Improvement of Unconfined Compressive Strength in Granite Residual Soil by Indigenous Microorganisms

Ya Wang, Meiqi Li, Hao Peng, Jiaxin Kang, Hong Guo (), Yasheng Luo and Mingjiang Tao
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Ya Wang: School of Civil Engineering and Architecture, Shaanxi University of Technology, Hanzhong 723001, China
Meiqi Li: College of Biological Science and Engineering, Shaanxi University of Technology, Hanzhong 723001, China
Hao Peng: College of Biological Science and Engineering, Shaanxi University of Technology, Hanzhong 723001, China
Jiaxin Kang: School of Civil Engineering and Architecture, Shaanxi University of Technology, Hanzhong 723001, China
Hong Guo: School of Civil Engineering and Architecture, Shaanxi University of Technology, Hanzhong 723001, China
Yasheng Luo: College of Water Resources and Architectural Engineering, Northwest A&F University, Yangling 712100, China
Mingjiang Tao: Department of Civil, Environmental, & Architectural Engineering, Worcester Polytechnic Institute, Worcester, MA 01609, USA

Sustainability, 2025, vol. 17, issue 15, 1-17

Abstract: In order to study how indigenous microorganisms can enhance the strength properties of granite residual soil in the Hanzhong area, two Bacillus species that produce urease were isolated from the local soil. The two Bacillus species are Bacillus subtilis and Bacillus tequilensis , and they were used for the solidification and improvement of the granite residual soil. Unconfined compressive strength tests, scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses were systematically used to analyze the influence and mechanism of different cementation solution concentrations on the improvement effect. It has been found that with the growth of cementing fluid concentration, the unconfined compressive strength of improved soil specimens shows an increasing tendency, reaching its highest value when the cementing solution concentration is 2.0 mol/L. Among different bacterial species, curing results vary; Bacillus tequilensis demonstrates better performance across various cementing solution concentrations. The examination of failure strain in improved soil samples indicates that brittleness has been successfully alleviated, with optimal outcomes obtained at a cementing solution concentration of 1.0 mol/L. SEM and XRD analyses show that calcium carbonate precipitates (CaCO 3 ) are formed in soil samples treated by both strains. These precipitates effectively bond soil particles, verifying improvement effects on a microscopic level. The present study proposes an environmentally friendly and economical method for enhancing engineering applications of granite residual soil in Hanzhong area, which holds significant importance for projects such as artificial slope filling, subgrade filling, and foundation pit backfilling.

Keywords: MICP technology; residual granite soil; improvement test; unconfined compressive strength test; characterization of microstructure (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2025
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