Effects of Moisture Content Variation on Shear Strength Properties of Flyash Samples

In a country where there is scarcity of land, it’s difficult to think free space for the disposal of wastes like Flyash. In many countries where coal burning power stations are the sources of power generation, fly ash produced in bulk and its production exceeds several folds of its usage. However, in geotechnical engineering, the usage of fly ash for backfill materials and admixture in ground improvements is relatively increasing. In this paper, an attempt was made to determine the appropriate water content for usage of Flyash in retaining walls as backfill material. The shear strength properties of fly ash were determined at various moisture contents. The main purpose of this experimental program was scheduled and performed to optimize the moisture content of fly ash, so that its angle of internal friction will be the maximum value and its apparent cohesion values will be the minimum. The standard proctor compaction test was performed on flyash samples and the optimum moisture content and maximum dry density values were calculated accordingly. The different moisture contents selected were 10%, 13% and 15% dry side of OMC, 20 % OMC and 25% wet side of OMC. The direct shear test experimentation was conducted at three different normal stresses; these were 50 kpa, 100 kpa and 150 kpa. The experimental results have shown decreasing of the angle of internal friction and increasing of apparent cohesion up to OMC value. However, on wet side of the OMC, both the apparent cohesion and angle of internal friction have been shown to be decreasing. As a result the moisture content at 10% dry side of optimum fulfilled the requirement and selected to be used for the ongoing retaining wall experimental work. In this study, the shear stress and horizontal displacements of the experiment, the angle of internal friction and apparent cohesion are discussed at various moisture contents.