Optimization of Design Parameters for Enhanced Integrity of Massive Drilled Shaft

This study focused on the optimization of concrete mixture and geometric design parameters for a drilled shaft to effectively reduce the potential degradation of mass concrete. At concrete's early hardening stage, the heat of hydration plays a pivotal role that affects the integrity of mass concrete. The Florida Department of Transportation (FDOT) currently designates concrete drilled shafts with a minimum diameter of 1.8 m as mass concrete due to a great concern about high temperature development. In this study, a validated thermal finite-element (FE) model for a drilled shaft with a diameter of 1.8 m was developed for a parametric analysis to determine the effects of concrete property, surrounding soil condition, geometric design, and pipe cooling on temperature development. The results indicated that the use of supplementary cementitious material (SCM) significantly reduced the temperature development in a drilled shaft. The temperature development increased as the placement temperature and volume: surface area (V:A) ratio increased. In particular, the use of a centroid void shaft and a pipe cooling system significantly decreased the maximum temperature and temperature differential, and could be a viable solution to effectively mitigate the temperature development, preventing potential disintegration due to the effects of delayed ettringite formation, strength reduction, or thermal cracking. (c) 2019 American Society of Civil Engineers.