Part 5 COMPACTION EQUIPMENT

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Part 5COMPACTIONEQUIPMENT
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• The sheepsfoot roller has evolved into a wide
  variety of forms. This shows the Allis Chalmers
  roller, which introduced replaceable hammerhead
  tips in the late 1930s, during construction of
  the San Gabriel Dam

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• Spike rollers are a sheepsfoot variant that can
  be employed to help break up and disaggregate
  soft or fissile bedrock materials, increasing the
  bulk density of the fill mixture

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SHEEPSFOOT ROLLERS

• Most sand and water-filled sheepsfoot rollers are
  capable of delivering 250 psi contact pressure,
  if the spike contact area is between 5 and 8
  square inches. The spikes compact a zone 2 to 8
  inches beneath their tips.

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• Sheepsfoot rollers walk out of the soil as it
  becomes densified, leaving the uppermost 1 to 2
  inches uncompacted
• For this reason it is important that cohesive
  soils be scarified prior to compaction (difficult
  if scrappers have been running over everything)

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PAD ROLLERS

• Self-propelled tamping or pad rollers are capable
  of delivering 5 to 75 psi contact pressures.
  They are well suited to most soil mixtures and
  may employ vibration (2500 to 4500 Hz) for
  compacting cohesionless (sandy) materials.

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SELF-PROPELED ROLLERS

• Self-propelled compactors like these CAT 835s can
  be fitted with different kinds of rollers. The
  machine at left has a pad roller while the one at
  right employs actual sheepsfoot roller pins.

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• 50 ton rubber tired roller being used to compact
  an damaged airport runway. Note box segments,
  which are semi-articulated.

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COMPACTIVE EFFORT

• Rubber tired (pneumatic) rollers exert a
  compactive effort equal to the air pressure in
  their tires (35 to 55 psi). Large towed
  pneumatic compactors (gt 50 tons) can exert 100
  psi contact pressure.

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• Ramex hand-operated compacter, used mostly in
  trenches and difficult access areas. Hand
  operated compactors such as this and smaller
  Whackers and pogo-sticks generally exert
  between 8 and 18 psi contact pressures, well
  below mechanized equipment

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• Plate compactors can be attached to tracked
  excavators to provide mechanical compaction of
  trench backfill, mostly for buried utilities.
  These trenches are not usually compacted in 6 to
  8 inch lifts, so can settle noticeably.

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CONTACT PRESSURES

• Contact pressure/Input energy for various types
  of compactors. Note that track-walking fill with
  dozers is not an adequate means of compaction.

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• TEST STRIPS
• Test strips are useful to determine which type of
  compactor and how many passes will be necessary
  to achieve the desired compaction
• In this example, P is pneumatic tire roller T is
  a tamping foot, or pad roller and V is a
  vibrating drum roller
• The example at left is for a granular soil
  mixture which benefit from vibratory compaction