Modeling of Installation and Quantification of Shaft Resistance of Drilled-Displacement Piles in Sand

Abstract

Drilled-displacement (DD) piles are installed using a drilling tool consisting of a partial-flight auger and a displacement body. This tool is inserted and advanced in the ground by both a vertical force and a torque. Despite the widespread use of DD piles throughout the world, most of the design methods available for calculation of shaft capacity were developed solely on the basis of results of pile load tests for which only the pile head capacity was known (no instrumentation that allowed separation of shaft and base loads was used in those tests). The shaft capacity of a pile depends on the stress state of the soil surrounding the pile that results after its installation. Proper analysis of the impact of installation of DD piles on the stress state in the in situ soil is fundamental to the development of reliable design methods. This paper presents the results of one-dimensional, quasi-axisymmetric finite-element analysis (FEA) performed with an advanced sand constitutive model that capture the essential stages of the installation and loading of DD piles in sand. In addition, a set of equations is proposed for the estimation of the unit limit shaft resistance of DD piles installed in sand that takes into account the initial soil state and the rate of penetration of the drilling tool into the ground during pile installation.