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Multiple Impact Surface Waves (MISW) or Multichannel Analysis of Surface Waves (MASW)
Nils Rydén, Lund University, Sweden
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Outline
• Background NDT of pavements
• Wave propagation in slabs (plates) and pavement structures
• Test procedures and equipment
• Example one layer
• Example multiple layers
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Background• Dynamic E-modulus and thickness of pavement layers
are the most important parameters against plastic deformations and fatigue cracks
Conventional quality control based on core samples
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Pavement materials
Base VS=200-500 m/s
Subgrade VS=80-250 m/s
Dynamic small strain modulus E=2ρVS
2(1+ν)
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Modulus – Unbound materials
Ekdahl modell SwePave
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2 extra geophones
Combined approach
Modulus – Unbound materials
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Asphalt (viscoelastic)
Vs=1000-2300 m/s
Materials
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Data acquisition using only one source and one receiver
Asphalt or concrete layer
Base layer
Subgrade
Resulting multichannel record
Transformation to frequency phase velocity domain
Multichannel Analysis of Surface Waves (MASW)
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Background• Dynamic E-modulus and thickness of pavement layers
are the most important parameters against plastic deformations and fatigue cracks
Conventional quality control based on core samples
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Pavement materials
Base VS=200-500 m/s
Subgrade VS=80-250 m/s
Dynamic small strain modulus E=2ρVS
2(1+ν)
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Modulus – Unbound materials
Ekdahl modell SwePave
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2 extra geophones
Combined approach
Modulus – Unbound materials
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Asphalt (viscoelastic)
Vs=1000-2300 m/s
Materials
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Typical data Frequency phase velocity domain
Wave propagation in pavements
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Lamb waves in a free plate
Anti-symmetric [A]
Symmetric [S]
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Lamb wave dispersion curves
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Lamb waves – excitability and sensitivity
Lowest frequency S1 (Impact Echo resonant frequency): most sensitive to h and VP (or ν)
Low frequency S0 (direct P-wave): most sensitive to VP (or ν)
High frequency A0 and S0 (Rayleigh wave): most sensitive to VS
Low frequency A0: intermediate sensitivity to VS and h
Impact Echo frequency(Gibson and Popovics 2005)
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Dispersionskurva
Wave propagation in pavements
3-layer pavement structure
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Nils Ryden, LTH
Wave propagation in pavementsTheoretical resolution with very long offset
range
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f=1000 Hz
f=1500 Hz
Analyzed region
Analyzed region
Frequency domain adaptive geometry
The complete geometry and mesh is optimized for each frequency
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FE model frequency domainExample layer model
Frequency response solution at 50-12000 HzHarmonic source
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Wave propagation in pavements
Data acquisition in the field
Data acquisition using only one source and one receiver
Asphalt or concrete layer Base layer
Subgrade
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Conventional field testing is slow
Accelerometer
Hammer with trigger
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Source and receiver coupling
Steel plate Steel spike Plastic plate
Sticky grease Quick cement
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Approximate evaluation of top layerUnknown system
??
?
Known plate
Vsi, hi, ρi, νi Calculation
Matching
Measurement
S0
A0
Lamb wave dispersion
curves
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Proposed analysis scheme
Lowest frequency S1 (Impact Echo resonant frequency): most sensitive to h and VP (or ν)
Low frequency S0 (direct P-wave): most sensitive to VP (or ν)
High frequency A0 and S0 (Rayleigh wave): most sensitive to VS
Low frequency A0: intermediate sensitivity to VS and h
Use all three modes in the analysis for
increased accuracy!
Use all three modes in the analysis for
increased accuracy!
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Example – Thick concrete wall
Thickness ?
Stiffness ?
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Example – Thick concrete wall
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Example – Asphalt pavement
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Example – Asphalt pavement
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ATREL blind test University of Illinois
0.0 m 1.0 m
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3232
2. Vr
1. Vp
3. Thickness
Automatic processing and analysis based on Lamb wave dispersion curves
Automatic Lamb Wave Analysis
THICKNESS (mm)
LOCATION ACTUAL PREDICTED ERROR (mm) ERROR(%)
1 256 252 -4 1.6%
2 263 244 -19 7.2%
3 246 242 -4 1.6%
4 261 237 -24 9.2%
5 337 309 -28 8.3%
6 281 254 -27 9.6%
7 239 223 -16 6.7%
8 179 179 0 0.0%
9 302 296 -6 2.0%
* Calculated Poisson's Ratio. Using Vr and tp
Results from ATREL blind test shows that the automatic MASW/Lamb Wave analysis consistently underestimates thickness with 2-10 % for all concrete slabs.
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Example quality control stabilised soil
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MethodologyNils Ryden, LTH
FEM design gives the required stiffness and strength of the stabilised soil
Lab tests give the required water cement ratio and the relation between strength and wave propagation speed
Seismic field test for quality control of obtained stiffness and strength
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Laboratory testingFree-free resonant frequency measurements
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Directly on site:
Vp=1698 m/s
Vs=1040 m/s
Thickness=0.25 m
fu=1.13 MPa
Example quality control stabilized soil
Maturity index = 72
(from in ground temperature sensor)
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Evaluation of multiple layersUnknown system
??
?
Known system
Vsi, hi, ρi, νi
Vsi, hi, ρi, νi
Vsi, ρi, νi
Measurement
Calculation
Dispersionskurva
Matching
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Surface wave testingUnknown system
??
?
Known system
Vsi, hi, ρi, νi
Vsi, hi, ρi, νi
Vsi, ρi, νi
Measurement
Calculation
Dispersionskurva
Matching
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0.20 m stabilized subgrade0.20 m stabilized subgrade
~8.00 m clay till~8.00 m clay till
0.30 m base0.30 m base0.13 m asphalt (80+50 mm)0.13 m asphalt (80+50 mm)
Evaluation of multiple layers
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~8.00 m clay till~8.00 m clay till
Unstabilized subgrade
VP=550 m/s
VS= 213 m/s
Reference measurements on each
layer
Evaluation of multiple layers
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Measured data on top of all layers
Frequency phase velocity domain
Range used for the inversion of embedded
layers
Evaluation of multiple layers
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Surface wave testingUnknown system
??
?
Known system
Vsi, hi, ρi, νi
Vsi, hi, ρi, νi
Vsi, ρi, νi
Measurement
Calculation
Dispersionskurva
Matching
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Finding the smallest mismatch?
Local minima
Global minimum
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Simulated Annealing Best match
Viscoelastic asphalt VS=b1*f b2
Evaluation of multiple layers
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Measured E-modulus in the laboratory (blue) and in the field (red)
Evaluation of multiple layers
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Field test exampleMeasured response at three different temperatures
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Asphalt viscoelastic properties
)/1(1log )log(
21
*43 rifaae
aaE +++= fAfr T=
Reference “mastercurve” one temperature AT = temperature shift factor
13° C
23° C
6° C13° C
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Asphalt viscoelastic properties
The complex modulus function for each temperature is used as input for the top asphalt layer in the FE model
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Field test exampleMeasured response at three different temperatures
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Field test examplePredicted (FE) response at three different temperatures
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Nils Rydén PEAB/LTH
Oförstörande provning av vägar med seismik ThankThank
you!you!