Tunnels are a common element of modern-day engineering, but that doesn’t take away from the fact that they seemingly defy gravity to the untrained eye. So how exactly do tunnels stay solid, and how is steel used to reinforce them?

Let’s take a look at some of the functions and uses of steel when it comes to building tunnels and keeping them sturdy. 

Lattice Girders – Steel in Tunnels

One use of steel in tunnels is in lattice girders, which can provide great levels of support when combined with shotcrete. Lattice girders are made out of steel bars welded together in a triangular shape, built to the shape of the tunnel, and tend to be lighter and easier to use compared to other steel products. 

So not only do lattice girders help the tunnel become sturdier, but they can also help builders be more efficient with their shotcrete use. 

Rock Bolting and Anchoring

For tunneling in soft or hard rock, the easiest and fastest way that builders can keep the rocks secure in place is to use steel rock bolts and anchors. Rock bolts are inserted into a drilled hole in the sidewall or roof of a tunnel, and are relatively easy and quick to install, and affordable. 

There are many different styles, shapes, and sizes of rock bolts and anchors, so each tunnel will use its own type, but in general, these are widely used in tunnel construction. 

Mesh Reinforcement

Another common use of steel in tunnels is mesh reinforcement. The product is made up of steel bars welded together at 90 degree angles to create a grid-like pattern. These are typically inserted after the rock bolts are in place, and get welded to the bolts to stay in place. 

Each new piece of mesh reinforcement place should be welded to the existing mesh sheets in place, as this gives added integrity to the whole structure. Plus, once the shotcrete is installed, the mesh provides added support

So now that you have a better idea of how tunnels are reinforced and supported by steel, you should have a clearer understanding of why they don’t collapse.

(Written by Bailey Schramm)