160 replies to this topic

[ocd]

I've done a fair amount of dry stone walling or cornish hedging as it is known here, with both granite and slate. Free standing hedges and retaining walls, walling is regional and has slight variations and different techniques throughout the country.
But the principles remain the same, the wall must be back filled and compacted well behind the stones, large grounders need to be placed at the bottom to spread the load.
Each course needs to be level ( as possible ) and the joints need to be covered by the next course, "throughs" can be used to strengthen the structure.
What you don't do is add concreted sections as these don't move with the rest of the structure, they bond large sections of wall together that basically puts pressure on the rest of the wall as it moves.
If the top 4 or 5 courses are cemented the structure underneath will move and the cemented section will crack and fall out in large sections or the stones beneath will fall out.
In cornwall the top stones of hedges can be pushed out by cattle so we lay turf across the top to prevent this. Concrete doesn't work.
If internal sections of a wall are made with concrete they won't allow water to drain through and so can put pressure on the external wall and push it over.
A major advantage of a dry stone wall over a cement wall is it allows the water to drain through whilst maintaining structural stability.

We've been building like this for at least 5,000 years........it works!

ocd

[shiny]

OCD..........I gather from what you write, that you fully expect further collapses unless the concrete is removed. Do you think the collapse will be gradual, or sudden?

[Bettina]

OCD,
thank you very much for your reply, it was much appreciated.
I am no engineer or mason. But over the last three years I had to obtain some basic knowledge and the most basic principles of engineering and construction have been ignored.
1) A concrete enforced building with no foundation
2) Concrete enforced and dry stone in one building
3) Straightening of the wall of the building in a extremely wind exposed position (top of hill) therefore providing more surface (aerodynamics)

I will put up some more photos soon, which I took yesterday. The quality of work applied is so bad, that I am embarrassed to use even these simple terms in the proximity or context regarding it. I knew, that stones can be pulled out on the outside of the wall. Yesterday even I found it hard to believe, how many stones I could pull out inside the gate (I put them back.). As far as the concrete is concerned, it has been slabbed on and left like this. I aslo found yesterday large gaps at the outside wall, which I didn't noticed before. The gaps are around 30cm and maybe bigger further up the wall.

If you could give Shiny and myself as much inside into the consequences of the changes applied to the monument, I would be very grateful.
Grianan Aileach has been opened to visitors again a fortnight ago. Busloads of tourists drive up there nearly every day during the summer season and walk on the wall.

[Bettina]

Here are three picture from inside the gate.

Attached Files

•  gateinside1.jpg   132.89K   6 downloads
•  gateinside2.jpg   142.43K   7 downloads
•  gateinside3.jpg   136.05K   7 downloads

[Bettina]

And three more from inside the gate.

Attached Files

•  gateinside4.jpg   153.27K   4 downloads
•  gateinside5.jpg   184.61K   4 downloads
•  gateinside6.jpg   160.94K   6 downloads

[Bettina]

These picture were taken from the pile of leftover stones from the 2000, 2003 and 2005 collapses. The impressions left in the concrete indicate, that the stones were forcibly pulled out.

Attached Files

•  pile1.jpg   158.33K   4 downloads
•  pile2.jpg   169.71K   3 downloads
•  pile3.jpg   155.79K   3 downloads

[Bettina]

And here are a few of the holes.

Attached Files

•  holes1.jpg   153.45K   11 downloads
•  holes2.jpg   157.99K   6 downloads
•  holes3.jpg   145.9K   5 downloads

[ocd]

Bettina, on 14 May 2007, 13:21, said:

Here are three picture from inside the gate.

These three photo's are worrying, when you look at them you can see the joints/gaps between the stones have not been covered by the stones on the next course above. This continues for 4 or 5 courses in places, any section of wall with a gap like this over a number of courses is likely in my humble opinion to collapse all of a sudden.
This a basic lack of understanding of dry stone wall construction, you can see where they've pushed a stone in after construction to plug a gap on one of the photo's.
This is poor technique, any places like this may start to bulge out before they fall down.

ocd

[Bettina]

Thanks again, OCD.
How sudden and could weather condition/visitor numbers it speed up?

[ocd]

Bettina, on 14 May 2007, 13:28, said:

And three more from inside the gate.

Even when they've used the cement it just looks like it's been slapped in, shoddy.

without visiting the site it's difficult to say what will collapse and what will stay.

What I can see from the photo's is basic building principles have been ignored. Was money an issue in the reconstruction?

In cornwall there are some fine cornish hedgers with far more skill than myself, but the majority of hedges are put up quickly without pride in workmanship - a money issue I'd guess.

I would say areas with concrete with back fill will push the outer face out due to water not being able to seep through the wall.

Any areas with cemented sections above dry stone sections will crack and fall apart as the wall moves, this will probably be gradual until whole sections start to fall out through being undermined.

Any bulges will be due to pressure forcing the wall out eg water, or overhanging stones above the course below, or joints continuously not covered course after course.

Any sections where the wall concaves in will be due to inadequate back filling.

Any sections that have sunk may be the dry stone sections and the problem may be the section next to it that hasn't sunk that's been cemented. The sunken section will have stones pushed out of place next to the cemented section and will bulge and collapse because the rest of the structure is static


The beauty of dry stone wall structures is they are easy to repair and maintain


ocd

[Bettina]

I believe that money was not the problem. The OPW is a state employed organisation and according to their own statements, they employed besides an architect in charge, an engineer and an archaeologist.

[ocd]

weather will play a role and I would guess that the structure would fair better if it had never been cemented in places.

There are cornish hedges in west penwith that have monument status and have stood on a wind battered peninsular for four thousand years.

I think the site is in more danger from so called experts who don't understand the qualities and benefits of dry stone walling.

It has stood the test of time because it can allow water to seep through whilst maintaining structure and is easily maintained and repaired.


A modern example that works in the same way is the "gabion" - large wire baskets filled with stone and placed in banks often river banks that give support and allow water to flow through them.

ocd

[ocd]

That's crazy - I taught dry stone walling to 14 year old kids earlier in the year and after one day their quality of work was superior to some of the photos you've posted here.

I wouldn't let them get away with not covering the joints and they had enough pride to do the job properly too!

ocd

[Bettina]

Your advice and knowledge helps a lot. But I am also more worried now than ever. I knew from the moment I saw the first concrete, that somethings is terribly wrong.
I need to be able to proof, that the wall will collapse again. Otherwise, no one will listen. I do not expect any response to my letter to the Taoiseach (Prime Minister). I fear, that someone has to get hurt, before anyone will take notice.

[Bettina]

OCD,

I can not understand either, why their demonstrated skills had to be so lousy over the last six years. I agree, children can do better. It is beyond believe, that something like this could be done to a National monument with people walking all year round on top of it.