Bearing Capacity of Auger‐Cast Piles in Sand

Abstract

Auger‐cast piles are formed by drilling a continuous flight auger into the ground and, on reaching the required depth, pumping grout or concrete down the hollow stem as the auger is steadily withdrawn. The sides of the hole are supported by the soil‐filled auger, eliminating the need for temporary casing or bentonite slurry. This paper outlines important features of auger‐cast pile installation that influence the structural integrity and geotechnical capacity of completed piles. These include soil decompression, correlation between the rotational and vertical speeds of the auger, and precise coordination of auger extraction and grout supply. The results of 66 loading tests on auger‐cast piles in sand are presented. Shaft resistance is found to be independent of the relative density of the sand, while point resistance can be directly correlated with results of standard penetration and cone penetrometer tests. Empirical design methods for bored piles were found to underestimate the failure loads of auger‐cast piles. New correlations, based on pile length and standard penetration resistance, are proposed.