1. Foundations

2. Foundations Feature common to bridge and building structures
Deep vs. shallow
Safely transfer dead and live loads with acceptable levels of settlement

3. Foundations Shallow 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. Foundations Deep 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. Foundations Piles Types timber piles
precast/prestressed concrete piles
cast-in-place concrete
steel H-piles
steel pipe piles
composite
minipiles or micro piles

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. Foundations Pile Driving Equipment follower mandrel Pile accessories
point attachments
splices
pile to cap connections

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. 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. 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. 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. 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. Pile Driving Pile 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. Pile Driving

15. Pile Driving Pile 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. Pile Driving Pile 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 (Qf)

18. Pile Driving Other 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

19. Pile Driving Inspection 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

20. Pile Driving Driving 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

21. Foundations toe, heel, & key Retaining Walls gravity or cantilever
components
stem wall
horizontal base includes:
toe, heel, & key
weep holes for drainage

22. Foundations Temporary Support Structures and
sheeting w/wales and tie-backs
soldier beams (piles) w/lagging
pipe sleeves
tremie concrete

23. Foundations Underpinning remedial or precautionary
remedial adds foundation capacity to inadequately supported structures
precautionary - higher loads or changes in ground conditions

24. Foundations Underpinning Temporary supports shores needle beams
grillage
Pit underpinning - used for installing or extending foundation walls or footings
Pile underpinning & various other methods