# Effect of Rock Abrasiveness on Wear of Shield Tunnelling in Bukit Timah Granite
## 3 Results
### Wear of Slurry Discharge Pipes  
The slurry discharge pipes were rotated or installed while the pipe thickness remained at an average of 6.2 mm based on the recorded data. The pipe installation or rotation periods lasted for 115 days on average.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Weathering**} & \multicolumn{4}{c}{**Wear Coefficient (mm/km)**} & \multicolumn{4}{c}{**Operation Parameters**} \\ \cline{2-9}  & **Centre** & **Face** & **Transition** & **Gage** & **Advance Speed** & **Cutterhead Speed** & **Total Thrust** \\  & **Cutters** & **Cutters** & **Cutters** & **Cutters** & **(mm/min)** & **(RFM)** & **(6N)** \\ \hline G(I) & 0.0510 & 0.0256 & 0.0287 & 0.0362 & 9.6 & 3.66 & 24,166 \\ G(II) & 0.0483 & 0.0244 & 0.0277 & 0.0342 & 10.1 & 3.28 & 21,936 \\ G(III) & 0.0361 & 0.0213 & 0.0249 & 0.0262 & 11.0 & 3.21 & 22,349 \\ G(IV) & 0.0251 & 0.0203 & 0.0211 & 0.0242 & 11.2 & 3.06 & 21,896 \\ G(V) & N/A & 0.0139 & 0.0140 & 0.0142 & 11.7 & 2.60 & 20,948 \\ Mixed & 0.0378 & 0.0200 & 0.0215 & 0.0306 & 12.6 & 2.84 & 21,114 \\ Overall & 0.0477 & 0.0240 & 0.0271 & 0.0335 & 11.0 & 3.10 & 22,068 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Wear coefficient of disc cutters.  
Figure 9: Histograms of the wear coefficient of disc cutters with respect to position: (**a**) centre cutters; (**b**) face cutters; (**c**) transition cutters; (**d**) gage cutters.  
The daily wear rate of the slurry discharge pipes was 0.055 \(\pm\) 0.048 mm/day on average, ranging from a minimum value of 0.011 mm/day to a maximum value of 0.243 mm/day. The wear rate per excavated distance had an average value of 0.017 \(\pm\) 0.016 mm/m, with minimum and maximum values of 0.002 and 0.087 mm/m, respectively.  
Table 5 lists the average values of the wear rate per excavated distance for the slurry discharge pipes with respect to the weathering grade of the Bukit Timah granite. The wear rates in weathering grades G(I) to G(IV) of Bukit Timah granite were similar. The wear rates for weathering grade G(V) of Bukit Timah granite, which was entirely weathered, and those for the mixed zone were 1.5 times higher than those for weathering grades G(I) to G(IV) of Bukit Timah granite. As can be observed in Figure 6b, the thickness measurement was recorded at three locations: front, middle, and rear of each pipe. The average wear rate per excavation distance at each location was 0.017, 0.016, and 0.018 mm/m, for the front, middle, and rear, respectively. The difference in the wear rate with respect to measurement position within the same pipe was negligible.  
Figure 10 shows the wear rate per excavated distance according to the position of the ring where the pipe thickness was measured. As the TBM was used to install the rings after excavation, increasing the ring number suggests that the rings are closer to the TBM. As shown in Figure 10, the wear rate closer to the TBM was generally higher. This higher wear rate indicates that rock chips (muck) became worn out as the moving path of the muck (including the rock chips) was greater, and the wear near the end of the pipe was less affected.