Multiple Impact Surface Waves (MISW) or Multichannel Analysis of Surface Waves (MASW)

Nils Rydén, Lund University, Sweden

Outline

• Background NDT of pavements

• Wave propagation in slabs (plates) and pavement structures

• Test procedures and equipment

• Example one layer

• Example multiple layers

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

Pavement materials

Base VS=200-500 m/s

Subgrade VS=80-250 m/s

Dynamic small strain modulus E=2ρVS

2(1+ν)

Modulus – Unbound materials

Ekdahl modell SwePave

2 extra geophones

Combined approach

Modulus – Unbound materials

Asphalt (viscoelastic)

Vs=1000-2300 m/s

Materials

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)

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

Pavement materials

Base VS=200-500 m/s

Subgrade VS=80-250 m/s

Dynamic small strain modulus E=2ρVS

2(1+ν)

Modulus – Unbound materials

Ekdahl modell SwePave

2 extra geophones

Combined approach

Modulus – Unbound materials

Asphalt (viscoelastic)

Vs=1000-2300 m/s

Materials

Typical data Frequency phase velocity domain

Wave propagation in pavements

Lamb waves in a free plate

Anti-symmetric [A]

Symmetric [S]

Lamb wave dispersion curves

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)

Dispersionskurva

Wave propagation in pavements

3-layer pavement structure

Nils Ryden, LTH

Wave propagation in pavementsTheoretical resolution with very long offset

range

f=1000 Hz

f=1500 Hz

Analyzed region

Analyzed region

Frequency domain adaptive geometry

The complete geometry and mesh is optimized for each frequency

FE model frequency domainExample layer model

Frequency response solution at 50-12000 HzHarmonic source

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

Conventional field testing is slow

Accelerometer

Hammer with trigger

Source and receiver coupling

Steel plate Steel spike Plastic plate

Sticky grease Quick cement

Approximate evaluation of top layerUnknown system

??

?

Known plate

Vsi, hi, ρi, νi Calculation

Matching

Measurement

S0

A0

Lamb wave dispersion

curves

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!

Example – Thick concrete wall

Thickness ?

Stiffness ?

Example – Thick concrete wall

Example – Asphalt pavement

Example – Asphalt pavement

ATREL blind test University of Illinois

0.0 m 1.0 m

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.

Example quality control stabilised soil

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

Laboratory testingFree-free resonant frequency measurements

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)

Evaluation of multiple layersUnknown system

??

?

Known system

Vsi, hi, ρi, νi

Vsi, hi, ρi, νi

Vsi, ρi, νi

Measurement

Calculation

Dispersionskurva

Matching

Surface wave testingUnknown system

??

?

Known system

Vsi, hi, ρi, νi

Vsi, hi, ρi, νi

Vsi, ρi, νi

Measurement

Calculation

Dispersionskurva

Matching

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

~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

Measured data on top of all layers

Frequency phase velocity domain

Range used for the inversion of embedded

layers

Evaluation of multiple layers

Surface wave testingUnknown system

??

?

Known system

Vsi, hi, ρi, νi

Vsi, hi, ρi, νi

Vsi, ρi, νi

Measurement

Calculation

Dispersionskurva

Matching

Finding the smallest mismatch?

Local minima

Global minimum

Simulated Annealing Best match

Viscoelastic asphalt VS=b1*f b2

Evaluation of multiple layers

Measured E-modulus in the laboratory (blue) and in the field (red)

Evaluation of multiple layers

Field test exampleMeasured response at three different temperatures

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

Asphalt viscoelastic properties

The complex modulus function for each temperature is used as input for the top asphalt layer in the FE model

Field test exampleMeasured response at three different temperatures

Field test examplePredicted (FE) response at three different temperatures

Nils Rydén PEAB/LTH

Oförstörande provning av vägar med seismik ThankThank

you!you!

nils.ryden@tg.lth.se