Tunnelling Products Range

Spear Bolts and Sockets

Spear bolts and the accompanying ‘cast in’ sockets are used to permanently fix tunnel segments together and can be used in both the radial and circumferential joints.

The major advantage of the spear bolt is that following installation, only one pocket per connection requires finishing.

We manufacture and supply the complete range of sizes from M16-M30 diameter with lengths to a customer’s specification. Other non-standard sizes can be made to order.

Mild steel 4.6 and high tensile 8.8 grades are standard. Other grades are available on request.

Spear bolts are supplied self-colour, galvanised or sherardized as standard but once again – other finishes are available where specified.

Curved Tunnel Bolts

Curved bolts are used to permanently fix tunnel segments together through a radius hole. They can be applied to both radial and circumferential joints.

A complete range of this product is readily available from M16 to M30 diameters. Length and radius can be made to a customer’s specific requirement.

Mild steel 4.6 and high-tensile steel 8.8 grades are standard with other grades available on application.

Curved tunnel bolts can be supplied in a range of finishes.

T-Head Bolts

T-Head bolts have been specifically developed for use in shaft construction. Typically, they are used when constructing a shaft using the underpin method.

These bolts can be manufactured in a range of sizes to suit the segment widths.

As with all other bolts, T-Head bolts come in a range of finishes and grades.

Our ModuLock Connecting System

Connecting systems are many and varied with new versions constantly in development.

Our ModuLock system was designed to meet the highest standards of performance demanded by the modern tunnelling industry.

It was designed to be the strongest, self-aligning locking connecting system in the world.

Our ModuLock system consists of a connecting dowel moulded from high strength, high durability plastic together with two locking assemblies, one cast into each adjacent tunnel lining segment.

Significantly, the ModuLock system can restrain the forces generated by both hydrophilic and compression gasket types, minimising joint gaps and offsets.

Our ModuLock system is uniquely flexible and can be used in all types of tunnel lining including trapezoidal rings whilst the non-ferrous quality promotes a long tunnel life.grades

Grouting/Lifting Sockets

Grout/Lifting sockets can be used for a variety of precast applications. Designed to be bi-functional, these sockets can be used in conjunction with the TBM’s segment erection system to lift segments into place in the ring, or for primary or secondary grouting through the segments.

They come in varying sizes and lengths to suite individual contract requirements. From the 80 mm long socket for casting at the bottom of the shear cone for vacuum erectors to the extendable sockets that with the addition of a plastic tube can be extended to any desired length.

They are manufactured in traditional triple start threads as well as single start threads and can be manufactured with closed or open ends. This range of sockets comes with a selection of accessories:

  • Grout Plugs to close off the inside of the sockets, normally used with a sealing ring and which can resist pressures up to 20 bar.
  •  Non-Return Valves for use during grouting to prevent the flow of grout back through the socket before the plug is inserted.
  • Hydrophilic Seals can be applied to the outside of the socket to prevent water passing between the socket and the concrete segment.
  • End Caps can be fitted to the open sockets or extension tubes to prevent ingress during casting.
  • They can also be used to prevent any debris

Complementary Products

We manufacture a range of complementary products for the tunnelling market.


Guide rods are extruded pieces of solid plastic that come in a variety of diameters and lengths to suit different ring sizes. They are glued into cast semi-circular groves in the radial face of the concrete segment. Once erected, the rod seats in a similar cast grove in the corresponding segment to eradicate any misalignment in the connection. Packers are simple and cost-effective products control the position between the concrete segments, providing a good shear resistance and full control of tight tolerances and slip hazards.


Plastic injected alignment dowels are used in conjunction with a straight bolt connection system to assist alignment in construction on the circumferential joint. They are placed into corresponding cast voids in the segments with the bolts passing through the centre of the dowel. They can be manufactured from a range of materials. This helps to maintain the integrity of the primary sealing system.


Segment spacers are an inexpensive alternative to wooden blocks and are positioned between the segments while they are stacked in the casting yard or during delivery to the back of the TBM. They are hard wearing and re-useable and can mean significant cost savings over the course of a contract.


Hole formers are small plastic sockets that are fixed into the moulds during the casting of the segments. When de-moulded these leave small holes in the segments for subsequent fixing of bracketing or other temporary or permanent items either  during or post construction. These negate the need for drilling multiple holes into the  segments after erection.


Cable Hangers are used extensively throughout rail & public mass transit systems for supporting power, signal and comms cable runs – this includes LVHV cable support and hanging for multi-core and bundled cables on extended horizontal cable runs and hanging cables on walls and support structures, e.g. tunnel cable installations and lighting system.

In addition to all the itemised products, we also manufacture and supply many other related items both standard and bespoke. These include; washers (in steel and plastic), grummets (in plastic and rubber) and varying ring seals (in nitrile and hydrophilic rubber). In-house manufacturing, adaptive tooling and design capability give us the flexibility to develop specialist, ‘one off’ products for clients from concept through the prototype stage to the finished product.