GENERAL:
Vibratory compaction is the art of densifying or increasing the unit weight of a material mass through the application of
dynamic forces, with the expulsion of air and in some cases moisture The extent to which a material can be compacted
depends on the characteristics of the particular material, the amount of force used to compact it, and the moisture
content of that particular material.
Compaction is necessary in order to form a stable foundation for any structure in which a future decrease in volume of
the material will be detrimental. This covers highways, buildings, and other structures However, there are actually two
purposes to compaction, one is to consolidate material to avoid future settlement, while the other is to build strength Into
the material
FIGURE 2
The theories advanced on vibratory compaction are numerous; and in many cases varied However, it appears that the
most efficient compaction by vibration occurs at or near the material resonance point These resonance points vary
among material types with the range of 1200 to 1800 vibrations per minute covering most of the materials In which
vibratory rollers are effective Functionally vibratory compaction is the inter- relationship of three factors frequency,
amplitude, and force. Frequency is the number of vibrations per minute while amplitude Indicates the vertical distance
the vibrating roll travels from a theoretical center to its maximum distance from this center Total vertical movement is
technically double-amplitude, although in some cases may be referred to simply as amplitude. Amplitude is greatest
when the roll is vibrating at material resonance.
Vibratory force is usually generated by a rotating eccentric weight Although this centrifugal force acts radially In all
directions from the center of the roll, only the vertical or near vertical components are used to compact.
FIGURE 3
Vibratory compaction is suited to granular type soils and in these materials will give excellent compaction results
Vibratory rollers are basically a deep type of compactor in soil, that is, they can compact deep lifts Smooth roll may,
vlbratories however, leave the top inch of the surface loose in granular soils This is generally attributed to the horizontal
vibrations traveling along the soil surface This uncompacted surface can be readily compacted with the roll in a non-
vibrating condition
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