COMPRESSIBILITY CHARACTERISTICS OF COMPACTED BLACK COTTON SOIL TREATED WITH RICE HUSK ASH

Abstract

One dimensional consolidation studies on compacted black cotton soil treated with up to 16% rice husk ash (RHA) at the British Standard light compactive effort was carried out to access the compressibility characteristics. The consolidation characteristics of black cotton soil containing 0, 4, 8, 12, and 16% RHA were observed at different moulding water contents (2% dry of optimum, optimum moisture content and 2% wet of optimum) simulating different field placement conditions. Variations of the soil’s index properties with ash treatment were also observed. The Atterberg limits showed improved index properties; plastic limit of the soil was found to increase while the liquid limit and plasticity index decreased with increased RHA treatment. The optimum moisture content (OMC) was observed to increase while Maximum Dry Density (MDD) decreased with increased RHA treatment. The swelling pressure decreased with increased RHA content. The consolidation parameters also showed appreciable changes; with the gross yielding stress irrespective of the particle state increasing with increased RHA treatment. The compression index decreased with increased RHA content but increased with increasing moulding water content. The coefficient of volume compressibility, coefficient of consolidation generally decreased with increased loading pressure and RHA treatment for up to 8%.  The coefficient of permeability decreased with increased RHA content for up to 8%. These results show an overall improvement in the consolidation properties for up to 8% treatment; suggesting the suitability of the material in fills for embankment and low lying marginal land for foundation works. This also helps in ameliorating the environmental problems associated with the disposal of waste rice husk ash.