Pile FoundationsModule #9

Prepared by

Dr. Randy R. RappJuly 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 (Cont’d)

• 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 = ρ 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 (Cont’d)

• 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 type—very 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