Estimation of Installation Torque and Axial Ultimate Capacity of Screw Piles in Tropical Soils Using SPT Data-Paper

Paper

Pdf Summary

The study evaluates methods for estimating installation torque and axial ultimate capacity of screw piles in tropical soils, particularly lateritic and residual soils in Brazil. It analyzes 14 piles at two sites: seven in lateritic soil at Ribeirão Pires and seven in mixed lateritic/residual soils at Rio Verde.<br /><br />The torque-estimation method combines pile geometry and soil–pile friction with SPT-based correlations. It represents friction mobilization using Cambefort’s first law and estimates shaft resistance using the Décourt–Quaresma method. Correction factors of 2.5–3.3 account for the distinctive mechanical behavior of lateritic soils, including their higher stiffness and cemented structure. Estimated torque profiles generally agreed with measurements taken during installation.<br /><br />Tension load tests on selected piles were interpreted using four established extrapolation methods to estimate ultimate capacity. Comparing these capacities with measured installation torque produced torque-correlation factors that were reasonably consistent across the dataset. The authors selected a conservative factor of 19.7 m⁻¹ for estimating capacity from torque.<br /><br />The findings support torque-based capacity prediction for screw piles in tropical soils when soil-specific frictional behavior is considered. The approach may help guide pile geometry, installation equipment, and design safety margins, while recognizing that the results are based on a limited number of piles and sites.

Keywords

screw piles

installation torque

axial ultimate capacity

tropical soils

lateritic soils

residual soils

Brazil

SPT correlations

Cambefort law

torque-correlation factor