helical piles defined presentation by: howard a. perko, ph.d., p.e. magnum geo-solutions, llc...
TRANSCRIPT
Helical Piles Defined
Presentation by: Howard A. Perko, Ph.D., P.E.Magnum Geo-Solutions, LLC
Copyright 2011 – Magnum Piering, Inc., All Rights reserved. May be distributed
and printed by express written permission of the author only.
MAGNUM Informational Bulletin ISO-MAG2-11A
Copyright 2011 – Magnum Piering, Inc.
HELICAL PILES
Definition
Installation
Advantages/Disadvantages
Bearing & Pullout Capacity
Minimum Embedment
Group Efficiency
Specifying Helical Piles
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Helical Piles Defined
Helical Piles:Central Steel Shaft with One or More Helix Shaped Bearing Elements that is Screwed Into the Ground to Support the Loads of Structures
(a.k.a. Helical Piers, Screw Piles, Torque Anchors, Auger Screw Piles, Helix Piers)
Plate Cap
Extension
Coupling
Lead
Helix
Pitch
Pilot Point
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January 2007
Helical Pile Installation
Position and Install Pile
Halt at Required Torque
Cut-Off Pile
Mount Cap
Cast Concrete
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Machine Installation
From Perko (2009) Helical Piles
Copyright 2011 – Magnum Piering, Inc.
Hand Installation
From Perko (2009) Helical Piles
Copyright 2011 – Magnum Piering, Inc.
Advantages Low noise and vibrations Small, maneuverable
installation equipment Removal and replacement Ease of transport Compression or tension All-weather installation Rapid installation Does not produce drill spoil Immediate post tensioning Shorter bond length Do not require casing
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Disadvantages Cannot penetrate very hard
rock (SPT N>100) Concrete and construction
debris is problematic Difficult in cobble and
boulders Ease of installation means
contractor pre-qualification important
Slender shaft makes lateral bracing imperative
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See Magnum Bulletin ISO-MHP4-11A Reliability and Theory of Helix Sizing for more information about calculating capacity.
Bearing & Pullout Capacity
From Perko (2009) Helical Piles
Copyright 2011 – Magnum Piering, Inc.
Minimum Embedment
• Bottom below potential unstable soils
• Penetrate a certain stratum
• Provide sufficient cover to resist shallow pulloutImproper Length
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Minimum Embedment
2
3
4
5
6
7
8
9
10
5 10 15 20 25 30 35 40 45 50
SPT Blow Count
Em
be
dm
en
t R
ati
o (
H/D
1)
6 [152]
8 [203]
10 [254]
12 [304]
14 [355]
18 [457]
24 [609]
Helix Diameter(in) [mm]
Buoyant Unit Weight=56
[0.90]pcf
[g/cm3]
62[0.99]
68[1.09]
72[1.15]
75[1.20]
81[1.30]
From Perko (2009) Helical Piles
Copyright 2011 – Magnum Piering, Inc.
Minimum Embedment
From Perko (2009) Helical Piles
Copyright 2011 – Magnum Piering, Inc.
Group Efficiency
Generally 3 to 4 Helix Diameter Pile Spacing
Required to avoid Group Effects
From Perko (2009)
Helical Piles
Copyright 2011 – Magnum Piering, Inc.
Specifying Helical Piles• Pile Locations
• Pile Type/Size
• Required Pile Capacity• Comp., Tension, Lateral
• Minimum Depth/ Bearing Stratum
• Required Torque
• Load Tests if Required
See www.magnumpiering.com for example plans and written specifications.
Contact InformationMagnum Piering, Inc.
www.magnumpiering.com800-822-PIER (7437)
6082 Schumacher Park DriveWest Chester, OH 45069