Spatial Variability of CPT Data
and Soil Parameters at NGES, Texas A&M
Tip qt (MPa)
0
Fawad S. Niazi
5
10 15 20 25 0.0
Sleeve fs (MPa)
0.1
0
10
20
30
Depth (m)
Geosystems Engineering Division
Civil & Environmental Engineering
Georgia Institute of Technology
April 27, 2010
40
50
60
70
80
90
100
www.clu-in.org
Niazi et al. 2010
0.2
Pore
0.3 0
1
Scope of Study
• Spatial variability of CPT readings for horizontal & vertical
variability in soil profiles (all soundings, each 10 cm depth):

Mean, min, max

Moment statistics (variance, skewness, kurtosis)

Residuals of principal comp. analysis of CPT readings (space and
depth)

Test of normality (χ2 test)
• Comparison of measured and evaluated soil unit weight, gt

LS regression, correlation coefficient

LS, principal component and reduced major axis regression

Higher order regression and residuals analysis
2
Cone Penetration Test – a Hybrid Method
• Site characterization:

Conventional boring/sampling methods

Lab investigations on disturbed samples
• Cone penetration test:

Fast, economical, and continuous data

up to 4 separate readings in one sounding

Soil parameter interpretation
Vs
fs
u2
qc
qc, fs, u2, Vs
Ic, gt, OCR, p', Ko, su, ', DR, Gmax
3
Typical Cone Penetration Sounding
Tip qt (MPa)
0
5
10
15
20
Sleeve fs (MPa)
25 0.0
0.1
0.2
Shear Wave Vs (m/s)
Porewater u2 (MPa)
0.3 0
1
2
3
4
0
100 200 300 400 500
0
10
20
Depth (m)
30
VS
40
50
fs
60
70
u2
80
90
qt
100
4
National Geotechnical Experimentation Site
Riverside Campus, Texas A&M University
Geotechnical
Experimentation Site
College Station
Texas A&M University
Location of Clay and Sand Sites on
Riverside Campus, Texas A&M University
Sand Site
Clay Site
Field Investigations at NGES
Clay Site, Texas A&M University
N
13
18
22 30
31
32
20
6
14
15
16
17
28
19
29
21
33
23
24
25
26
3
5
7
8
2
9
15
11
12
27
15 m
Clay Control
CPT:
CPTu:
MCPT:
SCPT:
BH:
4
1
10 cm2 Cone Penetration Test
Piezocone Penetration Test
2 cm2 Mini Cone Penetration Test
15 cm2 Seismic Piezocone Penetration Test
Borehole
16
10
Legend
CPT
CPTu
MCPT
SCPT
BH
Testing Program
1997
1977 to 1995
• Twelve MCPT
• Nine CPT
• Six CPT
1995 to 1996
• Three SCPT
• Three CPTu
Horizontal Variability of Tip Resistance Profiles
0
-3
Depth (m)
-6
-9
-12
-15
Mean
+1 S.D.
-1 S.D.
-18
0
Critical χ2 Value = 11.08
3 6 9 12 15 18 -1 0 1 2 3 4 5 0 3 6 9 1215 18 0 20 40 60 80 100
Tip Resistance, qc (MPa)
Skewness
Kurtosis
Chi2 Value
Tip Resistance, qc (MPa)
Spatial Variability Trend of Tip Resistance Profiles
for 33 CPT Soundings
16
14
Spatial Variability Trend of Tip Resistance w.r.t Distance from Clay Control
12
10
8
6
Mean
+1 S.D.
-1 S.D.
4
2
0
Chi2 Value Kurtosis
Skewness
5
4
3
2
1
0
15
12
9
6
3
0
400
300
200
100
0
20
Critical χ2 Value = 11.08
30
40
50
Distance from Clay Control (m)
60
70
Horizontal Variability of Sleeve Friction Profiles
0
-3
Depth (m)
-6
-9
-12
-15
Mean
+1 S.D.
-1 S.D.
-18
0
0.2
0.4
Critical χ2 Value = 11.08
0.6
0.8
Sleeve Friction, fs (MPa)
1 -1 0 1 2 3 4 5 0 3 6 9 12 15 18 0 20 40 60 80100
Skewness
Kurtosis
Chi2 Values
Spatial Variability Trend of Sleeve Friction w.r.t Distance from Clay Control
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2.5
2
1.5
1
0.5
0
15
12
9
6
3
0
300
240
180
120
60
0
20
Mean
+1 S.D.
-1 S.D.
Chi2 Value
Kurtosis
Skewness
Sleeve Friction, fs (MPa)
Spatial Variability Trend of Sleeve Friction Profiles
for 33 CPT Soundings
Critical χ2 Value = 11.08
30
40
50
Distance from Clay Control (m)
60
70
Residuals of Principal Comp. Analysis of qt at 0.16 m
Hist. of Res. 0.16 m Depth Hist. of Res. 0.16 m Depth
8
8
7
7
6
6
5
5
4
4
3
3
2
2
1
1
0
0
-5
0
Synthetic
0
5 -5
-6
0
5
Actual
Reg. Residuals of Tip Resistance
Res. of PC Analysis Horiz. Var. at 0.16 m depth
Depth (m)
Frequency
-3
-9
3
2
-12
1
0
-1
-15
-2
Mean
+1 S.D.
-1 S.D.
-3
-4
-5
20
30
40
50
60
Distance from clay control (meters)
70
Critical χ2 Value = 11.08
-18
0 0 31 26 3 4
9 5120 3156 18
-1
9 1215 18 0 20 40 60 80 100
Tip
Resistance, qc (MPa)
Skewness
Kurtosis
Chi2 Value
Residuals of Principal Comp. Analysis of qt at 10.56 m
Hist. of Res. 10.56 m Depth
5
Hist. of Res. 10.56 m Depth
7
0
6
4
Frequency
5
3
-3
4
3
2
-6
2
1
Regression Residuals of Tip Resistance
0
-2
0
0
2
-2
0
2
Synthetic
Actual
Res. of PC Analysis Horiz. Var. at 10.56 m depth
1.5
Depth (m)
1
-9
1
-12
0.5
0
-15
-0.5
Mean
+1 S.D.
-1 S.D.
-1
-1.5
20
30
40
50
60
Distance from clay control (meters)
70
Critical χ2 Value = 11.08
-18
0 0 31 26 3 4
9 5120 3156 18
-1
9 1215 18 0 20 40 60 80 100
Tip
Resistance, qc (MPa)
Skewness
Kurtosis
Chi2 Value
Residuals of Principal Comp. Analysis of
Tip Resistance at CPT4
Hist. of Res. at CPT4
120
35
Regression Residuals of Tip Resistance
40
100
Frequency
30
80
25
20
60
15
40
10
20
5
0
-40
-20
0
Synthetic
20
Res. of PC Analysis: Vert. Var. of Tip Resis. CPT4
Hist. of Res. at CPT4
0
-40
-20
0
Actual
20
10
5
0
-5
-10
-15
-20
-25
-30
-35
0
2
4
6
8
Depth (meters)
10
12
14
Chi2 Value Kurtosis
Skewness
5
4
3
2
1
0
15
12
9
6
3
0
400
300
200
100
0
20
Critical χ2 Value = 11.08
30
40
50
Distance from Clay Control (m)
60
70
Hist. of Res. at MCPT13
25
Hist. of Res. at MCPT13
30
25
20
Frequency
20
15
15
10
10
5
0
-4
5
-2
0
Synthetic
2
0
-4
-2
0
Actual
2
Regression Residuals of Tip Resistance
Residuals of Principal Comp. Analysis of
Tip Resistance at
MCPT13
Res. of PC Analysis: Vert. Var. of Tip Resis. MCPT13
2
1
0
-1
-2
-3
-4
0
2
4
Depth (meters)
6
8
Chi2 Value Kurtosis
Skewness
5
4
3
2
1
0
15
12
9
6
3
0
400
300
200
100
0
20
Critical χ2 Value = 11.08
30
40
50
Distance from Clay Control (m)
60
70
Results of Horizontal Variability Study
0
0
-3
-3
-6
-6
0 – 1.1 m
10.5 – 13.6 m
Depth (m)
Depth (m)
4.9 – 8.7 m
-9
-9
-12
-12
-15
-15
Mean
+1 S.D.
-1 S.D.
-18
0
3 6 9 12 15 18
Tip Resistance, qc (MPa)
Mean
+1 S.D.
-1 S.D.
-18
0
0.2
0.4
0.6
0.8
Sleeve Friction, fs (MPa)
1
Results of Vertical Variability Study
N
13
18
A
22 30
31
32
20
6
14
15
16
17
28
19
29
21
33
23
24
25
26
3
5
1
7
8
2
9
15
11
12
27
15 m
Clay Control
CPT:
CPTu:
MCPT:
SCPT:
BH:
4
10 cm2 Cone Penetration Test
Piezocone Penetration Test
2 cm2 Mini Cone Penetration Test
15 cm2 Seismic Piezocone Penetration Test
Borehole
16
10
A’
Legend
CPT
CPTu
MCPT
SCPT
BH
Testing Program
1997
1977 to 1995
• Twelve MCPT
• Nine CPT
• Six CPT
1995 to 1996
• Three SCPT
• Three CPTu
Correlations: CPT Readings and Soil Unit Weight, gt
3
g (kN/m ) = 11.46 + 0.33 log(z) + 3.10 log(f ) + 0.70 log(q )
t
t
I
0.06
0.06
g
=
1.95
g
(

/

)
(f
/

)
y = 1.0880x
t - 0.9792
w
vo
atm
s atm
22
Mayne et al. 2010
y = 0.7522x + 4.7613 3
r •= g0.8165
= Total unit weight (kN/m )
t
21.5
3)
• gw = Unit
weight
of
water
(kN/m
r = 0.8504
• qt21 = Cone tip resistance (kPa)
Unit Weight (kN/m )
3
22.5
s
• fs = Sleeve friction (kPa)
20.5
• z = Depth (m)
• vo20’ = Effective vertical overburden stress (kPa)
• atm = Atmospheric pressure (kPa)
18
Measured and Evaluated Soil Unit Weight Profiles
0
-2
-4
Depth (m)
-6
-8
-10
-12
-14
Measured
Evaluated Mean
Evaluated Minimum
Evaluated Maximum
Measured
Evaluated Mean
Evaluated Minimum
Evaluated Maximum
-16
g = 1.95 g
t
-18
10
w
( vo I/ atm) 0.06 (fs/ atm) 0.06
3
g (kN/m ) = 11.46 + 0.33 log(z) + 3.10 log(f ) + 0.70 log(q )
t
15
20
25
30
3
Total Unit Weight, g t (kN/m )
10
15
20
s
t
25
30
Total Unit Weight, g t (kN/m3)
Least Square Regression, Correlation Coefficient,
95% Confidence Bounds
26
26
r = -0.2999
22
20
18
16
22
20
18
16
g t = 1.95 g w (vo I/atm)0.06 (fs /atm)0.06
14
12
17
g t (kN/m 3 ) = 11.46 + 0.33 log(z) + 3.10 log(fs ) + 0.70 log(qt)
14
Raw Data
Fitted LS
95% Confidence Bounds
18
19
20
r = -0.2508
24
Evaluated Unit Weight (kN/m3)
Evaluated Unit Weight (kN/m3)
24
21
22
3
Measured Unit Weight (kN/m )
23
12
17
Raw Data
Fitted LS
95% Confidence Bounds
18
19
20
21
22
3
Measured Unit Weight (kN/m )
23
Results of Vertical Variability Study
N
13
18
22 30
31
32
20
6
14
15
16
17
28
19
29
21
33
23
24
25
26
3
5
1
7
8
2
9
15
11
12
27
15 m
Clay Control
CPT:
CPTu:
MCPT:
SCPT:
BH:
4
10 cm2 Cone Penetration Test
Piezocone Penetration Test
2 cm2 Mini Cone Penetration Test
15 cm2 Seismic Piezocone Penetration Test
Borehole
16
10
Legend
CPT
CPTu
MCPT
SCPT
BH
Testing Program
1997
1977 to 1995
• Twelve MCPT
• Nine CPT
• Six CPT
1995 to 1996
• Three SCPT
• Three CPTu
Least Square Regression, Correlation Coefficient,
95% Confidence Bounds
22.5
22.5
g t = 1.95 g w (vo I/ atm)0.06 (fs / atm)0.06
3
g (kN/m ) = 11.46 + 0.33 log(z) + 3.10 log(f ) + 0.70 log(q )
t
3
y = 0.7522x + 4.7613
21.5
r = 0.8504
21
p = 0.0001
20.5
20
19.5
19
18.5
Raw Data
Fitted LS
95% Confidence Bounds
18
17.5
18
s
t
22
Evaluated Unit Weight (kN/m )
Evaluated Unit Weight (kN/m3)
22
18.5
19
19.5
20
Measured Unit Weight (kN/m3)
20.5
y = 1.0880x - 0.9792
21.5
r = 0.8165
21
p = 0.0002
20.5
20
19.5
19
18.5
Raw Data
Fitted LS
95% Confidence Bounds
18
17.5
18
18.5
19
19.5
20
3
Measured Unit Weight (kN/m )
20.5
Least Squares, Principal Component
And Reduced Major Axis Regression Analyses
23
23
g t (kN/m 3 ) = 11.46 + 0.33 log(z) + 3.10 log(fs ) + 0.70 log(qt)
g t = 1.95 g w (vo I/ atm)0.06 (fs / atm)0.06
22.5
22.5
22
Evaluated Unit Weight (kN/m3)
Evaluated Unit Weight (kN/m3)
22
Raw Data
Principal Component Regression
Least Square Regression
Reduced Major Axis Regression
21.5
21
20.5
20
19.5
21.5
21
20.5
20
19.5
19
19
18.5
18.5
18
18
18.5
19
19.5
20
Measured Unit Weight (kN/m3)
20.5
21
Raw Data
Principal Component Regression
Least Square Regression
Reduced Major Axis Regression
18
18
18.5
19
19.5
20
20.5
3
Measured Unit Weight (kN/m )
21
Higher Order Regression Analysis
23
23
22
21
g t (kN/m 3 ) = 11.46 + 0.33 log(z) + 3.10 log(fs ) + 0.70 log(qt)
y = 0.2x 3 - 11.4x 2 + 209.1x - 1256.1
Evaluated g t (kN/m3)
Evaluated g t (kN/m3)
g t = 1.95 g w (vo I/ atm)0.06 (fs / atm)0.06
Raw Data
3rd Order LS Regression
95% Confidence Bounds
20
19
18
18
18.5
19
19.5
20
22
21
Raw Data
3rd Order LS Regression
95% Confidence Bounds
20
19
18
18
20.5
y = 0.7x 3 - 40.8x 2 + 765.3x - 4761.8
18.5
0.2
0.4
0.1
0.2
Residuals
Residuals
0.6
0
-0.1
20.5
20
20.5
0
-0.2
-0.2
-0.4
-0.3
-0.6
19
20
Residuals of 3rd Order Regression
Residuals of 3rd Order Regression
0.3
18.5
19.5
Measured g t (kN/m )
Measured g t (kN/m )
-0.4
18
19
3
3
19.5
20
3
Total Unit Weight, g t (kN/m )
20.5
-0.8
18
18.5
19
19.5
3
Total Unit Weight, g t (kN/m )
Conclusions
• Horizontal and vertical variability of CPT
readings for better site characterization
• CPT-based relationship for evaluating soil
unit weight
22.5
g t = 1.95 g w (vo I/ atm)0.06 (fs / atm)0.06
3
t (kN/m )
22
Mayne et al. 2010
y = 0.7522x + 4.7613
21.5
r = 0.8504
21
25
Spatial Variability of CPT Data
and Soil Parameters at NGES, Texas A&M
Tip qt (MPa)
0
Fawad S. Niazi
5
10 15 20 25 0.0
Sleeve fs (MPa)
0.1
0
10
20
30
Depth (m)
Geosystems Engineering Division
Civil & Environmental Engineering
Georgia Institute of Technology
April 27, 2010
40
50
60
70
80
90
100
www.clu-in.org
Niazi et al. 2010
0.2
Pore
0.3 0
1