Mitigation of sand liquefaction under static loading condition using biogas bubbles generated by denitrifying bacteria

Abstract

Nitrogen bubbles that is generated by microbial denitrification process is a new pollution-free clean material for mitigation of sand liquefaction. The current study aims to assess sustainability as well as distribution character of biogas bubbles in sand column under the condition of hydrostatics along with its performance of mitigating sand liquefaction under static loading. A series of laboratory experiments were conducted, and test results indicate that biogas bubbles has excellent sustainability in sand pores, and after 92 weeks, an increase of saturation from 84.5 to 85.1% marking only 0.6% rise. The volume of biogas generated by bacteria increases linearly with decrease of depth. Under undrained condition, if saturation of sample decreased from 100% to around 92.4%, strain softening behavior will transfer to strain hardening, and undrained shear strength can be increased by approximately two times in both of compression and extension tests. The excess pore water pressure ratio and liquefaction potential index have significant reduction with the decrease of saturation, and the magnitude of impact on compression is comparatively bigger than the extension tests. This study validates that as a new material, biogas bubbles are very stable in soil, desaturation using nitrogen bubbles is an effective method for mitigating the liquefaction of sand under static loading conditions. Moreover, the study provides support for the desaturation mitigating static liquefaction of sand to prevent geological disasters and reveals its potential engineering practical value.