Mitigation of soil liquefaction using microbially induced desaturation

Abstract

Soil liquefaction can cause disastrous consequences to buildings and human lives. Regular countermeasures against soil liquefaction are often overly expensive for normal buildings and structures. This could be the major reason that liquefaction induced damage is still widely encountered in large-and mid-size earthquakes in recent years. In this paper, a new method for the mitigation of soil liquefaction using the microbially induced soil desaturation is proposed and tested. The desaturation effect in soil is achieved by the generation of nitrogen gas produced from the microbial denitrification process. Some major issues related to this method are experimentally investigated. These include soil desaturation procedures, shapes and distribution of gas bubbles in soil, mechanical responses and liquefaction resistance of desaturated soils, and stability of gas in soils. The desaturation treatment of soils is made simply by introducing denitrifying bacteria and a desaturation solution into soil pores by mixing, flushing, or injection. The degree of saturation can be reduced as the microbial reaction proceeds. Experimental results show that the final degree of saturation is related to the initial nitrate concentration added to the soil: the higher the concentration of nitrate in the desaturation solution, the lower the degree of saturation that can be achieved. The existence of gas bubbles in soil is evidenced by computer tomography (CT) technology. The CT images reveal that gas is in the form of small pockets which has a size a little larger than the mean size of sand grains. It is shown in the shaking table tests that microbially induced desaturation can effectively improve the liquefaction resistance of soil by showing a much lower pore pressure generation, much smaller volumetric strain, and much smaller settlement of the structure in desaturated soil, as compared with those in saturated soil. Triaxial consolidated undrained tests reveal that the desaturation treatment of soil can improve the undrained shear strength of loose sand. The stability of gas is tested under hydrostatic and water flow conditions. The gas phase is stable under the hydrostatic condition, but unstable under water flow conditions. So measures ought to be taken to prevent steady flow in practice.

A critical review on microbial carbonate precipitation via denitrification process in building materials

“…Furthermore, the studies revealed that a 80 to 95% reduction significantly affects the undrained stress-strain behavior, reduces the pore pressure and makes the sand non-liquefiable [ 93 , 94 ]. The microscopic studies of the gas bubble by the computed tomographic image revealed that the gas bubbles are present in small pockets of all the pores and bigger than the average grain size [ 110 ]. MICP via denitrification is more feasible if applied in the two-stage process for liquefaction mitigation.…”

Recent development in biogeotechnology and its engineering applications

“…As shown in Eqs. ( 5)-( 8), denitrification is a multistep bacterial metabolism involving several enzymes that catalyze the stepwise reduction of nitrate to nitrogen [105,106].…”

“…Flow tests for sand columns treated using the combined bio-desaturation and bioclogging method under a hydraulic gradient of 0.1 with either upward or downward flow indicate that the combined method effectively enhances the stability of the bubbles. Other studies performed by O'Donnell et al [13,105,106,111], Wang et al [276], Kavazanjian and O'Donnell [285], and Hall et al [288] employed the denitrification process to induce calcium carbonate precipitation and generate nitrogen gas at the same time. The advantage of this process is that it provides an additional benefit for mitigating soil liquefaction through biogas (N 2 ) desaturation besides associated carbonate precipitation.…”

Dynamic Characteristics and Wall Effects of Bubble Bursting in Gas-Liquid-Solid Three-Phase Particle Flow

“…The above analysis concluded that the bubble deformation has little effect on particles. With the increase of bubble-wall velocity, the strength of the micro-jet gradually increases until the bubble completely bursts, and at that moment, the maximum of both micro-jet strength and instantaneous speed are reached [58][59][60]. Due to the effect of viscosity and the drag force, the particle velocity drops sharply until it reaches the initial velocity.…”