## 3 Results
### Permeability and Swell Behavior of Soils  
It was observed from the results obtained that the coefficient of permeability (K) of the untreated red soil was \(5.3\times 10^{-7}\) cm/s and for red soil treated with E2, K reduced to \(1.12\times 10^{-10}\) cm/s after a curing period of 21 days. Whereas black soil also portrayed appreciable reduction in K. Untreated black soil had K = \(7.83\times 10^{-8}\) cm/s and the same reduced to \(6.31\times 10^{-11}\) cm/s. This reduction in permeability is probably due to the adhesion of soil grains due to the precipitated CaCO\({}_{3}\) in the voids of the soil mass, making the movement of water through the existing pore spaces, which create a longer path [88]. It can be observed in Figure 7a that irrespective of the enzyme solutions used to treat the soils there is a minimum reduction of K = \(5.2884\times 10^{-7}\) cm/s for red soil and K = \(7.77779\times 10^{-8}\) for black soil and Figure 7b shows the variation of K for different curing periods for treated and untreated soils tested by contaminant (Ni + Cd + Pb) induced solution and the results obtained are almost nearer to that observed in the Figure 7a. Therefore, it can be inferred that percolation of contaminated fluid in the soil mass doesn't affect improved behavior of soil permeability after treatment by enzyme solutions. [PERSON] and [PERSON] [89] studied the effect on permeability of porous media by enzymatic CaCO\({}_{3}\) precipitation and found that precipitates successfully helped in reducing the permeability and EICP method depended on the concentration of urease and urea and calcium chloride reactants. Therefore, in this study it can be proposed that the CaCO\({}_{3}\) precipitates help in reducing the permeability of the treated soils as it can be observed from the Figure 7a. Further use of EICP to plugging of pores to reduce the permeability is also a promising and efficient method which can be adopted on porous media [90; 91]. It is also evident that CaCO\({}_{3}\) precipitates are effective in giving highest strength and minimum permeability [92], because it hardens in the soil pores [93]. E2 gave the best results in reducing the permeability of the soil which can be due to the use of not-fat milk powder. Non-fat milk powder facilitates the creation of nucleation sites in the soil mass paving the way to the precipitation of CaCO\({}_{3}\) in the soil mass stably [21]. CaCO\({}_{3}\) clusters formed in the soils by enzyme treatment also influence the permeability of soils in comparison with MICP, value of K happens to be more for enzyme treated soils [94] this scenario is probably due to use of enzyme without non-fat milk powder where distribution of nucleation sites in the soil mass doesn't take place uniformly. Reduction in permeability after enzyme treatment of porous media has been observed to reach up to 98% by [PERSON] et al. [89]. Swell test results obtained from the present study are plotted in the Figure 8. it is observed that the swell pressure reduced with treatment of enzyme solutions and age of specimen. It can be observed that E2 gave the best results for both soils, the swell pressure for the untreated red soil was  
Figure 7: Variation of K for both soils for curing period of 7, 14 and 21 days for treated and untreated soil: (**a**) for plain water; (**b**) for contaminant (Ni + Cd + Pb) solution. found to be 117.83 kPa and that for the untreated black soil was 167.1 kPa and after enzyme treatment the swell pressure reduced to 37.68 and 47.2 kPa respectively for soils treated with E2 and cured for 21 days. Control of swell characteristics of expansive soils can be achieved by precipitated CaCO\({}_{3}\)[95]. This improvement in the swell characteristics may be due to adhesion of soil grains to each other after CaCO\({}_{3}\) precipitation.