Practice Note 28 Screw Piles: Guidelines for Design ...

1 Engineering PracticeISSN 1176-0907 October Note 28 Screw Piles: Guidelines for Design , construction & InstallationIIPractice Note 28: Screw Piles: Guidelines for Design , construction and Installation Version 1, October 2015 PrefaceThe purpose of the Practice Note Screw Piles: Guidelines for Design , construction and Installation is to highlight many critical elements of the Design , installation and testing of Screw piles. It provides recommendations for good Practice in New Zealand, and should be used as a technical reference to inform engineers, developers, contractors and local Note Development This Practice Note has been facilitated by the Institution of Professional Engineers New Zealand (IPENZ), with support from principal sponsors Piletech, and authorship provided by Beca IPENZ Engineering Practice Advisory Committee has given the lead author the task of preparing a document to be adopted by the engineering industry that reflects a national perspective.

2 The Practice Note has been prepared in accordance with standard IPENZ Practice Note procedures, which includes reporting on progress to the Engineering Practice Advisory Committee, peer review and general Membership review. This review and reporting process ensures the delivery of a robust, good- Practice technical document. Practice Note 28: Screw Piles: Guidelines for Design , construction and Installation Version 1, October 2015 IIIA cronymsAS Australian StandardB1/VM4 New Zealand Building Code, Structure Foundations, Verification MethodBCAB uilding Consent AuthorityCPTCone Penetrometer testCHS Circular Hollow SectionDHelix DiameterIANZI nternational Accreditation New ZealandIPENZI nstitution of Professional Engineers New ZealandLPILE and GROUPS oftware program for analysing either single or pile groups under lateral loadingMBIEM inistry of Business.

3 Innovation and EmploymentNDTNon-destructive testingNZGSNew Zealand Geotechnical SocietyNZS New Zealand StandardPS1 Producer Statement DesignPS2 Producer Statement Design ReviewPS-CProducer Statement ConstructionPS4 Producer Statement construction ReviewSLSS erviceability Limit StateSPDS crew pile DesignerSPTS tandard Penetrometer TestULSU ltimate Limit StatetTonneIVPractice Note 28: Screw Piles: Guidelines for Design , construction and Installation Version 1, October 2015 GlossaryBearing capacityThe capacity of the soil to resist loadCohesive soilA sticky soil such as clay or clayey silt having a strength that depends on the surface tension of capillary waterCohesionless soils Any free -running type of soil such as sand or gravels having a strength that depends on the friction between particlesCompression capacityThe maximum amount of downward force (from the load of the structure or soil) that a Screw pile can resist before failing (may be limited by either the geotechnical capacity of the soil or structural capacity of the pile ).

4 DeflectionMovement of the installed pile in either or both the lateral or vertical plane(s)Founding layerThe layer of soil in which the helix plate is seated (also called the bearing layer ).Founding levelThe exact place or level where the lower plate of the bearing helix sitsInstallation torqueThe rotating force required to install the Screw pile into the groundLateral capacityThe maximum amount of horizontal force that a Screw pile can resist, such as earthquake shear loads before failing (may be limited by either the geotechnical capacity of the soil or structural capacity of the pile ). Negative skin frictionThe downward movement of a pile as a result of soft or liquefiable soils producing a down drag as they compress from an additional load. (For Design purposes NSF can either be taken either as an addition to structural capacity requirements or as a reduction in geotechnical capacity.)

5 Punch throughExcessive downwards deflection of the pile seat (under compression) into a weaker soil below when the geotechnical capacity of the stronger, but relatively thin, founding layer is soilsSoils that have a high loss of strength following a disturbance, such as volcanic ash or highly-weathered ignimbrite Soil consolidation (settlement)Lowering of the ground surface over time following deformation (over time) of a weak soil layer beneath when pore water pressures (generated after structural loading) have reduction factorA factor (of less than one) that provides a margin of safety to reduce the risk of failure applied to the ultimate soil capacity or pile capacity to cover variations and capacityThe maximum amount of upwards pulling force that a Screw pile can resist before failing (may be limited by either the geotechnical capacity of the soil or structural capacity of the pile ).

6 True helixA helix having perfect symmetry with a uniform pitch all round and parallel leading and trailing edgesUndrained shear strengthThe maximum amount of shear stress that may be placed on a cohesive soil before it yields or Note 28: Screw Piles: Guidelines for Design , construction and Installation Version 1, October 2015 VContents1. Introduction 12. Overview of Screw pile Technology What is a Screw pile ? Applications of Screw piles How Screw piles are installed 53. Advantages, Disadvantages and Suitability of Screw Piles Advantages Disadvantages Suitability of Screw piles in certain ground conditions 74. Factors Influencing Screw pile Capacity 85. Geotechnical Investigation Requirements for Screw pile Foundations 96.

7 Geotechnical Factors in determining Screw pile Capacity Seismic considerations Compression capacity Coarse grained soils Fine grained soils Tension capacity Lateral capacity Installation torque and capacity Vertical deflection pile spacing and group effects Strength reduction factors 197. Screw pile Structural Design General structural Design requirements Assessment of loadings Loadings during installation In-service loads Screw pile components Shaft Helix Connections and splices 228. Materials, Durability and Manufacturing Durability Materials Manufacture Shaft Helix 259. construction Practice Installation pile construction record card 2710. Testing Requirements and Practices Purpose of testing General testing requirements Other considerations 2911.

8 Producer Statements Producer statements pile designer Producer statements pile contractor 3012. Procurement 31 Bibliography 32 Appendix A: Considerations for Geotechnical Investigations for Screw Piles 33 Appendix B: Pre- Design , Design and Installation Checklist 36 Appendix C: Technical Specification for the Design , construction , Installation and Certification of Screw Piles 38 Appendix D: Screw pile Shaft Specification and Design 45 Appendix E: Example Screw pile Record Card 471 Practice Note 28: Screw Piles: Guidelines for Design , construction and Installation Version 1, October 20151. IntroductionScrew piles are a type of foundation system now widely used in the construction industry. They can offer significant advantages in terms of speed and ease of installation and by offering a reduction in the offsite disposal of drilling spoil.

9 New Zealand has recently seen a substantial increase in their popularity, especially following the 2010/2011 earthquakes in Christchurch. The Australian Standard AS 2159 Piling Design and Installation [1] can be used as a guideline in the Design ,testing and installation of Screw piles and is referred to extensively in this Practice , the lack of any published New Zealand code of Practice means that significant reliance is placed on individual practitioners to ensure that piles meet the performance requirements of each structure. An increasing number of designers and installers find themselves having to work within a largely unregulated have been expressed that New Zealand might experience similar problems to those encountered in Australia a decade ago when the evolution of Screw piling technology saw large numbers of practitioners entering a market where standards were not well defined.

10 This lack of standards and Codes of Practice resulted in performance issues and litigation. Adding to these concerns is the fact that any issues with Screw pile designs are unlikely to present themselves until the piles experience significant additional loadings, such as during a large seismic Practice Note highlights many critical elements of the Design , certification, installation and testing of Screw piles. It provides recommendations for good Practice in New Zealand, and should be used as a reference to inform engineers, developers, contractors and local , a specialist designer, supplier and installer of Screw piles, has led the way in establishing the Screw pile market in New Zealand and has sponsored the writing of this Practice Note 28: Screw Piles: Guidelines for Design , construction and Installation Version 1, October 20152.