Can you use sand as a backfill? Here are several Reasons for using sand when backfilling.

Is sand a good backfill material

Once the excavation or trenching work is complete, the cavity or hole that has been left empty has to be filled with soil. This is the process that we call backfilling. Depending on the particular project, the backfill material that can be used may be the excavated material from the hole or a new one from another source.  Since there are many purposes to backfilling, some materials may be better suited for some projects than others.

Often, contractors may use commercial-bought backfill from home improvement stores. There are several types of materials you can use for backfilling. Two of the most popular examples are sand and gravel.

Is sand a good backfill material?

Sand, which we often see on the beach, is considered to be a good backfill material. If it is not possible to reuse the excavated material, many professionals who work in the construction industry make use of store-bought sand or get it from another source. There are three main reasons why sand is reliable - it is compact, has a high drainage capacity, and is overall a stable material.

Let us go into each of the reasons and explain why sand works:

·      It has a high compaction rating

One of the primary reasons why sand is a good fill material is due to its ability to be compact. This factor is very crucial to the success of many construction projects. Because fill sand has a smaller grain, it is easier for the material to compress by using various compaction techniques. Hence, using sand to replace the excavated material in a particular hole or cavity allows it to stay in place for a long period of time.

·      It is good for drainage

Aside from having a small grain, sand particularly has a rough texture. Because of its coarseness, its particles do not extremely stick together. As a result, it is a nice fill material since it will allow water to flow through and drain. This is essential to many projects, as this will also mean that sand will not retain as much water as other dense backfill materials. Sand works best in areas that are highly likely to get wet or moist.

·      It can support and stabilize structures

When used in an area where it is compatible using a proper compaction technique, sand is a material you can trust to keep your structure stable. It holds its shape and can support the area well as it will not deteriorate in water.

Why is clay not used as a backfill material?

why clay shouldnt be used as backfill material

Clay may work wonderfully when using it for planting specific trees and other vegetation. Since it can give the plants the nutrients and water it needs, it is usually a staple in many gardens and flower nurseries. On the other hand, when it comes to backfilling, owners and experts often stay away from clay to use as fill material.

Clay is not a good fill material because

  1. It has poor drainage
  2. It can crack in extremely cold weather
  3. It can drown other plants and vegetation
  4. It expands when wet

Using clay for backfill does not always mean that your construction project will 100% fail. Since it is inexpensive to use, many people will still use clay as their fill material. However, if it is not your goal to sacrifice quality, you would do better to ask an expert first if doing so is a good idea.

What are the types of backfill?

Depending on the specific project, budget, and other factors such as the location of the worksite, some types of materials will work best or may be a bad option to choose.

Fill material categories

1.     Coarse-grained

Includes gravelly and sandy soils with slight or no plasticity. Works best for projects that require a compact material.

2.     Fine-grained

Includes organic clays and inorganic silts that have a low to medium plasticity.

3.     Rock

Crushed rock or stone fills often work best in areas that require a high drainage capability.

4.     Shale

Shale is often used in areas that are abundant in the material as they are often quite difficult to excavate.

5.     Marginal materials

This type of material includes several types that are not often the best choice for backfill due to their certain characteristics. Because of this, additives may be necessary to improve their properties.

6.     Commercial-by-products

Includes fly ash and furnace slag, which can be used on its own or added to other fill types when natural fill is not accessible.

What’s the difference in using fill sand and fill dirt?

Although they are both similar in nature, they are classified differently and are sometimes used in different applications.  Fill sand is derived from rock that may have been broken down naturally over many decades or even centuries.  This process could have also been sped up using other man-made methods which essentially crush large rock into extremely small particles of sand, such as the kind you might see at the beach, or the kind used in a sand box.  Sand backfill is great for scenarios where effective drainage is very important, although it’s typically not used where structural stability is critical because it tends to compact easily.

Fill dirt, on the other hand, is used in many construction or land renovation projects when you need to manipulate or artificially alter the grade or elevation of the land.  This process is known as land grading.  Fill dirt comes from the sub soil, meaning the layer beneath the top soil.  The sub soil is dug up a few feet below the surface where there is no naturally occurring biological activity nor where any biological activity can break down.  This is why fill dirt works well for construction projects as there is no organic matter to break down.  If organic matter were present, or if the top soil were being used, the organic matter would eventually break down and decompose leaving a large area of empty space that will cause a structure to lean, shift and settle.  To make sure that fill dirt is high quality, it will usually get sifted multiple times to ensure that rocks and larger debris get filtered out.  It is also known as clean fill.

What makes good backfill?

Using the right backfill for a specific construction project can be an important factor that may make or break the end results. Because of this, it is essential to choose the best backfill for the type of project you are currently doing. But how can we tell if we are picking a good backfill material or not?

Here are some of the things that a good backfill material should have:

1.    It should have the right grade

Backfill materials come in many grades. As mentioned earlier, it can be coarse, fine, rocks, shale, marginal materials, or commercial by-products. Depending on the project, some backfill grades may work best than others. As an example, for building a basement, most professionals prefer to use coarse-grained soil to keep the surrounding area dry and prevent rot.

Using the right grade of backfill allows you to keep your construction project last for years. After all, you would not want to redo the entire process just because you used the wrong backfill. To know which grade will work for your property, ask your contractor to inspect the soil in your area.

2.    It should encourage water flow

The backfill material you should choose also needs to drain enough water to keep your structure standing. Since drainage is an important factor that must be taken care of to prevent moisture issues and waterlogging, it is recommended to pick a material that encourages water flow. As said earlier, sand is a good example of a backfill material that allows excess water to seep through its coarse grade. Because of this, many construction benefits make use of sand as their primary backfill material.

Of course, not all projects are the same. In some situations, it may be better to use a combination of material that is coarse but still strong enough to support the structure.

3.    It should be stable and well-compacted

Another important factor that will determine whether a particular material will be good backfill or not is its stability. Soil is made compact by either manually packing in the material in the cavity using handheld tools or by using heavy machinery to do the work.

Since some materials do better when shape while some are not, there are several compacting techniques that professionals use.

The common compacting methods:

a)    Vibrating

This technique makes use of a hammer or mechanically driven plate to apply stress on the fill soil.

b)    Gyrating

This technique subjects the soil to a circular motion to compact the material in a particular spot.

c)    Static

This technique makes use of a heavy steel plate to slowly drop its weight into the backfill to apply stress.

d)    Impact

This technique makes use of a heavy object to suddenly drop its weight into the fill soil for compaction.

e)    Rolling

This technique makes use of a large cylinder and rolls it over a large area to compact the backfill.

f)     Kneading

This technique adds friction using alternating movements in adjacent positions.

Stable soils hold the structure well and put less stress on its walls and foundations. Hence, soil compaction can be an essential process before one can proceed with the next step in their construction project. For many experts in the industry, compacting fill soils should always be done, especially before placing a slab or footing on top.