Soil Compaction

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FM 5-410 CHAPTER 8 Soil Compaction Soil compaction is one of the most critical components in the construction of roads, airfields, embankments, and foundations. The durability and stability of a structure are related to the achievement of proper soil compaction. Structural failure of roads and airfields and the damage caused by foundation settlement can often be traced back to the failure to achieve proper soil compaction. Compaction is the process of mechanically densifying a soil. Densification is accomplished by pressing the soil particles together into a close state of contact with air being expelled from the soil mass in the process. Compaction, as used here, implies dynamic compaction or densification by the application…show more content…
Volume change is generally not a great concern in relation to compaction except for clay soils where compaction does have a marked influence. For these soils, the greater the density, the greater the potential volume change due to swelling, unless the soil is restrained. An expansive clay soil should be compacted at a moisture content at which swelling will not exceed 3 percent. Although the conditions corresponding to a minimum swell and minimum shrinkage may not be exactly the same, soils in which volume change is a factor generally may be compacted so that these effects are minimized. The effect of swelling on bearing capacity is important and is evaluated by the standard method used by the US Army Corps of Engineers in preparing samples for the CBR test. Section II. Design Considerations MOISTURE-DENSITY RELATIONSHIPS Nearly all soils exhibit a similar relationship between moisture content and dry density when subjected to a given compactive effort (see Figure 8-1). For each soil, a maximum dry density develops at an OMC for the compactive effort used. The OMC at which maximum density is obtained is the moisture content at which the soil becomes sufficiently workable under a given compactive effort to cause the soil particles to become so closely packed that most of the air is expelled. For most soils (except cohesionless sands), when the moisture content is less than optimum, the soil is more difficult to compact. Beyond optimum, most soils
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