Improvement of Strength and Permeability Attributes of Silty Sand Type of Soils using Enzyme Induced Calcite Precipitation

Abstract

ABSTRACT

Enzyme Induced Calcite Precipitation (EICP) is one of the soil stabilization techniques based on microbiological activity. In this technique, urea decomposes with the aid of urease enzymes in the presence of calcium chloride and produces calcite, which acts as a bio-clogging and bio-cementing material. In this study, test tube experiments are performed to assess the optimal amount of calcium chloride, urea, and urease enzymes to be used for engineering applications. The silty sand type of soil is treated with different proportions namely; P1 (0.1g urease enzymes, 0.375g urea, 0.9g CaCl₂), P2 (0.2g urease enzymes, 0.75g urea, 1.8g CaCl₂), and P3 (0.4g urease enzymes, 1.5g urea, 3.6g CaCl₂), to analyze their effect on strength and permeability attributes of soils after 14 days of curing time. It was observed that an increase in EICP content causes a substantial increase in shear strength particularly cohesion due to the bio-clogging phenomenon induced in soil particles by EICP which eventually leads to a decrease in permeability and inhibits the activity of urease. Overall, P3 yields higher cohesion (48 kPa) than P1(40 kPa), P2 (43kPa), and untreated soil samples (31 kPa). Furthermore, P3 causes a significant decrease in permeability as compared to P2, P1, and untreated soil samples tested after 14 days of the curing period. The findings of the study suggest the successful implementation of EICP for soil stabilization.

Key Words: Enzyme Induced Calcite Precipitation (EICP); permeability; shear strength; bio-clogging; bio-cementation.