New segment gasket gets UK patent 02 Nov 2017

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.