Improvement of Collapsible Soils Using Biocementation Method (Case Study of Gorgan Loess)

Aghaie Lahroodi, Mehrdad | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49464 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Haeri, Mohsen
  7. Abstract:
  8. Collapsible soils have been encountered in many parts of the world such as Gorgan (a city in North of Iran). In these soils, sudden and large volume changes occur while the water content, loading pressure or both, are passed a threshold limit. One of the serious problems that may occur in the structures constructed on collapsible soils is the catastrophic settlements resulting from increase of water content in the soils. In this research, improvement of mechanical properties of loessial collapsible soil taken from Gorgan has been investigated using biocementation method. There are some microbial processes that can lead to biocementation, which one of them is microbially induced calcite precipitation (MICP). For improvement of the soil using MICP, reconstituted soil specimens is stabilized using bacterial and cementation solutions, then conventional oedometer and unconfined compressive strength tests performed on treated and untreated specimens. Various parameters such as concentration of cementation solution (urea-calcium chloride solution), curing time, moisture content, ratio of bacterial solution to cementation solution, is evaluated for determining the effect of these parameters on soil improvement. The results show that MICP has a considerable effect on collapse potential and strength of loess specimens and results in a decrease in settlement and increase in shear strength of treated specimens. Also, the strength of loess specimens decrease with increase of cementation solution concentration, and increase with increase of curing time and moisture content. The optimal amount of curing time, cementation solution concentration, and moisture content for treated specimens is 28 days, 0.25M and 15% respectively
  9. Keywords:
  10. Loess Soil ; Collapsible Soils ; Oedometer ; Cementation ; Microbially Induced Calcite Precipitation ; Urea Hydrolysis

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