Iowa Department of Transportation
Brent Pharesbphares@iastate.edu email >
Bridge Research Engineer, BEC
About the research
The American Association of State Highway and Transportation Officials (AASHTO) has revised the design guidelines over the years to impose larger earth pressure 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 resistance factor design (LRFD) ratings, although they have performed satisfactorily for many, many years. Currently, the Iowa Department of Transportation (DOT) Office of Bridges and Structures uses the lateral earth pressure of 36/18 pcf specified in LFD and ASD and the 60/30 pcf in LRFD. It would be helpful to understand which load pressure is more realistic for Iowa soil conditions and our typical construction approach. This understanding is very important for culvert load ratings to avoid unnecessary load posting of many older culverts.
The Office of Bridges and Structures has been waiting for a construction project to instrument a culvert to monitor the earth pressure and especially the lateral earth pressure during and after construction. The four-lane widening of US 20 in Ida County presents a very good opportunity. The Ida County culvert is an interesting case study due to the extremely large earth fill depth (37 ft) and relatively large box size (8 by 12 ft). The objective of this work is to use strain gauges and pressure cells to monitor the culvert behavior during and after construction.
This project funding is to purchase the sensors needed to perform this work. All effort associated with this work will be covered under the Iowa DOT Bridge Engineer contract with the Bridge Engineering Center (BEC).