Effect of Biological Cementation on the Mechanical Behaviour of Dredged Soils with Emphasis on Micro-structural Analysis

Abstract

During the past few years, microbial geotechnology has gained a lot of attention from researchers as it is an eco-friendly method of soil improvement causing no impairment to the soil and groundwater. In this study, a bacillus species, B. subtilis has been used to enhance the unconfined compressive strength and the penetration resistance of weak dredged soil obtained from ‘Hokersar Wetlands’ in Bemina area of Srinagar. The microbes were added at different optical densities (0.4, 1.0 and 1.3) and treated with a cementing solution of urea and calcium chloride at different molarities (0.25 M, 0.5 M, 1.0 M) for 48 h. Testing was done in a temperature-controlled chamber (25–28 °C) maintaining a pH of 7–9 and the samples were cured for 7, 14 and 28 days, respectively. It is observed that with increasing optical density and molarity of cementing solution, there is an increase in calcium carbonate precipitation which in turn increases the unconfined compressive strength and the penetration resistance of the soil. The increase in strength from 197 to 537 kN/m2 was appreciable, the un-soaked California bearing ratio increased from 5.6 to 11.5%, whereas the soaked California bearing ratio increased from 1.3 to 7%. The results were in turn supported by scanning electron microscopy and X-ray diffraction technique. Treated dredged soil can be utilized in bulk, as a resource for various engineering applications for eco-friendly and sustainable development of environment.