Compaction and design of gypsiferous fill for hot desert road pavements

Abstract

A comparative study between a homogeneous road embankment constructed of gypsiferous soil and compacted throughout its full height at the dry optimum moisture content (DOMC) and an exactly similar embankment but with improved active zone (top 50 cm of the embankment compacted at the wet optimum moisture content WOMC), is presented. Two soils A and B were examined. Soil A was sandy lean clay (CL) containing about 35% total soluble salt (TSS) of which 33% was gypsum; soil B had a 28% TSS and a gypsum content of 25·6%. California bearing ratio (CBR) soil samples, prepared at DOMC and WOMC for soil A and at WOMC for soil B, showed serious reductions in soil strength and stiffness due to soaking, especially when the soil had been compacted at DOMC. A soaking period of 4 days was considered very reasonable and conservative for hot dry regions. Swelling of the soil during soaking was observed, especially when the soil was compacted at DOMC. For pavement design, it appears to be more economical to introduce an active zone compacted at WOMC instead of DOMC. The cost of the additional water required for compaction at WOMC instead of DOMC is much less than the savings in cost of sub-base material due to increased subgrade soil strength. It is concluded that the gypsiferous soil which occurs widely in the Middle East can be used to build embankments for hot desert road pavements.