Chemical and Mineralogical Evaluation of Soils for Their Suitability in Geotechnical Application: Fid-Bau Portal

Chemical and Mineralogical Evaluation of Soils for Their Suitability in Geotechnical Application

Vyas, Sameer / Anand, Beena / Pathak, R. P.

Soil is the basic foundation material which supports all natural and manmade infrastructures. The use of soil either as foundation or fill material is based on its physicochemical and engineering properties. Being a complex system made up of inorganic and organic components, the engineering behaviour of soil largely depends on its chemical composition. The chemical composition of soil depends upon a number of factors viz. grain size, surrounding geology, depth, moisture level, and climatic conditions. Therefore, geotechnical investigations of soil for any river valley project are associated with field and laboratory testing to assess its suitability for construction purposes. The core chemical parameters required for assessing the suitability of soil for construction purpose are pH, total soluble salts, (TSS), calcium carbonate content, organic matter, water soluble sulphate, water soluble chloride, sodium, potassium, calcium, and magnesium. pH of soil extract indicates its acidic and alkaline characteristics. Determination of soluble salt content (total soluble salts) is important to study the impact of ground water on concrete buried in the ground. Estimation of parameters such as organic matter, cation exchange capacity, silica sesquioxide ratio are important for the purpose of stabilization of soil. The dispersive nature of soil is also need to evaluate for stability of hydraulic earth structures. In specific conditions total chemical composition, cation exchange capacity (CEC) and soil mineralogical examination by X-ray diffraction (XRD) method are also need to investigate. The present paper deals with the chemical and mineralogical evaluation of soils collected from various projects to assess their suitability in geotechnical application. Selected soil samples were analysed for different chemical parameters as per standard procedures laid down in BIS and ASTM codes. The interpretation and correlation of results then evaluated for engineering applications for desired purposes. The pH of majority of soil samples was observed to be in the range of 6.5–8.5. However, some soil extracts were also shown pH values beyond this range. Both extreme ranges may pose threat to civil engineering structures. The total soluble salts (TSS) contents of majority of samples observed to be below 1 millimhos per centimetre showing normal presence of soluble salts. Few samples were also exhibit TSS values between 1–2 millimhos/cm showing fairly good amount of soluble salts. The presence of water soluble sulphates and chloride values observed to be in acceptable range for majority of soil samples except samples with high soluble salts. The high values of calcium carbonate content were observed in some calcareous soil samples which shows good cementing property of soils and values of organic matter were observed to be in the range of 0.2–2.5% by weight. The value of soluble sodium content was found to be more than 60% of TDS value (sum of the four metallic cations, i.e. Ca, Mg, Na, and K) in some clay soils and shows dispersive nature which were also supported by XRD analysis these soils. The presence of typical clay minerals is responsible for dispersive nature.