Permeability stability calculation model of foam‐conditioned soil based on the permeability constant

Abstract

Abstract The low permeability of discharged muck must last for at least tens of minutes to avoid water spewing during earth pressure balance (EPB) shield tunneling; however, foam, which is usually added to soil to reduce its permeability, has its own unique time‐varying characteristics. Thus, it is important to predict the stable time of permeability of foam‐conditioned soil for EPB shield tunneling. Based on theories of the effective permeation channel of pure foam and fluid mechanics, a constant is proposed to predict the duration of the initial period during which the coefficient of permeability of the conditioned soil remains stable. A series of large‐scale permeation tests were carried out to determine the duration of the initial stable period for various foam‐conditioned soils, and it was verified that the predicted results were in good agreement with the measured results. Furthermore, based on the constant, practical concepts, including duration reference curves, optimum fineness, optimum porosity and critical particle size, are proposed for the spewing control of EPB shield tunneling.