Abstract
Earthquake-induced liquefaction of saturated soils continues to cause severe damage to structures with shallow foundations. In recent years, artificially reducing the degree of saturation and forming partially saturated zones within saturated soils has been proposed as a liquefaction mitigation technique. This study experimentally investigates the liquefaction response of air-injected partially saturated soils beneath shallow foundations. A series of centrifuge tests were conducted on the shallow foundations with different bearing pressures. The results of the tests show that the generation of excess pore pressures and consequent liquefaction-induced settlements of shallow foundations were a strong function of the degree of saturation. Forming spatially distributed partially saturated zones in the liquefiable soils limited the development of high excess pore pressures and liquefaction susceptibility of soils, particularly at the higher confining stresses. The reduction in the degree of saturation of soils decreased the depth of liquefied soil layer, and increased the resistance of soil to the bearing capacity failure. On the other hand, the decrease in the degree of saturation of liquefiable soils led the larger accelerations to be transmitted to the foundations through unliquefied soil zones. It is therefore concluded that use of air-injection as a liquefaction mitigation measure does reduce structural settlements, but will have the consequence of larger structural accelerations.
Highlights
The liquefaction or softening of the foundation soils have repeatedly caused severe damages to structures with shallow foundations during earthquakes, such as recently during the 2010 Maule, Chile and the 2011 Christchurch, New Zealand earthquakes
The results of the tests show that the generation of excess pore pressures and consequent liquefaction-induced settlements of shallow foundations were a strong function of the degree of saturation
The effect of degree of saturation on the cyclic liquefaction behaviour of air-induced partially saturated soils beneath shallow foundations was investigated through a series of geotechnical centrifuge tests
Summary
The liquefaction or softening of the foundation soils have repeatedly caused severe damages to structures with shallow foundations during earthquakes, such as recently during the 2010 Maule, Chile and the 2011 Christchurch, New Zealand earthquakes. Some researchers have been investigating liquefaction mitigation techniques that involve the artificial introduction of gas bubbles and creating partially saturated zones in the liquefiable soil deposits. Some of these techniques are water electrolysis (Yegian et al 2007), drainage-recharge (Takemura et al 2008) and air injection (Okamura et al 2011). The research investigating the response of shallow foundations resting on these soils has suggested that in accordance with the laboratory test data, the liquefaction potential of liquefiable soils and relevant structural settlements significantly decrease as the degree of saturation reduces (e.g. Marasini and Okamura 2015). These results were confirmed for two sets of foundations with different bearing pressures, one classed as ‘light’ and other as ‘heavy’ (see Table 1)
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