Selected and Unselected Filling Materials Use – Construction of Embankments

Selected and unselected filling materials are an integral part of road, building, dam, and mine construction. To give you an indication of how these materials are used in large projects, we briefly look at embankments that raise the level of road surfaces above the surrounding earth.

What Filling Is

Unselected or selected filling refers to the materials used for filling an area where the materials are compacted with the aim of filling a depression. An embankment is thus just another type of fill. This type of fill contains anything from soil and aggregate to rock, crushed rock, and sand.

Best Practice in Using Unselected or Selected Filling Materials

In the case of an embankment, the normal procedure is to place the coarse filling at the base of the hole or depression to create a strong foundation for the fill. This also helps to ensure proper drainage and thus avoids a situation where the embankment is oversaturated. The upper part of the depression is normally filled with a higher-quality selected filling consisting of compact, subgrade aggregate that provides the necessary support for the layers on top and for vehicle loads without causing movement in the fill. It is essential to use fill materials of the correct specification and according to its capacity for compaction to the desired density in the remaining part of the embankment. Thin layering of the materials is needed, and each layer must be compacted thoroughly with the appropriate equipment. The rolling compaction method is usually used.

Unselected and Selected Filling Materials for Embankments

The preferred materials to use are sand and gravel, but silt and clay are also sometimes used. Well-graded materials must be used in the fill; such materials must be suitable for compaction and not contain roots, sludge, leaves, metal, or plastic. Rocks and larger stone can also be used for the lower part of the embankment. It is essential that these materials contain strong particles able to withstand the weight and movement of the machinery, but small enough in size to prevent empty or only partially filled spaces.

It is best to use well-graded filling consisting of a mixture of finely grained and granular materials. Though it is not essential, it is better to use filling low in unit weight for less transfer of dead weight onto the underlying surface upon which the embankment rests.

Where to Get Unselected and Selected Filling Materials

Make use of our supply services for sand, rock, crushed sand, and aggregate materials. We are bulk suppliers of selected and unselected filling materials to companies in Gauteng.