A STUDY ON CLAY SOIL IMPROVEMENT WITH BACILLUS SUBTILIS BACTERIA AS THE ROAD SUBBASE LAYER

Abstract

This study aims to investigate the bearing capacity of the high-plasticity clay soil with bacteria
stabilization (Bacillus subtilis). The growth of bacteria with the phase of 6 days was used as a stabilizing
agent. The assessment of bearing capacity was based on unconfined compressive strength value, California
Bearing Ratio (CBR), and modulus of soil reaction as a subbase layer. The test results show that the
compressive strength value tends to increase with the addition of 2% to 6% bacteria and decrease with 8%
bacteria. This phenomenon corresponds to the increase of CaO value due to Microbial-Induced Calcite
Precipitation (MICP) microstructurally. The compressive strength value curve pattern increases
proportionally with curing time of 3, 7, 14, and 28 days. According to the California Bearing Ratio (CBR)
value range criteria (20% ≤CBR˂40%) for subbase layer, the use of 3.5 to 6% bacteria can technically be
functionally justified as a road material with the modulus of stabilized clay soil reaction value of 68 to 110
kN/m2
/mm. The results of this study have technical implications for the significance of the use of Bacillus
subtilis bacteria as the biotechnology stabilization material to increase the bearing capacity and modulus of
soil reaction with high plasticity clay.