Dust, dirt, and soil. They’re the embodiment of the earth and, like us, they can be as delicate as a newborn or as calloused as a life-long labourer. As our flesh becomes calloused by wear, soils too become compacted by the simple application of pressure from foot traffic, vehicles, and even rain drops. The greater this pressure, the greater the soil compaction.
D W Jensen Drilling Ltd. is celebrating 40 years of dedicated service, throughout Alberta and British Columbia in 2016, including our expertise in dust compaction for residential, industrial, and construction applications. However, to fully understand compaction and its benefits, a bit of a history lesson is in order.
According to lecture notes from the Missouri University of Science and Technology the concept of compacting was first noted in 1816 when Scotsman John L. McAdam published a book on road building. It promoted a cambered 10-inch thick course of aggregate base rock, 16 feet wide that employed a top course of less than two inch rocks that each weighed less than 6 ounces, underlain by increasingly larger stones. These were then packed down or ‘compacted’ by animals and wagon wheels. From 1927-30, O.J. Porter developed the California Bearing Ratio (CBR) and soil swell test, which measured the penetration of compacted soil, and was intended to evaluate the load bearing capacity of the pavement subgrade.
Today, the benefits of soils compaction include:
- Mixtures of soil and rock to increase their effective shear strength, making them more able to resist deformations;
- To reduce the long-term settlement, and differential settlement - embankments are often differing thickness, which promotes differential settlement and differential heave; and
- Densifying fine grained soils so they absorb less free moisture. Soil tends to absorb moisture with time and softens, promoting bearing capacity failures, settlement, loss of strength, and slope creep.
There is no single compactor that will do everything in all applications and many factors that influence the choice of compaction equipment including the contractor’s previous experience, the type of soil, method specification, or available equipment. The three primary types of compactors include the:
- Vibratory steel drum roller compactor, seen on many roadways, where it is widely used to compress the surface being rolled to ensure a smooth, even surface.
- Pneumatic tire roller compactors are used on small to medium size jobs. With little bridging effect between the tires they seek out soft spots which may exist in the fill, because if this they are sometimes referred to as “proof” rollers.
- Padded drum compactors have involuted (rolled) edges to walk out of the lift without fluffing the soil and are tapered to help clean themselves.