Thomson Line Construction: Piling at Mayflower

The groundbreaking ceremony for Mayflower station was commemorated along with Lentor last Saturday. At the Mayflower site, Avenue 4 has just been diverted last week to facilitate the construction of the bored piles for the retaining wall. The diversion will remain till end 2015, when the SBP construction is completed.

The ERSS of a station can be constructed using diaphragm walls as seen at Springleaf and Lentor. Another method of constructing the underground structures would be the use of secant bored piles (SBP). Over at Mayflower station, this method will be adopted.

Secant Bored Pile Construction

The pile's casing is first drilled into the ground, leaving 1-2m of the casing head exposed to the surface. The exposed cylinder guides the excavation of the bored pile, which is carried out next using a rotary drilling rig. The soil surrounding the borehole is supported by the casing. If the casing is not long enough to reach the required depth in the ground, bentonite slurry is used to support the soil below the casing. After excavation is complete, the reinforced steel cage is inserted into the casing, and concrete is poured. The casing is then removed and the retaining wall or ERSS is completed.