Recently, artificially introducing gas/air into liquefiable soils has been presented as a method for reducing the risks from liquefaction. Although this method offers a simple and cheap solution, its use in practical applications is still very limited. This might be primarily ascribed to the concerns of practising engineers about the durability of gas/air bubbles in soils over time. This paper discusses the durability of entrapped air bubbles under various simulated field conditions that may potentially cause the dissolution, diffusion, compression and escape of air bubbles. Multiple series of 1g vertical sand column and high-g centrifuge tests were undertaken to provide insights into the problem. Air-induced partially saturated soils were prepared using an air-injection technique. The test results showed that the majority of entrapped air bubbles in soils can persist under several simulated field conditions for a sufficient period of time, indicating the long-term reliability of the mitigation accomplished.

Partially saturated soils associated with the presence of occluded air bubbles are commonly encountered in seismically active zones. Yet, there is a lack of deep understanding of the mechanisms of settlement that partially saturated soils suffer during seismic events. Consequently, a reliable seismic design approach for use in engineering practice is lacking. The aim of this paper is to show that seismically induced settlement of a level deposit of partially saturated soil can be estimated by summing the settlement related to excess pore pressure (EPP) generation/dissipation and increased soil mass compressibility in the presence of air bubbles, which are calculated separately. Predictions of the proposed effective stress-based methodology are found to be in good agreement with geotechnical centrifuge measurements. It is shown that the variation of degree of saturation is of significance. The proposed methodology utilizes the degree of saturation as a parameter and can satisfactorily predict the experimentally observed settlement.

Seismic liquefaction of loosely packed, saturated soils poses a significant threat to the built environment. Recently, air injection into liquefiable soil deposits has been introduced as an innovative and cost-effective liquefaction mitigation technique. However, few effective guidelines are available to the engineers for its application and performance. The way that air should be injected appropriately, most particularly, in the presence of structures, is not clearly defined. The distribution of retained air bubbles within the saturated soil medium and its effect on the seismic response also need further investigation. In an effort to offer insights into this problem, an experimental programme consisting of a series of centrifuge and 1g shaking table tests was undertaken. The results have shown that the use of higher air injection pressure provides a much wider and a more uniform air-entrapped zone, but increases the risk of soil deformations developed under the foundations. The distance from the air injector and preferential flow pathways influence the distribution of the retained air bubbles and seismic response of the soil models. Moreover, it was shown in a novel way that the air injection technique is not very effective at low confining stresses to reduce liquefaction-induced deformations beneath shallow foundations.