Some studies on volume change and strength behaviour of soils as affected by environmental factors

Abstract

The present investigation is an attempt to understand clay–organic pore fluid interactions, to check in the first place whether highly ligative organic molecules result in clay behaviours similar to those produced by weakly ligative molecules. Soil properties such as liquid limit, shrinkage limit, swelling potential, and consolidation behaviour have been considered. Secondly, the influences of climate (relative humidity and temperature) on swelling, shrinkage, and strength have been investigated, particularly with a view to understanding how these properties change as soil with water as pore fluid undergoes general shrinkage. The scope and nature of the work are presented in Chapter 1. Chapter 2 presents a brief review of literature on the effects of organic pore fluids and climate on the engineering behaviour of soils. The properties of red earth, black cotton soil, kaolinite, and montmorillonite, and of several organic fluids such as benzene, dioxane, acetone, ethanol, methanol, dimethylformamide (DMF), and dimethyl sulfoxide (DMSO), which have been used in the investigations, are listed in Chapter 3. Drastic changes in the liquid and shrinkage limits brought about by highly ligative organic molecules, which could not be explained based on dielectric constant, have been explained in Chapter 4 on the basis of fabric changes caused by clay–organic molecule bonding. Infrared spectral and X ray diffraction studies support this explanation. A non dimensional modified free swell index has been proposed in Chapter 5, to eliminate inaccuracies of earlier free swell test methods. The modified free swell index shows a unique relationship with liquid limit and oedometer percent swell. Swelling potentials of both kaolinite and montmorillonite are almost the same in the presence of DMSO. The clay–pore fluid bonding and fabric changes that make both montmorillonite and kaolinite exhibit the same swelling potential in DMSO are discussed in Chapter 5. Chapter 6 examines changes in soil moisture content, void ratio and density as soil shrinks under varying temperature and humidity conditions. Void ratio and volumetric shrinkage are observed to bear a linear relationship. Chapter 7 contains results of strength tests and analysis of pore water tensions under climatic influences. It has been brought out that pore water tension depends not only on surface area but also on pore size distribution, void ratio, and degree of saturation. Further, unconfined compressive strength is shown to have a unique relationship with initial tangent modulus of all soils undergoing shrinkage. The main features of the investigation are summarised in Chapter 8, together with the conclusions.