Change in Geotechnical Properties of High Plastic Soils on Exposure to Acid Rains of Varying Strength

Abstract

Acidification of rain caused by air pollutants like sulfur dioxide and oxides of nitrogen etc. reduces the pH as low as 3 to 4. The low H⁺ concentration of acid rain falling for a short duration may not affect soil properties instantaneously due to adequate cation exchange capacity of soil. But ever growing industrialization/pollution is increasing its  frequency, persistence and the intensity. The frequent, persistent and growing intensity of acid rain will certainly exceed buffering capacity of soil. This will enhance the rate of leaching of cations from the soil to a great extent. Absorption of H⁺, SO₄^2-, NO₃^- and CO₃^2- by the soil particles will alter physical, 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. The objective of present study is to find out the degree of variation in the texture, physico-chemical and the engineering properties of soil of high plasticity on exposure to acid rains of varying strength. 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 or HNO₃ to study short term influence of acid rain on soil properties.  The acidification causes deflocculation of soil particles which directly affects 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.