Sunday 29 June 2014

Thomson Line groundbreaking ceremony, 27 Jun 2014; LTA using ice walls for first time in MRT tunnelling

Work on Thomson Line gets into full swing
22-station line will open in 3 phases; North-South Line to have new station
By Royston Sim, The Straits Times, 28 Jun 2014

WORK to build the 30km Thomson Line will move into full swing, after a ground-breaking ceremony for Singapore's sixth MRT line yesterday.

The $18 billion, 22-station line will run underground from Woodlands to Gardens by the Bay, and open in three phases from 2019 to 2021.

At the ceremony, Transport Minister Lui Tuck Yew also announced that a new North-South Line station named Canberra will be built between Yishun and Sembawang. A feasibility study for the additional station has been completed, he said, and the Land Transport Authority (LTA) will provide more details later, such as its exact location and when it will open.

The Thomson Line will serve estates in the northern and central parts of the island, including Woodlands, Sin Ming, Thomson and Kim Seng. It will also ease crowding on the North-South Line and provide commuters with alternatives during service disruptions, said the minister.

"More than 400,000 commuters living and working along the Thomson Line will enjoy greater ease of access, more travel options and also shorter and more direct journeys," said Mr Lui.

He cited how residents from Springleaf estate in Sembawang will need only 35 minutes to travel to Great World City, compared to the current 60 minutes.

The Thomson Line will provide 60 per cent more capacity along the North-South corridor, Mr Lui added.

With six interchange stations, the line will give commuters more alternative routes and minimise inconvenience during disruptions, he noted.

The line will eventually be linked to Johor Baru via a rapid transit system link at Woodlands North station.

Asked for an update on the link, Mr Lui said details of Woodlands North have been finalised, and progress is dependent on the Malaysian side.

At the other end, Gardens by the Bay station will join the future Eastern Region Line, which Mr Lui said "is in the final stages of planning".

To date, 22 of 25 major civil contracts have been awarded to the tune of $6.5 billion, with the remaining three to be awarded by this year. The LTA has also ordered 91 four-carriage trains costing a total of $749 million.

In constructing Marina Bay station, Japanese contractor Taisei Corporation will use ice walls to prevent water seepage during tunnelling works - a first here.

This involves pumping refrigerant into pipes that will be inserted into the ground to freeze the groundwater.

As the Thomson Line will run below tunnels for the Circle and North-South Line for a 40m stretch, freezing the ground during excavation will ensure groundwater does not seep in and cause the ground to become unstable.

Other engineering challenges include carrying out mining works under the North-South Line at Orchard station, which requires engineers to ensure that surrounding structures like the station are not affected and rail operations are not disrupted.

Nee Soon GRC MP Patrick Tay welcomed news of the new Canberra station, noting that there are upcoming developments in the area.

MP Lee Bee Wah, who oversees the Springleaf estate in Nee Soon GRC, said many residents there are waiting for the line to be completed.

"Some residents who live nearby told me that once their cars' certificates of entitlement expire, they won't buy another."

New MRT station to be built between Yishun and Sembawang
By Sharon See and Joy Fang, Channel NewsAsia, 27 Jun 2014

An additional station will be built between Yishun and Sembawang on the North-South Line, and it will be known as Canberra station, said Transport Minister Lui Tuck Yew on Friday (June 27). The Land Transport Authority (LTA) will announce details later.

"I mentioned last year that LTA was studying the possibility of building an additional station between Yishun and Sembawang on the North-South Line. The more observant amongst you would have noticed a missing station number, NS (12), between these two stations. I am pleased to announce today that the feasibility study has been completed and we will be constructing the station, which will be known as Canberra station," Mr Lui said.

He was speaking at the groundbreaking ceremony for the Thomson Line, which will be opened in three phases in 2019, 2020 and 2021. When fully opened, the line will bring an additional 60 per cent capacity to the North-South corridor, he said.

When fully completed in 2021, the Thomson Line will have 22 stations, including six interchanges. The line will see a projected daily ridership of about 400,000 commuters, and will serve several housing estates in the north and central areas – including Woodlands, Sin Ming, Thomson and Kim Seng – and connect them to the city and the rest of the MRT network. The 30km-long line will also be eventually linked to Johor Bahru in Malaysia, he said.

"Like the MRT lines we have today, each new line or extension will shape the way residents along its corridor interact, live, work and play. Since we launched the first MRT in 1987, we have seen how communities have grown and thrived with stations in their midst," said Mr Lui.

"Residents and their estates have grown closer together and are better connected with the rest of the island, the facilities and other amenities. We are looking very much to the same for Thomson Line residents," the minister added.

LTA has also said that the names of the Thomson Line stations have also been finalised. All names remain the same except for Sin Ming, which has been renamed Bright Hill.

Ice walls to be used in MRT tunnelling
Precautionary step to prevent water seepage
By Royston Sim, The Straits Times, 28 Jun 2014

ICE WALLS are to be used for the first time in Singapore, to stabilise the ground during construction of the Thomson Line Marina Bay station.

Japanese contractor Taisei Corporation will freeze a section of earth to prevent water from seeping in when workers excavate a 40m stretch of tunnel for the station. Engineers will insert vertical freezing pipes into the ground and pump in brine, a refrigerant, to freeze the groundwater into watertight ice walls.

Mr Shaik Sha Marican, Land Transport Authority (LTA) director of the Thomson Line Civil Team 4, said the ice walls are a precautionary measure recommended by consultants who carried out an engineering study.

The 40m stretch of Thomson Line tunnel will run below the live Circle Line and North-South Line tunnels.

Mr Sha Marican explained that exposure to water over a period of time can weaken the soil and affect mining operations. This could have an impact on the two MRT lines running above.

"We are working below two live tunnels, so we do not want things to go wrong," he said.

Ice walls have been used in Japan, and Taisei has employed the method previously. It was awarded a $425 million contract to build the Thomson Line Marina Bay station and its tunnels.

Several steps must be taken before inserting vertical freezing pipes to create the ice walls.

Engineers must construct mining shafts on both sides of the 40m tunnel, then create openings to build a pedestrian linkway about 20m below the surface.

Shield tunnelling machines will be launched to cut existing steel piles that support the North-South Line tunnel. The machine will work in 1m sections, excavating and cutting piles before steel segments are installed to support the excavated surface.

After the piles are cleared, engineers will strengthen a section of the ground made up mainly of soft marine clay, which Mr Sha Marican described as "toothpaste-like material". The marine clay section extends to a depth of between 20m and 30m.

Cement and water will be injected into the marine clay to solidify it - a process called jet grouting. Vertical freezing pipes will also be installed to freeze the groundwater in the soil bed below the marine clay to a depth of 41m.

Brine will be pumped into the pipes to freeze the groundwater around and form ice walls. The refrigerant can range from -10 deg C to -40 deg C, depending on how thick the walls have to be.

Mr Sha Marican said details are being finalised. It could take a month for the ice walls to form. The LTA will monitor ground temperatures closely, and pump more brine into the ground if needed.

The ice walls will be in place for about six months while the lower Thomson Line tunnel is being excavated. Those working in the tunnel may have to wear winter clothing if it gets too cold, Mr Sha Marican said.

The freezing pipes will be deactivated after the lower tunnel is completed, so that the surrounding groundwater melts. Structural work for the Marina Bay station is expected to conclude in 2018.

* LTA using ice walls for first time in MRT tunnelling of Thomson-East Coast Line
Method to prevent water seepage employed 40m underground for work on TEL station
By Adrian Lim, Transport Correspondent, The Straits Times, 26 Jun 2018

For the first time, the Land Transport Authority (LTA) is using ice walls to stabilise the earth before conducting MRT tunnel excavation works.

The ground-freezing method is being employed about 40m underground for construction work on the Thomson-East Coast Line's (TEL) Marina Bay station, which is targeted to open in 2021.

It is required because the soil which workers are tunnelling through is old alluvium, which is highly permeable and susceptible to water seepage.

Giving an update during a site visit yesterday by Transport Minister Khaw Boon Wan and members of the Government Parliamentary Committee for Transport, the LTA said the ground-freezing process started in late March.

After about two months, two ice walls have been formed along a 40m stretch underground.

They are about 1.8m thick and will allow excavation for the northbound TEL tunnel - towards Woodlands - to be carried out safely.

Tunnelling using excavators has also started, and a 6m stretch has been excavated so far.

The freezing was done by installing 96 vertical pipes into the ground and circulating chilled brine - a mixture of salt and water - with a temperature of minus 30 deg C, to allow the surrounding soil to freeze and form ice columns.

These ice columns have expanded and joined together to form a continuous ice wall, which will help prevent water seepage during mining works.

The works are being carried out by Japanese contractor Taisei Corporation, which won a $425 million contract in 2014 to build the TEL's Marina Bay station and its associated tunnels.

The LTA said: "The ground freezing will also help ensure that works have no impact to the safe operations of the Circle Line and North-South Line tunnels located above the TEL tunnels."

The ice walls will be in place for about three months until the tunnel construction is completed.

Mr Ng Kee Nam, group director for the TEL and Cross Island Lines (Civil), said that throughout this period, the temperature of the ice walls will be monitored to ensure it is maintained.

Once the tunnel construction is finished, the freeze pipes will be deactivated, allowing the ground to thaw. Construction works for the upper eastbound TEL tunnel above will then commence.

Mr Ng said that multiple site investigations and soil checks were carried out before deciding on the ground-freezing method.

The 43km, 31-station TEL will open progressively from the end of next year, connecting commuters living in the eastern region to the city centre, as well as those living in the Woodlands and Thomson areas. It is expected to be fully operational in 2024.

Groundbreaking celebration for Thomson Line -27 Jun 2014

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