Of all the construction materials available, soil is more widely used than steel, concrete, and asphalt. A construction site is leveled for structures and graded for pavements by taking soil from high areas and putting in low areas. In order for soil to support buildings and roads, it must be compacted to a dense state while it is being placed. How dense? Well that depends on what’s being built. The job of a Geotechnical Engineer involves specifying how dense a soil needs to be for its intended use. The reason is that the desirable engineering properties of soils used in construction are controlled by how dense the soil is. The strength, compressibility, and permeability characteristics of a soil are all improved as the soil becomes more dense.
So how do soils move from a less dense state to a more dense state? Compactive effort or just compaction describes the process at which soil is densified. In construction, rollers, tamps, packers, tampers do this work for us. These machines impart lots of energy into the soil to densify a relatively thin layer of soil just beneath their wheels, pads, or drums. It’s the job of the people moving the earth to put it where it needs to be, make sure it’s placed in layers which their compactors can densify, and to compact the soil to a dense state so it can support the overlying structure or road.
One of our jobs at Falcon is to make sure the people moving the earth know that they’ve reached the right level of compaction. But in order to do that, we first need to know what the right level of compaction actually is! To figure this out, we perform compaction tests in the laboratory which are also known as Proctor tests. By following a standard testing method, we densify a sample of soil under controlled conditions by imparting a standard amount of compactive effort or energy. Once we know how dense the soil can get under ideal conditions in the lab, we can test the soil compacted by builders on a construction site and compare the results. Did the soil compacted in the field get the same results as the lab? Then we know the soil is densified and then next layer may be placed! But, how do we test compaction of soil in the field? Well…that’s a topic for another video.