1. 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

2. OUTLINE Background. Objectives. Site investigation. Piles properties.1
Background.
Objectives.
Site investigation.
Piles properties.
Dynamic testing setup.
Results – response curves.
Conclusions.
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

3. BACKGROUND 2
Helical screw piles: structural elements that consist of one or more helical shaped circular plate(s) affixed to a steel central shaft.
Embedment depth (H)
Helix-spacing (S)
Helix diameter (D)
Shaft diameter (d)
Helix pitch (p)
Shaft diameter (d)
Embedment depth (H)
Embedment depth (H)
Embedment depth (H)
Helix pitch (p)
Helix-spacing (S)
Helix diameter (D)
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

4. OBJECTIVES Dynamic testing (Full-scale) Loading frequency up to 60Hz3
Dynamic testing
(Full-scale)
Loading frequency up to 60Hz
Vertical quadratic harmonic loading
Horizontal quadratic harmonic loading
Evaluate Dynamic Behaviour of Helical Piles; Develop Methodology for Their Design
Response curves
Free vibration test
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

5. SITE INVESTIGATION 4
Test site is located 7.0 miles north of the town of Ponoka, Alberta.
Mechanical borehole (BH-1).
Three locations for seismic cone penetration test (SCPT), SCPT-1, SCPT-2, and SCPT-3.
I-Beam (wave source)
Cone rod
Cone rod
Cone rod
I-Beam (wave source)
Layout
Shear wave generation (SCPT)
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

6. SITE INVESTIGATION Poisson’s ratio varied from 0.4 to 0.47 5 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

7. PILES PROPERTIES property Value Double helix 6 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

8. System = Pile + Soil + Body mass + Oscillator
DYNAMIC TESTING SETUP 7
System = Pile + Soil + Body mass + Oscillator
Properties of body mass and oscillator
Vibration direction
Vertical
Horizontal
No. of plates 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
Instrumentation:
- One 3D accelerometer on one side at the C.G Two 1D accelerometers at equidistant positions from the body mass centre.
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

9. - Oscillator : Dynamic force up to 23.5 kN - Motor : 7.5 Hp
DYNAMIC TESTING SETUP 8
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
Quadratic Force : P = me.e.w2. sin(wt)
- Adopted Excitation: 5 excitation intensities expressed in me.e Pz Px Pz Px
Vertical vibration
Horizontal vibration
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

10. DYNAMIC TESTING SETUP 8 9
Oscillator
Flexible shaft
Motor 1D
Accelerometer 3D
(a)
(C)
(a) Vertical vibration; (b) Horizontal vibration.
(C) Instrumentation.
(b)
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

11. DYNAMIC TESTING Horizontal vibration test 10
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

12. RESULTS - RESPONSE CURVES11
Vertical & Horizontal amplitude response curves
Vertical vibration
Horizontal vibration
Resonant frequencies: 35.0 – 38.0 Hz
- Damping ratio: 6.8 – 7.5 %
Resonant frequencies: 3.4 – 3.6 Hz
- 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

13. RESULTS - RESPONSE CURVES12
Dimensionless Vertical & horizontal response curves
Horizontal vibration
Vertical 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

14. RESULTS - RESPONSE CURVES13
Free Vibration Test
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

15. Effect of Installation Disturbance
Vertical Response
1 week After Installation
Vertical Response
9 Months After Installation

16. Comparison of Experimental and DYNA5 Results
Vertical Response
Horizontal Response

17. CONCLUSIONS 14
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

18. THANK YOU.. ACKNOWLEDGEMENTS15
The Natural Sciences and Engineering Research Council of Canada (NSERC)
The University of Western Ontario
ALMITA Manufacturing Ltd, Alberta
THANK YOU..
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010
Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010