In response to problems with corrugated metal pipe (CMP) culvert uplift failures caused by unbalanced inlet hydraulic loading, full-scale field testing and numerical analysis were undertaken to develop a rational design methodology for CMP inlet tiedowns. Four uplift tests performed on a 2.44-m-diameter CMP under different backfill cover, foreslope, and restraint conditions are described. The objectives of the tests were to gain insight into the soil-structure interaction processes and to provide data for verification of the performance of the finite-element model used to calculate the required restraint forces. The test results indicate that the backfill foreslope has a significant effect on uplift response. For example, the force required to lift the CMP inlet 25 mm was about 50 percent greater with 0.6 m of backfill cover and a full 2:1 foreslope than with 0.6 m of backfill cover and approximately 4 m of the CMP exposed beyond the toe of the backfill foreslope. These results indicated that appropriate modeling of the soil-structure interaction and interface behavior in the foreslope region is extremely important.

Reusing whole scrap tires as a culvert is a cost-effective alternative to draining water from small drainage basins. The complete design of a scrap tire culvert must consider both structural and hydraulic performance. Hydraulic considerations are the focus of this report. The hydraulic capacity of a scrap tire culvert is largely affected by the limited size and the relatively rough barrel formed by scrap tires. In this analysis, the hydraulic capacities of culverts made of truck tires, at various slopes and lengths, were obtained by estimating Manning’s roughness coefficient and limiting the maximum flow depth in the culvert to 75 percent of the pipe diameter. The Manning’s roughness coefficient of a truck tire culvert was estimated to be 0.05 and 0.075, respectively, with and without sand ballast placed in the bottom of tires. The results show that a truck tire culvert can drain water up to 0.35 m 3 /s, and its hydraulic efficiency approaches that of conventional pipes of the same diameter when the slope is greater than 0.11 or 0.30, respectively, for culverts made of truck tires with or without sand ballast. The equivalent concrete and corrugated metal pipe sizes were obtained for corresponding flow capacities of truck tire culverts.

Grade control structures are used extensively to control river channel degradation. Although their use is widespread, the durability and performance of these structures, namely, sheet pile, H-pile, rock sill, and concrete block weirs have not been systematically evaluated. In this study, stream grade control structures in a loess area (western Iowa) were quantitatively evaluated with a performance number system to determine their field conditions and durability. For these evaluations, two dimensionless parameters (erosion control ratios and discharge ratios) were developed to correlate field observations and measurements. Structures that experienced small flows performed relatively well, whereas those that carried large discharges had poor performance. The stability of riprap decreases as the discharge ratio increases. Better riprap performance was obtained at structures with greater erosion control ratios. Based on these evaluations, problems associated with the structures were identified. In-channel movement of rock riprap was found to be a prevalent problem. Considerations for future designs and construction are recommended. The evaluation method and procedure can be applied to loess soil regions in the central United States and other regions worldwide. The information gathered can be used to guide field surveying and modeling studies.

In the beginning of the 20th century, many streams in western Iowa were channelized to reduce flooding and to open swamp land to cultivation. Channel straightening accomplished its goal. However, it resulted in greater streamflow velocities, causing stream channels to degrade. This degradation has resulted in significant loss of land and damage to transportation and communications infrastructure in western Iowa and in several states in the United States. Baumel et al. (1994; Impact of Degrading Western Iowa Streams on Private and Public Infrastructure Costs. Final Report Iowa DOT HR-352, Stream Stabilization in Western Iowa) estimated the historical cost of this degradation on land loss and damage to transportation and communications infrastructure in western Iowa. The purpose of this paper is to extend the Baumel et al. analysis to estimate future degradation costs on 141 streams in western Iowa. It also presents two types of degradation cost estimates. One is a time neutral cost that does not consider the dates on which the degradation costs are incurred. The second is a time value cost which considers the dates on which the costs are incurred and then discounts these costs back to 1992 dollars. The time value costs are the more accurate estimates of the cost of future degradation in 1992 dollars and should be used to evaluate stream stabilization project proposals.