Nebraska LTAP


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Song, C. R., Bitar, L., Wood, R. L., Kim, Y. R., Eun, J., Bekele, B. and Abualshar, B. (2021). Biopolymerized Slope/Subgrade Stabilization and Advanced Field Monitoring, NDOT Research Report M110.


The slightly overconsolidated glacial tills and weathered shales in Midwestern states of the USA often show substantial strength degradation after construction. This strength reduction often causes time dependent slope failures along the roadside. This study investigated the possibility of applying biopolymer based soil modification techniques to mitigate the strength reduction phenomenon of these soils. For this research, several different biopolymers were evaluated through laboratory tests, two biopolymers were selected for extensive weathering tests, then a higher-performing biopolymer, Xanthan, was applied to a test slope in Verdigre, Nebraska with heavy instrumentation. The followings are the summary of the results.

The unweathered laboratory shear strength of the weathered shales from Verdigre was improved by 20%, 30%, and 40% by mixing 0.5%, 1.5%, and 2.5% of Xanthan gum, respectively. On the other hand, the weathered shear strength of the weathered shales at Verdigre treated with 1.5% of Xanthan gum after 8 wet-freeze-thaw-dry cycles still retained 83% of the untreated unweathered ones. A similar result was obtained for glacial tills, manifesting that the Xanthan based polymerization method may be used as a new eco- friendly method to enhance the strength of weathered shales and glacial tills in Midwestern states. The field applied Xanthan treated soils showed similar behavior to laboratory test results based on pressuremeter and vane shear test results so far. However, further monitoring is required to fully verify the findings.