# Uniaxial Testing of Soil-Cement Composites to Obtain Correlations to Be Used in Numerical Modeling
## 5 Discussion on the Conducted Research  
Anticipating the conclusions, it can be said that in the sense of a qualitative analysis, the obtained results basically confirmed the engineering intuitions. 1. Despite the discussed variability of the achieved results, the general conclusion concerning the efficiency of soil improvement using deep mixing is positive. The \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Name of Sample** & **Density** & **Compressive Strength** & **Critical Deformation** & **Elastic Modulus** \\
**Days** & **g/cm\({}^{3}\)** & **kPa** & **\%** & **MPa** \\ \hline Solid 1.4 & 1.424 & 1116.354 & 1.20\% & 161.791 \\ Solid 1.4 + air & 1.380 & 560.559 & 1.30\% & 65.209 \\ Solid 1.4 & 1.429 & 1112.970 & 0.80\% & 343.852 \\ Solid 1.4 + air & 1.298 & 660.505 & 1.30\% & 155.771 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Averaged values of results of cubic samples testing. Figure 15: Significant increase in parameters when resigning of air jet mixing support. increase in material stiffness is very significant. If we compare the initial values of the elastic modulus of plastic and organic clays and salts from Table 1 with the values gathered from the trial (reference) samples of the composite and further samples from core drilling, one may observe a very significant increase ranging from 20 to 50 times and higher. That increase in stiffness directly decreases the potential settlements of the structure founded in the improved area. Similar values can be found in other studies [12; 17; 26] where composite stiffness was defined by elastic modulus. 2. Excessive dilution of cement grout with mixing water (increasing the water/cement W/C ratio) may facilitate the immersion of the mixing tool and speed up the execution of the works. However, it ultimately leads to increased porosity of the ground-cement material, and it potentially weakens the composite, as stated in work [12] (concerning clayey soils). Detailed studies on that issue are still in progress. The results given in Figure 15 suggest a positive impact of the opposite practice, meaning lowering the W/C ratio in order to obtain a higher capacity and stiffness of the composite. In real-world practice, that would mean a longer mixing time and, inevitably, a higher cost of execution. That is the prize for the composite's quality. 3. The use of compressed air also facilitates the immersion of the mixing tool and speeds up the execution of work. However, it also leads to a significantly increased porosity of the soil-cement composite and a very significant decrease in parameters. Looking at Figure 15, we can see again that compressed-air-supported mixing tends to lower the composite parameters. 4. It should always be kept in mind that an increased porosity will lead to a decrease in the stiffness of the obtained composite (smaller modules) and a decrease in the compressive strength. In the case of \"wet\" mixed composites, it is not possible to \"densify\" them before the setting process, so any measures to facilitate the work should be cautiously considered in light of this comment. Considering dry mixing (adding a dry binding agent), it has already been confirmed (reference [26]) that mechanical compaction of the composite before setting provides positive outcomes in terms of strength and stiffness. Additional research is recommended to cover the impact of various mixing technologies on the resulting composite's density. 5. Diverse results of strength and stiffness of the samples from different levels of deep mixing indicate a lack of homogenization of the parameters of the obtained composite within the column. Each weaker interbedding (e.g., due to an increased content of organic matter) is reflected in the results of the cement-soil samples (cores) taken from this depth. The assessment of column reliability is then determined by the relationship between the thickness of the weak interbedding and the diameter of the column.