Mine area ecological restoration and foundation treatment structure based on microbial mineralization

Abstract

The utility model relates to a mining area ecological restoration and foundation treatment structure based on microbial mineralization. The mining area ecological restoration and foundation treatment structure comprises a microbial macadam three-dimensional reinforcing structure of a middle-shallow layer, a microbial solution and a reaction solution are injected through a pre-buried grouting floral tube, calcium carbonate precipitates are generated and cemented with macadam to form a three-dimensional reinforcing layer, water is rapidly drained, and the bearing capacity of a foundation is improved; the deep layer is sealed by three layers of polyvinyl chloride films, and is combined with a horizontal drainage cushion layer and a drainage plate to form a vacuum combined surcharge preloading system to accelerate drainage of water in the deep layer; the backfill soil is formed by mixing mine tail mud with external soil, and recycling of the tail mud is achieved through layered paving and rolling; the disc pit tunnel is formed by spiral cutting along the mine pit wall, kerbs and stand columns are reserved to guarantee passing safety, and cut stones are recycled. And a horizontal / vertical observation marker post is used for monitoring the displacement and settlement of the foundation. The utility model solves the problems of tail mud stockpiling, low construction efficiency and low foundation stability, and has the advantages of environmental protection, economy and high efficiency.

Description

Technical Field

[0001] This utility model relates to the field of mine restoration technology, specifically to a structural design that integrates mine ecological restoration and backfill foundation treatment, and is particularly suitable for engineering practices of backfilling and reinforcing mine pits and utilizing tailings resources using microbial mineralization technology. Background Technology

[0002] In the mining sector, numerous abandoned concave mine pits commonly suffer from problems such as fragmented terrain, unstable slopes, and water accumulation. Furthermore, the tailings generated during mining (a mixture of fine-grained stone powder and water, with particle sizes mostly <75μm, high compressibility, and low strength) face challenges due to a lack of effective treatment measures, including high storage costs, significant pollution risks, and the occupation of land resources. Traditional mine pit backfilling methods have the following problems:

[0003] 1. Backfill soil source depends on external soil, which is costly and the soil source is scarce;

[0004] 2. Direct stockpiling of tailings can easily trigger geological disasters (such as landslides and debris flows) and pollute soil and water bodies;

[0005] 3. Foundation treatment methods (such as simple compaction and chemical reinforcement) are inefficient, time-consuming, and may cause secondary pollution;

[0006] 4. Construction access routes often employ stepped excavation, resulting in large rock excavation volumes, high transportation costs, and slow progress.

[0007] Existing technologies are insufficient to meet the multiple needs of ecological restoration, tailings disposal, and foundation reinforcement. There is an urgent need for an environmentally friendly and efficient integrated treatment solution to address the problems of existing technologies in mine ecological restoration, such as difficulties in tailings storage and treatment, insufficient backfill soil sources, low foundation treatment efficiency and easy pollution, and high construction channel excavation costs. It is difficult to achieve a balance between environmental protection, economy, and efficiency in mine pit backfilling and foundation reinforcement. Utility Model Content

[0008] The purpose of this utility model is to address the aforementioned problems in the existing technology by providing a mining area ecological restoration and foundation treatment structure based on microbial mineralization. This structure is achieved by constructing a "panel tunnel transportation system + layered vacuum combined surcharge preloading + microbial crushed stone three-dimensional reinforcement structure" within the mine pit, using mine tailings as backfill material, and combining microbial mineralization grouting technology to cement crushed stone to form a high-strength foundation, thus simultaneously realizing tailings disposal, mine pit backfilling, and foundation reinforcement.

[0009] To achieve the aforementioned objectives, this utility model employs the following technical solution: a mining area ecological restoration and foundation treatment structure based on microbial mineralization includes:

[0010] The microbial gravel three-dimensional reinforcement structure is set in the shallow backfill foundation and consists of crisscrossing rectangular gravel layers. It is used to quickly drain the foundation moisture and form a three-dimensional reinforcement structure through grouting.

[0011] Backfill soil is made by mixing mine tailings with external soil to fill the mine pit and form a backfill soil foundation.

[0012] Polyvinyl chloride film is laid in deep backfilled soil foundations for sealing and vacuum combined surcharge preloading reinforcement;

[0013] A horizontal drainage cushion layer is installed in the deep foundation to collect the water discharged during vacuum combined surcharge preloading;

[0014] Drainage boards are spaced out in the deep backfilled soil foundation for vertical drainage;

[0015] The pankeng tunnel is formed by spiraling downwards along the pit wall and is used to transport backfill materials and provide working space. The outside of the pankeng tunnel is equipped with curb stones and the inside is equipped with pillars.

[0016] Horizontal and vertical observation markers are set on both sides and the centerline of each layer of vacuum combined surcharge preloading foundation to observe the horizontal displacement and settlement of the foundation.

[0017] Furthermore, the cross-sectional side length of the crushed stone layer in the microbial crushed stone three-dimensional reinforcement structure is 50-100cm, the horizontal and vertical spacing is 3-5m, and the height extends from the middle of the mine pit to the top surface of the mine pit.

[0018] Furthermore, grouting pipes are pre-embedded in the crushed stone layer. After the foundation drainage is completed, microbial solution and reaction solution are injected through the grouting pipes to generate calcium carbonate precipitate to cement the crushed stone layer and form a three-dimensional reinforcement structure.

[0019] Furthermore, the moisture content of the backfill soil is controlled within ±3% of the optimum moisture content.

[0020] Furthermore, three layers of polyvinyl chloride film are laid, with a vacuum degree of not less than 80 kPa under the film; the thickness of the horizontal drainage pad is 30-50 cm; the drainage boards are spaced 0.8-1 m apart and are 9-12 m long.

[0021] Furthermore, the slope of the Pankeng Tunnel is less than 6%, the width is not less than 6m, and the height is 3-5m; the curbstone is a continuous rock mass reserved on the outside of the Pankeng Tunnel with a thickness of 5-10cm; the pillars are square-section rock masses with a side length of 1-2m, a thickness of 20-50cm, and a pillar spacing of 5-8m.

[0022] Furthermore, both horizontal and vertical observation markers are set every 50m. The vertical observation markers are located at the centerline of each layer of vacuum combined surcharge preloading foundation, while the horizontal observation markers are located on both sides of each layer of foundation.

[0023] Furthermore, the bottom of the mine pit is the starting point for backfilling, the top surface of the mine pit is the elevation after backfilling is completed, and the backfilling construction is completed and used as the foundation of the construction site.

[0024] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0025] 1. Tailings resource utilization and ecological restoration: Directly using mine tailings as backfill soil solves the environmental risks and land occupation problems of tailings storage, realizes a closed-loop treatment of "self-production and self-sale", and protects the ecological environment of the mining area;

[0026] 2. Efficient construction and cost control: By using a spiral tunnel structure (which spirals downward to cut through the mine wall to form a transportation channel), the amount of rock excavation is minimized, the transportation distance is shortened, construction efficiency is improved and costs are reduced, and the cut stone can be recycled.

[0027] 3. Layered treatment and foundation performance improvement: Layered paving and compaction combined with vacuum surcharge preloading can be used to accelerate the drainage of deep water and reduce foundation settlement; a three-dimensional microbial crushed stone reinforcement structure is set in the middle and shallow layers, and calcium carbonate precipitate cemented crushed stone is generated through microbial grouting to form a high-strength three-dimensional bearing network, which significantly improves the bearing capacity of the foundation.

[0028] 4. Environmental advantages: Microbial grouting technology uses a biochemical reaction (urea hydrolysis catalyzed by bacteria to produce calcium carbonate) to replace traditional chemical reinforcement, resulting in no secondary pollution and meeting the requirements of green mine restoration;

[0029] 5. Construction safety and systematic monitoring: The safety of passage through the tunnel is ensured by using curbs and pillars, and the foundation displacement and settlement are monitored in real time by using horizontal / vertical observation poles to ensure that the construction process is controllable and the foundation is stable in the long term. Attached Figure Description

[0030] Figure 1 This is a side view of the construction structure for mine pit backfilling;

[0031] Figure 2 It is a three-dimensional view of the construction structure for mine pit backfilling;

[0032] Figure 3 It is a three-dimensional view of the microbial stone fragmentation reinforcement structure;

[0033] Figure 4 This is a side view of the foundation treatment structure;

[0034] Figure 5This is a schematic diagram of a vacuum combined loading preloading embodiment of the present invention;

[0035] Figure 6 This is a schematic diagram of the drainage board arrangement according to an embodiment of the present invention;

[0036] Figure 7 This is a schematic diagram of the three-dimensional reinforcement structure of microbial lithotripsy according to an embodiment of this utility model.

[0037] In the diagram, 01 is the three-dimensional reinforcement structure of microbial crushed stone; 02 is the backfill soil; 03 is the polyvinyl chloride film; 04 is the horizontal drainage cushion layer; 05 is the drainage board; 11 is the horizontal observation pole; 12 is the vertical observation pole; 21 is the top surface of the mine pit; 22 is the bottom of the mine pit; 23 is the wall of the mine pit; 24 is the pit tunnel; 25 is the transport vehicle; 26 is the curb stone; 27 is the column; 6 is the horizontal crushed stone drainage channel; 7 is the vertical crushed stone drainage channel; 8 is the remaining part of the backfill tailings; and 9 is the mine pit. Detailed Implementation

[0038] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present utility model are within the protection scope of the present utility model.

[0039] Those skilled in the art should understand that in the disclosure of this utility model, the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as a limitation of this utility model.

[0040] like Figure 1-7 As shown, this structure for ecological restoration and foundation treatment of mining areas based on microbial mineralization is used to fill mine pits formed by mining and to reinforce backfilled soil foundations, including:

[0041] Microbial gravel three-dimensional reinforcement structure 01: Set in the shallow to medium layer of backfilled soil foundation, it is used to quickly drain the moisture in the backfilled soil foundation, and grouting forms a three-dimensional reinforcement structure to further improve the bearing capacity of the foundation.

[0042] In this embodiment, as Figure 3As shown, the microbial gravel three-dimensional reinforcement structure 01 consists of crisscrossing rectangular gravel layers (such as horizontal gravel drainage channels 6 and vertical gravel drainage channels 7). The cross-sectional side length of the gravel layers is 50-100cm, the horizontal and vertical spacing is 3-5m, and the height is set from the middle of the mine pit to the top surface of the mine pit 21. This is used to quickly drain the water in the backfill foundation soil and improve the soil strength and bearing capacity. Grouting pipes need to be pre-embedded in the drainage structure. After the foundation drainage is completed, microbial grouting is carried out through the grouting pipes to form the three-dimensional microbial gravel reinforcement structure 01, further improving the foundation bearing capacity. The grout used for microbial grouting includes a microbial solution and a reaction solution. The microbial solution is one or more of urea hydrolyzing bacteria and urease-producing bacteria, and the reaction solution is a mixture of calcium chloride and urea. After microbial grouting, calcium carbonate precipitate is generated as a solidified material, cementing the loose gravel three-dimensional reinforcement structure to form the microbial gravel three-dimensional reinforcement structure 01.

[0043] Backfill 02: Tailings from mining operations (such as...) Figure 3 The remaining part of the backfill tailings 8) and foreign soil are used to fill the mine pit 9, complete the surface restoration of the mining area, and form the backfilled soil foundation;

[0044] In this embodiment, the backfill soil 02 is tailings formed from mining and external soil. Before backfilling, the moisture content needs to be controlled within ±3% of the optimum moisture content. It is transported to the mine pit by transport vehicle 25 along the pit tunnel 24. It is reinforced by layering and leveling and vibrating compaction in each small layer of 0.5 to 1.5m, and layering vacuum combined surcharge preloading in a large layer of 8 to 12m.

[0045] Polyvinyl chloride film 03: Used for sealing deep backfilled soil foundations and for vacuum combined surcharge preloading reinforcement;

[0046] In this embodiment, three layers of polyvinyl chloride film 03 need to be laid, and the vacuum degree under the film reaches more than 80 kPa, which is used to seal the deep backfill foundation and carry out vacuum combined surcharge preloading reinforcement.

[0047] Horizontal drainage cushion layer 04: Used to collect water discharged during vacuum combined surcharge preloading of deep foundations;

[0048] In this embodiment, the horizontal drainage cushion layer 04 has a thickness of 30-50cm and is used to collect the water discharged during the deep foundation vacuum combined surcharge preloading.

[0049] Drainage board 05: Used for vertical drainage of deep backfilled soil foundations;

[0050] In this embodiment, the drainage boards 05 are spaced 0.8-1m apart and are 9-12m long, and are used for vertical drainage of deep backfilled soil foundations.

[0051] Horizontal observation beacon 11: Set on both sides of each layer of vacuum combined surcharge preloading foundation to observe the horizontal displacement of the foundation;

[0052] In this embodiment, horizontal observation markers 11 are set on both sides of each layer of vacuum combined surcharge preloading foundation to observe the horizontal displacement of the foundation, and one is set every 50m.

[0053] Vertical observation beacon 12: set at the centerline of each layer of vacuum combined surcharge preloading foundation, used to observe the settlement of the foundation;

[0054] In this embodiment, vertical observation markers 12 are set at the centerline of each layer of vacuum combined surcharge preloading foundation to observe the settlement of the foundation, and one is set every 50m.

[0055] Top surface of the mine pit 21: Elevation after backfilling is completed;

[0056] In this embodiment, the top surface 21 of the mine pit is the elevation after the backfill soil is completed, and it can be used as the site foundation for the project construction after the backfilling construction is completed.

[0057] Pit bottom 22: The starting point for backfilling soil;

[0058] Mine pit wall 23: Working face for cutting the pan-pit tunnel 24;

[0059] Pankeng Tunnel 24: A tunnel formed by spiraling downwards along the mine pit wall, used for transporting backfill soil and construction materials, as well as providing working space;

[0060] In this embodiment, after the water in the mine pit 9 is pumped out and the unstable rock mass is cleared, the pan-pit tunnel 24 is formed by using a large electric saw to cut the rock mass of the mine pit wall, spiraling downwards to the bottom of the pit. The tunnel slope is less than 6%, the width is more than 6m, and the height is 3-5m, ensuring the normal passage of personnel, vehicles, construction equipment, and materials. The cut stone is transported out by vehicles and equipment and can be collected as building materials.

[0061] Transport vehicle 25: Used to transport backfill soil to the bottom of the mine pit 22;

[0062] Curbstone 26: Located on the outside of the tunnel 24 to ensure driving safety;

[0063] Column 27: Used to support the pit tunnel 24, with a square cross-section, a length of 1-2m, a thickness of 20-50cm, and a column spacing of 5-8m.

[0064] Among them, surcharge preloading is to directly use backfill soil 02 to carry out layered preloading loads. The total load is controlled within the standard required by the design and shall not exceed the allowable bearing capacity of the foundation.

[0065] Example 2

[0066] Based on Example 1, this example focuses on the ecological restoration and foundation treatment of a 30m deep mine pit formed during the mining of a metal mine. The bottom elevation of the pit is -15m, and the designed top elevation is +15m. After backfilling, it will be used as industrial storage land. The soil type in the mining area is a mixture of silty clay and tailings, with tailings accounting for 40%, a natural moisture content of 35%, and a liquidity index of 0.85. Treatment is required to meet the requirement of a foundation bearing capacity ≥150kPa. Specifically, the structural composition and construction steps are as follows:

[0067] I. Three-dimensional reinforcement structure of microbial crushed stone 01

[0068] Parameter design: A rectangular crushed stone layer with a side length of 50cm is adopted, with a horizontal spacing of 3m and a vertical spacing of 3m, extending from the middle of the pit (elevation -5m) to the top surface (+15m). φ50mm grouting pipes are pre-embedded in the crushed stone layer, with a spacing of 2m and a quincunx arrangement.

[0069] Construction process:

[0070] (1) The crushed stone layer is filled in layers along the longitudinal centerline of the mine pit, with each layer being 0.5m thick, and compacted by a vibratory roller (excitation force 25t);

[0071] (2) After the backfill soil 02 is filled to the top surface of the crushed stone layer, inject a microbial solution (urea hydrolysis bacteria concentration 1×10⁻⁶) through the grouting pipe. 8 The mixture of CFU / mL and reaction solution (CaCl2 concentration 1.5mol / L, urea concentration 1.5mol / L) was injected at a pressure of 0.3MPa for 2 hours to form a calcium carbonate cement.

[0072] II. Backfill soil 02

[0073] Material ratio: Mine tailings and imported silty clay are mixed at a ratio of 4:6. The optimal moisture content is determined to be 18% by compaction test, and the construction control moisture content is 20% (within ±3%).

[0074] Construction parameters:

[0075] (1) The material was transported to the mine pit by dump truck along the Pankeng Tunnel 24, and then spread in layers of 0.8m each, and compacted by vibratory rolling (8t roller, 6 passes).

[0076] (2) Vacuum combined surcharge preloading is carried out every 8m of filling height (large layer) for 30 days.

[0077] III. Vacuum Combined Surcharge Preloading System

[0078] Polyvinyl chloride film 03: Three layers are laid, with a film thickness of 0.2mm, and the vacuum degree under the film is maintained at 85kPa (using a jet vacuum pump with a power of 7.5kW).

[0079] Horizontal drainage cushion layer 04: 40cm thick, filled with medium-coarse sand, with a permeability coefficient ≥1×10 -2 cm / s.

[0080] Drainage board 05: Model SPB-1, spacing 0.9m, board length 10m, square arrangement, extending 0.3m into the horizontal drainage layer.

[0081] Surcharge construction: Backfill soil 02 is used directly as surcharge material, the loading rate is controlled at 0.5m / d, and the total load is 120kPa (equivalent to the self-weight of 8m thick backfill soil).

[0082] IV. Pankeng Tunnel 24

[0083] Geometric parameters: 5% slope, 6m width, 4m height, formed by spiraling downwards along the mine wall, with a total of 4 platforms.

[0084] Safety Structure:

[0085] (1) An 8cm thick continuous rock mass is reserved on the outside of the tunnel as a curbstone 26;

[0086] (2) 27 square columns with a cross section of 1.5m×1.5m are installed inside the tunnel, spaced 6m apart, and anchor bolts (φ25mm, length 4m) are used to consolidate them with the surrounding rock.

[0087] V. Monitoring System

[0088] Observation benchmark:

[0089] (1) Horizontal observation beacon 11: set every 50m along both sides of the foundation of each layer, using φ50mm steel pipe, with a soil depth of 1.5m;

[0090] (2) Vertical observation marker 12: Located at the centerline of each foundation layer, using φ80mm concrete piles with a soil depth of 2m.

[0091] Monitoring frequency:

[0092] (1) During vacuum preloading: Observe once a day;

[0093] (2) During grouting construction: observations are conducted every 4 hours;

[0094] (3) After completion: Observe once a month for 1 year.

[0095] III. Principles of Collaborative Work

[0096] Drainage consolidation stage:

[0097] Vacuum preloading forms a vertical-horizontal drainage channel through the drainage board 05 and the horizontal drainage cushion layer 04, resulting in a cumulative drainage volume of approximately 28,000 m³ within 30 days. 3 The average settlement of the foundation is 1.2m.

[0098] Pankeng Tunnel 24 serves as a transportation channel, transporting approximately 5000 m³ of backfill soil daily. 3 Construction efficiency is increased by 40% compared to traditional methods.

[0099] Microbial mineralization and consolidation stage:

[0100] Seven days after grouting, the calcium carbonate precipitation in the crushed stone layer reached 25% (by mass), the unconfined compressive strength increased to 3.2 MPa, and the permeability coefficient decreased to 1×10⁻⁶. -5 cm / s.

[0101] Grouting waste liquid is collected in a sedimentation tank via a drainage ditch inside the tunnel (not shown), and then recycled after treatment, with a water reuse rate of 90%.

[0102] Monitoring feedback:

[0103] The maximum horizontal displacement occurred at the edge of the mine pit, at 35 mm (the allowable value is 50 mm according to the standard).

[0104] The vertical settlement rate decreased to 0.5 mm / d after 30 days of preloading, meeting the stability criteria.

[0105] The parts of this utility model not described in detail are existing technologies, therefore, this utility model does not describe them in detail.

[0106] It is understood that the term "a" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple, and the term "a" should not be understood as a limitation on the number.

[0107] Although this document uses terms such as "etc." extensively, the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing and explaining the essence of this invention; interpreting them as any additional limitation would contradict the spirit of this invention.

[0108] This utility model is not limited to the above-described preferred embodiment. Anyone can derive other forms of products under the guidance of this utility model. However, regardless of any changes made to their shape or structure, any technical solution that is the same as or similar to this utility model falls within the protection scope of this utility model.

Claims

1. A structure for ecological restoration and foundation treatment of mining areas based on microbial mineralization, characterized in that, include: Microbial gravel three-dimensional reinforcement structure (01) is set in the shallow backfill foundation and is composed of crisscrossing cuboid gravel layers. It is used to quickly drain the foundation water and form a three-dimensional reinforcement structure through grouting. Backfill soil (02) is made by mixing mine tailings with external soil to fill the mine pit and form a backfill soil foundation; Polyvinyl chloride film (03) is laid in the deep backfill soil foundation for sealing and vacuum combined surcharge preloading reinforcement; A horizontal drainage cushion layer (04) is set in the deep foundation to collect the water discharged during vacuum combined surcharge preloading; Drainage boards (05) are spaced out in the deep backfilled soil foundation for vertical drainage; The Pankeng Tunnel (24) is formed by spiraling downwards along the pit wall (23) and is used to transport backfill materials and provide working space. The Pankeng Tunnel (24) is equipped with curb stones (26) on the outside and pillars (27) on the inside. Horizontal observation markers (11) and vertical observation markers (12) are set on both sides and the centerline of each layer of vacuum combined surcharge preloading foundation to observe the horizontal displacement and settlement of the foundation.

2. The structure for ecological restoration and foundation treatment of mining areas based on microbial mineralization according to claim 1, characterized in that, The microbial gravel three-dimensional reinforcement structure (01) has a gravel layer with a side length of 50-100cm, a horizontal and vertical spacing of 3-5m, and a height extending from the middle of the mine pit to the top surface of the mine pit (21).

3. The structure for ecological restoration and foundation treatment of mining areas based on microbial mineralization according to claim 1, characterized in that, Pre-embedded grouting pipes in the crushed stone layer are used to inject microbial solution and reaction solution through the grouting pipes after the foundation drainage is completed, so as to generate calcium carbonate precipitate to cement the crushed stone layer and form a three-dimensional reinforcement structure.

4. The structure for ecological restoration and foundation treatment of mining areas based on microbial mineralization according to claim 1, characterized in that, The moisture content of the backfill soil (02) is controlled within ±3% of the optimum moisture content.

5. The structure for ecological restoration and foundation treatment of mining areas based on microbial mineralization according to claim 1, characterized in that, The polyvinyl chloride film (03) is laid in three layers, and the vacuum degree under the film is not less than 80 kPa; the thickness of the horizontal drainage pad (04) is 30-50 cm; the drainage board (05) is spaced 0.8-1 m apart and has a length of 9-12 m.

6. The structure for ecological restoration and foundation treatment of mining areas based on microbial mineralization according to claim 1, characterized in that, The slope of the Pankeng Tunnel (24) is less than 6%, the width is not less than 6m, and the height is 3-5m; the curbstone (26) is a continuous rock mass reserved outside the Pankeng Tunnel with a thickness of 5-10cm; the pillar (27) is a square cross-section rock mass with a side length of 1-2m, a thickness of 20-50cm, and a pillar spacing of 5-8m.

7. The structure for ecological restoration and foundation treatment of mining areas based on microbial mineralization according to claim 1, characterized in that, The horizontal observation marker (11) and the vertical observation marker (12) are set every 50m. The vertical observation marker (12) is located at the centerline of each layer of vacuum combined surcharge preloading foundation, and the horizontal observation marker (11) is located on both sides of each layer of foundation.

8. The structure for ecological restoration and foundation treatment of mining areas based on microbial mineralization according to any one of claims 1-7, characterized in that, The bottom of the mine pit (22) is the starting point for backfilling, and the top surface of the mine pit (21) is the elevation after backfilling is completed. After the backfilling construction is completed, it will serve as the foundation of the construction site.

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