VERTICAL AND HORIZONTAL DYNAMIC TESTING OF A
DOUBLE HELIX SCREW PILE
M. Elkasabgy
Prof. M. H. El Naggar
Ph.D. Candidate
Associate Dean of Engineering
University of Western Ontario
University of Western Ontario
Dr. M. Sakr
Senior Geotechnical Manager
Almita Manufacturing Ltd.
63rd Canadian Geotechnical Conference
September, 2010
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010
OUTLINE
Background.
Objectives.
Site investigation.
Piles properties.
Dynamic testing setup.
Results – response curves.
Conclusions.
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010
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BACKGROUND
2
Helical screw piles: structural elements that consist of one or more helical
shaped circular plate(s) affixed to a steel central shaft.
Shaft
diameter (d)
Embedment depth (H)
Helix
pitch (p)
Helix-spacing (S)
Helix diameter (D)
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010
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OBJECTIVES
Evaluate Dynamic Behaviour of Helical Piles;
Develop Methodology for Their Design
Dynamic testing
(Full-scale)
Loading frequency up to 60Hz
Vertical
quadratic
harmonic
loading
Horizontal
quadratic
harmonic
loading
Free vibration
test
Response curves
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010
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SITE INVESTIGATION
1,7m
Test site is located 7.0 miles north
of the town of Ponoka, Alberta.
4m
3m
Mechanical borehole (BH-1).
BH-1
5,4m
N
5,09m
Three locations for seismic cone
penetration test (SCPT), SCPT-1,
SCPT-2, and SCPT-3.
static and dynamic testing location
ScPT-2
13,38m
reaction pile location
seismic cone penetration test location
depth of penetration = 15.0 m
Mechanical augered borehole
depth of hole = 10.0 m
ScPT-3
2,21m
ScPT-1
17,26m
Cone rod
0
I-Beam (wave
source)
2.0m
Layout
Shear wave generation
(SCPT)
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010
SITE INVESTIGATION
Helix
Helix
End of pile
Poisson’s ratio varied from 0.4 to 0.47
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010
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6
PILES PROPERTIES
property
Value
Pile type
Steel pipe pile with two
helices
Outer diameter
0.324 m
Inner diameter
0.305 m
Moment of inertia
1.164×10-4 m4
Area
9.4102×10-3 m2
Length
9.0 m
Helix plate diameter
0.61 m
Helix plate thickness 0.019 m
Young’s modulus
210 GPa
Poisson’s ratio
0.3
Damping ratio
0.001
Unit weight
78.46 kN/m3
Double helix
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010
DYNAMIC TESTING SETUP
7
Mechanical
oscillator
1D
accelerometer
System = Pile + Soil + Body mass + Oscillator
Vibration direction
Horizontal
59
59
Mass of body mass-oscillator (kg)
4849.5
4849.5
Height of centre of gravity (CG) (m)
0.791
0.793
Height of excitation above C.G., (m)
0.860
0.938
Mass moment of inertia (kg.m2)
1152.5
1166.9
Pile cap plate is weldded
to the pile head
7.56m
Vertical
No. of plates
3D
accelerometer
0.60m
Properties of body
mass and oscillator
Body mass
(steel plates)
Instrumentation:
0.90m
m
Welded steel
plate
45°
- One 3D accelerometer on one side at the C.G.
- Two 1D accelerometers at equidistant positions
from the body mass centre.
Helix pitch of
0.15m
0.324m
0.61m
Drawing is not to scale
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010
DYNAMIC TESTING SETUP
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Excitation mechanism = Oscillator + Flexible shaft + Motor + Speed control unit
- Oscillator
: Dynamic force up to 23.5 kN
- Motor
: 7.5 Hp
- Speed control unit : Frequencies from 4 to 60 Hz
: P = me.e.w2. sin(wt)
- Quadratic Force
- Adopted Excitation: 5 excitation intensities
expressed in me.e
Pz
Pz
Px
Pz
Px
Px
Pz
Vertical vibration
Px
Horizontal vibration
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010
DYNAMIC TESTING SETUP
Oscillator
Flexible
shaft
89
Motor
1D
Accelerometer
1D
Accelerometer
(a)
3D
(C)
Accelerometer
(a) Vertical vibration; (b) Horizontal vibration.
(C) Instrumentation.
(b)
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010
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DYNAMIC TESTING
Horizontal vibration test
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010
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RESULTS - RESPONSE CURVES
Vertical & Horizontal amplitude response curves
0.5
2.0
0.18 kg.m
0.16 kg.m
0.12 kg.m
0.091 kg.m
0.4
0.3
0.2
0.1
Excitation intensity
0.21 kg.m
1.8
Horizontal vibratin amplitude (mm)
Vertical vibratin amplitude (mm)
Excitation intensity
0.21 kg.m
0.18 kg.m
0.16 kg.m
0.12 kg.m
0.091 kg.m
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.0
0
10
20
30
40
50
60
0
Frequency (Hz)
10
20
30
40
50
Frequency (Hz)
Vertical vibration
Horizontal vibration
- Resonant frequencies: 35.0 – 38.0 Hz
- Resonant frequencies: 3.4 – 3.6 Hz
- Damping ratio: 6.8 – 7.5 %
- Damping ratio: 2.7 – 2.9 %
Note: damping was obtained using the half-band method
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010
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RESULTS - RESPONSE CURVES
Dimensionless Vertical & horizontal response curves
12
35
0.18 kg.m
0.16 kg.m
0.12 kg.m
0.091 kg.m
10
Excitation intensity
0.21 kg.m
Horizontal dimensionless amplitude
Vertical vibratin amplitude (mm)
Excitation intensity
0.21 kg.m
8
6
4
2
0
0.18 kg.m
0.16 kg.m
0.12 kg.m
0.091 kg.m
30
25
20
15
10
5
0
0
10
20
30
40
Frequency (Hz)
Vertical vibration
50
60
0
10
20
30
40
50
Frequency (Hz)
Horizontal vibration
- Dimensionless response = (m/me.e)U , where U is the measured amplitude
- Figures show very slight nonlinearity in response with increased nonlinearity under
higher excitation intensities
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010
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RESULTS - RESPONSE CURVES
Free Vibration Test
0.08
0.06
0.04
Acceleration (g)
0.02
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
-0.02
Time (sec)
-0.04
-0.06
-0.08
-0.1
Response curve
Free vibration in field
- Using Logarithmic Decrement Method
- Damping ratio = 4.0 to 5.1 %
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010
Effect of Installation Disturbance
0.5
Excitation intensity
0.21 kg.m
0.5
0.18 kg.m
0.16 kg.m
0.12 kg.m
0.091 kg.m
0.4
Vertical vibratin amplitude (mm)
Vertical vibratin amplitude (mm)
Excitation intensity
0.21 kg.m
0.3
0.2
0.1
0.0
0.18 kg.m
0.16 kg.m
0.12 kg.m
0.091 kg.m
0.4
0.3
0.2
0.1
0.0
0
10
20
30
40
50
Frequency (Hz)
Vertical Response
1 week After Installation
60
0
10
20
30
40
50
Frequency (Hz)
Vertical Response
9 Months After Installation
60
Comparison of Experimental and DYNA5 Results
0.5
1.4
Excitation intensity
0.21 kg.m
0.18 kg.m
0.16 kg.m
0.12 kg.m
0.091 kg.m
0.4
Horizontal vibratin amplitude (mm)
Vertical vibratin amplitude (mm)
Excitation intensity
0.21 kg.m
Nonlinear analysis
0.3
0.2
0.1
0.0
0.18 kg.m
0.16 kg.m
0.12 kg.m
0.091 kg.m
1.2
1.0
Nonlinear analysis
0.8
0.6
0.4
0.2
0.0
0
10
20
30
40
Frequency (Hz)
Vertical Response
50
60
0
10
20
30
40
Frequency (Hz)
Horizontal Response
50
60
CONCLUSIONS
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Dynamic testing of a 9.0 m double-helix screw pile under vertical and horizontal
vibrations was carried out in field in clayey soil profile.
Complete response curves were measured under different excitation intensities.
A slightly nonlinear response was detected as excitation amplitude increased.
Pile installation causes some soil disturbance, which affects piles stiffness. As
time passes, the soil regains strength and the pile stiffness increases.
The program DYNA5 was able to accurately predict the dynamic response of
helical piles. Hence, it can be used for the design of machine foundations
supported by helical piles.
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010
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ACKNOWLEDGEMENTS
o The Natural Sciences and Engineering Research Council of Canada (NSERC)
o The University of Western Ontario
o ALMITA Manufacturing Ltd, Alberta
THANK YOU..
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010