Experimental and numerical assessment of biological soil improvement on the bearing capacity of shallow foundations

Shallow foundations are widely used where surface soils can sustain structural loads without excessive settlement. Various ground improvement methods, such as microbially induced carbonate precipitation (MICP), can increase bearing capacity in cases where soil strength is insufficient. MICP promotes the formation of calcium carbonate between soil particles, thereby improving interparticle bonding and enhancing soil strength. This study uses experimental testing and numerical analysis to examine the impact of a biologically treated thin layer on the ultimate bearing capacity and failure mechanisms of rectangular shallow foundations in sandy soils. Laboratory tests were conducted in a steel container measuring 100 cm in length, 70 cm in height, and 70 cm in width, examining the effects of different bacterial strains and varying treatment depths. Results show that bacterial inoculation and subsequent MICP treatment significantly increase the cohesion and strength of sandy soils. Introducing a biologically improved layer can increase the bearing capacity by up to three times. Positioning the treated layer at the surface yields a bearing capacity more than 10% higher than placing it at half the effective depth. Among the tested bacteria, Bacillus megaterium notably improves the soil's shear strength parameters compared to Sporosarcina pasteurii, resulting in an over 50% increase in foundation-bearing capacity. Numerical simulations using PLAXIS, based on the mohr-coulomb constitutive model, closely match the experimental findings, with a deviation of less than 10%.