Shi He

ORCID Identifier(s)

0000-0002-6056-409X

Graduation Semester and Year

2019

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Anand Puppala

Second Advisor

Xinbao Yu

Abstract

Traditional soil stabilizers such as lime and cement are widely used to reduce swell and shrinkage behavior and enhance strength properties of expansive soils through the formation of cementitious products. However, the manufacturing process of these calcium-based stabilizers, such as lime and cement, need large amounts of water and emit gases such as CO, CO2, NOx, and SO2 that are harmful to the environment. Hence, environmentally-friendly techniques are often sought out by the civil infrastructure industry (Puppala et al. 2018a, 2019b, George et al. 2019a, Congress and Puppala 2019). In this research, an alternative stabilizer termed as liquid ionic soil stabilizer (LISS) was used to treat expansive soils from North Texas. Although LISS has shown a reliable record of successful stabilization treatment of subgrades for over 20 years in Texas, there is a lack of in-depth studies which try to identify the probable stabilization mechanisms and quantitatively evaluate the efficacy of such treatments. This research work primarily aimed at addressing these issues through an extensive laboratory testing program encompassing a series of macro-scale engineering tests and microstructural analyses. Two types of expansive soils with different clay mineral compositions were collected from different locations in Texas and are used as control soils in the present laboratory testing program. These soils were modified by treating the soils with three different dilution ratios of LISS additive. The dilution ratio is defined as the volume of concentrated liquid ionic stabilizer per unit volume of water. The research study included four major tasks to study the effects of LISS stabilization and these are: (a) performing physical, chemical and microstructural tests, (b) evaluating engineering properties, (c) assessing stabilization mechanisms, and (d) numerical modeling to evaluate the post-treatment improvements in the performance of slopes and pavement subgrades stabilized with LISS. The collected soil samples were treated at three different dilution ratios to study the effect of stabilizer dosage on the improvements in basic and engineering properties of the problematic soil. Test results and analyses provided comprehensive characterization of the basic and advanced soil properties, improvements in engineering properties of treated soils, and an in-depth understanding of the stabilization processes at a micro level. The mineralogical and microanalysis studies were also performed to examine the stabilization mechanisms in terms of chemical reactions, mineralogical changes, and other modifications that might have resulted in improvements in the engineering properties at the macro level. The results from the macro tests that included physical, chemical, and engineering tests showed that the LISS is an effective alternative environmentalfriendly soil stabilizer, which can enhance the strength and stiffness of problematic expansive soils to moderate levels. The LISS also inhibits the swell potential of expansive soils and slightly reduces the plasticity index and linear shrinkage ratio. The reductions in swell potentials were associated with an increase in strength and stiffness (resilient moduli) properties for all the different soil-dilution ratio combinations used in this research study. Among the three dilution ratios used in this research, the double chemical ratio (10 ml/gallon) which had the highest concentration of LISS exhibited the optimum performance based on the overall improvements in engineering properties such as strength, stiffness, and reduction in swell potential. The probable stabilization mechanism was determined by comparing the microstructural test results of Field Emission Scanning Electron Microscopy with Energy Dispersive Spectroscopy (FESEM-EDS) and X-ray Powder Diffraction (XRD) for both untreated and soils treated at the third ratio. Additional macro tests, including variation in moisture content, pH, Consistency Limits and grain size distribution with curing time, were also used to comprehend the changes in the properties of the treated soil. The SEM images depicted that the soil particles flocculated upon addition of LISS and a phospho-rich compound were formed that bonded the soil particles after treatment. The intensity of the clay minerals peaks in the XRD plot was found to decrease when the soil was treated with LISS at the double chemical ratio. The FESEM and XRD results suggest the formation of products formed by the reactions of clay particles with the LISS additive. Moreover, the moisture content of soil gradually decreased by around 3%, and the grain size of the treated soils varied with an increase in curing time period, indicating the progressive utilization of water to form reaction products that can bind the clay particles and result in improvement in engineering properties of problematic soils. The pH of LISS increased from 3 to 7.8 in 20 days, which exhibited a progressive chemical reaction in this period of time. However, the consistency limits of LISS treated soils before and after treatments were nearly the same and no major enhancements were noted in the consistency limit values. In order to evaluate the feasibility of using LISS as an alternative soil stabilizer, two case study examples involved with pavement design and slope stability were analyzed. From the results and analysis of the modeling, the pavement design life of treated expansive soil was higher than that of untreated expansive soils. Also, the global factor of safety (FOS) of treated Dallas soil was slightly increased by 13% as compared to the section without any soil treatment. More studies and field treatment sections will provide more insights into the effectiveness of LISS treatments to enhance soil properties that can provide better support of civil infrastructure.

Keywords

Liquid Ionic Soil Stabilzier (LISS), LISS

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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