Tunnelling for utility services is a vital part of modern civilisation and in the busy urban centres the projects come large and small, and each has a challenge in its own right, whether that comes from geology, scale or other complications. But, in all instances the clients and construction teams are working toward achieving successful outcomes and delivery further infrastructure of significant use to the fabric of healthy and prosperous cities.
Among this short selection from the many, many utility projects underway across the world are: a large power cable tunnel project and a large sewer project, both in London; a large outfall and a small sewer, both in Toronto; a flood prevention scheme in Bangkok; and, a sewer in Macau.
BANGKOK DELIVERIES
Construction work is underway on the 13.3km-long Klong Prem Prachakorn Drainage Tunnel Project, in Bangkok, and the first Terratec TBMs were on site from late 2022 and more are due soon, taking the total to four machines.
Terratec is also supplying TBMs to the 9.1kmlong water tunnel being constructed in the city by the Metropolitan Waterworks Authority. The Ninth Bangkok Water Supply Improvement Scheme and the manufacturer is supplying three machines to the contractor on the project.
For the Klong Prem Prachakorn Drainage Tunnel Project, geology is soft, medium, stiff sandy clay and sand along the tunnel alignment between Klong Bang Bua and Chao Phraya River.
The 6.49m-diameter earth pressure balance machines (EPBMs) have cutterheads of a flat spoke type with copy cutters. The machines are also designed with capability to execute tight radius turns using active-type articulation.
Factory acceptance tests (FAT) of a further two EPBMs took place recently and by mid-year they are due to join the first two machines on flood prevention project site.
The EPBMs are to construct 1.4m-long (5+1) rings formed of 300mm-thick concrete segments. Batterypowered locos will handle segment supply and spoil removal.
On the other project – the Ninth Bangkok Water Supply Improvement scheme – Terratec recently had FAT milestones for the three EPBMs it is supplying to the contractor, a JV Italian-Thai (ITD) and Nawarat (NWR). The former JV partner will operate two machines, the latter one TBM.
Terratec is supply two 4.39m-diameter EBPMs and one 4.8m-diameter machine, and again the design of the TBMs includes active-type articulation for tight radius curves. Their cutterheads feature a spoke design with a 70% opening ratio and copy cutters.
The lining is 1.2m-long Universal rings (4+1) with 250mm-thick segments. Supplied will be delivered to the machines and mucking out by rail transport.
The water tunnel will be completed with a secondary, steel lining.
LONDON Submerged breakthrough for LPT2
A tunnel boring machine (TBM) working on UK utility National Grid’s London Power Tunnels (LPT), Phase 2 project, recently completed its drive in a flooded shaft in south-east London.
The Herrenknecht TBM, named ‘Christine’, took four months to bore a 2.5km section of the cable tunnel from the launch shaft in Hurst to the reception shaft in Crayford, navigating difficult terrain caused by the chalk aquifer across the route.
As the route to the breakthrough in Crayford passed through the aquifer, there was the risk of high-pressure water leakage flowing into the shaft. By choosing to flood the reception shaft, the Hochtief Murphy Joint Venture tunnelling team was able to balance the water pressure, creating the conditions to allow sealing gel to cure before draining down.
The 140-tonne TBM had been refurbished and modified in order to operate in these challenging conditions.
The breakthrough took place in three stages, which allowed the team to dismantle the TBM in three parts. The TBM was then lifted up from the shaft in an eightday operation.
This is the third drive to be completed on the LPT2 project, marking 26.8km of built tunnel. Tunnelling will be completed with the breakthrough of the two remaining drives – a total of 5.5km – scheduled for later this year. Four TBMs are working on the project.
Project manager, Malcolm Casewell, said the breakthrough at the Crayford reception shaft was unique on the project.
He said: “Ensuring Christine was fit for an underwater breakthrough was a great challenge and I’m proud of what we’ve achieved today alongside our engineering partners, HMJV and Herrenknecht.”
LPT is a £1bn, seven-year project to extend and improve the power grid network in London as demand increases. The large-scale tunnelling project was designed to carry the high voltage power cables at depth. In total, 32.5km of 3m-diameter tunnels are being constructed up to 60m below ground along a route between Wimbledon in south-west London and Crayford in the south-east of the capital.
The project is to be completed and the power cables operational in 2027.
Completing lining for Tideway
London’s Thames Tideway super sewer project recently completed the secondary lining on the 7km-long western section.
The 6.9m i.d. secondary lining works in the western section of the sewer tunnel started in March 2021. The works required more than 800 concrete pours to make the journey from Acton to Fulham in south-west London.
The concrete was batched on site at the Carnwath Road Riverside site, in Fulham, and delivered to the six shutters by concrete trains to a pump located at a logistics crossing within the tunnel. Approximately 48,000m3 of concrete was used to create the secondary lining in this section of sewer tunnel.
After the secondary lining works in the tunnel section were completed, then the final lining for the main shaft at Carnwath Road Riverside continued.
The main tunnel drive was completed by TBM ‘Rachel’ in late 2020.
TORONTO Outfall success
A new wastewater treatment plant along with a new 3.5km-long outfall tunnel are the key features of a project at Ashbridges Bay in Toronto to improve water quality from treated effluent discharge into Lake Ontario.
The current Ashbridges Bay treatment plant and discharge outfall are about 70-years old – one of city, and Canada’s, oldest such facilities. It does not meet discharge standards and its capacity in insufficient to meet modern demands. Further, the existing complex is also approaching the end of its service life.
Hatch performed the design, project and construction management for the Ashbridges Bay wastewater treatment project, including preparation of contracts with the geotechnical baseline report (GBR) – which included baselining marine conditions to reduce contractor risk. Geology comprises mainly shale with other sedimentary rocks – limestone, siltstone and sandstone.
The outfall tunnel will discharge the treated effluent up through 50 vertical risers and ports at its end for diffusion into the lake waters.
Contractor on the project is Southland/Astaldi JV, which used a Robbins 7.95m-diameter single shield TBM – which underwent remote acceptance during the covid pandemic – and was launched from an 85m-deep (279ft), 14m i.d. (46ft) shaft, in Spring 2021 to bore offshore. A Robbins-made continuous conveyor for muck removal also included vertical transport up the shaft.
The tunnel is entirely within the Georgian Bay Shale Formation, and such shales in southern Ontario have been known to cause time-dependent deformation (TDD). This factor was accounted for in design of the 7m i.d. concrete segmental lining. Daily progress rates up to 47m, or 30 rings, were achieved.
Tangle below
The City of Toronto recently issued an emergency, noncompetitive contract for retrieval of a micro TBM that has been stuck underground for a number of months after it became entangled among tensioned steel tieback wires of buildings during construction work for a new storm sewer.
The local authority and project owner said the steel tiebacks did not show up on infrastructure research, on as-built drawings, during design and before construction commenced on the 900mm diameter sewer.
The new contract – to the contractor, Clearway Construction Ltd – should be issued as a “matter of extreme urgency, as there was a significant health and safety hazard to the public” due to the unforeseen conditions, the City’s Engineering and Construction Dept said in the summary of its advisory Report for Action (RFA), issued mid-February, to the City Council, seeking approval.
The micro-TBM was launched in March 2022 to bore the sewer for the Basement Flooding Protection Program, Phase 4 Contract, on Old Mill Drive.
Wider complications arose from the micro-TBM meeting the tensioned tie-backs. They included, the RFA said: “The integrity of the roadway, nearby subway tunnel and surrounding infrastructure was undermined as a result of ground movement around the microtunnelling boring machine due to excessive ground water and poor soil conditions. This further led to the creation of a sinkhole in the work zone.”
It added that the non-competitive emergency contract was needed to allow the contractor to “review the impacted area and safely proceed with the micro-tunnelling boring machine rescue operations, including destressing and removing steel tiebacks; and, jet and compaction grouting to stabilise the ground.”
