Foamed concrete type large-diameter shallow buried pipeline assembled thermal insulation layer

Abstract

The utility model relates to road engineering technical field discloses foam concrete type large -diameter shallow -buried pipeline assembly type heat preservation layer, including from below to top layered structure: gravel drainage bottom layer, soft soil buffer layer, waterproof isolation layer, fibrous heat preservation board, cement mixed gravel sand bearing base layer, foam concrete heat preservation layer, reinforced soil layer and surface protective layer, the utility model discloses through the compound industrial waste in foam concrete, and combines multilayer enhancement design, so that the roadbed structure not only significantly reduces the heat transfer coefficient, improves the heat preservation performance, also satisfies the requirement of highway roadbed design specification to strength and deformation, adopts the assembly type heat preservation layer of the utility model, can reduce the use of traditional sandstone material, saves resources, reduces the project cost, improves the reusability of industrial waste simultaneously, has remarkable economic benefit and environmental benefit.

Description

Technical Field

[0001] This utility model relates to the field of road engineering technology, specifically to a prefabricated insulation layer for large-diameter shallow buried pipelines made of foamed concrete. Background Technology

[0002] Uneven distribution of water and oil and gas resources is a common problem worldwide. To address this, my country has implemented the South-to-North Water Diversion Project, transferring water resources from the abundant south to the north, and similar projects like the West-to-East Gas Pipeline. While pipelines remain a highly efficient and economical solution for fluid transportation, in cold regions, low winter temperatures and freeze-thaw cycles can cause frost heave damage to the roadbed, leading to road surface cracking and settlement, thus affecting the lifespan of buried pipelines. Furthermore, buried pipelines are susceptible to damage from external forces in freeze-thaw environments. Traditional pipeline insulation measures often fail to balance the load-bearing capacity of the roadbed with economic efficiency. Additionally, due to on-site construction methods, pipeline burial depths typically reach 2-3 meters, and even more than 3 meters in extremely cold regions, increasing maintenance costs and repair difficulties.

[0003] In existing technologies, foamed concrete is widely used in geotechnical engineering, slope protection, and mine pit repair due to its low density, high porosity, and good thermal insulation properties. However, foamed concrete alone suffers from insufficient mechanical strength and poor long-term stability, making it unsuitable as a direct load-bearing roadbed material. Furthermore, traditional pipe insulation materials often use polyurethane or rock wool insulation layers, but these materials are prone to aging and lack good structural support.

[0004] Currently, a large number of studies are applying polymer materials to the paving of roadbeds. The advantages of polymer materials are that they have good waterproof performance, excellent thermal insulation and mechanical properties, and low cost, making them an ideal new type of surface roadbed material.

[0005] Therefore, in response to the special needs of road engineering in cold regions, there is an urgent need for a new type of pipeline insulation engineering that integrates insulation, waterproofing, load-bearing capacity, and ease of construction, in order to improve construction efficiency, increase the overall stability of the road, extend its service life, and reduce maintenance costs. Utility Model Content

[0006] The purpose of this invention is to provide a prefabricated insulation layer for large-diameter shallow-buried pipelines made of foamed concrete, so as to solve the problems mentioned in the background art.

[0007] To solve the above-mentioned technical problems, this utility model provides the following technical solution: a foamed concrete type prefabricated insulation layer for large-diameter shallow buried pipelines, comprising a layered structure from bottom to top: The drainage bottom layer is made of crushed stone or gravel, with a particle size of 5-20mm, a thickness of 20-30cm, and a slope of 2%-3%. The soft soil buffer layer is composed of soft soil that has been sieved through 20 mesh and 200 mesh, and has a thickness of 10 cm. A waterproof isolation layer is constructed using HDPE geomembrane to isolate surface water and enhance the pipeline's protective capabilities. Fiber insulation board is made of fiber materials such as glass fiber, carbon fiber or nanocellulose combined with cement or asphalt substrate. The thickness is 5mm-10mm. The joints are sealed with adhesive to prevent thermal bridging. The cement-mixed gravel-sand load-bearing base course uses precast concrete slabs; Foamed concrete insulation layer has a thermal conductivity of less than 0.1 W / (m·K) and can be prefabricated or poured on-site into geocell chambers; The foamed concrete layer comprises the following components by weight percentage: composite foaming agent: expands 700-1000 times in volume after dilution; fiber: 0.6%-1.2%; expanded perlite: 5%-8%; water-reducing agent: ≤1%; antifreeze agent: 0.5%-2% of the total concrete mass; the components of the foamed concrete are mixed to form a lightweight thermal insulation structural layer. The reinforced soil layer is composed of multiple layers of high-strength steel slag sand material, which are connected by geosynthetic materials to form an integral structure, thereby improving compressive strength and deformation resistance. The surface protective layer uses polymer-modified cement concrete to improve durability and resistance to frost heave.

[0008] According to the above technical solution, the concrete slab uses ordinary Portland cement with a strength grade ≥32.5, and the sand material is medium or coarse sand with a mud content ≤3%; the gravel material is hard and clean, with good gradation, and the maximum particle size is ≤2 / 3 of the thickness of the concrete slab; the admixtures are antifreeze and water-reducing agent, which account for 0.5%-2% and 0.5%-1.5% of the total mass of concrete, respectively.

[0009] According to the above technical solution, the reinforced soil layer is composed of high-strength steel slag sand material with a particle size of 0.075-2mm and a mud content of no more than 5%. Each layer is reinforced and connected by geosynthetic geotextile to form an integral structure.

[0010] Compared with the prior art, the beneficial effects achieved by this utility model are: (1) Improve thermal insulation performance: Foamed concrete combined with expanded perlite improves the overall thermal insulation effect and reduces the damage of freeze-thaw cycles to the roadbed.

[0011] (2) Enhance mechanical properties: Introduce industrial waste such as steel slag and fly ash to improve the compressive strength of foamed concrete and enhance the overall stability through reinforcement measures.

[0012] (3) Optimize drainage function: The combined effect of the gravel drainage layer and the waterproof isolation layer effectively reduces the impact of groundwater on the roadbed and prevents frost heave damage.

[0013] (4) Save material costs: Using industrial waste as filler reduces the consumption of traditional sand and gravel materials, lowers project costs, and improves resource utilization.

[0014] (5) Easy to construct and maintain: The modular construction method allows for the disassembly and maintenance of pipelines, improving inspection efficiency and reducing maintenance costs.

[0015] (6) Adaptable to cold regions: Specifically designed for road engineering in cold regions, it takes into account multiple functions such as heat preservation, waterproofing, and load-bearing capacity, thereby improving the durability of roads. Attached Figure Description

[0016] The accompanying drawings are provided to further illustrate the present invention and form part of the specification. They are used together with the embodiments of the present invention to explain the present invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the overall structure of this utility model; Figure 2 This is a utility model Figure 1 Schematic diagram of the overall structure along the CC direction; Figure 3 This is a schematic diagram of the overall structure of the foamed concrete insulation layer of this utility model; Figure 4 This is a flowchart of the construction method of the prefabricated insulation layer according to an embodiment of this utility model; In the diagram: 1-Crushed stone drainage base layer, 2-Soft soil buffer layer, 3-Waterproof isolation layer, 4-Fiber insulation board, 5-Cement-mixed gravel bearing base layer, 6-Geocell, 7-Foamed concrete insulation layer, 8-Reinforced soil layer, 9-Surface protective layer. Detailed Implementation

[0017] 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. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0018] Please see Figure 1-4This utility model provides a technical solution: a prefabricated insulation layer for large-diameter shallow-buried pipes made of foamed concrete, comprising a layered structure from bottom to top: The bottom layer 1 is a gravel drainage system, made of crushed stone or gravel with a particle size of 5-20mm, a thickness of 20-30cm, and a slope of 2%-3%. The soft soil buffer layer 2 is composed of soft soil that has been screened through 20 mesh and 200 mesh, and has a thickness of 10 cm. Waterproof isolation layer 3 uses HDPE geomembrane to isolate surface water and improve the protection of the pipeline; Fiber insulation board 4 is made of fiber materials such as glass fiber, carbon fiber or nanocellulose combined with cement or asphalt substrate, with a thickness of 5mm-10mm. The joints are sealed with adhesive to prevent thermal bridging effect. The cement-mixed gravel-sand load-bearing base layer 5 is constructed using precast concrete slabs; The foamed concrete insulation layer 7 has a thermal conductivity of less than 0.1 W / (m·K) and can be prefabricated or poured on-site into the geocell 6; The foamed concrete layer 7 comprises the following components by weight percentage: composite foaming agent: expands 700-1000 times in volume after dilution; fiber: 0.6%-1.2%; quick-setting agent and other materials: 4%-6%; expanded perlite: 5%-8%; water-reducing agent: ≤1%; antifreeze agent: 0.5%-2% of the total concrete mass; the components of the foamed concrete are mixed to form a lightweight thermal insulation structural layer; The reinforced soil layer 8 is composed of multiple layers of high-strength steel slag sand material, which are connected by geosynthetic materials to form an integral structure, thereby improving compressive strength and deformation resistance. Surface protective layer 9 uses polymer-modified cement concrete to improve durability and frost heave resistance; This utility model provides a prefabricated insulation layer for large-diameter shallow-buried pipelines made of foamed concrete. It enables rapid and uniform pipeline insulation through simple assembly during pipeline construction, and the insulation layer exhibits better stability, significantly improving energy efficiency and freeze-thaw resistance in cold regions. It also enhances the stability and durability of the pipeline, making it particularly suitable for road construction in cold areas. Through reasonable material selection and layered design, it provides an efficient solution that balances roadbed insulation and strength. Furthermore, the use of prefabricated substrates and modular assembly of the insulation layer reduces construction difficulty and costs, significantly optimizes costs and simplifies construction by reducing pipeline burial depth, and significantly reduces labor and material costs associated with later maintenance. This utility model's integrated pipeline-roadbed composite structure comprises the following components: Crushed stone drainage layer 1: Located at the bottom of the roadbed, it uses crushed stone or gravel to ensure good drainage performance, reduce stress concentration caused by direct contact between the pipeline and the insulation layer, reduce the impact of groundwater on the roadbed, and lower the risk of frost heave; Soft soil buffer layer 2: Used to reduce the uneven impact of foundation settlement and improve overall stability; Waterproof isolation layer 3 and fiber insulation board 4: High-efficiency insulation board is laid around the pipeline, and high-density polyethylene (HDPE) geomembrane is used to isolate surface water, improving the pipeline's protective capabilities. The fiber insulation board 4 is made of the following materials: Fiber material, selected from one or more of glass fiber, carbon fiber, and nanocellulose; Substrate, selected from one or more of cement and asphalt; Adhesive, used to bond the fiber material to... Substrate bonding; Cement-mixed gravel load-bearing base layer 5: Used to provide the main load-bearing support, improve overall strength, and enhance resistance to traffic loads; Foamed concrete insulation layer 7: Foamed concrete is laid on top of the load-bearing base layer. This layer has an optimized mix ratio. Foamed concrete provides excellent insulation due to its low density and high porosity. The addition of expanded perlite further enhances its insulation effect. By introducing industrial waste such as waste steel slag, the mechanical properties and resource utilization of the material are improved. The mechanical properties are further enhanced by incorporating fiber materials; Reinforced soil layer 8: A reinforcement layer is laid on the foamed concrete insulation layer 7 to improve compressive strength and deformation resistance; High-performance composite surface protective layer 9: Polymer-modified cement concrete is used to enhance durability, improve freeze-thaw resistance, and improve the waterproof performance of the subgrade; Specifically, the concrete slab uses ordinary Portland cement with a strength grade ≥32.5, and the sand material is medium or coarse sand with a mud content ≤3%; the gravelly sand material is hard and clean, well-graded, and the maximum particle size is ≤2 / 3 of the thickness of the concrete slab; the admixtures are antifreeze and water-reducing agent, accounting for 0.5%-2% and 0.5%-1.5% of the total concrete mass, respectively; Specifically, the reinforced soil layer 8 is composed of high-strength steel slag sand material with a particle size of 0.075-2mm and a mud content of no more than 5%. Each layer is reinforced and connected by geosynthetic geotextile to form an integral structure. The construction method for prefabricated insulation layers of large-diameter shallow-buried pipelines using foamed concrete includes the following steps: S1, Foundation preparation and construction of crushed stone drainage layer 1: After the pipeline construction is completed, the crushed stone drainage layer 1 is assembled. The crushed stone drainage layer 1 reduces the stress concentration effect caused by direct contact between the pipeline and the insulation layer. The thickness of the crushed stone drainage layer 1 is controlled at 20-30cm, and uniform distribution and compaction are ensured. S2, Construction of soft soil buffer layer 2: Soft soil buffer layer 2 is laid on the crushed stone drainage bottom layer 1. The soft soil buffer layer 2 is leveled. The soft soil buffer layer 2 is made from soft soil excavated during the on-site pipeline construction. It is screened first through a 20-mesh sieve and then through a 200-mesh sieve to control the particle size within a certain range so as to play a buffering role. The thickness of the layer is 10cm, and the density is ensured by moist compaction. S3, Waterproof isolation layer 3 and fiber insulation board 4 construction: HDPE geomembrane is laid on soft soil buffer layer 2, and fiber insulation board 4 is laid on it. It is sealed by hot air welding or pressing process to ensure airtightness. S4, Cement-mixed gravel-sand load-bearing base course 5 construction: The cement-mixed gravel-sand load-bearing base course 5 uses precast concrete slabs. The concrete slabs are made of ordinary Portland cement with a strength grade of 32.5 or above. The sand should be medium or coarse sand with a mud content of no more than 3%. The gravel should be hard, clean, and well-graded. The maximum particle size should not exceed 2 / 3 of the thickness of the concrete slab. Antifreeze and water-reducing agent should be added. After preparation, the curing time should not be less than 14 days. Then, the slabs are laid alternately to ensure uniformity and levelness. S5, Construction of Geocells 6 and Foamed Concrete Insulation Layer 7: Multiple sets of alternating geocells 6 are placed on the surface of the cement-mixed gravel bearing base course 5 and fixed to the lower lateral geonet by anchoring rods. Then, the prepared foamed concrete is injected to form the foamed concrete insulation layer 7. The production of foamed concrete requires precise control of the proportion of foaming agent and the water-cement ratio of concrete. Composite foaming agent can be used, diluted 30-50 times and foamed to 700-1000 times the original volume. The water-cement ratio is 0.4-0.6 depending on the brand of concrete. The fiber content is 0.6%-1.2%. The quick-setting agent and other materials are controlled in the range of 4%-6%. The water-reducing agent content does not exceed 1%. The expanded perlite content is controlled in the range of 5%-8% to ensure its lightweight and loose structural characteristics, while ensuring its excellent mechanical properties. S6, Construction of reinforced soil layer 8 and surface protective layer 9: Lay a lateral geonet on the surface of foamed concrete insulation layer 7 and cover it with high-strength reinforced soil layer 8. Finally, lay a high-performance composite surface protective layer 9 on top of reinforced soil layer 8. S7, Quality Inspection and Acceptance: Conduct a comprehensive inspection of each layer, especially the stability, density, and structural connection of the foamed concrete insulation layer 7 and the reinforced soil layer 8, to ensure that the design standards are met. Specifically, in step S1, for areas with weak foundations or high water content, the foundation is replaced by using high-strength sand or stable soil, and then compacted mechanically. Specifically, in step S5, the foamed concrete insulation layer 7 can be selected from precast foamed concrete blocks or poured into the geocell according to the construction site conditions. The foamed concrete block adhesive used is lightweight concrete, and the aggregate-free or ultra-fine aggregate ratio is adopted. The foamed concrete blocks are made by mixing with the foaming agent. Specifically, in step S5, the geocells 6 are prefabricated. Multiple sets of geocells 6 are placed on the surface of the cement-mixed gravel bearing base course 5 according to the design position, and are fixed to the lower lateral geonet by anchor rods penetrating the mounting plate and the geocells 6. A reinforced soil layer and lateral geonet are laid on the outside of the geocells 6, and the first end of the geonet is hung on the anchor rods. The above process is repeated until the multiple sets of geocells 6 reach the design elevation. Specifically, in step S6, the multi-layer reinforced soil layer 8 is composed of high-strength steel slag sand material with a particle size of 0.075-2mm. The layers are reinforced and connected by geosynthetic materials and compacted by compaction machinery to ensure its density and stability. The density of each layer after compaction is ≥95%. Specifically, in step S6, the geonet is laid on the surface of the flat foamed concrete insulation layer 7, with a reserved reverse wrapping length at the tail end and wrapped around the pressure block in the reverse direction, and the reverse wrapping part is fixed by connecting rods. Specifically, in step S6, the thickness of the surface protective layer 9 is controlled at 5cm and reinforced with steel mesh to prevent the surface protective layer from cracking due to external forces.

[0019] Example

[0020] This embodiment details the structure and construction steps of a prefabricated insulation layer for pipelines, particularly suitable for insulation construction of large-diameter shallow-buried pipelines. This insulation layer possesses high-efficiency insulation performance and frost resistance, and effectively improves soil stability. The construction process is carried out according to the following steps: Step 1: Foundation preparation and construction of the gravel drainage sub-base 1 1.1 Foundation clearing After the pipeline construction is completed, the foundation around the pipeline is first cleaned up to remove debris, plant roots and unstable soil from the original surface to ensure the stability of subsequent construction. For soft foundations or areas with high water content, the foundation can be replaced with high-strength sand or soil with good stability, and compacted with machinery to improve the bearing capacity of the foundation.

[0021] 1.2 Construction of the Gravel Drainage Subbase After the foundation is cleared, a gravel drainage layer 1 is laid. The gravel layer generally uses gravel with a particle size of 5-20mm and a thickness of 20-30cm. During the construction of the gravel layer, it should be evenly distributed and compacted by vibratory compaction equipment. The slope of the gravel layer should be set according to the burial depth of the pipeline and the design requirements, generally 2%-3% slope, to ensure the drainage effect. The function of this layer is to reduce the direct contact between the pipeline and the insulation layer, reduce stress concentration and provide drainage function.

[0022] Step 2: Construction of Soft Soil Buffer Layer 2 2.1 Material Treatment for Soft Soil Buffer Layer The soft soil buffer layer 2 is made from soft soil material excavated during on-site construction. First, the soft soil is sieved using 20-mesh and 200-mesh screens to ensure that the particle size is controlled within a suitable range, avoiding excessively large or small particle sizes that could affect the buffering performance. The sieved soft soil should have good plasticity, capable of deforming without cracking under external pressure.

[0023] 2.2 Laying of Soft Soil Buffer Layer 2 The thickness of the soft soil buffer layer 2 is 10cm. During construction, attention should be paid to the flatness of the surface, and the material needs to be moistened and compacted to ensure its density and stability. During the construction process, a combination of manual and mechanical methods should be used to ensure that there are no voids or loose areas in the soft soil layer.

[0024] Step 3: Construction of waterproof isolation layer 3 and fiber insulation board 4 3.1 HDPE geomembrane laying HDPE geomembrane is laid on soft soil buffer layer 2. The main function of the geomembrane is waterproofing and isolation. During the laying process, the joints of the geomembrane should be sealed by hot air welding or pressing to ensure that the joints are tight and prevent water penetration. The membrane should be laid without damage and should be laid strictly according to the slope required by the design to ensure that its drainage function is not affected.

[0025] 3.2 Installation of Fiber Insulation Board 4 Fiber insulation board 4 is laid on HDPE geomembrane. The insulation board is made of materials such as glass fiber, carbon fiber, and nanocellulose, and uses cement or asphalt as the base material. The thickness is 5-10mm. During construction, the joints between each insulation board need to be bonded to ensure its airtightness. The insulation board should be laid without gaps to avoid thermal bridging.

[0026] Step 4: Construction of Cement-Mixed Gravel Bearing Base Course 4.1 Concrete mix proportion for load-bearing base course 5 The cement-mixed gravel load-bearing base course 5 is prepared by mixing ordinary Portland cement with a strength of not less than 32.5 grade with medium or coarse sand (mud content not more than 3%) and gravel. The maximum particle size of the gravel should not exceed 2 / 3 of the thickness of the concrete slab, and the gravel should have good gradation to ensure the strength and durability of the concrete.

[0027] 4.2 Construction of Precast Concrete Slabs During the prefabrication of concrete slabs, appropriate amounts of antifreeze and water-reducing agents should be added to enhance their frost resistance and impermeability. After the slabs are poured, they should be cured for no less than 14 days to ensure that they reach the design strength. During the laying of concrete slabs, uniformity and levelness should be maintained to avoid gaps or unevenness.

[0028] Step 5: Construction of geocell 6 and foamed concrete insulation layer 7 5.1 Geocell Installation Multiple geocells 6 are placed on the surface of the cement-mixed gravel-sand bearing base 5 at the positions required by the design. The geocells are prefabricated to ensure their strength and stability. Each geocell is fixed to the underlying geonet by anchor rods. The anchor rods penetrate the bottom of the geocell and are fixed in the base to ensure the stability of the geocell.

[0029] 5.2 Laying of Foamed Concrete Insulation Layer 7 After the geocell 6 is installed, depending on the site conditions, precast foamed concrete blocks or on-site poured foamed concrete can be selected. The thermal conductivity of foamed concrete is less than 0.1 W / (m·K), which has excellent thermal insulation performance. The production of foamed concrete requires precise control of the proportion of foaming agent and the water-cement ratio of concrete. Composite foaming agent can be used, diluted 30-50 times and then foamed to 700-1000 times the original volume. The water-cement ratio is 0.4-0.6 depending on the brand of concrete, the fiber content is 0.6%-1.2%, the quick-setting agent and other materials are controlled in the range of 4%-6%, the water-reducing agent content does not exceed 1%, and the expanded perlite content is controlled in the range of 5%-8% to ensure its lightweight and loose structural characteristics, while ensuring its excellent mechanical properties.

[0030] Step 6: Construction of reinforced soil layer 8 and surface protective layer 9 6.1 Laying of reinforced soil layer 8 Lateral geonets are laid on the surface of the foamed concrete insulation layer 7, and covered with a high-strength reinforced soil layer 8. The reinforced soil layer uses steel slag sand material with a particle size of 0.075-2mm and a mud content of no more than 5%. Each layer of reinforced soil material is reinforced and connected by geosynthetic materials. After each layer of reinforced material is laid, it is compacted by compaction machinery to ensure its density and stability.

[0031] 6.2 Surface Protective Layer 9 Construction A high-performance surface protective layer 9 is laid on top of the reinforced soil layer 8. This protective layer is made of polymer-modified cement concrete, with high molecular polymers added to improve its resistance to frost heave and durability. During construction, the thickness of the protective layer is controlled at 5cm and reinforced with steel mesh to prevent the surface protective layer from cracking due to external forces.

[0032] Step 7: Quality Inspection and Acceptance 7.1 Construction quality inspection at each level After construction is completed, a comprehensive inspection of each layer is conducted, especially the stability, density, and structural integrity of the foamed concrete insulation layer and reinforced soil layer. During the inspection, specialized instruments are used to measure parameters such as the thickness, strength, and thermal conductivity of the insulation layer to ensure that it meets design standards.

[0033] 7.2 Final Acceptance and Delivery After all construction work is completed and passes inspection, a final acceptance test is conducted to ensure that the construction quality and functionality of each layer of material meet the design requirements. In particular, the construction quality of the foamed concrete insulation layer requires close inspection to ensure it possesses the expected thermal insulation and frost protection properties. Ultimately, the construction quality and stability of the entire insulation layer are ensured before it is put into use.

[0034] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0035] Finally, it should be noted that the above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Although the utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A prefabricated insulation layer for large-diameter shallow-buried pipelines using foamed concrete, characterized in that: Includes a bottom-up hierarchical structure: The gravel drainage bottom layer (1) is made of gravel or sand and gravel material with a gravel particle size of 5-20mm, a thickness of 20-30cm, and a slope of 2%-3%; The soft soil buffer layer (2) is composed of soft soil that has been screened through 20 mesh and 200 mesh, and has a thickness of 10 cm. Waterproof isolation layer (3) uses HDPE geomembrane to isolate surface water and improve the protection of pipeline; Fiber insulation board (4) is made of glass fiber, carbon fiber or nanocellulose combined with cement or asphalt substrate, with a thickness of 5mm-10mm. The joints are sealed with adhesive to prevent thermal bridging effect. The cement-mixed gravel-sand load-bearing base course (5) is constructed using precast concrete slabs; The foamed concrete insulation layer (7) has a thermal conductivity of less than 0.1 W / (m·K) and can be prefabricated or poured on-site into the geocell (6); The reinforced soil layer (8) is composed of multiple layers of high-strength steel slag sand material, which are connected by geosynthetic materials to form an integral structure, thereby improving compressive strength and deformation resistance. The surface protective layer (9) uses polymer-modified cement concrete to improve durability and resistance to frost heave.

2. The prefabricated insulation layer for large-diameter shallow-buried pipelines using foamed concrete as described in claim 1, characterized in that: The concrete slab uses ordinary Portland cement with a strength grade ≥32.

5. The sand material is medium or coarse sand with a mud content ≤3%. The gravelly sand material is hard and clean, with good gradation and a maximum particle size ≤2 / 3 of the thickness of the concrete slab. The admixtures are antifreeze and water-reducing agent, which account for 0.5%-2% and 0.5%-1.5% of the total mass of concrete, respectively.

3. The prefabricated insulation layer for large-diameter shallow-buried pipelines using foamed concrete as described in claim 1, characterized in that: The reinforced soil layer (8) is composed of high-strength steel slag sand with a particle size of 0.075-2mm and a mud content of no more than 5%. Each layer is reinforced and connected by geosynthetic geotextile to form an integral structure.

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