Document Type

Thesis - Open Access

Award Date

2024

Degree Name

Master of Science (MS)

Department / School

Civil and Environmental Engineering

First Advisor

Aritra Banjee

Abstract

Problematic soil like expansive soil, and frost-susceptible soil causes significant damage to civil infrastructure. The use of calcium-based stabilizers in the treatment of sulfate-rich expansive soils is not suggested due to the formation of ettringite. Infrastructure such as pavements and embankments built on expansive soil are often exposed to the damaging impacts of freeze-thaw cycles in areas prone to seasonal freezing making them vulnerable to cracking and spalling. In this study, a native expansive soil from South Dakota with a sulfate content of more than 10,000 ppm was stabilized using biopolymer and cement. The experimental study investigated the strength and stiffness properties of the control and treated soil after the various freeze-thaw (F-T) cycles. Soil morphology provided insights into the configuration of biopolymer networks and the development of ettringite within treated soils. Biopolymers were used as an environmentally-friendly substitute for traditional energy-intensive stabilizers in expansive soil stabilization, and potentially reducing carbon footprints. The study found the incorporation of biopolymer as a co-additive with cement can be a viable alternative for stabilizing sulfate-rich expansive soil subgrade. The biopolymer can be introduced to the silty soil to improve the insufficient strength. The strength improvement in the early curing is not sufficient. Different cations (Na+, K+, Ca2+) are introduced to study the impact of cation-enhancement on biopolymer networks. Multivalent Cation (Ca2+ ) was found to be effectively cross-linking biopolymer and increasing the early strength comparable to 28 days curing strength of biopolymer treatment. Climate change is known to cause alterations in weather patterns and disturb the natural equilibrium. Changes in climatic conditions lead to increased environmental stress on embankments, which can result in slope failures. Due to wetting–drying cycles, expansive clayey soil often swells and shrinks, and matric suction is a major factor that controls the behavior. Increased temperature accelerates soil evaporation and drying, which can cause desiccation cracks, while precipitation can rapidly reduce soil shear strength. Desiccated slopes on embankments built with such soils can cause surficial slope failures after intense precipitation. This study used slope stability analysis to quantify how climatechange- induced extreme weather affects embankments. Historic extreme climatic events were used as a baseline to estimate future extremes. CMIP6 provided historical and future climatic data for two different study areas in different climate regions. Coupled hydromechanical finite element analyses used a two-dimensional transient unsaturated seepage model and a limit equilibrium slope stability model. The study found that extreme climatic interactions like precipitation and temperature due to climate change may reduce embankment slope safety. The reduction in the stability of the embankment due to increased precipitation resulting from different greenhouse gas emission scenarios was investigated. The use of unsaturated soil strength and variation of permeability with suction, along with the phase transition of these earthen embankments from near-dry to near-saturated, shows how unsaturated soil mechanics and the hydro-mechanical model can identify climate change issues on critical geotechnical infrastructure.

Publisher

South Dakota State University

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Rights Statement

In Copyright