Foundations
Foundations• Feature common to  bridge and building  structures• Deep vs. shallow• Safely transfer dead  and live loads wi...
FoundationsShallow Foundations     – spread footings: column,       combined, mat     – strip footings: walls•   placed on...
FoundationsDeep Foundations• Piles  – driven or drilled  – bearing capacity from end-bearing or skin     friction: usually...
FoundationsPiles• Types   – timber piles   – precast/prestressed     concrete piles   – cast-in-place concrete   – steel H...
Foundations     Pile Driving     •   Equipment          – mobile crane (usually crawler)          – leads: fixed or swingi...
FoundationsPile Driving• Equipment   – follower   – mandrel• Pile accessories   – point attachments   – splices   – pile t...
Foundations       Pile Driving       • Hammers          – steam or air: single-            acting, double-acting,         ...
Pile Driving• Dynamic analysis - wave equation “WEAP”  – based on wave propagation theory with input    from the static an...
Pile Driving• Benefits of using wave equation  – verify piles can be driven to required depth &    capacity  – determine m...
Pile Driving• Dynamic testing - Pile  Driving Analyzers (PDA)  and CAPWAP   – uses strain gauge &     accelerometers to   ...
Pile Driving• Dynamic testing - Pile Driving  Analyzers (PDA) and  CAPWAP   – cost effective method of     optimizing the ...
Pile DrivingPile Load Test (static)• many tests have been used over the years to  evaluate or confirm axial and lateral ca...
Pile Driving
Pile DrivingPile Load Test (static)• the test load is measured by a load cell• deformation is measured with dial gauges, w...
Pile DrivingPile Load Test (static)• incrementally increase load until reaching 200%  of the design load or until continuo...
Pile DrivingOther Factors• soil setup or “freeze” - common in clays• relaxation - much less common, found in  some silts o...
Pile DrivingInspection• position, plumb, or batter• check cushion; change as necessary• record blow counts• verify correct...
Pile DrivingDriving Records• prepare a sketch of foundation to identify  piles and order of installation• Drive records in...
FoundationsRetaining Walls• gravity or cantilever• components   – stem wall   – horizontal base     includes:       toe, h...
FoundationsTemporary Support  Structures and• sheeting w/wales and  tie-backs• soldier beams (piles)  w/lagging• pipe slee...
FoundationsUnderpinning• remedial or  precautionary• remedial adds  foundation capacity to  inadequately supported  struct...
FoundationsUnderpinning• Temporary supports   – shores   – needle beams   – grillage• Pit underpinning - used  for install...
Foundation notes
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Foundation notes

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Foundation notes

  1. 1. Foundations
  2. 2. Foundations• Feature common to bridge and building structures• Deep vs. shallow• Safely transfer dead and live loads with acceptable levels of settlement
  3. 3. FoundationsShallow Foundations – spread footings: column, combined, mat – strip footings: walls• placed on undisturbed or well-compacted soil• below frost line• consider effects of groundwater• typically reinforced or plain concrete
  4. 4. FoundationsDeep Foundations• Piles – driven or drilled – bearing capacity from end-bearing or skin friction: usually combination of both – driven plum or battered (1:6 to 1:3) – driven to attain minimum tip elevation or required resistance in blows per foot (bpf)
  5. 5. FoundationsPiles• Types – timber piles – precast/prestressed concrete piles – cast-in-place concrete – steel H-piles – steel pipe piles – composite – minipiles or micro piles
  6. 6. Foundations Pile Driving • Equipment – mobile crane (usually crawler) – leads: fixed or swinging – hammer, helmet, & cushion – compressor (if air driven) – hydraulic unit (if vibratory) – steam plant (becoming obsolete)
  7. 7. FoundationsPile Driving• Equipment – follower – mandrel• Pile accessories – point attachments – splices – pile to cap connections
  8. 8. Foundations Pile Driving • Hammers – steam or air: single- acting, double-acting, differential – diesel hammer: single- acting (open end) or double-acting (closed end) – vibratory
  9. 9. Pile Driving• Dynamic analysis - wave equation “WEAP” – based on wave propagation theory with input from the static analysis – provides relationship between pile capacity and driving resistance i.e.: equates capacity to blow counts – predicts pile driving stresses
  10. 10. Pile Driving• Benefits of using wave equation – verify piles can be driven to required depth & capacity – determine minimum required pile section – avoid overstressing pile during driving – optimize cost
  11. 11. Pile Driving• Dynamic testing - Pile Driving Analyzers (PDA) and CAPWAP – uses strain gauge & accelerometers to measure force & velocity (converts strain to force and acceleration to velocity) – field tests the driving hammer and system
  12. 12. Pile Driving• Dynamic testing - Pile Driving Analyzers (PDA) and CAPWAP – cost effective method of optimizing the driving system and estimating static pile capacity – using CAPWAP, hammer blows can be analyzed to estimate skin friction, end bearing, dynamic damping factors, and soil stiffness
  13. 13. Pile DrivingPile Load Test (static)• many tests have been used over the years to evaluate or confirm axial and lateral capacities• Quick pile load tests (QPLT) are most common• QPLT consists of constructing a reaction frame around the test pile• the frame is anchored to reaction piles• pile is incrementally loaded with an hydraulic jack
  14. 14. Pile Driving
  15. 15. Pile DrivingPile Load Test (static)• the test load is measured by a load cell• deformation is measured with dial gauges, wire- mirror-scale, and surveying instruments• apply load in 10 to 15% increments, maintaining a 2½ minute interval• check deformation readings immediately before and after applying load
  16. 16. Pile DrivingPile Load Test (static)• incrementally increase load until reaching 200% of the design load or until continuos jacking is required to maintain the test load• remove the load in 4 equal decrements• plot the load-settlement data using the Davisson method• the point where the load-settlement curve crosses the failure criterion is the failure load (Q f)
  17. 17. Pile DrivingOther Factors• soil setup or “freeze” - common in clays• relaxation - much less common, found in some silts or fine sand• restrike pile to verify strength gain or loss• 120 bpf is practical, safe, upper limit driving blow count• 200 to 240 bpf is practical refusal
  18. 18. Pile DrivingInspection• position, plumb, or batter• check cushion; change as necessary• record blow counts• verify correct operation of hammer• check splices• check piles for damage• check for heave
  19. 19. Pile DrivingDriving Records• prepare a sketch of foundation to identify piles and order of installation• Drive records include: – pile ID and order of installation – ground elevation – cut-off elevation – tip elevation – final length – blows per foot (final foot recorded in bpi) – driving duration – location of splices
  20. 20. FoundationsRetaining Walls• gravity or cantilever• components – stem wall – horizontal base includes: toe, heel, & key – weep holes for drainage
  21. 21. FoundationsTemporary Support Structures and• sheeting w/wales and tie-backs• soldier beams (piles) w/lagging• pipe sleeves• tremie concrete
  22. 22. FoundationsUnderpinning• remedial or precautionary• remedial adds foundation capacity to inadequately supported structures• precautionary - higher loads or changes in ground conditions
  23. 23. FoundationsUnderpinning• Temporary supports – shores – needle beams – grillage• Pit underpinning - used for installing or extending foundation walls or footings• Pile underpinning & various other methods

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