Direct Shear Test on The Mechanical Behavior of Aqueous Foam-Treated Sandy Soil

Abstract

Aqueous foam has demonstrated excellent performance in improving soil properties. To study the evolution of the mechanical behavior of foam-treated soil under varying foam contents, a series of direct shear tests were conducted. Experimental results reveal that foam markedly alter the mechanical characteristics of the soil by reducing interparticle friction and modifying its stress–strain response. But the improvement in soil behavior is strongly dependent on the foam content. A critical foam content threshold was identified, beyond which the foam effectively lubricates particle contacts and enhances plastic deformation, whereas below this threshold, the conditioning effect remains minimal. Thus, achieving the optimal foam content is essential to ensure both soil stability and flowability during tunneling operations.