The Thomson-East Coast Line (TEL)’s Orchard Station will serve as an interchange station between the TEL and the North-South Line (NSL). When completed in 2021, commuters will be able to transfer seamlessly between the TEL and NSL via an underpass across Orchard Boulevard and a new box structure that is being constructed right below the existing NSL’s Orchard Station at a depth of approximately 30m below ground. The underpass and new box structure is known as the paid-to-paid platform link.
2. The underpass across Orchard Boulevard that connects the TEL and NSL’s station platforms was constructed using the pipe-roofing method. The pipe roof consists of internally interlocked 1.2m diameter steel pipes that form the perimeter of a box tunnel, and is installed using a retractable micro-tunnel boring machine (mTBM) that tunnels through the ground horizontally to install one pipe at a time. It was the first time in Singapore that a retractable mTBM was used to install internally interlocking pipes.
3. Prior to this, ground improvement works were carried out to stabilise the ground and facilitate the micro-tunnelling and mining. Mining within the pipe roof with steel frame supports was completed in December 2017, and construction of the permanent reinforced concrete underpass structure is currently in progress.
4. The mining and underpinning method has been adopted to construct the new box structure underneath the existing NSL’s Orchard Station. Special drilling machines from Europe are being used. These are capable of drilling in all directions in a low headroom confined space. Close monitoring of the NSL’s Orchard Station for settlement and movement is carried out at all times with real-time monitoring instruments.
5. As the NSL’s Orchard Station is currently in operation, mining works must be carried out strictly according to the approved design, sequence and method in a safe manner without compromising the stability and serviceability of existing surrounding structures. About 20 per cent of the mining and underpinning works have been completed since works started in September 2017.
6. As part of the LTA-UITP Singapore International Transport Congress Exhibition 2018 (SITCE) 2018, LTA hosted congress delegates at the site of the TEL’s Orchard Station. The delegates were briefed on the construction challenges and innovative methods used to construct the station in a confined space close to an operational station.
Addition and Alteration to Existing NSL’s Orchard Station
7. Addition and Alteration (A&A) works to the existing NSL’s Orchard Station will be carried out to retrofit it with escalators, a lift and staircase. Detailed planning and close coordination with the NSL operator, SMRT, is required in order not to cause any major disruption to station operations or inconvenience commuters. Most of the A&A works can only be carried out during non-operating hours of the NSL’s Orchard Station and its tunnels, a time period beyond midnight and before the first train starts running in the morning. As such, these works must be carefully planned, coordinated and executed.