Assessment of Soil Stabilization Techniques for Sustainable Pavement Subgrades

Thesis Abstract

Inadequate soil stabilization techniques pose significant challenges to the sustainability, durability, and cost-effectiveness of pavement subgrades, compromising infrastructural integrity and increasing maintenance costs in urban and rural road networks. This study aims to comprehensively evaluate the performance and sustainability of various soil stabilization methods under local environmental conditions, providing empirical evidence to optimize pavement subgrade engineering practices. The primary objectives include assessing the mechanical properties of stabilized soils using different techniques, analyzing the environmental impacts associated with each stabilization method, and developing a sustainable framework for selecting the most effective stabilization approach tailored to specific soil types and climatic conditions. The research adopts a mixed-methods approach, integrating quantitative laboratory experiments with qualitative field assessments. The target population consists of soil samples from three distinct geomorphological zones within the study region, encompassing clay, silty sand, and sandy silt subgrades commonly used in local road construction. A stratified random sampling technique was employed to select 150 soil samples, subdivided equally among the three zones, ensuring representative variability. Laboratory experiments involved evaluating soil compaction, unconfined compressive strength, and permeability before and after stabilization. The stabilization techniques tested include cement stabilization, lime treatment, fly ash incorporation, and geopolymer applications, each applied at various dosage levels based on preliminary soil-test recommendations. Data collection instruments included standardized laboratory testing equipment, such as a Proctor compaction apparatus, unconfined compression testing machines, and permeameters. Additionally, environmental impact data were collected through life-cycle analysis (LCA) tools, measuring parameters such as carbon footprint, energy consumption, and leachate toxicity associated with each stabilization method. To ensure the validity and reliability of the laboratory results, calibration of testing equipment was conducted prior to experiments, and repeat tests were performed on 10% of samples. Data analysis involved descriptive statistics to summarize soil properties, ANOVA to compare the effects of different stabilization techniques on mechanical and permeability parameters, and multiple regression analysis to identify significant predictors of soil strength stabilization. A framework based on the Theory of Planned Behavior was employed to interpret stakeholder preferences and sustainability considerations in stabilization practices. Expected findings suggest that geopolymer stabilization demonstrates comparable or superior mechanical performance relative to traditional methods, with significantly reduced environmental impacts. Lime and fly ash treatments are anticipated to improve soil strength but exhibit higher leachate toxicity, while cement stabilization may offer the highest immediate strength gain with notable ecological concerns. It is projected that an optimal stabilization strategy will balance mechanical enhancement, environmental sustainability, and cost considerations, resulting in a decision-making framework adaptable across diverse soil types and climatic conditions. The study contributes to existing knowledge by systematically comparing traditional and emerging stabilization methods within a sustainable development context and providing empirical data aligning with environmental objectives. It also develops a decision-support model integrating technical and environmental metrics, thereby guiding engineers and policymakers toward environmentally responsible infrastructure investments. The main conclusion emphasizes the importance of selecting soil stabilization techniques not solely based on mechanical performance but also considering ecological footprints and long-term sustainability. The research recommends adopting geopolymer-based solutions where feasible, incorporating environmental impact assessments into routine geotechnical evaluations, and further investigating cost-effective stabilization formulations tailored to local material availability and climate variables. Additionally, future studies should explore long-term field performance monitoring of stabilized soils under real traffic loads and climatic fluctuations to validate laboratory findings and refine the sustainability framework.