Abstract: The microbial decomposition can reduce the organic content of peat soil and change its composition, thus affecting the engineering properties of soil. To explore this phenomenon, a model test device was developed to decompose the peat soil with enriched bacteria solution for 90 days. Then the physical and mechanical properties of the peat soil were analyzed and tested during the decomposition process. The results showed that the organic matter content of peat soil decreased from 67% to 61.5% within 90 days. As the decomposition time increased, the relative density Gs and saturation γsat of peat soil increased, the liquid limit wL decreased significantly, and the plastic limit wP almost maintains constant. The compression coefficient a1-2 of the decomposed peat soil decreased, while the compression modulus Es increased. The fast shear strength of the consolidated peat soil generally increased by 15%-25% after decomposition. The cohesion ccq decreased from the initial 18.3 to 15.6 kPa, while the internal friction angle φcq increased from 13.9oto 18.8o. The decomposition time increased, and the permeability coefficient of the pre-compressed peat soil sample decreased. The mechanism analysis shows that the change of engineering properties of peat soil is not only related to the decrease of organic matter content, but also related to the change of composition.

Key words: microbial geotechnical, organic matter degradation, peat soil, shearing strength, permeability coefficient