SINGAPORE MASS Rapid Transport's Singapore US$3.66bn, 33.3km Circle Line will orbit the city connecting lines already radiating north-south, east-west and north-east from its centre.
Its 29 stations will all be underground.
Contract C824, on which the collapse happened, is part of Phase 1, which consists of six stations along the shore line.
Much of this section of the alignment is in land reclaimed from the sea between the 1950s and 1970s.
Three of the line's six phases are under construction at present. Phases 4 and 5 are under design, and Phase 6 has still to gain planning consent.