Document Type

Article

Publication Date

Fall 9-30-2019

Keywords

Biopolymer, biomeditation, xanthan, degradability

Abstract

Earth dams and levees are constructed and retrofitted nowadays using the same materials that were used in the past, clays and sands. Despite the current advances in engineering, designing and constructing these critical infrastructure, earthen dams and levees continue to suffer from the same challenges over the years. These challenges include internal and surface erosions, loss of stability due to moisture migration, and inabilities to self-heal potential failure points. This project focuses on the use of biopolymers as additives to strengthen earthen dams and levees targeting an overall increase in their resilience.

Explicitly, the report for Milestone 3 presented the results of an experimental program aiming to assess the impacts of biopolymers on the physical and mechanical properties of the typical materials used in the construction of earth dams and levees: sands and clays. This program focused on determining the impact of biopolymers on (1) the index properties of cohesive soils as an easy way to assess the biopolymer impacts on the strength of these soils, (2) the compaction characteristics of sands and clays, and (3) the shear strength of sands and clays treated with biopolymers. Additionally, the report explains the observed behavior of the soils treated with biopolymers using known biopolymer responses and properties (i.e., viscosity).

The results of the experiments performed on the considered clayey soil showed that biopolymer treatment increases the plastic and liquid limits of the clay. Such increase in Atterberg limits is found to be independent of the used biopolymer type and percentage, which indicates that all biopolymer treatments for clays have the ability to increase their strength. In fact, the strength of the clay treated with biopolymers was found to increase significantly compared to that of the pure clay as evident by the unconfined strength of compacted clay samples.

Additionally, the report discusses a practical approach to overcome the reduction in the shear strength of sandy soils when treated with pure biopolymers. This technique relies on stabilizing the biopolymers with clay fillers prior to mixing them with or injecting to the sand. The results of the triaxial experiments performed here prove that the magnitude of the strength gain in sandy soils treated with biopolymer-filler composites depends on the filler type, percentage and interaction with the used biopolymer. For a given filler type, it is noticed that increasing the viscosity of the biopolymer-filler composite reduces the internal friction angle but increases the cohesion between the sand grains.

This current report presents the results of advanced molecular dynamics simulations and experimental program to assess the biodegradability of biopolymers used for soil stabilization. The focus of these models and experiments are on coarse-grained soils stabilized with biopolymers since the pore structure in fine-grained soils prevents the growth of any micro-organisms that may consume the biopolymers. The main conclusion of these numerical models and experimental program is that the biodegradability of biopolymers used to stabilized soils is not significant. The advanced molecular dynamics models showed that even at 50% degradation in the biopolymers, the viscosity of the biopolymer was reduced by 23%. This reduction is not considered significant since the initial viscosity is significantly higher than that of the pore water in untreated specimens. The experimental program, then, confirmed the finding of the numerical modeling as the experiments showed no significant reduction in the unconfined compressive strength of sand specimens treated with various xanthan gum-clay composites even after aging for 9 months.

Additional Files
Abdelaziz_NIPP_Final Presentation_Biopolymer Stabilized Soils.pdf (1824 kB)
Presentation PDF
Final Webinar.mp4 (386979 kB)
Recorded webinar
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