Some Recent Advances in In Situ
Measurement of Seismic Wave Velocity
Dr. Dennis R. Hiltunen
Associate Professor of Civil Engineering
Penn State University
November 10, 2003
Topics
!Tomography and evaluation of spatial
variation
!Liquefaction evaluation
!Permanently installed, remotely operated
test arrays
Site Characterization Needs
!Detailed characterization of foundation
conditions
!Detailed characterization of physical
properties of tailings materials
!Characterization of seismic hazards, e.g.,
ground motions, liquefaction evaluation
Introduction
! Seismic wave propagation methods highly
developed and accepted as engineering tool
! Borehole methods are nondestructive
! Surface methods non-intrusive and nondestructive
Computer
Spectrum Analyzer
C1 C2
Source
CL
Vertical
Receiver
Vertical
Receiver
X/2
S
X (Variable)
Introduction
! Fundamental: produce elastic modulus via the relationship between modulus and propagation velocity
! Other parameters also possible: coefficient of lateral
earth pressure, Poisson’s ratio
! Wide application: directly in design, quality control
measure during construction, and diagnostic
assessor after construction
The SASW Method
! SASW = Spectral Analysis of Surface Waves
! Nondestructive, no boreholes
! Based on Rayleigh (surface) waves
! Determines detailed shear modulus versus depth
profile of material
! Wide range of successful applications
Spectral Analysis of Surface Waves
Computer & Spectrum
Analyzer
Source
Geophones
X
X
X = 4, 6, 8, 12, 16 ft….
Power
Source
Equipment: Sources
Equipment: Sources
Equipment: Receivers
Composite Site Profile
Standard Penetration
Resistance
(SPT N-Value)
Shear Wave Velocity (ft/s)
0
500
1000
1500
0
2000
2500
0
0
10 20 30 40 50 60
8
5
Soil Profile
Clayey Sand
5
21
27
10
10
19
Depth (ft)
12
15
15
10
9
20
Sand
20
21
19
25
25
20
Clay assumed to
continue to ~200'
30
30
45
35
35
SASW
Seismic Crosshole Test
!In situ, borehole test method from which a
detailed seismic wave velocity profile can
be determined
!Seismic wave velocity determined via
travel time between boreholes a known
distance apart
!Applicable to wide range of engineering
materials: soil, aggregates, PCC, ACC
Crosshole Schematic
SH Wave
SV Crosshole Test
SV Source
3-D Receiver
Response (volts)
Response (volts)
SV Time Records
10
0
Trigger
-10
-20
0
0.02
0.03
0.04
2.E-02
1.E-02
5.E-03
0.E+00
-5.E-03
-1.E-02
0.05
0.06
0.07
0.08
0.09
0.1
1st Receiver
0
Response (volts)
0.01
0 01
0 02
0 03
0 06
0 07
0 08
0 09
01
∆T =
Interval
Travel
Time
0 04
0 05
0.04
0.05
4.E-04
2.E-04
0.E+00
2nd Receiver
-2.E-04
-4.E-04
0
0.01
0.02
0.03
T ime (sec)
0.06
0.07
0.08
0.09
0.1
Crosshole Schematic
SH Source: Mach 2
ODOT II-70
Standard Penetration
Resistance
(SPT N-Value)
Shear Wave Velocity (ft/s)
0
500
1000
0
1500
2000
Soil Profile
2500
0
0
10 20 30 40 50 60
Fill
5
5
17
10
10
12
10
15
Clay
15
4
Depth (ft)
20
20
11
25
Sand
17
30
11
35
Clay
25
30
35
27
Sand
40
40
51
45
45
Shale
50
50
SV
SH
Applications
! Site characterization and foundation design for
vibration-sensitive equipment: glass fibers, MRI,
automobile components
! Earthquake liquefaction assessment: Vincent
Thomas Bridge, VICC mine tailings impoundment
Applications
! Site characterization for hazardous waste landfills:
Ford Motor Co., Environmental Quality Corporation
! Assessment of soil/site improvement: DC Metro
Subway, Bryce Jordon Center
! Characterization of highway and airfield sites: I-99, I70, Pensacola NAS, Sheppard AFB, Selfridge ANG
Engineering Geophysics
!Use methods adapted from seismological
and petroleum industries for characterization of shallow subsurface ground
conditions
!Methods are analogous to medical
techniques, e.g., X-ray, CAT scan, MRI
!Enables “seeing” between boreholes or from
instruments along the ground surface
Medical Techniques
CAT scan of human chest
Engineering Geophysics
!Do not “touch” actual material, but
determine significant engineering
parameters from geophysical measurements
!Parameters such as seismic wave velocity
and electrical resistivity are highly
determined by material type and condition
!Thus, can infer subsurface characteristics
without actually touching material
Geophysical Characterization of
Bridge Foundation Sites in Karst
! Current site investigation practices for bridge
foundations are inadequate
! Bridges in PA are often founded on piles or other
deep foundations
! Highly variable subsurface conditions result in great
uncertainty in deep foundation design
Crosshole Test Results
10 ft
01
01
02
02
03
03
04
04
05
05
06
06
07
07
08
08
09
09
10
10
11
11
12
12
13
13
14
14
15
15
16
16
Crosshole Ray Shooting
30 ft
V1=1000 ft/sec
V2=7000 ft/sec
V1=1000 ft/sec
V2=3000 ft/sec
V3=5000 ft/sec
V4=7000 ft/sec
P-Wave Tomogram
Structure 318, Abut 1, PP-Wave
Structure 318, Abut 1, SVSV-Wave
Seismic Refraction Test
!Measures first arrival times of seismic
waves (P-waves) from the surface
!Arrival times can be used to determine
subsurface layer velocity and layer
interface structure
!Numerous CE applications
- profiling top of bedrock
- determining depth to bedrock
Seismic Refraction Test
Structure 319, Abutment 1
Structure 319, Pier 2
Electrical Resistivity
!Electrical current is introduced into the
subsurface through two electrodes while the
voltage difference is measured with two
other electrodes
!Recent advances have made this method
more widely used
!Works well in karst terrane where there is a
striking contrast between the carbonate rock
and moist clayey soil overburden
Electrical Resistivity
Structure 318, Abutment 1
Resistivity Test #3
Soil Profile
Sandy Silt
with Clay
5
10
Depth (feet)
0
Sandy Clay/
Dolomite Frag.
South
North
T o pso il
-10
Silt with Sand
-20
Silt/Clay/
Dolomite Frag.
-30
20
Clayey Sand/
Dolomite Frag.
40
60
80
100
120
Silt/Sand/
Dolomite Frag.
200
100
50
25
12
0
Resistivity (Ohm-ft)
0
5
10
15
140
Distance (feet)
15
20
Soil Profile
20
25
Silt with
Dolomite Frag.
30
25
Dolomite
35
30
Dolomite
40
45
35
50
End of Boring at 39.0'
End of Boring at 51.0'
Structure 319, Pier 2
Resistivity Test #7
Soil Profile
Unsampled
5
Depth (feet)
0
Dolomite/Clay
West
East
Soil Profile
T o pso il
-10
0
5
-20
Silt/Sand/Clay
10
20
30
40
50
10
60
70
80
90
100
10
Distance (feet)
15
3200
1600
800
400
200
100
50
25
12
0
15
20
Resistivity (Ohm-feet)
Limestone
25
20
Limestone
30
25
35
40
30
End of Boring at 31'
End of Boring at 41'
Liquefaction Evaluation
Uses and Limitations
! Vs and liquefaction similarly influenced by same
factors, e.g., e, stress, age
! Fundamental mechanical property
! Measurements possible in hard-to-sample soils, e.g.,
gravels
! Can be determined without boreholes
! Usually measured for site response studies
! Same parameters can be measured in laboratory
! No samples, can miss thin layers, small strain
Vincent Thomas Bridge
Vincent Thomas Bridge
Test Site A
Shear Wave Velocity (fps)
0
200
400
0
5
Depth(ft)
10
15
20
25
30
35
SV
SH
600
800
Shear Wave Velocity
0.7
Cyclic Stress Ratio (CSR)
0.6
0.5
0.4
0.3
Liquefaction
0.2
No Liquefaction
0.1
0
50
75
100
125
150
175
200
225
Overburden Stress-Corrected Shear Wave Velocity, V s1 (m/s)
Mag 7.25
AV
AH
BV
BH
250
Coal Refuse Impoundment
Shear Wave Velocity Profile
Shear Wave Velocity (fps)
0
600
0
500
400
20
300
Depth (ft)
Phase Velocity (fps)
700
200
100
0
40
60
80
0
20
40
60
Frequency (Hz)
80
100
100
200
400
600
800
1000 1200
Permanent, Remotely Operated
Test Arrays
! Rapidly improving availability of advanced testing
hardware
! Wireless transducers, repeatable sources, PC-based
data loggers, satellite modems
! Instruments can be operated and monitored via web
! Passive installations: monitor critical response
parameters, e.g., deformation, pore water pressure
! Active installations: remotely determine important
physical property, e.g., shear wave velocity
Thank You!