Pile Axial Load Capacity I

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Pile Axial Load Capacity I

• Prof. Jie Han, Ph.D., PE
• The University of Kansas

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Outline of Presentation

• Introduction
• Pile Load Test
• Pile Driving Analysis
• Case Study

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Load Transfer
Pult
Ps
Wf
D
Pt
B
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Load Transfer
Pu
?Pu
D
(6-10)B
?
(2-4)B
B
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Ultimate Load Capacity
Ultimate load capacity
Pt net toe bearing load
qt net toe bearing capacity
fs side friction resistance
At toe bearing contact area
As side surface area
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Ultimate Load Capacity of Pile in Multi-Layers of
Soil
Pult
Layer 1
fs1, As1
Layer 2
fs2, As2
Layer 3
fs3, As3
qt At
B
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Uplift (Tensile) Load Capacity
Pult
Ps
Wf
D
B
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Pile Load Test
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Static Load Test (ASTM D1143)
Hydraulic jack
Beam
Reference beam
Load cell
Dial gauge
Reaction pile
Test pile
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Pile Load Test
Courtesy of Caltran
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Interpretation of Test Results
Applied load, P
Pult
4mmB/120
1
D/(AE)
PD/(AE)
Davissons criterion
Settlement, d
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De Beers Method
Pu
Load, P (log scale)
Displacement, ? (log scale)
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Osterberg-Cell Pile Loading Test
Osterberg cell (jack)
Advantage separate tip resistance from side
resistance
Disadvantage expensive
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O-Cell Pile Loading Test
Reed et al
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O-Cell Pile Loading Test
Reed et al
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O-Cell Pile Loading Test
Reed et al
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O-Cell Pile Loading Test
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O-Cell Pile Loading Test
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Strain Gauge Attached on Rebar
Reed et al
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Pile Driving Analysis
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Pile Driving Analyzer (PDA)
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Strain and Acceleration Measurement
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Installing Gauges
CalTran
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PDA Testing
CalTran
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PDA Readout
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Pile Driving and Wave Propagation Theory
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Pile Driving Formulas
Method
Equation for Pu (kips)
FS
Gates
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Pacific coast Uniform Building Code
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,
,
Cp 0.25 for steel piles or 0.10 for other piles
Initially assume Cp2 0 and compute Pu reduce
Pu by 25, compute Cp2, then recompute Pu
Compute a new Cp2, compute Pu until Pu used Pu
computed
inches
3-6
Danish
,
Engineering News Record
Drop Hammers
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Other Hammers
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Aarea of pile cross section (ft2), Ehhammer
efficiency Eppile modulus of elasticity
(ksf) Ermanufacturers hammer-energy rating (or
wrh) (kips-ft) hheight of hammer fall
(ft) Lpile length (inches) Saverage
penetration in inches/blow for last 5 to 10 blows
for drop Hammers and 10 to 20 blows for other
hammers Wrweight of striking parts of ram
(kips) Wpweight of pile including pile cap,
driving shoe, capblock and anvil for
double-acting Steam hammers (kips)
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Case Study
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Vertical Expansion of Building
Additional
Existing
Micropiles
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Plan View of Instrumentation Setup
0.6
MP3
MP4
0.4
0.2
0.4
1.5
Micropiles
0.4
Earth pressure cells
0.2
Extensometer
MP2
MP1
0.2
0.6
0.25
1.5
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Cross-Section of Instrumentation Setup
Load plate
0.15
0.55
0.05
0.1
Sand cushion
2.6
8.0
2.6
Extensometer
2.6
Strain gauge
0.1
MP2 or MP4 for tension test
MP1 or MP3 for compression test
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Load Capacity Tests of Micropiles
Loading Type
Testing Method
Pile No.
MP1
Compression
Slow loading
MP2
Tension
Quick loading
Compression
Quick loading
MP3
MP4
Tension
Quick loading
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Plate Load Test on Natural Soil
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Back-Calculated Undrained Strength
Ultimate bearing capacity determined from
the plate loading test
qult 172 kPa
Back-calculated undrained strength
cu qult/5.14 33.5 kPa
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Micropile Load Tests
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Stress-Strain Relations of Micropiles
Average stress on pile section
Average stress on concrete
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Stress-Strain Relations of Micropiles
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Stress-Strain Relations of Concrete
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Axial force in Pile
Axial force in the pile can be calculated by
Pz Ep Ap ?
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Axial Force Distributions
MP1
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Axial Force Distributions
MP4