ETV thank you, what a find =D>
Due to work I have had some privileges over the years and one was when I was allowed a peak over the edge of the shaft in the pump house.
We were installing some new and uprated HV supplies in '91, maybe '92. There's a primary substation just outside the pumping station grounds. They needed some more power so IIRC four new 11Kv feeders were installed.
Anyway as is usual you make a few friends, so over the few days we were there we had got chatting with some of the guys there. One of the days one of the new friends came to call us up into the pump house, he had a surprise for us. As instructed we had a look out over the shaft head as he gave us a little background info.
Well this roar starts, getting louder and louder. Along with the noise the air pressure was building. He had timed his "visit" just as a train was going through the tunnel bellow us.
Wow! What a rush and I'm not just talking about the excitement, the gust of air coming up that shaft was unbelievable. I swear if you were on one of the ladders in it, it would have blown you up the beggar. Absolutely incredible.
One thing of note is how serious they take security there. Vehicles left outside, carry the kit in. Can't blame them though, if those pumps go off the tunnel will flood in a day so I was told.
The house I built/extended/refurbished in Caldicot is pretty much right on top of the tunnel. Late at night when all is quiet you can hear the tunnel as trains pass through, and a definite little tremor is felt.
In 2002 a friend who owns a fabrication company took on a contract to make very very heavy steel gratings. 30mm thick plate welded into the grating shape. Double galvanised and multiple coats of paint finished.
On a visit I asked what they were for, the Severn Tunnel was the answer.
Are you fitting these, are you going down, when ????? So by hook and by crook I got myself a little visit down the tunnel from our end. The principle contractor was amused that someone wanted a visit, but they were very quick in the answer of "Aye, have a look if you want".
I only went in a hundred metres or so, but wow, seriously wow. What a feat of engineering.
One thing that dawned on me when I was in the tunnel. I was there in steel toecaps, hard hat and waterproofs. There were those special rail riding vehicles and lighting, great big floodlighting everywhere. Walkie talkies for communications and a comforting feel of "everything is under control".
The guys who built the tunnel had none of this and I take my hat off to them, every single one of them.