## 4 Results and Discussions
### Results and Discussion of Mixing Test  
Various amounts of water content (25 w.t.% and 40 w.t.%) and foam injection ratios (0 vol.%, 10 vol.%, 20 vol.%, and 30 vol.%) were added to the tested soil to achieve different conditioned soils. Figure 10 shows the pictures of tested soils with various water content and _FIR_ after 2 min of mixing. For the soil sample with \(w=25\%\) &\(FIR=0\%\), the soil composed of loose soil clumps, which was caused by the gravel particle wrapped by silly clay and fine-medium sand, showed a dry, loose, and rigid state, as shown in Figure 10a. For \(w=25\%\) &\(FIR=10\%\), \(w=25\%\) &\(FIR=20\%\), and \(w=25\%\) &\(FIR=30\%\), the tested soils showed a sticky, stiff, and water shortage state, as shown in Figure 10b-d. The foam could not work in a water shortage soil because the water in liquid film of foam was easily absorbed by the unsaturated soil, which was found in the foam microstructure test. Therefore, it was necessary to improve the water content in the tested soils before the addition of foam, and then the other group soil samples with \(w=40\%\) were adopted. For tested soil with \(w=40\%\) &\(FIR=0\%\), the state was consistent and the flowability increased, as shown in Figure 10e. For \(w=40\%\) &\(FIR=10\%\), \(w=40\%\) &\(FIR=20\%\), and \(w=40\%\) &\(FIR=30\%\), the tested soils were turned into a loose and fluffy state, where the soil volume left on the rod decreased as \(FIR\) increased, as shown in Figure 10f-h. This indicates that the flowability increased and viscosity decreased because of the lubrication and dispersion induced by foam air bubbles. Each mixing test was conducted for 2 min and the mixing time necessary to obtain a homogeneous mixture without apparent foam was recorded by a timer, as shown in Figure 11. The time used for foamed soils with \(w=25\%\) &\(FIR=10\%\) was less than the time used for foamed soils with \(w=25\%\) &\(FIR=20\%\). This might have been caused by the smaller amount and faster defoaming in tested soils with \(w=25\%\) &\(FIR=10\%\). For tested soils with \(w=40\%\), the general mixing time was less than tested soils with \(w=25\%\) because the soils already had a good flowability at \(w=40\%\). The general mixing time for soils with \(w=40\%\) decreased as \(FIR\) increased, which might have been caused by the decrease of viscosity induced by foam dispersion and increase of flowability induced by foam lubrication. Figure 10: Photographs of tested soils with various water content and foam injection ratio (FIR) after mixing: (**a**) \(w=25\%\), \(FIR=0\%\); (**b**) \(w=25\%\), \(FIR=10\%\); (**c**) \(w=25\%\), \(FIR=20\%\); (**d**) \(w=25\%\), \(FIR=30\%\); (**e**) \(w=40\%\), \(FIR=0\%\); (**f**) \(w=40\%\), \(FIR=10\%\); (**g**) \(w=40\%\), \(FIR=20\%\); (**h**) \(w=40\%\), \(FIR=30\%\). Meanwhile, the net power of the electric mixer motor with a resolution of 1 W was monitored during the mixing test, as shown in Figure 12. The net power value and fluctuation value induced by the soils with \(w=25\%\) were higher than tested soils with \(w=40\%\), which might have been caused by the poor liquidity and high viscosity. The average net power and standard deviation, as well as the change rate of the net power for various tested soils, are further plotted in Figure 13. Figure 13a indicates that the fluctuation of net power for tested soils with \(w=25\%\) did not change significantly with increase of _FIR_, while the fluctuation of net power for tested soils with \(w=40\%\) decreased drastically as the _FIR_ increased from 0% to 10%. Figure 13b shows the change rate of net power with _FIR_. For tested soils with \(w=25\%\), the change rate of net power increased as _FIR_ increased from 0% to 10% and then decreased with the further injection of foam. This might have been caused by the increase of viscosity in the mixed soils because of the defoaming of foam at \(w=25\%\) &_FIR_ = 10% caused by insufficient water in soil.