Stabilisation of silt clay soil using molasses for small dam embankment construction as inner zone

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. Despite of its importance, agriculture is very much affected by inadequacy, seasonality and unreliability of rainfall and periodic droughts. It is for this reason that irrigation is considered necessary for providing protection against drought, a means of stabilizing crop production and assurance of household food security. In order to achieve food self-sufficiency to all, the government of Tanzania is now struggling to invest more in rainwater harvesting technology such as construction of small and big earth fill dams for purpose of collecting run-off water for irrigation and domestic purpose. However, construction of dams is found to be difficult to some identified potential areas due to lack of suitable soil for dam embankment. This research work aimed to stabilise silt clay soil using molasses for construction of small earthfill dam embankment as an inner zone. Specifically, this research examined the effect of adding molasses to silt clay soil in terms of consolidated-undrained triaxial test, soil permeability and compaction. 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 stabilisation. 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. By adding 6.5% of molasses to soil sample, cohesion of soil was increased from 6.0 to 43.8kPa, while decreasing friction angle of soil from 22.1o to 8.6o. Additionally, maximum dry density of soil was increased from 18.5 to 19.40kPa while bulk density of soil increased from 20.72 to 21.34kPa. Also, optimum moisture content of soil decreased from 12.0% to 10.0% at 6.5% molasses content. The permeability of the soil decreased from 6.062 x 10-5 to 2.413 x 10-5 mm sec-1 with increase of molasses up to 6%. Results showed that, stabilisation of silt clay soil with molasses, increased strength properties of soil, and therefore, molasses can be used as stabilising agent for silt clay soil. Based on cost analysis, it is clear that stabilisation of soil with molasses is cheaper than using chemical soil stabiliser. It is recommended that, further studies be conducted to determine effective duration of molasses as a stabilising agent. Also field trials would be necessary to assess the performance of dam embankment constructed with soil stabilised with molasses.