An investigation on physical characteristics and mechanical behavior of swelling gypsum soils and their improvement methods

The existence of swelling soils causes irretrievable damages to buildings all over the world. Due to the swelling property of the gypsum soils, located in South West of Mashhad, many problems such as cracking in building, heaving of walls, and pavement and bulging of floors have been reported. The soil in this region is generally fine and based on Unified Classification is predominantly ML and CL. In the present research, 6 typical samples, among many gathered samples, with identical gradation but different amount of gypsum, were selected. After determination of main geotechnical properties of samples (including gypsum percent, Atterberg limits, natural unit weight and density), the effect of gypsum amount on the swelling potential and swelling pressure was investigated. Considering the influence of degree of compaction, on the swelling potential and swelling pressure, 10 samples for each of 6 typical soils, with identical moisture content but different unit weight were prepared and the variation of the swelling potential and swelling pressure were studied. The results of this research indicate the harsh effect of the gypsum amount, degree of compaction and moisture content on the swelling potential and swelling pressure. The improvement of such soils which are a type of problematic soils has been of many researchers interest. In the present research a sample with 10.57% gypsum and unit weight of 1.83 g/cm3 and with a determined swelling potential was improved using three different methods, including mixing with lime, double mixing with lime and mixing with cement. The amount of admixture for all three methods was 1, 2, 3 and 4 percent. The results of this research indicate that mixing with cement is able to reduce considerably the swelling potential and to improve the swelling specifications of this type of soil.