Prof. Kenneth H. Stokoe, IIJennie C. and Milton T.

Graves Chair

Civil, Architectural and Environmental Engrg. Dept.

Univ. of Texas at Austin

Università di PisaMarch 12, 2008

The Increasing Role of Stress Wave Measurements in Solving

Geotechnical Engineering Problems

Outline

1. Brief Background• emphasis field measurements

2. Present a Number of Applications• static and dynamic problems

3. Show Importance of Field Seismic Measurements in Predicting the G – log γ and τ – γ Curves

4. Concluding Remarks

1. Soil Profile 2. Field: Linear Vs (and Vp)

3. Lab: Linear and Nonlinear G and D

60

40

20

0

Dep

th, m

4503001500Vs, m/s

Sand(SP)

Clay(CH)

Silt(ML)

Sand(SW)

Clay(CL)

G,MPa

Gmax

120

0

Dmin

D,%

16

00.001 0.1

Shear Strain, γ , %

0.001 0.1

1. Background: Role of Stress Wave Measurements

Gmax = ρvs2

Source Point 1 Point 2

Stress Wave (Seismic)Measurements in the Field

Objective: measure time, t, for a given stress wave to propagate a givendistance, d ... then velocity = d/t

d

Key characteristic: small-strain (linear) measurements

Field Measurements withCompression (P) and Shear (S) Waves

Gmax = VS2γt

g

Mmax = Vp2γt

g

Small-StrainModulus

Distortion

Vp

VS

Wave Velocity

ParticleMotion

WaveType

P

S

00 0.05 0.10 0.15

Shear Strain, γ (%)

Shear Stress,

τ (kPa)

Gmax

Small-strainwave propagation: Gmax = VS

2

Small-Strain Seismic Measurements

γ τ

τInitial Loading Curve

γtg

1. Crosshole Test

2. Downhole Test

First “Geotechnical” Field Seismic Methods (1970s)

DirectP and S Waves

Modified Seismic Method (1980s)

SCPT adapted from 1970s

Downhole Test

1. Seismic Cone Penetrometer Test (SCPT)

Direct S Wave

2. P-S Suspension Logger

1. Surface Wave (SASW) Test

*

Recent Field Methods (1990s)

Direct P and S Waves

MeasureRayleigh

(R) Waves

2. Increasing the Role in Solving Geotechnical Engineering Problems

Case Histories and Applications

• static conditions

• dynamic conditions

Solutions - Static Conditions1. Static Loading

• footing settlements• retaining wall movements

2. Site Characterization• layering, ground water table, etc.• underground cavity detection• tunnel investigations• pavement studies

3. Process Monitoring• grouting evaluations• ground improvement studies• areas of deterioration

4.Link Between Field and Lab

Static Application #1:Predicting Footing Settlements

Footing

Load

Settlement

0 Time

Soil

Static Loading

Settlement

Load Cell

Static Vertical Load

300 mm Reinforced Concrete Footing

900 mm

3-Point Loading Frame

Nonplastic Silt (ML):γt = 121.5 pcf Corrected SPT = 17 bpf

(19.1 kN/m3) Shear wave velocity: Vs = 600 fps (183 m/s)

Soil, Footing and Loading Arrangement

Telltales Beneath the Footing

25 10 25 cm Displacement Transducers

75

3015 cm

Telltales

Reinforced Concrete Footing

45

Reference Frame

Loading Footing with T-Rex

Typical Settlement Measurements: Top of Footing Near the Center

-0.030

-0.025

-0.020

-0.015

-0.010

-0.005

0

Set

tlem

ent,

in.

2500020000150001000050000Load, lb

-0.060

-0.040

-0.020

0

Settlem

ent, cm

100806040200Load, kN

Scatter caused by vibrations induced from loading apparatus and truck traffic.

Typical Settlement Measurements: Top of Footing Near the Center

-0.030

-0.025

-0.020

-0.015

-0.010

-0.005

0

Set

tlem

ent,

in.

2500020000150001000050000Load, lb

-0.060

-0.040

-0.020

0

Settlem

ent, cm

100806040200Load, kN

“Smoothed”Load - Settlement

Curve

v

Typical Settlement Measurements with Telltales: 15 cm Beneath

Center of Footing

Small permanent deformation, but within precision of instrumentation.

-0.030

-0.025

-0.020

-0.015

-0.010

-0.005

0

Set

tlem

ent,

in.

2500020000150001000050000Load, lb

-0.060

-0.040

-0.020

0

Settlem

ent, cm

100806040200Load, kN

Comparison of Measured and Predicted Settlements

8.0

6.0

4.0

2.0

0.0D

epth

bel

ow

Fo

oti

ng

, ft

0.50.40.30.20.10.0Settlement, in.

2.0

1.5

1.0

0.5

0.0 Dep

th b

elow

Fo

otin

g, m

1.21.00.80.60.40.20.0Settlement, cm

Average Field MeasurementsSchmertmann (1970) - SPT DataSchmertmann (1970) - Seismic DataFinite Element Method - Seismic DataBurland and Burbigde (1985)

Static Application #2: Tunnel Investigation

ConcreteLiner

Grout

Rock

tconcrete

tgrout

Some Questions

1. Quality of concrete liner?2. Thickness of concrete liner?3. Quality of grout in crown?4. Thickness of grout in crown?5. Any voids behind liner?6. Stiffness of rock behind liner?

(Answered all Questions)

Rock

Grout

Liner

“Crown”InvestigationPlane

SpringlineInvestigationPlane

SourceReceivers

SASW Array Axes

SASW Testing Arrangement andPlanes of Investigation

Conducting SASW Tests

Small Hammer

Accelerometers

0

2

4

6

80 1000 3000

Shear Wave Velocity, VS , m/sec2000 4000

Station 1(Springline)

Depth,m

Concrete Liner

Stiffer Rock

Interpreted VS Profile Behind Tunnel Wall at Springline

Results:1. high-quality

concrete2. thickness:

~ 0.3 m3. no voids4. rock stiffer

than liner

Static Application #3: EvaluatingSoil Improvement at a Blast-

Densification Field Trial

BulldozerSource

Blasting at Loose Sand Site

t = 2 sec

t = 3 sec

t = 0 sec

t = 5 sec

Depth, m

12

6

3

0

9

240180120600Shear Wave Velocity, m/s

1 Day AfterBlasting

LooseSandLayer

BeforeBlasting

1 Day After Blasting

Question:Did test plan work?

Answer:No. Need to modify.

12

6

3

0

Depth, m

240180120600Shear Wave Velocity, m/s

9

BeforeBlasting 10 Months After

Blasting

LooseSandLayer

Comparison of Before and After States

Question:Did site improve with time?

Answer:Slightly, but still less than “before blasting”.

1. Machine-Foundation Design

2. Vibration-Isolation Barriers

3. Earthquake Engineering• site response, soil-structure

interaction, liquefaction, etc.

4. Link Between Field and Lab

Solutions - Dynamic Conditions

Dynamic Application #1: Predict Ground Motions During Earthquake

Shaking

BEDROCK

SOIL LAYER 1

SOIL LAYER 2

SOIL LAYER ..

SOIL LAYER n

-0.5

0.0

0.5

6050403020100

Time, sec

Time, sec

-0.5

0.0

0.5

6050403020100

uground

..

ubedrock

..

Ground Accel,

u, g..

Bedrock Accel,

u, g..

Required: Dynamic Stress-Strain Curves in Shear in the Field

BEDROCK

SOIL LAYER 1

SOIL LAYER 2

SOIL LAYER n

uground

..

ubedrock

..

τ

τ

γ

γ

0.2%

0.02%

7 MPa

56 MPa

G

GSOIL LAYER ..

Example Site

La Cienega Overpass Bridge

1994 Northridge Earthquake (Mw = 6.7)

Epicentral Distance about 28 km

Peak Shearing Strain, γ , less than 0.20%

Resolution Of Site Response Issues in the Northridge Earthquake (ROSRINE)

Deep Soil Deposit (~ 300 m)

1994 Northridge Earthquake:Site of La Cienega Overpass Bridge

1994 Northridge Earthquake:La Cienega Overpass Bridge

150

100

50

0

Depth,m

0.200.150.100.050.00Shearing Strain, γ , %

Peak Shearing Strains: La Cienega

Mean

Mean - σ

Mean + σ

from Dr. Walt Silva, Pacific Engineering and Analysis

Soil

FixedBase

Accelerometer

Coil Support System

Flu

id

Flu

id

Top Cap

DriveCoil

Magnet

Torsional Resonant Column

Torsional Excitation

10-5 10 010 -110 -4 10 -3 10 -2

Shearing Strain, γ, %

0

Lab Curve

La CienegaDepth = 185 mSilty Sand (SM)σo' = 25 atm

2000

1500

500

Shear Modulus,

G, ksf1000

EQ

Resonant Column Test of Intact Soil Specimen

10-5 10 010 -110 -4 10 -3 10 -2

Shearing Strain, γ, %

0

Field

Lab Curve

La CienegaDepth = 185 mSilty Sand (SM)σo' = 25 atm

2000

1500

500

Shear Modulus,

G, ksf1000

EQ

Comparison of Field and Laboratory Gmax Values

Gmax = VS2

γtg

Field

Lab Curve

10010-110-5 10-4 10-3 10-2

Shearing Strain, γ, %

2000

1500

500

0

Shear Modulus,

G, ksf 1000

Estimated Field Curve

Estimating the FieldG – log γ Relationship (Soil)

EQ

Subtitle: The overwhelming need for in-situ seismic measurements in nonlinear static and dynamic analyses.

Key: Seismic measurements link field and laboratory tests.

General Applications (Static and Dynamic): Impact of “Sample Disturbance” on G - log γ and

τ - γ Curves

1000

800

600

400

200

0

1.21.00.80.60.40.20.0

(Trend Line)

(Range)

No. of Specimens = 63

Shear Wave Velocity Ratio, Vs, lab/Vs, field

In-S

itu

Sh

ear

Wav

e V

elo

city

, Vs,

fie

ld,m

/s

Relationship Between Field and Laboratory Vs Values

2500

2000

1500

1000

500

0

Shear Modulus, G, MPa

Shearing Strain, γ, %

Lab Curve

Estimated Field CurveField

í

10-5 10-4 10-3 10-2 10-1 100

“Actual” Field G-log γ Relationship Compared to Potential Range

PotentialRange(no Vs, field)

“Actual” Field τ−γ CurveCompared to Potential Range

5

4

3

2

1

0

ShearStress,

τ, MPa

1.00.80.60.40.20.0Shearing Strain, γ, %

Lab Curve

Estimated Field Curve

τ = G * γ PotentialRange(no Vs, field)

• Designated as first permanent geologic repository for high-level radioactive waste in U.S.

• DOE has been studying the site for more than 25 years

• UTexas is involved with field seismic tests:1. on top of the mountain, 2. in the exploratory tunnels, and 3. at the proposed site of the Waste

Handling Building (WHB).

Dynamic Application #2: Yucca Mountain Site, Nevada

General Location of Yucca Mountain Site, Nevada

Nevada Test Site

Reno

SH95

IH80

SH95

Yucca Mountain Site(Area 25)

Las Vegas

N

Recent Testing: Yucca Mountain Site

Top of Yucca Mountain

1

2

3

Generalized Geologic Framework Model of Yucca Mountain Site

South Ramp

North Ramp

WHB Pad Area

Future Emplacement

Area

N

SASW Testing at

Yucca Mountain

SiteTunnels

~

Liquidator Working on Top of Yucca Mountain

Recording Surface Waves up to 1000 m Long

Liquidator

Source

Receiver #1

Receiver #2

Testing in Tunnel Beneath Mountain

0 5 10 15 20

0

100

200

300

400

500

600

No. of Profiles0 5 10 15 20

Dep

th (m

)

0.0 0.5 1.0

COV0.0 0.5 1.0

Shear Wave Velocity (m/sec)0 1000 2000 3000

Shear Wave Velocity (ft/sec)0 2000 4000 6000 8000 10000

Dep

th (

ft)

0

500

1000

1500

2000

19 SASW Vs Profiles Measured from the Ground SurfaceMedian16th and 84th Percentile

Repository Level

Statistical Analysis of 19 SASW VS Profiles around the Proposed Repository Area

N ≥ 3

σmean

COV =

0 2 4 6 8 10

0

100

200

300

400

500

600

No. of Profiles0 2 4 6 8 10

Dep

th (m

)

0.0 0.5 1.0

COV0.0 0.5 1.0

Shear Wave Velocity (m/sec)0 1000 2000 3000

Shear Wave Velocity (ft/sec)0 2000 4000 6000 8000 10000

Dep

th (

ft)

0

500

1000

1500

2000

SASW Vs ProfilesMedian

16th and 84th PercentileTptpmn (High Velocity Group from Tunnel)

Repository Level

Comparison of Stiffer VS Profiles Measured on the Surface and in the Tunnel

N ≥ 3 σmean

COV =

0 2 4 6 8 10

0

100

200

300

400

500

600

No. of Profiles0 2 4 6 8 10

Dep

th (m

)

0.0 0.5 1.0

COV0.0 0.5 1.0

Shear Wave Velocity (m/sec)0 1000 2000 3000

Shear Wave Velocity (ft/sec)0 2000 4000 6000 8000 10000

Dep

th (

ft)

0

500

1000

1500

2000

SASW Vs ProfilesMedian16th and 84th PercentileTptpmn (Low VelocityGroup from Tunnel)

Repository Level

N ≥ 3

Comparison of Softer VS Profiles Measured on the Surface and in the Tunnel

σmean

COV =

10-5 10 010 -110 -4 10 -3 10 -2

Shearing Strain, γ, %

0

Lab Curve

500

400

100

300

Resonant Column Test of Tuff Core

200

Yucca Mt.Depth 1000 ft~=Topopah Spring TuffTptpmn

600

Shear Modulus,

G, 1000 ksf

σo= 31 atm

10-5 10 010 -110 -4 10 -3 10 -2

Shearing Strain, γ, %

0

Lab Curve

500

400

100

300

Comparison of Field and Laboratory Gmax Values

200

Yucca Mt.Depth 1000 ft~=Topopah Spring TuffTptpmn

600

Gmax = VS2

γtg

Field

Shear Modulus,

G, 1000 ksf

10-5 10 010 -110 -4 10 -3 10 -2

Shearing Strain, γ, %

0

Lab Curve

500

400

100

Shear Modulus,

G, 1000 ksf300

Estimating the Field G – log γ Relationship (Rock)

200

Yucca Mt.Depth 1000 ft~=Topopah Spring TuffTptpmn

600

Field

Estimated Field Curve

Concluding Remarks

� Stress wave (seismic) measurements play an important role in geotechnical engineering.

� This role will continue to grow in solving static and dynamic problems.

� The growth will involve four areas: 1. education, 2. integration, 3. automation, and 4. innovation.

THANK YOU

National Science Foundation

Università di PisaProf. Diego Lo PrestiSupporting Organizations:

PEER Center at University of CaliforniaBechtel SAIC L.L.C.U.S. Department of Energy

United States Geological Survey