Backfilling is the process of returning dirt to a trench or foundation after it has been excavated and the associated work has been done. Backfilling demands expertise, heavy equipment, and a thorough understanding of the specifications, contract requirements, and soil conditions. Each type of soil has its own properties, necessitating the use of diverse construction approaches to achieve the best results.

When pouring and compacting backfill, backfill personnel must also take care to avoid impact loading any pipeline, shaft, structure, cabling, or other subterranean elements. Backfilling and compacting backfill can be done in a variety of ways. Special precautions must be taken while filling and compacting ditches for utility lines.

Trenching Compacting

Following the backfilling of earth into a trench, the loose material is crushed using a compactor, an excavator, or a “jumping jack”-type compactor. As a general rule, soils should be compacted to at least the ASTM D698 Method A minimum percentages of maximum dry density (Standard Proctor). 1

Backfilling soil is usually done in layers or lifts. The soil lift will be determined by the type of backfill utilized and the compaction equipment used. To aid compaction, water can be introduced at any time during the operation. The main procedure is broken down into three parts, which are repeated until the backfill reaches grade level:

  • Backfill with non-organic fill material that is free of debris in 4 to 6-inch layers.
  • Compact using a 1,000-pound compactor, or as needed.
  • Thoroughly wet
  • Using Water Jets

Backfilling with water jetting eliminates the need for mechanical compaction. Instead, a probe is used to apply pressured water to the bottom of the backfill, compacting it. Water jetting is excellent for sand or sandy soils, as well as the bedrock that is extensively fissured. Plastic soils and thick clay soils are not suited.

You utilize the jetting technique to shift bedding or backfill material around by pumping water under pressure and using the force of the jetted water. The material should be deposited gently and in lifts, just like any other backfilling. To improve compaction, the water is allowed to drain from the soil after it has been poured. Crews must take precautions to confine sediment-filled water and prevent it from entering drains and watercourses due to the mixing of water and soil, all in compliance with EPA guidelines. 2

Filling That Flows
Flowable fill, a cementitious material with a low water-cement ratio that is brought to the construction site by a ready-mix truck, can also be used for backfill. Flowable fill is typically dumped in the trench directly from the truck, exactly like conventional concrete, once the utility pipe or other equipment in the trench has been covered with an aggregate material. The aggregate that surrounds the pipe makes it easier to reach the pipe in the future for repairs. When using flowable fill, one of the issues is the fill’s liquidity. To prevent the fill from seeping into other trench locations, contractors must confine or restrict it.
Utility Trenches Backfilling
Backfilling trenches with utility lines necessitates the use of specific procedures and considerations. The following are standard recommendations:
Unless other protection is ordered or indicated, backfill trenches and excavations immediately after the pipe is laid.
Backfill materials should be chosen and deposited with great attention to the pipes’ long-term safety.
Fill the lower portion of the trench with appropriate backfill and bedding material in layers no thicker than 6 inches, compacting with suitable tampers to the density of the nearby soil until a cover of not less than 12 inches is achieved, taking extra care not to damage pipe and pipe coatings.
Backfill the trench with material that is free of stones larger than 6 inches or 1/2 the layered thickness, whichever is less (in any dimension). It may not apply to certain pavement materials.
Using heavy-duty pneumatic tampers, tamp in 6-inch layers under roadways and other paved areas (or equivalent). Tamp each layer to an ASTM D698 Proctor Curve density of not less than 100%. Allow for further compaction by leaving the backfilled trenches open to traffic while keeping the crushed stone surface.
Source: Thebalancesmb