About the research
The American Association of State Highway and Transportation Officials (AASHTO) has revised the design guidelines over the years to impose greater design/rating earth pressures on buried structures. This is one of the major reasons that many old culverts designed with allowable stress design (ASD) or load factor design (LFD) do not pass load and resistance factor ratings (LRFR) although they have performed satisfactorily for many years. Currently, the Iowa Department of Transportation (DOT) Office of Bridges and Structures uses the lateral earth pressure of 36/18 pcf specified for LFD and ASD and the 60/30 pcf for load and resistance factor design (LRFD). It would be helpful to understand which load pressure is more realistic for Iowa soil conditions and typical construction methods. This understanding is very important for culvert load rating so as to avoid unnecessary load postings of many older culverts.
A culvert located in Ida County, which consists of multiple 8×12 ft concrete boxes was selected during the initial phase of this project and has been monitored for two years (Stage 1 of Design #1115). The monitoring system consists of six strain gauges and five pressure cells, and was installed on 1/28/2016. After two full seasonal cycles, and with the amount of the accumulated data, a systematic analysis of the acquired data is now necessary. The goal of this project is to analyze the collected data from the Ida County culvert and develop practical Iowa-specific earth pressure recommendations that can be used in culvert design and load rating.