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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!