علوم آب و خاک (Sep 2023)
Performance Evaluation of MICP Method for Sustainable Improvement of Expansive Soils
Abstract
The use of biotechnology-based methods in the field of geotechnical engineering has led to the birth of new knowledge of biogeotechnology and several studies have been conducted using this new knowledge in various geotechnical issues including reducing permeability and increasing shear strength, especially in sandy soils and the desired results have been obtained. Nevertheless, little research has been done using biogeotechnology in the field of improving the mechanical properties of clay soils, especially in reducing the swelling of expansive soils, which is considered one of the types of problematic soils. The main cause of swelling of expansive soils is the presence of montmorillonite clays in these types of soils. Using chemical additives to stabilize expansive soils such as lime and cement is a common practice. However, environmental concerns related to greenhouse gas production caused by the production of chemical substances and the destructive effects of these substances on the environment and soils have encouraged researchers to use other sustainable stabilization alternatives. Microbial Induced Carbonate Precipitation (MICP) is a technique that can be a promising solution to solve this problem. The objective of the present study was to investigate the effect of the MICP method on the swelling of expansive clay soils and its effect on the mechanical strength of this type of soil. One-dimensional swelling tests, uniaxial compressive strength tests, and Atterberg limits tests were performed on clay soil with a liquid limit of 53 using Sporosarcina pasteurii bacteria, calcium chloride, and urea as nutrients. Taguchi's method was used for the design of the experiments and the statistical analysis of the results. This method designs experiments through partial factorial and reduces their number without a significant effect on the results. Bacterial concentration, nutrient molarity ratio, treatment time, and soil moisture were selected as four factors with Four levels of variation. The results showed that the (MICP) method was effective in reducing the swelling potential of expansive soils and also caused a significant increase in the unconfined compressive strength of the soil and its undrained shear strength.
