Soil-Structure Interaction for a Tension Pile Pulled with Strand-Paper

Paper

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The paper examines a tension pile in which the uplift force is transferred below the pile top rather than directly at the top. High-tensile strands carry the load and flare into the concrete at the base of a high-density polyethylene (HDPE) duct. The duct prevents bonding between the strands and the upper pile concrete; a one-metre annular space at the pile head allows horizontal movement.<br /><br />Soil friction acts downward along the pile as it moves upward. Below the point where the force enters the pile, this friction opposes the applied pull, leaving the pile in tension. Above that point, the lower section pushes the upper section upward, while soil friction resists it; consequently, the upper section is in compression. This differs from a conventional tension pile, which is generally in tension throughout.<br /><br />The 600 mm diameter pile formed part of the foundation for an underground reservoir in Qatar, where uplift could occur when the reservoir was empty. It was load-tested and instrumented with strain gauges at six levels, with displacement measured at the pile head. Strain readings were converted to forces to show how the internal force varied with depth. The measurements broadly confirmed the predicted change from compression above the force-transfer level to tension below it, though the discrete gauge locations could not fully capture the stress reversal between measurement points.<br /><br />The pile was tested up to 250% of its design load. Reported pile-head movements were small: 0.06 mm at design load, increasing to 1.42 mm at 250%. The author concludes that the strain measurements provided a useful picture of the unusual stress distribution in this strand-loaded tension pile.

Keywords

tension pile

uplift force

high-tensile strands

HDPE duct

soil friction

strain gauges

load testing

stress distribution

pile foundation

underground reservoir