Aside from the backfill timing, backfill material is also as important. Backfill material can be classified grade of which the most common examples are sand, gravel, clay stone and topsoil. These material will be decided according to the design requirement of the backfill material to support the structure.
These are gravelly and sandy type of soil and ranges from clayey sands to high quality gravel-sand mixture. Coarse-grade soil are the most popular because it has high quality properties and exhibits slight to no plasticity. These type of soil are easy to compact and provides a good support for the foundation.
These are the organic clays, fine sands, inorganic slits. These materials have a property of low to medium plasticity. They are relatively impervious and can be compacted fairly using a heavy duty compaction material and is considered as a good stable backfill.
Rocks can be suitable as a backfill material considering its hardness and gradation. Since rocks are bigger in sizes, before using as a backfill material, hard rocks will undergo a crusher process to ensure that it passes the requirement as a cohesion less material.
To ensure that it passes the design requirement, the bearing capacity of the backfill material should be determined. The sample will undergo field test to determine if it is applicable to be used as a backfill material.