# 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  
#### 3.3.1 Conditioning with Foam and Water-Absorbing Polymer  
As mentioned in Section 3.1, if the water content in excavated soil exceeds the upper bound shown in Figure 5, the workability requirement of slump value less than 20 cm will not be satisfied; solidification agents need to be added in addition to foam. Therefore, a series of tests were performed on excavated soils in which water contents exceeded the  
Figure 5: Allowable water contents and upper/lower bounds depending on fine particle contents.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Soil** & **FER** & **FIR (\%)** & **w (\%)** & **Slump (cm)** & \begin{tabular}{c} **Permeability** \\ **Coefficient (cm/s)** \\ \end{tabular} & \begin{tabular}{c} **Compressibility** \\ **(\%/0.5 Bar)** \\ \end{tabular} \\ \hline \begin{tabular}{c} Weathered \\ Granite Soil 1 \\ (\#200 finer = 17.1\%) \\ \end{tabular} & 0 & 0 & 10 & None & \(2.93\times 10^{-4}\) & 0.48 \\ \begin{tabular}{c} Granite Soil 1 \\ (\#200 finer = 17.1\%) \\ \end{tabular} & 10 & 22 & 30 & 11.8 & - & 3.18 \\ \begin{tabular}{c} Weathered \\ Granite Soil 2 \\ (\#200 finer = 11.8\%) \\ \end{tabular} & 10 & 45 & 30 & 13 & - & 4.36 \\ \begin{tabular}{c} Granite Soil 3 \\ (\#200 finer = 11.8\%) \\ \end{tabular} & 10 & 67 & 30 & 16.5 & - & 5.02 \\ \hline \begin{tabular}{c} Weathered \\ Granite Soil 3 \\ (\#200 finer = 6.5\%) \\ \end{tabular} & 0 & 0 & 10 & None & \(4.46\times 10^{-4}\) & 0.38 \\ \begin{tabular}{c} Granite Soil 4 \\ (\#200 finer = 1.2\%) \\ \end{tabular} & 10 & 22 & 22.5 & 11 & - & 3.02 \\ \hline \
\begin{tabular}{c} Weathered \\ Granite Soil 4 \\ (\#200 finer = 1.2\%) \\ \end{tabular} & 10 & 45 & 22.5 & 14.5 & 1.98 \(\times 10^{-6}\) & 4.16 \\ \hline
\begin{tabular}{c} Weathered \\ Granite Soil 3 \\ (\#200 finer = 6.5\%) \\ \end{tabular} & 10 & 67 & 22.5 & 19 & - & 4.98 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Properties of conditioned soils depending on foam mix ratios.  
upper bound shown in Figure 5. In these tests, all the soil samples were conditioned with foam added at a minimum FIR of 22% and with and without adding the water-absorbing polymer; typical results are shown in Figure 7.  
When only foam was added, the soil samples were too fluidic, whereas when both foam and water-absorbing polymer are added together, the conditioned soil appears to be in a plastic state. Experimental results are summarized in Table 4; the table shows that if only foam was added as a conditioning agent, the soil samples appeared to be too fluidic to measure the slump value. However, when water-absorbing polymer (not diluted) was added along with foam, we were able to match the slump value requirement of 10 cm to 20 cm; please see Figure 8 showing pictures of soil samples taken after slump tests. The \"N/107.8 N\" in Table 4 indicates the amount (in Newtons) of water-absorbing polymer injected into the conditioned soil with the amount of 107.8 N.  
Figure 6: Permeability coefficient changes of conditioned soils with elapse of time (Soil 2–4).  
Figure 7: Samples conditioned with and without adding water-absorbing polymer in addition to foam: (**a**) foam only, (**b**) foam and water-absorbing polymer.  
Even though it was observed that the compressibility decreased (slightly reduced by adding the water-absorbing polymers by up to 26%), these values were still larger than the required 1.9%/0.5 bar. In summary, excavated soils with water contents above the upper bound values proposed in Figure 5 can meet the workability, permeability, and compressibility requirements if they are conditioned with foam added at approximately 22% FIR and around 0.39 N of water-absorbing polymer per 107.8 N of excavated soil.