Understanding the effect of acid rain on physico-chemical and engineering properties of black cotton soil

Abstract

Population outburst have forced over exploitation of natural regimes of biosphere. Rapid urbanization and industrialization are posing constant threat to environment. Continuous addition of air pollutants like sulfur dioxide and oxides of nitrogen etc. not only pollutes the atmosphere but also indirectly causes degradation of lithosphere. These gases are major source of acid rain whose pH may be as low as 3 to 4. The frequent, persistent and growing intensity of acid rain will certainly exceed buffering cation exchange capacity of soil which will enhance the rate of leaching of cations from the soil to a great extent. Absorption of H+, SO42-, NO3- and CO32- by the soil particles will alter physico-chemical and engineering properties of soil which cannot be ignored. Therefore it is imperative to examine the properties of soils eroded due to acid rain in order to augment understanding of its influence on geotechnical engineering. To monitor the degree of variation in the texture, physico- chemical and the engineering properties of soil of different plasticity on exposure to acid rains of varying strength have been taken up. The present paper focuses on the findings observed on black cotton soil. The soil fraction passing 4.75 mm sieve was shaken for eight hours with varying probable simulated strength of acid rain equivalent to normality 0.005N, 0.01N, 0.02N and 0.04N of H2SO4, HNO3 and 1:1 mixture of H2SO4 / HNO3 (expected composition of acid rain) to study influence of acid rain on soil properties. The acidification lowers the cation exchange capacity, affects the grain size distribution and alters the consistency as well as strength properties of the soil. The paper presents the observed degree of variation in these properties under varying strengths of acid rain.