Reinforcement of silty sand riverbank using hydroxyethyl cellulose-assisted enzyme-induced carbonate precipitation

To improve the erosion resistance of silty sand riverbank, this study innovatively integrates EICP with hydroxyethyl cellulose (HEC), and the effect and mechanism of EICP-HEC on the solidification of silty sand riverbanks in Yellow River flooding area of China were analysed through tests involving aqueous solutions, specimens, scale models, and microstructures. The results showed that HEC can balance the acidity and alkalinity of the treatment solution, increase urease activity, and promote the formation of CaCO₃ precipitate. Compared with traditional EICP, the surface strength and calcium carbonate content (CCC) of silty sand riverbank treated with EICP-HEC increase by 0.63 and 6.84% times, respectively, with a one-fold extension in water scouring resistant duration. This enhancement is due to the fact that HEC provides nucleation sites for CaCO₃ precipitation, and its water retention properties promote continuous precipitation reaction of CaCO₃, as well as the encapsulation, connection, adsorption, and cementation effects of HEC on soil and precipitated CaCO₃. Notably, excessive calcium source concentration (CSC) may inhibit urease hydrolysis of urea. The formation of the surface protective layer affects the infiltration of subsequent treatment solution to some extent, and the growth rate of soil surface strength and CCC decreases gradually with the increase of spray frequency. When HEC is 0.6 g/L, the soil surface strength and CCC reach the peak value. Considering the economic factors and reinforcement efficiency, a CSC of 1 M and spray frequency of four are recommended for the solidification of riverbanks in the Yellow River flooding area.