Influence of injection methods on calcareous sand cementation by EICP technique

Calcareous sands are widely distributed on continental shelves, coastal zones, islands and reefs in the tropical oceans. For being used as construction materials, calcareous sands should be artificially treated to improve their engineering properties. Enzymatically induced carbonate precipitation (EICP) is an innovative soil treatment technique. In this paper, urease was extracted from soybean powder using artificial seawater for calcareous sands cementing by the EICP technique. Cementation tests were conducted with three injection methods (the pre-mixed, staged and proposed parallel injections) and two injection rates (2 and 5 mL/min). The hydraulic conductivity, shear wave velocity (SWV) and unconfined compressive strength tests were conducted and the cementation effects were evaluated. The hydrodynamic diameter of the particles generated in the mixed solutions was measured with reaction time by a laser particle size analyzer and the influence of injection rate on the CaCO3 distribution in the specimen was discussed. The coefficient of variation of the SWV values along the cemented specimen height was calculated for evaluation of the cementation uniformity. Results show that a high injection rate was conducive to reducing clogging and improving the cementation uniformity by completing injection within the urea hydrolysis phase. The promising parallel injection method proposed in this study provided a lag time for reaction by simultaneous injection of crude urease and cementation solutions using two separate tubes. Specimens treated at a high parallel injection rate were uniformly cemented with high mechanical strengths and high overall hydraulic conductivities because of a high proportion of CaCO3 in contact-cementing distribution.