` Proceedings of Indian Geotechnical Conference December 13-15,2012, Delhi (Paper No G 744) A STUDY ON CORRELATION BETWEEN SPECIFIC SURFACE AREA AND SOIL-WATER CHARACTERISTIC CURVE Chinumani Choudhury, Post-Graduate Student, Assam Engineering College, chinumani.choudhury@gmail.com Malaya C., Assistant Professor, Assam Engineering College, gogoi_chetia@yahoo.co.in ABSTRACT: Specific surface area (SSA) of a soil plays an important role in the adsorption of water molecules and the soil- water characteristic curve (SWCC) measures the water storage capacity of a soil. SSA of a soil influences the behaviour of fine-grained soil and the SWCC is central to the behaviour of unsaturated soil. An effort has been made to understand the relationship between SSA and SWCC. In this study, SSA and SWCC have been considered for twelve soil samples. It is noted that there are very few studies available in the literature on the correlation between SSA and SWCC. Hence, an attempt has been made in this study to investigate whether or not a meaningful correlation exists between SWCC parameters and SSA of the soil. Such a study would be of great help to ensure a better understanding of the unsaturated soil behavior by knowing the physical properties of the soil. INTRODUCTION SSA is the most important parameter of fine-grained soils which is defined as the total area contained in a unit mass of soil and expressed as m 2 /gm. Moreover, SWCC is a fundamental constitutive relationship in unsaturated soil mechanics [1]. In general terms, the SWCC describes the relationship between soil suction and soil water content. More specifically, the SWCC describes the thermodynamic potential of the soil pore water relative to that of free water as a function of the amount of water adsorbed by the soil system. At relatively high value of water content and correspondingly low values of suction, the dominant pore water mechanism becomes capillarity, governed primarily by the particle and pore structure and pore size distribution. On the other hand, at relatively low water content and correspondingly high values of suction, where pore water primarily in the form of thin films on the particle surfaces, the mechanism contributing to suction are the relatively short-range adsorption effects governed by the surface properties (e.g. SSA) of the soil solids. There are very few studies carried out by the researchers to find the relationship between SSA and SWCC. Therefore an attempt has been made in this study to find the correlation between SSA and the different parameters of SWCC. The study indicates that there exists a good correlation between SSA and SWCC parameters. Theoretical background The Van Genutchen (VG) (1980) [2] SWCC equation used in this study for analysis is ( ) s r r m n ...................... (1) 1 a θ -θ θ ψ =θ +   ψ   +           where (),  s ,  r , and  are the volumetric water content at any suction , saturated volumetric water content, residual water content, suction respectively and a, n and m are the fitting parameters. The key points that are relevant for SWCC are: 1. The volumetric water content at saturation,  s , describes the water content at which the soil is completely saturated and typically depicts the initial state for the evaluation of the drying path. 2. The air-entry value (AEV),  a , is the suction at which air enters the largest pore present in the soil sample during a drying process [3]. This is the point where the desaturation process starts. 3. Residual water content ( r ) is the minimum water content below which there is no appreciable change in . Suction corresponding to  r is called residual soil suction,  r [4]. RETC RETC [5] is a computer code for analyzing the soil-water characteristic of unsaturated soils. The program uses VG SWCC equation to represent the SWCC. The SWCC estimation is based on the VG SWCC equation (Eq. 1) using particle size distribution of the soil. SSA SSA is defined as the total surface area contained in a unit mass of soil and expressed as m 2 /gm. SSA can be classified as external, internal and total surface area. Non-expanding mineral shows only internal surface area while expanding mineral shows both external as well as internal surface area. Different methods exist to measure SSA. Estimation of SWCC Twelve numbers of SWCC are estimated using the data available in the literature [6] as shown in the Table 1. The estimated SWCCs are presented in the Fig.1. The parameters