# Application Ranges of EPB Shield TBM in Weathered Granite Soil: A Laboratory Scale Study
## 3 Results and Discussion
### Optimal Mixing Ratio of Conditioning Agents: With Foam and Polymer
#### 3.3.2 Conditioning with Foam and Multiple Polymer
This means that the plastic behavior of excavated soils is disrupted when excess polymer slurry is used. In contrast, when the polymer slurry was added at PIR of 8%, the compressibility increased; this was because the highly viscous polymer slurry trapped the foam so that it did not flow out from the soil sample. In other words, the polymer slurry changed the rheology of the excavated soils, preventing the segregation behavior [16]. Table 5 and Figure 10 show that the soils conditioned by adding foam at FIR = 22% together with polymer slurry at PIR = 8% or 15% met the required permeability coefficient of 1 \(\times\) 10\({}^{-3}\) cm/s. \begin{table}
\begin{tabular}{c c c c c c c} \hline  & **w (\%)** & **FIR (\%)** & **PIR (\%)** & **Slump (cm)** & \begin{tabular}{c} **Compressibility** \\ **(\%/0.5 Bar)** \\ \end{tabular} & \begin{tabular}{c} **Permeability** \\ **Coefficient (cm/s)** \\ \end{tabular} \\ \hline \multirow{2}{*}{\
\begin{tabular}{c} Foam \\ conditioning \\ \end{tabular} } & 10 & 22 & 0 & 12 & 1.22 & - \\  & 10 & 45 & 0 & 16 & 2.67 & 1.17 \(\times\) 10\({}^{-3}\) \\  & 10 & 67 & 0 & 22 & 3.90 & - \\ \hline \multirow{2}{*}{
\begin{tabular}{c} Foam and \\ Polymer slurry \\ conditioning \\ \end{tabular} } & 10 & 22 & 8 & 18 & 2.07 & 1.67 \(\times\) 10\({}^{-4}\) \\  & 10 & 22 & 15 & 16 & 1.72 & 1.87 \(\times\) 10\({}^{-4}\) \\  & 10 & 22 & 30 & - & - & - \\ \hline \end{tabular}
\end{table} 
Table 5: Properties of conditioned Soil 5 depending on the mixing ratios of conditioning agents. Figure 9: Slump test results depending on added conditioning agents: (**a**) Foam conditioning only, (**b**) Foam and polymer slurry conditioning. In summary, the conditioned soils satisfied all the requirements when conditioned with foam at 22% and polymer slurry at 8% as long as the water content in the chamber could be controlled at around 10%. However, as we mentioned in the introduction, the natural water content of the saturated granite soils (below the groundwater table) on the Korean Peninsula are within the range of 11-21% in most cases [14]. In the laboratory experiments, it was not easy to prepare soil samples for slump tests (even when polymer slurry was added along with foam) if the water content was greater than 10%. Since the water content was mostly greater than 11%, it might be necessary to add solidification agents along with foam and polymer slurry for tunnels excavated below the groundwater table. It is concluded that the EPB shield TBM is feasible even though weathered granite soil is extremely coarse (cohesionless) and exceeds the applicable boundaries proposed by [1]. However, the process requires conditioning with foam, polymer slurry, and/or water-absorbing polymers, and it is necessary to test different conditions through trial and error to produce soils that meet the three requirements or workability, compressibility, and permeability requirements. Finally, a flow chart describing the process of how to choose a suitable conditioning agent is prepared as shown in Figure 11 so that readers can easily follow the process by themselves. Figure 11: Soil conditioning agent selection for EPB shield TBM in weathered granite soil. Figure 10: Permeability coefficient changes of the conditioned Soil 5 with elapse of time.