Geotechnical Aspects for Roads on Expansive Soils

This paper presents some issues of geotechnical investigation for roads built on expansive soils. The aim of the study is to provide road engineers with guidance on site investigation, field and laboratory identification of expansive soils. A clear understanding of the expansive subgrade soils behavior and their geotechnical characteristics has been of more interest to the study in order to assess properly the source of the swelling problem. Two case study sites, representative known problem-areas in Khartoum were carefully selected for geotechnical site investigation. The field exploration consisted of excavating trial pits and collecting soil samples from the subgrade. These soils were subjected to laboratory testing for measuring the particle size analysis, consistency, strength and swelling characteristics. The soils were found to have over 50 % clay particles, high plasticity index more than 30 % and high free swell index of 160 % to 250 %. The compacted samples were found to have swell potential of 7 % to 15 % coupled with high swelling pressure in excess of 90 kPa and low strength, CBR values less than 4 %. General conclusions have been drawn from the study findings.