Soil frost heave is a destructive phenomenon for engineering structures in cold climates. This phenomenon can be problematic for engineering structures in two ways; Heaving in the soil due to freezing and reducing soil resistance due to melting the created ice lenses. Frost heaving is a swelling phenomenon for the soil prone to freezing conditions and heaves due to the formation of ice lenses. The advance of freezing is from the surface to the depth where the freezing temperature has penetrated. This phenomenon often occurs in fine-grained soils or coarse-grained soils containing fine-grained soil. Common methods of preventing or controlling this phenomenon face two challenges; The use of materials whose production and usage are dangerous for the environment or humans and the impracticality of using some of these methods in deep layers of the soils. In this research, the biological soil improvement method was introduced to reduce the soil frost heaving to provide a more environmentally friendly approach that does not have other disadvantages of conventional methods. The bacteria used in this research is Sporosarcina pasteurii, a urease, and none pathogen strain. In line with this research, a laboratory testing apparatus with unique specifications was designed and built to measure the soil frost heave and other desired parameters. The effect of three input factors was investigated at four levels. In this research, the effect of the bacteria concentration was assessed at 105, 106, 107, and 108 CFU/mL levels. Also, the concentration of cementing solution was eva‎luated at the 0.3, 0.6, 0.9, and 1.2 mol levels. The effect of curing time was investigated at 0, 7, 14, and 21 days in the test output. The output was the total soil frost heave, which was investigated for two different soil samples. The L16 array of Taguchi design of the experiment (TDOE) method was deployed to plan the tests for each soil sample. In order to compare the results with each other and the results of other methods, the heave ratio (the ratio of the treated to untreated samples) was used. The heave ratios of the first soil type were between 0.14 and 0.34, and the second soil type were between 0.21 and 0.42. The coefficient of determination (R2) obtained for each soil type confirmed the results' accurate prediction by the Taguchi method. By using the analysis of the means and analysis of variance, it was found that the bacteria concentration contributes the most to the output for both soil samples. In both soil samples, the second contribution rank was the curing time with a small difference compared to the bacteria concentration. Also, the concentration of the cementing solution contributed very little to the final result compared to the other two factors. The optimal level of the bacteria concentration for both soil samples was 108 CFU/mL. Also, the optimum curing time was 21 days, and the optimum cementing solution concentration was 0.6 mol. The results obtained for the two tested soil types were very promising compared to conventional methods. Only lime, cement, and Nanosilica had better results, each of which faced severe challenges. Also, the SEM images prepared before and after the biological treatment of the samples confirmed the homogenous and dense calcite precipitation.

محمدعلي روشن ضمير، مهدي ابطحي

صبيحه سليمانيان زاد

حميد هاشم الحسيني، هاجر شرع اصفهاني، رسول اجل لوئيان