NGF Grunnundersøkelskomiteen - 15th Oktober 2013
Use of shallow seismic measurements –
what information can analysis of surface
waves (MASW) provide?
Mike Long
UCD
(Shane Donohue, ex UCD / Peter O’Connor APEX
Geoservices)
UCD School of Civil, Structural
and Environmental
Engineering.
Presentation Outline
• Introduce techniques in general
• MASW
• MASW work in Norway
• Correlations with soil properties
• Link with CPTU
• Other applications
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Seismic Waves
P-wave
Fastest ;compressional
Particle motion parallel
to direction of
propagation
S-wave
Shearing and rotation
Particle motion
perpendicular
to direction of
propagation
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Some common techniques
• Intrusive / active methods
 Seismic cone (SCPT)
 Cross hole
(or down hole)
Campanella et al. (1986)
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Surface waves
• Seismic wave propagating along the surface
• Elliptical particle motion
• Wave used is the Rayleigh wave (largest
amplitude)
• Use dispersive properties of soil – velocity of
propagation depends on frequency.
 High frequency near surface
 Low frequency affects deeper layers
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Surface wave techniques
CSW: Continuous surface wave
GDS Ltd.
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Surface wave techniques
SASW: Spectral analysis of surface waves
NTNU quick clay research
site Tiller (Kvenild)
7/40
SASW in Sweden
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MASW
 MASW (multi-channel analysis of surface waves)
 MASW “The wave of the future” (Crice, 2005)
 Similar equipment and acquisition procedures
as used in conventional seismic reflection surveys
 Multiple receivers
allow easier isolation
of noise
NGI research site
Museumparken, Drammen
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General methodology for MASW
1. Generate vertical ground motions
2. Detection and measurement of surface wave
3. Record the surface wave
4. Produce a dispersion curve
5. Inversion of the dispersion curve
6. Derive a stiffness-depth profile
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(1) Generation of surface wave
(2) Measure & (3) Record surface wave
Low Frequency Geophones (4.5Hz)
(4) Surface wave dispersion
Low frequency (Long wavelength)
waves travel deeper than higher
frequency (short wavelength)
surface waves
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(4) Dispersion curve
Typical shot record and
dispersion curve from Onsøy
Plot of surface wave velocity and
frequency (dispersion curve)
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(5) Inversion of surface wave dispersion
curve
1. Converting dispersion curve into a shear
2.
3.
4.
5.
wave velocity (Vs) – depth profile
Software Surfseis
Assumed soil model (layer thickness, Vs, , )
is inputted and a synthetic dispersion curve is
generated
Synthetic curve compared to field dispersion
curve.
Vs is updated after each iteration until the
synthetic dispersion curve closely matches
the field curve
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(6) Shear wave velocity to stiffness
 Gmax may then be calculated from:
Gmax = Vs2
 Use in deformation analyses (seismic,
dynamic, machine, wind, wave, liquefaction
potential etc.
15/40
Research sites in Norway
Approach was:
 Initially investigate sites
where Vs profiles already
known to give confidence
 Later then study other
sites
 To date 22 sites studied
 MASW (20)/ SASW (5)
 + 2 Swedish
Long and Donohue (2007,
2010) Can. Geo. Jnl.
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Onsøy: Gmax from SCPT
Compared with 5 MASW profiles
Gmax (MPa)
0
5
10
15
20
30
35
40
0
Crust
SCPT 1
SCPT 2
SCPT 3
2
Depth (m)
4
Soft Clay
25
MASW 1
MASW 2
MASW 3
MASW 4
MASW 5
6
8
10
12
14
16
Bender Element
(Slightly lower Gmax)
18
20
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Drammen clay sites: Danviksgata &
Museumpark
18/40
Berg - Trondheim
Vs (m/s)
0
50
100
150
200
250
300
350
0
2
Depth (m)
4
6
8
10
12
Site1
Cross hole Barnehage site
19/40
Holmen Drammen - sand site
Vs (m/s)
0
25
50
75
100
125
150
175
200
0
2
Depth (m)
4
6
8
10
MASW
12
Raleigh wave
SCPT1
SCPT2
14
SCPT3
Cross hole avg.
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All sites
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Correlations between Vs and soil
properties
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Correlations for clays - I
• Vs or Gmax depends on , e, OCR
(Hardin, 1978)
• Gmax / 'v0 should vary with e
• Janbu / Langø
Gmax
g max 
 m `a
• Use high quality (block) samples only
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Correlations - II
24/40
su versus Vs correlation Irish till
25/40
Link to CPTU
26/40
Mayne and Rix correlation
 Gmax not Vs
 qc not qt
 Log scales
 Worldwide database
 Norwegian soils?
27/40
Norwegian clays
 Best quality data only
 Each point refers to a block sample
28/40
Use of CPTU Bq
29/40
Subsequent trial - Fredrikstad
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Combined use of MASW and CPTU
31/40
Other applications
32/40
“Continuous” MASW
33/40
O’Connell St – Central Dublin
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Can create 2d stiffness profiles
Onsøy – little variation, highly uniform
35/40
Canal embankment – Chester, UK
36/40
Passive MASW
Nödinge
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Assessment of ground improvement
Vs (m/s)
0
100
200
0
300
400
Shallow “wet” till improved by
lime / cement stabilisation
and assessed using MASW
Depth (m)
2
4
6
8
Zone 1
Zone 2
Zone 3 Untreated
Zone 3 Treated
Zone 4
Zone 5
Zone 6
10
38/40
Assessment of sample disturbance
Vs (m/s)
0
20
40
60
80
100
120
0
140
160
54
76
2
Blocks
MASW 1
4
MASW 2
6
MASW 3
Depth (m)
MASW 4
8
MASW
10
12
14
16
Remoulded
18
20
Air
(After extrustion)
MASW 5
Remoulded
Conclusion
• MASW now well proven “mature” technique
• Scope for further work on link between Vs
and parameters of Norwegian clays (su, pc',
M0 etc.)
• Scope for similar work in other Nordic
countries
• Industry / University collaboration essential
Thank You For Listening
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