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Copyright 2011 – Magnum Piering, Inc. Helical Pile Selection and Sizing Presentation by: Howard A. Perko, Ph.D., P.E. Director of Engineering, Magnum Geo-Solutions,

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Presentation on theme: "Copyright 2011 – Magnum Piering, Inc. Helical Pile Selection and Sizing Presentation by: Howard A. Perko, Ph.D., P.E. Director of Engineering, Magnum Geo-Solutions,"— Presentation transcript:

1 Copyright 2011 – Magnum Piering, Inc. Helical Pile Selection and Sizing Presentation by: Howard A. Perko, Ph.D., P.E. Director of Engineering, Magnum Geo-Solutions, Inc. 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-MHP1-11A

2 Copyright 2011 – Magnum Piering, Inc. STEP 1: Select Helical Pile Shaft Size STEP 2: Check Shaft Buckling STEP 3: Determine Bearing Stratum STEP 4: Required Ultimate Capacity STEP 5: Size Helical Bearing Plates Specification Contact Information Outline

3 Copyright 2011 – Magnum Piering, Inc. STEP 1: Select Shaft Size Magnum’s Product Catalog Contains a Summary of Popular Sizes (Other Custom Sizes are Available) Select product sizes based on required capacity. Compare with geotechnical capacity in catalog. Note that allowable capacity is given in “tons”! See pg. 9 Magnum 2011 Product Catalog

4 Copyright 2011 – Magnum Piering, Inc. Geotechnical capacity in Product Catalog summary table is the theoretical capacity of the helical pile in ground when installed to the maximum torque. (i.e. Ultimate Capacity = Maximum Installation Torque x Capacity to Torque Ratio) Geotechnical Capacity

5 Copyright 2011 – Magnum Piering, Inc. STEP 2: Check Buckling Magnum’s Product Catalog Contains a Summary of Popular Sizes (Other Custom Sizes are Available) Buckling strength is given in structural capacity. See pg. 9 Magnum 2011 Product Catalog

6 Copyright 2011 – Magnum Piering, Inc. Structural capacity in Product Catalog summary table is the buckling strength of the shaft in firm soil with pinned head conditions. A depth of fixity of 5 feet was used as per IBC2009 Chapter 18 and Perko Buckling strength needs to be revised in soft soils (SPT N<4) or fluid soils (SPT N=WOR, WOH). Contact Magnum-Geo for support. From Perko (2009) Helical Piles, Wiley, NY Structural Capacity

7 Copyright 2011 – Magnum Piering, Inc. Typically the “bearing stratum” selected as the most competent and stable material reachable within an economic depth. The project geotechnical engineer should assist in determining the most suitable bearing statum. Determine bearing stratum material type and representative SPT Blow Count. Recognized Material Types: Cohesive = Clay, Silt Non-Cohesive = Sand, Gravel Bedrock = Medium Hard, Sedimentary Rock Types STEP 3: Bearing Stratum SPT Blow Count, Average = 41 bpf Material Type = Cohesive

8 Copyright 2011 – Magnum Piering, Inc. STEP 4: Ultimate Capacity Industry Standard Factor of Safety = x Working Capacity = Required Ultimate Capacity Example: 2 x 35,000 lbs = 70,000 lbs (35 Tons) F.S.Working CapacityUltimate Capacity Shown on Plans

9 Copyright 2011 – Magnum Piering, Inc. Magnum Piering, Inc. sizing charts are provided for cohesive soils, non-cohesive soils, and weak bedrock. Based on the SPT Blow Count and required ultimate capacity, they can be used to size helical piles. STEP 5: Helix Sizing See pgs Magnum 2011 Product Catalog SPT Blow Count, Average = 41 bpf Required Ultimate Capacity (e.g. 35 Tons)

10 Copyright 2011 – Magnum Piering, Inc. Nomenclature 10D12D14D= 10” Diam. DCE, 12” Diam. DCE, 14” Diam. DCE, Triple Helix Lead D= Dual Cutting Edge Helix (DCE) S= Single Cutting Edge Helix (Standard)

11 Copyright 2011 – Magnum Piering, Inc. Specification For example CAD drawings and written specifications, see the engineering section of Magnum’s website. Also, check out the examples in Magnum’s engineering reference manuals.

12 Copyright 2011 – Magnum Piering, Inc. Contact Information Magnum Piering, Inc PIER (7437) 6082 Schumacher Park Drive West Chester, OH 45069


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