1. Special Design and Construction Considerations
2009 PDCA Professor Pile Institute
Patrick Hannigan
GRL Engineers, Inc.

2. SPECIAL DESIGN CONSIDERATIONS
Time effects on pile capacity.
Pile driveability
Scour
Densification effects on pile capacity
Additional design and construction topics in FHWA Pile Manual Chapters 9.9 and 9.10

3. 590
560
530
500
14” CEP
470
430

4. TIME EFFECTS ON PILE CAPACITY
Time dependent changes in pile capacity occur with time.
Soil Setup
Relaxation

5. SOIL SETUP
Soil setup is a time dependent increase in the static pile capacity.
Large excess positive pore pressures are often generated during pile driving.
Soil setup frequently occurs for piles driven in saturated clays as well as loose to medium dense silts and fine sands as the excess pore pressures dissipate.
The magnitude of soil setup depends on soil characteristics as well as the pile material and type.

6. Economically desirable Technically desirable
Soil Setup
1 day
10 days
100 days
1000 days
Semilog-linear process
When to test?
capacity
Economically desirable
Technically desirable
Restrike testing generally performed
1 to 10 days after installation
log time

7. SOIL SETUP FACTOR
The soil setup factor is defined as failure load determined from a static load test divided by the ultimate capacity at the end of driving.

8. TABLE 9-20 SOIL SETUP FACTORS (after Rausche et al., 1996)
Predominant Soil Type Along Pile Shaft
Range in
Soil Set-up
Factor
Recommended
Factors*
Number of Sites
and (Percentage
of Data Base)
Clay
2.0
7 (15%)
Silt - Clay
1.0
10 (22%)
Silt
1.5
2 (4%)
Sand - Clay
13 (28%)
Sand - Silt
1.2
8 (18%)
Fine Sand
Sand
3 (7%)
Sand - Gravel
1 (2%)
* - Confirmation with Local Experience Recommended

9. RELAXATION
Relaxation is a time dependent decrease in the static pile capacity.
During pile driving, dense soils may dilate thereby generating negative pore pressures and temporarily higher soil resistance.
Relaxation has been observed for piles driven in dense, saturated non-cohesive silts, fine sands, and some shales.

10. RELAXATION FACTOR
The relaxation factor is defined as failure load determined from a static load test divided by the ultimate capacity at the end of driving.
Relaxation factors of 0.5 to 0.9 have been reported in case histories of piles in shales.
Relaxation factors of 0.5 and 0.8 have been observed in dense sands and extremely dense silts, respectively.

11. TIME EFFECTS ON PILE DRIVEABILITY AND CAPACITY
Time dependent soil strength changes that affect the soil resistance at the time of driving should be considered during the design stage.
Remolded shear strength in clays
Estimate of pore pressures during driving
Soil setup / relaxation factors

12. PILE DRIVEABILITY

13. PILE DRIVEABILITY
Pile driveability refers to the ability of a pile to be driven to the desired depth and / or capacity at a reasonable driving resistance without exceeding the material driving stress limits.

14. Soil Profile Illustrating Driveability Considerations
Estimated Tip EL 14” Pipe
Estimated Tip EL 12” H-pile

15. FACTORS AFFECTING PILE DRIVEABILITY
Driving system characteristics
Pile material strength
Pile impedance, EA/C
Dynamic soil response
Primary factor controlling driveability

16. PILE DRIVEABILITY
Pile driveability should be checked during the design stage for all driven piles.
Pile driveability is particularly critical for closed end pipe piles.

17. PILE DRIVEABILITY EVALUATION DURING DESIGN STAGE
1. Wave Equation Analysis
Computer analysis that does not require a pile to be driven.
2. Dynamic Testing and Analysis
Requires a pile to be driven and dynamically tested.
3. Static Load Tests
Requires a pile to be driven and statically load tested.

18. Soil Profile – 12.75 In CEP 3 ft Silty Clay = 127 lbs / ft3
qu = 5.5 ksf
Dense, Silty F-M Sand
= 120 lbs / ft3
 = 35˚
3 ft

19. Student Exercise #2 Revisited
Static analysis indicates a in O.D. closed-end pipe pile driven to 63 ft below grade can develop an ultimate capacity of 420 kips. A static load test will be used for construction control. No special design conditions exist (scour, downdrag, etc.). Therefore, a maximum axial design load of _______ kips can be used.
210

20. Pick Pile Section – (Appendix C2-4)
Given: in O.D. closed-end pipe pile
Select: wall thickness – try in wall (lowest cost)
ASTM A-252 Grade 3 steel – FY = 45 ksi
28 day concrete strength – f’c = 5 ksi

21. Check Allowable Design Load (10-5)
Design Load = 0.25 (FY)(steel area) (f’c)(concrete area)
= 0.25(45 ksi)(4.33 in2) (5 ksi)(123.0 in2)
= 48.7 kips kips
= 294 kips
Is this section suitable for an 420 kip ultimate pile capacity? ____
Yes

22. Check Pile Driveability
Driveability Requirements:
Driving resistance between ____ and ____ blows/ft
(see pg 11-15)
Driving stress limit of 0.9(FY) = _____ ksi
(see pg 10-5) 30
120
40.5

23. Check Pile Driveability
Determine Hammer Size:
Rated energy for 420 kip ultimate capacity ____ ft-kips
(see pg 21-36)
Select trial hammer __________________________
(see Appendix D-1)
Perform Wave Equation Analysis 38
Delmag D (ID #5)

24. GRLWEAP
Driveability
Results
For D-16-32

25. Piles Subject to Scour

26. Piles Subject to Scour Types of Scour Aggradation / Degradation Scour
- Long-term stream bed elevation changes
Local Scour
- Removal of material from immediate vicinity of foundation
Contraction and General Scour
- Erosion across all or most of channel width

27. Pile Design Recommendations in Soils Subject to Scour
Reevaluate foundation design relative to pile length, number, size and type
Design piles for additional lateral restraint and column action due to increase in unsupported length
Local scour holes may overlap, in which case scour depth is indeterminate and may be deeper.

28. Pile Design Recommendations in Soils Subject to Scour
4. Perform design assuming all material above scour line has been removed.
5. Place top of footing or cap below long-term scour depth to minimize flood flow obstruction.
6. Piles supporting stub abutments in embankments should be driven below the thalweg elevation.

29. Densification Effects on Pile Capacity

30. Densification Effects on Pile Capacity
Densification can result in the pile capacity as well as the pile penetration resistance to driving being significantly greater than that calculated for a single pile.
Added confinement from cofferdams or the sequence of pile installation can further aggravate a densification problem.

31. Densification Effects on Pile Capacity
Potential densification effects should be considered in the design stage. Studies indicate an increase in soil friction angle of up to 4˚ would not be uncommon for piles in loose to medium dense sands.
A lesser increase in friction angle would be expected in dense sands or cohesionless soils with a significant fine content.

32. Pile Driving Induced Vibrations
Vibrations from pile driving sometimes perceived as a problem.
Vibrations can cause damage.
Vibrations can cause soil densification and settlement.
Pile driving vibrations often a perceived problem than an actual problem and can often be controlled by construction procedures
PDCA database –

33. Charleston SC Project 220 piles monitored 2 failed vibration criteria
No significant movement (> 1 mm) recorded by crack monitoring devices
No damage to masonry facade
Hydraulic hammer (30 ft-kip)
HP 12 x53 H-piles
Predrill 12” diameter hole to 40 ft.

34. Any Questions