Ex tunnel engineers Norman Ervine and Harold McCaughan look through photographs of their work from 50 years ago

On 19th December 2001 Your Place & mine received an email from Norman Ervine of Lisburn which said: "I worked on the tunnel as Assistant Engineer to the Resident Engineer 1950-51. I was present when the breakthrough was made. I well remember the celebrations afterwards!"

Having contacted him we learnt of another engineer, Harold McCaughan living near Bangor Co. Down. That one short email therefore opened a new chapter to the tunnel story. Norman Ervine also graciously provided all of the black and white photographs on this site including the all-important "meeting" picture on page 3.

The two engineers met with us in January 2002 and spent a great day discussing many of the details about the tunnel from their perspective. There were two groups of assistant engineers on the job. One group worked directly for the Consultant Engineers (Binnie, Deacon & Gourley) and the other for the Water Commissioners. Mr Ervine and Mr McCaughan were in the latter group. All engineers worked to a supreme boss known as the "Resident Engineer", who was a characterful and somewhat notorious Englishman called Dr Cyril F Colebrook who didn't much care for being around when dynamite was being used. Our engineers discuss..

Listen to Engineers discussing their chief

Which way is down?

The gradient of the tunnel was vital to ensure that the volume and flow of the water was what the engineers had predicted. It is easy to see how a mistake in these calculations could have had catastrophic results. Put simply, the tunnel intake had to be an exact prescribed height above the exit. In order to make sure that this was the case the contractors had to make a topographical survey of the land, taking precise levels the whole way round from the Silent Valley to Dunnywater, drawing a contour line as they went. Only then could the relative heights of the two tunnel mouths be determined. The man with the level (left) is Contractor's Engineer, Sam McMurray. The man on the right is the "chainman" - Mr. S McKibben.

An Ingersoll-Rand Drifter used for drilling deep holes in the granite face into which explosives were packed.

At the sharp end

Blowing up hundreds of tons of granite in a confined space is an exact science. A series of holes was drilled in the workface to a depth of about nine feet. The pattern and number of these holes was important in order to make the granite break out in the size and shape they wanted. The firing order of the charges was also extremely important, working from the centre outwards in very quick succession, only fractions of a second apart. Click here to view an interactive demonstration of the blasting process.

Engineer Harold MCCaughan

The drill was mounted on a frame rather like scaffold poles (seen here on left) which had to be reset for each and every hole. Later in the tunnel's development a more streamlined arrangement was used with just a single hydraulic leg, known as an "air-leg". In the picture on the left you can see a number of holes that have been bored.

The drill bit was tungsten carbide tipped and water-cooled. The drill-rig was powered by compressed air which was pumped from the outside world. Curiously the compressors were driven by engines from old Sherman Tanks. Harold takes up the story..

Listen to Engineer talk about the crude equipment

The lighting in the tunnel was provided by an outside generator. All of the equipment including the lighting rig had to be moved well away from the face for blasting as it would be destroyed otherwise.

View showing a flooded tunnel. The metal horseshoe ribs which were put in place to uphold the ceiling can clearly be seen.

A serious setback

It wasn't all plain sailing. When the Dunnywater team was well underneath the mountain the workers ran into what is somewhat understated as "bad ground". There is a huge fissure or 'dyke' in the middle of Slieve Binnian and when they ran into it, instead of drilling into solid granite they were faced with a substance which resembled flowing sand and running water - almost like quicksand. The entire fissure appeared to be draining its contents into the tunnel. No-one knew how far up into the mountain this fissure reached. There might well have been millions of gallons of the semi fluid substance sitting under the pressure of its height, waiting to disgorge into the tunnel. Experts on cementation were called in and it took both great ingenuity and very hard work to overcome the problem.

Pumping concrete into a void.

The solution

It was decided that a concrete bulkhead should be made to stop the flow of water and sand into the tunnel. Once they had succesfully plugged it, holes were drilled though it and cement and water were pumped through them into the void beyond in the hope that when they mixed with the sand, concrete might be formed on the other side. The picture on the left shows the holes in the roof through which the materials were pumped. Repeating this cycle of plugging and drilling, they eventually filled the dyke with solid material and were able to break through to solid granite once more on the far side of it. This was a very serious setback which slowed the progress of the tunnelling dramatically. For the next six months the tunnel only progressed 42 feet in that heading. Harold explains further..

Listen to Harold - serious setbacks

Light at the end of the tunnel for a three year job of mammoth proportions.

The day the two tunnels met

During the slow progress of driving two tunnels which would join into one, careful calculations and measurements were repeated frequently. There was also the occasional miscalculation to be corrected. Norman and Harold cast more light on the candle theory..

Listen to Engineers - calculations

As the two teams of workers gradually drove towards each other there came a time when everyone was aware that they should be getting very near to a breakthrough. This was an unnerving time for the engineers as it would prove their calculations to be right or wrong. There were even rumours going about that the teams had passed each other somewhere in the bowels of the mountain. They did meet up as planned however, on the 6th December 1950. it took a few days to recover from the celebrations! Norman Ervine remembers..

Listen to Norman - celebrations