Fasteners for Metro & Shield Tunnel Linings

Fastener types for tunnel linings

What the tunnel lining has to resist

A metro or shield tunnel is a wet, confined structure that is assembled segment by segment under time pressure. The bolted connections therefore have to do more than hold two pieces of steel together. They locate the ring during erection, maintain joint compression, survive repeated loading and remain inspectable after the tunnel is in service.

• Geometry first. A curved bolt that does not follow the segment duct cannot be pulled through, however good its mechanical properties. Bend radius, chord length and thread position belong on the drawing.
• Consistent preload. The bolt, nut and washer work as a set. Coating friction changes the torque coefficient, so the assembly torque has to match the surface condition actually supplied.
• Corrosion protection for the life of the lining. Groundwater, humidity, chloride ingress and wash-down can all affect exposed or recessed steel. The coating system should follow the exposure and the specified salt-spray duration.
• Traceability after delivery. Material certificates, inspection records and batch marking let a pallet on site be connected back to the production run.

Fasteners by location in the tunnel

Segment bolts: the ring geometry decides the part

The segment bolt is usually the first item to lock because it cannot be corrected on site. Curved bolts are bent to suit the circumferential duct; longitudinal bolts run straight through consecutive rings. Both are commonly supplied in M16 to M36 with property class 8.8 or 10.9, although other diameters and grades can be produced to drawing.

For a curved bolt, send the radius measured to the bolt centreline, the chord and the overall length. Also state where the threaded length starts, which end is assembled first and whether the nut sits in a recess. A drawing that gives only “M24 curved bolt” leaves the two dimensions that decide whether the part fits.

Thread form also matters. A trapezoidal thread may be specified for segment bolts, while other projects use a metric coarse or fine thread. Tell us the gauge or standard to be used rather than relying on a nominal diameter alone. The same applies to the nut: property class, thread tolerance and coating have to match the bolt set.

See the full segment bolt range and coating notes →

Channels and embedded parts: adjustable versus fixed

Cast-in channels and anchor plates both create a connection in concrete, but they are not interchangeable. A channel leaves a continuous slot, so the fixing point can move along the profile after casting and no site welding is needed. An embedded plate creates a fixed, high-capacity connection at one location. Tunnel projects often use both: channels for services and secondary supports, plates for the main equipment or structural interfaces.

• Keep the channel slot clean. Fit the specified slot filler before the concrete pour. Once the profile is filled with grout, cleaning it can damage the lips and the T-bolt may not seat.
• Supply channel and T-bolts together. Slot width and tooth pitch differ between manufacturers. A matched set removes a common site mismatch.
• Freeze the embedded-part drawing before casting. Plate position is controlled by formwork and setting-out, but plate size, bar length and weld details are manufacturing decisions that have to be right before production.
• Agree the weld and coating sequence. Embedded assemblies are normally welded first and galvanized afterwards, so the weld is protected as well as the plate and bars.

Read the cast-in channel guide or see embedded plate and anchor bar details →

Coating selection for tunnel exposure

Do not carry one torque value across different coatings. The friction coefficient changes the preload produced by the same wrench setting. Confirm the assembly torque against the coating and lubricant of the batch actually supplied, or ask us for the torque coefficient for the production lot.

Inspection and documents

Routine checks cover dimensions, thread, hardness, coating appearance and marking. Tensile or proof-load testing and neutral salt spray at 240 h, 480 h, 720 h or 960 h can be specified according to the coating system and exposure. Material certificates and factory inspection reports are issued with the goods; independent third-party testing can be arranged when the contract requires it.

• First-article check against the drawing before the batch run
• Bolt, nut and washer properties matched as a set
• Heat number carried through to the packing list
• Batch and packing identity preserved for site traceability
• Third-party hardness, tensile and salt-spray testing on request

See the quality control and testing page →

Project experience

Huilang fasteners have been supplied into metro and shield-tunnel lining works in more than twenty cities across China. Company project experience also includes the Beijing–Zhangjiakou railway, the Hong Kong–Zhuhai–Macao Bridge project, undersea tunnel works in Shanghai and underground utility tunnels. These are given as project types and regions; current project references can be discussed directly with our sales and technical team.

What to send for a tunnel fastener quotation

Reducing interface risk before the first batch

• Approve the drawing revision, not just the part name. Record the revision that was quoted and produced so a later duct or plate change does not reach the site unnoticed.
• Check a first article. A bent bolt, channel assembly or welded plate is cheaper to correct before the batch than after packing.
• Keep the set together. Supply bolt, nut and washer from the same batch where torque verification matters.
• Pack by ring or installation zone. Clear marks on bags, boxes and pallets reduce sorting in the tunnel and help traceability.
• Release against the programme. Staged delivery can keep material close to the installation sequence instead of filling the site yard.

FAQ

Do you make curved segment bolts to the ring radius?

Yes. Curved segment bolts are made to the drawing, with the bend matched to the duct geometry of the segment. Send the radius, chord length, overall length, thread and grade so the bending tooling can be checked.

Can bolts, nuts and washers be supplied as a matched set?

Yes. Supplying the set from the same production batch keeps the coating system and torque coefficient consistent. This is useful where the contractor has to verify assembly torque on site.

Which coating should be used in a tunnel?

It depends on humidity, chloride exposure and the required salt-spray duration. Zinc-flake coatings are common where a controlled friction coefficient is needed; hot-dip galvanizing gives a thicker sacrificial layer; stainless is used for aggressive chloride exposure. Confirm the system for the actual exposure.

Can you supply cast-in channels with the T-bolts?

Yes. Channel, T-bolts and nuts can be supplied as a matched system. Slot width and tooth pitch vary between manufacturers, so matching them avoids a bolt that will not seat correctly.

Do you work to project specifications and standards?

Yes. We work from project drawings and specifications, as well as common fastener standards. Send the governing standard, grade, coating and inspection requirements so they can be confirmed in the quotation.

What documents can be supplied with a shipment?

Material certificates, factory inspection reports and a packing list with batch identity can be supplied. Third-party hardness, tensile and salt-spray testing can be arranged where the contract requires it.