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

The new ‘compliant compressible corner’ ensures delivery of consistent load performance along the entire perimeter of the tunnel segment gasket (TSG).

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.

VIP, based in Huntingdon, Cambridgeshire, is a global leader in the manufacture of rubber seals and gaskets for the tunnelling and water utility industries.

Steve Casey, VIP’s Sales and Technical Director, said: “We are delighted that the innovative design and manufacture of our new compressible corner joint, which is used across our entire cast-in gasket range, has been recognised with a UK patent. An international patent is also pending.

“Segment cracking during tunnelling operations is a significant cause for concern for both tunnel designers and tunnelling contractors. It is this concern we directly sought to address when we set out to design this new corner joint.

“Our innovation has been very favourably received within the tunnelling industry, and has already been used in a number of tunnel-building projects, with excellent results. VIP’s design has already been specified for use in future tunnelling projects.

“Tunnel segment cracking is a hidden cost in all tunnelling projects, through the need for post-installation repairs and other associated costs. By using our new corner joint, tunnelling companies can reduce the risk of TSGs contributing to these costs.”

Most cast-in TSGs 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 the tunnel segments are installed, the compression of solid corners is very limited, which can result in corner point loading, thus increasing the risk of the segment becoming cracked.

Caption: Tunnel incorporating VIP's Patented gasket

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

These benefits have been demonstrated through rigorous comparative testing. This has shown solid corner joints are more resistant to closure, resulting in increasing loads, which could, potentially, affect closure between segments. In contrast, VIP’s new corner joint maintains a uniform closure performance around the whole TSG.

The new corner joint can also be manufactured at a variety of angles – 90 degrees, obtuse, and acute – so the TSG can be moulded to the exact shape and angle of each segment in the design. No tunnelling project is the same, however VIP can ensure a perfect fit, regardless of the shape of the segment.

VIP can also vary the profile orientation along the gasket’s Z axis. This can greatly help with the precise installation of final segments, or non-uniform segment systems, again reducing the risk of segment damage or partial sealing of joints.

Steve Casey said: “A multi-disciplinary team across our sales, laboratory, and product development departments has contributed to a new product that is now being used on international tunnelling projects, and is an innovation that can save the industry both time and money.

“Excellent test results we’ve witnessed, through to the positive feedback received from within the tunnelling industry, are testament to the hard work and collaborative effort put in by everyone at VIP.”