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Soil pH is a measure of the acidity and alkalinity in soils, ranging from 0 to 14 that measured in a slurry of soil mixed with water. Soil pH normally falls between 3 and 10, with 7 being neutral, acid soils have a pH below 7 and alkaline soils have a pH above 7. Ultra-acidic soils have pH value less than 3.5 and very strongly alkaline soils have pH value more than 9 which are rare. Extremes in acidity or alkalinity may affect mechanical behaviour physical properties of soil. Recently, the rapid development of cities and the industrial revolution have caused enormous environmental impacts and become a serious environmental problem. About 80% of the pollutants in the atmosphere, including suspended particles and gases, result from vehicular traffic and industrial activities. Precipitation acts as a significant natural cycle to clean up atmospheric pollutants such as gases and particles in the air. The major sources of acid water are strong presence of SO₂ and NO_x gases in the atmosphere. One of the most important effects of acid water is its effect on soil, including washing nutrient cations, releasing toxic elements, and acidifying the soil. Also, acid mine drainage and the contaminants associated with it, is a common occurrence in waste dumps of mining sites results in acidic conditions with a pH of less than 4 develop over time. On the other hand, mineral deposits, over liming in some parts of the land and the use of limestone to improve the different soil natural and control the pH in waste dumps leads to alkaline conditions (pH more than 7) at mine sites. One of the most important effects of air pollution is acid rain. The increasing expansion of cities, the rapid growth of urbanization and the industrial revolution have caused enormous environmental impacts in and around cities. Industrial activities, production of energy and fuel, the use of fertilizers and pesticides cause significant amounts of contaminants to the atmosphere. The entry of metal contaminants and acidifying compounds such as sulfur, nitrogen compounds or their reaction to the atmosphere in the rain will increase the acidity of the rain which can change the quality of atmospheric precipitation. In general, it can be stated that the meaning of acid rain is a rain that has a pH of less than 5.5 which is a lower natural pH. In the current study, the effect of acid rain on the mechanical behavior and physical properties of lime stabilized sand with respect to the eastern regions of Isfahan has been investigated. At first, the various lime content was added to the soil and the specimens were tested after treatment and saturation under various pH values. The results show that adding lime increased the optimum moisture content, shear strength of the specimens, the cohesion and the friction angle of the soil. On the other hand, reducing the pH value results in continuously decreasing the shear strength parameters of the soil specimens. Finally, based on the scanning electron microscopy (SEM) image from the specimens, the effect of pH and lime content on the bonds between the sand grains was investigated.

Keywords: Acid rain, pH, Mechanical behavior, Shear strength, Stabilization, Lime

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