Bio-improved hydraulic properties of sand treated by soybean urease induced carbonate precipitation and its application Part 2: Sand-geotextile capillary barrier effect

Abstract

Nonwoven-geotextile is used to construct soil-geotextile capillary barrier for minimizing water infiltration. However, the sand-geotextile capillary barrier breakthrough can occur due to the low water retention ability and the high saturated permeability coefficient of sand. To address this, enzyme induced carbonate precipitation (EICP) technology was applied to the overlying sand layer to improve its hydraulic properties and enhance the sand-geotextile capillary barrier. The precipitated calcium carbonate has the potential to enhance the capillary barrier effect by coating soil particles and filling the soil macro-pores. To investigate the effect of EICP treatment on the sand-geotextile capillary barrier, three column tests were conducted, including one untreated sand-geotextile column and two sand-geotextile columns treated with 0.5 and 1 mol/L urea-calcium chloride solutions and soybean urease liquid, respectively. Transient seepage analysis was carried out based on the column tests to calibrate the hydraulic parameters. A numerical parametric analysis was conducted to assess the effect of EICP-enhancement on the hydraulic behavior and slope stability of a sand-geotextile capillary barrier retaining wall during exposure to rainfall with a 100-year return period. The results of the column infiltration tests show that the occurrence of breakthrough in the sand-geotextile capillary barrier is significantly delayed with increasing concentration of the urea-calcium chloride solutions. The enhanced capillary barrier effect is attributed to the increased water retention ability and reduced saturated permeability coefficient. The results of the parametric analysis show that the matric suction within the backfill is maintained and the factor of safety remains almost unchanged due to the EICP-enhanced sand-geotextile capillary barrier effect.