Tunnel Structure
Steel arches, linings, rock support and pipe roofs.
Overview
Tunnel support starts right behind the excavation face. I-beam arches and lattice girders hold the ground, welded mesh and shotcrete form the initial lining, and steel pipe is used as pipe-roof or small-duct pre-support where the ground is weak.
Steel use follows the excavation rate and ground conditions, which can change quickly. A reliable supply of the right sizes matters as much as the unit price, because a shortage at the face can hold up the whole heading.
Where each steel product is used
| Structure | Steel product | Typical grades / standards |
|---|---|---|
| Steel arches for initial support | I-beam | Q235B, I16–I22, GB/T 706 |
| Lattice girders and permanent lining | Rebar | HRB400, GB/T 1499.2 |
| Shotcrete reinforcement | Welded steel mesh | GB/T 1499.3 |
| Pipe roofs and pre-support | Seamless pipe | 20# / Q345B, GB/T 8162 |
Grades shown are typical examples. The project's design documents and applicable codes decide the final specification.
Common standards: GB/T 706, GB/T 1499.2, GB/T 1499.3
What the project needs
- I-beams bent to arch profiles
- Welded mesh and rebar in project quantities
- Steady supply matched to excavation progress
What to consider when selecting steel
Arch forming
I-beams are bent to the tunnel profile, usually in segments. Section size and bending radius should be checked against the drawing and the transport limits underground.
Matching supply to ground class
Support types change with the rock class. Keep a stock plan for the likely range of arch spacing, mesh and pipe sizes.
Pipe-roof details
Pipe diameter, wall thickness, joint type and grouting holes must suit the drilling rig and the ground. Confirm these before producing the pipe.
Recommended products
What to include in your inquiry
- I-beam sizes, arch drawings and segment lengths
- Mesh size, wire diameter and sheet dimensions
- Pipe size, threaded or welded joints and hole patterns
- Monthly demand forecast based on excavation rate
Frequently asked questions
Can I-beams be supplied already bent?
Bent segments can be requested to drawing. Many projects also bend beams at a site workshop, so compare both options at the quotation stage.
What pipe is used for pipe roofs?
Seamless and welded pipe are both used, depending on the design. The pipe size and joint must suit the drilling equipment.
Can rebar and mesh be delivered in project quantities?
Phased delivery can be discussed for project volumes. A forecast from the excavation programme helps to plan supply.
Photos: tunnel boring machine — “2012 Eurotunnel tunnel boring machine 02”, Wikimedia Commons, CC BY-SA 4.0.