McConnell Dowell is pleased to announce that on Thursday 8th of May at 0500hrs, a major milestone was reached on the DTL2 C917A project in Singapore. The Tunnel Boring Machine (TBM) S-603 Sophia reached her final destination, completing excavation from her starting point at King Albert Park (KAP) Station and docking in the station wall at the Sixth Avenue (SAV) Metro Station. This is a very important moment in the project, with the risk level on tunnelling productivity dropping significantly with the completion of the first of the twin metro tubes. Sophia's sister TBM, S-602 Grace is anticipated to catch up with her sister TBM and reach the SAV Station in mid to late June.
The tunnelling in Singapore has been challenging, with several major episodes in the life of Sophia and her sister Grace. The Contract C917 was originally awarded to the contractor ALPINE, with S-603 Sophia starting tunnelling excavation in late February 2013 on the Expo Bound Tunnel Drive. Grace S-602 commenced in late April 2013 on the parallel Bukit Panjang Bound Tunnel Drive. Both of these Tunnel Boring Machines are of Earth Pressure Balance (EPB) technology.
On 20 June 2013, with Sophia at Ring 131, just 191m into the 1395m tunnel drive, Sophia stopped indefinitely due to the insolvency of ALPINE. Grace, S-602 also stopped on the same date at Ring 32, just 52m into the Bukit Panjang Bound Tunnel Drive due to the same cause. At this time the Expo Bound Tunnel (by Sophia S-603) was only 13% complete and the Bukit Panjang Bound Tunnel (by Grace S-602) was only 3% complete.
For a period of 7 weeks both TBM's lay dormant whilst McConnell Dowell worked with the client, Singapore Land Transit Authority (LTA) in offering and establishing a Caretaker Team to look after the Tunnelling site and get the TBM's moving before too much deterioration set-in. During this caretaker role, McConnell Dowell managed to get the TBM's un-stuck, repaired and restarted, with Sophia advanced 41 rings (56m), and Grace advanced one ring (1.4m). McConnell Dowell also played a similar parallel Caretaker Role on the C918 Contract where the two mixshield TBM's, also previously operated by ALPINE, were holed up underground. The Caretaker Role continued over 5 weeks, and, during this time a competitive tender was issued, priced, and awarded by the LTA to McConnell Dowell for taking over the C917 Contract, now renamed C917A. The C918A Contract was awarded to another Contractor.
After Contract Award, McConnell Dowell rapidly mobilised additional resources to supplement the Caretaker Team and seamlessly recommenced full TBM tunnelling operations on S-603 Sophia from 9 September 2013 and on S-602 Grace on 19 September 2013. This was a remarkable effort to manage, tender, finance, achieve commercial agreement and employ / mobilise and train a significant site team in this very short period.
The notorious Bukit Timah Granite geological formation with extremely hard rock ranging to soft, easily destabilised residual soils in a short depth range meant that the TBM was often cutting very hard rock in the tunnel invert, yet soft, easy to loosen soils in the crown at the same time. This hard rock took its toll on the TBM cutting tools, requiring regular stoppage and replacement work, yet at the same time the TBM Operator and Support crews had to be extremely careful and diligent not to cause surface settlement or subsidence due to potential loosening of the soft soils above the TBM. These major challenges caused several delays on the TBM tunnelling, but, in the end, the production rates achieved were equal to, if not better than, those achieved by the adjacent Contractors and others using EPB technology in Singapore.
The McConnell Dowell Team on Singapore DTL2 Contract C917A, led by Project Director Frank Hemmert have achieved a fantastic result through determination, diligence, investment in the local workforce through their up-skilling, challenging the status quo, promoting the highly respected McConnell Dowell safety culture and just plain old hard work in getting the first TBM over the line.
The project is still far from complete however, with the second tunnel drive, cross passages, track-bed concrete, brackets and the two stations construction all on programme critical path.
Media enquiries:
Cameron McIver
Brand & Marketing Leader
+ 61 3 9816 2582
cameron.mciver@macdow.com.au