Pre-construction preparations

• Blueprint VerificationVerify the location, specifications, well depth, and connection parameters (such as pipe inner diameter, joint type, and elevation difference) of the manhole. Pay special attention to confirming that the center elevation of the reserved joint on the manhole base is consistent with the center elevation of the pipe (deviation must be ≤5mm).

• Material InspectionDuring the arrival of prefabricated components, inspect the appearance (no cracks, missing corners, even interfaces), dimensions (diameter deviation ≤10mm, wall thickness deviation ±5mm), and conduct a random check of concrete strength (using rebound meters, with a 100% strength compliance rate); provide a mix proportion report for concrete used for on-site casting, and retain one set of test blocks for every 50m³.

• Excavation of the foundation pitThe trench is excavated to a diameter 40-60cm larger than the manhole outer diameter (to provide operational space), with the excavation depth equal to the well shaft design depth plus the bedding layer thickness (usually 100-150mm). For soft soil foundations, the ground must be replaced with 300mm thick graded sand and stone and compacted (compaction rate ≥93%).

2. Core Construction Process

• Subgrade constructionAfter the foundation pit passes the acceptance, pour a C15 plain concrete base layer, and finish the surface for leveling (flatness deviation ≤ 5mm). Proceed to the next stage once the base layer's strength reaches 70%.

• Component Installation / Casting：

• Pre-fabricated Well: The well base is lifted by a crane (hoist points are symmetrically set to prevent tilting). After aligning the center position and elevation, backfill the well base with 200mm thick sand and gravel, and compact it. Next, install the well casing, apply waterproof mortar (thickness 10mm) at the joints, and reinforce with steel hoops at 300mm intervals.

• Cast-in-place well: Construction follows the template, reinforcement binding, and concrete pouring process. At the junction between the well bottom and pipeline, an "eight-character angle" (concrete chamfer, radius 100mm) must be set up to enhance impact resistance.

• Join Pipeline Connection：

• Socket Weld Pipe: Apply lubricant to the pipe socket, slowly insert into the reserved socket of the well seat, with the insertion depth measured by the joint marking. Fill the gap with an expanding rubber strip and seal the outer side with waterproof mortar.

• The flat joint pipeline: After the pipeline is connected to the reserved holes in the wellbore wall, additional rebars are tied around the pipeline (welded to the rebars of the wellbore). Then, the interface is encased with C30 fine aggregate concrete, with a thickness of ≥100mm. The concrete is cured for 3 days before backfilling.

• Waterproofing TreatmentThe inner and outer sides of the well bore are coated with cement-based waterproofing paint (thickness ≥1.2mm). At the joints, glass fiber cloth is wrapped and coated with two layers of polyurethane waterproofing paint (width 300mm). A 20mm thick waterproof mortar leveling layer is applied at the bottom of the well with a gradient of 1% (slope towards the pipe joint for easy drainage).

• Backfilling and Manhole Installation：

• Backfill: Fill symmetrically around the well with uncompacted soil (stone and frozen soil excluded), with each layer 200mm thick. Use a small compactor to lightly compress (the compaction rate within 30cm of the well wall should be ≥90%, and outside ≥93%). Once backfilled to 50cm below the top of the well, it can be compacted normally.

• Manhole Installation: The well ring and top of the well casing are secured with C30 concrete (the manhole cover is installed after the concrete strength reaches 70%). The manhole cover level is aligned with the surrounding road surface or ground (road manhole covers are 5mm lower than the road surface to prevent vehicle noise), and reinforced steel mesh (φ12 steel bars, 150mm spacing) must be set below the well ring for heavy-duty manhole covers (carrying capacity ≥200kN).

3. Special Scene Construction Precautions

• Rainy Season ConstructionAfter excavation, drainage ditches and sump pits must be set up to promptly remove accumulated water; check if the interfaces are damp before installing prefabricated components, and waterproof mortar should be mixed with an impermeable additive; cover cast-in-place concrete with rainproof tarpaulins to prevent surface erosion by rain.

• Winter ConstructionConcrete is mixed with hot water (temperature ≤ 80℃) and added with an early strength anti-freezing agent (quantity as required by specifications); during curing, rock wool blankets and plastic film are used to ensure the concrete reaches 70% of its designed strength before freezing occurs; backfill soil must not contain frozen soil blocks (blocks with a particle size > 50mm must be removed).

• Construction Below the RoadThe well backfilling requires graded sand and gravel (not plain soil). After being compacted in layers, C30 concrete "reinforcement rings" (500mm wide and 200mm thick) are poured around the well casing to prevent road settlement and cracking due to vehicle碾压.