Underground Singapore 2011
Figure 2. Plan of Bukit Panjang Station, showing the outline of the secant pile wall
The majority of the grouting, and the grouting trial, have been carried out in Zone 2 of Bukit Panjang Station, shown in Figures 2 and 3.
Figure 3, secant piling in progress for the east wall of Bukit Panjang Station
4. DRILLING AND GROUTING METHODS PROPOSED The specified minimum width of the grout curtain is 1m, with a minimum depth of 10m below rockhead or final exaction level, whichever is less. It was considered impractical to control rock fissure grouting to limit the width to 1m. The grouting was planned on the basis of achieving a radius of grouting of 3m in the smallest fissure that could be penetrated by the grout. This gave a theoretical minimum curtain width of 6m. For simplicity of control on site, the depth of the curtain was set at 10m below the toe of the secant pile wall, which resulted in a slightly greater grouted depth than the minimum required. It was decided to use conventional rock fissure grouting, in open holes, rather than the tubes-amanchette (TaMs) commonly used for grouting in Singapore. For rock fissure grouting, TaMs, and the sleeve grout installed around the TaM, close off many of the fissures intercepted by the drill hole, so that they may not be grouted. Provided that the drilled hole in the rock is stable, grouting in an open hole
5