Effect of hydrogel particle additives on water-accessible pore structure of sandy soils: A custom pressure plate apparatus and capillary bundle model

摘要

To probe the effects of hydrogel particle additives on the water-accessiblepore structure of sandy soils, we introduce a custom pressure plate method inwhich the volume of water expelled from a wet granular packing is measured as afunction of applied pressure. Using a capillary bundle model, we show that thedifferential change in retained water per pressure increment is directlyrelated to the cumulative cross-sectional area distribution $f(r)$ of thewater-accessible pores with radii less than $r$. This is validated bymeasurements of water expelled from a model sandy soil composed of 2 mmdiameter glass beads. In particular, the expelled water is found to dependdramatically on sample height and that analysis using the capillary bundlemodel gives the same pore size distribution for all samples. The distributionis found to be approximately log-normal, and the total cross-sectional areafraction of the accessible pore space is found to be $f_0=0.34$. We then reporton how the pore distribution and total water-accessible area fraction areaffected by superabsorbent hydrogel particle additives, uniformly mixed into afixed-height sample at varying concentrations. Under both fixed volume and freeswelling conditions, the total area fraction of water-accessible pore space ina packing decreases exponentially as the gel concentration increases. The sizedistribution of the pores is significantly modified by the swollen hydrogelparticles, such that large pores are clogged while small pores are formed.