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

This study investigates the relationship between installation torque and ultimate bearing capacity of screw piles in tropical soils, with a focus on both lateritic and non-lateritic (residual) conditions. Building upon earlier research in São Paulo, Brazil, this work evaluates many screw piles installed in Goiás, Brazil, both in lateritic and non-lateritic soils. Standard Penetration Tests (SPT) were conducted at each site, and installation torque was monitored during pile installation. The Yanez & Renosto (2019) method, combined with semi-empirical pile design approaches, was used to estimate unit shaft resistance and predict installation torque as a design parameter. Predicted torque values showed good agreement with field observations, particularly when adjusted for the distinct shear modulus characteristics of lateritic soils. Tension load tests were also performed to determine the ultimate capacity of each pile, enabling the calculation of the torque-to-capacity factor (Kt). Results indicate that lateritic soils exhibit lower Kt values, implying that installation torque is largely influenced by shaft friction, while ultimate pile resistance is primarily governed by end-bearing. These findings highlight the limitations of conventional torque-based capacity predictions when applied to lateritic tropical soils. Incorporating soil-specific frictional behaviour into design methodologies may improve prediction reliability and can inform more accurate equipment selection, pile geometry, and safety margins. This research contributes to safer and more efficient screw pile design in tropical environments.