4 Popular Tunnel Construction Methods You Need to Know

Tunnel construction makes up a significant component of our world’s civil engineering infrastructure. Just look at a map. The instances are here, there—everywhere.
Each included its fair share of unprecedented construction challenges.
Take the world’s longest road tunnel, the Laerdal Tunnel in Norway, which carries two lanes of traffic through a mountain range.
Or the Gotthard Base Tunnel in Switzerland, the world record-holder for longest rail tunnel. It passes under several mountain massifs.
The Seikan Tunnel in Japan, the longest underwater rail tunnel, is submerged under a seabed. At the same time, the Drogden Tunnel in Denmark is a bridge that slants down into a tunnel, carrying road and rail transport aboveground, then underground.
No wonder tunnel work and engineering are considered two of the most specialized—and challenging—construction arts.
There are other types of tunnels, too, which enable cable, pipes, drainage, sewage, and water supply to flow freely beneath our feet, roadways, and buildings. Each requires a different kind of method of tunnel construction.
But what are those methods? Why are they used, and when? The answers to those questions depend on numerous factors, including:
  • Geometrical configuration
  • Geology
  • Route path
  • Support and lining
  • Ground condition
  • Type of crossing
  • Project requirements
  • Environmental requirements

Let’s detail four common methods used for tackling the above variables, plus the advantages to each.
Why the Cut-and-Cover Tunneling Remains So Popular
Cut-and-cover is the oldest method of tunneling. It’s also the go-to method for relatively shallow tunnel construction in soft-ground conditions when safe excavation is possible from the surface without the wall of the excavation failing.
In essence, here is what happens: You excavate a trench from above ground, construct the tunnel within the channel, then backfilled it with new or excavated soil to return the surface to its original state.
It’s a common tactic for the construction of underpasses and tunnels in flat terrain. Another interesting tidbit is that this method is also executed in the construction of many underground train and subway stations.
In many cases, it’s the most economical construction method. It also tends to be more disruptive, though a well-planned top-down cut-and-cover construction method (as opposed to a bottom-up approach) can drastically curtail disruption.
How Tunnel Boring Speeds Up Your Project
Bore construction differs in that tunnels are built without excavating the ground surface. The process involves digging a tube-like passage through the earth and installing linings. It’s a standard method for drilling a tunnel through a mountainside, thus its nickname mountain tunneling, though it also applies to other applications, like tunning underneath large bodies of water.
The technique includes the use of a Tunnel Boring Machine (TBM) device, which uses a massive, rotating wheel at the front to barrel through rock, sending waste material to the back of the machine for disposal. Bored construction works as a strong substitute for conventional tunneling methods that involve explosives and extensive manual labor.
This method, which can handle various ground conditions, traditionally takes place at the portal or a shaft, limiting the impact on traffic, air quality, noise pollution, and nearby utilities. Industry leaders agree that it is a more efficient, faster way of digging and building tunnels beneath towns, cities, rivers, and tall structures.
How to Drill and Blast Your Way Through a Tunnel Project
Another tunnel construction technique for drilling through mountains without lining is the drill-and-blast method, which utilizes a tactic that bore tunnel construction avoids—using explosives to break up soil and rock.
Here’s the consensus of what happens: You drill holes into the rock surface, install explosives into the holes, then kaboom. After detonation, the fragmented rock and soil are mucked—or moved—out of the tunnel. Don’t forget to install support before doing additional blasting.
Advantages include less disturbance to local traffic and the environment compared to the cut-and-cover approach. Compared to using a TBM machine, vibration levels are generally higher, though the initial costs are traditionally lower.
Why Microtunneling Is a Win For Utilities
As we said before, not all tunnels have massive forms of 20th-century transportation running through them, nor are they always enormous in diameter. They can—and are—far smaller.
Take microtunneling, which, as its name suggests, is a method for constructing small tunnels typically only a few feet in diameter.
The construction method installs drainage or other municipal infrastructure. It’s most popular with the utilities construction sector.
A trenchless tunnel construction technique, the process excavates a borehole before cables or pipes are laid down concurrently. Personnel entry is not required for routine work. The microtunneling boring machine (MTBM) is remotely operated from the surface, using a closed-circuit television (CCTV) to control the machine’s location and orientation to ensure the boring accuracy.
The technique allows cables and pipes to crisscross underneath roadways, rivers, harbors, rail tracks, and runway taxis at airports—without disrupting any surface traffic. It is often a chosen method for environmentally sensitive areas.
It’s mostly a remote-controlled, continuously supported, pipe-jacking method since the boring machine is pushed through the soil by pipes. However, it’s more pricey than traditional pipe jacking—for a good reason. Pipes and cables that require pinpoint precision over curved or exceptionally long distances need this construction process.
What Kind of Tunnel Construction Do You Need?
Tunnels make life easier for towns, local businesses and commercial trade to communicate and move around—if it’s completed with the right type of construction method and industry expertise. Like your structure, your construction crew needs to be versatile and efficient. Your budget and schedule have little wiggle room. Neither should your project.
Consider contracting a global expert in delivering superior trenching projects in a variety of complex environments and urban applications today.
Posted: 8/4/2021 1:44:51 PM