Measurements of erosion on highway slopes and use of the Universal Soil Loss Erosion Equation
Abstract
A rainfall simulator was modified and successfully operated on highway slopes with steepnesses from 9% to 50% at Putnamville and Evansville, Indiana in 1985 and 1986. Modifications of the structure frame, special techniques for preparation of the test plot and special operating sequences of the rainfall simulator were also developed. Theoretical and experimental approaches were developed to study distribution of the simulated rainfall intensity and its effects on erosion under different conditions. The conditions included different nozzle heights, slope steepnesses and nozzle tilting angles for single nozzles and group nozzles. The predicted values were found to be reasonably close to the measured data. It was found that average intensity is not sensitive to nozzle height and tilting angle, but increases with slope steepness. From the field erosion tests on highway slopes at Evansville, the slope steepness factor, S, of the Universal Soil Loss Equation was extended to 50% from 18%. The S factor appears to reach a maximum value of 1.5 at a slope steepness of 20%. The S factor of the site on a 2 to 1 slope at Putnamville was estimated to be 1.50 to 1.75. Erosion rate was found to be very sensitive to discharge rate, but not sensitive to slope steepness. The soil erodibility factor by measurement is lower than that from the nomograph of Wischmeier, Johnson and Cross (1971) because of the compaction effect. A rotational shear device was modified and successfully operated in 1986 and 1987. It was found that for compacted and fully (or nearly fully) saturated soil samples, the soil erodibility factor decreases with critical shear stress. Critical shear stress is not recommended for use in determination of the soil erodibility factor for soils with low densities, or low cohesion or high permeabilities. Using the Universal Soil Loss Equation and findings in this study, examples of predicting soil erosion on highway slopes at five different locations in or around the state of Indiana are given.
Degree
Ph.D.
Advisors
Lovell, Purdue University.
Subject Area
Civil engineering
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