Water spewing and muck plugging often occur during earth pressure balance (EPB) shield machines tunnelling in water-rich sandy strata, even though the conventional foam has been employed to condition sandy soils. In this study, a novel thickened foaming agent suitable for EPB shield tunnelling in water-rich sandy strata is developed. In contrast to conventional foam-conditioned sands, the thickened foam-conditioned sand has a low permeability due to the consistent filling of soil pores with the thickened foam, and the initial permeability coefficient decreases by approximately two orders of magnitude. It also exhibits a suitable workability, which is attributed to the enhanced capability of the thickened foam to condition sandy soils. In addition, the effect of concentration on the stability of the foam is explained by the Gibbs-Marangoni effect, and conditioning mechanisms for the thickened foam on sands are discussed from the evolution of foam bubbles.

The material point method (MPM) has been gaining increasing popularity as an appropriate approach to the solution of coupled hydro-mechanical problems involving large deformation. In this paper, we survey the current state-of-the-art in the MPM simulation of hydro-mechanical behaviour in two-phase porous geomaterials. The review covers the recent advances and developments in the MPM and their extensions to capture the coupled hydro-mechanical problems involving large deformations. The focus of this review is aiming at providing a clear picture of what has or has not been developed or implemented for simulating two-phase coupled large deformation problems, which will provide some direct reference for both practitioners and researchers.