The construction of municipal PVC-U large-diameter spiral wrapping pipes must focus on key aspects such as material management, foundation preparation, pipe installation, joint sealing, backfilling, and acceptance testing. Meticulous operations ensure the long-term, stable operation of the pipeline system.
Material handling and storage are crucial for construction. PVC-U large-diameter spiral wrapping pipes must be hoisted using soft slings or specialized clamps to prevent scratches caused by direct contact between the wire rope and the pipe wall. The stacking site should be hardened. Pipes should be stacked in layers with wooden wedges and rubber sheets placed between layers to prevent rolling damage. During transportation, straw mats should be laid on the contact surface between the pipes and the vehicle. Nylon straps should be used for securing the ropes; metal chains are strictly prohibited.
Foundation preparation directly impacts the load-bearing capacity of the pipeline. Trench excavation slopes must be strictly controlled. Stepped slopes should be constructed in soft geological areas, and the slopes should be sprayed with concrete. During base preparation, any soft soil layers should be replaced with graded crushed stone, compacted every 300mm, to a compaction level of at least 95%. The sand cushion layer must be laid evenly, with thickness deviations within ±20mm to avoid localized settlement that could lead to stress concentration in the PVC-U large-diameter spiral wrapping pipe.
Pipeline installation should follow the "lower-first, then up" principle. Two cranes should be used to simultaneously lift the PVC-U large-diameter spiral wrapping pipe, maintaining a level pipe section. The spacing between the lifting points should not exceed 1/3 of the pipe length. During installation, the centerline deviation of the pipe sections must be controlled within ±20mm, and the misalignment of adjacent sections must not exceed 1/10 of the wall thickness. For pipe diameters N1200 and above, temporary supports must be installed to prevent the sections from rolling during installation.
Joint sealing is critical to ensuring the watertightness of the piping system. Before installing a spigot-and-socket joint, sandpaper the spigot end to remove the oxide layer. When installing the rubber ring, apply a special lubricant to ensure even insertion into the groove. During the hot-melt joining process, the heating plate temperature must be controlled at 210±10°C, and the butt joint pressure must be maintained at 0.15 MPa. The holding time should be adjusted according to the pipe diameter to ensure full fusion of the weld surface. After completion, a 100% visual inspection is required; the absence of bubbles or cracks is considered acceptable.
Backfilling should be carried out in layers. For PVC-U large-diameter spiral wrapping pipes, the base layer should be made of medium-coarse sand with a thickness of at least 200 mm and manually compacted to a relative density of ≥ 0.7. When backfilling the pipe side, graded crushed stone should be used within 500 mm below the pipe top, mechanically compacted every 200 mm to a compaction level of ≥ 90%. From 500 mm above the pipe top to the ground, backfill soil should be screened to remove rocks, and the layer thickness should be controlled to no more than 300 mm. Direct backfilling using a bulldozer is strictly prohibited.
A closed-water test is a key method for verifying pipeline sealing. The test section should not exceed 1 km in length, and the water injection height should reach 2 m above the top of the upstream pipe. After 24 hours of stabilization, record the hourly water level drop. The allowable leakage rate should comply with the requirements of the "Water Supply and Drainage Pipeline Construction and Acceptance Specifications." In areas with complex geological conditions, additional settlement observation points should be added, with a monitoring period of at least seven days.
Finished product protection should be implemented throughout the entire construction process. Installed pipes should be wrapped with colored strips to prevent contamination from the concrete pour. Warning signs should be posted in the backfill area, prohibiting heavy machinery from passing through. A 200mm expansion gap should be reserved at the connection to the manhole, and polysulfide sealant should be used. After construction is completed, an as-built drawing should be prepared, noting the pipe locations, elevations, and manhole coordinates to provide a basis for subsequent maintenance.
