Thames Tideway has awarded a further three contracts for cast-in gaskets for the East section of the main tunnel, the Greenwich connection tunnel and the Frogmore connection tunnel. All three were awarded to UK based seals and gaskets manufacturer VIP-Polymers, who already have the contracts to supply the Central section of the main wastewater tunnel and Beckton shaft and syphon tunnel projects.

Sites where VIP cast-in gaskets will be used

The Thames Tideway project is required to upgrade the outdated combined sewer system that was built in the 1860’s. Originally designed for a population of 2 million, it now lacks the capacity to serve a population nearing 9 million, which continues to grow.

The VIP patented cast-in gasket is designed to eliminate cracking and spalling of concrete segments caused by solid corners. Solid corners result from the traditional ‘shot joining’ manufacturing process to join lengths of extruded gasket profile together to form the trapezoid gasket that encompasses the concrete segment.

As the gasket is unable to compress at the corners, higher loads are experienced which can lead to cracks and spalling. VIP’s innovative gasket allows compression performance that is virtually uniform around the entire gasket, ensuring that loads experienced when the segments are closed together do not exceed the specification of the design.

The 8.5m o.d. East section of the main tunnel will connect to the Central section at Chambers Wharf and travel 5.5km East, terminating at Abbey Mills pumping station. Gaskets are being supplied to a Max Bogl / Tarmac joint venture, who will cast the gaskets directly into the segments which eliminates the need to glue them in at a later stage.

35mm gasket profile for deepest sections

At depths of between 45m and 65m, this is the deepest section of the tunnel where the ground is predominantly chalk. Due to these conditions, a 35mm profile is being used to cope with the higher water pressure at the deepest point of the tunnel.

For the 4.6km long, 6.1m o.d. Greenwich pumping station, a 28mm cast-in profile will be used. This tunnel connects to the main tunnel at the join between the Central and East section and to the Greenwich pumping station.

“It is great to be involved with all sections of the project from West through Central to East. Collaborating with several different stakeholders from the design teams through to the contractors and precasters involved, the VIP cast-in system offers assurance for longevity of the structure and reduction in unplanned future expenditure,” said Matthew Levitt, VIP Business Development Manager.

The 1.1km of 3.2m o.d. Frogmore connection tunnel, connecting the West section of the main tunnel to the existing combined sewer overflow at Frogmore storm relief-Buckhold Road will use the VIP 28mm cast in profile gasket.

Patented gasket design spreads load

For Frogmore, VIP will supply gaskets to segment pre-casters FP McCann, who they also worked with on the Glasgow Shieldhall tunnel, and for the East and Greenwich tunnels VIP will work with the Costain, Vinci Construction Grands Projets joint venture (CVB) who were also the contractor for the Glasgow Shieldhall project.

“CVB selected VIP cast-in gaskets for waterproofing the Shieldhall tunnel lining as they offered the best option for moderate corner compression loads and consequent avoidance of segment damage arising from ‘hard corner’ overload.

The gaskets performed extremely well in service with no related segment damage and excellent groundwater exclusion.

On the basis of their performance at Shieldhall, CVB specified VIP gaskets for the tunnels at Tideway East, and Costain specified VIP for the Tideway overflow tunnel at Beckton,” said Tony Parsons, Director of Engineering (Tunnelling) at Costain.

Casting for the projects began in August 2018.

Two major tunnelling projects in the United Kingdom and India will be completed using tunnel segments with cast-in gaskets designed to reduce segment cracking from UK based VIP Gaskets; The 12.7km Thames Tideway Central wastewater tunnel in London and an extension to the Mumbai Metro.

"Winning contracts for both projects demonstrates our ability to deliver a wide range of products and technologies for supporting major water and transport infrastructure projects anywhere in the world.

Tunnel segments ready for Thames Tideway Central

"These are exciting tunnelling projects that are vital to the sustainable development and growth of two great cities, and we're delighted to be involved with them," said Matthew Levitt, VIP Technical Business Development Manager.

The Thames Tideway Central is the longest of three sections of a 25km tunnel, due for completion in 2024, and designed to prevent the discharge of untreated storm water and sewerage from 34 combined sewer overflows into the tidal River Thames.

The Ferrovial Agroman and Laing O'Rourke (FLO) JV has commissioned the gaskets for the central section, which runs from Fulham to Blackfriars and will have 6,100 tunnel segment ring sets with a 7.8m i.d. VIP is supplying its cast-in gasket with patented corners to Spanish tunnel segment pre-caster Pacacar for the section. Supply commenced in December 2017.

Recent success with the VIP compliant compressible corner technology includes the 5km Shieldhall wastewater tunnel in Glasgow, commissioned by Scottish Water.

VIP has also been commissioned by J Kumar Infraprojects to supply gaskets for the Mumbai Metro Line 3 (Packages 5 and 6) tunnel, which is being built for the Mumbai Metro Rail Corporation, a joint venture between the Indian Government and the Government of Maharashtra.

The project involves the construction of a 4.5km twin tunnel, with a 6.6m o.d. requiring a total of 17,800 tunnel segment ring sets. Production of the glued-in gaskets selected for the tunnel has already begun at the VIP factory in Huntingdon.

VIP has previously supplied gaskets for the four phases of the Delhi Metro project and the Ghatkopar High Level Tunnel in Mumbai.

"The gasket has been specifically developed as a modification of our VIP024 gasket to provide additional sealing assurance sought by project engineers as the tunnel passes under the Mithi River," said Levitt.

Construction of the largest waste water tunnel in Scotland has been completed with the help of a new tunnel segment sealing gasket developed by VIP Polymers. The 4.9km long Shieldhall tunnel beneath Glasgow has been one of the first projects to make use of the rubber gaskets manufactured by VIP, designed to reduce the risk of segment cracking during installation.

VIP gaskets contributed to zero segment cracking from high corner contact pressure

The TBM broke through in October 2017 after 15 months excavating the 4.7m-diameter tunnel for Scottish Water. Its journey from Craigton to Queen's Park, across the south of Glasgow, has created the largest-diameter bored tunnel in Scotland.

Construction JV Costain Vinci Construction Grands Projects chose VIP Polymers to supply cast-in tunnel segment gaskets with compliant compressible corner technology to ensure consistent load performance along the entire gasket perimeter. This eliminates the risk of a build-up of pressure at one or more of the gasket's corners during installation, which could contribute to segment cracking.

"Our new cast-in gaskets have performed very well throughout the Shieldhall tunnel construction process, demonstrating reliability,” said Matthew Levitt, VIP Technical Business Development Manager.

Gasket being installed in a segment mould

VIP cast-in gaskets at FP McCann's segment production centre

"The steel fibre reinforced concrete segment manufacturing process was achieved within the tightest of specifications and the VIP gaskets contributed to an exceptionally well-built tunnel, with no reported segment cracking arising from high corner contact pressure, or segment ram loading transfer, cracks or leakage, meeting the tunnel lining specification without compromise,” said Sam Simons, Tunnel Lining Supply Manager for Costain.

Prior to manufacturing any gaskets, members of the Costain waterproofing team witnessed corner loading (T and Cruciform) and pressure testing of the gaskets in VIP's testing facilities in Huntingdon.

Over the last 18 months, VIP has manufactured more than 19,500 individual TSGs for the project which have been cast into each tunnel segment at FP McCann's site in Drakelow, Derbyshire, England.

"The geometry of the segments meant that the gaskets required intricately formed corners to fit the steel moulds correctly and provide a draft angle to the sealing face of the key and adjacent segments along the Z axis,” said Dave Derbyshire, Operations Manager for Underground Products at FP McCann. "Technical representatives from VIP visited our facility at Drakelow prior to segment production, to ensure the correct fit was achieved on all six segment types.”

The £100 million Shieldhall tunnel is one of the most important wastewater infrastructure projects in Glasgow since Victorian times. It will help tackle flooding and improve river water quality across the city and will provide 90,000m³ of extra storm water storage.

The cast-in rubber gasket compressible corner joint system designed by VIP Polymers to reduce the risk of tunnel segment cracking during installation has been awarded a UK patent.

Tunnel under construction with VIP patented gaskets

The new compliant compressible corner system ensures a consistent load performance along the perimeter of the tunnel segment gasket to avoid build-up of pressure at one or more of the gasket corners during installation which can lead to segment cracking.

“The design and manufacture of our new compressible corner joint, which is used across our range of cast-in gaskets, has been recognised with a UK patent and an international patent pending,” said Steve Casey, VIP Sales and Technical Director.

“Segment cracking during tunnelling operations is a major cause for concern for tunnel designers and tunnelling contractors as it can be costly and we sought to address this when designing the new corner joint. Our new design has been favourably received, used in a number of tunnel-building projects, and been chosen for use in future projects.”

Most cast-in segment gaskets are made with conventional shot-joint corners. During the moulding process, the rubber in these corners fills the compression cavities in the extruded gasket sections, creating a solid rubber corner. When these tunnel segments are installed, the compression of solid corners is limited and can lead to corner point loading, increasing the risk of segment cracking.

Close-up of VIP Polymers cast-in tunnel segment gasket

The VIP patented corner joint is created with a particular joining process that maintains the gasket profile right to the corner edge. This makes the complete gasket compliant with all specified load requirements and provides greater assurance to designers, builders, and clients on the quality of the segmental ring build.

Rigorous comparative tests have shown that solid corner joints are harder to close, resulting in increasing loads. In contrast, the VIPcorner joint maintains a uniform closure performance around the full cast-in gasket.

The new corner joint can also be manufactured to a variety of angles from90 degrees, to obtuse or acute allowing the gasket to be moulded to the exact shape and angle of each segment in the design.

The profile orientation can also vary along the Z axis of the gasket which helps with the precise installation of final segments, or non-uniform segment systems, to again reduce the risk of segment damage or partial sealing of joints.

“A multi-disciplinary team of sales, laboratory, and product development departments has contributed to a new product that is now being used on international tunnelling projects, and can save the tunnelling industry both time and money,” said Casey. “Test results and positive feedback from within the industry are testament to the collaborative effort from staff at VIP.”

VIP gaskets are manufactured from the company headquarters in Huntingdon, Cambridgeshire in the UK.