Multi-row buried pipeline construction method for soft soil texture in narrow space

Abstract

The invention discloses a construction method for multiple rows of buried pipelines of a soft soil texture in a narrow space. The construction method comprises the following steps that the pipelines are optimally arranged through the BIM technology; earth excavation is conducted; a formwork is erected, and a cushion layer is poured; groove machining is conducted on the lower-layer pipeline; the lower-layer pipeline of the finished product is hoisted in place to the pipeline arrangement position; a manhole is formed in the top of the lower-layer pipeline close to the weld joint; a welder enters the lower-layer pipeline through the manhole, an inner groove is formed in the lower portion of the lower-layer pipeline, and the pipeline is welded; after coming out of the manhole, a welder plugs the manhole by welding the plugging plate; temporarily plugging the pipeline, and performing a hydrostatic test; after the water pressure test is qualified, concrete encapsulation is poured; laying an upper-layer pipeline, wherein the butt welding method of the pipeline is the same as that of a lower-layer pipeline; after the water pressure test of the upper-layer pipeline is qualified, performing external corrosion prevention on the pipeline; and backfilling earthwork. The problems that multiple layers of pipelines are difficult to weld, and an existing construction mode cannot meet pipeline construction under the narrow space and soft soil geological conditions can be solved.

Description

Technical Field

[0001] This invention relates to the field of sewage treatment facility installation and construction technology, specifically a method for constructing multiple rows of buried pipelines in soft soil in narrow spaces. Background Technology

[0002] With the rapid advancement of urbanization, urban land resources are becoming increasingly scarce, especially in the field of wastewater treatment engineering. Wastewater treatment plants often have compact layouts and close spacing between various water tanks and structures. At the same time, the special nature of water treatment processes dictates that related pipelines are typically large in diameter and numerous, which poses a significant challenge to the layout and construction of buried pipelines.

[0003] Traditional multi-row buried pipeline construction methods employ a parallel laying pattern, where multiple pipelines are arranged side-by-side on the same horizontal plane. This method requires a large amount of lateral space, which is often impossible to implement in land-constrained wastewater treatment plant projects due to insufficient space. Furthermore, urban wastewater treatment plant sites are often located in soft soil, which has low bearing capacity and high compressibility. Traditional construction methods lack specific foundation treatment measures, easily leading to problems such as settlement and displacement after pipeline laying, affecting the stability of pipeline operation.

[0004] More importantly, if multi-layer pipe layout is attempted in traditional construction to save space, the narrow spacing between the upper and lower pipes makes it difficult to weld the bottom joints of the lower pipes from the outside, resulting in compromised welding quality. This not only increases construction difficulty and reduces construction efficiency, but also greatly increases the risk of joint leakage during later operation of the pipeline, affecting the normal operation of the sewage treatment system.

[0005] Furthermore, traditional pipeline route planning relies heavily on experience and lacks precise digital optimization methods. This makes it difficult to find the optimal pipeline route in complex site environments such as water tanks, main roads, and green belts, further exacerbating problems such as low site utilization efficiency and frequent construction conflicts. Therefore, there is an urgent need for a multi-row buried pipeline construction method that can adapt to narrow spaces and soft soil conditions, solve the challenges of welding multi-layer pipelines, and improve site utilization and construction quality. Summary of the Invention

[0006] This invention provides a method for constructing multi-row buried pipelines in narrow spaces and soft soil conditions, which can solve the problems of difficult welding of multi-layer pipelines and the inability of existing construction methods to meet the requirements of pipeline construction in narrow spaces and soft soil conditions.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for constructing multi-row buried pipelines in soft soil geology within narrow spaces, comprising the following steps: S1. Determine the pipeline laying plan and use BIM technology to optimize the pipeline layout in the green belt between the water tank structure and the main road; S2. Earthwork excavation, excavating to 100mm below the design pipe bottom elevation, forming a slope on one side of the main road after excavation; S3. Erect formwork and pour the foundation layer; S4. Beveling of the lower-level pipes; S5. Hoist the finished lower-level pipes into place at the pipe layout location; S6. Assembly and welding of lower-level pipes and butt welds; S7. Make a manhole at the top of the lower-level pipe near the weld, the size of which should be sufficient for the welder to enter; S8. The welder enters the lower pipeline through the manhole, cuts an inner bevel at the bottom of the lower pipeline, and welds the pipeline. S9. After the weld seam on the inner wall of the pipeline has cooled, apply anti-corrosion treatment. S10. After the welder comes out of the manhole, he seals the manhole with a welding sealing plate. The sealing plate and the outer wall of the lower pipeline are welded together with fillet weld. S11. Temporarily seal the pipeline and conduct a water pressure test; S12. After the water pressure test is passed, pour concrete to enclose the pipe. When pouring concrete, pay attention to the uniformity and symmetry of the left and right sides to prevent the pipe from moving or floating. S13. Once the concrete has reached a certain strength, the upper-level pipes can be laid. The butt welding method for the pipes is the same as that for the lower-level pipes. S14. After the upper pipeline passes the water pressure test, the pipeline shall be externally protected against corrosion. S15. Erect formwork and encase the pipe with concrete. S16. Earthwork backfilling.

[0008] The above construction plan uses BIM technology to precisely optimize pipeline routes, placing pipelines in the green belt between the water tank structure and the main road to make full use of idle space. At the same time, it adopts a double-layer pipeline laying mode to adapt to the construction needs of narrow spaces. By pouring a concrete cushion layer as the pipeline foundation, the pipeline load is effectively distributed, the foundation bearing capacity is improved, and the problems of pipeline settlement and displacement caused by insufficient bearing capacity of soft soil are solved, ensuring the stability of the pipeline after laying. The innovative use of top-mounted manholes and internal welding processes solves the problem of external welding of the bottom interface of the lower layer pipe when the spacing between multiple layers of pipes is narrow. Welders can perform precise welding directly inside the pipe with ample welding space, which greatly reduces the difficulty of construction.

[0009] Preferably, the slope ratio in step S2 is selected as 1:1 or 1:0.5 depending on the soil conditions and excavation depth.

[0010] Preferably, the butt weld and the weld between the bevel and other pipes include a root pass, a filler pass, and a cap pass, using a three-pass welding process of "root pass-filler-cap pass". The root pass ensures good fusion at the root of the weld and avoids incomplete penetration defects; the filler pass increases the weld thickness to meet strength requirements; the cap pass optimizes the surface quality of the weld and prevents defects such as porosity and slag inclusions. The weld has high tensile strength, significantly improves sealing performance, and further reduces the risk of leakage.

[0011] Preferably, the sealing plate is 5cm larger than each side of the manhole, which ensures sufficient welding contact surface between the sealing plate and the outer wall of the pipe, making the fillet weld more secure and avoiding problems such as weak welding and easy cracking caused by insufficient contact surface. This minimizes the risk of leakage at the manhole sealing point.

[0012] Compared with the prior art, the beneficial effects of the present invention are: Digital modeling and simulation analysis based on BIM technology enables precise planning of pipeline routes, making full use of the idle green belt space between the water tank structure and the main road; through a two-layer three-dimensional layout, the horizontal space requirement is transformed into vertical space utilization, breaking the spatial limitations of traditional parallel laying and achieving efficient utilization of narrow spaces.

[0013] Meanwhile, the concrete cushion layer, as a rigid foundation, forms a composite foundation structure with the soft soil foundation. Through the diffusion effect of the cushion layer, the vertical load of the pipeline is evenly transferred to the soft soil below, reducing the stress concentration in the soft soil, improving the overall bearing capacity of the foundation, and meeting the mechanical requirements for long-term stable operation of the pipeline.

[0014] When welding pipes, a manhole is opened at the top of the pipe for internal welding, allowing welders to directly reach the bottom interface of the lower pipe that is inaccessible by traditional methods, thus achieving visualization and precision in welding operations. At the same time, a three-pass welding process of "root pass - fill pass - cover pass" is adopted to form a complete weld protection system from root fusion and strength enhancement to surface quality optimization, ensuring weld strength and sealing.

[0015] The internal anti-corrosion treatment isolates the welds from sewage corrosion, the water pressure test detects potential leaks in advance, the concrete encapsulation not only fixes the position of the pipes but also isolates them from external moisture and soil erosion; symmetrical concrete pouring avoids displacement caused by uneven stress on the pipes. These multiple measures work together to reduce the risk of leakage from the source. Attached Figure Description

[0016] Figure 1 This is a diagram of the overall construction structure of the present invention; Figure 2 This is a schematic diagram of the welding of the pipeline of the present invention; Figure 3 This is a cross-sectional view of the pipeline structure of the present invention; Figure 4 This is a partial view of the welding point of the present invention.

[0017] Figure label: 1. Lower layer pipe, 11. Manhole, 12. Inner bevel, 13. Butt weld, 14. Sealing plate, 2. Upper layer pipe, 3. Concrete, 4. Water tank structure, 5. Subbase, 6. Slope, 7. Bottom layer, 8. Filling section, 9. Cover section. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0019] like Figure 1-4 As shown, this invention provides a technical solution to address the problems of difficult welding of multi-layer pipelines and the inability of existing construction methods to meet the requirements of pipeline construction in narrow spaces and soft soil geological conditions: a method for constructing multi-row buried pipelines in narrow spaces and soft soil geological conditions, comprising the following steps: S1. Determine the pipeline laying scheme and use BIM technology to optimize the pipeline layout in the green belt between the water tank structure 4 and the main road; S2. Earthwork excavation: excavate to 100mm below the design pipe bottom elevation. After excavation, a slope 6 is formed on one side of the main road. The slope 6 is selected as 1:1 or 1:0.5 depending on the soil conditions and excavation depth. S3. Erect formwork and pour the foundation layer 5; S4. Beveling of lower-level pipe 1; S5. Hoist the finished lower-level pipe 1 into place at the pipe layout position; S6, Assembly of the lower pipe 1 and welding of the butt weld 13; S7. Make a manhole 11 at the top of the lower pipe 1 near the weld, the size of which should be sufficient for the welder to enter; S8. The welder enters the lower pipe 1 through the manhole 11, makes an inner bevel 12 at the bottom of the lower pipe 1, and welds the pipe. The butt weld 13 and the weld between the bevel 12 and other pipes include a root pass 7, a filler pass 8, and a cover pass 8. A three-pass welding process of "root pass-filler-cover pass" is adopted. The root pass 7 ensures good fusion at the root of the weld and avoids incomplete penetration defects. The filler pass 8 increases the weld thickness to meet the strength requirements. The cover pass 9 optimizes the surface quality of the weld and prevents defects such as porosity and slag inclusion. The weld has high tensile strength and significantly improves sealing performance, further reducing the risk of leakage. S9. After the weld seam on the inner wall of the pipeline has cooled, apply anti-corrosion treatment. S10. After the welder comes out of the manhole 11, he seals the manhole 11 by welding the sealing plate 14. The sealing plate 14 and the outer wall of the lower pipeline 1 are welded together by fillet weld. The sealing plate 14 is 5cm larger than the manhole 11 on each side, so that the welding contact surface between the sealing plate and the outer wall of the pipeline is sufficient and the fillet weld is more secure. This avoids the problem of weak welding and easy cracking caused by insufficient contact surface, and minimizes the risk of leakage at the manhole sealing point. S11. Temporarily seal the pipeline and conduct a water pressure test; S12. After the water pressure test is passed, pour 3 bags of concrete. When pouring concrete, pay attention to the uniformity and symmetry of the left and right sides to prevent the pipe from moving or floating. S13. Once the concrete has reached a certain strength, the upper layer pipe 2 can be laid. The butt welding method of the pipe is the same as that of the lower layer pipe 1. S14. After the upper pipeline passes the water pressure test, the pipeline shall be externally protected against corrosion. S15. Erect formwork and encase the pipe with concrete. S16. Earthwork backfilling.

[0020] The above construction plan uses BIM technology to precisely optimize the pipeline route, placing the pipeline in the green belt between the water tank structure and the main road, making full use of the idle space. At the same time, it adopts a double-layer pipeline laying mode to adapt to the construction needs of narrow spaces. By pouring a concrete cushion layer 5 as the pipeline foundation, the pipeline load is effectively distributed, the foundation bearing capacity is improved, and the problems of pipeline settlement and displacement caused by insufficient bearing capacity of soft soil are solved, ensuring the stability of the pipeline after laying. The innovative use of top-mounted manholes and internal welding processes solves the problem of external welding of the bottom interface of the lower layer pipe when the spacing between multiple layers of pipes is narrow. Welders can perform precise welding directly inside the pipe with ample welding space, which greatly reduces the difficulty of construction.

[0021] As a specific example: This example illustrates a new construction project for a large-scale urban wastewater treatment plant. Located in the suburbs, the site covers a total area of ​​80,000 square meters. The green belt between the water tank structure (4) and the main road is 5.5 meters wide, requiring the laying of eight DN1000 wastewater treatment process pipes. The pipes are made of Q235B steel and are 12 meters long. The site soil is primarily silty clay, a typical soft soil geological condition. The natural foundation bearing capacity is 75 kPa, the groundwater level is -1.2 meters, and the designed excavation depth for the pipe trench is 3.0 meters.

[0022] (I) Construction Preparation Technical preparation: Collect site geological survey reports, location maps of water tank structures, and distribution maps of underground pipelines along the main road. Use BIM software (such as Revit) to create a 3D model of the site, input pipeline parameters (such as pipe diameter, length, material, etc.) and site boundary conditions (such as width of green belt, groundwater level, etc.), optimize pipeline routing, and determine to adopt a double-layer pipeline laying mode, with 4 pipes in each layer, a center-to-center spacing of 1.2m between pipes, and a distance of 0.7m between the bottom of the upper layer pipe 2 and the top of the lower layer pipe 1. The pipeline route is arranged in a straight line along the length of the green belt, avoiding underground pipelines and structure foundations.

[0023] Material preparation: Purchase Q235B pipes, C15 concrete, C30 concrete, epoxy coal tar coating, polyurethane coating, E4303 welding rods, sealing plates, steel formwork, excavators, truck cranes, beveling machines, welding equipment, and other materials and equipment, and conduct quality inspections to ensure they meet design requirements.

[0024] (II) Specific construction steps Surveying and setting out: Based on the pipeline route and elevation optimized by BIM, a total station is used to conduct surveying and setting out to determine the trench excavation boundary line and slope line. Control stakes and leveling points are set outside the excavation boundary line, with a control point set every 20m to ensure the accuracy of the excavation position and depth.

[0025] Earthwork excavation: Excavators will be used to excavate the pipe trench, proceeding from one end of the green belt to the other, with a depth of 100mm below the designed pipe bottom elevation, i.e., -2.6m. Since the site consists of silty soft soil, the excavation depth is 3.0m. A 1:1 slope can be used for the side slope. During excavation, loose soil on the slope will be promptly cleared to prevent slope collapse. Simultaneously, drainage ditches and sump pits will be installed on both sides of the pipe trench, using submersible pumps to drain water and control the groundwater level to 0.5m below the bottom of the trench, preventing water accumulation in the foundation pit from affecting construction.

[0026] Foundation construction: After the trench excavation is completed, the bottom of the trench is leveled and compacted, and then steel formwork is erected. The formwork is fixed with bolts to ensure it is firm and does not loosen. C15 concrete is used to pour the subbase layer 5, which is 4.2m wide and 100mm thick. During the pouring process, a vibrator is used to compact it, and the surface is smoothed. After curing for 7 days, it reaches the design strength.

[0027] Lower-level pipe construction: Beveling: A pipe beveling machine is used to perform V-shaped beveling on the end of the lower pipe 1.

[0028] Pipe hoisting and positioning: Use a 25t truck crane to hoist the finished lower layer pipes 1 one by one to the predetermined position above the subbase. Two-point hoisting is used during hoisting to avoid pipe deformation.

[0029] Assembly and external wall welding: After the pipe assembly is completed, the external welding of butt weld 13 is carried out first. Manual arc welding is used, and the welding process is carried out in three passes: the bottom 7 uses φ3.2mm E4303 welding rod, current 100-120A, weld thickness 3-4mm; the filling part 8 uses φ4.0mm E4303 welding rod, current 140-160A, filling in 2 layers, weld thickness reaches 8mm; the capping part 9 uses φ4.0mm E4303 welding rod, current 130-150A, weld width is 2-3mm wider than the bevel edge, surface reinforcement is 0-3mm.

[0030] Manhole 11 at the top of the pipe: Manhole 11 is opened at the top of the lower pipe 1 near the butt weld by gas cutting to ensure that the welder can carry the welding equipment into the pipe. After the gas cutting is completed, the burrs on the edge of the manhole are cleaned.

[0031] Pipe welding: Welders wearing protective equipment and lighting equipment enter the pipe through manhole 11 to weld the inner bevel 12 at the bottom of the lower pipe 1. The welding process is the same as that of the external weld, namely the above-mentioned three-pass welding of "root pass - fill pass - cover pass", to ensure that the inner bevel weld and the external weld form a complete weld structure. After welding, the weld slag on the surface of the weld is cleaned.

[0032] Internal wall corrosion protection: After the weld seam on the inner wall of the pipeline has cooled naturally for 24 hours, use power tools to clean the rust and oil stains in the weld seam and surrounding area, and then apply epoxy coal tar coating. The coating is applied in two coats. The first coat is 0.4mm thick, and the second coat is applied after drying, with a total thickness of 0.8mm. The coating surface is smooth and free of missed areas or drips.

[0033] Manhole sealing: Use Q235 material sealing plate 14. The sealing plate is 5cm larger than the manhole 11 on each side. Align the sealing plate with the outer wall of the pipe. First, fix the position with intermittent welding, and then perform continuous fillet welding. The weld height is 8mm. During the welding process, ensure that the weld is full and free of defects such as porosity and slag inclusion.

[0034] Water pressure test: Use blind flanges to temporarily seal both ends of the lower pipeline, install an air vent valve at the highest point of the pipeline and a drain valve at the lowest point, inject clean water into the pipeline to purge the air, and then slowly increase the pressure to the design pressure of 0.6 MPa and maintain the pressure for 24 hours. Record the pressure value every 2 hours during this period. If the pressure drop does not exceed 0.02 MPa and there is no leakage at the pipeline joints, the water pressure test is considered qualified.

[0035] Concrete Encasing: After the water pressure test is passed, steel formwork is erected around the lower-level pipe, with the formwork height reaching the bottom elevation of the upper-level pipe. C30 concrete (3) is poured for encasing, using symmetrical placement on both sides during pouring, with the pouring speed controlled at 0.4 m / h to prevent the pipe from shifting or floating due to excessive force on one side. During pouring, a vibrator is used to compact the concrete, and the surface is smoothed. After 7 days of curing, the concrete strength reaches 75% of the design strength.

[0036] Upper-level pipeline construction: Following the construction process of the lower-level pipeline, the upper-level pipeline 2 undergoes beveling, hoisting and positioning, assembly and welding, manhole opening at the top of the pipe, internal welding, internal wall corrosion protection, manhole sealing, and water pressure testing. After the upper-level pipeline passes the water pressure test, polyurethane coating is applied to the outer wall for corrosion protection, with a coating thickness of 1.0 mm. Then, formwork is erected, and C30 concrete is poured to encase the upper-level pipeline with a thickness of 300 mm. After curing for 7 days, it reaches the design strength.

[0037] Backfilling: After the concrete encapsulation and curing of the upper pipeline is completed, all formwork is removed. Silty clay is used to backfill the trench in layers, with each layer being 300mm thick. Each layer is compacted using a rammer and backfilled to the original ground level of the green belt. During the backfilling process, avoid directly rolling the top of the pipeline with machinery to ensure that the pipeline is not damaged.

[0038] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0039] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly and specifically defined.

[0040] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0041] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

Claims

1. A method for construction of multi-row buried pipeline in soft soil in narrow space, characterized in that, Includes the following steps: S1. Determine the pipeline laying scheme and use BIM technology to optimize the pipeline layout in the green belt between the water tank structure (4) and the main road; S2. Excavation of earthwork to 100mm below the design pipe bottom elevation. After excavation, a slope (6) is formed on one side of the main road. S3. Erect the formwork and pour the foundation layer (5); S4, Beveling of the lower-level pipe (1); S5. Hoist the finished lower-level pipe (1) into place at the pipe layout position; S6. Assembly of the lower pipe (1) and welding of the butt weld (13); S7. Make a manhole (11) at the top of the lower pipe (1) near the weld, the size of which should be such that the welder can enter; S8. The welder enters the lower pipe (1) through the manhole (11), makes an inner bevel (12) at the bottom of the lower pipe (1) and welds the pipe. S9. After the weld seam on the inner wall of the pipeline has cooled, apply anti-corrosion treatment. S10. After the welder comes out of the manhole (11), he seals the manhole (11) with a welding sealing plate (14). The sealing plate (14) and the outer wall of the lower pipeline (1) are welded together with fillet welds. S11. Temporarily seal the pipeline and conduct a water pressure test; S12. After the water pressure test is qualified, pour concrete (3) to seal it. When pouring concrete, pay attention to the uniformity and symmetry of the left and right sides to prevent the pipe from moving and floating. S13. After the concrete reaches a certain strength, the upper layer pipe (2) can be laid. The butt welding method of the pipe is the same as that of the lower layer pipe (1). S14. After the upper pipeline passes the water pressure test, the pipeline shall be externally protected against corrosion. S15. Erect formwork and encase the pipe with concrete. S16. Earthwork backfilling.

2. The method for constructing multi-row buried pipelines in narrow spaces with soft soil, as described in claim 1, is characterized in that: In step S2, the slope (6) is selected as 1:1 or 1:0.5 depending on the soil conditions and excavation depth.

3. The method for constructing multi-row buried pipelines in narrow spaces with soft soil, as described in claim 2, is characterized in that: The butt weld (13) and the weld between the bevel (12) and other pipes include a bottoming (7), a filling (8) and a capping (9).

4. The method for constructing multi-row buried pipelines in soft soil geology in narrow spaces according to claim 1, characterized in that: The sealing plate (14) is 5 cm larger than each side of the manhole (11).

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