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HDPE Pipeline Construction Specifications: Burial Depth, Support and Backfill Requirements

HDPE (High-density Polyethylene) pipeline construction must follow strict specifications to ensure its long-term stability and performance. The following are key construction requirements, including the key points of burial depth, support and backfill:

 

1. Burial Depth Requirements

Minimum Cover Thickness:

Under the roadway: ≥1.0m (need to be combined with load calculation, and additional protection measures if necessary).

Non-roadway (green belt, sidewalk, etc.): ≥0.7m.

Frozen areas: need to be buried below the freezing line, or insulation measures must be taken.

Special load areas (such as heavy vehicle traffic areas): The burial depth needs to be determined through structural calculations, and a concrete protective layer or casing may need to be added.

 

2. Trench Excavation and Support

Trench Width:

Single pipe: outer diameter of pipe diameter + 0.5m (≥0.25m on each side).

Multiple pipes in parallel: pipe spacing ≥0.3m, and the total width must meet the backfill compaction requirements.

Slope or support:

Loose soil: need to be sloped (such as 1:1 slope) or use steel sheet piles or channel steel for support.

Rock formation: need to lay a 10~15cm sand cushion at the bottom of the trench to prevent scratching the pipe.

Base treatment: ensure it is flat and free of sharp objects, compact or replace sand and gravel if necessary.

 

3. Pipeline installation and support

Foundation cushion:

General soil: 10cm thick medium-coarse sand or gravel cushion.

Soft soil foundation: needs to be replaced or reinforced (such as crushed stone + geotextile).

Pipeline connection:

Hot-melt butt or electric fusion connection, must be strictly operated according to process parameters (temperature, pressure, time).

After connection, it needs to be cooled and fixed to avoid stress.

Pipeline fixing:

Concrete piers or special clamps are required at elbows, tees and other parts to prevent displacement.

Expansion joints are set every 50 meters for long straight sections (especially in areas with large temperature differences).

 

4. Backfill requirements

Layered backfill:

30cm above the bottom of the pipe to the top of the pipe: use medium-coarse sand or fine soil (particle size ≤10mm), compact in layers (15~20cm per layer), and the compaction degree is ≥90%.

Pipe top 30cm or more: original soil can be used for backfilling, but stones, frozen soil, etc. need to be removed, and the compaction degree should be ≥85% (≥95% under the roadway).

Notes:

Backfilling should be carried out symmetrically to prevent the pipeline from shifting.

Unilateral dumping or mechanical direct rolling of the pipeline is prohibited.

Density testing is required after backfilling.

 

5. Special working condition treatment

High water level areas: anti-floating measures (such as weight blocks and anchors) need to be taken.

Crossing roads/structures: steel casing or concrete protection box needs to be added.

Drainage of trenches: avoid water accumulation during construction, and set up drainage ditches and water collection wells when necessary.

 

6. Acceptance criteria

Appearance inspection: no scratches or deformation of the pipeline, no leakage at the joints.

Pressure test: water supply pipelines need to undergo water pressure test (1.5 times the working pressure, no leakage after 30 minutes of stable pressure).

Elevation and coordinates: meet the design requirements, deviation ≤±50mm.

 

According to the specification

Domestic standard: "GB 50268-2008 Water supply and drainage pipeline construction and acceptance specification"

International reference: ISO 4427 (HDPE water supply pipe), ASTM F714 (polyethylene pressure pipe)

Before construction, it is necessary to adjust the plan in combination with the specific engineering geology, load conditions and design documents, and consult professional engineers when necessary.

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