Compaction piles

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Compaction piles

• compacted by driving piles into soil
• Compaction achieved by simple displacement
• For granular soil displacement vibration
• Amount of compaction depends on
• Spacing
• Size
• Vibrating energy (proportional to fine content ,lt
  20)

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• Compaction piles
• Structural piles (timber / pre-cast/ concrete)
• Fill material pile (Sand piles, gravel)
• Structural piles densifies loose soil
• Sand piles
• installed by driving a hollow steel mandrel with
  a false bottom to the required depth
• fill the mandrel with sand
• applying air pressure to the top of the sand
  column
• Withdraw the mandrel
• Pore water pressure increases

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• Design based on
• stability of the sand column
• the piles and soil are subjected to equal
  vertical deformation
• soils of low permeability below the water table-
  sand piles as drains
• A well-compacted layer of soil is placed on top
  of the sand piles to obtain a better load
  concentration on the piles by arching

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• Vibro-composer method
• driving a casing to the required depth by means
  of a vibrator.
• A quantity of sand is then placed in the pipe
  which is partially withdrawn as compressed air is
  blown down the casing
• Next the pipe is vibrated downwards to compact
  the sand pile.
• The process is repeated until the ground surface
  is reached

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Vibro composer sand piles
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Gravel compaction piles

• a tube closed by a plug of gravel (or zero slump
  concrete) is driven into the ground by means of a
  drop-hammer striking the plug
• the soil is compacted radially around the tube
  while driving
• tube _at_ design depth an expanded base is formed by
  ramming with a high-energy hammer
• tube is then raised in lifts gravel is driven
  from the tube so forming a continuous pile of
  compacted gravel

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Concrete columns

• support structures on weak cohesive, organic or
  loose granular soils and fills
• vibrator which contains a special hollow shoe
  that houses a tremie pipe down to which concrete
  is pumped
• pipe is connected by hose to a trailer-mounted
  concrete pump
• Pipe pumps concrete under pressure
• Vibrations _at_ 3000Hz

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• the vibrator is withdrawn about a metre while
  pressurized concrete is tremied in at the toe
• The vibrator is then driven back to the original
  depth to create a bulbous bearing end
• withdrawn at a slower speed than the pumping flow
  so as to maintain pressure in the concrete column
• Once grade level is reached the concrete is shut
  off
• the vibrator is briefly re-immersed in the
  concrete to finish off the column

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Dynamic compaction

• repeatedly impacting the ground surface by
  dropping a pounder from a given height from a
  heavy duty crane
• _at_ of one blow every 13 mins
• the distances between the centres of impact
  frequently ranging between 4 and 20 m
• set out on a grid pattern
• The energy per blow is chosen to maximize
  penetration of the resultant stress impulses
• Densify a wide range of soils from organic and
  silty clay to loosely packed coarse-grained soil
  sand fills 

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• The energy required to achieve a given result
  increases with the amount of fines in the ratio
  13 when going from coarse gravel to silty clay.
• Compactor with Wt 200t n height 40 m can
  compact 50-60m of clayey silt
• Vibration frequency is around 5 Hz, and usually
  lower than 12 Hz
• The threshold vibration velocity above which
  damage may occur in buildings is normally taken
  at 50 mm/s
• extensive site investigation must be carried out
  prior to the commencement of dynamic compaction

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Dynamic compaction
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• Dynamic compaction is carried out in several
  phases 
• spacing between the points of impact is large in
  the first pass and is reduced successively in
  subsequent ones
• The modulus of deformation of the soil maybe
  increased by two to ten times
• the depth of the imprint does not exceed half the
  width of the pounding mass
• must have three or four types of tamping weights
  available on site.

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• After each pass the craters formed in the ground
  by tamping are filled with soil (ideally
  well-graded granular) before the next pass
• Finally ground is given a final ironing pass in
  which the weight is dropped from 1 to 2 m at
  spacings smaller than the width of the weigh
• saturated or partially saturated soils and soft
  peaty or organic deposits are not subjected
  to direct dynamic compaction
• For soft clays use vertical drains to result in
  compaction
• Small machine (a large hydraulic pile hammer
  mounted on a crawler crane) consolidates upto 4m
  for small constructions