Soil-structure interaction of underreamed piles

Underreamed piles are cast-in-place drilled shafts that have one or more bulbs added to the straight shaft to increase their axial capacity. The underreams are typically formed by using a belling tool and filling the cavity with plain concrete. This study explores the mechanisms that contribute to the gain in capacity of underreamed piles relative to their straight counterparts. Soil-structure interaction of underreamed piles is explored using a synthetic transparent soil made of fused quartz and a mixture of mineral oils with matched refractive indices. The effect of the number of underreams and the distance between them, as well as the ratio between the diameters of the underreams and the straight shaft, were explored. Several underreamed pile configurations were 3D printed in-house. Load deformation response was obtained during uplift and compressive loading. Soil movements were obtained by tracking the successive movements of the speckle pattern resulting from the interaction of a laser light sheet and the fused quartz. Successive images were analyzed using digital image correlation (DIC) to obtain the resulting, displacement, and strain fields. The study aims to provide guidance on designing more efficient underreams for these structures.