The road collapse last November was caused by a sinkhole which in turn was caused by a TBM undergoing maintenance, according to the Building and Construction Authority (BCA). The Japanese construction company Nishimatsu's TBM was excavating a tunnel for Deep Tunnel Sewerage System (DTSS) Phase 2.

https://www.straitstimes.com/singapore/transport/farrer-road-sinkhole-tunnelling-machine-under-maintenance-when-ground-destabilised