# 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  
If the weathered granite soil is extremely cohesionless (coarse) with fine particle percentage less than 1.2% (Soil 5 in Table 1), the particle-size gradation curve shown in Figure 2 is located outside (to the right) of the applicable ranges proposed by [1], as mentioned in Section 3.1. In other words, according to their proposal, the EPB shield TBM cannot be adopted in this region. However, to take advantage of the particle-crushing characteristics of weathered granite soil, the feasibility should be checked of applying the EPB shield TBM in this region also. However, the region may need additional conditioning agents such as water-absorbing polymers or polymer slurries in addition to foam. A series of tests were performed on Soil 5 shown in Figure 2 and Table 1, in which the fine particle content was zero. As the conditioning agents, foam was added at FIRs ranging from 22% to 67% with and without polymer slurry added at PIRs ranging from 8% to 30%. The optimal water content was obtained following trial and error; to satisfy the workability requirement of slump value between 10 and 20 cm, 10% water content \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Soil**} & \multirow{2}{*}{**FIR (\%)**} & \multirow{2}{*}{**w (\%)**} & \multicolumn{2}{c}{**Water-Absorbing**} & \multirow{2}{*}{**Slump (cm)**} & \multirow{2}{*}{**Compressibility**} \\  & & & **Polymer/Excavated Soil** & & & **(\%/0.5 Bar)** \\ \hline Soil 1 & 22 & 36.5 & 0 & Too fluidic & 3.18 \\ (\#200 finer = 17.1\%) & 22 & 36.5 & 0.38 & 14 & 2.70 \\ \hline Soil 2 & 22 & 28 & 0 & Too fluidic & 3.02 \\ (\#200 finer = 11.8\%) & 22 & 28 & 0.39 & 15 & 2.52 \\ \hline Soil 3 & 22 & 24 & 0 & Too fluidic & 2.90 \\ (\#200 finer = 6.5\%) & 22 & 24 & 0.38 & 14.5 & 2.44 \\ \hline Soil 4 & 22 & 21 & 0 & Too fluidic & 2.75 \\ Soil 4 & 22 & 21 & 0.34 & 19 & 2.40 \\ (\#200 finer = 1.2\%) & 22 & 21 & 0.39 & 14.5 & 2.20 \\  & 22 & 21 & 0.44 & 12 & 2.02 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Properties of conditioned soils depending on added amount of water-absorbing polymer. Figure 8: Soil samples after slump tests at varying amounts of added water-absorbing polymers. was used. Experimental results are summarized in Table 5, and pictures of the slump test results are shown in Figure 9. Table 5 shows that even though the slump value and compressibility requirements were satisfied by adding foam only at FIR of 45%, it was not possible to meet the permeability requirement (slump requirement was not satisfied with FIR = 67%; compressibility requirement was not satisfied with FIR = 22%). Soil 5 was too porous to reduce the permeability coefficient to the thrust value of 1 \(\times\) 10\({}^{-3}\) cm/s with only foam. As can be observed from the appearance of the conditioned soil in Figure 9a, foam and soil did not interact as a fully mixed material. The foam segregated from the soil, moved upward when tamped with a tamping rod to prepare for the slump tests, and finally flowed out from the soil samples as shown in Figure 9a. This segregation behavior between foam and excavated soil might reduce compressibility and/or impede reducing permeability. Table 5 also presents the experimental results when the soil samples were conditioned with both foam and polymer slurry. Since the compressibility requirement can be easily met by adding polymer slurries, the minimum FIR was chosen to be 22%. The PIR of the polymer slurry (concentration of 0.3%) was varied from 8% to 30%. The table shows that the slump value requirement was satisfied when the PIR was either 8% or 15%. However, foam and polymer outflow were observed during the slump test, as can be seen in Figure 9b when the PIR was at a higher value of 15%. The segregation behavior also reduces the compressibility of the conditioned soil. At PIR of 30%, the foam and the polymer experienced more serious material segregation during the slump test, and the specimen collapsed (see Figure 9b).