Compaction
6.2 Construction Methods and Equipment 207 The grading contractor has a much more difficult problem when the soil is too wet, mixing it with dryer soil is difficult, especially with clays, because it is very hard to achieve thorough mixing.The result often consists of alternating clumps of wet and dry soil instead of a uniform mixture. The most common technique is to spread the wet soil over a large area and allow the sun to dry it.
This works well so long as a rainstorm does not occur, Compaction The next step is to compact the lift. compaction is the use of equipment to compress soil into a smaller volume, thus increasing its dry unit weight and improving its engineering properties. Figure 6.19 shows the typical changes in the volumes of the three phases in the soil from the time when the soil was in its natural condition to when it is compacted into a fill.
Because the solids and water are virtually incompressible and because typically the water in the soil cannot move out of the soil during compaction, compaction produces a reduction in the volume of air, with the vol-umes of solids and water remaining unchanged during compaction. Although many early fills were built without any special effort to compact them, some engineers recognized the importance of compaction as early as the nineteenth cen-tury.
Animals were used as compaction “equipment” on some projects, including a team of 115 goats used to compact an earth dam near Santa Fe, New Mexico, in 1893 (Johnson and Sallberg, 1960). Heavy rollers also began to be used. Initially these rollers were pulled by teams of horses, but by 1920 the horses had been replaced with tractors. Fur-ther developments during the twentieth century enhanced the capabilities of compaction equipment.
Today, a wide variety of effective compaction equipment is available. All of the equipment that drives over a fill, from pickup trucks to loaded scrapers, contributes to its compaction. However, we generally cannot rely only on this incidental compaction because of the following reasons:
• Some construction equipment is intentionally designed to have low contact pres-sures between the tires or tracks and the soil. This allows them to travel more quickly and easily through soft ground. For example, a Caterpillar 973 track
Air Water Solids
In natural condition FIGURE 6.19 a COMpa Excavate
Being hauled Phase diagrams showing the changes in soil as it moves from it natural location to fill. Note that the volume of solids does not change during the process.
Add water Moisture conditioning Compact in compacted fill
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Description
Begin by reading about the various compaction equipment (I have attached the pages). Select any two compaction rollers. State and discuss one similarity between them (other than the fact that they are used for compacting). State and discuss one difference between them. Similarities and differences may be discussed in the context of equipment design, type of soil being compacted, compaction requirements, size of project, etc.
