Drilled shaft foundation construction problems

Abstract

Various problems were encountered during the construction of three full-scale Drilled Shaft Foundations (DSF) at the Monticello Arkansas Test Site (MATS). These construction problems included, but were not limited to: loss of slurry, broken equipment and premature set-up of the concrete. Comparisons between the results obtained from the Bi-directional Load Cell (BLC) testing that was performed on each of the DSF aided in the determination of the effects of the construction problems on the axial capacity of the DSF. The measured unit end bearing resistance values were investigated to determine the effects of using a 1.2 m diameter clean-out bucket on a 1.8 m diameter DSF. In the South 1.2 m diameter DSF, the bottom plate of the BLC moved more than predicted (approximately 10 cm) due to the premature set-up of concrete below the BLC. Soil data obtained by using the Arkansas State Highway and Transportation Department (AHTD) and University of Arkansas (UofA) geotechnical investigation methods, in conjunction with the FB-Deep software program, were used to accurately predict the unit side resistance responses for the three DSF at the MATS. Therefore, the use of these geotechnical investigation techniques and this software programme are recommended for further use within the state of Arkansas. Due to the problems associated with maintaining an open DSF excavation overnight and the associated construction savings that may be obtained by constructing a DSF during a single day (for cohesionless soils), it is recommended that DSF be constructed (drilled and poured) in a single day.