Enhanced Shrinkage Characterization of Clayey Soils

Abstract

Surficial slope failure is a common problem experienced by most of the compacted earth dams in Texas and several other southern states in USA as a result of desiccation or shrinkage induced cracking of the surficial soils. Cracking of the soil occurs when the tensile stress exceeds the tensile strength during drying process. Tensile stress increases with an increase in shrinkage strain and thus soil chemical admixtures can reduce the tensile stress by reducing the shrinkage potential of soil. Inclusion of such admixtures invariably affects the tensile strength. Yet there are not many test methods that could be utilized for shrinkage characterization of the expansive soils and hence there is a major need to develop a method to perform better shrinkage characterization of soils. This has been the main objective of the present dissertation research. A test method presented as a shrinkage induced pressure (SIP) test was further refined to study the shrinkage potential, tensile strength, and desiccation cracking of soils. As a part of this study, several expansive soils were utilized and studied with the refined characterization method. A statistical tool was also developed to predict the SIP based on different soil variables. Also, three dimensional unsaturated slope stability analysis of the dam slope was conducted using the finite difference program FLAC3D to study the effects of seasonal moisture content fluctuations, formation of desiccation cracks and how these impact surficial slope stability. Also, a new treatment method that utilizes biopolymer to amend the soil to reduce desiccation cracking was evaluated using the developed characterization method. The moderate increase in the shear strength of the biopolymer treated soil compared to the untreated soil may work well in natural slope conditions of dam and highway embankments. This dissertation uses same characterization tool in the assessment of biopolymer treatment of expansive soils in reducing their shrinkage behavior. Future research directions are also presented in this field.