Method for constructing an inner dump based on a carbon dioxide reservoir of fly ash-based cementitious material

Abstract

The application discloses a method for constructing an internal dumping site based on a fly ash-based cementing material carbon dioxide storage, and utilizes the cementing properties of fly ash of a pit mouth coal-fired power plant to prepare a fly ash-based cementing material with super high content, and utilizes the high-strength fly ash-based cementing material to construct a carbon dioxide storage, and utilizes a cement-free low-strength fly ash-based cementing material to backfill an open-pit mine pit, so that the resource utilization and efficient collaborative disposal of fly ash solid waste are realized; the carbon dioxide storage is constructed in the internal dumping site space, the open-pit mining space is effectively utilized, and the problem of insufficient material for land reclamation backfilling in the late mining stage is solved; the carbon dioxide storage reinforced by the anchor rod prestress has high strength and large internal space, the mine pit bottom plate impermeable layer and the overlying clay cover layer increase the airtightness, and the safe and efficient large-scale storage of critical state carbon dioxide is realized; the fly ash-based cementing material can mineralize carbon dioxide in a humid environment, increases the carbon dioxide storage amount, and improves the carbon dioxide storage strength and airtightness.

Description

Technical Field

[0001] This invention relates to a method for constructing an internal spoil heap, specifically a method for constructing an internal spoil heap based on a fly ash-based cementitious material carbon dioxide storage tank. Background Technology

[0002] Coal-fired power plants generate large amounts of solid waste such as slag and ash. Much of this slag and ash is discharged as waste, causing serious environmental problems and social pressure. Firstly, the large-scale stockpiling of waste slag and ash severely encroaches on arable land, generates significant amounts of dust, and pollutes the atmosphere. Secondly, the accumulation of slag and ash, under the influence of rainwater, pollutes local irrigation and drinking water. Simultaneously, coal-fired power generation is a major source of carbon dioxide emissions. Currently, most coal-fired power plants release carbon dioxide directly into the atmosphere without treatment. Only a small number of power plants capture, separate, and purify the emitted carbon dioxide, then transport it via pipeline to suitable geological reservoirs for underground storage, such as abandoned oil fields, deep saline aquifers, and unminable coal seams.

[0003] During the mining process of open-pit coal mines, the rock overlying the coal seam needs to be stripped and transported to a spoil heap for disposal. To reduce land occupation, shorten the stripping haulage distance, and increase end-face stability, the stripped material is directly dumped into the goaf of the open-pit mine, forming an internal spoil heap. Land reclamation work is carried out when the internal spoil heap elevation reaches a certain requirement. However, due to the extraction of valuable minerals, even if all the stripped material is dumped internally into the goaf of the open-pit mine, it is still insufficient to restore the original ground elevation, increasing the subsequent reclamation costs.

[0004] Specifically, regarding carbon dioxide sequestration in coal mining spaces, the existing solutions and their respective problems are as follows.

[0005] 1. Patent publication CN106946255A, "A Method for Waste Treatment and Carbon Dioxide Sequestration in a Pithead Coal-fired Power Plant", only involves underground mining and does not involve open-pit mines. The description of the construction process and underground structures is unclear, and no groundwater protection scheme is proposed during the backfilling of industrial solid waste from the power plant underground.

[0006] 2. Patent CN114856689A, "An Integrated Method for Mineralization and Sequestration of Fly Ash and CO2 and Backfilling of Goaf," only involves underground mining and not open-pit mines. It focuses on filling mineralized waste fly ash and gangue into the goaf, mineralizing CO2 while filling. The construction is difficult, the amount of carbon dioxide that can be sealed is limited, and the stability and airtightness of the caprock are required.

[0007] 3. Patent CN113101789A, "Method, Structure and Mining Method for Sealing Carbon Dioxide in Open-Pit Mine", describes the process of layering and landfilling mining waste rock (or coal gangue), power plant ash (if any), and waste clinker (if any), and then injecting supercritical carbon dioxide and mine water into the waste rock mixed storage area in layers. This only involves the mineralization and sealing of carbon dioxide from solid waste such as fly ash. Furthermore, the mineralization process consumes a large amount of water resources, which will further exacerbate the water shortage in ecologically fragile mining areas in arid and semi-arid regions of western China. It does not consider the cementitious properties of fly ash, the efficient utilization of the discharge space in open-pit mines, or the physical sealing of CO2 using underground closed spaces. In the later stage, there will be insufficient materials for land reclamation and backfilling. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a method for constructing an internal waste disposal site for carbon dioxide storage based on fly ash-based cementitious materials, thereby realizing the resource utilization of fly ash, the effective utilization of internal waste disposal space in open-pit mines, alleviating the shortage of materials for land reclamation and backfilling, and the safe and efficient storage of carbon dioxide.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a method for constructing an internal spoil heap for a carbon dioxide storage facility based on fly ash-based cementitious materials, comprising the following steps:

[0010] S1: A mobile grouting and mixing station is set up at the bottom of the mine pit. Fly ash, coal gangue, cement, water-reducing agent and air-entraining agent are injected into the mobile grouting and mixing station in different proportions to mix and prepare fly ash-based cementitious materials with different strengths.

[0011] S2: After the main coal seam working face has advanced 50-100m, the mine pit floor is leveled. The high-strength fly ash-based cementitious material prepared in step S1 is sprayed onto the non-working slope to the boundary to reinforce the non-working slope. Then, loose clay material is dumped onto the mine pit floor and compacted to construct a seepage-proof layer. The thickness of the seepage-proof layer is not less than 1.5m and the permeability coefficient is less than 1.0×10⁻⁶. -7 cm / s;

[0012] S3: 50-100m behind the main coal seam working face, install a steel mesh box to be filled on the seepage prevention layer of the mine pit floor, consisting of steel mesh, tie rods and template. The overlap length of the steel mesh is not less than one grid spacing or 30d, where d is the diameter of the steel bar. Connect the steel mesh with double-row wire buckles and pull the steel mesh tightly against the template surface. Pass the tie rods through the steel mesh, put the tray on the outer end of the tie rods and tighten the nuts.

[0013] S4: Inject the high-strength fly ash-based cementitious material prepared in step S1 into the steel mesh box to be filled. After the injected high-strength fly ash-based cementitious material has solidified, remove the formwork and apply pre-tightening force to the nuts at both ends of the anchor rod to form a prestressed carbon dioxide storage tank. The carbon dioxide storage tanks are arranged at intervals from the inner spoil heap slope towards the working slope, with an interval of 10-30m.

[0014] S5: Backfill the stripped material of the original strata into the space between the reinforced non-working slope and the carbon dioxide storage, and backfill the cement-free low-strength fly ash-based cementitious material prepared in step S1 into the space between two adjacent carbon dioxide storages.

[0015] S6: After the cement-free low-strength fly ash-based cementitious material in step S5 has solidified, a clay overlay layer is constructed by compacting and discharging loose clay material above the carbon dioxide storage tank. The thickness of the clay overlay layer is not less than 1.5m and its permeability coefficient is less than 1.0×10⁻⁶. -7 cm / s, and then the stripped material from the original strata is dumped above the overlying clay cover to construct an inner dump backfill layer until it is backfilled to the designed inner dump elevation;

[0016] S7: Inject critical state carbon dioxide into the carbon dioxide storage tank to achieve physical sequestration of carbon dioxide;

[0017] S8: As the main coal seam working face continues to advance, the carbon dioxide storage tanks are constructed according to the above steps until the main coal seam working face reaches the end. The high-strength fly ash-based cementitious material prepared in step S1 is sprayed onto the working face to the boundary slope to form a reinforced working face to the boundary slope. The original stratum stripping material is backfilled in the space between the last carbon dioxide storage tank and the reinforced working face to the boundary slope.

[0018] S9: Then, construct the overlying clay cover layer in step S6 on the stripped material of the original stratum that was backfilled. After that, dump the stripped material of the original stratum above the overlying clay cover layer to construct the inner dump backfill layer until the design inner dump elevation is reached. At this point, the entire mine pit is backfilled to the design inner dump elevation.

[0019] Furthermore, in step S1, fly ash, coal gangue, cement, water-reducing agent, and air-entraining agent are prepared according to the following proportions: 102–341 kg fly ash, 0–69 kg cement, 89–125 kg water, 2330 kg coal gangue, 2.04–3.43 kg water-reducing agent, and 0.067–0.240 kg air-entraining agent per cubic meter. The cement content is controlled at 0–8%, and the water-cement ratio is controlled at 0.261–0.43.

[0020] Furthermore, in steps S2 and S8, the high-strength fly ash-based cementitious material is prepared by adding 274 kg of fly ash, 69 kg of cement, 89 kg of water, 2330 kg of coal gangue, 3.43 kg of water-reducing agent, and 0.240 kg of air-entraining agent per cubic meter, and its strength at 180 days is not less than 40 MPa.

[0021] Furthermore, in step S5, the cement-free low-strength fly ash-based cementitious material is prepared according to the following proportions: 343 kg fly ash, 89 kg water, 2330 kg coal gangue, 2.04 kg water-reducing agent, and 0.067 kg air-entraining agent per cubic meter.

[0022] Furthermore, in step S3, the minimum thickness b' of the steel mesh box to be filled is determined by the ground stress, the mechanical parameters of the tie rods, and the mechanical parameters of the fly ash-based cementitious material:

[0023]

[0024] In the formula, r a Let E be the radius of the prestressed solid body arch, μ be the Poisson's ratio of the prestressed solid body, and E be the radius of the arch arch. s E m These are the elastic moduli of fly ash-based cementitious materials and prestressed reinforced bodies, respectively. c. P0 represents the shear strength parameter of fly ash-based cementitious materials, and P0 represents the in-situ stress.

[0025] Furthermore, in step S3, the spacing between the tie anchor bolts... In the formula, L is the length of the tie rod.

[0026] Furthermore, the preload force in step S4 is:

[0027]

[0028] Furthermore, the top height of the reinforced non-working slope to the boundary and the reinforced working slope to the boundary are the same as the top height of the carbon dioxide storage tank, and the top and bottom of the reinforced non-working slope to the boundary and the reinforced working slope to the boundary are respectively connected to the boundary of the overlying clay cover layer and the seepage prevention layer of the mine pit bottom plate.

[0029] Compared with existing technologies, this invention utilizes the cementitious properties of fly ash from pithead coal-fired power plants to prepare ultra-high content fly ash-based cementitious materials. These high-strength fly ash-based cementitious materials are used to construct carbon dioxide storage tanks, while low-strength, cement-free fly ash-based cementitious materials are used to backfill open-pit mines, achieving resource utilization and efficient co-processing of fly ash solid waste. Constructing carbon dioxide storage tanks within the internal spoil heap space effectively utilizes open-pit mining space and solves the problem of insufficient materials for land reclamation and backfilling in the later stages of mining. The carbon dioxide storage tanks, reinforced with prestressed anchor bolts, have high strength and large internal space. The impermeable layer on the mine pit floor and the overlying clay cover layer increase airtightness, achieving safe, efficient, and large-scale sealing of critical-state carbon dioxide. Furthermore, the fly ash-based cementitious materials can mineralize carbon dioxide in humid environments, increasing the amount of carbon dioxide sealed, improving the strength and airtightness of the carbon dioxide storage tanks, and reducing the precipitation of heavy metal ions from fly ash. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0031] Figure 2 This is a schematic diagram of the steel mesh box to be filled according to the present invention;

[0032] Figure 3 This is a schematic diagram of the end of the tie rod of the present invention;

[0033] Figure 4 This is a schematic diagram of the final structure of the present invention;

[0034] Figure 5 A schematic diagram of the final state structure of the multi-layer carbon dioxide storage tank constructed according to the present invention;

[0035] In the diagram: 1-Original strata, 2-Non-working slope to boundary, 3-Reinforced non-working slope to boundary, 4-Backfill layer of inner spoil heap, 5-Overlying clay cover layer, 6-Carbon dioxide storage, 7-Cement-free low-strength fly ash-based cementitious material, 8-Seepage prevention layer of mine pit floor, 9-Mine pit floor, 10-Main coal seam, 11-Working slope, 12-Tie anchor, 13-Plate, 14-Nut, 15-Reinforcing mesh, 16-Wire, 17-Formwork, 18-Working slope to boundary, 19-Design inner spoil heap elevation, 20-Reinforced working slope to boundary. Detailed Implementation

[0036] The invention will now be further described with reference to the accompanying drawings.

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] This invention provides a technical solution, such as Figures 1 to 3 As shown, it includes the following steps:

[0039] S1: Steel mesh 15, tie rods 12, wire 16, formwork 17, fly ash, coal gangue, cement, water-reducing agent, and air-entraining agent are transported to the bottom of the pit. The fly ash is taken from the coal-fired power plant at the pithead. A mobile grouting and mixing station is set up at the bottom of the pit. Fly ash, cement, water, coal gangue, water-reducing agent, and air-entraining agent are added to the mobile grouting and mixing station at a ratio of 102-341 kg fly ash, 0-69 kg cement, 89-125 kg water, 2330 kg coal gangue, 2.04-3.43 kg water-reducing agent, and 0.067-0.240 kg air-entraining agent per cubic meter to prepare fly ash-based cementitious materials with different strengths. The cement content is controlled at 0-8%, and the water-cement ratio is controlled at 0.261-0.43. The strength of the fly ash-based cementitious materials is adjusted by controlling the cement content and water-cement ratio.

[0040] S2: After the main coal seam 10 working face has been pushed forward for 50-100m, the mine pit floor 9 is leveled. The high-strength fly ash-based cementitious material prepared in step S1 is sprayed onto the non-working slope 2 to reinforce the non-working slope 3, thus reinforcing the boundary slope. This high-strength fly ash-based cementitious material is prepared by adding 274kg fly ash, 69kg cement, 89kg water, 2330kg coal gangue, 3.43kg water-reducing agent, and 0.240kg air-entraining agent per cubic meter, and the material's strength at 180 days is not less than 40MPa. Then, loose clay is dumped and compacted on the mine pit floor 9 to construct a seepage-proof layer 8. The seepage-proof layer 8 consists of a clay layer, a geotextile waterproofing fabric, and another clay layer from bottom to top. The thickness of the seepage-proof layer 8 is not less than 1.5m, and the permeability coefficient is less than 1.0×10⁻⁶. -7 cm / s.

[0041] S3: A steel mesh box to be filled, consisting of steel mesh 15, tie rods 12, and formwork 17, is installed on the seepage-proof layer 8 of the mine pit floor, 50-100m behind the main coal seam 10 working face. The tie rods 12 should be made of HRB335 or HRB400 steel, with a diameter of 16-32mm. Both ends of the rods should be threaded with a thread length of 120mm. The thread bearing capacity at the tail end should be ≥225KN. The bearing efficiency coefficient of the nut 14 should be ≥0.90. The bearing capacity of the pallet 13 should be ≥225KN. The formwork 17 should have sufficient bearing capacity, rigidity, and stability to reliably withstand various loads generated during construction. Figure 2 As shown, the lap length of the reinforcing mesh 15 is not less than one mesh spacing or 30d, where d is the diameter of the reinforcing bar. It is connected with double-row interlocking wire 16, and the reinforcing mesh 15 is pulled tightly against the surface of the formwork 17. The tie rods 12 are then passed through the reinforcing mesh 15. Figure 3 As shown, a tray 13 is fitted onto the outer end of the tie rod 12, and a nut 14 is tightened, with the tightness of the nut 14 adjusted appropriately. The minimum thickness b' of the steel mesh box to be filled is determined by the ground stress, the mechanical parameters of the tie rod 12, and the mechanical parameters of the fly ash-based cementitious material.

[0042]

[0043] In the formula, r a denoted as , where is the radius of the prestressed solid body arch, taken as 2.74 m; μ is the Poisson's ratio of the prestressed solid body, taken as 0.3; E s E m The elastic moduli of fly ash-based cementitious materials and prestressed reinforced bodies are taken as 18.5 GPa and 25.8 GPa, respectively. c. The shear strength parameters for fly ash-based cementitious materials are taken as 0.97 MPa and 15°, respectively; P0 is the ground stress, calculated based on a main coal seam burial depth of 180 m, and is taken as 4.5 MPa; the minimum spacing between tie rods 12 is... In the formula, L is the length of the tie rod 12, which is taken as 2.5m.

[0044] S4: Inject the high-strength fly ash-based cementitious material prepared in step S1 into the steel mesh box to be filled through the grouting pipeline and grouting port. After the injected high-strength fly ash-based cementitious material has solidified, remove the formwork 17 and apply pre-tightening force to the nuts 14 at both ends of the anchor rod 12. A prestressed carbon dioxide storage tank 6 is formed; the carbon dioxide storage tank 6 is arranged at intervals from the non-working slope 2 to the working slope 11, and the interval between two adjacent carbon dioxide storage tanks 6 is 10-30m. The cross-section of the carbon dioxide storage tank 6 is preferably arched.

[0045] S5: Backfill the stripped material of the original stratum 1 into the space between the reinforced non-working slope 3 and the carbon dioxide storage 6, and backfill the space between the two adjacent carbon dioxide storage 6 with the cementless low-strength fly ash-based cementitious material 7 prepared in step S1; the cementless low-strength fly ash-based cementitious material 7 here is prepared according to the ratio of 343kg fly ash, 89kg water, 2330kg coal gangue, 2.04kg water-reducing agent and 0.067kg air-entraining agent per cubic meter.

[0046] S6: After the cement-free low-strength fly ash-based cementitious material 7 in step S5 has reached the required consolidation strength, a clay cover layer 5 with a certain seepage prevention function is constructed above the carbon dioxide storage tank 6 by discharging and compacting loose clay material. The thickness of the clay cover layer 5 is not less than 1.5m and the permeability coefficient is less than 1.0×10⁻⁶. -7 cm / s, according to the stripping plan, and then the stripped material of the original stratum 1 is dumped above the overlying clay cover layer 5 to construct the inner dump backfill layer 4 until it is backfilled to the designed inner dump elevation 19.

[0047] S7: Inject critical state carbon dioxide into carbon dioxide storage tank 6 to achieve physical storage of carbon dioxide. In a humid environment, fly ash-based cementitious materials can mineralize carbon dioxide, increase the strength and airtightness of the storage tank, and reduce the precipitation of heavy metal ions in fly ash.

[0048] S8: As Figure 4 As shown, as the main coal seam 10 working face continues to advance, the carbon dioxide storage tank 6 is constructed according to the above steps until the main coal seam 10 working face reaches its end. The same high-strength fly ash-based cementitious material as in step S2 is sprayed onto the working face to boundary slope 18 to form a reinforced working face to boundary slope 20. The stripped material of the original stratum 1 is backfilled in the space between the last carbon dioxide storage tank 6 and the reinforced working face to boundary slope 20. Then, the overlying clay cap layer 5 in step S6 is constructed on the backfilled stripped material of the original stratum 1. After that, the stripped material of the original stratum 1 is dumped again above the overlying clay cap layer 5 to construct the inner dump backfill layer 4 until it is backfilled to the designed inner dump elevation 19. At this point, the entire mine pit is backfilled to the designed inner dump elevation 19.

[0049] To save costs while ensuring the prevention of fly ash seepage and leakage, the reinforced non-working boundary slope 3 and reinforced working boundary slope 20 do not need to cover the entire boundary slope. The top height of the reinforced non-working boundary slope 3 and reinforced working boundary slope 20 is the same as the top height of the carbon dioxide storage tank 6. The top and bottom of the reinforced non-working boundary slope 3 and reinforced working boundary slope 20 are connected to the boundaries of the overlying clay cover layer 5 and the anti-seepage layer 8 of the mine pit floor, respectively, to prevent fly ash seepage and leakage from both the top and bottom.

[0050] Based on the actual site conditions, the carbon dioxide storage facility 6 can be configured as multiple layers, with each layer constructed using the same method. For example... Figure 5 As shown, the original stratum 1 is laid and compacted between the seepage-proof layer 8 of the mine pit bottom plate at the bottom of the upper carbon dioxide storage 6 and the overlying clay cover layer 5 at the top of the lower carbon dioxide storage 6, so that the two adjacent carbon dioxide storage 6 are separated and staggered.

[0051] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any minor modifications, equivalent substitutions, and improvements made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for constructing an internal spoil heap for a carbon dioxide storage facility based on fly ash-based cementitious materials, characterized in that, Includes the following steps: S1: A mobile grouting and mixing station is set up at the bottom of the mine pit. Fly ash, coal gangue, cement, water-reducing agent and air-entraining agent are injected into the mobile grouting and mixing station in different proportions to mix and prepare fly ash-based cementitious materials with different strengths. S2: After the main coal seam (10) working face has been pushed 50-100m, the mine pit floor (9) is leveled, and the high-strength fly ash-based cementitious material prepared in step S1 is sprayed onto the non-working slope to the boundary slope (2) to form a reinforced non-working slope to the boundary slope (3). Then, loose clay is dumped on the mine pit floor (9) and compacted to construct a seepage-proof layer (8) for the mine pit floor. The thickness of the seepage-proof layer (8) is not less than 1.5m and the permeability coefficient is less than 1.0×10. -7 cm / s; S3: 50-100m behind the main coal seam (10) working face, install a steel mesh box to be filled on the seepage prevention layer (8) of the bottom plate of the mine pit, consisting of steel mesh (15), tie rods (12) and template (17). The overlap length of the steel mesh (15) is not less than one grid spacing or 30d, where d is the diameter of the steel bar. It is connected with double-row buckles of iron wire (16) and the steel mesh (15) is pulled tightly against the surface of the template (17). The tie rods (12) are passed through the steel mesh (15). The tray (13) is put on the outer end of the tie rod (12) and the nut (14) is tightened. S4: Inject the high-strength fly ash-based cementitious material prepared in step S1 into the steel mesh box to be filled. After the high-strength fly ash-based cementitious material is solidified, remove the template (17) and apply pre-tightening force to the nuts (14) at both ends of the anchor rod (12) to form a prestressed carbon dioxide storage tank (6). The carbon dioxide storage tanks (6) are arranged at intervals from the inner spoil heap slope (3) to the working slope (11), with an interval distance of 10-30m. S5: Backfill the stripped material of the original stratum (1) into the space between the reinforced non-working slope (3) and the carbon dioxide reservoir (6), and backfill the space between the two adjacent carbon dioxide reservoirs (6) with the cementless low-strength fly ash-based cementitious material (7) prepared in step S1. S6: After the cement-free low-strength fly ash-based cementitious material (7) in step S5 has solidified, the loose clay material above the carbon dioxide storage tank (6) is compacted to construct an overlying clay cover layer (5). The thickness of the overlying clay cover layer (5) is not less than 1.5m and the permeability coefficient is less than 1.0×10⁻⁶. -7 cm / s, and then the stripped material of the original stratum (1) is dumped above the overlying clay cover layer (5) to construct the inner dump backfill layer (4) until it is backfilled to the designed inner dump elevation (19); S7: Inject critical state carbon dioxide into carbon dioxide storage tank (6) to achieve physical sequestration of carbon dioxide; S8: As the main coal seam (10) working face continues to advance, the carbon dioxide storage tank (6) is constructed in accordance with the above steps until the main coal seam (10) working face is advanced to the end. The high-strength fly ash-based cementitious material prepared in step S1 is sprayed onto the working slope to the boundary slope (18) to form a reinforced working slope to the boundary slope (20). The stripped material of the original stratum (1) is backfilled in the space between the last carbon dioxide storage tank (6) and the reinforced working slope to the boundary slope (20). S9: Then, the overlying clay cover layer (5) in step S6 is constructed on the stripped material of the original stratum (1) after backfilling. Then, the stripped material of the original stratum (1) is dumped again above the overlying clay cover layer (5) to construct the inner dump backfill layer (4) until it is backfilled to the designed inner dump elevation (19). At this point, the entire mine pit is backfilled to the designed inner dump elevation (19).

2. The method for constructing an internal spoil heap for a carbon dioxide storage facility based on fly ash-based cementitious materials according to claim 1, characterized in that: In step S1, fly ash, coal gangue, cement, water-reducing agent, and air-entraining agent are prepared according to the following ratio: 102-341 kg fly ash, 0-69 kg cement, 89-125 kg water, 2330 kg coal gangue, 2.04-3.43 kg water-reducing agent, and 0.067-0.240 kg air-entraining agent per cubic meter. The cement content is controlled at 0-8%, and the water-cement ratio is controlled at 0.261-0.

43.

3. The method for constructing an internal spoil heap for a carbon dioxide storage facility based on fly ash-based cementitious materials according to claim 2, characterized in that: In steps S2 and S8, the high-strength fly ash-based cementitious material is prepared by adding 274 kg of fly ash, 69 kg of cement, 89 kg of water, 2330 kg of coal gangue, 3.43 kg of water-reducing agent, and 0.240 kg of air-entraining agent per cubic meter, and its strength at 180 days is not less than 40 MPa.

4. The method for constructing an internal spoil heap for a carbon dioxide storage facility based on fly ash-based cementitious materials according to claim 2, characterized in that: In step S5, the cement-free low-strength fly ash-based cementitious material (7) is prepared by adding 343 kg of fly ash, 89 kg of water, 2330 kg of coal gangue, 2.04 kg of water-reducing agent, and 0.067 kg of air-entraining agent per cubic meter.

5. The method for constructing an internal spoil heap for a carbon dioxide storage facility based on fly ash-based cementitious materials according to claim 1, characterized in that: In step S3, the minimum thickness b of the steel mesh box to be filled is determined by the ground stress, the mechanical parameters of the tie rod (12), and the mechanical parameters of the fly ash-based cementitious material. In the formula, r a Let E be the radius of the prestressed solid body arch, μ be the Poisson's ratio of the prestressed solid body, and E be the radius of the arch arch. s E m These are the elastic moduli of fly ash-based cementitious materials and prestressed reinforced bodies, respectively. c. P0 represents the shear strength parameter of fly ash-based cementitious materials, and P0 represents the in-situ stress.

6. The method for constructing an internal spoil heap for a carbon dioxide storage facility based on fly ash-based cementitious materials according to claim 1, characterized in that: In step S3, the spacing between the anchor bolts (12) is... In the formula, L is the length of the tie rod (12).

7. The method for constructing an internal spoil heap for a carbon dioxide storage facility based on fly ash-based cementitious materials according to claim 1, characterized in that: The preload force in step S4 is:

8. The method for constructing an internal spoil heap for a carbon dioxide storage facility based on fly ash-based cementitious materials according to claim 1, characterized in that: The top height of the reinforced non-working slope to the boundary (3) and the reinforced working slope to the boundary (20) are the same as the top height of the carbon dioxide storage tank (6). The top and bottom of the reinforced non-working slope to the boundary (3) and the reinforced working slope to the boundary (20) are respectively connected to the boundary of the overlying clay cover layer (5) and the seepage prevention layer (8) of the mine pit bottom plate.

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