evaluation of dynamic soil properties

Soil Dynamics Week # 15

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Evaluation of Dynamic Soil Properties

June 3, 2008

Sun, Chang-Guk

[ [email protected] ] Earthquake Research Center

Korea Institute of Geoscience and Mineral Resources (KIGAM)

SNU Geotechnical and Geoenvironmental Engineering Lab.

mailto:[email protected]


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Introduction

1) Seismic testing methods from exploration geophysics for dynamic soil properties

A variety of geophysical methods have been widely applied to geotechnical

engineering for determining various subsurface soil properties. In particular, seismic

methods such as borehole seismic testing methods and surface wave methods are

recently applied to obtain dynamic soil properties, to require primarily for seismic

design and seismic performance evaluation. From the geotechnical perspective,

shear wave velocity (VS) which were usually emphasized as a seismic design

parameter could be determined only from in-situ seismic tests.

2) Determination of shear modulus from in-situ tests

Seismic field tests measure the small strain response of a relatively large volume

of ground (ref., Fig. 1).

2

0max SVGG ρ==

Where, , : maximum shear modulus at small strain level, maxG 0G

ρ : total mass density, : shear wave velocity SV

)1(2 ν+=

EG

Where, : shear modules, G E : elastic modulus, ν : Poisson’s ratio

2

2

1

2( / ) 1

( / ) 1

P S

P S

V V

V Vν

−=

−

Where, : compression wave velocity, : shear wave velocity PV SV



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Shea

r M

odul

us, G

Shear Strain, γ (%)10 -4 10 -3 10 -2 10 10010 -1 1

Shea

r M

odul

us, G

Shear Strain, γ (%)10 -4 10 -3 10 -2 10 10010 -1 1

Seismic Tests

Unload-Reload Pressuremeter Test

Ini tial Loading Pressuremeter Test

Flat Di latometer Test

Screw Plate Load Test

Penetration Tests (CPTu, SPT, etc.)

Pressuremeter Test

Fig. 1. Shear modulus with strain determined from various in-situ tests

3) Importance of in-situ tests for seismic design of geotechnical structures

For the reliable seismic design and seismic performance evaluation of both

geotechnical structures and super structures, dynamic soil properties should be

determined from in-situ tests and laboratory tests. The VS profiles from the field

seismic tests are very important to reflect the site-specific characteristics (ref., Fig. 2).

Evaluation of Dynamic stability

Dynamic analysis

Evaluation of Liquefaction of ground

SPT-NCPT-qc

Vs profile

Cyclic Tri-axial test1? D nonlinear effective

stress analysis

Simple method Detailed method

RC/TS testCTX test

Downhole, SPT-Uphole, Crosshole,HWAW,SASW, SPS logging

Recorded earthquakeArtificial earthquake

In-situ tests

Determination of Design Ground Motion

1D ground response analysisSeismic design guide

Determination of design peak ground acceleration

Equivalent-linear

2D linear/nonlinear analysis

input earthquake

Site investigation and determination of input parameters

Non-linearDistrict guide seismic hazardmap

Determination of design section

Determination of seismic performance level

lab. tests

VsProfile

Fill

Clay

Weathered Residual Soil

Weathered RockRock

In-situ test Soil profile

G/Gmax

DDmin

Particle –size distribution, PIConfining Pressure

Lab. test

Fig. 2. Importance of dynamic soil properties for seismic design



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Conventional Field Tests

Since the beginning of geotechnical engineering, a good number of different

geotechnical in-situ tests have been developed and, nowadays, several methods are

available for site investigation in soil deposits with the most common being the SPT,

CPTu (also CPT), flat dilatometer test (DMT), pressuremeter test (PMT) and vane

shear test (VST). Besides these geotechnical in-situ investigation tests, the recent

site investigation program could include various geophysical methods for obtaining

the VS profile. Among the common in-situ tests, the most widely used dynamic and

static penetration testing methods coupled with the geophysical seismic methods are

the SPT with borehole drilling and sampling and the CPTu.

1) Standard penetration test (SPT) with borehole drilling investigation (ref., Fig. 3)

Fill

Alluvial

Weathered Soil

Soft Rock

(Bedrock, Seismic Base)

Boring Machine

Weathered Rock

Fig. 3. Schematic of borehole drilling and SPT (modified from Mayne et al., 2001)



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2) Piezocone penetration test (CPTu) (ref., Fig. 4)

Fig. 4. Schematic of CPTu (after Mayne et al., 2001)

Outline of Seismic Field Tests

The testing methods for measurement of VS are divided as in-situ tests and

laboratory tests (ref., Fig. 5). The in-situ tests are composed of non-intrusive

methods such as surface seismic tests and intrusive methods such as borehole

seismic tests. The surface seismic tests are often less expensive and can be

performed relatively quickly, whereas the borehole seismic tests are usually more

accurate and have generally the information gained directly from the boring

investigation. Typical surface seismic tests include spectral analysis of surface

waves (SASW) test, multi-channel analysis of surface waves (MASW) test, harmonic

wavelet analysis of waves (HWAW) test, seismic reflection test, seismic refraction



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test and steady-state vibration (or surface wave) test. And representative borehole

seismic tests are crosshole test, downhole test, uphole test, inhole test, suspension

logging test and seismic cone test.

Fig. 5. Field and laboratory tests for obtaining VS (after Schneider et al., 2001)

Crosshole Seismic Test

- Need more than two boreholes: one for source and the others for receivers

- Generation of body wave within a borehole and its detection at another borehole

at the same depth (ref., Fig. 6)

- More reliable than other seismic testing methods and more simple for

interpretation.

VS = (Distance from Source to Receiver) / (Travel Time of Shear Wave)



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Dynamic Signal Analyzer

Test Depth

Mechanical Source (Mok

Source)

S (SV or SH) Wave and P Wave Generated by Source

Crosshole Sources

Air Pressure

Triggering

Air Pressure

Velocity Transducer(3-Component

Geophone Receiver)

Piezoelectric Source

Spring-loaded Source

Fig. 6. Schematic of crosshole seismic test

Downhole Seismic Test

- Need only one borehole: use surface source (ref., Fig. 7)

- Limitation of exploration depth due to use surface source

- Rigorous interpretation method is required considering refracted ray path

- After obtaining waveforms with depth from the downhole seismic test in a field,

wave arrival times with the testing depth should be first picked by means of

several picking methods: cross-over method, peak-to-peak method, and cross-

correlation method.

- After picking the wave arrival times or time differences, the VS profile is deduced

by means of several downhole interpretation methods: direct method, interval

method, modified interval method, and refracted ray path method.



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Test Depth of Lower Receiver

Air Pressure

Test Depth of Upper Receiver

Source Plank(Wooden Plate)with Static Load Trigger

System

S (SH) Wave and P Wave Generated by Source

Hammer

Velocity Transducer(3-Component

Geophone Receiver) Fig. 7. Schematic of downhole seismic test

1) Wave arrival time picking method

a) Cross-over method (ref., Fig. 8)

Time (ms)

Am

plitu

de (m

V)

Leftward S-Wave SignalRightward S-Wave SignalDirect

Arrival Time

Direct Arrival Time

Arrival Time Differences

Fig. 8. Concept of cross-over method



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b) Peak-to-peak method (ref., Fig. 9)

Time (ms)

Am

plitu

de (m

V)

S-Wave Signal of Upper ReceiverS-Wave Signal of Lower Receiver


Fig. 9. Concept of peak-to-peak method

c) cross-correlation method (ref., Fig. 10)

Cro

ss-C

orre

latio

n, C

orr(

τ)

Time Shift, τ (ms)

0


Fig. 10. Function of cross-correlation for selected waveform windows

2) Downhole interpretation method

a) Direct method

- Determination of mean velocity profile using direct (corrected) travel time



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- Corrected travel time ( ) (ref., Fig. 11) ct

RtDtc =

Where, : depth of receiver, : measured travel time, D t

: Inclined travel path R

D R

Source Plank

Receiver

Fig. 11. Concept of direct method

- Shear wave velocity ( ) of each soil layer having similar travel time SV

cS t

DVΔΔ

=

b) Interval method

- Using travel time ( or ) delay between two receivers lT uT

- Shear wave velocity ( ) between two receivers (or adjacent testing depth) (ref.,

Fig. 12)

SV

ul

ulS TT

RRV

−−

=



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Rl

Ru

Source Plank

Receiver

Fig. 12. Concept of interval method

c) Modified interval method

- Considering the stiffness of upper layers and straight ray path (ref., Fig. 13)

∑−

=

−=

1

1

,,

.i

j jS

lijli

liiS

VL

T

LV

Z1

Di,u

Di,l

S

VS 1

Z2VS 2

Zi-1VS i-1

ZiVS i

ZN-1VS N-1

VS N

Li1,u

Li2,u

Li1,l

Li2,l

Li(i-1),u

Lii,l

Source Plank

Receiver

Li(i-1),l

Ri,u

Ri,l

Fig. 13. Concept of modified interval method



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d) Refracted ray path method

- Considering refracted ray path due to the stiffness differences between layers

(ref., Fig. 14)

- Adopt Snell’s law and the equation same as the modified interval method

iS

ii

jS

ij

S

i

S

i

VVVVθθθθ sinsinsinsin

2

2

1

1 =====

∑−

=

−=

1

1

,,

.i

j jS

lijli

liiS

VL

T

LV

Z1VS 1

Z2VS 2

Zi-1VS i-1

ZiVS i

ZN-1VS N-1

VS N

θi1,l

θi2,l

θi(i-1),l

θii,l

Source Plank

S

Receiver

θi1,u

θi2,u

θi(i-1),u

Di,u

Di,l

Li1,u

Li2,u

Li1,l

Li2,l

Li(i-1),u

Lii,l

Li(i-1),l

Fig. 14. Concept of refracted ray path method

3) Other field testing technique coupled with the downhole seismic test

a) Seismic piezocone penetration test (SCPTu)



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- Use the seismic cone which is an ordinary CPTu probe with a built-in geophone

(or accelerometer)

- Perform the downhole seismic test during the CPTu (ref., Fig. 15)

Mechanical Hammer

Geophone Receiver

Source Plank

Ray Path of Shear Waves

Small Strain Level for Seismic Downhole TestLarge Strain Level for

Penetration Test

Plastic Failure (Disturbed) Zone by Penetration

Undisturbed Zone

Undisturbed Zone

Fig. 15. Procedure and dual strain levels of the SCPTu

b) Seismic dilatometer penetration test (SDMT)

- Use the seismic dilatometer probe which is an ordinary DMT probe with a built-in

geophone (or accelerometer)

- Perform the downhole seismic test during the DMT

Uphole Seismic Test

- Need one borehole: use several sources within the borehole (SPT, blasting and

so on) and surface geophones (ref., Fig. 16)

- Rigorous interpretation method is required considering refracted ray path similar

to the downhole test with inverse geometry



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Test Depth of Source

Drop of Weight

Weight

Geophone Receivers

Trigger

S (SV) Wave and P Wave Generated by Source

Fig. 16. Schematic of uphole seismic test

Inhole Seismic Test

- Need one borehole: locate source and receivers in the same borehole

- Conduct the Inhole seismic technique mostly for open-hole typed rock formation

(ref., Fig. 17)

- Perform the suspension PS logging for the ground usually lower than ground

water level adopting for PVC casing or open-hole filled with bentonite slurry (ref.,

Fig. 18)

VS = (Distance from Source (Receiver) to Receiver) / (Travel Time of Shear Wave)



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Near Test Depth

Air Pressure

Far Test Depth

Trigger System

Far Velocity Transducer

(1- or 3-ComponentGeophone Receiver)

Near Velocity Transducer

(1- or 3-ComponentGeophone Receiver)

S Wave Generated by Source (Spring-

loaded Source)

Isolation Bar (Damper)

Isolation Bar (Damper)

Direction of Wave

Propagation

Fig. 17. Schematic of inhole seismic test Fig. 18. Schematic of suspension PS logging

Surface Wave Methods

Surface or Rayleigh waves are distortional stress waves that propagate near to the

boundary of an elastic half space, in this case the ground surface. The propagation

velocity of surface waves is controlled by the stiffness of the ground within one half

and one third wavelength of the surface and so measurements therefore need to

determine their wavelength as well as their velocity. The VS profile can be

determined by using the inversion of the experimental dispersion curve obtained

based on the signals in the field (ref., Fig. 19).



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Field Test

Experimental Dispersion Curve Vs Profile

Signal Processing Inversion

Step #1 Step #2 Step #3

SignalsEarth

0

10

20

30

40

50

0 300 600 900 1200 1500Shear-wave Velocity (m/s)

Dep

th (m

)

0100200300400500600700800

0 20 40 60 80 100Frequency (Hz)

Phas

e Ve

loci

ty (m

/s)

Fig. 19. Three steps of surface wave methods

1) Spectral analysis of surface waves (SASW) method

- A variety of sources: impact sources (sledge hammer or drop weight) and

continuous source (heavily equipment with caterpillar or massive vibrator)

- Use two geophone (generally 1 Hz) receivers

- Perform with several receiver spaces mostly with 1 m, 2 m, 4 m, 8 m, 16 m, 32 m,

and more (ref., Fig. 20)

Receiver 1

3

2

1

0Spec

tral A

mpl

itude

8006004002000Frequency, Hz

D D

2000

1000

0

Unw

rapp

ed P

hase

, deg


Spec

tral A

mpl

itude 3

2

1

0 8006004002000Frequency, Hz

FFT

Phase Difference :φ 2 – φ 1

600

400

200

0

Phas

e Ve

l., m

/sec

1 10 100Wavelength, m

ExperimentalDispersion Curve

Receiver 2

FFT

-150-100-50

050

100150

Phas

e An

gle,

deg


Phase Unwrapping

Impact, Swept Sinusoidal Vibration, orRandom Noise

D=1m

Fig. 20. Basic configuration and phase velocity calculation for SASW method



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2) Muti-channel analysis of surface waves (MASW) method

- Use simply impact source (sledge hammer) and a series of twelve geophones

(4.5 Hz) receivers (ref., Fig. 21)

Fig. 21. Overall setup and obtaining of signals for MASW method

3) Harmonic wavelet analysis of waves (HWAW) method

- Use simply impact source (sledge hammer) and two geophone (1 or 4.5 Hz)

receivers

- Perform with only 2 m receiver space and 4 m source offset from near receiver

(ref., Fig. 22)



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Time-Frequency AnalysisTime-domain Signals

1 2

Determine Emax Points

3

Signal #1

Signal #2

Signal #1 Signal #2

Emax Points

Determine Phase Delay Time

tg2

0 10000.00E+0

4.00E-13

8.00E-13

Time

Mag

nitu

de

t g 2

2 n d Receiver

tg1 1000 0

0 . 0 0 E + 0

4 . 0 0 E - 1 3

8 . 0 0 E - 1 3

Time

Mag

nitu

de

t g 1

1 s t Receiver4 5

0100200300400500600700800

0 20 40 60 80 100Frequency (Hz)

Phas

e Ve

loci

ty (m

/s)

tg1

θ 1

− 180 °

180 °

2 5 0 3 5 0

Phas

e An

gle

Time(*10-4 sec)

tL tRgt 2

Phas

e An

gle

Time(*10-4 sec)

θ1

- 180 °

180 °

tph2

tph1

3 0 0 4 0 0

Experimental Dispersion curve Fig. 22. Determination of experimental dispersion curve by HWAW method

Evaluation of Representative VS profile

- Deduce VS profile from ground free surface to bedrock depth based on several

types of filed seismic tests

- Consider different reliability of test results according to site conditions and test

methods

- Need to combine results of each test properly (ref., Fig. 23)

- Evaluation of representative VS profile considering reliability region



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0

5

10

15

20

25

30

0 300 600 900 1200Shear Wave Velocity, Vs (m/s)

Dep

th (m

)

Downhole

Uphole

Inhole

Representative Vs

Fig. 23. Typical example of evaluation of representative VS profile

References

Mayne, P. W., Christopher, B. R., and DeJong, J., 2001, Manual on Subsurface

Investigations: Geotechnical Site Characterization, National Highway Institute Publication

No. FHWA NHI-01-031, Federal Highway Administration, Wahsington, D.C., 2001.

Schneider, J. A., Mayne, P. W., and Rix, G. J., 2001, “Geotechnical site characterization in

the greater Memphis area using cone penetration tests,” Engineering Geology, Vol. 62,

pp. 169-184.

evaluation of dynamic soil properties

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