Centrifuge testing to evaluate the liquefaction response of air-injected partially saturated soils beneath shallow foundations

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.

Closure to “Simplified Procedure for Prediction of Earthquake-Induced Settlements in Partially Saturated Soils” by Abdülhakim Zeybek and Santana Phani Gopal Madabhushi

“…It was assumed that the bubbles in discrete forms fit into the void spaces without interacting with the soil structure, whereas they affect the compressibility of the pore fluid and soil mass. Zeybek and Madabhushi (2017a) conducted a series of dynamic centrifuge experiments on partially saturated sand models with high degrees of saturation, providing evidence of the validity of these assumptions. Visual observations based on the enlarged and high-quality images of the sand specimens revealed that the size of the air bubbles was generally smaller than or on the same order as the size of the sand particles.…”

Liquefaction induced displacement and rotation of structures with wide basements

“…Most previous investigations into earthquake induced liquefaction and soil-structure interaction have used structures with a significantly greater effective bearing pressure than that applied by the structures in these tests, which has prevented full liquefaction occurring directly beneath the structure [ 10,7,15,9]. There are few documented cases for structures with low effective bearing pressure (<20 kPa) resting upon liquefiable soils.…”

“…Ground improvement methods can be used to reduce liquefaction induced settlement of structures, for example soil improvement [10,12,13,14], reducing the degree of saturation of the soil [15] and improving drainage using vertical drains [16]. However, these methods have the result of increasing the seismic demand of the structure [15,13,14]. By reducing the extent of soil liquefaction the natural isolation provided by attenuation of horizontal accelerations in liquefied soil is removed.…”

Physical modelling of air injection to remediate liquefaction

“…The depth of liquefaction also markedly reduced, and a complete bearing failure mechanism under the shallow foundation did not form, leading to significantly smaller foundation settlements. Moreover, it was exclusively shown by Zeybek and Madabhushi (2017a) that the deformation mechanisms, generation of excess pore pressures and consequent liquefaction-induced settlements of shallow foundations were a strong function of the degree of saturation of airinjected soils. Seed et al (2003) have stated that the selection and implementation of liquefaction mitigation techniques require a thorough evaluation of the important parameters: (a) applicability, (b) effectiveness, (c) verifiability of the reliability of the mitigation achieved, (d) cost and (e) other sources of concern (e.g.…”