Effect of EICP Treatment on the Unconfined Compressive Strength and Soil Water Characteristic Curve of a Clayey Sand Material

The influence of enzyme-induced carbonate precipitation (EICP) treatment on the unsaturated soil properties of a clayey sand was investigated in the laboratory. The carbonate precipitated by EICP treatment is known to change the porosity and permeability of the soil, but few studies have looked at its effect on capillarity and the soil moisture retention characteristics. The unconfined compressive strength and soil water characteristic curve (SWCC) of a local clayey sand were evaluated for two types of the EICP treatment: a conventional EICP treatment and one using xanthan gum (X-EICP). The EICP treatment was 1.5M:1M solution of urea and calcium chloride mixed with 30 ml/L jack bean urease enzyme solution. For X-EICP treatment, xanthan gum at a concentration of 3 g/L mixed with 3 ml vegetable glycerin was added to an equimolar 1M solution of urea and calcium chloride and 30 ml/L jack bean urease solution. Untreated and treated specimens were prepared in 70-mm-diameter 25 mm-high rings. The specimens were prepared by mixing and compaction of the soil with 24 ml of treatment solution for EICP and 25 ml of treatment solution for X-EICP, then sprayed with an additional 2 ml of treatment solution. The specimens treated with EICP showed no statistical change in the unconfined compressive strength when compared to the untreated specimens, but specimens treated with X-EICP showed a strength increase. The treated specimens showed a decrease in the air entry value compared to the untreated specimen, and the residual volumetric water content was reduced, especially for the specimen treated with X-EICP.