Construction Management and Technology Program

About the research

The Iowa secondary road system has a large number of scour-susceptible bridges or bridges with unknown foundation conditions. These structures are commonly required to have a plan of action (POA) to close them during flood events, or have countermeasures installed to keep them open. In the case of unknown foundations, countermeasures must be installed.

Among the many different countermeasures available is a potentially viable technique known as a partially grouted revetment. Partially grouted revetment construction involves the placement of rock, stone, and/or recycled concrete on a filter layer that is compatible with the subsoil. The voids of the matrix are then partially filled with a portland cement-based grout material.

Partially grouted revetment appear to achieve a desirable balance between full and no grouting of revetment. Specifically, partial grouting increases the stability of the system without eliminating the flexibility of a looser matrix. In addition, a partially grouted revetment system allows for the use of smaller (and less expensive) rock, stone, and/or recycled concrete, which also results in decreased layer thickness. The ideal system adheres adjoining pieces together while leaving relatively large voids between the stones.

The final project report presents background information on countermeasure types and their frequency of use, including a field review of existing countermeasures to determine quality of performance. These efforts were followed by several pilot installation sites on county infrastructure in Iowa using partially grouted riprap. These pilot installations are described and their performance documented after years of service.