Earth is almost never at the desired elevation at the intended location of a structure, and even if it was the case, almost always modifications must be done, to serve as a foundation base material that is capable of supporting the loads and at the same time settling only within tolerable limits. Therefore, earthwork operations are performed to bring the soil to correct elevation. Bringing the soil to desired properties will be covered under ground improvement and soil stabilization sections.
To modify the elevation of natural soil, there are basically two types of activities. When the natural soil is higher than the intended elevation of the bottom level of the foundation of the structure, the soil is removed down to that elevation, which is called “cut” or “excavation”. The opposite, where natural ground elevation is lower than the bottom of intended foundation of the structure, new earth material must be brought in, which is called “fill” or “backfill”. The filled soil is compacted by compaction equipment. Note that before filling still some cut may be necessary up to a depth determined by engineer, if the natural ground is not made of strong enough material. Also, in case of roads or pavements, the bottom level of the foundation means the bottom level of the sub base materials below the road.
In the next post of this series, we will discuss “Earthwork Quantity Calculations”