Works took 7 years in total:

Tunnel works started July 1957

First tunnel opened July 1963

Second tunnel opened March 1964.

Total cost - £10,500,000.

The average house price in 1964 was £3,600, a small car cost £500. To build it today would cost £200million.

Estimated numbers in planning - 9000 daily

Actual Number of Vehicles in 1965 - 22,000 daily

Number of Vehicles in 2004 - 65,000 daily.

No, the cycle paths run under the road tunnels.

Although the Clyde tunnel appears to be an arch, it is in fact a complete circle, with ventilation shafts and cycle routes underneath. (See diagram)

The tunnel replaced two ferry routes; the Govan ferry and the Renfrew ferry.
(Bob explains - old ferries memory).
Photo: Ferry.

What was there before the Tunnel was built?
Ferry terminals, 250 houses, a church, as well as bowling greens and allotments.

They used a Tunnel Shield invented 139 years before by Marc Brunel for use in the Thames Tunnel. The Clyde Tunnel version was smaller, having space for 16 miners instead of 36.
Photo: Side view of Brunel's Shield

1818 -The ‘Circular Tunnel Shield’ was patented by Marc Brunel, who got the idea from watching a wood-boring worm while he was in prison for debt.

1825- Marc Brunel and his son Isambard Kingdom Brunel began work on the Thames Tunnel in London, using the Tunnel Shield. It was divided into 36 cells, each holding a miner digging independently.
Photo: Brunel's Shield. Thirteen years later...

1843 -The Thames tunnel was opened. This was an unprecedented success as the Thames River had quicksand under it, and all previous attempts had failed. They held a candlelit banquet in the tunnel to celebrate. It later became part of the London Underground.

1957- Clyde tunnel work started.
Completed 1964.
Photo: Clyde Shield

 

It was cylinder shaped, like a short piece of pipe.

The front end was divided into 16 cells, each cell had space for one miner digging with a pick axe or pneumatic drill.

The miners stood on platforms, in front of them were planks of wood holding back the soil. They would unscrew one plank and remove 18 inches (45.7cm) of soil from behind it. Replace that plank further forward, then unscrew the next plank and do the same. Eventually all the planks had moved forward by 18 inches; at which point, the whole Tunnel Shield was moved forward by pistons.

A cast iron hoop was then fitted into the new space at the back of the Shield, and bolted into place.

As you can imagine, progress was quite slow… Typically,

30 feet a week through soft brown clay
15 feet a week through gravel
9 feet a week through Boulder Clay
(see glacier - below)

A modern Tunnel Boring Machine can dig 250 feet (76.2m) a day

Thousands of years ago, a glacier travelling just south of the River Clyde cut a huge channel in the earth. It left behind it a trail of large rocks, gravel and sand.

Clyde Tunnel Engineers knew that the ground under the Clyde would be very unstable and likely to cave-in...(A bit like digging a moat around a sandcastle).

A small railway with open wagons took earth back to the surface, the wagons passed through airlocks to preserve the air pressure in the tunnel shield.

By injecting cement and clay into the earth as they went.

This stuck the gravel and sand together so that the walls didn’t collapse.

To stop water coming into the tunnel as they dug, they increased the air pressure in the digging chamber. If the air pressure inside the tunnel is higher than the pressure outside of the tunnel, it stops water and gravel coming in.
(graham explains - air pressure memory)

This technique is not used much today, as working under pressure is like deep sea diving. The miners had to be decompressed every time they came out into normal air pressure, to stop them getting ‘the bends’.
Photo: decompression chambers

Decompression could take over an hour each time. If it wasn’t done properly, the men had to be recompressed to the original pressure and go through the whole process again
(Photo: Air compression plant)..

It was discovered in the 1960s that working in conditions more than 2 times normal air pressure could damage your bones, (Bone Necrosis) because gases in the bloodstream stop oxygen getting to the bones and cause parts of the bone to die.

What are the symptoms of ‘the bends’?
To the outsider, the person can look as though they are drunk.
(Graham explains - drunk? memory)

During the digging of the Clyde Tunnel 469 workers had to be recompressed due to ‘the bends’ 71 cases were serious, as listed below:

Vertigo, nausea and vomiting	36
Collapse and/or unconsciousness	18
Severe abdominal pains	10
Respiratory distress	5 (2 fatal)
Pain in chest	1
Severe pains in head	1

This was caused by compressed air finding an escape route up into the river, it built up an air pocket and then burst out through the water in a huge fountain.
(Graham explains - explosion memory)

Modern Tunnel Boring Machines (TBM’s), like the ones that dug the Channel tunnel are as long as two football pitches and can dig 250 feet (76.2m) a day.

One of the TBMs used to dig the Channel Tunnel (from the English side) was later sold on e-bay for £39,999.
Another was driven off course and concreted into the seabed when it met the TBM from the French side. It is still there.

It is 762 metres long - approximately 7 football pitches. It is 21 feet (6.4m) below the river surface, depending on the tide.

In 1964 it was the steepest tunnel ever built. (1 in 16 ratio or 6%). If you imagine a piece of string looped between your hands, (your hands represent the tunnel ends) the deeper the loop, the closer your hands are. Engineers calculated the depth so that the tunnel would connect to existing roads.

57 seconds.

(There is a rumour that some cruel parents drive slower towards the end...)

Because ‘one way’ traffic has almost double the flow of ‘two way’ traffic. It also allows traffic to continue in one tunnel while the other is closed for maintenance.

Secret passage…
Although access is difficult (up a small ladder) it is possible to cross from one tunnel to the other at the lowest point (the “nadir”).

The tunnel roof is 16 ft 7”(5.05m) from the roadway, this is only just high enough for large lorries to get through. The road surface
is a ‘W’ shape ( i.e. higher in the centre and at the edges). This tilts the lorries slightly so that they fit into the widest parts of the roof.

The tunnel drips because the cast iron bands that form the tunnel arch, contract in cold weather. This makes a tiny gap, and allows a small amount of water into the tunnel (more so in the winter and at night). It collects in sumps sat the lowest point of the tunnels, and is pumped away.

The Clyde Tunnel actually leaks very little compared to other tunnels. Drips are more visible at the moment because the old pvc lining has been removed, it will soon be replaced with a new fire-proof lining.

The Portal Buildings at either end of the tunnels were given a nautical design, as they are near the Clyde Shipyards. They are filled with 18 huge fans that take away car fumes and pump fresh air in.

The North Portal building holds a control room with a high tech. camera system, it can sense if traffic has stopped and will sound an alarm. There are water pumps under both buildings, and one in the middle of each tunnel. Water and rain is collected in underground chambers and is then pumped into the main drain system.

If your vehicle breaks down, stay in your car.

The cameras will spot you and tunnel staff will come and help you. The current charge for this service is £36.