STUDY OF RESILIENT MODULUS AND GEOTECHNICAL PROPERTIES OF POLYMER STABILIZED HIGH PLASTICITY CLAY

Author

Sushanta Bhattarai, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2024

Degree Name

Master of Science

Department

Civil Engineering

First Advisor

K. Kolay, Prabir

Abstract

Soil stabilization is a widely used technique in the field of geotechnical engineering for a wide range of applications. Traditional stabilizers such as cement and lime, although very efficient, are not environmentally friendly as they leave major carbon footprints, therefore the demand for sustainable stabilization methods is escalating. This research investigates the potential of two different polymers e.g., a biopolymer derived from organic source, and an inorganic commercially manufactured polymer, as viable alternatives for soil stabilization. The current study focuses on exploring the efficacy of polymers stabilized soil in improving the engineering or geotechnical properties such as plasticity, compressibility, shear strength, and stiffness behavior.The research methodology involves using locally available high plastic clay for stabilization using two different types of polymers and performing laboratory experiments to analyze the strength parameters of the stabilized soil. Xanthan Gum (XG) is a biopolymer which is being studied is used in the percentages of 0.5%, 1.0% and 1.5% by dry weight of soil mass to understand the mechanism of biopolymer-soil interactions and to conclude optimum percentage suitable for stabilization in terms of technical and economical value. Similarly, Soiltac (ST) a vinyl copolymer inorganic polymer is used in 1.5% of dry mass of soil (optimum dosage as per previous literature) to compare its effectiveness with that of Xanthan Gum. After the determination of Atterberg limits and Optimum Moisture Content (OMC) and Maximum Dry Density (MDD), the samples were subjected to tests such as Unconfined Compressive Strength (UCS), Ultrasonic Pulse Velocity (UPV), Resilient Modulus (RM) test and Consolidation test. The prepared UCS samples were cured for 0, 7, 14, and 28 days in open air condition before performing test on them. Atterberg limits test on untreated Carbondale Soil were conducted to classify the soil as CH (Clay with high compressibility) type as per USCS (Unified Soil Classification System) classification. While tests on treated sample showed significant increasement in Liquid Limit (LL), slight increment in Plastic Limit (PL), thus quite surge in the Plasticity Index (PI) with increase in XG percentage in the soil. UCS value increased with the increase in percentage addition of XG. Also, UCS results from both untreated and polymer treated samples showed increase in compressive strength with increase in curing period. UCS value increased from 417.75 psi to 490.24 psi, 504.05 psi, and 542.91 psi for 0.5%, 1.0%, and 1.5% XG addition, respectively. This increase in UCS value was 17.35%, 20.66%, and 29.96% for the corresponding XG concentrations. The treated samples had a significant increase in the UCS for all the curing period in comparison to their respectively cured untreated sample. The percentages increase in the UCS for 1.5% XG sample in comparison to untreated sample cured for the same period is 6.45%, 59.57%, and 29.96%, respectively for 7, 14 and 28 days of curing. However, for the zero-day test, the UCS of 1.5% XG stabilized sample was found to be less than the zero-day untreated sample. With the addition of ST polymer, the UCS value increased for all the curing period while comparing with the UCS of untreated soil for the same curing period. The UCS of the ST treated soil increased from 58.56 psi to 467.367 psi when cured for 0 and 28 days which is an increase of 698.1 % i.e. 7 times the strength at 0 day. When UPV (Ultrasound Pulse Velocity) tests were compared with the UCS value for the same sample, the result showed that the higher UPV value corresponded to the higher UCS value. This relationship was supported by the high degree of correlation between the two measurements. The consolidation test showed that the Compression Index (Cc) of XG stabilized soil decreased as the percentage of XG added increased. Cc decreased from 0.2795 for pure Carbondale Soil (CS) to 0.2003 for 1.5% XG addition which is a drop of 28.33%. Likewise, Cc decreased by 3.0% and 19.33% for 0.5% and 1.0% XG doses respectively. The primary aim of this study is to simplify the understanding of the Resilient Modulus (RM) test, which yields vital data for pavement design. The efficacy of inclusion of stabilizer was further substantiated by RM testing which confirmed the enhancement of soil resilient qualities compared to the untreated soil. The RM values exhibited a growing trend, indicating an enhancement in the soil's stiffness and capacity to endure repetitive loads. This attribute is extremely important for applications such as the construction of pavements and foundations that are subjected to dynamic loads. The samples containing 1.0% XG showed significant increases in their RM values. Specifically, the RM values increased by 18.5%, 40%, and 39.5% after being cured for 7, 14, and 28 days, respectively, at a confining pressure of 6 psi. Similarly, the RM for the case of ST ranges from 15227.60 psi for 0 days of curing and 2 psi of confining stress to 45375 psi for 28 days of curing and 6 psi of confining pressure. The performance of ST against XG is higher.