Key Quality Control Aspects

• Strength ControlBefore the prefabricated components are dispatched, three samples from each batch are randomly selected for compressive strength tests (loading rate of 0.3-0.5MPa/s), with the strength requirement being equal to or greater than the design value (e.g., for a C30 manhole, the test strength must be ≥30MPa); after the concrete test blocks are cured for 28 days at the construction site, the rate of strength meeting the standard must be 100%.

• Sealant ControlUpon completion, a closed-water test will be conducted. The ends of the manhole and connected pipes will be sealed, and water will be filled to 20cm above the top of the well. After soaking for 24 hours, observe for 30 minutes. If there is no significant drop in water level (≤5mm) and no leakage at the joints, it is considered合格. The pass rate for the closed-water test of the sewage manholes must be 100%.

• Dimensional Tolerance ManagementThe manhole center position deviation is ≤15mm, elevation deviation ±10mm, well cylinder verticality deviation ≤5mm/m, and the gap between the manhole cover and rim is ≤3mm (measured with a feeler gauge), ensuring both appearance and functionality meet standards.

2. FAQs and Solutions

• Borehole Wall Cracks：

• Reason: Poor compaction of concrete during prefabrication and improper curing; deformation of formwork and rapid shrinkage of concrete during on-site casting.

• Address: For crack widths less than 0.2mm, use an epoxy resin slurry for sealing; for crack widths of 0.2mm or more, carve a V-shaped groove along the crack (depth 10-15mm), clean, then fill with waterproof mortar and apply a waterproof coating on the surface.

• Interface leakage：

• Reason: Sealed gasket aging, misaligned interfaces, and non-compressed waterproof mortar.

• Resolve: Remove the interface, replace with a new O-ring (made of EPDM rubber for good elasticity and aging resistance), reconnect, then apply polymer waterproof mortar (thickness 15mm) to the outer side of the interface. Cure for 7 days.

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• Reason: Inadequate compaction of backfill soil and uneven junction between the well casing and the road surface.

• Solution: Excavate around the well for settlement, remove loose backfill soil, replace with graded sand and gravel, compact in layers (compaction rate ≥95%), resurface with new concrete, ensure the manhole cover is level with the pavement, and fill the joint between the pavement and the well ring with asphalt sealant.

• Loose manhole cover causing unusual noise：

• Reason: Inadequate connection between the wellhead and the wellbore, and excessive gap between the well cover and the wellhead.

• Solution: Pour C30 concrete at the bottom of the well ring (thickness 100mm) for fixation, and after the required strength is achieved, apply anti-vibration rubber strips (width 20mm) between the well cover and ring to reduce gap collisions during vehicle碾压.