Cast-in gaskets (also known as anchored gaskets or cast in situ gaskets) are integrated with the segment during the casting process.
This is opposed to being glued into a pre-made groove once the concrete segments have been cast.
Cast-in seals ‘anchor’ themselves to the segment as the concrete surrounds the legs at the base of the seal.
This process ensures a consistent positioning of the gasket around the segment.
The design of the legs ensures that the seal is secure in the segment and will not move during or after the segment is cast.
This is especially important during installation of the tunnel segments.
Benefits of Cast-in Gaskets
No need to apply adhesive
Cleaner to work with
Provide cost savings due to the removal of adhesive and the gluing process.
A more secure fit in the segment leading to reduced movement of the seal during installation and increased performance
UNIQUE CORNER JOINTING SYSTEM
No Solid Corners
Cracked or damaged segments caused by corner point loading has traditionally been a problem faced by tunnelling engineers and designers.
VIP’s Cast-in gaskets are designed specifically to eliminate this due to the unique patented (GB2541978 – international patent pending) corner jointing system.
This has allowed us to dramatically reduce the volume of rubber at the corners, thus ensuring the gasket can collapse into the groove and the load on the corners is equal to the rest of the gasket.
MINIMISING RUBBER VOLUME AT THE CORNER JOINT
VIP’s unique jointing process results in the profile of the gasket being maintained up to the corner edge. This ensures that the compression performance of the gasket is equal along the entire face of the gasket.
This differs to a traditional shot-joint corner which can result in excess rubber travelling along the gasket voids during the moulding process.
This results in making the gasket unable to compress at the corners due to the voids being full of rubber, creating a ‘solid’ corner.
The energy exerted at these points during closure of the segments can lead to cracks and spalling as it dissipates through the segment, finding the path of least resistance.
CORNER ANGLES THAT PERFECTLY MATCH THE SEGMENT
VIP can manufacture corners for cast-in gaskets to obtuse, acute and 90° angles, therefore matching the profile of the segment design perfectly.
90° Angles
Acute Angles
Obtuse Angles
Z Axis Angles
Segment design can differ with each project. Recognising this and the importance of the gasket matching the exact shape of the segment.
VIP can also vary the profile orientation along the Z axis.
The following profiles comprise VIP’s cast-in core range.
Further profiles are available or can be developed on request to meet specific design requirements.
Traditionally the industry has used elastomeric gaskets that are glued into pre-formed grooves in the concrete segments.
VIP manufactures a range of profiles which are compatible with many pre-existing segment mould groove designs.
The following profiles comprise VIP’s glued-in core range. Further profiles are available or can be developed on request to meet specific design requirements.
CORNER ANGLES THAT PERFECTLY MATCH THE SEGMENT
VIP’s glued-in profiles have corner joints that can be manufactured to match the angles of the segment design including 90°, acute and obtuse angles.
The corners are formed using an injection process in moulds that match the profile of the extruded gasket.
This ensures that when the segments are joined together, the gasket can collapse into the groove and the load on the corners is equal to the rest of the gasket.
VIP’s tunnel segment gaskets are manufactured in our Cambridgeshire headquarters in the UK, which is certified by The British Standards Institute to ISO 9001, using the latest manufacturing equipment and processes.
RUBBER COMPOUND
VIP compounds its own rubber at our on-site mixing facility to proven formulations developed by VIP’s rubber technologists. The compounds used meet WRAS and other internationally recognised standards where required.
Predominantly EPDM is the rubber of choice for tunnel segment gaskets as it provides the sealing and material qualities required. However in instances where resistance to more aggressive chemicals is required, VIP can compound and manufacture using NBR (Nitrile).
LIFE EXPECTANCY
A study carried out by Loughborough University in the UK on behalf of VIP concludes that one of the major elements affecting the gaskets’ long term sealing ability is ‘Stress-Relaxation’. This is the measurement of the force that a compressed gasket exerts over time which is crucial to the sealing performance.
The research also revealed that with correctly formulated and processed rubber, as supplied by VIP, the life expectancy of our gaskets is in excess of 120 years.
EXTRUSION
To begin the manufacturing process, VIP’s gasket profiles are extruded through one of the most modern microwave curing lines. This manufacturing technique creates the profile length by forcing the rubber through a die prior to curing. This is then cut to lengths determined by the segment requirements.
CORNER JOINTS
All VIP’s corner joints can be manufactured in obtuse, acute and 90° angles to perfectly fit with the corresponding segments.
Using the latest laser guided cutting technology enables virtually any joint angle to be achieved and their design ensures that the sealing properties and closure forces match the extruded gasket section.
QUALITY INSPECTIONS
In order to ensure the final product meets the high standards set by VIP, physical checks are made by our quality team both during the manufacture process and on final completed gaskets against:
Profile Size – to ensure a consistent profile shape during the extrusion process
Joint Integrity – to check the strength of moulded joints
Geometric Requirements – to check the shape of the finished gasket meets the segment design requirements
VIP’s laboratory and quality team undertake various tests and inspections throughout the manufacturing process of our TSGs.
These tests provide assurance that our products are produced to the highest standard and perform as expected.
Tests are undertaken on both the uncured rubber compound prior to manufacture with further tests on the final extruded product which check for:
Rheometry
Hardness
Tensile strength
Elongation
Compression set
Dimensional checks
Stress relaxation
Completed gaskets are finally checked on specially designed jigs to ensure they are the correct dimensions for the corresponding segment shape.
Tests Designed to Replicate Real World Applications
Gaskets are also tested at our UK headquarters in specially designed test rigs, which replicate the build of a segment ring in order to measure their performance.
VIP undertake a range of tests using T & X rig testing in order to replicate closure forces and pressures experienced both during the tunnel build and throughout the service life of a tunnel.
Pressure testing is undertaken at maximum and minimum gaps, and zero-to-maximum offset / deflection.
This replicates the gaps and displacements that occur between segments either as a result of building tolerances, changes in direction of the tunnel or due to the effects of ground movement.
VIP can recommend a number of approved adhesive suppliers for the application of glued-in gaskets onto the segment. If required, we can also arrange the supply of the adhesive.
LUBRICANTS
VIP recommends applying lubricant to the surface of the gasket during segment installation to assist the segments sliding into place.
This process reduces the friction between gaskets, ensuring corner positioning and reducing the risk of gaskets moving or pinching during installation which can potentially affect their performance. We can recommend and supply an appropriate WRC-approved lubricant.
STORAGE
TSGs should be stored in the same conditions as for most elastomeric products and ideally in accordance with ISO 2230:2002 (rubber products guidelines for storage). VIP can supply details upon request.
QUALITY
VIP operates a quality system, which is approved to ISO 9001 standard and certified by BSi. We are renowned in the seal and gasket industry for the high quality of all of our products, and our approach to quality extends to TSGs.
Available to download, VIP have created a new product brochure specifically for the tunnel segment gasket product group. The brochure includes details of our gasket corner jointing system which eliminates corner point loading during installation – often the cause of cracked and damaged concrete segments.
