Special Design and
Construction Considerations
2009 PDCA Professor Pile Institute
Patrick Hannigan
GRL Engineers, Inc.
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
590
560
530
500
470
430
14” CEP
TIME EFFECTS ON PILE CAPACITY
Time dependent changes in pile capacity
occur with time.
Soil Setup
Relaxation
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.
1000 days
100 days
10 days
capacity
1 day
Soil Setup
Restrike testing generally performed
1 to 10 days after installation
log time
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.
TABLE 9-20 SOIL SETUP FACTORS
(after Rausche et al., 1996)
Predominant Soil
Type Along Pile
Shaft
Range in
Soil Set-up
Factor
Recommended
Soil Set-up
Factors*
Number of Sites
and (Percentage
of Data Base)
Clay
1.2 - 5.5
2.0
7 (15%)
Silt - Clay
1.0 - 2.0
1.0
10 (22%)
Silt
1.5 - 5.0
1.5
2 (4%)
Sand - Clay
1.0 - 6.0
1.5
13 (28%)
Sand - Silt
1.2 - 2.0
1.2
8 (18%)
Fine Sand
1.2 - 2.0
1.2
2 (4%)
Sand
0.8 - 2.0
1.0
3 (7%)
Sand - Gravel
1.2 - 2.0
1.0
1 (2%)
* - Confirmation with Local Experience Recommended
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.
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.
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
PILE
DRIVEABILITY
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.
Soil Profile
Illustrating
Driveability
Considerations
Estimated Tip EL 14” Pipe
Estimated Tip EL 12” H-pile
FACTORS AFFECTING
PILE DRIVEABILITY
• Driving system characteristics
• Pile material strength
• Pile impedance, EA/C
• Dynamic soil response
Primary factor
controlling driveability
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.
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.
Soil Profile – 12.75 In CEP
3 ft
Silty Clay
 = 127 lbs / ft3
46 ft
qu = 5.5 ksf
Dense, Silty F-M Sand
20 ft
 = 120 lbs / ft3
 = 35˚
Student Exercise #2 Revisited
Static analysis indicates a 12.75 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 _______
210 kips can be
used.
Pick Pile Section – (Appendix C2-4)
Given: 12.75 in O.D. closed-end pipe pile
Select: wall thickness – try 0.109 in wall (lowest cost)
ASTM A-252 Grade 3 steel – FY = 45 ksi
28 day concrete strength
– f’c = 5 ksi
Check Allowable Design Load (10-5)
Design Load = 0.25 (FY)(steel area) + 0.40(f’c)(concrete area)
= 0.25(45 ksi)(4.33 in2) + 0.40(5 ksi)(123.0 in2)
= 48.7 kips + 246.0 kips
= 294 kips
Yes
Is this section suitable for an 420 kip ultimate pile capacity? ____
Check Pile Driveability
Driveability Requirements:
Driving resistance between ____
30 and ____
120 blows/ft
(see pg 11-15)
40.5 ksi
Driving stress limit of 0.9(FY) = _____
(see pg 10-5)
Check Pile Driveability
Determine Hammer Size:
Rated energy for 420 kip ultimate capacity ____
38 ft-kips
(see pg 21-36)
Delmag D-16-32 (ID #5)
Select trial hammer __________________________
(see Appendix D-1)
Perform Wave Equation Analysis
GRLWEAP
Driveability
Results
For D-16-32
Piles Subject to Scour
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
Pile Design Recommendations in
Soils Subject to Scour
1. Reevaluate foundation design relative to
pile length, number, size and type
2. Design piles for additional lateral restraint
and column action due to increase in
unsupported length
3. Local scour holes may overlap, in which
case scour depth is indeterminate and
may be deeper.
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.
Densification Effects on Pile Capacity
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.
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.
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 – www.piledrivers.org
Charleston SC Project
• 220 piles monitored
• Hydraulic hammer (30 ft-kip)
• HP 12 x53 H-piles
• No significant movement (> 1 mm)
recorded by crack monitoring devices
• Predrill 12” diameter hole to 40 ft.
• No damage to masonry facade
• 2 failed vibration criteria
1
2
4
6
8
10
20
40
60
100
80
3
USBM (1985)
Hajduk et al. (2004) - New
Hajduk et al. (2004) - Older/Historic
HP 12x53 Piles
12in OD CEP Piles
60
40
1
20
124
123
10
8
6
4
0.1
2
1
2
4
6
8
10
20
Vibration Frequency (Hz)
40
60
80
100
Peak Particle Velocity (mm/sec)
Peak Particle Velocity (in/sec)
2
Any Questions