Lesson 09-Chapter 9 Deep Foundations - Part 1B (Piles)
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Transcript of Lesson 09-Chapter 9 Deep Foundations - Part 1B (Piles)
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NordlundNordlundMethod ProcedureMethod Procedure
STEP 10 Compute the ultimate capacity, Qu.
Qu = Rs + Rt
STEP 11 Compute the allowable geotechnical pile load, Qa.
SafetyofFactorQ=Q ua
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Example 9Example 9--22
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Tomlinson orTomlinson or--MethodMethod
Unit Shaft Resistance, fs
:
fs = ca = cu
Where:
ca = adhesion (Figure 9-14)
= empirical adhesion factor (Figure 9-15)
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Tomlinson orTomlinson or
--MethodMethod
Shaft Resistance, Rs:
Rs = fs As
Where:As = pile surface area in layer
(pile perimeter x length)
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Concrete, Timber, Corrugated Steel Piles
Smooth Steel Pilesb = Pile Diameter
D = distance from ground surface to bottom ofclay layer or pile toe, whichever is less
Tomlinson orTomlinson or--Method (US)Method (US)
Figure 9-14
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Tomlinson orTomlinson or--MethodMethod
Sand or
Sandy Gravels
Stiff ClayDb
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Tomlinson orTomlinson or--Method (US)Method (US)
b = Pile Diameter
D = distance into stiff clay layer
Figure 9-15a
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Tomlinson orTomlinson or--MethodMethod
Db
Soft Clay
Stiff Clay
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Tomlinson orTomlinson or--Method (US)Method (US)
b = Pile DiameterD = distance into stiff clay layer
Figure 9-15b
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Tomlinson orTomlinson or--MethodMethod
D
b
Stiff Clay
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Tomlinson orTomlinson or--Method (US)Method (US)
b = Pile DiameterD = distance into clay layer
Figure 9-15c
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HIGHLY OVERCONSOLIDATED CLAYSHIGHLY OVERCONSOLIDATED CLAYS
For 1.0, = 0.5 -0.5
For > 1.0, = 0.5 -0.25
In highly overconsolidated clays, the undrained shear strength
may exceed the upper limits of Figures 9-14 and 9-15.
In these cases, the adhesion factor should be calculated
according to API procedures based on the ratio of the
undrained shear strength of the soil, cu, divided by the
effective overburden pressure, po. The ratio of cu / po is .
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Tomlinson orTomlinson or--MethodMethod
Unit Toe Resistance, qt:
qt = cu Nc
Where:
cu = undrained shear strength of the soil at pile toe
Nc = dimensionless bearing capacity factor
(9 for deep foundations)
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Tomlinson orTomlinson or--MethodMethod
Toe Resistance, Rt:
Rt = qt At
The toe resistance in cohesive soils is sometimes ignoredsince the movement required to mobilize the toe resistance
is several times greater than the movement required to
mobilize the shaft resistance.
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Qu = RS + RT
Qa = QU / FS
and
Tomlinson orTomlinson or--MethodMethod
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Example 9Example 9--33
Whi h il h th hi h t tWhich pile has the highest toe
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Which pile has the highest toeWhich pile has the highest toeresistance ?resistance ?
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Plugging of Open Pile SectionsPlugging of Open Pile Sections
(a) Open Toe Condition
b
qt
qt
fso fsi
(b) Plugged Toe Condition
qt
D
fso
(a) Open Toe Condition
b
qt
qt
fso fsi
(b) Plugged Toe Condition
qt
D
fso
Figure 9-18
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Plugging of HPlugging of H--Pile SectionsPile Sections
Figure 9-19
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The DRIVEN Computer ProgramThe DRIVEN Computer Program
ggDeveloped by FHWA in 1998Developed by FHWA in 1998
ggUse for calculation of static pileUse for calculation of static pilecapacitycapacity
ggDemonstration of the DRIVEN computerDemonstration of the DRIVEN computer
programprogram
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Piles Driven to RockPiles Driven to Rock
The capacity of piles driven to rock should be based on driving
observations, local experience, and load test results.
RQD values from NX size rock cores can provide a qualitative
assessment of rock mass quality.
RQDRQD Rock Mass QualityRock Mass Quality
9090
100100
ExcellentExcellent
7575 9090 GoodGood
5050 7575 FairFair
2525 5050 PoorPoor00--2525 Very PoorVery Poor
What is RQD? See Chapter 3
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Piles Driven to RockPiles Driven to Rock
Except for piles driven to soft rock, the structural capacity of
the pile will be lower than the geotechnical capacity of the rock
to support a toe bearing pile. (Fair to excellent quality rock).
The structural capacity of the pile then governs the pile
capacity.