Bio-improved hydraulic properties of sand treated by soybean urease induced carbonate precipitation and its application Part 1: Water retention ability

Enzyme induced carbonate precipitation (EICP) is an innovative ground improvement technique which can enhance soil properties including soil strength, stiffness and hydraulic conductivity by cementing and filling soil pores. The calcium carbonate precipitation has the potential to influence the water retention ability through altering pore-size distribution and void ratio. This study aims to investigate the effects of soybean urease induced carbonate precipitation on the water retention ability of the ISO standard sand. Three tests using simplified evaporation method were performed to measure the water retention curves (WRCs) of one untreated sand and two treated sands with 0.5 and 1 mol/L urea-calcium chloride solutions and soybean urease liquid. Scanning Electron Microscopy (SEM) and Mercury Intrusion Porosimetry (MIP) were used to assist the interpretation. A new and simple WRC model for the EICP-treated sand is proposed with an attempt to consider the effects of calcium carbonate precipitation on the void ratio as well as the pore-size distribution. Based on the measured results, it is found that the calcium carbonate precipitation is prone to fill the macro-pores in the sand, resulting in an increase in air-entry value with the increasing concentration of urea-calcium chloride solutions. The pore-size distribution becomes more uniform with the increase in calcium carbonate precipitation amount, leading to an increase in desorption rate of WRC. The proposed model is found to be able to well simulate the WRC of sand.