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![4/30/2015
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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
13
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!
14
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
SPT 15
ASTM D4633 – earlier versionsASTM D4633 – earlier versions](https://image.slidesharecdn.com/3-150530040525-lva1-app6892/85/3-6-spt-energy-calibration-gray-5-320.jpg)
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- 2. 4/30/2015 2 SPT Introduction SPT equipmenthas 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% 4 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 5 • N-value for Soil strength, E, G, … Liquefaction potential • Soil Type from sample Grain size Why SPT? SPT 6
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- 4. 4/30/2015 4 Standardization of SPTN-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) SPT 10 Normalized N-Value: N60 N60 = Nm EMX Wh (60%) Nm, measured N-value EMX, measured transferred energy SPT 11 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 2 Measure vi with HPA vi = √(2 g h) (8.96 ft/s or 2.73 m/s) SPT 12 WP mR hWR vi
- 5. 4/30/2015 5 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 13 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! 14 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 SPT 15 ASTM D4633 – earlier versionsASTM D4633 – earlier versions
- 6. 4/30/2015 6 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 17 SPT Instrumentation Instrumented section with calibration tag 18
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- 9. 4/30/2015 9 SPT Example: Spooling Winchon AW RodExample: Spooling Winch on AW Rod EMX = .135 k-ft η = 39% 25 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% 26 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 SPT 27
- 10. 4/30/2015 10 58 SPTHammers 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 29 Note Scatter! Florida DOT SPT Energy Study SPT 30
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