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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
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)
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
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
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)
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
South Ramp
North Ramp
WHB Pad Area
Future Emplacement
Area
N
SASW Testing at
Yucca Mountain
SiteTunnels
~
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.