The Mingary Castle restoration blog was written by Jon Haylett, who lives in the local village of Kilchoan. Now that restoration is almost complete Holly and Chris Bull will take over to report on bringing the Castle back to life.

Thursday, 30 April 2015

Stabilising the Dolerite

Architect Francis Shaw of Shaw & Jagger and the project's structural engineer Brian Smith of Arc Engineers were on site yesterday morning to look at the last remaining major engineering problem of this work - what to do about the dolerite layer which lies below the granophyre.  This picture was taken back in 2010, before any work began.

Readers will recall that the granophyre was stabilised in a spectacular way back in May 2013 by inserting steel rods which pinned back the falling blocks of rock, an operation which saved the castle's curtain walls from tumbling into the sea.

Even though it showed signs of erosion by the pounding of seven centuries of storm waves, the dolerite wasn't fixed at the same time because it is exceptionally hard, and was quite strong enough to bear the additional weight of the scaffolding.  But, now that the scaffolding is close to being removed, decisions have to be made about stabilising the dolerite.

Francis, right, and Brian, pointing, spent some time with builders Mark Rutherford Thompson (to Brian's left) and John-Paul Ashley (left) looking at the problem.

Not only does Brian have to come up with a way of stabilising the rock, he is also determined that any 'fix' will last a good few hundred years.

While decisions have yet to be made, the outline of Brian's ideas is shown in this sketch. The bulk of the 'fix' is concrete, held in against the dolerite using two metre 'rock nails'.  Outside this concrete is a further layer of corrosion-resistant concrete to which a facing of local rocks will be held using high-grade stainless steel brackets through which a reinforcing wire mesh will be threaded.

It's little wonder that Mark looks worried in this picture as it will be J-P and he that are doing the work.  But it's the sort of challenge they seem to relish, though there's one other problem the builders to contend with - the tide comes in twice a day and covers this area.

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