Soil–water characteristic curve of sediments containing a polyacrylamide solution

Abstract

Recent developments using organic agents for soil improvement have shown promising results. Among the organic agents, polyacrylamide (PAM) has been considered to have a good impact on irrigation for increased water infiltration due to the capacity of PAM to absorb and store substantial amounts of water. In this study the authors explored the soil–water characteristic curves (SWCCs) of a PAM at different concentrations. Experimental results have shown that as the PAM concentration increases, (a) air-entry pressure increases; (b) SWCCs shift to higher capillary pressure at a given water (or PAM solution) saturation; and (c) the saturation of residual water (PAM solution) increases. The results obtained using theoretical models have been used to compare with experimental results. The results of comparison show good consistency and relatively constant m- and λ-values in theoretical models with an increase in PAM concentration. Besides, the measured SWCCs are quantitatively compared with capillary scaling predictions. These comparisons show that SWCCs for air–PAM solution do not comply with expectations from scaling in silica sand, unlike SWCCs for air–water, due to (a) the inconsistency of the contact angle between the flat and spherical surfaces in pores; (b) a wide range of contact angle values in pores; (c) the difference between equilibrium- and receding-contact angles; and (d) due to the higher viscosity of PAM solution.