Improvement and Soil Consistency of Sand–Clay Mixtures Treated with Enzymatic-Induced Carbonate Precipitation

Abstract

Recently, microbially induced carbonate precipitation (MICP) has been studied as an alternative for the improvement of sand–clay mixtures. However, the cementing uniformity of MICP-treated sand–clay mixtures cannot be guaranteed. In this present study, enzymatic-induced carbonate precipitation (EICP) was used to deal with it. The ions used in kaolin clay was predicted to affect the production rate for calcium carbonate (CaCO3), which was studied using the calcification test. The solidification test was conducted using two different methods (the premixing method and the diffusion method). The permeability, unconfined compressive strength and the content of CaCO3 of treated samples were obtained to evaluate the solidification effect of the EICP method. Moreover, in EICP treatment, the particle aggregation decreased the liquid limit, but the addition of solution increased it. Therefore, there were contrary effects to the soil consistency. In this study, the two types of liquid limits of treated samples were measured with deionized water and 2M-NaCl brine, respectively. The results show that the Al2O3, NaCl and MgCl2 in the kaolin clay had a slight impact on the production rate for CaCO3, while FeCl3 significantly inhibited it. The EICP method can improve sand–clay mixtures and decrease their permeability. Different from MICP, the EICP method can guarantee the uniformity of treated samples. Moreover, the liquid limit of the sample treated with the premixing method decreased, while that of the sample treated with the diffusion method increased firstly and then decreased with the increasing treatment cycles. Different from the deionized water, the pore-fluid chemistry had a larger effect on the liquid limit with 2M-NaCl brine.

Influence of Alternating Temperature on the Effectiveness of EICP in Consolidating Aeolian Sand

“…T2 exhibited the greatest influence on the permeability coefficient, followed by T3 and then T1. The increase in calcium carbonate content can decrease the permeability coefficient of the samples to a certain extent [45][46][47]. The final calcium carbonate content of T2 is higher than that of T1, and theoretically, the influence on the permeability coefficient of T2 will also be greater than T1, which is also demonstrated in Figure 7.…”

Biocalcification of Sandy Gypseous Soil by Bacillus Pasteurii

“…The liquid media was prepared by autoclaving 1L (pH 9,0) Tris buffer, 10g (NH 4 ) 2 SO 4 , and 20 g yeast extract at 121°C and a pressure of Ib/in 2 before use. A similar procedure can be found in (32) . A single colony from the surface of the agar plate with the highest concentration was cultured in 100 ml of this solution.…”