Stabilization of Silt Clay Soil Using Molasses for Small Dam Embankment Construction as inner Zone

Abstract

The Agriculture sector contributes 45% of Tanzania’s GDP and about 30% of its export earnings, while employing over 80% of the nation’s work-force (National Irrigation Master Plan, 2002). The government of Tanzania is investing more in rainwater harvesting technology such as construction of earth fill dam in the country to continue supporting agricultural production. This research work was aimed to stabilize silt clay soil using molasses for construction of small earthfill dam embankment as inner zone. The study used blackstrap molasses with a density of 1.4 g cm-3 and viscosity of 2.9 x 10-6 m2 sec-1 for soil stabilization. Molasses can improve the adherence between soil particles and, thus, enable formation of a strong interparticle bond that enhances the stability of the constructed embankment. This research was conducted to study the effect of adding molasses to silty clay soil as a construction material. Seven soil samples were collected in a test pit and modified by adding 0% ,5%, 5.5% 6.0%, 6.5%, 7.0% and 7.5% of molasses to soil sample .The soil was tested for shear strength, permeability and compaction. An optimum of 6.5% of molasses when added to a soil sample was found to increase soil cohesion from 6.0 kN/m2 to 43.8 kN/m2 and decreased the friction angle of soil from 22.1° to 8.6°. Also, 6.5% molasses treatment, increased the maximum dry unit weight of soil from 18.5kN/m3 to 19.40kN/m3. Unit bulk weight of soil increased from 20.72kN/m3 to 21.34kN/m3. The optimum moisture content of soil decreased from 12.0% to 10.0% with the increased in molasses percentage. The permeability of the soil decreased from 6.062 x 10-5 mm sec-1 to 2.105 x 10-5 mm sec-1 with increase of molasses up to 6%. These results showed that stabilization of silt clay soil with molasses increased strength properties of soil; implying that by using 6.0 to 6.5% molasses treatment improved properties of soil. More studies are recommended to determine organic decomposition of molasses and impacts on soil properties. Also field trials would be necessary to assess the performance of dam embankment constructed with soil stabilized with molasses.