Evaluation of Shear Strength of Soil Stabilized by Microbiological Method

Biogrout is a new method in soil improvement on microbial induced calcium carbonate precipitation (MICP). In this study was utilized Sporosarcina pasteurii bacteria, an aerobic bacterium which exists pervasive in natural soil deposits, in order to control soil erosion. The undrained shear strength of the soil was measured using an in situ miniature van shear apparatus. The evaluation of shear strength are done for three types of sandy soil (Siliceous and carbonate), in four OD= 1, 1.5, 2, 2.5 levels, at different the curing time of 3, 7, 14, 20, 28 days, and, the re- injection of the bacteria solution and cementation in the interval of 6 days. Also, the influence of environmental conditions on the performance of the bacteria and the amount of shear strength are investigated. The results show that the shear strength were improved with the time. The highest shear strength was obtained in the carbonate sand and fine silica sand equals to 0.64 and 0.39 kg/cm2 in the periods of 28 days, respectively. The optimal balance between nutrients and the number of bacteria was observed at OD=1.5. Also, the results showed that the re- injection of the bacteria solution and cementation was more effective than once rejection in the shear strength, especially in the silica sand equals to 55% in a curing period of 28 days.