VERTICAL AND HORIZONTAL DYNAMIC TESTING OF A DOUBLE HELIX SCREW PILE

M. Elkasabgy

Ph.D. Candidate

Prof. M. H. El Naggar

University of Western Ontario

Associate Dean of Engineering

University of Western Ontario

63rd Canadian Geotechnical ConferenceSeptember, 2010

Dr. M. Sakr

Senior Geotechnical Manager

Almita Manufacturing Ltd.

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

1

BACKGROUND

Helical screw piles: structural elements that consist of one or more helical shaped circular plate(s) affixed to a steel central shaft.

2

Embedment depth (H)

Helix-spacing (S)

Helix diameter (D)

Shaft diameter (d)

Helix pitch (p)

Embedment depth (H)Embedment depth (H)Embedment depth (H)

Helix-spacing (S)

Helix diameter (D)

Shaft diameter (d)

Helix pitch (p)

Embedment depth (H)Embedment depth (H)

Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

3OBJECTIVES

Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

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

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.

Layout

Shear wave generation (SCPT)

Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

Cone rod

I-Beam (wave source)

Cone rod

I-Beam (wave source)

Cone rod

5SITE INVESTIGATION

Poisson’s ratio varied from 0.4 to 0.47

Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

Helix

Helix

End of pile

PILES PROPERTIES 6

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

7DYNAMIC TESTING SETUP

Vibration direction

Vertical Horizontal

Properties of body mass and oscillator

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

System = Pile + Soil + Body mass + Oscillator

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

8DYNAMIC TESTING SETUP

Excitation mechanism = Oscillator + Flexible shaft + Motor + Speed control unit

- Quadratic Force : P = me.e.2. sin(t)

- Adopted Excitation: 5 excitation intensities expressed in me.e

- Oscillator : Dynamic force up to 23.5 kN

- Motor : 7.5 Hp

- Speed control unit : Frequencies from 4 to 60 Hz

Vertical vibration Horizontal vibration

Pz

PxPz

Px

Pz

Px

Pz

Px

Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

8DYNAMIC TESTING SETUP

1D

Accelerometer

1D

Accelerometer

3D

Accelerometer

Oscillator Flexible shaft

Motor

(a)

(b)

(C)

(a) Vertical vibration; (b) Horizontal vibration.

(C) Instrumentation.

9

Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

10

Horizontal vibration test

DYNAMIC TESTING

Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

11RESULTS - RESPONSE CURVES

Vertical vibration

Vertical & Horizontal amplitude response curves

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 %

Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

Note: damping was obtained using the half-band method

12RESULTS - RESPONSE CURVES

Dimensionless Vertical & horizontal response curves

Horizontal vibrationVertical vibration

- Dimensionless response = (m/me.e)U , where U is the measured amplitude

Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

- Figures show very slight nonlinearity in response with increased nonlinearity under higher excitation intensities

13RESULTS - RESPONSE CURVES

Free Vibration Test

Free vibration in fieldResponse curve

- Using Logarithmic Decrement Method

- Damping ratio = 4.0 to 5.1 %

Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Time (sec)Ac

ce

lera

tio

n (

g)

Effect of Installation Disturbance

Frequency (Hz)

0 10 20 30 40 50 60

Ver

tica

l vib

rati

n a

mp

litu

de

(mm

)

0.0

0.1

0.2

0.3

0.4

0.5

0.21 kg.m 0.18 kg.m0.16 kg.m0.12 kg.m0.091 kg.m

Excitation intensity

Vertical Response

1 week After Installation

Vertical Response

9 Months After Installation

Comparison of Experimental and DYNA5 Results

Frequency (Hz)

0 10 20 30 40 50 60

Ver

tica

l vib

rati

n a

mp

litu

de

(mm

)

0.0

0.1

0.2

0.3

0.4

0.5

0.21 kg.m 0.18 kg.m0.16 kg.m0.12 kg.m0.091 kg.mNonlinear analysis

Excitation intensity

Vertical Response

Frequency (Hz)

0 10 20 30 40 50 60H

ori

zon

tal v

ibra

tin

am

plit

ud

e (m

m)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0.21 kg.m 0.18 kg.m0.16 kg.m0.12 kg.m0.091 kg.mNonlinear analysis

Excitation intensity

Horizontal Response

14CONCLUSIONS

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

15ACKNOWLEDGEMENTS

Department of Civil & Environmental Engineering, University of Western Ontario, Canada, 2010

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