Characteristics of sandy soil treated using EICP-based urease enzymatic acceleration method and natural hemp fibers

Abstract

This study presents the use of biocementation process with EICP-based urease enzymatic acceleration method and natural hemp fibers to improve the strength of sandy soil. The amount of hemp fibers mixed in the sandy soil is varied up to 20% by volume. Different tests are used, and results are observed. From real-time bender element tests, the optimum amount of natural hemp fibers for mixing in biocemented sand is found to be 2.5% by volume, based on shear wave velocity and initial shear modulus. Moreover, the process of biocementation requires a few days before the start of reaction, and the reaction fully occurs at 4-day while finishes at 6-day. Using pH meter, it is found that the process of biocementation reaches its maximum value at 3-day, because the solution pH in sand becomes higher than 7. After that, the biocementation reaction rate decreases due to the reduction of the solution pH. From spectophotometer, the ammonification occurs from 0-day to 4-day, and reaches its maximum at 4-day. After that, it gradually decreases showing the gradual end of biocementation reaction. The SEM results show that the surface of natural hemp fibers and precipitated calcium carbonate (CaCO3) crystals are rough indicating the potential for bonding between them. The SEM results also show that the precipitated CaCO3 fills within the voids between sand particles and natural hemp fibers, resulting in the enhancement of sandy soil strength. The XRD results show the relationship between the occurrence of CaCO3 and the process of biocemented in sand. Finally, the direct shear tests confirm the improvement of sandy soil properties via increasing cohesion and internal friction angle due to biocementation and hemp fibers.