Precast Assembly Manhole Production Process

• Material PreparationThe company is using ordinary silicate cement with a strength grade of ≥42.5, aggregate selected as continuous gradation crushed stone with particle size of 5-20mm (silt content < 1%), medium sand (silt content < 3%), and adding appropriate water-reducing admixture (improving workability of concrete) and air-entraining agent (enhancing frost resistance), with water-cement ratio controlled at 0.4-0.45.

• Reinforcement Frame FabricationThe steel framework for the wellhead and wellbore was bound according to the design drawings, with longitudinal reinforcement spacing ≤200mm and hoop reinforcement spacing ≤150mm. The lap length of the reinforcement was ≥35d (where d is the diameter of the reinforcement), and梅花-shaped binding was used to ensure the stability of the framework.

• Mold Assembly and CastingUsing steel molds (precision error ≤ 2mm), apply a release agent before assembly, pour concrete layer by layer after placing the steel reinforcement frame, with each layer no thicker than 300mm. Simultaneously, use an internal vibrator for 10-15 seconds until no bubbles are visible on the surface, to prevent honeycomb and rough surfaces.

• Maintenance and DemoldingUpon completion of casting, cover with geotextile for moisture retention and pre-curing for 24 hours. Then transfer to a steam curing kiln and follow the process of "heating (10℃/h) → constant temperature (60±5℃, 6 hours) → cooling (8℃/h)" for curing. Once the concrete strength reaches 70% of the design strength (usually after 48 hours of curing), it can be demolded. After demolding, continue with natural curing for an additional 7 days.

2. In-situ cast manhole construction technology (core process)

• Rebar tyingReinforcement supports are set up at the designed elevation within the foundation pit, with the reinforcement for the well wall and bottom tied together. Double-reinforced steel bars are placed at the bottom (spacing of 150mm), and a transition section of steel bars (length ≥ 500mm) is left at the pipe interface for easy connection with the pipeline reinforcement.

• Template SetupUtilizing bamboo plywood or steel formwork, the inner side of the form is coated with a release agent, and the gaps are sealed with sponge strips to prevent leakage. The outer side is reinforced with steel pipe scaffolding, with a support spacing of ≤1.5m to ensure the formwork does not deform during pouring, and the verticality deviation of the formwork is ≤3mm/m.

• Concrete PouringThe concrete is poured in layers from the bottom to the walls of the well, with a minimum thickness of 150mm at the bottom. When浇筑 the walls, pipe interface holes must be reserved (the hole size is 50mm larger than the outer diameter of the pipe). After pouring, the surface should be smoothed promptly, and then covered and kept moist after initial setting.

• NourishmentCover with geotextile and water the concrete within 12 hours after pouring, and maintain for at least 7 days (in winter, cover with rock wool blankets to insulate and ensure the ambient temperature is ≥5℃), and no heavy objects should be placed on the well wall during the curing period.