Loose soil is low-density soil. It has many voids, or, let’s say, empty spaces in it compared to other soils. Because of this, loose soil compresses easily and isn’t very strong. Before construction, it must be adequately compacted and free of organic material that can rot and create voids and sinkholes. Compacting strengthens the soil by reducing the number of voids and increasing its density.
Sometimes, loose soil is brought into a construction site to be used as fill. Since fill is always looser than other soils, it will need to be adequately compacted before anything can be built on top of it. If fill isn’t properly compacted, it will start to compress after the structure is built, leading to differential settlement and foundation damage.