

[0127] Step S7: Design of on-site test scheme and effect evaluation. Research is conducted on the mine pressure in gob-side entry-retaining tunnels and the patterns of rock movement during mining. Combined with the principle of segmented and graded bearing capacity, this provides a scientific basis for calculating the deformation of the side support and the reserved deformation of the entry-retaining tunnel. This also provides an accurate on-site monitoring basis for more accurate calculation of support pressure, better understanding of the timing of entry-retaining support (the time and critical locations for entry-retaining wall formation and reinforcement support installation), and wall strength design.

[0128] In this embodiment, preferably, in step S2, Figure 3 The calculation model shown in the figure, the calculation method of the pressure borne by the support body is:

[0129] Where, Q is the weight of the cantilever beam, L is the width of the tunnel, B is the width of the wall, and R is the supporting force of the wall.

[0130] From formula (1), the wall support force can be obtained as:

[0131] Among them, the calculation formula of the cantilever beam weight can be obtained from formula (3): Q = (L + B) × M × r (3), where M is the thickness of the direct top and r is the capacity of the direct top.

[0132] Substituting formula (3) into formula (2), the support body pressure can be obtained as follows:

[0133] In this embodiment, preferably, in step S2, Figure 4 The calculation model shown in the figure, the calculation method of the roadside support deformation and reserved deformation is:

[0134] The calculation formula for the deformation of the tunnel side support is: Where, C is the width of the cantilever beam, and D is the overall subsidence of the cantilever beam, i.e., the deformation of the tunnel side support.

[0135] Taking into account the changes in roof pressure and the errors in the theoretical calculation model, for safety reasons, the reserved deformation is increased by 2 times, and the reserved deformation is twice the deformation of the tunnel side support.

[0136] In this embodiment, preferably, in step S3, the theoretical single compressive strength [D] of the filling body is further calculated by the supporting body pressure formula (4) and the wall width B: [D] = R / B (6). Substituting formula (4) into formula (6) yields the theoretical single compressive strength calculation formula of the filling body:

[0137] In this embodiment, preferably, in step S3, the compressibility of the filling body S c According to formula (8), we can obtain:

[0138]

[0139] Where,

[0140] L0—the distance from the fracture line in the coal wall to the central axis of the filling body width, which is obtained by measurement;

[0141] ΔS is the maximum settlement at the point where the old roof touches the gangue. The calculation formula of ΔS is: ΔS = h1-h2(K-1)(9), where h1 is the thickness of the coal seam; h2 is the height of the immediate roof; K is the expansion coefficient of the gangue falling from the goaf, and the range of K is 1.25-1.35.

[0142] L—Last roof lateral fracture span, L calculation formula is: Where, S is the working face inclination width; d is the periodic pressure step distance;

[0143] In this embodiment, preferably, in step S5, the filling material of the secondary wall is MINOVA International Materials Company's Remi Sealed No. 3, which has the following material characteristics:

[0144] (1) Rapid solidification, with initial setting taking only 3 minutes and reaching a final setting strength of 0.8 MPa in 18 minutes. The solidified foam can withstand the deformation of the rock formation and meet the requirements for maintaining the integrity of the roof rock formation;

[0145] (2) Rapidly develop strength, and the strength is adjustable, adopting a scheme with a final unidirectional compressive strength of 4 MPa;

[0146] (3) Long-distance pumping can reach 300m, and the construction operation is easy to master;

[0147] (4) High expansion rate, able to meet the sealing requirements;

[0148] (5) Scope of application:

[0149] a. General cavity and stent wall filling;

[0150] b. Used for backfilling of supports along goaf and sealing of small coal pillar cracks along goaf, isolating gas in goaf and preventing spontaneous combustion of coal.

[0151] In this embodiment, preferably, in step S6, Figure 6 According to the principle of segmented and graded bearing, the construction process of compressible gangue brick wall along the goaf is as follows:

[0152] (1) Based on the field measured data, the mine pressure law and actual geological conditions are sought to determine the filling stage and timing of the target area. Based on the "segmented and graded" bearing theory, the main wall construction area, auxiliary wall construction area and pressure-bearing area are determined;

[0153] (2) According to the above-mentioned segmentation and classification results, the corresponding filling range and process of the goaf-side tunnel are established according to the timing of the working face advancement. For example, in the first stage, the main wall is built in the main wall construction area, and in the second stage, the auxiliary wall is constructed. The third area is the state when the auxiliary wall is in effect in the previous stage. This process is continuously cycled forward (as the working face advances), and a new main wall construction area is re-established. The original main wall area becomes the auxiliary wall construction area in the next stage, and the original auxiliary wall construction area becomes the pressure-bearing area in the next stage;

[0154] (3) The specific construction process is as follows: cleaning the foundation of the compressible gangue brick wall, laying the main wall of the compressible gangue brick wall, and placing the steel bars in place; when filling the working face with gangue, using a gangue thrower to fill the goaf of the working face; filling the foaming chemical material, including: laying high-strength fiber bags, filling the foaming chemical material, and forming the auxiliary wall; withdrawing the temporary support, including: withdrawing the single temporary support at the rear of the working face after the foaming material solidifies for 1 hour, withdrawing and cleaning the foaming pipes, etc.; the construction of the main and auxiliary walls in the next stage;

[0155] (4) During the entire construction process, corresponding support operations are required. The various supports before the tunnel include: advance anchor beam support, advance support, and temporary single support behind the working face.

[0156] In this embodiment, preferably, in step S6, the specific construction method of the compressible gangue brick wall mainly includes the following steps:

[0157] (1) During the construction of the tunnel wall, according to the movement of the tunnel surrounding rock and the mine pressure law in the tunnel sections before and after the working face, the structure of the tunnel surrounding rock before and after the working face is divided into three main dynamic pressure stages, namely, the expansion stage of the surrounding rock damage range in front of the working face, the stage of roof fracture behind the working face, and the creep and stability stage after the tunnel side support;

[0158] (2) Analyze the support requirements at each stage in (1) and adopt different auxiliary support methods;

[0159] ① In the stage of expanding the scope of surrounding rock damage in front of the working face, advance reinforcement support is adopted, that is, within 20m in front of the working face, close to the top plate on one side of the working face, a strike anchor beam is installed; the specific parameters are: I-beam length 2.4m, one beam and two cables, anchor cable length 7.5m, diameter 14mm, breaking force 20 tons; the direction is inclined towards the working face, and the angle with the plumb line is 60-70°, such as Figure 7 As shown;

[0160] ② For the roof fracture stage behind the working face, temporary support of the tunnel construction section is adopted, that is, within 50m behind the working face, a row of single hydraulic pillars are supported on the side of the goaf, with one beam and two pillars, and the distance between the pillars is 1m; 3-5 single pillars are supported on the inner side of the gangue wall behind the working face. These pillars are withdrawn and supported in sequence as the working face advances; Figure 8 As shown, the dynamic pressure of the roof fracture at this stage is mainly borne by the single pillar;

[0161] ③ For the creep and stabilization stage after the roadside support, reinforced support after dynamic pressure action is adopted; after the mine pressure observation and confirmation that the rock formation movement is stable, the single hydraulic prop can be withdrawn. The general withdrawal distance is 60-80m from the working face. During this period, the single prop can be repeatedly relieved of small amounts of pressure to allow the gangue wall to slowly bear the load. Due to the great changes in the geological conditions and mining height of the coal seam along the strike, it is necessary to determine when and what kind of reinforced support after dynamic pressure action to be adopted based on the stability of the surrounding rock (determined by mine pressure observation). The auxiliary support parameters are as follows:

[0162] A. Advance reinforced support in front of the working face: an additional 2.4m long anchor beam is driven in front of the working face.

[0163] B. Temporary support for the tunnel construction section: Drive point columns with a spacing of 1m behind the working surface.

[0164] C. Reinforcement support after dynamic pressure action: determined based on mine pressure observation results.

[0165] In this embodiment, preferably, in step S7, three measuring stations are set up in the gob-side entry retaining section, and pressure measuring points and displacement measuring points are installed in each measuring station. Figure 10 As shown in Figure 9(a), the distance between adjacent measuring stations is 30m. The first measuring station is installed outside the range of the advance support pressure of the working face (thin and medium-thick coal seams are generally 30m in front of the working face). The planar schematic diagrams of the pressure and displacement monitoring points in the roadway construction section are shown in Figures 9(a), 9(b) and 9(c). Then the second and third measuring stations are installed. When the pressure and deformation measuring points are installed, the pressure and displacement measuring points are recorded.

[0166] In this embodiment, preferably, in step S7, the following contents are monitored:

[0167] (1) Pressure observation: When constructing the wall, install the hydraulic pillow in the main wall and the hydraulic gauge outside the wall (see Figure 10 ), one is placed at each of the two interfaces of the filling body, with a depth of 0.75m. The purpose of observing the contact pressure of the anchor is to understand the growth of the anchor force at different stages with the deformation of the surrounding rock, so as to provide a basis for evaluating whether the support parameters are reasonable and adjusting the support design;

[0168] (2) Observation of roadway deformation law: In order to obtain the mine pressure law of the roadway retained along the gob and provide a scientific basis for the next step of improving parameters and evaluating the effect of the roadway retained, an observation section is set up every 50m to observe the movement of the roof and floor plates and the movement of the two sides;

[0169] (3) Anchor bolt and cable stress: An observation section is set up every 30m, and anchor bolt and cable stress gauges are installed to observe the stress change pattern of anchor bolts and cables, providing a scientific basis for optimizing the anchor bolt and cable support design;

[0170] (4) Wall stress and deformation: Focus on monitoring the wall deformation and internal stress variation. The deformation is measured with a steel tape measure, and the internal stress of the wall is measured with a hydraulic pillow at a depth of 0.75m.

[0171] (5) Wall sealing performance monitoring: The concentration of gas and CO in the tunnel is monitored to evaluate the sealing performance of the wall.

[0172] Some specific requirements for lane retention process organization are as follows:

[0173] (1) Preparation of compressible gangue brick wall construction materials: including: the required number of gangue bricks, preparation of high-strength fiber bags, preparation of the number of steel bars, the number of single hydraulic supports to be used, steel rulers, tools for cleaning the foundation of the gangue wall, gas monitors, etc.

[0174] (2) Technical parameters of compressible gangue brick wall: including: construction plan and construction drawings of gangue wall, temporary support construction drawings, construction parameters of main and auxiliary walls, operating procedures of chemical foaming materials, regulations for the use of high-strength fiber bags, etc.

[0175] (3) Construction safety technical measures: including ① support requirements: before construction, the roof of the construction area should be guaranteed to be safe and the temporary support should be firm and reliable; ② ventilation requirements: the concentration of harmful gases such as gas in the construction area should be within the range specified in the coal mine safety regulations. ③ wall construction requirements: first, the foundation of the gangue wall should be leveled, and the slope area should be leveled before the wall is constructed; ④ during construction, the gangue brick kiln should use gangue bricks with good integrity, and gangue bricks with cracks or incompleteness should be avoided. ⑤ auxiliary wall construction requirements: ensure that the auxiliary wall is in full contact with the roof rock layer, avoid air leakage in the tunnel section and the goaf, and ensure the sealing of the wall.

[0176] In the above description, many specific details are set forth in order to fully understand the present invention. However, the above description is only a preferred embodiment of the present invention. The present invention can be implemented in many other ways different from those described herein, so the present invention is not limited to the specific implementation disclosed above. At the same time, any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention using the methods and technical contents disclosed above without departing from the scope of the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

Claims

1. A method for supporting gob-side entry with compressible gangue brick wall in coal mines, characterized by: The steps include: Step S1: Based on the load-bearing principle of gob-side entry retention, in order to ensure that the surrounding rock mine pressure and backfill pressure in the entry retention section of deep mining gob-side entry retention are consistent with the required deformation and meet the requirements for preventing gas leakage, the gob-side entry retention support structure of the coal mine is divided into two parts: the lower part of the entry retention is the main wall, built with waste rock bricks, used to support the pressure of the roof; the upper part of the entry retention is the auxiliary wall, used to release the pressure of the roof rock deformation and prevent gas leakage; Step S2: Since the gangue brick wall only bears the force from the direct top, a pressure-yielding strategy is adopted for the old top, and the pressure of its support body, the deformation of the roadside support, and the reserved deformation are calculated; Step S3: Calculate key parameters of the filling body, including theoretical single compressive strength, design strength, and compressibility of the filling body; Step S4: Design and build the main wall, mainly including the following steps: Step S41: establishing key parameters of gangue bricks and making standard gangue brick specimens; Step S42: using gangue bricks to build walls; Step S5: secondary wall parameter design and material selection; Height of secondary wall Calculation: Based on the positional relationship between the direct roof, old roof, and auxiliary wall, the triangle similarity is obtained: (11), where S A —The settlement of the uncollapsed rock layer at the point of contact with the gangue, S A The range is 0.1 h ~ 0.5 h, h is the mining height; C is the movement step; L is the b ——Control top distance; The filling material of the auxiliary wall is yellow mud, loose gangue or chemical foaming material; Step S6: For the construction process of the "main wall + auxiliary wall" filling process, carry out filling operation steps in stages and areas; Step S7: Field test plan design and effect evaluation.

2. The method for supporting gob-side entry retaining with compressible gangue brick wall in coal mines according to claim 1, characterized in that: In step S2, the pressure borne by the support body is calculated as follows: (1), where Q is the weight of the cantilever beam, L is the width of the tunnel, B is the width of the wall, and R is the supporting force of the wall. From formula (1), the wall support force can be obtained as: (2); The calculation formula of the cantilever beam weight can be obtained from formula (3): (3), where M is the thickness of the immediate roof and r is the capacity of the immediate roof; Substituting formula (3) into formula (2), the support body pressure can be obtained as: (4).

3. The method for supporting gob-side entry retaining with compressible gangue brick wall in coal mines according to claim 2, characterized in that: In step S2, the calculation method of the deformation amount and the reserved deformation amount of the roadside support is: The calculation formula for the deformation of the tunnel side support is: (5), where C is the width of the cantilever beam, and D is the overall sinking of the cantilever beam, i.e., the deformation of the tunnel side support. The reserved deformation is twice the deformation of the tunnel side support.

4. The method for supporting gob-side entry retaining with compressible gangue brick wall in coal mines according to claim 2, characterized in that: In step S3, the theoretical single compressive strength of the filling body [ D ] The following is further obtained from the support body pressure formula (4) and the wall width B: (6), substituting formula (4) into formula (6), the theoretical single compressive strength calculation formula of the filling body can be obtained as follows: (7).

5. The method for supporting gob-side entry retaining with compressible gangue brick wall in coal mines according to claim 1, characterized in that: In step S3, the compressibility of the filling body S c According to formula (8), we can obtain: （8）； Where, L 0—the distance from the fracture line in the coal wall to the central axis of the filling body width, which is obtained by measurement; —The maximum settlement at the point where the old roof touches the gangue, The calculation formula is: (9), where h 1—coal seam thickness; h 2—direct top height; K —The expansion coefficient of the gangue falling from the goaf, K, ranges from 1.25 to 1.35; L —Last roof lateral fracture span, L The calculation formula is: (10), where S —Inclination width of working face; d —Cycle to reduce step length.

6. The method for supporting gob-side entry retaining with compressible gangue brick wall in coal mines according to claim 1, characterized in that: In step S5, the filling material of the secondary wall is Remi Sealed No. 3 produced by MINOVA International Materials Company.

7. The method for supporting gob-side entry retaining with compressible gangue brick wall in coal mines according to claim 1, characterized in that: In step S6, according to the principle of segmented and graded bearing, the construction process of compressible gangue brick wall along the gob retaining lane is as follows: (1) Based on the field measured data, the mine pressure law and actual geological conditions are sought, the filling stage and timing of the target area are determined, and based on the "segmented and graded" bearing theory, the main wall construction area, the auxiliary wall construction area and the pressure-bearing area are determined; (2) According to the above-mentioned segmentation and classification results, the corresponding filling range and process of the goaf-side tunnel are established according to the timing of the working face advancement. In the first stage, the main wall is built in the main wall construction area, and in the second stage, the auxiliary wall is constructed. The third area is the state when the auxiliary wall is in effect in the previous stage. This process is continuously cycled forward to re-establish a new main wall construction area. The original main wall area becomes the auxiliary wall construction area in the next stage, and the original auxiliary wall construction area becomes the pressure-bearing area in the next stage. (3) The specific construction process is: cleaning the foundation of the compressible gangue brick wall, laying the main wall of the compressible gangue brick wall, and putting the steel bars in place; when filling the working face with gangue, use a gangue thrower to fill the goaf of the working face; Filling of foaming chemical materials includes: laying of high-strength fiber bags, filling of foaming chemical materials, and forming of auxiliary walls; withdrawal of temporary supports includes: withdrawal of single temporary supports behind the working surface after the foaming materials solidify, withdrawal and cleaning of foaming pipes, etc.; construction of the main and auxiliary walls in the next stage; (4) During the entire construction process, corresponding support operations are required. Various types of support before the tunnel are included: advance anchor beam support, advance support, and temporary single support behind the working face.

8. The method for supporting gob-side entry retaining with compressible gangue brick wall in coal mines according to claim 1, characterized in that: In step S6, the specific construction method of the compressible gangue brick wall mainly includes the following steps: (1) During the construction of the retaining wall, according to the movement of the surrounding rock and the mine pressure law of the retaining section in front of and behind the working face, the structure of the surrounding rock in the lanes in front of and behind the working face is divided into three main dynamic pressure stages, namely, the expansion stage of the surrounding rock damage range in front of the working face, the stage of roof fracture behind the working face, and the creep and stability stage after the lane side support. (2) Analyze the support requirements at each stage in (1) and adopt different auxiliary support methods; ① In the stage of expanding surrounding rock damage in front of the working face, advance reinforcement support is adopted, that is, anchor beams are driven on the top plate on one side of the working face within 20m in front of the working face; ② In the stage of roof fracture behind the working face, temporary support is adopted in the tunnel-retaining construction section. That is, within 50 m behind the working face, a row of single hydraulic pillars are supported on the side of the goaf, with one beam and two pillars, and the pillars are spaced 1 m apart. On the inner side of the gangue wall behind the working face, 3-5 single pillars are supported. These pillars are withdrawn and installed in sequence as the working face advances. ③ In view of the creep and stabilization stage after the tunnel side support, reinforced support after dynamic pressure action is adopted; after the mine pressure observation and confirmation that the rock formation movement is stable, the single hydraulic support is withdrawn.

9. The method for supporting gob-side entry retaining with compressible gangue brick wall in coal mines according to claim 1, characterized in that: In step S7, three measuring stations are set up in the gob-side tunnel section, and pressure measuring points and displacement measuring points are installed in each measuring station. The distance between adjacent measuring stations is 30m. The first measuring station is installed outside the range of the working face advance support pressure, followed by the second and third measuring stations. When the pressure and deformation measuring points are installed, the pressure and displacement measuring points are recorded.

10. The method for supporting gob-side entry retaining with compressible gangue brick wall in coal mines according to claim 9, characterized in that: In step S7, the following contents are monitored: (1) Pressure observation: When constructing the wall, the hydraulic pillow is installed in the main wall, and the hydraulic gauge is outside the wall. One hydraulic gauge is placed at each of the two interfaces of the filling body, with a depth of 0.75m. The purpose of observing the contact pressure of the anchor rod is to understand the growth of the anchor rod force with the deformation of the surrounding rock at different stages, so as to provide a basis for evaluating whether the support parameters are reasonable and adjusting the support design. (2) Observation of roadway deformation law: In order to obtain the mine pressure law of the roadway retained along the gob and provide a scientific basis for the next step of improving parameters and evaluating the effect of the roadway retained, an observation section is set up every 50m to observe the movement of the roof and floor plates and the movement of the two sides; (3) Anchor bolt and cable stress: An observation section is set up every 30m, and anchor bolt and cable stress gauges are installed to observe the stress change law of anchor bolts and cables, providing a scientific basis for optimizing the anchor bolt and cable support design; (4) Wall stress and deformation: Focus on monitoring the wall deformation and internal stress variation. The deformation is measured with a steel tape measure, and the internal stress of the wall is measured with a hydraulic pillow at a depth of 0.75m. (5) Wall sealing performance monitoring: The concentration of gas and CO in the tunnel is monitored to evaluate the sealing performance of the wall.

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