cone penetration test and liquefaction evaluation for
TRANSCRIPT
Monday, June 24, 2019 2:00-4:00 PM ET
TRANSPORTATION RESEARCH BOARD
requirements of the Registered Continuing Education Providers Program.
Credit earned on completion of this program will be reported to RCEP. A
certificate of completion will be issued to participants that have registered
and attended the entire session. As such, it does not include content that
may be deemed or construed to be an approval or endorsement by RCEP.
Purpose
To discuss the cone penetration test (CPT), which can provide data for investigating and characterizing site specific subsurface conditions.
Learning Objectives
At the end of this webinar, you will be able to:
• Describe CPT technology and how to apply it to design highway bridges
• Describe how to use CPT technology to investigate subsurface characterization on a highway bridge
• Describe how to use CPT technology to evaluate liquefaction on a highway bridge
CPT Technology Gerald Verbeek – Verbeek Management Services
The disclaimers
0
4
8
12
16
20
24
28
qt
u2
fs
Georgia Institute of Technology
Tom Casey
*10 -ton ne cone used for first 15.35 meters and the 15 -ton ne cone used for remainder of sounding
Alec McGillivray
Vs (m/s)
A =
0.66
GWT =
6
gtotal =
17.5
Depth
qc
Fs
U2
Incl
qt
qt
FR
U0
svo
svo'
Bq
(m)
(MPa)
(kPa)
(kPa)
Degrees
(MPa)
Bar
Final Evaluation
Georgia Institute of Technology
Tom Casey
*10 -ton ne cone used for first 15.35 meters and the 15 -ton ne cone used for remainder of sounding
Alec McGillivray
Vs (m/s)
A =
0.66
GWT =
6
gtotal =
17.5
Depth
qc
Fs
U2
Incl
qt
qt
FR
U0
svo
svo'
Bq
(m)
(MPa)
(kPa)
(kPa)
Degrees
(MPa)
Bar
Final Evaluation
Georgia Institute of Technology
Tom Casey
*10 -ton ne cone used for first 15.35 meters and the 15 -ton ne cone used for remainder of sounding
Alec McGillivray
Vs (m/s)
A =
0.66
GWT =
6
gtotal =
17.5
Depth
qc
Fs
U2
Incl
qt
qt
FR
U0
svo
svo'
Bq
(m)
(MPa)
(kPa)
(kPa)
Degrees
(MPa)
Bar
Final Evaluation
Depth (m)
Marriott, Memphis/TN
Electronic Steel Probes with 60° Apex Tip ASTM D5778 Procedures Hydraulic Push at 0.8 inch/s No Boring, No Samples, No Cuttings, No Spoil Continuous readings of stress, friction, pressure
What is CPT
5
Soil Behavior Type (Robertson et al., 1986; Robertson & Campanella, 1988) 1 – Sensitive fine grained 5 – Clayey silt to silty clay 9 – sand 2 – Organic material 6 – Sandy silt to silty sand 10 – Gravelly sand to sand 3 – Clay 7 – Silty sand to sandy silt 11 – Very stiff fine grained* 4 – Silty clay to clay 8 – Sand to silty sand 12 – Sand to clayey sand*
*Note: Overconsolidated or cemented
.
For site investigations CPT’s are usually carried out in combination with a few boreholes for soil sampling. Next to an almost continuous profile is speed another advantage. Per unit 200 to 300 meter of soil profile can be collected per day.
Reality – Aspect 2
9
Why not CPT (or so people claim) • It is supposedly a new method … or is it?
10
1932 -1934 Pieter Barentsen develops the first internationally recognized cone model for Cone Penetration Testing (CPT). All testing and production was performed at GMF Gouda. The Dutch Cone was born and also the first patent in CPT history, applied in 1934 and granted in 1938 to Goudsche Machinefabriek and Pieter Barentsen. GMF Gouda became the first manufacturer of CPT equipment on an industrial scale.
1959 GMF Gouda introduces the first hydraulic pushing rigs for 10 ton and later also 20 ton capacity setting a new standard for efficient CPT soundings.
1965 H.K.S. Begemann improved the Dutch cone and added an extra sliding shaft for measuring the sleeve friction, resulting in the Friction Jacket Cone, also known as Begemann Cone.
1971 After a period of testing, failing and improving the electric cone penetrometers with strain gauged measuring bodies become more reliable and popular.
One of the first CPT devices (around 1940)
Reality – Aspect 3 “New? It has always been there”
11
Reality – Aspect 3 “New? It has always been there”
12
Reality – Aspect 3 “New? It has always been there”
13
Hand operated 50 kN pusher installed on old army truck
Reality – Aspect 3 “New? It has always been there”
14
Reality – Aspect 3 “New? It has always been there”
15
16
and HMI screen (right)
• It is a supposedly a new method … or is it
• Not specified … but things are changing
• Too hard … or is it
17
• It is a supposedly a new method … or is it
• Not specified … but things are changing
• Too hard … or is it
• No samples …. why not
• It is a supposedly a new method … or is it
• Not specified … but things are changing
• Too hard … or is it
• No samples …. why not
19
CPT Technology Bridge Site Investigation
Sharid K. Amiri Caltrans
Highway Bridge- Subsurface Exploration
Subsurface explorations shall be performed to provide the information needed for the design and construction of foundations. The extent of exploration shall be based on variability in the subsurface conditions, structure type, and any project requirements that may affect the foundation design or construction. The exploration program should be extensive enough to reveal the nature and types of soil deposits and/or rock formations encountered, the engineering properties of the soils and/or rocks, the potential for liquefaction, and the groundwater conditions. The exploration program should be sufficient to identify and delineate problematic subsurface conditions such as karstic formations, mined out areas, swelling/collapsing soils, existing fill or waste areas, etc. Ref: AASHTO Bridge Design Specification
Variability in Subsurface Conditions
7
• Highway Bridge- (Replacement)
• Vertical & Battered Piles • ( 2nd row) at the Abutments
Highway Bridge
Foundation- (Replacement)
• 24 inch Diameter Driven Pipe Piles at the Abutments & H Piles at the Bent
• Battered Piles Not Allowed
Battered Piles Not Allowed Due to Liquefaction Potential at the Bridge Site 12
Highway Bridge-
Original(1959) Subsurface
15
Investigation for Liquefaction
Sharid K. Amiri Caltrans
Canadian Geotechnical Journal
0 100 200 300 400 500 600 700 800 900
Cone Tip Resistance (tsf) vs Depth (ft)
4
5
0 1 2 3 4 5 6 7 8 9
Cone Friction Ratio vs Depth (ft)
6
Effective Friction Angle (Kulhawy and Mayne, 1990)
= 17.6 + 11 log (Qtn)
Qtn= Normalized Cone Tip Resistance, where Qtn = [( qt /σatm)/(σ
v0 /σatm)]0.5
v0 : Vertical effective stress
Undrained Shear Strength ( Robertson and Cabal, 2015)
Su = ( qt –σv0)/Nkt qt = Cone tip resistance σv0= Vertical total stress Nkt = Empirical cone factor
Guide to Cone Penetration Testing for Geotechnical Engineering
8
Liquefied Soil Residual Strength ( Kramer and Wang, 2015)
Sr (psf) = 2116.exp[{-8.444+0.109(N1)60 +5.379(σ’vo/2116 )0.1}]
Empirical Model for Estimation of the Residual Strength of Liquefied Soil, Journal of Geotechnical and Geoenvironmental
Engineering
9
SPT (N1) relationship with CPT
Evaluation of Soil Properties for Seismic Stability Analyses of Slopes, Martin. G.R., 1992
10
Guide to Cone Penetration Testing For Geotechnical Engineering, Robertson, P.K. & Cabal, K.L., 2015
11
18
CPT derived N60 can be compared with the actual N60
SPT based liquefaction is compared with the CPT based liquefaction
Laboratory samples for liquefaction analysis are taken by targeting specific layers
Very important for creating, calibrating and building on a CPT based data base
CPT-Boring Calibration- Side by Side Per Bridge Structure
19
20
21
Depth (ft) vs Pore Pressure ( tsf)
22
Foundation
23
CPT: a very powerful tool for site investigation at sites prone to liquefaction
CPT : a very effective tool for site characterization at sites subject to liquefaction
It is essential to conduct a side by side CPT-Boring for bridge foundation subject to liquefaction
It is essential that adequate investigation is performed to capture spatial variability for liquefaction, which makes CPT an ideal tool
CPT offers superior data for bridge foundation design subject to liquefaction
CPT- Site
Investigation &Site
Testing Gerald Verbeek – Verbeek Management Services
What is SCPT
Seismic sensor
Seismic source
Shear wave
You push the cone with a seismic adapter into the soil; at each test depth the seismic source is triggered and the response of the seismic sensor is recorded.
Building Code requires estimation of Vs
National Earthquake Hazards Reduction Program-Uniform Building Code (NEHRP-UBC)
Site Class Description Mean Shear Wave Velocity to 30m (VS
30) m/sec
SA or A Hard Rock > 1500 SB or B Firm to Hard Rock 760-1500 SC or C Very Dense Soil and Soft Rock 360-760 SD or D Stiff Soil Profile 180-360 SE or E Soft Soil (Clays) Profile < 180 SF or F Special Study Soils (e.g.,
liquefiable soils, sensitive clays, organic soils, soft clays > 36 m thick)
Why Near Surface Site Characterization?
3
Liquefaction Assessment (Vs is influenced by many of the variables that influence liquefaction, such as void ratio, soil density, confining stress, stress history, and geologic age)
Why Near Surface Site Characterization?
Analyses on the catastrophic liquefaction in Christchurch, New Zealand in 2010 and 2011 showed very clearly that near surface rather than deep liquefaction resulted in extensive foundation damage.
4
Why not SCPT (or so people claim) • It is a supposedly a new method … or is it
• Not specified … but things are changing
• Too hard … or is it
• No samples …. why not
• Boulders or debris … yes, that’s a problem
• Near surface estimates are difficult to obtain and subsequent interval velocity estimates are inaccurate … but only if you don’t test or analyze the data correctly
Interval Depth (m)
Arrival Time (ms)
0-0.5 28.00 0.5-2.5 27.46 2.5-3.5 33.51 3.5-4.5 43.09 4.5-5.5 51.40 5.5-6.5 58.54 6.5-7.5 66.23 7.5-8.5 70.84 8.5-9.5 75.83
5
SH-wave “point sources” should be utilized: • Source location can be quantified. • It is preferable to excite a small area so
that irregular and complex source waves are not generated.
• A point source mitigates the concern of proper coupling between the beam and the soil underneath along the entire length of the beam.
SCPT in the field
di, ti
di-1, ti-1
Seismic source
Relatively large radial sensor source offsets should be used: • This minimizes both the "rod" noise. • The near-field particle motions can be ignored.
The near-field terms tends to decay as 1/r2 where r is the distance from the source, while the far-field terms decay as 1/r due to geometrical spreading.
• It increases the characterization of the layer or depth under analysis due to the fact that the source wave refracts and travels within stratigraphic layers for a longer period of time
SCPT in the field
7
During data processing it is commonly assumed that seismic ways travel in straight lines. This straight ray geometry is only applicable if there is no radial seismic source offset, but that is not practical (e.g. rod noise). When there is an offset this geometry does not necessarily adhere to Fermat’s principle, which means that the raypath travels along the trajectory which requires minimum time between points.
SCPT Data Processing
Data processing requires Iterative Forward Modeling (IFM) that assumes: •Laterally homogeneous medium. •Refraction at layer boundaries (Snell’s Law). •Fermat’s principle of least time.
SCPT Data Processing
(%) SRA IFM
0 - 1.5 22.98 112 112 0 1.5 - 2.5 24.26 536 181 196 2.5 - 3.5 27.31 267 209 28 3.5 - 4.5 36.69 94 101 -7 4.5 - 5.5 40.70 230 214 7 5.5 - 6.5 44.54 246 232 6 6.5 - 7.5 52.12 126 128 -2 9
Possible Use of SCPT Data Analysis Results
10Liquefaction Potential Assessment
Sharid K. Amiri Caltrans
• Prestressed cast in place box girder
• Close-end cantilever seat type abutment 1
• Open-end seat type abutment 3
• 7 feet diameter round columns at the bent 2
• Proposed bridge deck : 130 feet wide & 472 feet long
3
• CPT cross sectional area: 1.55 inch2
• CPT cylindrical friction sleeve surface area: 23.25 inch2
• CPT penetration rate: 0.79 inch/sec
• CPT data recorded every 1.967 inch
• CPT truck : 25 ton
profile
0.00
20.00
40.00
60.00
80.00
100.00
120.00
0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.0 400.0 450.0 500.0
Cone tip resistance (tsf) vs Depth (ft)
5
0.00
20.00
40.00
60.00
80.00
100.00
120.00
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
6
Cone friction ratio (%) vs Depth (ft)
7
0.00
20.00
40.00
60.00
80.00
100.00
120.00
0 50 100 150 200 250 300
Q = (qc – σv0)/((σv0)n) n : 0. 5 (clean sand) to 1.0 (Clays)
8
0.00
20.00
40.00
60.00
80.00
100.00
120.00
F = (fs /(qc - σv0)) x 100%
9
I c= [(3.47- log Q)2 + (1.22+log F)2]0.5
0.00
20.00
40.00
60.00
80.00
100.00
120.00
10
Normalized cone penetration resistance vs Depth (ft)
qc1N= CQ(qc/Pa) CQ = (Pa/σ’
11
: kc profile
Kc= 1.0 for Ic ≤ 1.64 Kc= -0.403 Ic
4 + 5.581 Ic 3 - 21.63 Ic
2 + 33.75 Ic - 17.88 for Ic > 1.64
0.00
20.00
40.00
60.00
80.00
100.00
120.00
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00
12
(qc1N)cs = Kcqc1N
13
7.5 : CRR7.5 profile
Cyclic resistance ratio (for magnitude 7.5) vs Depth (ft)
If (qc1N)cs < 50 CRR7.5 = 0.833[(qc1N)cs/1000]+0.05 If 50≤ (qc1N)cs< 160 CRR7.5 = 93 [(qc1N)cs/1000]3 + 0.08
0.00
20.00
40.00
60.00
80.00
100.00
120.00
14
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
110.00
0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00
15
MSF: Idriss ( NCEER 1997)
16
CSR = 0.65 (amax/g)(σv0/σ’ v0)rd
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
110.00
0.30 0.32 0.34 0.36 0.38 0.40 0.42 0.44 0.46 0.48 0.50
17
FS = (CRR7.5/CSR)MSF
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
110.00
0.10 0.30 0.50 0.70 0.90 1.10 1.30 1.50 1.70 1.90 2.10 2.30 2.50 2.70 2.90
18
• Determine Ground Water Elevation :
( Design GW elevation may be different from the actual GW elevation encountered during the subsurface investigation)
• Identify the soil layer for quantitative liquefaction analysis
• Obtain the CPT data
• Evaluate soil unit weight
• Normalize cone penetration resistance
19
20
Analysis
• Evaluate liquefaction potential at the soil Layer: depth of 15.26 feet • Earthquake Magnitude, Peak Ground Acceleration at the site: • M : 7.0 • PGA : 0.6 • Design Ground water elevation: 0 feet ( depth: 15 feet)
• Obtain cone tip bearing and sleeve friction values from the CPT data:. • Cone Tip bearing: qc = 40.2 tsf (depth 15.26 feet)
& Cone sleeve friction: fs = 0.6 tsf
• Soil Unit Weight Determine soil unit weight = 120 pcf = 0.06 tcf
21
Ic = [(3.47 – log Q)2 + (1.22 + Log F)2]0.5 = 2.30
Where
and F = [fs/qc – σvo)] x 100% = 1.48 %
n : Exponent = 1.0 (clay)
First calculate Soil Behavior Index (Ic) with n=1 . If the calculated Ic is greater than 2.6, the soil behavior is clayey and is not liquefiable. If the calculated Ic is less than 2.6, the soil is most likely granular in nature and Q should be recalculated using an exponent, n = 0.5 .
22
Q = [(qc – σv0)/Pa][(Pa/σ vo)n] = 37.8 x1.07 = 40.48
n : Exponent = 0.5 (sand)
σv0 : Total Overburden Pressure = 15.26 x 0.06 = 0.92 tsf
σ vo : Effective Overburden Pressure = (15.26 -15) x (0.06 - 0.031) +
(15 x 0.06) = 0.91 tsf
23
Cone penetration resistance is corrected for overburden stress as follows:
qc1N = CQ (qc/Pa) in this case = 41.42
where
24
Calculate Clean Sand Equivalent Normalized Cone Penetration Resistance
correct the normalized penetration resistance, (qc1N), of sands with fines to an equivalent clean sand value, (qc1N )cs:
(qc1N )cs = Kcqc1N = 84.16
Where the CPT correction factor for grain characteristics, Kc , is defined by:
For Ic ≤ 1.64 Kc =1.0
For Ic > 1.64 Kc = -0.403 Ic 4 + 5.581 Ic
3 -21.63 Ic 2 + 33.75 Ic -17.88
In this case Ic = 2.3 and Kc = 2.03
25
If (qc1N )cs < 50 CRR7.5 = 0.833 [(qc1N )cs/1000]+0.05
If 50 ≤ (qc1N )cs < 160 CRR7.5 = 93 [(qc1N )cs/1000]3 +0.08 = 0.14
26
Where:
σo and σ’o are total and effective vertical overburden stresses, respectively. amax is peak horizontal acceleration (PGA) in g. rd is a stress reduction coefficient.
amax = 0.6g
Determine Stress Reduction Coefficient, rd. Depth (z) is 15.26’= 4.65 m rd=1.0-0.00765 · z
rd =1.0-0.00765 · 4.65 = 0.96
Mw = 7.0
= 1.19
Calculate the Factor of Safety against Liquefaction FS = (CRR7.5/CSR) x MSF
FS = (.14/.38) x 1.19 = .42
28
Consulting Engineering and Geology, [email protected]
• Sharid Amiri, California Department of Transportation, [email protected]
• Gerald Verbeek, Verbeek Management Services, [email protected]
(http://bit.ly/TRBcommittees) – Networking opportunities – May provide a path to become a Standing Committee
member • Sponsoring Committees: AFF50, AFS30 • For more information: www.mytrb.org
– Create your account – Update your profile
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• Must attend entire webinar (including Q&A) to receive credits
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intro
Slide Number 1
The Transportation Research Board has met the standards and requirements of the Registered Continuing Education Providers Program. Credit earned on completion of this program will be reported to RCEP. A certificate of completion will be issued to participants that have registered and attended the entire session. As such, it does not include content that may be deemed or construed to be an approval or endorsement by RCEP.
Slide Number 3
CPT Technology
CPT Technology
Slide Number 2
Slide Number 3
Slide Number 4
Slide Number 5
Slide Number 6
Slide Number 7
Slide Number 8
Slide Number 9
Slide Number 10
Part 5- CPT Based Liquefaction Evaluation at a Bridge Site
CPT Technology
TRANSPORTATION RESEARCH BOARD
requirements of the Registered Continuing Education Providers Program.
Credit earned on completion of this program will be reported to RCEP. A
certificate of completion will be issued to participants that have registered
and attended the entire session. As such, it does not include content that
may be deemed or construed to be an approval or endorsement by RCEP.
Purpose
To discuss the cone penetration test (CPT), which can provide data for investigating and characterizing site specific subsurface conditions.
Learning Objectives
At the end of this webinar, you will be able to:
• Describe CPT technology and how to apply it to design highway bridges
• Describe how to use CPT technology to investigate subsurface characterization on a highway bridge
• Describe how to use CPT technology to evaluate liquefaction on a highway bridge
CPT Technology Gerald Verbeek – Verbeek Management Services
The disclaimers
0
4
8
12
16
20
24
28
qt
u2
fs
Georgia Institute of Technology
Tom Casey
*10 -ton ne cone used for first 15.35 meters and the 15 -ton ne cone used for remainder of sounding
Alec McGillivray
Vs (m/s)
A =
0.66
GWT =
6
gtotal =
17.5
Depth
qc
Fs
U2
Incl
qt
qt
FR
U0
svo
svo'
Bq
(m)
(MPa)
(kPa)
(kPa)
Degrees
(MPa)
Bar
Final Evaluation
Georgia Institute of Technology
Tom Casey
*10 -ton ne cone used for first 15.35 meters and the 15 -ton ne cone used for remainder of sounding
Alec McGillivray
Vs (m/s)
A =
0.66
GWT =
6
gtotal =
17.5
Depth
qc
Fs
U2
Incl
qt
qt
FR
U0
svo
svo'
Bq
(m)
(MPa)
(kPa)
(kPa)
Degrees
(MPa)
Bar
Final Evaluation
Georgia Institute of Technology
Tom Casey
*10 -ton ne cone used for first 15.35 meters and the 15 -ton ne cone used for remainder of sounding
Alec McGillivray
Vs (m/s)
A =
0.66
GWT =
6
gtotal =
17.5
Depth
qc
Fs
U2
Incl
qt
qt
FR
U0
svo
svo'
Bq
(m)
(MPa)
(kPa)
(kPa)
Degrees
(MPa)
Bar
Final Evaluation
Depth (m)
Marriott, Memphis/TN
Electronic Steel Probes with 60° Apex Tip ASTM D5778 Procedures Hydraulic Push at 0.8 inch/s No Boring, No Samples, No Cuttings, No Spoil Continuous readings of stress, friction, pressure
What is CPT
5
Soil Behavior Type (Robertson et al., 1986; Robertson & Campanella, 1988) 1 – Sensitive fine grained 5 – Clayey silt to silty clay 9 – sand 2 – Organic material 6 – Sandy silt to silty sand 10 – Gravelly sand to sand 3 – Clay 7 – Silty sand to sandy silt 11 – Very stiff fine grained* 4 – Silty clay to clay 8 – Sand to silty sand 12 – Sand to clayey sand*
*Note: Overconsolidated or cemented
.
For site investigations CPT’s are usually carried out in combination with a few boreholes for soil sampling. Next to an almost continuous profile is speed another advantage. Per unit 200 to 300 meter of soil profile can be collected per day.
Reality – Aspect 2
9
Why not CPT (or so people claim) • It is supposedly a new method … or is it?
10
1932 -1934 Pieter Barentsen develops the first internationally recognized cone model for Cone Penetration Testing (CPT). All testing and production was performed at GMF Gouda. The Dutch Cone was born and also the first patent in CPT history, applied in 1934 and granted in 1938 to Goudsche Machinefabriek and Pieter Barentsen. GMF Gouda became the first manufacturer of CPT equipment on an industrial scale.
1959 GMF Gouda introduces the first hydraulic pushing rigs for 10 ton and later also 20 ton capacity setting a new standard for efficient CPT soundings.
1965 H.K.S. Begemann improved the Dutch cone and added an extra sliding shaft for measuring the sleeve friction, resulting in the Friction Jacket Cone, also known as Begemann Cone.
1971 After a period of testing, failing and improving the electric cone penetrometers with strain gauged measuring bodies become more reliable and popular.
One of the first CPT devices (around 1940)
Reality – Aspect 3 “New? It has always been there”
11
Reality – Aspect 3 “New? It has always been there”
12
Reality – Aspect 3 “New? It has always been there”
13
Hand operated 50 kN pusher installed on old army truck
Reality – Aspect 3 “New? It has always been there”
14
Reality – Aspect 3 “New? It has always been there”
15
16
and HMI screen (right)
• It is a supposedly a new method … or is it
• Not specified … but things are changing
• Too hard … or is it
17
• It is a supposedly a new method … or is it
• Not specified … but things are changing
• Too hard … or is it
• No samples …. why not
• It is a supposedly a new method … or is it
• Not specified … but things are changing
• Too hard … or is it
• No samples …. why not
19
CPT Technology Bridge Site Investigation
Sharid K. Amiri Caltrans
Highway Bridge- Subsurface Exploration
Subsurface explorations shall be performed to provide the information needed for the design and construction of foundations. The extent of exploration shall be based on variability in the subsurface conditions, structure type, and any project requirements that may affect the foundation design or construction. The exploration program should be extensive enough to reveal the nature and types of soil deposits and/or rock formations encountered, the engineering properties of the soils and/or rocks, the potential for liquefaction, and the groundwater conditions. The exploration program should be sufficient to identify and delineate problematic subsurface conditions such as karstic formations, mined out areas, swelling/collapsing soils, existing fill or waste areas, etc. Ref: AASHTO Bridge Design Specification
Variability in Subsurface Conditions
7
• Highway Bridge- (Replacement)
• Vertical & Battered Piles • ( 2nd row) at the Abutments
Highway Bridge
Foundation- (Replacement)
• 24 inch Diameter Driven Pipe Piles at the Abutments & H Piles at the Bent
• Battered Piles Not Allowed
Battered Piles Not Allowed Due to Liquefaction Potential at the Bridge Site 12
Highway Bridge-
Original(1959) Subsurface
15
Investigation for Liquefaction
Sharid K. Amiri Caltrans
Canadian Geotechnical Journal
0 100 200 300 400 500 600 700 800 900
Cone Tip Resistance (tsf) vs Depth (ft)
4
5
0 1 2 3 4 5 6 7 8 9
Cone Friction Ratio vs Depth (ft)
6
Effective Friction Angle (Kulhawy and Mayne, 1990)
= 17.6 + 11 log (Qtn)
Qtn= Normalized Cone Tip Resistance, where Qtn = [( qt /σatm)/(σ
v0 /σatm)]0.5
v0 : Vertical effective stress
Undrained Shear Strength ( Robertson and Cabal, 2015)
Su = ( qt –σv0)/Nkt qt = Cone tip resistance σv0= Vertical total stress Nkt = Empirical cone factor
Guide to Cone Penetration Testing for Geotechnical Engineering
8
Liquefied Soil Residual Strength ( Kramer and Wang, 2015)
Sr (psf) = 2116.exp[{-8.444+0.109(N1)60 +5.379(σ’vo/2116 )0.1}]
Empirical Model for Estimation of the Residual Strength of Liquefied Soil, Journal of Geotechnical and Geoenvironmental
Engineering
9
SPT (N1) relationship with CPT
Evaluation of Soil Properties for Seismic Stability Analyses of Slopes, Martin. G.R., 1992
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Guide to Cone Penetration Testing For Geotechnical Engineering, Robertson, P.K. & Cabal, K.L., 2015
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CPT derived N60 can be compared with the actual N60
SPT based liquefaction is compared with the CPT based liquefaction
Laboratory samples for liquefaction analysis are taken by targeting specific layers
Very important for creating, calibrating and building on a CPT based data base
CPT-Boring Calibration- Side by Side Per Bridge Structure
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Depth (ft) vs Pore Pressure ( tsf)
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Foundation
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CPT: a very powerful tool for site investigation at sites prone to liquefaction
CPT : a very effective tool for site characterization at sites subject to liquefaction
It is essential to conduct a side by side CPT-Boring for bridge foundation subject to liquefaction
It is essential that adequate investigation is performed to capture spatial variability for liquefaction, which makes CPT an ideal tool
CPT offers superior data for bridge foundation design subject to liquefaction
CPT- Site
Investigation &Site
Testing Gerald Verbeek – Verbeek Management Services
What is SCPT
Seismic sensor
Seismic source
Shear wave
You push the cone with a seismic adapter into the soil; at each test depth the seismic source is triggered and the response of the seismic sensor is recorded.
Building Code requires estimation of Vs
National Earthquake Hazards Reduction Program-Uniform Building Code (NEHRP-UBC)
Site Class Description Mean Shear Wave Velocity to 30m (VS
30) m/sec
SA or A Hard Rock > 1500 SB or B Firm to Hard Rock 760-1500 SC or C Very Dense Soil and Soft Rock 360-760 SD or D Stiff Soil Profile 180-360 SE or E Soft Soil (Clays) Profile < 180 SF or F Special Study Soils (e.g.,
liquefiable soils, sensitive clays, organic soils, soft clays > 36 m thick)
Why Near Surface Site Characterization?
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Liquefaction Assessment (Vs is influenced by many of the variables that influence liquefaction, such as void ratio, soil density, confining stress, stress history, and geologic age)
Why Near Surface Site Characterization?
Analyses on the catastrophic liquefaction in Christchurch, New Zealand in 2010 and 2011 showed very clearly that near surface rather than deep liquefaction resulted in extensive foundation damage.
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Why not SCPT (or so people claim) • It is a supposedly a new method … or is it
• Not specified … but things are changing
• Too hard … or is it
• No samples …. why not
• Boulders or debris … yes, that’s a problem
• Near surface estimates are difficult to obtain and subsequent interval velocity estimates are inaccurate … but only if you don’t test or analyze the data correctly
Interval Depth (m)
Arrival Time (ms)
0-0.5 28.00 0.5-2.5 27.46 2.5-3.5 33.51 3.5-4.5 43.09 4.5-5.5 51.40 5.5-6.5 58.54 6.5-7.5 66.23 7.5-8.5 70.84 8.5-9.5 75.83
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SH-wave “point sources” should be utilized: • Source location can be quantified. • It is preferable to excite a small area so
that irregular and complex source waves are not generated.
• A point source mitigates the concern of proper coupling between the beam and the soil underneath along the entire length of the beam.
SCPT in the field
di, ti
di-1, ti-1
Seismic source
Relatively large radial sensor source offsets should be used: • This minimizes both the "rod" noise. • The near-field particle motions can be ignored.
The near-field terms tends to decay as 1/r2 where r is the distance from the source, while the far-field terms decay as 1/r due to geometrical spreading.
• It increases the characterization of the layer or depth under analysis due to the fact that the source wave refracts and travels within stratigraphic layers for a longer period of time
SCPT in the field
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During data processing it is commonly assumed that seismic ways travel in straight lines. This straight ray geometry is only applicable if there is no radial seismic source offset, but that is not practical (e.g. rod noise). When there is an offset this geometry does not necessarily adhere to Fermat’s principle, which means that the raypath travels along the trajectory which requires minimum time between points.
SCPT Data Processing
Data processing requires Iterative Forward Modeling (IFM) that assumes: •Laterally homogeneous medium. •Refraction at layer boundaries (Snell’s Law). •Fermat’s principle of least time.
SCPT Data Processing
(%) SRA IFM
0 - 1.5 22.98 112 112 0 1.5 - 2.5 24.26 536 181 196 2.5 - 3.5 27.31 267 209 28 3.5 - 4.5 36.69 94 101 -7 4.5 - 5.5 40.70 230 214 7 5.5 - 6.5 44.54 246 232 6 6.5 - 7.5 52.12 126 128 -2 9
Possible Use of SCPT Data Analysis Results
10Liquefaction Potential Assessment
Sharid K. Amiri Caltrans
• Prestressed cast in place box girder
• Close-end cantilever seat type abutment 1
• Open-end seat type abutment 3
• 7 feet diameter round columns at the bent 2
• Proposed bridge deck : 130 feet wide & 472 feet long
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• CPT cross sectional area: 1.55 inch2
• CPT cylindrical friction sleeve surface area: 23.25 inch2
• CPT penetration rate: 0.79 inch/sec
• CPT data recorded every 1.967 inch
• CPT truck : 25 ton
profile
0.00
20.00
40.00
60.00
80.00
100.00
120.00
0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.0 400.0 450.0 500.0
Cone tip resistance (tsf) vs Depth (ft)
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0.00
20.00
40.00
60.00
80.00
100.00
120.00
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
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Cone friction ratio (%) vs Depth (ft)
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0.00
20.00
40.00
60.00
80.00
100.00
120.00
0 50 100 150 200 250 300
Q = (qc – σv0)/((σv0)n) n : 0. 5 (clean sand) to 1.0 (Clays)
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0.00
20.00
40.00
60.00
80.00
100.00
120.00
F = (fs /(qc - σv0)) x 100%
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I c= [(3.47- log Q)2 + (1.22+log F)2]0.5
0.00
20.00
40.00
60.00
80.00
100.00
120.00
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Normalized cone penetration resistance vs Depth (ft)
qc1N= CQ(qc/Pa) CQ = (Pa/σ’
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: kc profile
Kc= 1.0 for Ic ≤ 1.64 Kc= -0.403 Ic
4 + 5.581 Ic 3 - 21.63 Ic
2 + 33.75 Ic - 17.88 for Ic > 1.64
0.00
20.00
40.00
60.00
80.00
100.00
120.00
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00
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(qc1N)cs = Kcqc1N
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7.5 : CRR7.5 profile
Cyclic resistance ratio (for magnitude 7.5) vs Depth (ft)
If (qc1N)cs < 50 CRR7.5 = 0.833[(qc1N)cs/1000]+0.05 If 50≤ (qc1N)cs< 160 CRR7.5 = 93 [(qc1N)cs/1000]3 + 0.08
0.00
20.00
40.00
60.00
80.00
100.00
120.00
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0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
110.00
0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00
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MSF: Idriss ( NCEER 1997)
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CSR = 0.65 (amax/g)(σv0/σ’ v0)rd
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
110.00
0.30 0.32 0.34 0.36 0.38 0.40 0.42 0.44 0.46 0.48 0.50
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FS = (CRR7.5/CSR)MSF
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
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110.00
0.10 0.30 0.50 0.70 0.90 1.10 1.30 1.50 1.70 1.90 2.10 2.30 2.50 2.70 2.90
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• Determine Ground Water Elevation :
( Design GW elevation may be different from the actual GW elevation encountered during the subsurface investigation)
• Identify the soil layer for quantitative liquefaction analysis
• Obtain the CPT data
• Evaluate soil unit weight
• Normalize cone penetration resistance
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Analysis
• Evaluate liquefaction potential at the soil Layer: depth of 15.26 feet • Earthquake Magnitude, Peak Ground Acceleration at the site: • M : 7.0 • PGA : 0.6 • Design Ground water elevation: 0 feet ( depth: 15 feet)
• Obtain cone tip bearing and sleeve friction values from the CPT data:. • Cone Tip bearing: qc = 40.2 tsf (depth 15.26 feet)
& Cone sleeve friction: fs = 0.6 tsf
• Soil Unit Weight Determine soil unit weight = 120 pcf = 0.06 tcf
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Ic = [(3.47 – log Q)2 + (1.22 + Log F)2]0.5 = 2.30
Where
and F = [fs/qc – σvo)] x 100% = 1.48 %
n : Exponent = 1.0 (clay)
First calculate Soil Behavior Index (Ic) with n=1 . If the calculated Ic is greater than 2.6, the soil behavior is clayey and is not liquefiable. If the calculated Ic is less than 2.6, the soil is most likely granular in nature and Q should be recalculated using an exponent, n = 0.5 .
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Q = [(qc – σv0)/Pa][(Pa/σ vo)n] = 37.8 x1.07 = 40.48
n : Exponent = 0.5 (sand)
σv0 : Total Overburden Pressure = 15.26 x 0.06 = 0.92 tsf
σ vo : Effective Overburden Pressure = (15.26 -15) x (0.06 - 0.031) +
(15 x 0.06) = 0.91 tsf
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Cone penetration resistance is corrected for overburden stress as follows:
qc1N = CQ (qc/Pa) in this case = 41.42
where
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Calculate Clean Sand Equivalent Normalized Cone Penetration Resistance
correct the normalized penetration resistance, (qc1N), of sands with fines to an equivalent clean sand value, (qc1N )cs:
(qc1N )cs = Kcqc1N = 84.16
Where the CPT correction factor for grain characteristics, Kc , is defined by:
For Ic ≤ 1.64 Kc =1.0
For Ic > 1.64 Kc = -0.403 Ic 4 + 5.581 Ic
3 -21.63 Ic 2 + 33.75 Ic -17.88
In this case Ic = 2.3 and Kc = 2.03
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If (qc1N )cs < 50 CRR7.5 = 0.833 [(qc1N )cs/1000]+0.05
If 50 ≤ (qc1N )cs < 160 CRR7.5 = 93 [(qc1N )cs/1000]3 +0.08 = 0.14
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Where:
σo and σ’o are total and effective vertical overburden stresses, respectively. amax is peak horizontal acceleration (PGA) in g. rd is a stress reduction coefficient.
amax = 0.6g
Determine Stress Reduction Coefficient, rd. Depth (z) is 15.26’= 4.65 m rd=1.0-0.00765 · z
rd =1.0-0.00765 · 4.65 = 0.96
Mw = 7.0
= 1.19
Calculate the Factor of Safety against Liquefaction FS = (CRR7.5/CSR) x MSF
FS = (.14/.38) x 1.19 = .42
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Consulting Engineering and Geology, [email protected]
• Sharid Amiri, California Department of Transportation, [email protected]
• Gerald Verbeek, Verbeek Management Services, [email protected]
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intro
Slide Number 1
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CPT Technology
CPT Technology
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Part 5- CPT Based Liquefaction Evaluation at a Bridge Site
CPT Technology