Investigation of the Tensile and Compression Capacity of Mono Helix Screw Piles for Anchoring Lightweight Residential Footings on Expansive Soils-PPT Presentation

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The study investigates whether mono-helix screw piles can anchor lightweight residential footings on expansive soils, where moisture-driven ground heave can cause substantial uplift forces and damage to slabs, floors, and walls.<br /><br />A field-testing program evaluated 24 screw piles under tension or compression. The piles had helix diameters of 290–450 mm and installation depths of 1.7–5.8 m, with products from three manufacturers. The project included geotechnical and laboratory investigations, monitoring installation torque and penetration, load testing, comparisons with theoretical capacity predictions, and excavation of piles to inspect failure mechanisms.<br /><br />The findings indicate that screw-pile tension capacity was approximately 90% of compression capacity. The study concludes that the 1%-of-helix-diameter displacement criterion in AS 2159 is more appropriate for defining failure in residential screw-pile applications. Installation can disturb soil around the shaft, and measured rotations may exceed ideal values. Most failures in soft soils were geotechnical, although helix-plate failure could occur in stiff clay under higher loads.<br /><br />For reactive-ground movements, allowing greater pile deflection may help redistribute loads among piles and reduce heave pressure. The research aims to improve understanding of how pile depth and helix size affect capacity and how theoretical predictions compare with field performance.

Keywords

mono-helix screw piles

expansive soils

residential footings

ground heave

uplift forces

tension capacity

compression capacity

helix diameter

load testing

geotechnical failure