Civil Engineering Association

FIELD AND LABORATORY PERFORMANCE EVALUATION OF SPREAD FOOTINGS

The performance of five highway bridge structures, located in Ohio and supported by spread footings on cohesionless soils or cohesive soils, was monitored in the field throughout construction and under service conditions. The performance of these structures was also examined through centrifuge modeling in the laboratory. Factors used in evaluating these bridges were overall settlement, tilting of abutment walls/pier columns, and pressure distribution under the footings. Field and experimental measurements were then compared against estimates made by selected geotechnical methods. None of the spread footings in these five bridge structures experienced an average settlement of more than 2 in. (5 cm) prior to service load application. Contact pressure monitored at the footing/bearing soil interface in the field remained less than 40 psi (276 kPa) and was generally close to the theoretical estimate. Poorer agreement resulted between the measured and predicted abutment wall tilting. None of the six geotechnical methods for predicting settlement of footings on cohesionless soils was accurate in all cases. The method proposed by Hough appeared to be the best. Standard methods used to estimate immediate and time dependent consolidation settlements were reasonably accurate when compared to field data. Centrifuge testing techniques provided settlement results superior to those predicted by any of the six geotechnical methods. One limitation of centrifuge testing, however, is the simulation of complex subsurface conditions in the laboratory.