Effect of carbonate precipitating bacteria on strength and hydraulic characteristics of loess soil
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ORIGINAL PAPER
Effect of carbonate precipitating bacteria on strength and hydraulic characteristics of loess soil Shima Atashgahi 1 & Alireza Tabarsa 1 & Ali Shahryari 2 & Seyedeh Sedigheh Hosseini 3 Received: 2 November 2019 / Accepted: 20 May 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Microbial-induced calcite precipitation (MICP) is one of the environmentally friendly techniques that has recently become popular amongst geotechnical engineers. Two bacterial species of Bacillus family, i.e., B. pasteurii and B. megaterium have been used to improve the loess soil properties. A set of unconfined compressive, permeability, ultrasonic, and collapse potential tests have been applied to assess the characteristics of natural soil compared to those of MICP-treated ones. The effects of curing time (1, 3, and 7 days), bacterial optical density (OD = 0.5, 1, and 1.5), and soil density (13, 14, and 15 kN m3 ) have been investigated. Results indicate that biological enhancement has improved the engineering properties of the loess soil. MICPtreated soil using B. megaterium provides higher strength improvement ratios (1.15–4.4 times) rather than B. pasteurii-treated samples (1.05–3.4 times). Correspondingly, specimens containing B. megaterium have greater permeability reduction ratios (3.9–93.7%) compared with those of B. pasteurii ones (2–95%). Moreover, scanning electron microscope (SEM) analysis has been employed to confirm the findings. It is worth noting that various bacteria concentrations, curing periods, and soil densities can affect the stress-strain curve considerably. The results indicated that MICP reduced the collapse potential between 24 and 54.8% and increased the longitudinal wave velocity between 1.1 and 2.4 times more than the untreated soil. Keywords Loess . Soil improvement . Microbial induced calcite precipitation . MICP
Introduction As per the increasing population and the need for construction in proper places, over the past decade, special attention has been paid to geotechnical issues to modify the problematic soils (Dejong and Kavazanjian 2019). Collapsible soils are mostly found in dry areas and have various problems such as high porosity, low specific gravity, poor particle classification, potential collapsibility, and insignificant adhesion (Haeri et al. 2012; Tabarsa et al. 2018). However, the behavior of
* Alireza Tabarsa [email protected] 1
Depatrment of Civil Engineering, Faculty of Engineering, Golestan University, P. O. Box 49138-15759, Gorgan, Iran
2
Environmental Health Research Center, Faculty of Health, Golestan University of Medical Sciences, P. O. Box 49189-36316, Gorgan, Iran
3
Department of Laboratory Sciences, Faculty of Paramedicine, Golestan University of Medical Sciences, Gorgan, Iran
collapsible soils is strongly influenced by the soil moisture variation contents and the stresses (Zamani and Badv 2019). Most of the loess sediments, being considered as one of the main groups of collapsible soils, are naturally low in moisture content, creat
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