Biopolymers for enhancing the engineering properties of soil
Type of DegreePhD Dissertation
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The need for constant construction rapidly expands the built environment which often spreads over areas with unfavorable site conditions. In such events, soil stabilization is an inevitable process. Increasing soil strength with chemical stabilizing agents such as cement often rises environmental concerns. Therefore, the need for eco-friendly solutions for soil stabilization is in constant demand. One of the most promising solutions for that issue is the utilization of biopolymers. This study experimentally and numerically investigated five different biopolymers and their effect on soil strength. Biopolymers that were investigated were xanthan gum, guar gum, beta 1.3/1.6 glucan, chitosan, and alginate. Their effect was observed while interacting with three types of soil: sand, clay, and silty sand. The experimental research included unconfined compression tests, splitting tensile tests, triaxial tests, direct shear tests, and water durability tests. The testing was performed under different biopolymer concentrations and different curing times. The broad experimental research showed that the strength of treated soil tends to increase with the biopolymer concentration and curring time, but that it also depends on the volume of the soil, type of the soil and type of biopolymers. The tests indicate an optimum biopolymer concentration and optimum curing time after which the soil improvement does not increase. This study focused more on the biopolymers that showed a more promising effect on the increase of soil strength. Therefore, some sections of this study focused more on xanthan gum, guar gum and beta-glucan. In the majority of cases, the biopolymer xanthan gum showed the most dominant effect on the increase of the soil strength. Xanthan gum and guar gum demonstrated promising properties to reduce soil degradation through the process of wetting and drying. Furthermore, it was observed that the regenerative properties of xanthan gum can restore some levels of lost soil strength. From the experimental studies, the three most influential polymers were investigated in the numerical part of this study. The numerical part was focused on investigating the effect of biopolymers on the onset of strain localization. For the needs of the numerical study, an analytical-numerical model was created in order to capture the stress-strain response of biopolymers-treated soil under the state of pressure. The extensive experimental investigation provided large sets of data from which were used either for calibration or verification. Analyzing the stress-strain response of the treated and plain soil, it was noticed that the presence of biopolymers tends to postpone the onset of strain localization and by that, the failure of soil mass can be postponed.