Contemporary conceptual models for predicting carrying capacity of multi helices screw piles

Abstract. Contemporary civil constructions are based on foundation systems consisting mainly of shallow, semi deep and deep foundations. The screw pile resembles essentially to a large screw that is inserted into the ground by a special machine. Basically, it acts as a foundation or an anchor. In general, it is composed of a central shaft and one or more graded steel helices. Screw piles have made great progress in recent decades, particularly when it comes to their axial capabilities and installation processes. Using screw piles for anchoring and supporting structures is advancing rapidly. Despite this, screw piles are still lacking design methods that require further research. This study consists on developing three conceptual models to predict the carrying capacity of a screw pile of multi helices. The first analytical model takes into account shaft friction, grooves’ geometry, and configuration of helices’ assembly. The second analytical model is based on the observed failure surface of screw piles proclaimed in literature. Whereas, the third empirical model considers the existing correlation between the torsional resistance generated during screw pile installation and its carrying capacity. The three models were validated against some actual testing results and some experimental data reported in literature. It was noted that the first analytical model underestimate the compressive carrying capacity of screw piles by about 5 to 15%. For the second model, a reasonable agreement was noted between the calculated and the measured results when the ratio L/B ≥ 10. However, in the opposite, the model overestimates the ultimate capacity of screw piles by about 15.3%. Likewise, the empirical model (third model) overestimates the tensile carrying capacity of screw piles by 10 to 20% with an average of 12.4%.