A new relationship between the mobile and the adsorbed water in fine-grained soils using an effective void-ratio estimation

Abstract

Firmly adsorbed water on the surfaces of clay minerals and the water that fills the unconnected and dead-end pores in saturated fine-grained soils is immobile, which means that it cannot impact on the hydraulic conductivity of these soils. Therefore, only the volume of the voids occupied by mobile water is important. This volume can be expressed as the effective porosity or the effective void ratio. In the past, many methods were proposed to determine these values: however, the obtained values varied, leading to a difference in the proposed correlation with the saturated hydraulic conductivity. This article describes a process for determining the effective void ratio and has a completely different basis to so-far suggested procedures. Determining the volume of the mobile and immobile water in the saturated fine-grained soils assumes that the quantity of the mobile water and the thickness of the adsorbed water film on the external surfaces of the clay grains are equal at the same effective stress. The total quantity of adsorbed (immobile) water on the external surfaces of clay minerals in this case depends on their size and quantity in the soil’s composition. On the basis of the determined quantities of immobile and mobile water, the ineffective and effective void ratios are calculated. The results show that the interdependence between the total void ratio and the ineffective void ratio is linear, which allows for a simple calculation of the effective void ratio. However, it should be taken into consideration that this expression can only be used for soils that do not contain swelling clay minerals. The evaluation of the hydraulic conductivity of the soils using effective void ratios, determined with the proposed method, shows good agreement with the measured values.