The Behavior of Single Under-Reamed Piles under Compression Load in Clay - Numerical Study

Abstract

Under-reamed piles with one bulb or more have been widely used in various types of soil to support structures to resist compression, lateral, and uplift load. In the current study, a 3D numerical model done by PLAXIS 3D software was used to predict the behavior of floating under-reamed piles subjected to compression load in medium clay. The study focuses on the effect of pile geometrical features on bearing load such as bulb spacing, bulb diameter, and the bulbs number compared with the conventional pile. Considering medium clay as a single layer in the analysis with the cohesion of 38 kN/m², the comparison of results for multi under-reamed pile compared with a conventional pile takes into account the bulbs number ranging from one to three, bulb diameter ratio (Du/D) from 1.5 to 2.5, the spacing ratio (S/D) from center to center of bulb from 2 to 8 and bulb location, the pile length is constant in this study. The linear elastic constitutive model was considered to simulate the pile material, and the Mohr-Coulomb model was chosen to represent the clay surrounding the pile. The results of the numerical model show that when the bulb diameter ratio becomes 2.50, the bearing load increases by 50.31 % for an under-reamed pile with a single bulb compared with a pile without a bulb. Also, using an under-reamed pile with a bulb diameter ratio (Du/D = 2.5), bulb spacing ratio (S/D = 8), and when the bulbs number were three, the bearing load increased by 165.50% compared with a pile without a bulb. Moreover, if bulb spacing ratio (S/D) increased from 2 to 8, the bearing load increased by 25.15% for a bulb diameter ratio (Du/D = 2.5) and the bulbs number were two.