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Scoil na hAiltireachta, na
Tidhreacha agus na
hInnealtoireachta Sibhialta
UCD
UCD School of Architecture,
Landscape and Civil
Engineering
Multichannel Analysis of Surface Waves: Applications and Developments
Dr. Shane Donohue
Transport, Infrastructure and Land Use Research Group
Introduction
n NDT Research at UCDn Surface Wavesn Multichannel Analysis of Surface Waves (MASW)n Introductionn Applications
n Summary
Engineering Geophysical Research, UCDn Non-destructive, cost effective solutions to geotechnical and
infrastructure problems
n MASW, Seismics, Resistivity, GPR, Microgravity
n UCD research applications:n Slope stability (natural & man-made) assessmentn Parameters for geotechnical designn Ground improvementn Karst Detectionn Pavement Quality Assurancen Railway Ballast degradation
Surface Wave Techniquesn CSW, SASW, MASW
n Surface Wave / Lamb Wave propagationn Elastic stiffness & thicknessn Differences in source / receivers / inversionn MASW “Pattern Recognition” technique n Extraction of noise and different modes of surface wave propagation
(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
General Methodology: MASW
Multichannel Analysis of Surface Waves (MASW)
4.5-10Hz Geophones Sufficient (min 12)5-10kg Hammer
1-2m spacing
Approx. 2/3 of the energy from a hammer blow propagates away from the source in the form of Surface Waves
rainfall
Suction
Pressure
n In-situ monitoring of water content and applied traffic stresses
n We cannot monitor every slope, we need to identify critical sections
n Geophysical NDT for real time assessment of infrastructure reliability
Stability of Earth Embankments
Embankment Stability Assessment, River Dee Flood Defences, ChesterMultichannel Analysis of Surface Waves (MASW)
n 2D stiffness mappingn Identify soft ground within embankmentn Identify geological boundaries
Railway Embankment Failure, Enniscorthy, Co. Wexford
-4
-2
0
2
4
6
8
16 18 20 22 24 26 28
Distance (m)
Elev
atio
n
Soft Clay
Peat
Stiff Clay
Siltsone
Cross-Section
2D Resistivity across track through failure plane
2D Resistivity & MASW along track
0
2
4
6
8
10
12
14
0 200 400 600
Vs (m/s)
Dep
th (m
)
0
2
4
6
8
10
12
14
0 200 400 600
Vs (m/s)
Dep
th (m
)
0
2
4
6
8
10
12
14
0 200 400 600
Vs (m/s)
Dep
th (m
)
Ground Improvement Quality Control
MASWn Quantify improvement in terms
of small strain stiffnessn Non-invasiven Direct and Rapid measure of
improvement
Jamaica St., Belfastn Excavation of unsuitable material
(2-4m)n Treated with Limen Compacted
Jamaica St. site, Belfast
0 100 200 300 400
Vs (m/s)
10
8
6
4
2
0
Dep
th (m
)
Zone 6
0 100 200 300 400
Vs (m/s)
10
8
6
4
2
0
Dep
th (m
)
Zone 1Zone 3 TreatedZone 4
0 100 200 300 400
Vs (m/s)
10
8
6
4
2
0
Dep
th (m
)
Zone 3 Untreated
0 100 200 300 400
Vs (m/s)
10
8
6
4
2
0
Dep
th (m
)
Zone 2Zone 5
Vs (m/s)
Dep
th (m
)
0 100 200 300 4000 40 80 120 160 200Gmax (MPa)
10
8
6
4
2
0
Dep
th (m
)
Zone 1Zone 2Zone 3 UntreatedZone 3 TreatedZone 4Zone 5Zone 6
Gmax = ρ.Vs2
1 Day5 Days14 Days
Pavement MASW
High frequency accelerometer200g impact hammer ~0.1m spacing
MSOR (Ryden et al. 2001)
Source and Receivers
Impulse Force Hammer n Integral quartz force sensor n Superior triggeringn Selection of tips
High frequency accelerometersn Natural frequency – 25kHzn Mount with grease
UCD Pavement MASW n “True” Multichannel systemn Quickern Eliminates need for Time break
corrections
Performance of Coldmix Pavement Materialsn Cheaper and more Energy Efficient in construction (cost
and sustainability)
n Review of cold-mix materials, laboratory trials of different mix specifications, and full-scale trials
n MASW for quality assurance
n Funded by National Roads Authority (NRA)
MASW feasibility trial at National Roads Authority (NRA) test site, Dublin
Coldmix material
Subgrade
Freq
uenc
y (H
z)
Phase Velocity (m/s)
Surface wave “dispersion image” Pavement stiffness profile
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 100 200 300 400 500
Gmax (MPa)
Dep
th (m
) EmulsionFoam
Summary
n Surface wave techniques for measurements of
elastic stiffness and layer thickness
n MASW geotechnical and pavement applications
n UCD “true multichannel” system for quicker
acquisition without need for corrections
Acknowledgements
nn APEX APEX GeoservicesGeoservices, Ireland, Irelandnn CONCON--FORMFORMnn HalcrowHalcrow Group Ltd.Group Ltd.nn UK Environment AgencyUK Environment Agency
nn Thank you!Thank you!
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