The Circle Line Stage 2 works comprised 5 underground stations and an underground depot that serves the corridor from Stadium Boulevard to Upper Paya Lebar Road/ Bartley Road. Contract 823 was the second stage of the Circle Line medium transit system. The project comprised of design-and-build works for 3 underground stations: Old Airport Road Station, Tanjong Katong Station and Paya Lebar Interchange Station, including a 2.5km twin bored tunnel.

CPG Consultants provided both the geotechnical and structural design for all three underground stations.