A method for welding and laying large-diameter spiral steel pipes in different geological environments

Abstract

The present invention relates to the technical field of construction engineering construction, and particularly relates to a method for welding and laying large-diameter spiral steel pipes in different geological environments. The method includes (1) excavating a trench, (2) the pipe foundation and base, (3) pipe laying, and (4) pipe protection and backfilling. This method can avoid the problems of leakage, corrosion of the steel pipe affecting its service life, and excessive cost under complex geological conditions that occur to buried large-diameter spiral steel pipes in groundwater for a long time.

Description

Technical Field

[0001] The present invention relates to the technical field of construction engineering construction, and particularly relates to a method for welding and laying large-diameter spiral steel pipes in different geological environments. Background Art

[0002] At present, buried large-diameter spiral steel pipes are applied to outdoor water supply, petrochemical, electric power, agricultural irrigation, municipal water conservancy and other engineering constructions, and higher requirements are put forward for the welding, anti-corrosion and service life of buried large-diameter spiral steel pipes. The existing technologies for the laying construction of buried large-diameter spiral steel pipes mainly focus on solving the convenience of lowering large-diameter spiral steel pipes, reducing pipeline damage, welding environmental problems, and laying stability. For example, the large-diameter non-compensated direct-buried pipeline laying device and construction method in CN113757449A provide a safe and fast method for lowering into the trench for the damage of the pipeline during hoisting, and can be locally adjusted according to the position of the butt-jointed pipeline, mainly by means of the corresponding laying device structure to adjust the pipeline during hoisting; A natural gas pipeline construction method based on a construction protection device in CN108916470A discloses a method for moving the pipeline in a small range and short distance and adjusting the heights of both ends of the construction pipeline, mainly to solve the problems of wind prevention, rain prevention, heat preservation, temperature and humidity control during pipeline welding, and reduce the incidence of welding problems. Although such construction methods can achieve better welding of pipeline laying and reduce pipeline damage, etc., due to insufficient consideration of the influence of external environmental changes on laying construction, it is difficult to adapt to the adjustment of laying construction processes in different environments. In particular, when laying pipelines under special environmental conditions in the existing technology, corresponding devices are generally used. For example, a water-laying method pipeline laying facility in CN206347201U provides a water-laying method pipeline laying structure to prevent the support from being damaged and deformed and reduce the frictional resistance of the pipeline under the buoyancy force.

[0003] In order to better apply the welding and laying construction of large-diameter spiral steel pipes in different geological environments, aiming at the welding, anti-corrosion and protection problems of buried large-diameter spiral steel pipes, improving their service life, achieving advanced technology, economic rationality, safety and applicability, facilitating construction and management, ensuring quality, and standardizing and standardizing similar engineering constructions, the present invention discloses a construction method for applying buried large-diameter spiral steel pipes in different geological environments. Summary of the Invention

[0004] The present invention provides a method for welding and laying large-diameter spiral steel pipes in different geological environments, avoiding the problems of leakage, corrosion of steel pipes affecting service life, and excessive cost in complex geological conditions of buried large-diameter spiral steel pipes in groundwater for a long time, and solving the problems existing in the prior art.

[0005] The technical solution adopted by the present invention to solve the above technical problems is:

[0006] A method for welding and laying large-diameter spiral steel pipes in different geological environments, including the following operating steps:

[0007] (1) Excavating trenches

[0008] When excavating trenches above the groundwater level, direct excavation can be carried out without dewatering; when excavating trenches below the surface water or groundwater level, dewatering measures should be taken in advance for diversion and drainage before excavation;

[0009] (2) Pipe foundation and base

[0010] Carry out bearing capacity tests on the pipe parts in different geological environments and reinforce them according to the design requirements; the pipe foundation adopts a sand cushion foundation;

[0011] (3) Pipe laying

[0012] Lift the pipe to the pipe position of the sand cushion foundation of the pipe, butt the joints section by section, and then carry out step-by-step welding:

[0013] The first step is to carry out V-groove butt spot welding to fix the ends of the steel pipes. After completion, the second step is to use argon arc welding to carry out circumferential sealing at the pipe joints. Then, the third step is to use CO2 shielded welding to carry out full-circle filling welding of the welds. The fourth step is to continue multi-layer filling welding, and the last step is to carry out cover welding. The welding thickness of each layer and each step is 3-4 mm. After all are completed, the welding slag on the surface is removed;

[0014] After detecting the pipe welds, carry out anti-corrosion protection on the welded joints and other parts where anti-corrosion is not in place;

[0015] (4) Pipe protection and backfilling

[0016] According to the design requirements, different construction protection measures are taken for different geological environment positions where the pipes are located, including:

[0017] On land, after backfilling with gravel or original soil without stones around the large-diameter spiral steel pipe, continue backfilling with the original soil; the soil cover on the pipe top is ≥1.5 m;

[0018] In the river channel, after continuously pasting asphalt felt closely to the steel pipe and using reinforced concrete capping for enveloping on the upper part of the large-diameter spiral steel pipe, continue backfilling with the original soil; the soil cover on the pipe top is ≥2 m;

[0019] In the reservoir area, after locally pasting asphalt felt closely to the steel pipe and using partial reinforced concrete capping for enveloping on the upper part of the large-diameter spiral steel pipe, continue backfilling with the original soil; the soil cover on the pipe top is ≥1 m.

[0020] Furthermore, in step (2), the sand cushion foundation adopts medium coarse sand or stone chips; the compaction degree: ≥90% at the bottom; ≥95% on the pipe side.

[0021] Furthermore, in step (3), the weld reinforcement of the cover welding for pipe laying is controlled within 2 mm.

[0022] Further, in step (3), an anti-corrosion product is used to protect the welded joints and other parts that are not easily reachable for anti-corrosion; the anti-corrosion product is H55 anti-corrosion coating for drinking water containers.

[0023] Further, in the fourth step of multi-layer filling welding in step (3), the number of welding layers for multi-layer welding is determined according to the pipe thickness.

[0024] Further, after laying the felt on the large-diameter spiral steel pipe in step (4), a steel bar mesh is laid and tied, and concrete is poured to form a reinforced concrete coping.

[0025] Further, the gravel or original soil without stones used in step (5) for backfilling is gravel with a particle size less than 40 mm or original soil that meets the requirements; the compaction degree: on the side of the pipe: ≥ 95%; on the top of the pipe: ≥ 85%; the compaction degree of continuous original soil backfilling ≥ 90%.

[0026] Further, before excavating the trench, the method of the present invention also includes the following preparatory work:

[0027] (1) Construction survey

[0028] According to the layout plan of the buried large-diameter spiral steel pipe, organize the survey and setting out for trench excavation according to the construction cross-section diagram, pipe diameter, burial depth, and trenching slope, determine the pipe center line, release the trench excavation range, and set the side stakes on both sides of the trench;

[0029] (2) Protection of existing pipelines

[0030] Conduct a joint review of the existing underground pipelines within the determined trench excavation range.

[0031] Further, the method of the present invention also includes step (5) hydrostatic test: after the pipeline is laid and passes the acceptance, conduct the hydrostatic test of the pipeline; after passing the inspection, enter the acceptance process.

[0032] Further, in step (1), the dewatering measure adopts the method of open drainage and diversion dewatering; the trench excavation adopts slope excavation and mechanical excavation with manual cooperation.

[0033] Further, in step (1), the dewatering measure is determined according to the site hydrogeological conditions of the project location and the depth of the trench bottom to be excavated, considering whether dewatering measures are required; if dewatering is required, it is required to drain the perched water, phreatic water, and interlayer water, and lower the confined water level, and preferably adopt the method of open drainage and diversion dewatering.

[0034] Further, the specific operation content of the pipeline foundation and base in step (2) includes: conducting a bearing capacity test on the pipeline parts in different geological environments, and for the soft soil foundation or the sections where the bearing capacity does not meet the requirements and there is uneven settlement of the foundation, carry out reinforcement treatment according to the design requirements;

[0035] The pipeline foundation is laid according to the design requirements. Generally, a sand cushion foundation is adopted. For general soil sections, only one layer of sand cushion needs to be laid at the base, with a thickness of 0.2 m. For soft soil foundations where the bottom of the trench is below the groundwater level, it is advisable to lay a layer of gravel foundation with a thickness of not less than 0.2 m; alternatively, a construction method using large gravel with a particle size of 5 - 40 mm and coarse sand on top can be adopted. To facilitate the welding operation of steel pipes, a groove sufficient for welding personnel should be excavated in the pipeline foundation at the welding position. After welding is completed and passes the flaw detection and the anti-corrosion layer protection acceptance, it should be immediately filled with sand.

[0036] Advantages of the present invention:

[0037] 1. First, a medium - coarse sand cushion is laid at the bottom of the pipeline. After the pipeline is laid and passes the inspection, different pipeline protection and backfilling methods are adopted for different positions of the pipeline during construction. When laying large - diameter spiral steel pipes in different geological environments, the mechanical strength of the pipeline itself and its accessories are used to jointly bear the internal pressure of the pipeline and the load on the top of the pipe. The large - diameter spiral steel pipes are customized in the factory, and the on - site installation work is simple. There is no need to build a trench, and the earthwork and civil engineering quantities are small. The construction progress is fast, and the investment cost of the pipe network can be saved.

[0038] 2. The anti - corrosion products used in the anti - corrosion treatment of the present invention have a health permit approval, and have good adhesion, convenient construction, fast drying, good corrosion resistance to acids, alkalis, and salts, and excellent water - resistance, oil - resistance, and weather - resistance.

[0039] 3. The connection of the large - diameter spiral steel pipes of the present invention adopts the "step - by - step welding method for butt joints". The construction process is convenient for quality control, the quality standards are clear, and the welding quality of the pipeline is reliable and the sealing performance is good.

[0040] 4. For the pipeline laid in different geological environments, such as on land, in reservoirs, and rivers, the present invention adopts different construction protection measures for pipeline protection and backfilling, saves investment as much as possible, and solves the problem of excessively high construction cost of pipeline projects in complex geological conditions. Description of the Drawings

[0041] Figure 1 It is the buried pipe cross - section view of the land geological environment of the present invention;

[0042] Figure 2 It is the buried pipe cross - section view of the river geological environment of the present invention;

[0043] Figure 3 It is the buried pipe plan layout view of the reservoir geological environment of the present invention;

[0044] Figure 4 is Figure 3 the buried pipe cross - section view;

[0045] Figure 5This is a schematic diagram of the V-groove welding joint of the large-diameter spiral steel pipe of the present invention.

[0046] Among them, 1. Existing communication optical cables, 2. Large-diameter spiral steel pipes, 3. Tar paper, 4. Steel bar mesh, 5. C25 reinforced concrete coping, 6. Welds, 7. Pipeline center line, 8. Tack welding, 9. Peripheral sealing, 10. Full-circle filling welding, 11. Continuing full-circle filling welding, 12. Surfacing welding, ①. Medium-coarse sand cushion layer, ②. Gravel or original soil backfill without stones, ③. Original soil backfill. Specific implementation manners

[0047] To clearly illustrate the technical features of this solution, the present invention will be elaborated in detail below through specific implementation manners in conjunction with the accompanying drawings.

[0048] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0049] Before the formal construction of the buried large-diameter spiral steel pipe welding in different geological environments, it is necessary to review the on-site construction conditions, ensure power supply, water supply, roads, communication, site leveling, measure and set out the lines, set up the pipeline plane control traverse, conduct elevation measurement, organize the materials to enter the site, and ensure the quality of pipeline materials.

[0050] In this embodiment, the welding construction of the DN1600 buried water conveyance pipeline is carried out under different geological conditions such as land, reservoir, and river.

[0051] The inner diameter D of the water conveyance pipeline to be laid in this embodiment is 1600 mm, the outer diameter D' is 1628 mm, the operating space on both sides of the pipe is taken as 500 mm, the length L of the pipe section used in the construction is 12 m, and the thickness h of the pipeline cushion layer is 200 mm. Among them, the material preparation includes 2 DN1600 steel pipes, welding electrodes, steel bar mesh sheets, medium-coarse sand (①), tar paper 3, etc.; the preparation of construction mechanical equipment includes the entry, installation and commissioning of mechanical equipment, mainly including 320C backhoe excavators, ZL40 loaders, 25t - 50t truck cranes, welding machines, gas cutting equipment, small rollers, submersible pumps, etc.

[0052] The labor allocation arrangement for each construction team is as follows: 7 people in a group, including 4 people welding two welds at both ends of the pipeline simultaneously, 1 on-site commander, and 1 driver for each of the excavator and the truck crane.

[0053] In this embodiment, the value of m in the slope coefficient 1:m is determined according to the hydrogeological conditions and the excavation depth. According to the plan layout of the buried large-diameter spiral steel pipe, the trench excavation is organized based on the cross-section diagram, pipe diameter, burial depth, and slope coefficient of the construction location. For the protection of the existing communication optical cable 1, methods such as channel steel, I-beam, wire, and steel bar are used to lift it up.

[0054] The specific implementation process includes the following operating steps:

[0055] 1. Construction survey

[0056] According to the plan layout of the buried large-diameter spiral steel pipe, the trench excavation is organized based on the construction cross-section diagram, pipe diameter, burial depth, and grooving slope. The surveying and setting out are carried out to determine the pipe center line, release the trench excavation range, and set the side stakes on both sides of the trench.

[0057] 2. Protection of existing pipelines

[0058] For the existing underground pipelines within the determined trench excavation range, a joint signature is carried out: insert signs to mark the types, sizes, positions, and covering depths of the underground pipelines; for important pipelines, ask the competent unit to send personnel to the site for on-site supervision. For key positions such as existing crossing pipelines and the intersection points of new and old pipelines, arrange special personnel to excavate exploratory trenches. After finding the existing pipelines, make written records, obvious marks, take photos or leave video materials, take protective measures to prevent damage, and make eye-catching signs to make the construction personnel pay attention; for the suspension of existing pipelines, methods such as channel steel, I-beam, wire, and steel bar can be used to lift them up.

[0059] 3. Dewatering of the trench

[0060] According to the site hydrogeological conditions of the project location and the depth of the trench bottom to be excavated, consider whether dewatering measures are required; if dewatering is required, it is required to drain the perched water, phreatic water, and interlayer water, and lower the confined water level. The open drainage and diversion dewatering methods are preferably used.

[0061] 4. Trench excavation

[0062] Slope excavation is preferably used, and the slope coefficient is determined according to the hydrogeological conditions and excavation depth.

[0063] During mechanical excavation, the elevation of the foundation bottom is strictly controlled. If local overexcavation or disturbance occurs, the soil cannot be backfilled. Instead, natural graded gravel with a maximum particle size of 10 - 15 mm or crushed stone with a maximum particle size less than 40 mm can be replaced and leveled and tamped. The width of the trench bottom is: the outer diameter of the large-diameter spiral steel pipe plus 0.5 - 0.7 m; during rainy season construction, the grooving length should be shortened as much as possible to achieve fast grooving, fast backfilling, and anti-flooding measures for the trench. Once flooding occurs, the water should be drained, the flooded soil layer should be removed, and gravel or medium-coarse sand should be replaced to do a good job in foundation treatment.

[0064] 5. Pipeline foundation and base

[0065] For the pipeline parts in different geological environments, conduct foundation bearing capacity tests. For soft soil foundations or areas where the bearing capacity fails to meet the requirements and there are uneven settlements, carry out reinforcement treatment according to the design requirements.

[0066] The pipeline foundation is laid according to the design requirements. Generally, a sand cushion foundation is adopted. For general soil sections, only one layer of sand cushion with a thickness of 0.2m needs to be laid at the base; for soft soil foundations where the bottom of the trench is below the groundwater level, it is advisable to lay a layer of gravel foundation with a thickness of not less than 0.2m. It can also be constructed by using large gravel with a particle size of 5 - 40mm and spreading coarse sand on top. To facilitate the welding operation of steel pipes, a groove sufficient for personnel welding should be excavated and reserved at the welding part of the pipeline foundation. After the welding is completed and passes the flaw detection and the anti-corrosion layer protection acceptance, it should be immediately filled with sand.

[0067] 6. Pipeline laying

[0068] Pipeline hoisting: In this embodiment, for the pipeline hoisting during pipeline laying, a 25t - 50t truck crane is used in cooperation with manual labor. The pipeline is hoisted into the trench using non-metallic ropes or special soft belts, and the pipeline is placed smoothly on the pipe position of the medium - coarse gravel foundation.

[0069] Pipeline alignment: Use a truck crane to slightly move the next section of the steel pipe so that one end of the steel pipe is aligned with the end of the previous section of the steel pipe, the pipeline is centered, and the beveled edges are flush to meet the welding conditions. With the cooperation of the crane, the welder spot - welds a small section at intervals at the beveled edge of the steel pipe to fix the ends of the two steel pipes. Then the truck crane continues the alignment work of the next section of the pipeline.

[0070] Pipeline welding: Weld step - by - step according to the wall thickness of 14mm of the DN1600 large - diameter spiral steel pipe 2. First, the first step is butt - joint spot - welding 9, which is V - type bevel butt - joint spot - welding to fix the ends of the steel pipe. Then, the second step is to use argon arc welding to perform circumferential sealing 10 at the pipeline interface. The third step is to use CO2 shielded welding to perform full - circle filling welding 11 of the weld joint. The fourth step is to continue multi - layer filling welding 12. The number of multi - layer welding layers can be determined according to the pipeline thickness. Finally, the cover - face welding 13 is carried out, and the weld reinforcement is controlled within 2mm. The welding thickness of each layer and each step is 3 - 4mm. After all are completed, the surface slag is removed, as Figure 5 shown.

[0071] In this embodiment, pipeline weld inspection: Ultrasonic inspection is carried out according to NB / T47013.3 - 2015, the inspection quantity is 100%, and the quality grade is not lower than Grade Ⅱ; X - ray flaw detection inspection is carried out according to NB / T47013.2 - 2015, the inspection quantity is 5% (calculated based on the total length of the weld, and each weld should be divided into at least 4 parts for inspection in the up - down, left - right directions), and the quality grade is not lower than Grade Ⅲ.

[0072] Anti-corrosion of pipe weld joints: After the pipeline welding flaw detection is qualified, wooden planks are used to temporarily position the pipeline to prevent the center and elevation of the pipeline from displacement and change, and the design elevation and design centerline are re-measured. The deviation should be controlled within the allowable error range, and then the welding interface and other parts that cannot be anti-corroded are protected against corrosion. The anti-corrosion product uses H55 anti-corrosion paint for drinking water containers; color: the primer is colorless, the internal anti-corrosion topcoat is gray, and the external anti-corrosion topcoat is black. Coating composition and characteristics: Component 1: epoxy modified acrylic polyurethane resin, non-toxic anti-corrosion pigments and fillers, additives, etc.; Component 2: curing agent and environmentally friendly solvents, additives, etc.

[0073] Anti-corrosion structure: The inner wall of the pipeline is anti-corrosion, two bottoms and two sides (ordinary anti-corrosion); the outer wall of the pipeline is anti-corrosion, two cloths and six oils (enhanced anti-corrosion).

[0074] After the anti-corrosion protection is accepted, the next construction process will be carried out.

[0075] 7. Inspection well construction

[0076] Construct according to the design drawings. When the concrete strength of the inspection well bottom plate reaches 5Mpa, reinforced concrete wall or masonry wall work can be carried out. If the inspection well is built with masonry, its inner surface needs to be plastered with 1:2 mortar with a thickness of 2cm. The mortar mix ratio must be accurate to prevent leakage in the inspection well.

[0077] 8. Pipeline protection and backfilling

[0078] According to the design requirements, different construction protection measures are taken for different locations of pipelines - land, river, reservoir, such as Figures 1-4 shown.

[0079] The backfill is compacted in layers, and the height of each backfill layer is not more than 0.2m. From the bottom foundation of the pipe to the range of 0.5m above the top of the pipe, manual backfill is adopted, and mechanical bulldozing is strictly prohibited. The backfill materials are generally medium and coarse sand, crushed stone chips, etc. When backfilling, there must be no water, organic matter and frozen soil in the groove. The chest area can be backfilled with gravel or good quality soil, see Table 1. Backfilling is carried out symmetrically from both sides of the pipeline, inspection well and other structures at the same time to ensure that the pipeline and structures do not move, and limit measures are taken when necessary.

[0080] Table 1 General buried pipe backfill

[0081]

[0082] On land, medium-coarse sand cushion (①) + large-diameter spiral steel pipe + gravel or stone-free original soil backfill around the pipe (②) + original soil backfill ③, the top of the pipe is covered with soil ≥ 1.5m. Figure 1 As shown;

[0083] In the river channel, medium-coarse sand cushion layer (①) + large-diameter spiral steel pipe + upper uninterrupted tarpaulin 3 close to the large-diameter spiral steel pipe and C25 reinforced concrete top 5 encapsulation + original soil backfill ③, the pipe top soil cover ≧2.0m, such as Figure 2 As shown;

[0084] The reservoir area adopts medium-coarse sand cushion (①) + large-diameter spiral steel pipe + upper local tarpaulin 3 close to the large-diameter spiral steel pipe and local C25 reinforced concrete top 5 encapsulation + original soil backfill (② or ③), the pipe top soil cover ≧1.0m, such as Figure 3 , Figure 4 shown.

[0085] Note that the reinforced concrete top 5 should be at least 0.5m away from the weld 6.

[0086] 9. Water pressure test

[0087] After the pipeline is laid and accepted, a water pressure test is conducted on the pipeline. Before the test, the height of the backfill on both sides of the pipeline and above the top of the pipe should not be less than 0.5m, and the joint part should be exposed for observation at 0.2m. The water pressure test in this embodiment is divided into sections with a length of 1km. According to the actual situation on site, a pressure test pipe is set at the open end, an exhaust pipe and a pressure gauge are set at the high part of the pipe section, and a drain pipe is set at the low part. Before the project is delivered for use after the test is qualified, a completion acceptance is carried out, the completion acceptance materials are verified, and necessary re-inspections and appearance inspections are carried out. The project is delivered after the acceptance is qualified.

[0088] Back design after the pressure test pipe section is sealed: According to the requirements of the design and specifications, the back design after the pressure test pipe section is sealed generally adopts steel support and top support, and the end of the pipeline adopts concrete piers as back support on the soil of the foundation pit. The back pressure verification is required: including the design maximum test pressure, the area of ​​the sealing plate, the total thrust of the back, the total area of ​​the back, the pressure of the back, etc., to determine the blind plate design plan of the hydraulic pipe section.

[0089] The large-diameter spiral steel pipe blind plate is backed by an original soil reinforced back wall or a plain concrete back wall, and then multiple 100T jacks are used on the back wall to evenly support the blind plate in the up, down, left and right directions, so that the blind plate will not be displaced in the axial direction of the pipe due to the increase in pressure in the pipe when it is pressed.

[0090] After the water pressure rises to the test pressure, record the pipeline pressure every 3 minutes for 30 minutes. If the pipeline pressure continues to rise during these 30 minutes, the water pressure test result is qualified. If the residual water pressure in the test pipeline has no upward trend within 30 minutes, continue to observe for another 60 minutes. If the pressure drop does not exceed 0.02MPa within the entire 90 minutes, the water pressure test result is qualified.

[0091] The above specific embodiments shall not be construed as limiting the scope of the present invention. For those skilled in the art of this technology, any alternative improvements or transformations made to the embodiments of the present invention shall fall within the scope of protection of the present invention.

[0092] Those details not described in the present invention are all well-known technologies to those skilled in the art of this technology.

Claims

1. A method for welding and laying large-diameter spiral steel pipes in different geological environments, characterized in that, It includes the following operating steps: (1) Excavate the trench When excavating the trench above the groundwater level, it can be directly excavated without dewatering; when excavating the trench below the surface water or groundwater level, dewatering measures shall be adopted in advance for diversion drainage before excavation; (2) Pipe foundation and base Carry out bearing capacity tests on the pipe parts in different geological environments and reinforce them according to the design requirements; the pipe base adopts a sand cushion base; (3) Pipe laying Lift the pipe to the pipe position of the sand cushion base of the pipe, butt the joints section by section, and then carry out step-by-step welding: The first step is to carry out V-groove butt tack welding to fix the end of the steel pipe. After completion, the second step is to use argon arc welding to seal the circumference of the pipe joint. Then the third step is to use CO2 shielded welding to fill and weld the entire circumference of the weld. The fourth step is to continue multi-layer filling welding. The last step is to carry out capping welding. The welding thickness of each layer and each step is 3-4 mm. After all are completed, remove the welding slag on the surface; After inspecting the pipe welds, carry out anti-corrosion protection on the welded joints and other parts that are not anti-corroded; (4) Pipe protection and backfilling According to the design requirements, different construction protection measures shall be taken for different geological environment positions where the pipe is located, including: On land, after backfilling with gravel or original soil without stones around the large-diameter spiral steel pipe, continue backfilling with the original soil; The soil cover on the pipe top is ≥1.5 m; In the river channel, after continuously pasting asphalt felt closely to the steel pipe and using reinforced concrete capping for enclosure on the upper part of the large-diameter spiral steel pipe, continue backfilling with the original soil; the soil cover on the pipe top is ≥2 m; In the reservoir area, after locally pasting asphalt felt closely to the steel pipe and using partial reinforced concrete capping for enclosure on the upper part of the large-diameter spiral steel pipe, continue backfilling with the original soil; the soil cover on the pipe top is ≥1 m; (5) Hydrostatic test After the pipe laying is completed and passes the acceptance, carry out hydrostatic inspection of the pipe; after passing the inspection, enter the acceptance process.

2. A method for welding and laying large-diameter spiral steel pipes in different geological environments according to claim 1, characterized in that, In step (2), the sand cushion base adopts medium-coarse sand or stone chips; the compaction degree: at the bottom ≥90%; on the pipe side: ≥95%.

3. A large-diameter spiral steel pipe welding and laying method for different geological environments according to claim 1, characterized in that, In step (3), the weld reinforcement of the capping welding for pipe laying is controlled within 2 mm.

4. A method for welding and laying large-diameter spiral steel pipes in different geological environments according to claim 1, characterized in that, In step (4), the gravel or original soil without stones used for backfilling is gravel with a particle size less than 40 mm or the original soil that meets the requirements; the compaction degree: on the pipe side: ≥95%; on the pipe top: ≥85%; the compaction degree of the continued backfilling with the original soil is ≥90%.

5. A method for welding and laying large-diameter spiral steel pipes in different geological environments according to claim 1, characterized in that, Before excavating the trench, the following preparatory work is also included: (1) Construction survey According to the plane layout diagram of the buried large-diameter spiral steel pipe, organize the survey and setting out for trench excavation according to the construction section drawing, pipe diameter, burial depth and trenching slope, determine the pipe center line, release the trench excavation range, and set out side stakes on both sides of the trench; (2) Protection of existing pipelines Carry out joint signature for the existing underground pipelines within the determined trench excavation range.

6. A method for welding and laying large-diameter spiral steel pipes in different geological environments according to claim 1, characterized in that, In step (1), the dewatering measure adopts the method of open drainage and diversion drainage; the trench excavation adopts slope excavation and mechanical excavation with manual cooperation.

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