Engineers Australia

South Australian collapsing soils

Ratamanee Nuntasarn, Don A. Cameron and Peter W. Mitchell


The study was designed to evaluate and compare typical collapsing soils from South Australia and to evaluate the use of such soil in pavement construction after chemical stabilization with cement and rice husk ash (RHA). The three soils in the study were classified as silty sands, usually with calcium carbonate. Shear strength decreased markedly with inundation. In the natural state, a severe degree of collapse could be reached following saturation. The stabilization of soil from Port Augusta resulted in reduction of the collapse index and an increase of the shear strength. Even after heavy compaction, the soil still had slight potential for collapse upon wetting. On the other hand, the chemically stabilized and compacted soil exhibited minor swelling upon wetting. The saturated shear strength of compacted soil increased when compared to that of undisturbed soil. For evaluation of application of the stabilized soil in pavement construction, the California Bearing Ratio (CBR), unconfined compressive strength and durability were determined. Based on the soaked CBR and strength tests, the non-stabilized, compacted soil was classified as a good sub-grade. The chemically stabilized soil with a low percentage of additives could be used as a sub-base. However durability testing indicated stabilization with either 6% cement and 2% RHA is required. Further work is required to determine the resilient properties of compacted stabilized collapsing soil.