توصيفگر ها :
بهسازي بيولوژيكي , MICP , آزمايش بارگذاري بر روي بستر ماسه اي , بهسازي ستون ماسه اي به روش بيولوژيكي , ارزيابي ظرفيت باربري , بايو ستون , گروه بايو ستون
چكيده انگليسي :
Bio-mediated soil improvement is a new method through which the chemical and biological processes improve the mechanical and physical properties of the soil. Since this method is environment-friendly and applicable to any sort of soil, it is widely used as an effective method for the soil improvement. Microbial induced calcite precipitation (MICP) is one of the best and most well-known techniques for bio-mediated improvement of soil whereby bacterial suspension is injected into the soil to form precipitated calcium carbonate, thereby improving the properties of the soil. The current research was intended to analyze the effect of the bio-mediated soil improvement on the bearing capacity of sand bed. To carry out the research, sand from Varzaneh desert was used, characterized as uniformly and poorly graded sand. For improvement purpose, we used the bacteria, B. pasteurii. The sand bed stabilized through sand columns was biologically improved. In general, this research can be divided into three parts. In the first part (or first series of tests), the bearing capacity of a single bio-column was analyzed. Considering the history of the study, we used three variables: (1) the ratio of length to diameter (L/D) of bio-columns, with the values of 2, 3, and 4; (2) the ratio of cementation suspension to bacteria (Cem/Bac), with the values of 1, 1.5, and 2; and (3) the rate of injection of 10, 20, 30 ml/hr. A circular rigid foundation, 5 cm in diameter, was used for the loading. Taguchi Design of Experiments was used to achieve the best state of target variable. In this part, we considered two target variables: first, the maximum bearing capacity (final bearing capacity) of bio-columns, and second, the residual bearing capacity. According to Taguchi analysis, the best state of a single bio-column is obtained when the ratio of length to diameter of bio-column, ratio of cementation solution to bacteria, and injection rate are 4, 2, and 10 ml/hr, respectively. In the second part (or second series of tests), the bearing capacity of bio-column group was analyzed using the best bio-column obtained in the first series of tests. In this part, only one variable was used. Considering the previous studies, the ratio of distance to the diameter of bio-columns, which was 2.5, remained unchanged, and only number of bio-columns was regarded as the variable of choice, with the values of 1, 2, 3, and 4. In this part, a square rigid foundation, 18 cm wide, was used for loading. According to the diagrams obtained in the second part, we used just one target variable, which was maximum bearing capacity (final bearing capacity) of bio-column group. Finally, the result showed that the optimal state of bio-columns is obtained when three bio-columns are used. In the third part of the study, we analyzed the scour of bio-columns in the first series of tests using Taguchi method. According to Taguchi method, the optimal state for minimum scour of a bio-column is obtained when the ratio of length to diameter of bio-column, ratio of cementation solution to bacteria, and injection rate are 1, 2, and 10 ml/hr, respectively.
