Penmorfa showed me this cast iron bridge as he thought I would like this... and I very much did as it represents a fabulous piece of casting.
🔗Personal-Album-856-Image-42717[linkphoto]Personal-Album-856-Image-42717[/linkphoto][/link]
This cast iron bridge appears to be 3 cast iron beams the outer beam bearing the legend..
CAST AT THE PENYDARRAN IRONWORKS GLAMORGANSHIRE MDCCCXXI
🔗Personal-Album-856-Image-42718[linkphoto]Personal-Album-856-Image-42718[/linkphoto][/link]
🔗Personal-Album-856-Image-42719[linkphoto]Personal-Album-856-Image-42719[/linkphoto][/link]

However... It appears that the bridge was a single piece casting as the following detail shot shows making this an exceptional piece of casting work. The 3 beam are indeed cast into the end frame! 😮
🔗Personal-Album-856-Image-42720[linkphoto]Personal-Album-856-Image-42720[/linkphoto][/link]

This would have in volved extremely complex sand cores of a huge size being inserted into a pit mould not dissimilar to how they make marine diesel cylinder blocks today. The lattice work would have been a nightmare. The runner system for this would be a work of art having to carry hot iron almost simultaneously around the massive mould without chilling/cooling.
Just imagine one bit does not run and thats it back then you have just scrapped your casting.
My estimate is that this fine piece of work probably took a week just to build the mould, the pattern would have been fabulous and taken a vast amount of input from engineers as the contraction and shrinkage issues on such an item are prime during design, the pattern makers skill in getting this together would have required a life times experience and an ability to picture the final casting as a negative in sand.
A fine survivor this and an exceptional tribute to the men and skills of all the Ironworkers at Penydarren in 1821. I very much doubt this could even be attempted in the UK today and most large foundries in the world that I visit would be dubious.
A sobering reminder how great our manufacturing abilities once were.

---

Is that a joint at the centre in pic 3?

It certainly could be but the beam behind doesn't seem to have it. Even if in two pieces still a remarkable piece of casting, it would certainly have made it more transportable.

If it was in two they could have leaned the two pieces to gether effectively, pivoting around the end brackets but usually there is some form of joint plates, but these could be nicely hidden under the cast deck beams.

---

The bridge, Pont Aber Ogwen, is cast in two halves. The joint in the middle can be seen, as can the tie/jointing plates which appear to be on both sides of the central span, but only on the insides of the two outer spans. None the less, a fine example of the ironworkers' skill. It has a two ton, maximum load limit.

I did a job in the early 80s, a tunnel connection in the Warrington area ( part of the Vyrnwy aqueduct upgrading, as it happens )

the reception shaft consisted of a wrought-iron shaft sunk as a caisson. The exit tunnel was constructed of cast-iron segments, and the junction was cast to fit exactly against the curve of the shaft. This meant that to allow for the significant mis-alignment of the tunnel against the shaft, and the out-of-plane of the shaft, the 'saddle' shape was assymetric and all sections were slightly different.

the only way I can see this was done, would be for the main moulds to have been substantially made, then fitted exactly after the junction, modified as required, then cast. Wish I'd managed to get some pictures, beautiful job

---

The bridge, Pont Aber Ogwen, is cast in two halves. The joint in the middle can be seen

Only an opinion, if you look at pic 4 (fullsized) I would suggest that the spans were cast in an open floor mould, all spans were cast identically the two with recessed lattice work facing out and the span at the far side reversed for appearance.

There also seens to be a joint where the arch meets the abutment plate.

the only way I can see this was done, would be for the main moulds to have been substantially made, then fitted exactly after the junction, modified as required, then cast. Wish I'd managed to get some pictures, beautiful job

I suspect the patterns would be done off the calculations and drawings and the bits would fit nearly perfectlly with a bit of lead wool or similar caulking

the only way I can see this was done, would be for the main moulds to have been substantially made, then fitted exactly after the junction, modified as required, then cast. Wish I'd managed to get some pictures, beautiful job

I suspect the patterns would be done off the calculations and drawings and the bits would fit nearly perfectlly with a bit of lead wool or similar caulking

This would be the usual practice but I don't believe so, not in this instance. The misalignment is significant ( approximately 300mm off line, around 25mm out-of-square, with an out-of-plumb on the shaft approaching 4 degrees at this level ).

the location of the shaft is on a spit of land called No-Mans-Land, between the Mersey and Manchester Ship Canal. There are severe problems with high water pressures in the running sand and silts which form the ground there.

Another shaft, believed to be the working shaft and forming the drop-shaft for the aqueduct pipes coming under the Manchester Ship Canal, only 50 meters or so away, was constructed as a brick caisson in traditional Victorian style, and a timber piled cofferdam constructed about the shaft to provide cover for the outgoing cast-iron segmental tunnel. The MSC crossing was constructed in open-cut as part of the Canal construction.

no records survive, but it would appear from the extensive temporary works present in the ground outside the shaft, the distorted shape of the shaft and subsequent ring-beam within it, and various other factors, that the original design was abandoned and the pipes brought to surface, across the spit of land in open-cut, and then down a cast-iron shaft into the Mersey crossing.

The need for a close seal between the shaft and outgoing tunnel meant that tolerances had to be very small, and the joint was constructed using tallow-and-tar soaked felt gasket pads with lead caulking in a purpose-made groove on the inside face.

the original tunnel shield was abandoned against the outside of the shaft, cut to profile and shoved up tight. No part of the original shield is visible from inside, but that's what is believed to have been done; at least there is no sign of a junction large enough for the shield to have entered the shaft.

---

Interesting, I assume the shield was normal circular and a bit larger than the lining?

Some pictures of Pont Aber Ogwen..🔗Personal-Album-385-Image-42878[linkphoto]Personal-Album-385-Image-42878[/linkphoto][/link]
🔗Personal-Album-385-Image-42879[linkphoto]Personal-Album-385-Image-42879[/linkphoto][/link]
🔗Personal-Album-385-Image-42880[linkphoto]Personal-Album-385-Image-42880[/linkphoto][/link]
It is, perhaps, worth contrasting/comparing Pont Aber Ogwen with the contemporaneous bridge over the Afon Cegin at Port Penrhyn- the old harbour bridge-which is now in sections, in the undergrowth near the start of Lon Las Ogwen. Note that the abutment/thrust plates are in one casting with the spans.
🔗Personal-Album-385-Image-42881[linkphoto]Personal-Album-385-Image-42881[/linkphoto][/link]
🔗Personal-Album-385-Image-42886[linkphoto]Personal-Album-385-Image-42886[/linkphoto][/link]

Still looks like a joint (minus filler) to me. The centre span joint seems to show the filler starting to break down.

🔗Personal-Album-1695-Image-42907[linkphoto]Personal-Album-1695-Image-42907[/linkphoto][/link]

Interesting, I assume the shield was normal circular and a bit larger than the lining?

http://www.subbrit.org.uk/sb-sites/sites/t/tower_subway/index.shtml 

given the date it was probably hand-jacked rather than hydraulic.

it's now usual for the shield to have an internal diameter approximately 50mm greater than the external diameter of the rings, for steering and for providing an annulus for grouting, but in running ground it may be less because there will be no annulus, and it's necessary to provide a seal around the tailskin

---

I'm just trying to figure out how they got the shield out and fitted the last few sections of lining.
I am just guessing they push it into the shaft and fit rings behind, cutting the shield up if it's too long for the shaft diameter?

depends on the job.

disregarding special cases like wedgeblock shields which have no tailskin, or articulated and TBM shields which are a different kettle of fish, a generic Greathead hand-excavation shield consists of a steel 'can' which is around 50mm greater than the tunnel lining rings in diameter.

It will have a hood, or forward extension, approximately 125% the length of the rings, around the upper 120 - 180 degrees of the front end. It will also have a tailskin, approximately 150% of the length of the rings, at the rear. This tailskin may, or may not, be removable as a single piece, or in segments.

the shield will be lowered into the pit bottom on rails and jacked forward, using jacks or more usually, rams, contained within its main 'can'. When it has advanced one riing, a part-ring is built within the tailskin and the shield advances again, jacking off that part-ring.

when the shield enters the ground, full rings will be built and grouted once they are outside the tailskin.

on approaching the target shaft, either an eye will have been constructed, or a reception eye will be broken out, depending on the ground and the design.

the shield will continue to advance until it is far enough into the shaft to be retrieved. The tailskin may, or may not, be disconnected at this stage.

if the shield is to be abandoned, for example if two shields have been steered up to each other underground head-to-head for the purpose ( I set out a connection of this sort in the early 90s, on a cable tunnel in the Regent Street area, for example ) then the shields will be advanced, the internal fittings stripped out, and rings built internally and the final length made good with an in-situ concrete lining.

that's a rather generic answer, but the main points are there

---

Thanks, from what I've seen on films/video etc it must have been a real pain in wet ground before the freezing techniques were perfected.

ground freezing has always been something of a last resort.

the Selby coalfields, Boulby shafts and Sherburn-in-Elmet drift were design solutions for the specific purpose of penetrating the Bunter sandstone aquifer. Foraky did a job in South Africa in the 80s, the Orange River Tunnel, which involved supporting the crown

Foraky did a series of jobs in the 70s and early 80s which were essentially 'rescues' of various tunnel projects which had lost control of the local ground. The Vyrnwy Aqueduct was originally a design, but the final job was hugely complicated by the various temporary works around the brick shaft.

however modern grouting agents and more particularly, the development of micro-tunnelling, earth pressure balance and other forms of closed-face TBMs have greatly reduced the scope of the technique.

---

Yes, things have moved on.

Thanks Gwyn for the usual informative response. I don't think the end abutment plate is seperate either. I had until recently access to a large number of drawings on loan showing pit casting techniques done by Butterley co for huge bridge sections and engine beds, they were capable of some amazing things. Often it seems the decision was taken to cast as much detail as poss as they did not have the fine grinding tools to finish rough castings in small detail areas/nooks an crannys, nor was it considered good use of men file finishing such things. They were true iron masters.

---

You may well be correct gentlemen, but having done a fair bit of filing (fettling) during my apprenticeship I still have reservations. 🙂

Your reservations are well founded, Morlock.
I've just spent some time at Port Penrhyn cutting back some of the undergrowth and removing ivy from the remains of the old port bridge, so as to get a better look at it.
It was indeed cast in constituent parts, most/all of which appear to be flat, rather than three dimensional.
The method of jointing seems rather reminiscent of simple wood-working joints,-rebates, mortices and tenons etc.
The joints on the outward facing sections of the abutment thrust plates are perfect, I was unable to get a thin blade into them. No sign of any packing such as lead wool, caulking or bitumen, just an excellent fit, which on a cursory inspection looks like a single casting. Mea culpa.
However, on the inside of all of them there is a gap of approx. 1", indicating a simple rebate/slot joint to hold the spans, which has been partially filled (randomly?) with small blocks of what appears to be cast iron, creating an interference fit. The ends of the rebates appear to have had hot metal poured onto/into them to seal them once erected.
I saw no sign of any maker's mark nor date, but since I didn't expose all of the metal works there could be one somewhere.
Myrvin Elis-Williams in his book, Bangor: Port of Beaumaris suggests that this bridge dates from the early/mid 1830's so it's slightly younger than Pont Aber Ogwen.
This leads me to deduce that Pont Aber Ogwen was probably also cast in flat sections, another "flat-pack"!
My apologies... I stand corrected.