SPECTRAL-ANALYSIS-OF-SURFACE-WAVES (SASW)

METHODS

KH 4653 Site Investigation

1 0 1 5 2 0 2 5 3 0 3 5

L o c a t i o n , m

-25

-20

-15

-10

-5

0

Dep

th, m

PRE-REQUISITE COURSE

KKKH 2253 Geotechnic I

KKKH 3153 Geotechnic II

**Pre-requisite knowledge -> Physic Form 5**

***KKKH 4223 Geotechnical Engineering Practice***

Kursus Wajib

OBJECTIVES Explain the importance of site

investigation in engineering practice and SASW technique

Categorize types of site investigation methods available nowadays

Leaning Tower of Pisa

WHY DO WE NEED TO INVESTIGATE SOIL?

Petronas Twin Towers 

Highland Towers

WHAT ARE WE GOING TO EXPLORE TODAY?

Soil Investigation

TraditionalMethods

Boring

etc

Geophysical Methods

Seismic

Refraction

Reflection

Surface Wave

SASW

MASW

etc

etc

Electrical

etc

CONTENTSFundamental of Surface Wave Methods

Principles of Surface Wave Methods

Spectral Analysis of Surface Wave(SASW) Technique

7

Fundamental of Surface Waves

8Body Waves Surface Waves

Wavelength

· · · ·· · · ·

Compression Wave or Primary Wave (P Wave)

Wavelength

Shear Wave or Secondary Wave (S Wave) Wavelength

Wavelength

air-soil boundary

within soil

Surface Waves and Body Waves

9

Propagation of waves

Surface Waves(Rayleigh Waves)

Body Waves(P or S Waves)

12

3.0

2.5

2.0

1.5

1.0

0.5

0.00.50.40.30.20.10.0

Poisson's Ratio, n

Constrained Compression Wave, VP

Shear Wave, VS

Rayleigh Wave, VR

Nor

mal

ized

Wav

e Ve

loci

ty, V

/VS

0.50.40.30.20.10.0

Constrained

Propagation Velocities of Stress Waves

13

Freq=66.48 HzWavelength = 2.0 mVph = 133.0 m/sec

5.0 m

5.0 m

Half-Space

150 m/sec

300 m/sec

700 m/secShear-WaveVelocity

Freq=15.8 HzWavelength = 9.26 mVph = 146.4 m/sec

Freq=11.9 HzWavelength = 17.0 mVph = 202.4 m/sec

Phase-VelocityDispersion Curve

2 m

400

300

200

100

0Phas

e V

eloc

ity, m

/sec

5 6 7 8 91

2 3 4 5 6 7 8 910

2 3 4 5 6 7 8 9100

Wavelength, m

Dispersion Phenomenon of Surface Waves

16

Principles of Surface Wave Methods

17

Analysis Procedure of Surface-Wave Methods

Determination of Phase-Velocity Dispersion Curves

Measurement of Surface Waves[Time or Frequency Domain]

Determination of Shear-Wave Velocity Profile

Inversion Analysis

Iterative Forward Modeling Analysis

SASW Method, CSW Method, MASW Method, ReMi Method, f-k Method, etc.

Measurement ofSurface-Wave Phase Velocities

Determination of 1-D Shear-Wave Velocity (VS) Profile

Construction of 2-D Shear-Wave Velocity ContourUsing a series of1-D VS Profiles

Inversion Analysis

ForwardModeling of Surface-Wave Propagation

A Series of 1-D VS Profiling

(10~20 Profiles)

Analysis Flow of Surface-Wave Measurements

Analysis Procedure of Surface Wave Methods

18

Surface-Wave Methods

Spectral-Analysis-of-Surface-Waves (SASW) Method

Multichannel Analysis of Surface Waves (MASW) Method

Harmonic Wavelet Analysis of Wave (HWAW) Method

Continuous Surface Wave (CSW) Method

Refraction Microtremor (ReMi) Method

Passive Method

f-k Spectrum Method

19

Spectral Analysis of Surface Wave(SASW)

Technique

20

Setup for SASW Measurements

DR

Dynamic Signal Analyzerwith anti-aliasing filter Frequency Span: 25~52000 Hz Real-time FFT 2 to 4 input channels

Geophones4.5 Hz (for D=0.5~1m)1.0 Hz (for D ≥ 2m)Shielded Cables

Impact SourceAssorted Hammers 100-kg Drop WeightBulldozer

Inter-Receiver Spacings0.5, 1.0, 2.0, 4.0, 8.0 m (for Hammers)16.0, 32.0 m (for 100-kg Drop Weight)64.0, 128.0 m (for Bulldozer)

Source-Receiver DistanceR=D (Conventional SASW)R=1, 2, 4, 8, and 16 D (for CAP-SASW)

21

FFT Analyzer Seismic Sources

Geophones

22

Principles of Phase-Velocity Measurement

360sec 01504.0t

Frequency = 66.48 HzPeriod = 0.01504 sec

phase difference:travel time:

ft

2

Relationship between and t :

2 m

m/sec 0.13301504.0

0.2

tDvphPhase Velocity:

fDvph

2

Receiver 1

Receiver 2

23

Surface-Wave Methods

Receiver 1

3

2

1

0Spe

ctra

l Am

plitu

de

8006004002000

Frequency, Hz

D D

2000

1000

0

Unw

rapp

ed P

hase

, deg

8006004002000Frequency, Hz

Spe

ctra

l Am

plitu

de 3

2

1

0 8006004002000Frequency, Hz

FFT

Phase Difference :2 – 1

600

400

200

0

Pha

se V

el.,

m/s

ec

1 10 100Wavelength, m

ExperimentalDispersion Curve

Receiver 2

FFT

-150-100-50

050

100150

Pha

se A

ngle

, deg

8006004002000Frequency, Hz

Phase Unwrapping

(a)

(b)

(c)

Impact, Swept Sinusoidal Vibration, orRandom Noise

D=1m

Receiver 1

3

2

1

0Spe

ctra

l Am

plitu

de

8006004002000

Frequency, Hz

D D

2000

1000

0

Unw

rapp

ed P

hase

, deg

8006004002000Frequency, Hz

Spe

ctra

l Am

plitu

de 3

2

1

0 8006004002000Frequency, Hz

3

2

1

0 8006004002000Frequency, Hz

FFT

Phase Difference :2 – 1

Phase Difference :2 – 1

600

400

200

0

Pha

se V

el.,

m/s

ec

1 10 100Wavelength, m

ExperimentalDispersion Curve

Receiver 2

FFT

-150-100-50

050

100150

Pha

se A

ngle

, deg

8006004002000Frequency, Hz

Phase Unwrapping

(a)

(b)

(c)

Impact, Swept Sinusoidal Vibration, orRandom Noise

D=1m

SASW Method

24

-150

-100

-50

0

50

100

150

Pha

se A

ngle

, deg

8006004002000

Frequency, Hz

-150

-100

-50

0

50

100

150

Pha

se A

ngle

, deg

4003002001000

Frequency, Hz

-150

-100

-50

0

50

100

150

Pha

se A

ngle

, deg

200150100500

Frequency, Hz

-150

-100

-50

0

50

100

150

Pha

se A

ngle

, deg

100806040200

Frequency, Hz

-150

-100

-50

0

50

100

150

Pha

se A

ngle

, deg

50403020100

Frequency, Hz

-150

-100

-50

0

50

100

150

Pha

se A

ngle

, deg

2520151050

Frequency, Hz

800

600

400

200

0

Pha

se V

eloc

ity, m

/sec

3 4 5 6 7

12 3 4 5 6 7

102 3 4 5 6 7

1002 3

Wavelength, m

D = 1m

D = 2m

D = 4m

D = 8m

D = 16m

D = 32m

25

20

15

10

5

0

Dep

th, m

8006004002000Shear Wave Velocity, m/sec

InversionAnalysis

CompositeExperimental Dispersion Curve

Inversion Analysis in the SASW Method

25

WinSASW, Dedicated Software for the SASW Method

26

D=3 m

1 2

S=3, 6, 12, 24, and 48 m

ReceiversNear SourceFar Source

40

30

20

10

0

Dep

th, m

25000Vs., m/sec

0

5

10

15500 5 10 15 20 25 30 35 40 45

Location, m

Dep

th, m

55

Evaluation of 2-D Shear-Wave Velocity Profiles

(100kg) (5kg)

WHICH ONE?

Traditional Geophysical

Drill a hole Reliable – sample Result refer to one

point only Expensive Can be performed

by labor with supervision

Non-destructive No soil sample Cover large area Cheaper Relatively Fast Expertise needed

throughout the test

CONCLUSION Today lecture

Importance of site investigationSite investigation categories SASW method

Next lectureRecent Development in SASW MethodSome Applications of SASW in Practice

THANK YOU!

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