Effects of Shape and Technology of Installation on the Bearing Capacity of Pile Foundations in Layered Soil

Abstract

Among other factors, which influence the bearing capacity of piles, the shape of its external configuration, as well the installation technique employed during construction, also play major roles. This paper presents the results of recent experimental investigation on effects of shape and technology of installation on the bearing capacity of pile foundations. The results from both laboratory and field investigations conducted on modeled prototype test piles of cylindrical, prismatic (square) and tapered conical sections are presented in this study. The piles were installed by driving (hammering and vibration) and boring techniques. The results of influence of installation methods, show bearing capacity increments of 10% in bored piles, 20-22% in hammered driven piles, and 20-30% in vibrated driven piles. The bearing capacity of tapered conical piles is 1.5 – 2 times higher than prismatic (square) piles and 2-3 times higher than cylindrical piles respectively. Tapered conical piles have higher bearing capacity in fairly homogenous soils, (whether soft or stronger). In sandy and silty sand soils, especially where fine sand overlaid a stronger coarse sand layers, driven piles (hammer or vibration) have higher bearing capacity than bored piles, whereas the latter have higher bearing capacity where soft fine sand sandwiched between stronger coarse sand layers. Cylindrical piles installed by boring method have higher bearing capacity in sandy soils than prismatic pile installed by driven, but the latter gave higher bearing values in layered soil with thicker stiff silty clay above sandy layers.