Special Design and Special Design and Construction Construction

ConsiderationsConsiderations

2009 PDCA Professor Pile 2009 PDCA Professor Pile InstituteInstitute

Patrick Hannigan

GRL Engineers, Inc.

• Time effects on pile capacity. Time effects on pile capacity.

• Pile driveabilityPile driveability

• ScourScour

• Densification effects on pile capacityDensification effects on pile capacity

• AAdditional design and construction topics in FHWA Pile Manual Chapters 9.9 and 9.10

SPECIAL DESIGN SPECIAL DESIGN CONSIDERATIONSCONSIDERATIONS

590

560

530

500

470

430

14” CEP

TIME EFFECTS ON PILE TIME EFFECTS ON PILE CAPACITYCAPACITY

Time dependent changes in pile capacity occur with time.

Soil SetupSoil Setup RelaxationRelaxation

Soil setupSoil setup is a time dependent increaseincrease 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 clayssaturated clays as well as loose to medium loose to medium dense silts and fine sandsdense 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.

SOIL SETUPSOIL SETUP

1 d

ay1

day

10 d

ays

10 d

ays

100

day

s10

0 d

ays

1000

day

s10

00 d

ays

log timelog time

cap

acit

yca

pac

ity

Technically desirable

Technically desirableEconomically desirable

Economically desirable

Restrike testing generally performedRestrike testing generally performed

1 to 10 days after installation1 to 10 days after installation

Soil SetupSoil Setup Soil SetupSoil Setup

When to test?

When to test?

Semilog-linear process

Semilog-linear process

SOIL SETUP FACTORSOIL 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 inSoil Set-up

Factor

RecommendedSoil Set-up

Factors*

Number of Sitesand (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

RelaxationRelaxation is a time dependent decreasedecrease 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, dense, saturated non-cohesive silts, fine sands,

and some shalesand some shales.

RELAXATIONRELAXATION

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.

RELAXATION FACTORRELAXATION FACTOR

TIME EFFECTS ON PILE TIME EFFECTS ON PILE DRIVEABILITY AND CAPACITYDRIVEABILITY 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 claysRemolded shear strength in clays

• Estimate of pore pressures during drivingEstimate of pore pressures during driving

• Soil setup / relaxation factorsSoil setup / relaxation factors

PILE PILE DRIVEABILITYDRIVEABILITY

PILE DRIVEABILITYPILE 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 Soil Profile Illustrating Illustrating Driveability Driveability

ConsiderationConsiderationss

Estimated Tip EL 14” Pipe

Estimated Tip EL 12” H-pile

FACTORS AFFECTING FACTORS AFFECTING PILE DRIVEABILITYPILE DRIVEABILITY

• Driving system characteristicsDriving system characteristics

• Pile material strengthPile material strength

• Pile impedance, EA/CPile impedance, EA/C

• Dynamic soil responseDynamic soil response

Primary factor controlling driveability

PILE DRIVEABILITYPILE DRIVEABILITY

Pile driveability should be checked during the

design stagedesign stage for all driven piles.

Pile driveability is particularly critical for closed end

pipe piles.

PILE DRIVEABILITY PILE DRIVEABILITY EVALUATION DURING DESIGN EVALUATION DURING DESIGN

STAGESTAGE1. Wave Equation Analysis1. Wave Equation Analysis

Computer analysis that does not require a pile to be driven.

2. Dynamic Testing and Analysis2. Dynamic Testing and Analysis

Requires a pile to be driven and dynamically tested.

3. Static Load Tests3. Static Load Tests

Requires a pile to be driven and statically load tested.

46 ft

20 ft

Silty Clay

= 127 lbs / ft3

qu = 5.5 ksf

Dense, Silty F-M Sand

= 120 lbs / ft3

= 35˚

3 ft

Soil Profile – 12.75 In Soil Profile – 12.75 In CEPCEP

Student Exercise #2 RevisitedStudent 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 _______ kips can be used.

210210

Pick Pile Section – (Appendix C2-Pick Pile Section – (Appendix C2-4)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 Check Allowable Design Load (10-5)(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

Is this section suitable for an 420 kip ultimate pile capacity? ____YesYes

Check Pile DriveabilityCheck 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)

1201203030

40.540.5

Check Pile DriveabilityCheck 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

3838

Delmag D-16-32 (ID #5)Delmag D-16-32 (ID #5)

GRLWEAPGRLWEAP

DriveabilityDriveability

ResultsResults

For D-16-32For D-16-32

Piles Subject to ScourPiles Subject to Scour

Piles Subject to ScourPiles Subject to Scour

Aggradation / Degradation Scour

Types of ScourTypes of Scour

Local Scour

Contraction and General Scour

- Long-term stream bed elevation changes

- Removal of material from immediate vicinity of foundation

- Erosion across all or most of channel width

Pile Design Pile Design Recommendations in Soils Recommendations in Soils

Subject to ScourSubject to Scour1.1. Reevaluate foundation design relative to Reevaluate foundation design relative to

pile length, number, size and typepile length, number, size and type

2.2. Design piles for additional lateral restraint Design piles for additional lateral restraint and column action due to increase in and column action due to increase in unsupported lengthunsupported length

3.3. Local scour holes may overlap, in which Local scour holes may overlap, in which case scour depth is indeterminate and case scour depth is indeterminate and may be deeper. may be deeper.

Pile Design Pile Design Recommendations in Soils Recommendations in Soils

Subject to ScourSubject to Scour4. Perform design assuming all material above 4. Perform design assuming all material above scour line has been removed.scour line has been removed.

5. Place top of footing or cap below long-term 5. Place top of footing or cap below long-term scour depth to minimize flood flow scour depth to minimize flood flow obstruction.obstruction.

6. Piles supporting stub abutments in 6. Piles supporting stub abutments in embankments should be driven below the embankments should be driven below the thalweg elevation. thalweg elevation.

Densification Effects on Pile Densification Effects on Pile CapacityCapacity

Densification Effects on Densification Effects on Pile CapacityPile Capacity

Densification can result in the pile capacity as Densification can result in the pile capacity as

well as the pile penetration resistance to well as the pile penetration resistance to

driving being significantly greater than that driving being significantly greater than that

calculated for a single pile.calculated for a single pile.

Added confinement from cofferdams or the Added confinement from cofferdams or the

sequence of pile installation can further sequence of pile installation can further

aggravate a densification problem.aggravate a densification problem.

Densification Densification Effects on Pile Effects on Pile

CapacityCapacityPotential densification effects should be Potential densification effects should be

considered in the design stage. Studies considered in the design stage. Studies

indicate an increase in soil friction angle of up indicate an increase in soil friction angle of up

to 4to 4˚ would not be uncommon for piles in loose ˚ would not be uncommon for piles in loose

to medium dense sands. to medium dense sands.

A lesser increase in friction angle would be A lesser increase in friction angle would be

expected in dense sands or cohesionless soils expected in dense sands or cohesionless soils

with a significant fine content.with a significant fine content.

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

Pile Driving Induced Pile Driving Induced VibrationsVibrations

• 220 piles monitored

• 2 failed vibration criteria

• No significant movement (> 1 mm) recorded by crack monitoring devices

• No damage to masonry facade

1 10 1002 4 6 8 20 40 60 80

Vibration Frequency (Hz)

0.1

1

2

3

Pea

k P

arti

cle

Vel

oci

ty (

in/s

ec)

1 10 1002 4 6 8 20 40 60 80

1 0

2 0

4 0

6 0

8

6

4

2

Peak P

article Velo

city (mm

/sec)

U SBM (1985)

H ajduk et a l. (2004) - N ew

H ajduk et a l. (2004) - O lder/H istoric

H P 12x53 P iles

12 in O D C EP P iles

123

124

Charleston SC ProjectCharleston SC Project• Hydraulic hammer (30 ft-kip)

• HP 12 x53 H-piles

• Predrill 12” diameter hole to 40 ft.

Any QuestionsAny Questions