The evaluation of changes in permeability and chemical composition of Gypseous soils through leaching in southern Mashhad

Abstract

Solubility is the main problem of gypseous soils. In dry state, these soils are resistant and have good engineering properties. However, when saturated by rainwater or rising groundwater table, the minerals in these soils are washed out, making the structures built on them prone to subsidence. In the recent decades, buildings constructed in southern area of Mashhad Metropolitan, Iran, have been widely faced with this problem. Since permeability and chemical composition of these soils are varying in time due to the solubility of gypsum, the current study is an effort to determine hydraulic and chemical properties of the soluble soils of the area and their changes throughout the leaching process. Seven soil samples with different gypsum contents were selected from the area for analysis in four major groups of tests including physical tests (grain size analysis, Atterberg limits and specific gravity), chemical tests (chemical analysis of soils, Total Dissolved Solids (TDS), Electrical Conductivity (EC), and leaked water chlorine), hydraulic tests (permeability and solubility) and statistical analysis to determine the depth of maximum gypsum and sulfate ion concentration. Changes in the mentioned parameters were investigated through a 5-day leaching process. In the early stages of the tests, high variability was observed in permeability coefficient and concentration of minerals in the soil. These changes were gradually decreased and tend to constant values.