Saturated and unsaturated hydraulic conductivity of synthetic gel structures in coarse textured soil substrates

Saturated and unsaturated hydraulic conductivity as a function of a thermodynamic potential (pressure) of soil water K(P) are investigated in the sandy samples with admixtures of strongly swelling polymer hydrogels (SSPHs) in a wide concentration range from 0.01 to 0.3 %SSPHs. The author's original centrifugation method has been used along with a kinetic model of the water removal process, which enables to determine the function of water conductivity of gel compositions operating in an unsteady state. In saturation state and within the range of low absolute values of soil water pressure |P| = 0.3-20 kPa the SSPHs significantly (2-10 up to 50 times) reduced the hydraulic conductivity in proportion to the dose of a superabsorbent. A heterogeneous layered structure with a layer of pure gel or gel composition 0.1-0.3% SSHP reduces the saturated conductivity by 10-80 times.In the range | P | = 100-3020 kPa, the K(P) function, on the contrary, strongly increased up to 10–20 times under the action of SSPHs. The calculation of K(P) using the Mualem theory disagrees with our experimental estimation, especially in a range of low water content, where such a calculation strongly (up to 100-1000 times) underestimates the values of K(P). (paper)