Amirkabir University of Technology Amirkabir Journal of Civil Engineering 2588-297X 53 7 2021 09 23 Experimental Study of the Effect of Chemical and Biological Stabilization on Clay Subgrade Soil Experimental Study of the Effect of Chemical and Biological Stabilization on Clay Subgrade Soil 2821 2836 3793 10.22060/ceej.2020.17493.6588 FA Siamak Shafaghatian Department of civil engineering-Geotechnical engineering,University of tabriz,Tabriz,Iran Gholam Moradi Department of civil engineering-Geotechnical engineering,University of tabriz,Tabriz,Iran Hooshang Katebi Department of civil engineering-Geotechnical engineering,University of tabriz,Tabriz,Iran 0000-0001-7347-6999 Journal Article 2019 12 10 Chemical stabilization of weak subgrade soil is a viable and essential method of avoiding weak soil replacement problems with selected borrow pit from an economically and environmentally point of view. Although the use of new materials such as polymers instead of traditional materials such as lime accelerates operations and reduces resource pressure, the environmental impact and long-term resistance in these methods are concerns for experts. Recently, according to the “Kyoto Environmental Protocol” recommendation on soil stabilization with geotechnical purposes, research on new biological methods of soil stabilization including "soil microbial stabilization" has been developed. In this study, the effect of clay subgrade stabilization with chemical and biological methods was investigated and compared through different experiments. Cationic polyelectrolyte as a liquid polymer and microbial-induced calcium carbonate precipitation (MICP) was used to stabilize chemically and biologically respectively. In both methods, the specific dry weight of soil decreases, and its optimum moisture content increases. Chemical stabilization increases plastic index and microbial stabilization decreases it. Both materials at low concentrations raise the pH for up to three days. Both materials increase the uniaxial compressive strength and elasticity modulus of the soil almost equally. In terms of project economy (time and cost), chemical stabilization with cationic polyelectrolyte, and terms of environmental issues, the MICP method is suitable for the studied soil. Chemical stabilization of weak subgrade soil is a viable and essential method of avoiding weak soil replacement problems with selected borrow pit from an economically and environmentally point of view. Although the use of new materials such as polymers instead of traditional materials such as lime accelerates operations and reduces resource pressure, the environmental impact and long-term resistance in these methods are concerns for experts. Recently, according to the “Kyoto Environmental Protocol” recommendation on soil stabilization with geotechnical purposes, research on new biological methods of soil stabilization including "soil microbial stabilization" has been developed. In this study, the effect of clay subgrade stabilization with chemical and biological methods was investigated and compared through different experiments. Cationic polyelectrolyte as a liquid polymer and microbial-induced calcium carbonate precipitation (MICP) was used to stabilize chemically and biologically respectively. In both methods, the specific dry weight of soil decreases, and its optimum moisture content increases. Chemical stabilization increases plastic index and microbial stabilization decreases it. Both materials at low concentrations raise the pH for up to three days. Both materials increase the uniaxial compressive strength and elasticity modulus of the soil almost equally. In terms of project economy (time and cost), chemical stabilization with cationic polyelectrolyte, and terms of environmental issues, the MICP method is suitable for the studied soil. https://ceej.aut.ac.ir/article_3793_c157297d1a1ff043255bfb18530caaa2.pdf