# Application Ranges of EPB Shield TBM in Weathered Granite Soil: A Laboratory Scale Study
## 3 Results and Discussion  
### Ranges of Water Content for Workability Requirement  
As mentioned in Section 1, in order to provide the desired workability for the EPB shield TBM operation, slump values of the conditioned soils should be between 10 cm and 20 cm. [PERSON] et al. [10] mentioned that controlling the water content inside the working chamber is as important as controlling the FIR. Figure 3 shows typical measured slump values with different water contents and FIRs for the four soil samples (Soil 1 to 4) in Figure 2 and Table 1; pictures taken after slump tests are shown in Figure 4. The FIRs varied from small (22%) to large (88%); the normal range is 30% to 80%. Referencing the experimental results of Figure 3a, slump tests were not conducted thereafter if we expected the slump values to either exceed 20 cm or be much less 10 cm (please see missing data in Figure 3b,d). For each sample, the water content that reached the slump value of as small as 10 cm was obtained in spite of adding foam with the maximum FIR of 88% was designated the lower bound of water content. On the contrary, the water content that reached the slump value as large as 20 cm was obtained in spite of adding foam with the minimum FIR of 22% was designated the upper bound of water content. These results are summarized in Figure 5; the figure shows the upper and lower bounds of water content for slump values of 10-20 cm as a function of the percentage of fine particles in excavated soil passed through a #200 sieve (from 1.2% to 17.1%). As shown in Figure 5, the water content to reach the slump values of 10 cm to 20 cm increased as the fine particle content increased. Curve A in Figure 5, indicating the median between the lower and upper bounds, might represent the optimum water contents as a function of the fine particle content passing through the #200 sieve. From this figure, the following strategy for choosing a soil conditioning agent can be proposed. 1. If the water content of the excavated soil is within the allowable range proposed in Figure 5, the workability requirement is satisfied with slump values between 10 cm and 20 cm. In this case, we have to check whether the conditioned soils also satisfy the permeability and compressibility requirements; if these are satisfied, it is sufficient to add only foam as the soil conditioning agent. This will be further discussed in Section 3.2
2. If the water content of the excavated soil is below the lower bound values, the workability requirement for slump value greater than 10 cm will not be satisfied; water must be added to the working chamber to reach the optimum values shown on curve A. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Category** & **Foam** & **Polymer 1** & **Polymer 2** \\ \hline Product name & MAK Foam & SUPER MUD (emusion) & MAK SOL-L (liquid) \\ Type & Foam & Polymer slurry & Water-absorbing polymer (solidification agent) \\ Property & Biodegradable surfactant & Polyacrylic acid polymer & Acrylates polymer \\ Density & 1.00–1.10 & 1.00–1.10 & 1.20–1.30 \\ pH & 8–9 & 7–9 & 7–9 \\ Concentration (\%) & 2 & 0.3 & Undiluted solution \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Properties of conditioning agents used in the experiment. 3. If the water content is above the upper bound shown in Figure 5, the workability requirement for slump value less than 20 cm will not be satisfied, requiring added solidification agents in addition to foams. This will be discussed in Section 3.3.1. 4. Finally, if the weathered granite soil is extremely coarse and cohesionless 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] (see Figure 1). To take advantage of the particle-crushing characteristics of weathered granite soil, it may be necessary to check the feasibility of applying the EPB shield TBM in this outside region also.