Soil bio-cementation using an improved 2-step injection method
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ORIGINAL PAPER
Soil bio-cementation using an improved 2-step injection method Ming-Juan Cui 1 & Jun-Jie Zheng 1 & Rong-Jun Zhang 1 & Han-Jiang Lai 1 Received: 7 May 2020 / Accepted: 26 October 2020 / Published online: 26 November 2020 # Saudi Society for Geosciences 2020
Abstract To improve the uniformity of calcium carbonate distribution in soil treated by microbially induced carbonate precipitation (MICP), an improved biological injection method, namely “2-step method”, was proposed. This method was achieved by first injecting a certain volume of pure bacterial suspension into soil, followed by injecting the remaining pore volume with the mixed bacterial suspension, which was prepared by mixing pure bacterial suspension and fixation solution containing CaCl2. The method was validated through various physical and mechanical properties of the bio-cemented sand, including the bacterial adsorption efficiency, calcium carbonate content and distribution, and unconfined compressive strength. The results showed that the proposed 2-step method could effectively improve the bacterial adsorption, calcium carbonate content, and strength of bio-cemented sand. The prepared bio-cemented sand had relatively uniform distribution of calcium carbonate and higher strength. The optimal volume ratio between the mixed bacterial suspension and pure bacterial suspension for the 2-step method was 0.6:0.4. Keywords Soil improvement . Microbially induced carbonate precipitation . Biological injection method . Calcium carbonate distribution . Unconfined compressive strength
Introduction Microbially induced carbonate precipitation (MICP) is an emerging ground treatment technique that has drawn increasing attention from researchers (Ivanov and Chu 2008; Al Qabany et al. 2012; Cheng et al. 2013; Zhang et al. 2015; Ou et al. 2019; Wu et al. 2019; Lei et al. 2020) due to its environmentally friendly features. MICP treatment utilizes the cementitious calcium carbonate crystals induced by urease-producing bacteria to bond soil particles (i.e., bio-cementation) and to fill interparticle pores (i.e., bio-clogging) (Ivanov and Chu 2008; Weil et al. 2012), and in turn to improve soil properties (e.g., strength, stiffness, and dynamic response) (Mitchell and Ferris 2006; van Paassen et al. 2010; Weil et al. 2012; Montoya et al. 2013; Han et al. 2020). Al Qabany and Soga (2013) have reported that the strength enhancement of the biocemented soil is closely related to the distribution of the precipitated calcium carbonate crystals. Meanwhile, the bacteria Responsible Editor: Zeynal Abiddin Erguler * Jun-Jie Zheng [email protected] 1
Institute of Geotechnical and Underground Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
adsorbed on soil particles have been shown to serve as the nucleation sites for the precipitation of the calcium carbonate crystals (Mitchell and Ferris 2006; DeJong et al. 2006; Dupraz et al. 2009; Chu et al. 2014; Achal et al. 2015; Ghosh et al. 2019). In this regard, uniformity of the distribution
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