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St George Landscaping, Masonry and Excavation

Understanding Backfill Compaction Requirements

Backfilling is an important part of the construction process. Backfilling happens after excavation, when the soil is compacted back into the trench or foundation. It is used to help protect foundations, roadways, walkways and other structures by using a mixture of soil, rocks, and stones.

There are many different ways backfilling is approached, but there are basic requirements used in each method. Here are three major steps to remember when backfilling and compacting soil.

1. Backfill in Layers

Backfilling in layers is one of the most important steps to remember. It is important to do it in intervals to let the soil properly compact. These layers are referred to as “lifts.” The amount of inches filled per lift depends on the requirements of the project (soil or the type of structure being backfilled). There are some who say increments of 4”-6” is ideal, but others say that up to 12” works well. After the lift is compacted, it is important that the fill is equal to the ground surrounding it before putting on the next lift.

2. Compacting

There are six different methods used to compact substances. Some are more suitable for soil while others are used to compact non-soil materials such as asphalt. The most effective techniques are generally the ones that apply the most compressive stress.

  • Static – a large amount stress is slowly applied to the soil and then is released
  • Impact – a large mass is dropped onto the soil to apply the stress
  • Vibrating – a mechanically driven plate or hammer is used repeatedly to apply stress
  • Gyrating – soil is subjected to a gyratory motion while the stress is maintained in one direction
  • Rolling – stress is applied via a large cylinder rolling over the surface of the soil
  • Kneading – shear is applied by alternating movement in adjacent positions

To determine whether or not the natural soil is ready to be filled, there is a technique called proofrolling. Proofrolling is when heavy construction/compacting equipment is rolled over the area, looking for deflections all over the fill site.

3. Water Thoroughly

Be sure to water the soil thoroughly after the fill layer is set. Then, repeat these three steps until the whole process is done!

Backfilling With Pipe

  • When laying down pipe, be sure to backfill the excavation immediately.
  • Select backfilling materials that will be beneficial to the safety of pipes.
  • Be careful not to damage pipe coatings.

If you have any questions about the backfilling process, let us know! It’s our goal here at Stonetree to offer our expertise and help you every step of the way.

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