The FHW A believes that spread footings on soils are underutilized because designers encounter one or more of the following obstacles: (a) limited knowledge of AASHTO/FHWA technical references that pertain to spread footings on soils to support bridges; (b) limited knowledge of adequate performance data for spread footings; (c) unrealistic tolerable settlement criteria; (d) overestimation of loads used to calculate settlement; and (e) the use of conservative settlement prediction methods. These obstacles have resulted in institutional biases and overly conservative designs that lead to the unnecessary use of costlier deep foundation systems. The primary goal of this report is to promote the use of spread footings bearing on competent natural soils, improved soils, and engineered fill materials as a routine alternative to deep foundations for support of highway structures by addressing the factors identified above. The introduction of Load and Resistance Factor Design (LRFD) permits a rational approach to the consideration of spread footings on soils as a viable alternative to deep foundations. Using documented performance data, the report presents powerful concepts such as the use of construction-point analysis and angular distortions to demonstrate the efficacy of using spread footings. The report presents sources of information that agencies and designers can use as references in their project applications. It is hoped that this report will provide the impetus for agencies and transportation designers to evaluate the use of spread footings for all conditions other than those where their use is precluded (e.g., scour conditions).
Download Selection of Spread Footings on Soils to Support Highway Bridge Structures by Naresh C. Samtani, PE, PhD, Edward A Nowatzki, PE, PhD and Dennis R. Mertz, PE, PhD from the NCS Consultants, LLC website. [Disclosure] NCS is my day job employer. [/Disclosure]