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Pore-water pressure in soil is caused by three physically distinguishable sources: ambient (environmental) pressure, surface tension–induced capillary pressure, and the soil's electromagnetic potential–induced adsorptive pressure. The former two form the conventional concept of pore-water pressure, which is considered a constant within a soil-water-air representative elementary volume and can be directly measured by piezometer (under saturated and compressive states) or tensiometer (under unsaturated and tensile states). The third one can be called adsorption-induced pore-water pressure and is localized within a certain distance to the particle surface of soil or intercrystalline surface of swelling clay. The adsorption-induced pore-water pressure is always compressive and dictates the water phase transition in soil by altering water's freezing point, density, and viscosity, among other physical properties. A framework of quantifying the adsorption-induced pore-water distribution via the measured soil water isotherm is presented for any soil type under any given water content. It is demonstrated that the adsorption-induced pore-water pressure can be up to 1.6 GPa in the first few layers of hydration, but will diminish to zero at a distance equivalent to the gravimetric water content >1% for sandy soil and greater than a few percent for silty soil. In clayey soil, the adsorption-induced pore-water pressure can sustain tens of megapascals even at much farther distance, equivalent to ∼30% water content. In expansive clay, the adsorption-induced pore-water pressure inside the crystalline lamellae can exceed 800 MPa. The soil water density functions of a silty soil and a bentonite clay predicted by the proposed framework matched well with that measured independently from the conventional consolidation testing, validating the framework to determine the spatial distribution of the adsorption-induced pore-water pressure in soil. [ABSTRACT FROM AUTHOR]

The Atterberg limits are empirical indices of the critical water contents defining mechanical states of soil-water mixtures between the semisolid state and plastic state (the plastic limit or wP), and between the plastic state and liquid state (the liquid limit or wL). They reflect semiquantitatively a fine-grained soil's ability to resist external loading. They are controlled by four fundamental factors: soil mineralogy, particle size distribution, pore fluid chemistry, and pore structure. However, general quantitative relationships among the Atterberg limits and these controlling factors are yet to be established. The authors hypothesize that the total amount of adsorptive water content for a given soil is directly related to the soil's wL and wP. A broad suite of 35 soils with measured soil-water retention (SWR) and the Atterberg limits from the literature were synthesized to explore these relationships. Using the measured SWR data and interpreting them through a generalized SWR model, the adsorptive water contents of all 35 soils were quantified. The authors demonstrate that the Atterberg limits, including wP , wL , and plasticity index IP(=wL−wP) , were all correlated to mechanisms of soil-water interaction, specifically to a soil's total adsorptive water content in terms of gravimetric water content, confirming the hypothesis. Further, the correlation between the Atterberg limits and a soil's volumetric water content was poor, indicating the Atterberg limits' independence from capillary water retention mechanism. The correlations provide a new pathway to move beyond the Atterberg limits to classify soil directly using more representative soil physical properties like adsorption suction stress, which could be linked to all four fundamental factors of soil mineralogy, particle size distribution, pore fluid chemistry, and pore structure. [ABSTRACT FROM AUTHOR]