Water Supply and Drainage Pipeline Construction Specifications

Pre-construction Preparation and Foundation Control

Precise Measurement and Layout

Measure, locate, and lay out strictly in accordance with the design drawings, clearly defining the pipeline's route, elevation (burial depth), and coordinates.

Pay special attention to the fact that the pipeline's burial depth must exceed the local maximum permafrost depth and take into account overhead loads (such as roads).

Consider the pipeline slope (especially for gravity flow pipelines) to ensure smooth drainage.

Trench Excavation and Foundation Treatment

The excavation width must meet the requirements for pipeline installation, jointing, and backfill and compaction.

The trench bottom must be flat and free of sharp debris. If weak foundations or disturbed soil are encountered, replacement backfill (e.g., gravel) or compaction must be performed according to design requirements.

Foundation Bearing Capacity: Unless otherwise specified, the foundation bearing capacity after compaction must be ≥100 kPa.

Bedding Requirements: For plastic pipes (such as UPVC, PPR, PE, and FRPP), a medium-coarse sand bedding layer ≥150 mm thick should be laid at the trench bottom and leveled and compacted. After trench excavation, re-surveys are required to ensure that the elevation, slope, and width meet the requirements.

Pipeline Materials and Connection Quality

Material Acceptance and Storage

All pipes, fittings, valves, etc. must be strictly inspected upon arrival. Specifications, model numbers, material certifications, and certificates of conformity must be verified, and the appearance quality must be checked (for cracks, dents, severe scratches, etc.).

Pipes of different materials (ductile iron, UPVC, PPR, steel-reinforced polyethylene, FRPP, steel pipe, stainless steel, etc.) should be stored separately to avoid mixing and contamination. Plastic pipes should be protected from direct sunlight.

Pipe Connections

Choose the Correct Connection Method: Strictly follow the pipe material characteristics and design requirements to select connection methods such as welding (steel pipe, stainless steel), clamps (ductile iron), bonding (UPVC, FRPP, etc.), and electrofusion (PE, steel-reinforced polyethylene).

Joint Quality: Ensure that joints are clean, dry, and free of oil and dirt. Strictly follow the corresponding connection process procedures (e.g., welding parameters, even and sufficient application of adhesive, and electrofusion time and temperature control). Prefabrication and Inspection: Whenever possible, prefabricate pipelines on the ground to minimize trench work. After prefabrication, conduct necessary inspections (such as weld appearance and electric heat-melting flanges).

Pipeline Corrosion Prevention (Top Priority - Key to Leak Prevention)

Surface Treatment

Rust Removal Grade: For metal pipes such as carbon steel, rigorous rust removal is essential. Rust removal using manual or power tools should achieve St3 (surface free of oil, loose scale, and rust, revealing a metallic luster). This is essential for the adhesion of the anti-corrosion coating.

Anti-corrosion Coating Application

Wrap tightly, evenly, without wrinkles or bubbles.

Lap Width: Each layer must overlap at least 25mm.

Circumferential Lap: End overlap must be at least 1/4 of the pipe circumference and no less than 100mm.

Primer Application: Apply evenly, avoiding any gaps, clumps, or runs. Allow the primer to dry before proceeding to the next step. Tape/Coating Wrapping/Application: (Using common tape as an example)

Full-Process Contamination Prevention: From rust removal to the completion of the anti-corrosion coating, strictly prevent the surface from being contaminated by water, oil, dirt, and other substances. Anti-corrosion treatment of trench weld joints must be completed before backfilling and meet the same quality requirements.

Anti-Corrosion Coating Inspection

Electro-Spark Leak Detection: This is a mandatory requirement! 100% of the anti-corrosion coating applied on-site must be inspected for leaks.

Test Voltage: Adjust the leak detection voltage based on the designed thickness of the anti-corrosion coating (e.g., 9kV for a 1.4mm thickness, 11kV for a 2mm thickness). Any pinholes must be repaired and retested.

Thickness Inspection: Spot-check the anti-corrosion coating thickness according to specifications to ensure it meets design requirements.

Pipeline Cleanliness Control (Key to Preventing Blockages)

Pre-Installation Cleaning

Before installation, the interior of pipes and fittings must be thoroughly cleaned to remove all debris (such as mud, welding slag, cutting chips, packaging, etc.). This is a key step in preventing blockages after commissioning. For pipes with strict cleaning requirements (such as domestic water supply), flushing should be performed as necessary.

Installation Process Protection

During pipe installation, open pipe ends should be temporarily sealed (using special pipe caps or sturdy plastic sheeting, etc.) to prevent the entry of dirt, debris, and small animals.

Avoid stepping on or placing tools or other debris on the pipes.

Pipeline Laying and Installation

Laying Operations

When lowering the pipe, use appropriate lifting equipment (such as flexible slings) and lift and lower gently to avoid impact with the trench wall or damage to the pipe and anti-corrosion coating.

The pipe should be laid according to the designed elevation and slope, horizontally and vertically (or according to the designed slope). Use measuring instruments for real-time monitoring.

The pipe must be laid on a compacted foundation or subgrade to avoid overhanging.

Pipeline Crossing Treatment

Road Casing: When the cover soil thickness is less than 1 meter, steel casing must be installed. The casing diameter should be 1-2 grades larger, and both ends of the casing must extend ≥0.5 meters beyond the curb. When the water supply pipe is located below the sewage pipe, a steel casing must be installed. The casing length must be ≥ 1.5 meters on each side of the intersection, and both ends must be tightly sealed with waterproof material to prevent sewage from seeping into the casing and corroding the water supply pipe.

Approach the intersections by following the principle of "small pipes give way to larger pipes, pressurized pipes give way to gravity-flow pipes (non-pressurized pipes), and shallow pipes give way to deep pipes."

Installing casings at intersections strictly in accordance with design or specification requirements:

Ensure that the main pipe within the casing can freely expand and contract (especially for heat pipes or pipes with large temperature differences).

Pipeline Testing

Pressure Test (Pressure Test)

After the pipeline is installed, the welds are non-destructively tested (if applicable), and the anti-corrosion coating has passed inspection, a pipeline pressure test (primarily a hydrostatic test) must be conducted in accordance with design requirements and specifications.

The test pressure, pressure stabilization time, and acceptance criteria must strictly comply with the specifications. Pressure testing is a key step in verifying the strength and tightness of the piping system.

Final corrosion protection and backfilling of the welds can only be performed after the pressure test has passed. Clean water should be used for the pressure test. Tightness Test (if applicable): For gravity flow pipes (sewage, rainwater), a closed water (water filling) test may be required to check their tightness.

Backfill and Compaction (Protecting Pipelines and Preventing Settlement)

Backfill Materials

Preferred materials are good-quality excavated soil (free of large rocks, frozen soil, or organic matter), or sand, stone dust, etc. that meet the requirements.

Fine-grained soil (such as sand or sandy clay) free of sharp rocks and hard objects should be used for backfill on both sides of the pipe and within a certain range above the pipe top (usually 500mm).

Backfill Construction

Backfill must be performed in layers, with each layer thickness not exceeding 300mm (approximately 200-250mm after compaction).

Compaction in Layers: Each backfill layer must be thoroughly compacted using an appropriate machine (frog compactor, plate compactor, etc.) or manually. Density Control: The backfill soil must meet design requirements or specifications (generally ≥95% on the pipe side and ≥85-90% above the top 500mm). This is key to preventing uneven stress on the pipe, deformation, joint leakage, and road subsidence.

Symmetrical Backfill: Backfill should be applied symmetrically on both sides of the pipe simultaneously, with minimal height differences to prevent pipe displacement.

Pipe Top Protection: Within the top 500mm of the pipe, perform light manual tamping to avoid damage. Mechanical tamping may be used above the top 500mm.

Shaft Chamber Construction

Structural Quality

Construct strictly according to the drawings, ensuring that the foundation pit dimensions, cushion thickness, rebar specifications and spacing, formwork support, and concrete strength grade meet the requirements.

Concrete pouring requires vibration compaction and proper curing.

Waterproofing and Anti-seepage

The plastering (especially the "e" plastering) inside and outside the shaft wall must be smooth, dense, and free of cracks and hollows. This is key to preventing groundwater infiltration or sewage seepage. Pipes passing through the wellbore must be waterproofed and sealed properly (e.g., using waterproof sleeves, water-swellable rubber rings, sealants, etc.).

Drain Trough

Drain troughs should be constructed or cast smoothly, with a correct slope (pointing toward the sump) and a smooth surface to ensure smooth water flow and minimize siltation.

Manhole Cover Installation

The manhole cover should be installed smoothly and securely, fitting well within the wellbore. The manhole cover elevation should be consistent with the final ground elevation.

Construction Management and Other

Process Records: Keep detailed construction records (including surveying and layout, material acceptance, welding, corrosion protection, testing, concealed work acceptance, and backfill compaction testing).

Product Protection: During and after construction, protect installed pipes, valves, instruments, well chambers, etc. to prevent mechanical damage and vandalism.

Safe and Civilized Construction: Strictly adhere to safety procedures, provide support to prevent collapse during trench excavation, post safety warnings, and clear the site after work and materials are completed. Addressing Regional Differences: Fully consider factors such as the construction area's geology (e.g., soft soil, rock), soil corrosivity, groundwater level, and permafrost depth. Targeted measures should be taken in material selection (corrosion resistance level), foundation treatment, burial depth determination, and construction methods.

Buried water supply and drainage pipeline construction is a systematic project, with each step interconnected. We must firmly uphold the concept of "quality first," ensuring a thorough understanding of the source of materials, strict control of key processes (corrosion protection, cleaning, connections, and backfilling), meticulous management, and strict adherence to specifications and design requirements. Only then can we effectively eliminate the two persistent problems of "leakage" and "blockage," ensuring the long-term safe and stable operation of the pipeline system.