Using gypsiferous soil for embankments in hot desert areas

A study of the strength characteristics of a fine-grained gypsiferous soil intended for use as a construction material for forming highway and airport embankments in desert areas is reported herein. The tested soil was a sandy lean clay (CL) according to the Unified Soil Classification System and an A-6 (6) soil according to American Association of State Highway and Transportation Officials (AASHTO) soil classification system, containing about 35% total soluble salts (TSS) of which 33% was gypsum. To study the properties of the tested soil, various California bearing ratio (CBR) soil samples were prepared at the dry optimum moisture content of 2% and soaked for 0, 4, 7, 15 and 30 days. The CBR tests revealed that there was a serious drop in the CBR due to soaking, which is in full agreement with the drop in c and φ with soaking period, indicating that if gypsiferous soils are used as fill material they should be protected from ingress of water. To study the deformation properties of the tested soil, vertical swelling/settlement measurements were carried out on each CBR sample during soaking using a 0·002 mm dial gauge. The effect of soaking period on the distribution of moisture, TSS and gypsum content was also studied. It was observed that there was an increase in moisture content and a decrease in TSS and hence gypsum with increasing soaking for CBR samples compacted at the dry optimum moisture content.