Pile Foundations Module

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Pile FoundationsModule 9
Prepared by Dr. Randy R. Rapp July 2005
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Site Investigation

• Equipment auger (hollow-stem), split-spoon
  sampler, Dutch cone
• Data sought and recorded

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Types of Bearing

• Friction piles
• In deposits with very deep bearing strata,
  perhaps minimal end-bearing
• End-bearing piles
• Compaction piles

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Augering Caissons
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Pile Types

• Timber
• Beware delivery and storage
• Cast-in-place concrete
• Cased
• Pipe
• Shell
• Fluted
• Uncased
• Wet holes must be remediated

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Pile Types (Contd)

• Precast (typically prestressed)
• Plant inspection may be required
• Handling is critical beware hard-to-see failures
• Steel (H-pile)
• Superior if splicing perhaps needed

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Driving Piles

• Match hammer, pile, cushions for efficiency
• Impedance ? x c x A, potential capacity
• Specified number of blows per inch driven
  indicates that capacity is achieved
• Wave equation analysis by instrumentation
• Empirical formulas (dynamic behavior relates to
  static capacity?)

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Driving Piles (Contd)

• Count blows per foot, until design blow count
  approached
• Then count blows per inch until specification
  achieved
• Underdriving is costly, but overdriving might
  cause irreparable damage to any pile typevery
  costly
• Pile heave neighboring piles, frost

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Driving H-Piles for Pile Cap
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Hammer Types

• Hammers
• Drop
• Air
• Steam
• Diesel
• Vibratory
• Leads
• Fixed A-frame
• Hanging or swinging

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Pile Load Tests

• Load imparted to pile in gradual steps to twice
  design load, as settlement data recorded
• Often, load removed in steps, too, to produce
  load-deflection curve, p. 228
• Behavior
• Elastic deformation
• Buckling
• Puncture
• Ensure multiple deflection references, in case
  one is lost

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Pile Load Test
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Inspector Duties

• Review the hammer manual, if available
• Be sure that the contractor is consistent
• Technique
• Equipment settings
• See pp. 241-44

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Sheet Piling

• Differences from bearing piles
• Subsurface flow cutoff
• Soil retention
• Alignment critical interlock usually desired
• Anchored bulkheads
• Soil nails

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Driving Sheet Piles w/ Hydraulic Hammer