Study of the Mechanical Properties and Water Stability of Microbially Cured, Coir-Fiber-Reinforced Clay Soil

Abstract

Clay soil is widely distributed in engineering foundations. Because of its poor stability, low load-bearing capacity, and poor water stability, it does not provide a high-quality foundation. Microbial-induced calcium carbonate precipitation (MICP) is a novel soil consolidation technique. The basic principle of this technique is that microorganisms induce calcium carbonate deposition in the soil, solidifying it. The reinforcement treatment of clayey soil via MICP with fiber reinforcement can make full use of the advantages of both techniques to improve the mechanical properties and water stability of the soil. In this study, in order to facilitate engineering applications, bacillus pasteurii liquid was mixed with coconut-fiber-reinforced soil using the mixing method, and a microbial solidification test was carried out on the reinforced clayey soil with fiber contents of 0, 0.2%, 0.4%, and 0.6% (mass ratio). By conducting triaxial consolidation without a drainage test, the calcium carbonate content determination test and the disintegration test were combined with SEM microscopic image analysis to compare and analyze the mechanical properties and water stability of clayey soil under different fiber treatments. The results show the following: (1) The coupling of the two techniques can effectively improve the shear strength of the soil. The shear strength first increased and then decreased with the increase in the fiber content. The optimum fiber content is 0.4%, and the shear strength is 120% higher than that of plain soil. (2) The addition of fiber significantly increased the cohesive force of the clayey soil. In addition, the friction angle was also increased by the synergistic effect of the fiber and calcium carbonate. The cohesive force was increased in the range of 3.2~24.4 kPa, and the internal friction angle was increased in the range of 2.2°~6.4°. (3) As the fiber content increased, the disintegration resistance of the solidified soil was obviously improved, and the disintegration rate decreased with the increase in fiber content. When the fiber content was 0.6%, the final disintegration rate was the lowest. (4) Fiber reinforcement increased the colonization space of the microorganisms and improved the deposition efficiency and yield of the calcium carbonate, and the cementing effect of the calcium carbonate promoted fiber reinforcement.