Liquefaction resistance of sand remediated with carbonate precipitation at different degrees of saturation during curing

In recent years, innovative soil improvement methods have provided more environmentally friendly and sustainable solutions for liquefaction countermeasure techniques. One such technology is enzymatically induced calcite precipitation (EICP), in which urease enzyme is used, instead of bacteria, as a promoter for the hydrolysis of urea. Utilizing the urease enzyme itself, which causes Ca2+ and CO32− to precipitate CaCO3 crystals in the void spaces and surface of grains, is more straightforward than using bacteria. In this study, the effects of the degree of saturation during the precipitation of calcite on the behavior of sand that has been lightly cemented using EICP were investigated through a series of undrained cyclic triaxial tests. Liquefaction strength curves correlating the cyclic stress ratio with the number of cycles needed to cause 5% double amplitude (DA) axial strain were compared for treated and untreated sand. It was found that the lower the degree of saturation during calcite precipitation and the higher the calcite content in the samples, the higher the liquefaction resistance of the EICP-treated sand. This can be clearly explained by the spatial distribution of the calcite in the sand. Microscopic observations by scanning electron microscopy (SEM) revealed that, in sand cured at a lower saturation degree, the precipitated calcite tended to be more concentrated at particle contacts than was the case in fully saturated sand. It was confirmed that only 1% of calcite precipitation at a lower degree of saturation (30%) can double the liquefaction resistance. However, excessive strain in the order of 1% degrades the bonding between sand particles.