Wednesday, March 4, 2015

Epiphany Bridge

Not long after it was built I was taken to see this very old looking dry stone bridge. I am not that old. Nor in fact was the bridge. The bridge had been built by Master Craftsman Norman Haddow and Dieter Schneider several months before. 

It was however the first dry stone bridge I had ever seen in the flesh. 

While visiting Scotland in 2003 ( meeting and working with certified wallers, researching how the DSWA was run and getting advise from their members on establishing a similar organization in Canada) I had an opportunity to meet Norman and travel with him to see examples of good quality 'dry stane dyking'. Norman was eager to show me the bridge which had just been built using local boulders and a random selection mostly the mica schist stone found on the large estate which is located near the village of Butterstone in the Highlands. 

We drove up some narrow roads and then walked quite a distance to get to what seemed like a very remote part of Scotland. As we walked Norman informed me that the design of the bridge was based on the bridge at Glenn Lion (another remote area of Scotland) which he had visited with his family many times as a boy and he had always been fascinated with. 

He told the story of how he had been commissioned to build this new bridge by a wealthy landowner to replace the wooded one which was situated over the 'burn' (the Scottish word for stream or brook) where the man had proposed to his wife many years prior. Obviously it was to be a very special project to commemorate that engagement and a successful marriage which had lasted five decades. At first Norman was reluctant to take on the challenging task of building a completely mortarless stone arched bridge, but after some continued persuading by the landowner he agreed to do it. I'm so glad he did as it was from that bridge that many other bridges arose.

I had a bit of an epiphany when I saw it. In all my travels I had never seen anything as fittingly beautiful, as that sturdy stone bridge. I couldn't imagine it ever having not been there. I was also quite sure I hadn't seen or heard of any bridges built like it anywhere in Canada either. I remember starting to get really excited. I took many photos of it with Norman standing, or rather squatting, near it. (He explained the scale of the bridge looked more impressive that way) He took the photo of me there. Standing or squatting, after seeing Norman's lovely bridge I was suitably 'impressed'. I understood for the first time how it was actually possible to span distances by carefully fitting random stones together in a proper arched configuration. From that day on I became absorbed with the idea of building one someday somewhere in Canada. That was back in 2003

The Construction

The bridge sprang off four large boulders which were found on site and moved with heavy equipment close to where they needed to be placed in pairs on opposite sides of the burn, after which they were barred into their final position manually. More very large rocks were bedded together in the earth over these boulders creating the two stone cribs which formed the abutments for the future bridge either side of the burn. They protruded roughly to the height of the level that the water was known to rise during spring run off. Next Norman and Dieter carefully fixed in place the wooden form that had been constructed by local carpenters (to temporarily take the weight of the bridge arch) It was propped in such a way that the supporting wedges could be removed and the form could be slid out from under the structure after the two sides of the arch were built up and joined at the top so that the bridge would be then able to support itself.

Perfectly flat, suitably thick, squarish stones work best in the construction of a challenging bridge like this one. Most of the local stone available for the bridge was predominantly rounded and consequently Norman and Dieter strove to find enough naturally flat bedded stones to do the job.

These valuable flatter stones (voussoirs) were carefully laid in bands, basically upright with their best faces down (forming the intrado) across the wooden arch, so that each row leaned up against the previous one, ensuring that all of the rows were gently leaning in a radial pattern up against the initial row of larger 'springer' stones. This was repeated until the rows of stones met almost in the middle. 
Finally across that remaining gap, where the rows nearly met, a row of the best 'keystone-like' stones were wedged in securely. All the radiating stones over the form were then pinned with granite wedges of varying sizes. Pinning and wedging the structure thoroughly ensured that even the slightest wiggling of the larger stones in the arch would be eliminated 

The rows of stones at this point in the construction look quite jagged (like a hedgehog's back, says Norman) A second and third layer of more horizontal stones was then built into and over top of the radiating rows of voussoirs so that the arch becomes thicker and heavier. This extra weight actually helps make the bridge even sturdier. Providing a bridge has proper solid built up sides (abutments) that can not move, it is a known principle of physics that the stone arch will become stronger as additional weight is added to it.

2 comments:

  1. Thank you John for sharing the bridge at Riemore with your followers. Dieter and I had great fun and excitement building it. I still exchange work with him and am off to Switzerland next week to repair dry stone walls round his vineyard , I also hope to share some of the products! Norman

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  2. This is a lovely post about a subject that is near and dear to my heart. I love stone arches and these are great.

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