An assessment of the effect of water content and soil texture on the process of consolidation in unsaturated soils

Soil consolidation plays an important role in practical applications of engineering, and prevention of disaster. In particular, subsidence is a common disaster in coastal and alluvial fan of Taiwan. Therefore, using analytical solutions to quantify the results of soil consolidation can supply useful information to engineers and policymakers. In the current study, we apply the consolidation theory of poroelasticity developed by Lo et al. (2014) to illustrate the effect of water content and soil texture on one-dimensional consolidation in unsaturated soils. Based on Lo et al. (2014), closed-form analytical solutions describing the excess pore air and water pressure along with the total settlement in response to time-invariant external loading under two opposite semi-permeable boundary drainage conditions were formulated by employing the Laplace transform. In respect to establish the initial conditions, the Biot’s assumption (1941) that water is not allowed to escape when the loading is instantly applied on a porous media is used, together with loading efficiencies (Lewallen and Wang, 1998). Although soil texture and water content has been recognized that they give a strong influence on saturated soil consolidation, it does not receive much attention as to its impact on consolidation behavior in unsaturated soils thus far. Hence, numerical calculations are then implemented for unsaturated soils with eleven different textures with respect to three initial water saturations (0.7, 0.8, and 0.9) as representative examples. Our results show that the dissipation of excess pore water pressure is significantly sensitive to soil texture, which is almost completed in very shorter elapsed time in sand, followed by loamy sand, sandy loam, loam, sandy clay loam, silt loam, clay loam, sandy clay, silty clay loam, silty clay, and clay at. This trend is consistent with the coefficient of consolidation for water. Irrespective of the elapsed time, the excess pore water pressure is always dissipated faster under both permeable boundaries than asemi-permeable boundary. As far as the same soil texture is concerned, the rate of dissipation of excess pore water pressure is higher in wetter soil. In the early stage of consolidation, the initial pore water pressure is affected by loading efficiency for water. Our results show that the loading efficiency for water is strongly controlled by initial water saturation. This efficiency shows a concave upward relationship with initial water saturation in silty clay and clay, whereas it increases with an increase in initial water saturation for other soil textures. With regard to total settlement, it has a positive relationship with the inverse of bulk modulus of soil (compressibility). As a result, although wetter soil can dissipate excess pore water pressure faster, it has the highest value of excess pore water pressure and smallest total settlement initially.