Coefficient of Thermal Expansion and their Importance.pptx
Standard Penetration Testing Energy Measurements
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SPT
SPT Energy Measurements
... or how to calibrate
SPT equipment to
obtain normalized
SPT N-values
1
SPT
SPT Energy Measurements
Outline
Introduction
Instrumentation
Processing Equipment
Examples
Summary
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SPT
Introduction
• 1902 Charles Gow of Gow Construction (Boston) used 1 inch dia. drive
samplers driven by 110-lb hammer
• mid 1920’s split spoon sampler introduced by Sprague & Henwood of
Scranton PA (2.0 to 3.5 inch diameters)
• 1927 Gow used 2 inch split spoon sampler, recording blows to drive 12
inches for 140 lb hammer and 30 inch drop
• 1947 Terzaghi christened the Raymond Sampler as the “Standard
Penetration Test” at 7th Conf. on Soil Mechanics and Foundation Eng.
• 1948 Terzaghi and Peck publish first SPT correlations
• 1958 ASTM adopted ASTM D1586
Ref: “Subsurface Exploration Using the Standard Penetration Test and the Cone Penetration
Test” by David Rogers; Environmental & Engineering Geoscience, Vol XII No.2, May 2006.
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SPT
Introduction
SPT equipment has standard ram weight and
drop height and, therefore, supposedly the same
rated energy:
ER = Wh
With W = 140 lbs and h = 2.5 ft we get ER-SPT = 350
ft-lbs
We can measure EMX, the energy transferred to
the drive rod
EMX values range from 30 to 95%
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SPT
Introduction
Historically and on average, transferred energy,
EMX, has been 60% (typical for safety hammers
with cathead and rope)
In order to maintain context with data bases, N-
values should be adjusted based on measured
transferred energy EMX (see ASTM 4633-05) to
the expected value of 60% of ER-SPT
N60 = N * (EMX / 0.6 ER )
0.6 ER = 210 ft-lbs
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• N-value for
Soil strength, E, G, …
Liquefaction potential
• Soil Type from sample
Grain size
Why SPT?
SPT 6
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Standardization of SPT N-Value
“Non-standard” SPT systems deliver highly variable energy
values to drive rod. Energy transfer affects N - value
Soil strength estimated from N-value based on experience,
i.e. on average N-value
Obtain normalized, N60, value for more reliable static soil
analysis
Also: Liquefaction potential estimated from N60 (ASTM D
6066)
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Normalized N-Value: N60
N60 = Nm
EMX
Wh (60%)
Nm, measured N-value
EMX, measured transferred energy
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What Energy?
Potential, Wrh
Measure weight, Wr (0.140 kips or 0.623 kN)
Estimate stroke, h (2.5 ft or 0.762 m)
Potential Energy, Wrh (0.350 ft-kips or 0.474 kJ)
Kinetic, ½(Wr/g) vi
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Measure vi with HPA
vi = √(2 g h) (8.96 ft/s or 2.73 m/s)
SPT 12
WP
mR
hWR
vi
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SPT
Transferred EnergyTransferred Energy
Energy = Sum of Force times Displacement
ER(t) = ∫ F du; but v = du/dt
EFV(t) = ∫ Fv dt; transferred energy
EMX = max[EFV(t)]
ηT = EMX / ER-SPT ; transfer ratio
Energy = Sum of Force times Displacement
ER(t) = ∫ F du; but v = du/dt
EFV(t) = ∫ Fv dt; transferred energy
EMX = max[EFV(t)]
ηT = EMX / ER-SPT ; transfer ratio
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F,
v
WR
vi
SPT
ASTM D4633 – earlier versionsASTM D4633 – earlier versions
Since
EFV = ∫ F v dt and
F = Z v (in a downward traveling wave)
Z = EA/c ... Pile impedance; E ... Young’s modulus,
A ... Cross sectional area; c ... Stress wave speed
Then
EF2 = Z ∫ F 2 dt (only requires force measurement)
But ONLY if there are no forces due to wave reflections; thus, this method is
inherently incorrect and obsolete!
Since
EFV = ∫ F v dt and
F = Z v (in a downward traveling wave)
Z = EA/c ... Pile impedance; E ... Young’s modulus,
A ... Cross sectional area; c ... Stress wave speed
Then
EF2 = Z ∫ F 2 dt (only requires force measurement)
But ONLY if there are no forces due to wave reflections; thus, this method is
inherently incorrect and obsolete!
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EF2 = 209 N-m
η = 44%
EFV = 0.281 N-m
η = 59%
Safety Hammer, Cathead, PE = 0.475 kN-m
EF2 Short L corrections
EF2corr = EF2(1.17)(1.45)(1/1.36)
= 260 N-m (η = 55% )
1.17 due to energy in rod
above sensors
1.45 due to short rod length
1.36 due to c ratio
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ASTM D4633 – earlier versionsASTM D4633 – earlier versions
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Loose Joint Effects
EMX = .232 k-ft
η = 66%
EF2 = .146 k-ft
Safety Hammer with Cathead on AW rod
SPT 16
Second
loose
joint
(BTA =
30%)
First
loose
joint
SPT
•Choose rod section matching the
rod used during test
•Attach strain gages for 2 full bridge
strain circuits and 2 accelerometers
•Needs PR accelerometers
•Cancel bending effects and
provide backup measurements
•Perform traceable calibration
Measuring F and v
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SPT
Instrumentation
Instrumented
section with
calibration tag
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Calibration of Force Sensors
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Force Measurement
Strain Measurement
SPT
Pile Driving Analyzer® - Model PAK
Processing Equipment
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SPT
Pile Driving Analyzer - Model PAX
Processing Equipment
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SPT
SPT Analyzer
Processing Equipment
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SPT
Pile Driving Analyzer - Model PAX
Processing Equipment
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SPT
SPT hammers are uncushioned which requires special
accelerometers and some higher frequency data
processing.
ASTM 4633 requires digitizing frequency
• ≥ 20,000 sps for analog integration
• ≥ 50,000 sps for digital integration
EC7 requires digitizing frequency
• ≥ 100,000 sps for digital integration
May require special software in PDA or an SPT Analyzer
Processing Equipment
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SPT
Example: Spooling Winch on AW RodExample: Spooling Winch on AW Rod
EMX = .135 k-ft
η = 39%
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SPT
Safety Hammer + Cathead on
AW Rod with Loose Joint
Safety Hammer + Cathead on
AW Rod with Loose Joint
EMX = .232 k-ft
η = .232/.35 = 66%
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Florida DOT SPT Energy Study
“Standard Penetration Test Energy Calibrations”
performed by University of Florida, Gainesville
by Dr. John Davidson,
assisted by John Maultsby and Kimberly Spoor
report issued January 31, 1999
report number WPI 0510859
contract number BB-261
Florida state project 99700-3557-119
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58 SPT Hammers tested with SPT Analyzer
44 Safety Hammers
14 Automatic hammers
13 Different drill rig Acker (1)
Florida DOT SPT Energy Study
SPT 28
SPT
Florida SPT Energy results
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Note
Scatter!
Florida DOT SPT Energy Study
SPT 30
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SPT
Utah State University StudyUtah State University Study
GRL data compiled by Utah State University
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Comparison of Studies
SPT 32
Energy similar with 1.25 to 2.25 rope turns on
cathead
Extra 10% energy loss for 2.75 rope turns; should
be avoided (per ASTM D1586)
Rod type no major effect in energy transfer (AW or
NW)
Conclusions from Florida
DOT SPT Energy Study
SPT 33
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Energy higher for automatic hammers (80%) than for
safety hammers (66%)
Short rods (<40’) have lower energy transfer
SPT energy data is “useful in spotting performance
problems of a system”
Conclusions from Florida
DOT SPT Energy Study
SPT 34
“SPT Analyzer may be useful in assessing sites where
data appear suspect”
“On large or critical projects, energy testing may verify
SPT performance to allow for increased design
confidence and economy”
Conclusions from Florida DOT
SPT Energy Study
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Significance
Assume measured Nm = 20
Automatic Hammer (assume 80% efficient)
N60 = 20 (80/60) = 27
Donut Hammer (assume 35% efficient)
N60 = 20 (35/60) = 12
SPT 36
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SPT
SUMMARY
SPT rigs and rods are not truly standardized and
transferred energy values vary greatly
Energy is important quantity when assessing
strength of soil and/or liquefaction potential from
N-value
Force and velocity measurements can be
evaluated for transferred energy in real time by
PDA or SPT Analyzer according to ASTM 4633-
05
N-value is then corrected as per energy ratio
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SPT
SPT Energy Considerations
Questions?
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• Measure F, v with PDA
• Calculate soil resistance
against sampler or special
toe plate or cone
• Measure Torque
• Measure static uplift
Rausche, et al., 1990. Determination of Pile
Driveability and Capacity from Penetration
Tests, FHWA Research Report
SPT 39
Using PDA on SPT to Predict
Pile Capacity
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• 1996 Research: SPT toe configurations
SPT 40
Using PDA on SPT to Predict
Pile Capacity
Using PDA on SPT to Predict Pile
Capacity
Torque Measurements
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SPT 42
Using PDA on SPT to Predict
Pile Capacity
Static Uplift Measurements
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Pile top F and v
measured and from
GRLWEAP
SPT 43
Using PDA on SPT to Predict
Pile Capacity
Pile top F and v
Measured and from
GRLWEAP
Pile bottom F and v
calculated from
Measurement and
GRLWEAP
SPT 44
Using PDA on SPT to Predict
Pile Capacity
SPT 45
• Integrate v to
bottom
displacement
• Plot Force vs
displacement at
bottom
• Compare with
Uplift test
Using PDA on SPT to Predict
Pile Capacity
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SPT 46
Using PDA on SPT to Predict
Pile Capacity
• Integrate v to
bottom
displacement
• Plot Force vs
displacement at
bottom
• Compare with
Compression
test
SPT 47
Using PDA on SPT to Predict
Pile Capacity
Based on SPT
measurements,
compare
calculated
capacities from:
• Wave equation
• CAPWAP
With static test
Conclusions from additional
SPT measurements
Potential to determine soil properties with a
CAPWAP type analysis
For static design implications
For dynamic driveability predictions
More testing and research are needed!
SPT 48
