Effect of bulk density, age, and water content on the erosional strength of streambank soils

Abstract

The purpose of this study is to investigate the influence of physical properties, more specifically the bulk density and water content, to the erosional strength of streambank soils. Thirty (30) soil samples were extracted from the crest, midbank and toe of the bank at Clear Creek in Iowa City, Iowa. Out of those thirty (30) samples, six (6) samples were tested in the standard soil laboratory for obtaining their bulk density and particle size distribution, six (6) samples were tested their bulk density and heterogeneity using Gamma radiation scanning, and eighteen (18) samples were tested their erosional strengthr*f. In addition, six (6) pure Kaolinite-clay samples were constructed with various degrees of consolidation or age and water content for measuring their T>-:f using conduit flume technique. The results of the conduit flume tests revealed an increasing trend in magnitude of Hf moving from the crest to the toe of the bank. The T<--t values were 1.57, 1.53, and 1.92 Pa for the crest, midbank, and toe soils from the left bank. In similar order, the Tc.f values were 1.46, 1.47, and 1.83 Pa for the soils from the right bank. A similar trend was obtained for the bulk density based on standard laboratory test and gamma radiation scanning. According to standard laboratory test, the average bulk density values for the crest, midbank, and toe of the right bank were 1299, 1618, and 1880 kg/m3. Similarly, based on gamma radiation technique, the average bulk density values for the crest, midbank, and toe of the right bank soils were 1273 kg/m3, 1594 kg/m3 and 1863 kg/m3, respectively. This agreement in the trend of Tr-f and bulk density suggests a positive correlation between those to parameters. The results of Kaolinite-clay sample experiments demonstrated that samples with higher degree of consolidation or more age would have higher ^V. In addition, the Kaolinite-clay samples with higher water content would have lower rct. These findings suggest the presence of spatial and temporal variability in Ta of streambank soils. Therefore, incorporating this Tc,i variability in modelling streambank erosion will give more accurate results.