The most accessible tunnels in the world are those which cut through the earth enabling a canal to pass through. There are commonly tow-paths next to the canal where popular walks exist; this enables safe photographing opportunities. Alongside and within the canal is a unique, manmade habitat and wildlife can be seen co-habiting with mankind. Also, colourful canal narrow boats are often moored nearby.
We are looking for both disused and used Canal Tunnels in this category.
A canal is a manmade channel for water. They are used for creating manmade waterways which are navigable by transport and can carry boats shipping goods and people.
How Tunnels are Constructed for Canals
A canal tunnel is a method to cross an area of land, where a bridge is not appropriate. They have an opening at either end enabling the boat to traverse from one area to another; these ends are known as the ingress and egress.
Generally a tunnel is longer than its width. As they are manmade passages they normally have a horizontal orientation with a vertical entrance. This is often sealed with a surround and many tunnels are lined with bricks/tiles/concrete etc. Lining techniques include sprayed concrete, steel arches, rock bolts and mesh. However, there are also tunnels which are bored through the earth’s rock and they are left with the exposed rock on display, sometimes with suspended netting to catch any loose rocks which fall.
Investigations are always necessary before a tunnel is constructed. These assess the nature of the substrate that is going to be bored, with boreholes and pilot tunnel runs. Ground water is a major factor as is the type of soil or rock; this defines the machinery needed to create the tunnel. A method used to prevent ground water flooding tunnels, is to lay pipes which are cooled until the earth around them freezes, preventing leakage of water through the soil; another common way is to lay pipes and pump water out of the tunnel.
The main types of tunnel construction we might see in this category consist of:
Cut and cover tunnels – these are areas of earth which are cut out then covered over once the structure of the tunnel is in place.
Bored tunnels – bored through the earth or rock as it is and usually with a circular or horse-shoe cross-section.
Manual techniques of tunnelling include Clay-Kicking where an almost silent method of extracting clay was used. This was popular in the Victorian period and was used during the First World War.
Today Boring Machines are used as they are fast, effective and automated. An operator still has to renew machinery parts and they rely on balancing the water pressure ahead of the tunnel to create a safe passage. This process replaced the method of using compressed air where the operator had to stay in a decompression chamber to relieve decompression sickness afterwards.
Along the route of a tunnel there are often shafts. These are features in our landscape hiding an underground world beneath. Shafts are used to lower boring equipment down into the tunnel so it can be completed. When the tunnel is finished the shafts remain and act as ventilation points; these structures alone are feats of engineering in their own right with their circular, strong design.
Tunnels need maintenance and stand-up time is an estimate as to how long the tunnel will stand-up to its purpose; supporting the weight and forces around and on top of it.
Tunnels are hidden, enable the earth to grow above them, can have entire cities above them and can be less easy to destroy in acts of war. They can also cross long distances. Along a canal a tunnel enables the water to be held more effectively as many locks traversing a hill suffer from a drop in water and are time-consuming for canal users to pass along.
Use of Canal Tunnels
In some cases the towpath continues through a canal tunnel, but when it doesn’t the horse which pulled the narrow boat was led over the top of the tunnel. The boat would be transported through the tunnel by a process known as legging. This is where the person lies on their back on top of the boat and pushes the boat along with their feet on the tunnel roof.
When the early canal tunnels were built they were often constructed by miners. They would sink shafts and tunnel along and hopefully meet at a designated point, but these were the days without technology and kinks in tunnels exist today because the point was missed!
Underground water, quicksand and difficult rock formations caused much difficulty and many workers lost their lives whilst constructing canal tunnels. There is an interesting website available here which describes these tunnels and gives examples: Canal Junction
Canal Tunnels can be found across the world including the following locations:
Paw Paw Tunnel on the Chesapeake and Ohio Canal, USA
Union Canal Tunnel in Lebanon County, USA
Blisworth Tunnel on the Grand Union Canal, England
Foulridge Tunnel on the Leeds and Liverpool Canal, England
The Burgundy Canal Tunnel in France
Malpas tunnel in France
Some of the longest canal tunnels can be seen here: Visit This Website