SOIL-WATER CHARACTERISTICS OF UNSATURATED TROPICAL SOILS UNDER HIGH AND LOW SUCTION CONDITIONS

Abstract

In this work, three tropical soil types were compacted under different moisture conditions (dry of optimum, wet of optimum and optimum) and compactive efforts (Reduced proctor, Standard proctor, West African standard and Modified proctor). Using the pressure plate extractor device, the Soil-water characteristic (SWC) were obtained and SWC Curves were plotted as gravimetric water content versus logarithm of matric suction for the selected soil samples. Experimental results were compared with results obtained using existing soil-water characteristics mathematical models. The selected SWCC models were fitted using correlation equations. The air entry values (i.e. suction at which water is removed from the large pores of the soil) obtained from experimental work ranged from 21 kPa to 59 kPa and compared favourably well with those estimated from predicted models with ranged values of 4 kPa to 52 kPa but with slight variations. Compaction at greater compactive effort (Modified proctor) and optimum moisture content resulted to large air entry values of 59 kPa, 57 kPa and 49 kPa for samples A, B and C respectively and reduced air voids. Changes in the shape of the SWCC were consistent with changes in pore size which occur by varying compaction conditions. The shape of the soil-water characteristics curve was found to depend on the soil structure, compactive water content and compactive effort and not solely on the percentage of fine particles. Models used in this study was observed to be non-generic to all type of soils (plastic and non-plastic) and as such appropriate models were proposed for estimating the soil-water characteristics of any given tropical soil type.