1

GEOPHYSICAL SITE CHARACTERIZATION

Mechanical Wave Measurements

Electromagnetic Wave Techniques

Geophysical Methods

Mechanical Wave Measurements• Crosshole Tests (CHT)• Downhole Tests (DHT)• Spectral Analysis of Surface Waves• Seismic Refraction• Suspension Logging

Electromagnetic Wave Techniques• Ground Penetrating Radar (GPR)• Electromagnetic Conductivity (EM)• Surface Resistivity (SR)• Magnetometer Surveys (MT)

Mechanical Wave Geophysics

Nondestructive measurements (γs < 10-4%)Both borehole geophysics and non-invasive types (conducted across surface).Measurements of wave dispersion: velocity, frequency, amplitude, attenuation.Determine layering, elastic properties, stiffness, damping, and inclusionsFour basic wave types: Compression (P), Shear (S), Rayleigh (R), and Love (L).

Mechanical Wave Geophysics

Compression (P-) wave is fastest wave; easy to generate.

Shear (S-) wave is second fastest wave. Is directional and polarized. Most fundamental wave to geotechnique.Rayleigh (R-) or surface wave is very close to S-wave velocity (90 to 94%). Hybrid P-S wave at ground surface boundary.Love (L-) wave: interface boundary effect

Mechanical Body Waves

Initial

P-wave

S-wave

Mechanical Body Waves

HammerSource Receiver (Geophone)

OscilloscopeP

S RTime

Amplitude

Source Rich in Compression Mode

2

Mechanical Body Waves

HammerSource

Receiver (Geophone)

OscilloscopeP

S RTime

Amplitude

Source Rich in Shear Mode

Mechanical Waves (Compression)

0 1000 2000 3000 4000 5000 6000 7000 8000

Compression Wave Velocity, Vp (m/s)

Fresh Water

Sea Water

Clay

Sand

Till

Ice

Weathered Rocks

Intact Rocks

Steel

P - Wave Velocities

Mechanical Waves (Shear)

0 1000 2000 3000 4000

Shear Wave Velocity, VS (m/s)

Fresh Water

Sea Water

Clay

Sand

Till

Ice

Weathered Rocks

Intact Rocks

Steel

S - Wave Velocities

} V s = 0

Geophysical Equipment

Seismograph Spectrum Analyzer

Portable Analyzer Velocity Recorder

Seismic Reflection Seismic Reflection

3

Seismic Refraction Seismic Refraction

Vertical GeophonesSource(Plate)

Rock: Vp2

ASTM D 5777

Soil: Vp1

oscilloscope

x1x2x3x4

t1t2

t3t4

Note: Vp1 < Vp2

zR

Determine depthto rock layer, zR

Seismic Refraction

0.000

0.005

0.010

0.015

0.020

Trav

el T

ime

(sec

onds

)

0 10 20 30 40 50 Distance From Source (meters)

Horizontal Soil Layer over Rock

Vp1 = 1350 m/s

1

Vp2 = 4880 m/s

1z

x2

V VV Vc

c p2 p1

p2 p1=

−+

Depth to Rock:zc = 5.65 m

xc = 15.0 m

x values

t va

lues

Results from Seismic Refraction

Shear Wave Velocity, Vs

Fundamental measurement in all solids (steel, concrete, wood, soils, rocks)

Initial small-strain stiffness represented

by shear modulus: G0 = ρΤ Vs2

(alias Gdyn = Gmax = G0)

Applies to all static & dynamic problems at small strains (γs < 10-6)

Applicable to both undrained & drained loading cases in geotechnical engineering.

CrossholeSeismic Testing

Equipment(ASTM D 4428)

4

Crosshole TestingOscilloscope

PVC-cased Borehole

PVC-cased Borehole

DownholeHammer(Source) Velocity

Transducer(GeophoneReceiver)

∆t

∆x

Shear Wave Velocity:Vs = ∆x/∆t

TestDepth

ASTM D 4428

Pump

packer

Note: Verticality of casingmust be established by

slope inclinometers to correctdistances ∆x with depth.

SlopeInclinometer

SlopeInclinometer

© Paul Mayne/GTx = fctn(z)from inclinometers

Results from Crosshole

Seismic Tests

Reference: McLamore, Anderson, & Espana(1978), ASTM STP 654

Downhole Seismic Setup andTesting Equipment

Wilson, et al., (1978) ASCE EESD

Raw DownholeSeismic P-and S-Wave Data

Wilson, et al., (1978) Proceedings, Earthquake Engrg. & Soil Dynamics, ASCE Conference Pasadena, CA

Downhole TestingOscilloscope

Cased Borehole

TestDepth

Interval

HorizontalVelocity

Transducers(GeophoneReceivers)

packer

PumpHorizontal Plank

with normal load

Shear Wave Velocity:Vs = ∆R/∆t

z1 z2

∆t

R12 = z1

2 + x2

R22 = z2

2 + x2

x

Hammer

© Paul Mayne/GT

SensorsSource

SignalAnalyzer

Accelerometer

RayleighSurfaceWaves

In-Situ Surface Wave Testing

Layer 1

Layer 2

Layer 3

Layer 4

5

Surface Wave Measurements

Spectral Analysis of Surface Waves (transient)Continuous Surface Waves (CSW): variable excitation using surface vibratorModal Analysis of Surface Waves (MASW)

Passive Analysis of Surface Waves (low frequency content)

Shear Wave Measurements

Seismic Piezocone Test (SCPTu)

Shear Wave MethodsCost to Profile Vs to 30 m depth:

Crosshole ≈ $ 10,000 to $12,000

Downhole ≈ $ 6,000 to $ 7,000

SASW ≈ $ 2,500 to $3,500

Suspension Logging (deep > 50 m)

SCPTu ≈ $ 1,500 to $2,000 which includes 5 readings: qt, fs, ub, t50, Vs 60o

fs

qc

Vs

u1

u2

Cone Tip Stress, qtPenetration Porewater Pressure,uSleeve Friction, fsArrival Time of Downhole Shear

Wave, ts

Obtains Four Independent Measurements with Depth:Hybrid of Penetrometerwith Downhole Geophysics

Seismic Piezocone Test

6

Manual Shear Wave Sources Automated Seismic Sources

Downhole Shear Wave Velocity

Anchoring SystemAutomated SourcePolarized WaveDownhole Vs with

excellent soil coupling.

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0 50 100 150 200Time (ms)

Am

plitu

de

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0 50 100 150 200Time (ms)

Am

plitu

de

-400

-300

-200

-100

0

100

200

300

400

500

-200 -150 -100 -50 0 50 100 150 200

-400

-300

-200

-100

0

100

200

300

400

500

-5 0 5 10 15 20

Time shift (ms)

Maximum crosscorrelation at Dt = 6.75 ms

Shear wave velocity = 155 m/s

Right Strike

CROSSOVER Method

Left Strike

Shear Wave at 8.15 m

Shear Wave at 9.20 m

CROSSCORRELATION

Downhole Shear Waves

Complete Set of Shear Wave TrainsMud Island Site A, Memphis TN

Comparison of Shear Wave Methods

Mud Island, (Site B) Geophysics Comparisons

0

5

10

15

20

25

30

0 100 200 300 400 500 600

Shear Wave Velocity, Vs (m/s)

Dep

th (m

)

Reflection/Refraction

SH Refraction

Downhole (SCPTu)

7

SCPTU Sounding – Memphis, Shelby County, TN

0

5

10

15

20

25

30

35

0 10 20 30 40

qt (MPa)

Dep

th (m

)

0

5

10

15

20

25

30

35

0 100 200 300fs (kPa)

0

5

10

15

20

25

30

35

0 1000 2000 3000u2 (kPa)

0

5

10

15

20

25

30

35

0 100 200 300 400

Vs (m/sec) d = 35.7 mm

qt

fs

u2

Vs

More Better

More Measurements

is

Specialized In-Situ TestsBorehole Shear Test (BHT)Push-In PressuremeterLateral Stress ConeVibrocone Penetrometer for LiquefactionSelf-Boring Pressuremeter TestsIowa Stepped Blade (ISB)Vision Cone (VisCPT)Torsional Impulse Shear DeviceCone Pressuremeter (CPMT)Push-in Total Stress Cells (TSC)Hydraulic Fracturing (HF)

Hybrid In-Situ TestsCombination of Two Tests:

Cone Pressuremeter (CPT + PMT)

Seismic Cone Penetrometer (SCPTù) with dissipation (DHT + CPTu)

Seismic Flat Dilatometer (SDMTà) with dissipation (DHT + DMT)

Resistivity Piezocone (RCPTu): combine electrical conductivity + CPTu.

Dilatocone (DMT + CPT)

Saturated Unit Weight of Geomaterials(Burns & Mayne, TRR 1996)

8

Unit Weight Evaluation for Saturated Geomaterials

10

12

14

16

18

20

22

24

26

28

10 100 1000 10000

Shear Wave Velocity, Vs (m/s)

Sat

. Unit

Weigh

t, γ

T (k

N/m

3 )

Intact Clays Fissured ClaysSilts PeatSands GravelsWeathered Rx Intact Rocks

Saturated Soil Materials:γT (kN/m3) = 8.32 log Vs - 1.61 Log z

with Vs (m/s) and depth z (m)n = 727 r2 = 0.808 S.E. = 1.05

z (m) = 1

10

100

Additionaln = 163Rock

Materials

(Mayne, In-Situ Measurement 2001 Bali) Seismic Flat Dilatometer (SDMT)

Seismic DMTs at UMASS, Amherst

0

2

4

6

8

10

12

0 2 4 6 8

Lift-off Pressure po (bars)

De

pth

(m

)

0

2

4

6

8

10

12

0 20 40 60 80

Travel Time of Shear Wave (ms)

SDMT1

SDMT4

SDMT5

6

8

10

12

DMT 2

DMT 3

SDT 4

0

2

4

6

8

10

12

0 5 10 15

Expansion Pressure p1 (bars)

SDMT 1

DMT 2

DMT 3

SDMT 4

SDMT 5

True-Interval Seismic Dilatometer (SDMT)

SDMT in Layered Soils of Venetian Lagoon

0

2

4

6

8

10

12

14

16

0 500 1000 1500 2000 2500

DMT Pressures (kPa)

Dep

th (m

eter

s)

Po

P1

0

2

4

6

8

10

12

14

16

0 100 200 300 400

Shear Wave, Vs (m/s)

True-SDMT

Pseudo-SCPT

TreportiEmbankment

Seismic Piezocone in Soft Chicago ClaysNorthwestern University

Tip Resistance

0

5

10

15

20

25

30

0 5 10 15qT (MPa)

Dep

th (m

)

Sleeve Friction

0 200 400 600fs (kPa)

Porewater Pressure

0 500 1000 1500u2 (kPa)

Shear Wave Velocity

0 100 200 300 400 500Vs (m/s)

Friction Ratio

0 2 4 6 8 10FR (%)

9

Special True-Interval VsProbe in Soft Chicago Clays, Northwestern University

0

5

10

15

20

25

0 100 200 300 400Shear Wave, Vs (m/s)

PseudoSCPTu

True-IntervalProbe

0

5

10

15

20

25

0 2 4 6 8 10

Tip Stress, qT (MPa)

Dep

th (m

)

Lake Michigan

FREQUENT INTERVAL Vs METHOD Electromagnetic Wave Geophysics

Surface Mapping Techniques:• Ground Penetrating Radar (GPR)

• Electrical Resistivity (ER) Surveys

• Electromagnetic Conductivity (EM)

• Magnetometer Surveys (MS)

Downhole Techniques• Resistivity probes, MIPs, RCPTu

• 2-d and 3-d Tomography

Electromagnetic Wave Geophysics

Nondestructive methods

Non-invasive; conducted across surface.Measurements of electrical & magnetic properties of the ground: resistivity(conductivity), permittivity, dielectric, and magnetic fields.Cover wide spectrum in frequencies (10 Hz < f < 1022 Hz).

Ground Penetrating Radar (GPR)

Xadar Sensors & Software GeoRadar

Electrical Resisitivity Measurements Electrical Resisitivity Measurements

10

Electromagnetic Conductivity (EM) References on Geophysics

Application of Geophysical Methods to Highway Related Problems (FHWA Manual DTFH68-02-P-00083; 2003)Soils and Waves by Santamarina, Klein, and Fam (2001, Wiley & Sons)ISSMGE TC 10 – Geophysics in Geotechnical Engineering:

• www.geoforum.com/tc10

RCPTu

Resistivity (or Conductivity) PenetrometersDielectric (or Permittivity) Penetrometers

Seismic Resistivity Soundings (SRCPTu)

Tip Resistance

0

5

10

15

20

25

30

35

0 10 20 30 40qT (MPa)

Dep

th (m

)

Sleeve Friction

0

5

10

15

20

25

30

35

0 100 200 300 400fs (kPa)

Pore Pressure

0

5

10

15

20

25

30

35

0 500 1000 1500U1 and 2 (kPa)

Conductivity

0

5

10

15

20

25

30

35

0 50 100 150k (mS/m)

Shear Wave

0

5

10

15

20

25

30

35

0 100 200 300 400Vs (m/s)

ss

u2

u1

SB-1SB-2

SB-1SB-2

Combined RCPTu1 and SCPTu2 at Mud Island, Memphis

Applicability of In-Situ Tests

0.0001 0.001 0.01 0.1 1 10 100 1000

Grain Size (mm)

In-S

itu

Test

Met

hod

SPT

CPT

DMT

PMT

VST

Geophysics

CLAYS SILTS SANDS GRAVELS Cobbles/ Boulders

0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40 50 60 70 80

Horizontal Distance (meters)

Elev

ation

(met

ers

MSL

)

Silty SAND (SM)

Alluvial ClayeySILT (ML)

GRAY SAND (SP) EoceneCLAY (CH)

Excavation SubgradeClay Crust

HB-2 HB-4HB-5 HB-8 HB-11Boring

1715

11

6

5

6

17

22

24

28

2115

10

5

6

7

3

9

12

23 36

29

1918

13

5

7

3

4

7

27

33 31

25

1511

13

7

6

4

5

9

14

28 31

22

1811

12

7

5

5 16 25

15

19 22

25

SPT-N

Subsurface Profile Developed from Geotechnical Investigations

11

Fully Integrated Ground Behavior

LaboratoryTesting

Drilling & Sampling

In-SituTesting

NumericalSimulationAnalytical

Modeling

Geophysics

eo, γT, σvo’, DR, σp’, OCR, Go, D, Ko, ν, φ’, Ψ, Λ, Γ, c’, k, cv, K’, M’, G’, E’, Cc, Cr, Cs, Cα, su, Eu

Constitutive Models

Constitutive Models

Soil Parameters Evaluation

Subsurface Profile

Sandy SILT:φ’ = 37o

E’ = 45 MPaKo = 0.74

Silty CLAY:φ’ = 29.1o

E’ = 15 MPaKo = 0.57

Silty SAND:φ’ = 39.1o

E’ = 96 MPaKo = 1.44