# Uniaxial Testing of Soil-Cement Composites to Obtain Correlations to Be Used in Numerical Modeling
## 2 The Current State of Knowledge and Basic Data on the Research Project
### Implementation of Test Columns  
The research program aims to build and test an innovative device for making soil-cement columns. Modifications (calibration) of the method of making the columns are also aimed at the selection of appropriate operational parameters, such as the selection of the density of the injected cement slurry, the applied injection pressure, and the process of feeding the hydraulic binder to the substrate, considering the mixing efficiency. Another important element of the implementation of the test columns was the selection of a hydraulic binder that met the criteria of sustainable development to the maximum extent while guaranteeing the target material parameters of the composite obtained. Through preliminary analyses, it was decided to choose the cement of multi-component Portland cement CEM II B-V with the addition of by-products from coal combustion in the power industry. The choice was determined by the fact that silica fly ashes, which are in fact processed post-production waste, are a significant addition to this cement. As part of recycling, they are reused in the technological process of manufacturing the cement.  
The following devices were used on the test plot:  
- Crawler excavator (yellow color--see Figure 2a).  
- Multifunctional SPD mast (red color--see Figure 2b).  
- Various mixing devices: DSM dry, standard wet DSM (Figure 2a), foldable tool for DMS wet (Figure 2b), and soil stabilization.  
\begin{table}
\begin{tabular}{l c c c c c c} \hline \hline
**Type of Soil** & **Depth** & **Plasticity/Density Index** & **Density** & **Cohesion c** & **Internal Friction** & **Elastic Modulus E** \\  & **m** & **I\({}_{\text{L}}\)/I\({}_{\text{D}}\)** & **g/cm\({}^{3}\)** & **kPa** & \({}^{\circ}\) (**deg**) & **MPa** \\ \hline Ia—slity clay & 0–1 & 0.10 & 2.08 & 8.9 & 31.7 & - \\ Ib—slit & 1–3, 4–6 & 0.42–0.81 & 1.96 & 1.2 & 17.7 & 1.8–7.7 \\ IIa—mud & 3–4 & 0.36 & 1.60 & 15.7 & 17.3 & 2.7 \\ Iib—peat & 4–5 & - & - & - & - & - \\ IIIa—sand & 6–9 & 0.78 & 1.90 & - & 31.2 & 34.9 \\ IIIb—sand & 9–10 & 0.78 & 2.00 & - & 35.9 & 79.6 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Basic data from field investigation report [37] derived from laboratory testing and CPT sounding.  
Figure 2: Deep mixing device during the works. (**a**) Equipped with standard mixer. (**b**) Equipped with foldable tool (multidiameter mixer).  
DSM columns were successfully installed at a depth of 6 m using various construction methodologies presented above. The foldable tool has been patented since 2021. Further considerations are focused on the effects of the work performed, focusing attention on the quality of soil-cement composite measured in terms of compressive strength and stiffness achieved for various modes of composite production, e.g., rotation speed, mixing cycles, and grout density and pressure, with one constant value of cement amount for every cubic meter of soil-cement composite. Such a procedure made it possible to evaluate the impact of production technology on practically uniform composites (in terms of their composition--soil/water/cement).