Compressibility characteristics and coefficient of consolidation determination for unsaturated sand treated with micro silica

This study investigated the influence of Micro-Silica (MS) on the compressibility of poorly graded sand, with the aim of determining coefficient of consolidation ([Formula: see text]). Tests were conducted using different MS contents:0%, 1%, 3%, and 5% under various saturation conditions: S_r = 1, 0.9, 0.7 and 0.3. The results showed, as expected for untreated specimens, that a higher normal stress value led to higher immediate settlement ([Formula: see text]) for S_r = 1; however, the inclusion of MS as an additive significantly reduced [Formula: see text] in both unsaturated and, unexpectedly, saturated states. For example, at S_r = 1 and σ = 200 kPa, the addition of 5% MS resulted in a 62.5% reduction in [Formula: see text] which was not in line with the case of S_r = 1 and MS = 0%. The sole effect of S_r was also found to be significant. A 7.79-fold reduction in [Formula: see text] was obtained between S_r = 1 and 0.7 at MS = 0% for σ = 200 kPa. More significantly, the combined effect of MS and S_r resulted in a 92.2% reduction in [Formula: see text], 12.8-fold maximum. The optimal MS% depended on several factors such as particle size, suction stress and soil fabric. Experimental [Formula: see text] values were obtained using the Taylor (1942) method, then compared with [Formula: see text] values obtained from a reformulated equation that took the slope of soil water retention curve and the unsaturated coefficient of permeability into consideration. The unsaturated coefficient of permeability was obtained using different equations, which took into account suction, effective degree of saturation and residual degree of saturation. The comparison showed reasonable agreement between the experimental results and some of the equations used.