Nebraska LTAP



Ronald K. Faller

Date of this Version


Document Type



Rosenbaugh, S.K., Schmidt, T.L., Faller, R.K., and Reid, J.D. "Development of Socketed Foundations for S3x5.7 Posts" (2015) Nebraska Department of Roads Research Report


The objective of this study was to develop a socketed foundation for use with the S3x5.7 (S76x8.5) weak post. The design focused on cylindrical, reinforced concrete foundations with a steel tube placed in the center for use as the socket. The foundation was to prevent both damage and displacements exceeding 1 in. (25 mm), as measured at groundline, during an impact event. To evaluate various foundation designs, ten dynamic bogie tests were conducted over three separate rounds of testing. Round 1 was conducted in a weak, sandy soil; Round 2 was conducted in a strong, stiff soil; and Round 3 was conducted within a 4-in. (102-mm) thick asphalt pad. The results of the bogie testing led to the development of three socketed foundation design options. Option 1 consisted of a 12-in. (305-mm) diameter foundation; Option 2 was a 15-in. (381-mm) diameter foundation; and Option 3 was a foundation installed within an asphalt mow strip. Option 1 carried a risk of concrete damage during severe impacts, but it was included for those agencies wishing to be more aggressive and accept the risks of damage. Each design option had a unique reinforcement configuration and minimum embedment depth. Further, the recommended minimum embedment depths were also a function of the surrounding soil conditions and the frost line depth of the installation site.