JWSS - Journal of Water and Soil Science

To improve the engineering properties of fine-grained soils, the use of various additives has always been considered important. In this study, the effect of hydrated lime on compressive strength of clay soils was studied in both optimum moisture and saturated modes. For this purpose, by adding varying amounts of hydrated lime (0, 1, 3and 5%) to the clay, several samples were prepared and tested by the standard proctor and Harvard miniature compaction apparatus. Then the samples were tested for unconfined compressive strength in optimum moisture and saturated modes after different curing days (7, 14, 28 and 90 days). The results showed that by increasing the amount of hydrated lime, the maximum dry unit weight was reduced and the optimum moisture was increased. Increasing the hydrated lime also increased the compressive strength of the soil in both dry and saturated modes and this resistance increase was significantly influenced by cured days and the amounts of hydrated lime. The results showed that the rate of 5% hydrated lime was the maximum compressive strength, but with regard to softening factor, the amount of 3% hydrated lime was determined as the optimum value.

Improvement of soils is among the major concerns in civil engineering, therefore a variety of approaches have been employed for different soil types. The annual budget of implementing the projects of this kind in countries clearly implies the importance of the subject. The loose granular soils and sediments have always imposed challenges due to their low strength and bearing capacity. Bio-mediated soil improvement has recently been introduced as a novel link of biotechnology (biotech) and civil engineering for improving the problematic soils, i.e. utilizing some bacteria to precipitate calcite on the soil particles. Bio-grouting is a branch of Bio-mediated soil improvement which is a method based on microbial calcium carbonate precipitation. In this regard, the soil samples were stabilized by injecting the bacterium Sporosarcina pasteurii in the first phase of the process and Urea and Calcium Chloride in the second phase of the process (two-phase injection) as the nutrients into the sandy soil columns and subjected to unconfined compressive strength test. In this research, Taguchi method was utilized for design of experience (DOE). Based on results obtained, the activity of the bacteria caused the precipitation of calcium carbonate in soil samples so that after 21 days, the unconfined compressive strength of the soil increased from 85 kPa in the control sample to 930 kPa at optimum condition.