Effect of wastewaters on the geo-technical properties of laterite

Abstract

Soil contamination arises from variety of sources, which include acid rain, hazardous liquid and solid waste from industries, animal waste, salt-water intrusion, etc. Literature relevant to the soil-pollutant interaction reveals that soil properties and behaviour is influenced and altered due to contamination by pollutant. The soil pollutant interaction depends on various factors such as nature and chemical composition of soil, dielectric constant of pore fluid, organic matter etc. Sulphur dioxide and oxides of nitrogen are the two most important parameters responsible for acid rain. Atmospheric pollution has resulted in the precipitation having pH less than 5.6 disturbing the nature's delicate balance and also contamination of soil. The soil and ground water contamination will result in Socio-economic and environmental impact. Several studies by various researchers have highlighted the influence of physico-chemical factors on the engineering properties of soil. The alteration of characteristic properties of the soil in the vicinity of industrial plants occurs mainly as a result of their pollution. Literature review on the effect of acid rain on soils indicated that the pH value of soils generally decreased with continuous infiltration. The major soil chemical parameters affecting the contaminant partitioning are hydrogen ion concentration in the soil, which influences all chemical reactions and biological activities. Laterites and lateritic soil have a very important place in Civil Engineering activities in India, especially in the South and Central parts. They form a good foundation material and are composed essentially of hydrated aluminium and iron oxides. In this paper, the results of an investigation on the effect of pH on the characteristic properties of laterite soil procured from the quarry near Mangalore, located on the western coast of south India, has been discussed. The effect of pH on the characteristic properties of laterite was studied under different pH conditions (i.e. pH =5.0, pH=7.0, pH=8.0). The pH of water in which the laterite blocks were soaked (up to ninety days) was maintained using buffers. The important properties considered for the study are: compressive strength of laterite blocks, Atterbeig limits, shear strength properties and chemical characteristics of laterite soil (pH, conductivity, alkalinity, hardness, chloride, sulphate and ammonia nitrogen). From the investigation it is observed that the engineering properties and chemical characteristics of laterite soil are altered in all the three pH conditions (pH=5.0, pH=7.0, pH=8.0). The compressive strength of laterite blocks reduced under all the pH conditio is and considerable reduction in strength was observed when the pH of water was maintained as 5.0. The pH of adjoining water body has remarkable influence on the pH of soil. Accordingly when the pH of water was low (p -1=5.0), the corresponding pH of soil decreased from its initial value. Similarly soil pH increased when the pH of water was maintained as 8.0 for soaking up to ninety days. The various other effects on the engineering behaxiour and chemical characteristics of laterite are noted and discussed in the present work.