Multiple Impact Surface Waves (MISW) or Multichannel Analysis of Surface Waves (MASW) Nils Rydén, Lund University, Sweden

Transcription

1 Multiple Impact Surface Waves (MISW) or Multichannel Analysis of Surface Waves (MASW) Nils Rydén, Lund University, Sweden

2 Outline Background NDT of pavements Wave propagation in slabs (plates) and pavement structures Test procedures and equipment Example one layer Example multiple layers

3 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

4 Pavement materials Dynamic small strain modulus E=2ρV S 2(1+ν) Base V S = m/s Subgrade V S = m/s

5 Modulus Unbound materials Ekdahl modell SwePave

6 Modulus Unbound materials Combined approach 2 extra geophones

7 Materials Asphalt (viscoelastic) Vs= m/s

8 Multichannel Analysis of Surface Waves (MASW) Data acquisition using only one source and one receiver Resulting multichannel record Asphalt or concrete layer Transformation to frequency phase velocity domain Base layer Subgrade

9 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

10 Pavement materials Dynamic small strain modulus E=2ρV S 2(1+ν) Base V S = m/s Subgrade V S = m/s

11 Modulus Unbound materials Ekdahl modell SwePave

12 Modulus Unbound materials Combined approach 2 extra geophones

13 Materials Asphalt (viscoelastic) Vs= m/s

14 Wave propagation in pavements Typical data Frequency phase velocity domain

15 Lamb waves in a free plate Anti-symmetric [A] Symmetric [S]

16 Lamb wave dispersion curves

17 Lamb waves excitability and sensitivity Impact Echo frequency (Gibson and Popovics 2005) Lowest frequency S1 (Impact Echo resonant frequency): most sensitive to h and V P (or ν) Low frequency S0 (direct P-wave): most sensitive to V P (or ν) Low frequency A0: intermediate sensitivity to V S and h High frequency A0 and S0 (Rayleigh wave): most sensitive to V S

18 Wave propagation in pavements 3-layer pavement structure Dispersionskurva

19 Nils Ryden, LTH Wave propagation in pavements Theoretical resolution with very long offset range

20 Frequency domain adaptive Analyzed region geometry Analyzed region f=1000 Hz The complete geometry and mesh is optimized for each frequency f=1500 Hz

21 FE model frequency domain Example layer model Harmonic source Frequency response solution at Hz

22 Data acquisition in the field Data acquisition using only one source and one receiver Wave propagation in pavements Asphalt or concrete layer Base layer Subgrade

23 Conventional field testing is slow Hammer with trigger Accelerometer

24 Source and receiver coupling Steel plate Steel spike Plastic plate Sticky grease Quick cement

25 Approximate evaluation of top Unknown system layer?? Measurement? Matching Known plate Vs i, h i, ρ i, ν i Calculation A0 S0 Lamb wave dispersion curves

26 Proposed analysis scheme Low frequency S0 (direct P-wave): most sensitive to V P (or ν) Use all three modes in in the analysis for increased accuracy! Lowest frequency S1 (Impact Echo resonant frequency): most sensitive to h and V P (or ν) Low frequency A0: intermediate sensitivity to V S and h High frequency A0 and S0 (Rayleigh wave): most sensitive to V S

27 Example Thick concrete wall Stiffness? Thickness?

28 Example Thick concrete wall

29 Example Asphalt pavement

30 Example Asphalt pavement

31 ATREL blind test University of Illinois 0.0 m 1.0 m

32 Automatic processing and analysis based on Lamb wave dispersion curves 1. Vp Results from ATREL blind test shows that the automatic MASW/Lamb Wave analysis consistently underestimates thickness with 2-10 % for all concrete slabs. 3. Thickness 2. Vr Automatic Lamb Wave Analysis THICKNESS (mm) LOCATION ACTUAL PREDICTED ERROR (mm) ERROR(%) % % % % % % % % % 32 * Calculated Poisson's Ratio. Using Vr and t p

33 Example quality control stabilised soil

34 Nils Ryden, LTH Methodology 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

35 Laboratory testing Free-free resonant frequency measurements

36 Example quality control stabilized soil Directly on site: Maturity index = 72 (from in ground temperature sensor) Vp=1698 m/s Vs=1040 m/s Thickness=0.25 m f u =1.13 MPa

37 Evaluation of multiple layers Unknown system??? Measurement Dispersionskurva Known system Matching Vs i, h i, ρ i, ν i Vs i, h i, ρ i, ν i Vs i, ρ i, ν i Calculation

38 Surface wave testing Unknown system??? Measurement Dispersionskurva Known system Matching Vs i, h i, ρ i, ν i Vs i, h i, ρ i, ν i Vs i, ρ i, ν i Calculation

39 Evaluation of multiple layers 0.13 m asphalt (80+50 mm) 0.30 m base 0.20 m stabilized subgrade ~8.00 m clay till

40 Evaluation of multiple layers Reference measurements on each layer Unstabilized subgrade V P =550 m/s V S = 213 m/s ~8.00 m clay till

41 Evaluation of multiple layers Measured data on top of all layers Frequency phase velocity domain Range used for the inversion of embedded layers

42 Surface wave testing Unknown system??? Measurement Dispersionskurva Known system Matching Vs i, h i, ρ i, ν i Vs i, h i, ρ i, ν i Vs i, ρ i, ν i Calculation

43 Finding the smallest mismatch? Local minima Global minimum

44 Evaluation of multiple layers Simulated Annealing Best match Viscoelastic asphalt V S =b 1 *f b 2

45 Evaluation of multiple layers Measured E-modulus in the laboratory (blue) and in the field (red)

46 Field test example Measured response at three different temperatures

47 Asphalt viscoelastic properties Reference mastercurve one temperature A T = temperature shift factor log * a2 E = a1 + ( a3 + a4 logifr 1+ (1/ e ) fr = AT f ) 6 C 13 C 23 C

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

49 Field test example Measured response at three different temperatures

50 Field test example Predicted (FE) response at three different temperatures

51 Oförstörande provning av vägar Thank you! med seismik Nils Rydén PEAB/LTH