Bridge Foundations

The abutment foundations we built for that first bridge in Port Hope are not the only kind we've used. The foundations described below have also worked well and in a couple of other cases I've discovered a combination of stone and concrete has been quite a suitable solution for small dry stone footbridges of this type. Below is a description of two other ways it can be done if the situation allows for it.

Here at the public bridge in Russell Ontario, ten foot wide, four foot deep holes were dug by machine and U shaped forms were assembled of plywood and then concrete poured to make the abutments. Less concrete was needed because of the clever U shape design. Clear gravel was used to fill up the four feet of depth around the abutments and tapered back to eventually be the support the tails of the bridge. 

Stones were embedded in the fresh concrete to be a resistance to any sheering action across the top of the flat surface of the abutment. Re-bar or long bolts can be used here instead.

In Wellington Ontario we used concrete forms again but created six inch high steps in combination with embedded re-bar to act as resistance to the lateral push of the arch.

At Bruce's bridge we dug precise 8x8 by 8 foot deep holes in the hard subsoil and then added clear sharp 3/4 gravel to within 12 inches of the surface. After compacting it thoroughly we built our bridge on top of this dense gravel foundation. Lateral movement of the bridge was avoided by bedding the first larger foundation stones below grade into the gravel. 

The bridge is 8 years old and has showed no sign of movement or slumping.

Shaping Stone 2

I believe that 'shaping' should differentiated from 'splitting' stone in that it involves breaking a stone across its narrower thickness. It can also involve breaking a stone to create a rough face and/or obviously giving it some sort purposeful shape. 

Splitting on the other hand involves opening a stone up along its grain or sometimes across, (sometimes using feather and wedges or a 'tracer') but usually involves bigger pieces than ones we will be shaping and splitting generally is done more at the rough beginning stages of a project. 

I rarely 'split' stones unless perhaps I come across a stone that is layered and has a fault or a fissure where it seems like it would be easy to chisel open to separate it into two matching halves. The twin stones with newly revealed surfaces are sometimes called 'shiners'. Shiners are rarely used structurally, that is, with their faces showing out in a dry stone wall because they are generally too thin and the bulk of the stones can't be embedded into the wall deep enough.

Shaping is more likely to be what we do to the stones in normal dry stone walling. It is what you see going on in this photo above. The stone is too long and the wrong 'shape' to go into the abutment we are making for the bridge. If we need to make a new face on a stone we can cut (shape) it this way too. 

To use the stone we have to shape it with a chisel and hammer. Ironically the chisel is a two inch 'splitter'. It has a carbide tip blade and a one inch shank (which makes it easy to grip and sends the blow of the hammer down with more force into the stone) 

Granted, a single hammer known as a walling hammer could be used inserted to do this kind of shaping but it involves more of a gradual chopping away at one side of the stone to get the stone to the right size. I prefer to just cut across the stone the way you see it is being done here along the line scratched on the stone in the photo above.

I use a three pound lump hammer holding the splitter firmly gripping it nearer the pointed end of the chisel. The chisel blade has to be positioned exactly along the line I want it to break. It needs to touch the stone's surface in at least two points so that the chisel isn't resting on a high point which would only allow the force of the blow to one small (directionless) point. With the chisel blade touching the surface in at least two places on the line, the force of the blow is spread/connected? along the length of the chisel width at least, and so sends the message/energy of the impact along the proper orientation. 

Enough hard whacks will eventually tell the stone where it should think about breaking. If it the stone I am shaping is fairly flat and big enough I sometimes put a straight piece of metal ( T-bar or rail or even a pry bar) under it parallel to my line  so that the blow from the hammer is sent directly down below along the line where the stone is resting. Sometimes if it is taking a while and I want to make sure it breaks in the right place I turn the stone over and chisel the other side too.

Eventually the stone will break and usually if it is the right kind of stone (granite sandstone and limestone are good) it will produce a clean flat straight break which can often be used as a 'face'. 

Shaping Stone

Before going any further on the story of the bridge we built in Port Hope in 2004 let's talk about splitting, shaping  and dressing stone material. We needed to know how to do these things to be able to make some of the stones we used in the bridge.

This seemingly demanding task of trying to change the shape of rocks and stones has been going on for a long of time. Not that it always takes a long time, though it can, but it's certainly been going on since the beginning of time. 

Workers in stone in early civilizations in almost every part of the globe discovered all sorts of clever ways (some of their techniques still remain a mystery ) of prying/removing chunks of rock out of the ground or cutting slabs away from outcroppings of bedrock, and then taking these big rocks and making them smaller, shaping them perfectly and even decorating their surfaces with textures and intricate designs. Various theories on how the Incas and other ancient people did this with such accuracy and on such a spectacular scale makes for great reading. 

The methods employed by humble dry stone wallers however are not wrapped in any great mystery, nor are their ways a closely guarded secret that only a few craftsmen ever properly grasp to become truly proficient. Stacking stones is not rocket science. Nor is the shaping, splitting or even the dressing of stones.  Only a few tools are needed along with a certain understanding of some basic methods. Whether one is building a wall, a cairn, a seat, or a small bridge, the things you have to know about the subject are pretty simple. 

See tomorrow's post.

Less than a year later

Less than a year later and with Norman's help we organized the first DSWAC 'pack horse' dry stone bridge building workshop in Canada. A handful of enthusiastic stone aficionados signed up for the course a couple months before the event ( at 100 dollars for three days hands-on instruction ) and together that October we made bridge building history at 

Port Hope Ontario's first Canadian Dry Stone Wall Festival.

The property I had chosen to build the bridge on was in the town my family and I had just recently moved to. There was a good bed and breakfast there off main street that had a beautiful 4 acre property with a gentle swale going through a grassy clearing near the huge Victorian house. I made a scary cold call and proposed the idea of having a bridge built there to the owner who I had never met. He was was not as surprised or as cautious as I had been expecting. Instead he listened intently and was quite enthusiastic as I told him I had chosen his property for a very unusual stone project. When I inquired whether he would object to the idea of me constructing a traditional Scottish style dry stone bridge somewhere on his estate, at a cost to him of only the twenty four tons of stone material, he replied "Am I an idiot? " Which I took to mean that he was all for it.

As the days got closer he got more and more enthusiastic about the free bridge he was going to get and offered to serve lunches to everyone who would be working on the project.

Before the three day public event during which I hoped to complete the bridge, a fair amount of prep work had to be done. Enough suitable stone material had to be procured. This was coming from a stone quarry I had recently discovered about an hour away. 

The foundation holes had to be dug and the abutments built up to the height of finished grade either side of the creek we were planning to span. Holes are usually not much fun to dig but these were. The excitement of what we were going to be creating was mounting by the shovel full. It was a hot day and shirts came off almost immediately. 

The 6 by 4 foot squares had to be dug to below the creek bed, which fortunately was not flowing during that uncomfortably hot week back in late September 2004. Large limestone slaps, similar, but slightly smaller than the squarish huge chunks of armour stone used by landscapers, were lowered into the holes and fitted in a dove tail fashion to create a kind of dry stone crib below grade. From these bases there would be support to spring the bridge off of. 

These two 'abutments' had to be low enough to not move with the frost.

My hope was that if they did move at all they would both move the same amount and at the same time and in the same direction so that the bridge would still stay tight. 

This bridge was to be an experiment. I needed to see if dry laying stone was a suitable method for building small foot bridges in Canada. I had already by that time built many smaller dry stone garden arches and realized that as long as the matching bases were dug evenly, with the same size and depth of footprint into similarly undisturbed ground, over time, very little evidence of conflicting movement occurred across the arches. Would a dry stone bridge have the same success? 

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.

Abridgement

Perhaps those of us who love dry-laid stonework and/or build with stone, using only stone (no mortar) can better understand what it is about a dry stone bridge that makes it so profoundly attractive  - and so 'right'. 
Many of us can certainly appreciate the rewarding sense of accomplishment Anne Halliday must feel having recently completed her first bridge at the Westwood Hotel Golf and Country club near Glasgow Scotland.

Unlike thousand of others made with steel, wood or concrete, a properly built dry stone structure like this beautiful arched bridge that Anne built, is not just a thing of beauty, it is also a delightful demonstration and resonating expression of what it is we associate the word 'bridge' to mean.

It is this expressive manifestation of the 'dry stone bridge' alone that so mysterious spans the gap of our own imagination of what 'bridging' is. 

We begin to understand not only why and how it 'stands', but even what it is a 'bridge' stands for.

While some of us will never get over the charm of a dry stone bridge (when we do indeed have the pleasure coming across one) we recognize that it intrinsically capsulizes, in its unique structural design, all that is involved in the concept  of  'comprehending' , literally 'trying to get over' something.  

The stones are all joined together in a magical pattern to actually reach across the opening, which is less like an 'understandable opening' and more like a challenging expanse of nothingness presenting a kind of invisible barrier. 

A bridge of this type that is uniquely constructed of skillfully fitted stones in an arch is in itself the 'abridgement' of the concept of dry stone walling. It epitomizes the artistry and craftsmanship involved. 

Such a bridge will always represent more than the sum of its parts (the stones) 

Sadly there are relatively few dry stone bridges here in Canada that are built of dry laid stone. Not many can be found even back in Britain or Ireland or the rest of Europe either. And while there there are still very few being built Anne's project does represent a growing movement, a new resurgence in the interest in building permanently with stone, and without mortar. 

It mostly involves using common sense (and physics) to fit the stones together. Skilled artisans like Anne are helping demystify the concept of working with this plentifully available and naturally structural material.  All that is required is a dedication to building properly with stone the way people simply used to in the past, with an understanding that bridges needed to be built way before manufactured products and speciallized technology came along. 

The stones in Anne's bridge rely solely on their own friction and weight to keep the whole arch suspended in air.

They join together in a continuous bond facilitating not just our 'getting across' the real bridge (and also the concept), but they also help us to make that intuitive connection between form and function.

Click here to see more photos and read what Anne Halliday has to say about building her bridge

To see the a previous Thinking With My Hands post I wrote about Anne and her bridge visit Anne Halliday and her Bridge

Finished California Workshop Project

Demonstration Arch

The arch building went well on Saturday and Sunday in California. The students watched this simple demonstration arch we built and were able to build three of their own on Sunday. The finished installation will be posted tomorrow. A big thanks and congratulations to our students for hanging in there to the end and finishing the project in between hurricane-like weather conditions.

Design for workshop in California

I enjoy coming up with new ideas for workshop projects especially at one place in California that I have taught for the last six years each winter. The one we are building this weekend involves three dry stone pillars. They will be joined by three low dry stone arches. The wide pillars will also be recessed in the centres so they can be used as planters. Patric McAfee and I have a great group of students and the project should be completed by this afternoon.  

The tower shot !

Some of the guys who worked on the tower. 

Photo courtesy of Kathryn Gleason

Quick lime, red brick dust and coarse sand. This is the special mix, before it's mixed 

After you mix it just add water.

But watch out it gets hot !   As you can see Matt Harvey has discovered how highly corrosive hot lime is! 

A misty tower shot

Photo courtesy of Kathryn Gleason

2015 Canadian Dry Stone Festival

Dry Stone Walling Association of Canada.

More from the tower build

Mark Ricard waves to the workers on the ground, nearly ten feet below 

Patrick McAfee, incorporating a traditional style of stonework, pounds smaller 'pin stones' into the larger spaces created by the lime mortar between the builder stones. 

David Claman makes sure the joints are finished properly to ensure the final mortar surface is flush. It will have the correct texture and grainy look (with tiny specks of aggregate exposed ) when it is worked with brush.

Thirteen steps are now in place.

They each have 12 inches of tread at the widest point.

There are at least ten more to go.

Kyle Schlagenhauf has carved a beautiful candle niche for the inside wall near the bottom of the staircase

The tower already has a commanding view down to the ocean.

Monroe waits for the huge granite lintel to be hoisted into place.

Matt Driscoll checks the final measurements for the lintel he has been shaping an dressing for several days.

The front door lintel is set into place on a bed of lime mortar using a chain hoist and a tripod.

 Next phase will be October 2015

The Finished Stones.

The stones on the shore are all at various stages of completion.
Some have not yet become fully rounded. Some are still too big. Most have no identity at all. There are countless numbers of them all huddle together, each waiting to one day become interesting.

A few unusual candidates I see have small round holes in them. Some, the holes go right through to the other side. They are special.

The stones where the holes don't quite go through to the other side will need a few more years to become ready.


A couple stones along my beach walk appear to be perfect, both in shape and smoothness - tumbled by the ocean and then cleverly left lying there on the beach, just waiting to be discovered.

An holey stone catches my eye. I reach down and pick it up.
It will stay in my hand as I walk.
I roll it's smooth shape in my hand and probe the finger sized holes as I walk along the beach looking for others

There is no rush. No agenda.
My eyes go into neutral looking down at me feet.
My focus is on nothing, so that I see only the stones that are really something. The 'finished' stones.

I will bring back two or three of them in my pockets every time I visit the beach

In time, eventually, if I keep coming back here over an infinite number of visits, the sea will have completed the task of tumbling every one of her stones into unique works of art. And I, by then, will have brought back the entire beach with me.

Work on the tower continues upwards

Any questions?

Walk the Walls Tour - The Old Stones

Tour dates  -  May 27-June 08, 2015          

This year our Walk the Walls Tour will take us to Northern Scotland, the Orkney Islands and on to the western Islands of Mull and Iona.  This will be our fourth tour. We will visit stone age ruins and contemporary sites of stone walls, bridges, buildings, gardens and follies. We will learn about the lost arts of dry stone structures, the history  and legends of the castles and glens. Come absorb yourself in the landscape, the music, the food and the traditions of the region.

The first half of the trip will take us to the Orkney Islands, just a short step from the Scottish mainland.  These  islands are mainly “low lying, gently sloping, fertile valleys, where spring days are long and skies enormous”.  However, our interests are the well preserved treasury of Stone Age settlements and the recent discovery of Ness of Brodgar.  As National Geographic describes  this site in their August 2014 article, “Before Stonehenge...one long day ago around 3200 B.C., the farmers and herdsmen on Scotland’s remote Orkney Islands decided to build something big...”.   
neolithic-orkney

From Orkney we will take the ferry to the mainland to meet our friend and DSWA Master Dry Stone waller George Gunn, (winner of and International Award for the Built Environment and Architectural Heritage). George also used to guide motorcycle tours in the Highlands, so he knows the backroads of this remote area and beautiful country, a land of legendary stones.

We will also meet singer, songwriter, poet and mountaineer Dave Goulder and  his wife Mary, our hosts  Lairg/Rosehall/Summerland.  Dave totes his Master Craftsmen/instructor walling certificate around with him,  as well as his guitar and members of his Rosehall Ceilidh band.

There is a wide variation of building styles and stones in the Lairg/Dornoch vicinity, -- double and single walls (dykes), sheep fanks, cairns and castles.  Our tentative plans are to stay in a Scottish Castle (Dornoch Castle Hotel), on the edge of the Dornoch Firth, a designated National Scenic Area in the Highlands of Scotland.

The second half of the tour we will travel south to the Inner Hebrides Islands of Mull and Iona. Here we will be joined by our very good friend and past host from the Balmoral portion of our 2011 tour, our waller at Balmoral, Norman Haddow (DSWA Master’s Certificate). 

Historically the island was known for crofting, whiskey distilling and fishing, yet now is known for castles and stone structures as well as one of the best seabird viewing areas in Great Britain. 

Most of our time will be spent on Iona, a pilgrimage site for several centuries and a place of Christian worship for more than 1400 years.  The extensive pink granite ruins of the Augustinian nunnery, and the Abbey that dates from the arrival of the Benedictines around 1200, as well as the sacred burial ground  which is said to contain the graves of kings of Norway, France, Iceland, and Scotland, including Duncan and Macbeth, are all within a walking tour of the island.

We will leave the islands behind and spend our last night in Glasgow. 

The Walk the Walls portion of the tour  and the flight portion are priced separately so  those wishing to make their own travel plans to and from  our destination  may do so.  Our tentative itinerary is to depart from Toronto-Glasgow the evening of May 27, and Glasgow-Toronto, June 08. We are designing this tour for the hikers, walkers or  wanderers. Our itinerary will be as casual as possible.

Our goal is to introduce the culture, the history, the ecology and for many, to connect with the stones of our past!

The dates have been set for our tour of walls but we are still working on finding the best prices  . So stayed tuned.

For general tour information contact:

Margot Miller    < margotm@1000island.net >  613 659 3415
  
Jackie Moir, branch manager with Merit Travel will be our travel agent.  <Jackie.Moir@merit.ca>   (613.342.1412 x7230 | 1.800.938.2677 | www.merit.ca

Work continues on the tower

Patrick is in a race with Royce in the background. They are shaping arches out of very hard black granite. Royce barely keeps up, but then his arch is four times bigger !

The tower entranceway, with its lower stone posts is starting to take shape. The mica quartzite slabs are now being dry fit before we set them permanently in lime mortar. 

The first lift of builder stones is now in place, ready to be taken back down and mortared. We were waiting for lime to be delivered by train and truck from many miles away

The ramp is to roll the heavy spiral stair treads up.

Here is a blind arch - a niche, for sitting in and looking out over the ocean.

Here is Patrick's smaller arched window which will allow daylight to illuminate the lower section of the spiral stairs.