Soil with low bearing capacity is not able to support the construction on it so that a soil improvement method is needed to improve the soil structure. Soft soil stabilization has been carried out with various stabilizers, namely lime, cement, a combination of cement and fly ash, asphalt, and others, but this stabilizing agent is not environmentally friendly. Currently alternative environmentally friendly biostabilization is growing with the use of microorganisms (bacteria). The purpose of this study was to obtain the characteristics of the soft soil stabilized with bacteria by testing unconfined compression strength (UCS) and the direct shear test experimentally. The bacteria used were 3 days cultured bacillus subtilis bacteria with a composition of 4, 6, and 8% at optimum density conditions. The curing time was carried out for 7, 14, and 28 days after the preparation of the test object. The test results showed that the optimum bacteria content for stabilizing soft soil based on the test was obtained at 6%. At the curing time of 28 days, the unconfined compression strength value was 1073.83 kPa, and the elastic modulus was 368.88 kPa or an increase of 527% when compared to soil without bacteria stabilization. The soil shear stress was obtained at 194.66 kPa, an increase of 400% when compared to soil without bacteria stabilization.
