An experimental investigation for improvement of sands using microbially induced calcium carbonate precipitation

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Civil Engineering, Turkey

Approval Date: 2016


Supervisor: ONUR PEKCAN


The development of innovative solutions to improve the engineering characteristics of sands becomes an emerging field of Geotechnical Engineering, as the environmental aspects, the economic feasibility and application practicability are concerned. In this scope, many improvement methods have been proposed to satisfy sustainability constraints, to reduce the overall the cost of construction and to be applied safely in the field. Among those, the use of biological means as derived from the nature gets popular which generally works through the process called Microbially Induced Calcium Carbonate Precipitation (MICP). Research studies indicate successful application of MICP based improvement using various types of bacteria and on several soils. Given the proven performance of MICP, this study aims to examine the MICP process thoroughly by comparing the calcium carbonate precipitation ability of widely studied bacteria, i.e., Sporosarcina pasteurii (ATCC 11859) and relatively under-recognized bacteria, i.e., Bacillus licheniformis (ATCC 14580) to outline the formation characteristics. For this purpose, two different sands are tested for observing precipitation behavior using syringes and then with a series of unconfined compression tests. Furthermore, various factors such as relative density of sands, concentration of substances for nutrition of bacteria, treatment numbers and durations are examined. The improvement in the strength characteristics of these soils are also interpreted with the use of sophisticated techniques such as X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. Successful results of this study highlight many questions regarding MICP application in sands. With that, this study opens new horizons for future works.