Technical Visits are only open to registered congress delegates. To register as a congress delegate, please visit here and select the Technical Visit option within the registration form.

Digitalisation at Tuas West Depot

Overview of Tuas West Depot

Tuas West Depot (TWD) is Singapore’s seventh and newest MRT depot. Since operations commenced on 18 Jun 2017, TWD has been servicing and maintaining up to 33 trains daily and has the largest stabling capacity amongst the 4 depots for the North-South and East-West Line in Singapore, stabling up to 60 six-car trains.

Autonomous Robotic Movers

Autonomous Robotic Movers (ARM) will be used in Tuas West Depot to perform delivery and transportation tasks within the Train Workshop. The ARM can carry payloads up to 600kg and allows for automated pick-up and drop-off due to its omnidirectional motion capability. As such, the use of ARM will improve efficiency and resource management within the Main Depot Workshop by redirecting existing manpower to provide more value-added services.

Mixed Reality

Mixed Reality (MR) utilises the merging of the physical and virtual worlds to create a new environment. In Tuas West Depot, the use of MR devices will enhance staff technical competency and learning experience by performing training and maintenance works through an interactive, collaborative and safe environment. Such tools are also being explored by LTA to use the optical detection capability of MR for the use of daily train checks and inspections. Through leveraging on technology, staff will be able to harness the computational and systematic strengths of computers to perform checks and detect anomalies.  

Mining works at TEL Orchard Station

About the project

Contract T219 Orchard station is an interchange station between the existing North South Line (NSL) and upcoming Thomson-East Coast Line (TEL) which is located at the busy intersection at Orchard Boulevard and Paterson Road. Orchard Station is a fully underground station with five entrances, with the station box being approximately 210m long and 40m wide. The new Platform Link undercrossing Orchard Boulevard is approximately 25m below ground level and will provide commuters with a seamless underground connection, between the existing NSL station and the new TEL station, beneath the busy carriageway.

Challenges

Building an underground structure is difficult.

Building an underground structure beneath an existing structure is challenging.

How about building an underground structure right below an existing underground MRT station, which is beneath an occupied mixed development consisting of 7 stories of commercial spaces and 55 stories of residential?

An impressive engineering feat, isn’t it? That is exactly what we are currently doing at T219 Orchard station. A major portion of the Platform Link which connects the platforms of both NSL and TEL Orchard stations is right below the existing NSL Orchard station as well as ION Orchard (shopping mall) and Orchard Residences (condominium). 

The link is located approximately 25 metres below the ground level, undercrossing the NSL tunnel tracks. Platform Link works have to take place while ensuring that the NSL Orchard station and tunnels remain in operation throughout the construction period. Due to the close proximity of the proposed Platform Link to the existing underground and above ground structures, it is essential for the mining works to be carried out in a planned, incremental and co-ordinated manner without compromising the above ground activities and amenities as well as the structural integrity or serviceability of these structures.

Under such constrained working conditions, these mining works also include complicated works such as:

  • Restricted width (top heading in 3 drives & invert mining in single drive) and incremental mining progression (167 mines, in total) with ascertained face stability measures;
  • Underpinning of NSL Orchard base slab (156 mini piles, in total);
  • Cutting several NSL Orchard station piles; and
  • Proper control on water ingress from the excavated ground.

Addition and alteration (A&A) works to existing NSL Orchard station to facilitate connection also require intensive and proper coordination with the Operator. Such A&A works can only be carried out within restricted hours i.e. during non-operational hours of the NSL station and tunnels.

Ground Freezing Works at TEL Marina Bay Station

Introduction

The new 43km Thomson-East Coast Line (TEL) is part of Singapore Land Transport Authority’s (LTA) vision to double the length of the island’s railways system by 2030. The project will be opened in five phases from 2019 to 2024. The TEL will be completely underground, comprising of 31 stations connecting Gardens by the Bay in central Singapore with Woodlands in the north and Bedok in the east. The TEL will interchange with five existing metro lines at seven stations strategically located to help alleviate crowding. One of the key challenges with the project is that the Marina Bay area, through which the line will pass, is already densely populated with two pre-existing railway lines, the North-South Line and Circle Line, already in place.

For the first time in Singapore’s rail history, the technique of ground freezing has been chosen to stabilise the soil during construction of Singapore’s new Thomson-East Coast Line (TEL) Marina Bay Station. The works are underway to build a pedestrian walkway and the two tunnels, Thomson Line tunnels, one on top of the other, underneath the existing lines. To do this, the team has utilised a rectangular shield tunnelling machine to cut away a section of approximately 20 existing piles that support the North-South Line’s tunnel. The level of complexity is raised as the current live MRT lines are in use coupled with the poor soil conditions which make the project even more challenging.

What is ground freezing about?

The process of ground freezing stabilises soil by converting pore water into ice by the continuous circulation of a cryogenic fluid, (usually liquid nitrogen, salt-brine or anhydrous ammonia) through a series of pipes inserted vertically into the ground. When the soil temperature reaches 0°C (32°F), ice begins to form around the pipes in a cylindrical shape. The frozen pore water then acts much like grouting mixtures that fuse together with soil and significantly increases compressive strength to create an impermeable ice wall, beside which tunnelling and construction can commence. Ground freezing is however a highly energy intensive process, requiring the refrigeration of large volumes of soil over extended periods of time. With its implementation, it is a relatively expensive process compared to more conventional ground stablisation methods, meaning that it is often reserved for especially challenging projects. Of the three types of refrigerants available, the use of salt-brine is generally the most cost effective, whilst liquid nitrogen and ammonia are the most expensive due to their fast freezing capabilities.

One of the key benefits of ground freezing is that is a minimally invasive technique that has limited penetration into the earth, given that it works thermally, rather than by displacement. This means that the ground remains mostly undisturbed when installing the pipes and during the freezing process, thereby reducing the impact on surrounding structures. It is also environmentally friendly as the surrounding soil largely reverts to its original state once the ice wall is no longer needed and allowed to melt. Then perhaps best of all, due to the versatility of grounding freezing and its applicability to all types of soils —which is the major challenges in the Thomson-East Coast Line (TEL) Marina Bay station — it has been selected as the ideal option in this project.