Downtown Line 3 shafts

Some readers were wondering what are Prison, Stadium and PIE shafts. So thought it would be a good idea to explain in a post what these are and where they are located that more people may understand.

In essence, the three shafts are cylindrical-shaped shafts that are constructed from ground level down. Once excavation has completed, these are used to launch 2 TBMs twice, once for each bound in each direction. For instance, TBM A will bore the Expo bound track from the shaft to station 1. TBM A will then be brought back once that drive has been completed and relaunched for the Expo bound track towards station 2. Once the drives are completed, a cross-passage (emergency walkway that connects both tunnels) will be built within the shaft prior to it being back filled.

An exhibit explaining about the shafts on 11 July 2013 - DTL3 tunnel works commencement ceremony

Construction sequence

Settlement at Upper Changi

While caves in are rare occurrence during the tunnelling phase, they do happen. Every TBM that launches is accompanied by a watchmen which is station on the surface within a safe distance of the cutterhead location to monitor and phone back to the control room any depressions should they appear. In the inevitable situation where a passing vehicle gets timed with the sinkhole, it gets carried in with the ground. Quoting a press release by the LTA earlier today, "At about 8.30am on 24 April, a depression appeared at the centre lane of Upper Changi Road East (in direction towards Expo). A tipper truck that was passing tilted into the hole."

Photo credit - @Andre_Giam

Cave in near apartment 704 of Changi Court

Though the sinkhole's location is near the Upper Changi station site, the tunnelling works north of the station are carried out by its sister contract C923A. A good gauge of progress as the 2 TBMs from the PIE shaft is nearing the end of its final drive. I presume the authority and STEC would conduct stringent soil improvement works at the area before resuming activities at the cutterhead.

Tampines East update

Tampines East station has made great progress with excavation starting at the station box as well as the cut & cover cripple siding section. Tunnel boring began on 5th December towards Tampines Central station. Once there, the internal parts of the TBM will be stripped out and a new shield used for re-assembly of the TBM before driving the Bukit Panjang track towards Tampines Central. Already, the Expo bound track under C923A has been completed and final breakthrough will take place once the excavation has reached formation level. TBM Argo by C923A contractor Shanghai Tunneling has been stripped out with the shield abandoned in-situ and the machine redeployed for its drive towards Upper Changi from the PIE shaft.

Panoramic view of the Tampines East worksite - the middle is the cut & cover portion, the right is the launch shaft.

DTL3 October update

In this post, we bring you up to date on the goings on of construction on Downtown Line stage 3 for the month of October.

Firstly, a listing of the TBM shields that we have.

C923 - S-761
C923A - TBM1 (Argo) & TBM2 (Hermes)
C925 - TBM1
C926 - TBM1 (Chloe), TBM2 (Beatrix), TBM3 (Hayley) & TBM4 (Lizzi)
C927 - TBM1 (Tierra) & TBM2 (Kaida)
C928 - TBM1
C929A - S-685 (Harmonica), S-686, S-693 (Jupiter) & TBM4
C930 - TBM1 (Gaia) & TBM2
C931 - S-737 (Jet)
C932 - TBM1 (Xena) & TBM2 (Gabrielle)
C933 - S-739 (Whampoa), S-740 (Bendemeer), S-741 & S-742
C935 - S-759 & TBM2
C937 - TBM1, TBM2 & TBM3

Green - completed
Orange - tunneling in progress
Aqua - launching soon

So here's an update on some of the TBM tunneling progress. We don't have all the progress available unfortunately. More details and an easy display will be coming up down the line in November and beyond.

C923A PIE shaft to TPE
TBM1 - Completed
TBM2 -
Total: 1074 rings

C926 Stadium shaft to TPW
TBM1 50+ rings at end August
Total:

C927 BDN to BDR
TBM1 678 rings. TBM2 75 rings.
Total:

C937 FCN to BCL
TBM1 at 105 rings
TBM3 - - - - -
Total:

FCN to CNT
TBM 2 at 54 rings
Total:

 In addition, excavation seems to be progressing pretty well overall.

C922 - Expo station has already reached the base slab level at portions of the station.

C925 - Tampines East station is in the process of constructing the retaining walls. The TBM was lowered within the last month and assembled at the launch shaft ready for the Expo-bound drive to Tampines Central station.

C926 - Tampines West is still in the process of constructing the retaining walls as the Tampines Avenue 4 was only shifted over the completed portion a few months ago.

C928 - Bedok North has excavated most of the soil from the station pit area. They will be progressing onto the structural works soon.

C929 - Kaki Bukit station has the top layer casted and excavation work is progressing below using the top-down method where the permanent structure is cast before moving lower to commence excavation at the preceding level below.

C933 - Bendemeer station has seen some under-platform level work go on. Concrete pouring has also been taking place.

 C935 - Jalan Besar station is also employing the top-down method of construction. Most areas have progressed to level 2 of excavation.

C937 - Fort Canning station is progressing swiftly with the top-down method as well. Excavation continues on.

Do check back for more updates as we begin filling up the individual station pages with photos. Feel free to drop us a line if you have anything to contribute too, via the comments section. Have a great day all!