Civil and Environmental Engineering


First Advisor

Chung R. Song

Date of this Version

Summer 7-2020


Bitar, 2020


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Civil Engineering, Under the Supervision of Professor Chung R. Song. Lincoln, Nebraska: July, 2020

Copyright 2020 Layal Bitar


Verdigre located in North Eastern Nebraska experienced slope failures. The geological formations of theses slopes largely consist of several layers of weathered shales and glacial tills. It is believed that the weathering process reduced the shear strength of the soils leading to slope failures.

In this study, strength characteristics of Xanthan and Gellan gums treated soil specimens compacted at the optimum moisture content for field application were investigated so that the biopolymer treated soils may be properly used to stabilize the slopes. The untreated and treated samples were subjected to a wet-freeze(-6oF)-thaw(167oF)-dry weathering process up to 8 cycles, then sheared by the direct shear device to investigate the effects of weathering on the strength characteristics of compacted soils samples. It was found that:

  • Increasing Xanthan and Gellan gums concentrations increased the shear strength of the glacial tills and weathered shales. Xanthan gum was more effective than Gellan gum.
  • For untreated and treated glacial tills and weathered shales, the shear strength of the soils decreased as the number of weathering cycles increased. However, the reduction from 4 cycles to 8 cycles was insignificant.
  • The shear strength of the treated glacial tills and weathered shales mixed with 1.5% of Xanthan gum at 8 weathering cycles was 88% and 83% of the untreated unweathered ones, respectively.
  • The effect of using a biopolymer content higher than 1.5% on the shear strength of the glacial tills and weathered shales was not apparent at higher weathering cycles.

Advisor: Chung R. Song