Evaluation indicators of saturation on partially saturated sand induced by microbial gas

The induced partial saturation (IPS) technique introduces a certain amount of air/gas into soil voids to mitigate sand liquefaction. The microbial desaturation method utilises biological metabolic processes which are good for environmental protection and disaster prevention. Real time monitoring and quantitative analysis of the saturation after microbial bubble generation are the first step in the field application of the IPS method. In this study, shear wave velocity measurements were taken using the pre-vibration technique through an array of accelerometers at different depths on the basis of shaking table model tests. The shear wave velocity was obtained during the desaturation of microbial gas production. The arrival time of the first wave peak increased and the shear wave velocity decreased with the decreasing saturation. The shear wave velocity decreased with the saturation, and the rate of shear wave velocity decreased when the degree of saturation reduced to 90 %. This result indicates that the shear wave speed is effective as an indicator of saturation in microbial gas production. The shear wave velocity decreases with the saturation, and the relationship between the two satisfies the exponential functions. A quantitative relationship was established between the saturation and shear wave velocity during microbial gas production. The maximum shear modulus decreases with the saturation during the gas production process. Meanwhile, the relationship between shear wave velocity and resistivity was established using resistivity meters. The resistivity value decreases with the degree of saturation. The power function relationship between resistivity and saturation was satisfied in this experiment. The explicit analysis of the saturation data at each point in the desaturation method has significant research value for field trials using high-density electrical resistivity tomography. The research results obtained in this experiment can help in the quantitatively analysis of the uniformity and effectiveness of bubble distribution in the field test application of the microbial desaturation method and provide a basis for the engineering application of the microbial desaturation method in field tests.