Ductile iron water pipes are widely used in municipal water supply, industrial water transmission, and infrastructure projects due to their high strength, good toughness, strong pressure resistance, and mature connection methods. After passing the hydrostatic pressure test, the correct backfilling procedure directly affects the operational stability and service life of the pipeline.
Improper backfilling may lead to the following issues:
Uneven pipe stress causing joint deformation or leakage;
Damage to the external anti-corrosion layer leading to corrosion and reduced lifespan;
Voids caused by unclean or poorly compacted backfill, resulting in surface collapse;
Structural misalignment caused by thermal expansion, contraction, or soil settlement not being considered.
To help you perform proper backfilling, I provide standard procedures for two typical working conditions for your reference. For more complex or special applications, please contact our technical team for customized recommendations.
Condition 1: High-temperature arid region, pure sand, slight salinity
Environmental Features
Soil: pure sand, dry and well-ventilated
Climate: average temperature 35–42°C, almost no rainfall
Geology: stable, low risk of settlement
Slight salinity present, posing minor corrosion risk
Backfilling Procedure
Inspection and Preparation Confirm that the hydrostatic pressure test is passed; repair any damaged FBE coating. Clean the bottom of the trench; remove stones, water, and debris.
Bedding Layer Installation Lay 100–150mm thick fine sand bedding, level and lightly compact, avoiding pipe suspension.
Side Backfilling Use fine sand or screened fine soil in layers (200–300mm/layer); backfill both sides simultaneously and compact to prevent displacement.
Top Backfilling (up to 0.3m above pipe crown) Use the same material as the sides, compact manually; heavy machinery is not allowed directly over the pipe.
Upper Fill You may use native soil, but avoid high-salinity surface layers. If necessary, wrap the pipe with PE film or non-woven fabric to enhance corrosion protection.
Additional Protection Recommendation You may install sacrificial anodes (e.g., magnesium) as cathodic protection for trunk pipelines.
Condition 2: Urban area, pure soil, moderate temperature, low rainfall
Environmental Features
Soil: natural pure soil, fine particle size
Climate: moderate (10–30°C), low rainfall
Terrain: flat, minimal settlement risk
No salinity, low corrosion risk
Backfilling Procedure
Pre-construction Inspection Confirm that the pressure test is passed, no leakage at joints, and FBE coating is intact.
Bedding Installation Lay 100–150mm of fine soil or fine sand bedding at the bottom of the trench and compact evenly.
Side Backfilling Use native soil in layers (≤300mm/layer), compacted manually or with light machinery. Ensure simultaneous backfilling on both sides to prevent pipe misalignment.
Top Backfilling Continue backfilling up to 300mm above the pipe crown; avoid using compaction machinery directly over the pipe.
Upper Fill After 0.3m coverage, use native soil with machinery-assisted compaction, meeting the road load-bearing requirements (for pipelines under municipal roads).
Suggested Measures In heavy traffic zones, you may add warning tape 0.2m above the pipe crown to assist future maintenance.
The above are standard backfilling procedures for two typical working conditions of ductile iron water pipes. In different environments—such as highly corrosive soil, high groundwater levels, rock foundations, frozen soil, or areas under heavy traffic—backfill material selection, corrosion protection, and pipe protection measures vary significantly.
If you encounter special geological conditions, specific use cases, or are uncertain about material selection during installation, feel free to contact our professional technical team. We provide complete engineering support including material recommendation, installation guidance, and failure prevention solutions to ensure stable, durable, and leak-free pipeline operation.
