Musings on building a workshop and a new machine...

[irving2008]

Well best laid plans etc....

The hole is still there, though its now doing a very poor impression of a swimming pool filled with porridge.

I was rushed with the digger and hadn't realised it was 100mm narrower than I needed and a little wasp waisted. Fortunately being relatively soft due to the water content I've managed to tidy up the edges and now its sides are parallel, vertical and the correct distance apart and I have dug the post holes for the 4 x 3 posts that will hold the retaining wall at the back. That'll be made of 4.2m long 225 x 50 (9 x 2) boards.

In the meantime I have finally completed the design of the steelwork needed in the concrete. Why do I need steelwork, isn't that a bit overkill I hear you ask? Well maybe if you dont care about cracks appearing in a couple of years time, but I want this to last 20years and still be stable and because its on a clay base and near a tree it has to cope with heave and shrinkage. The normal solution to that is to dig deep piling into the clay, about 4 - 5m deep or more and suspend the raft on top. Thats not an option for me, so the alternate is to build a concrete raft thats sufficiently strong to stand the lifting forces and also support itself if the clay shrinks from underneath a section of it.

The research into how to design such a raft has been interesting, there's surprisingly little info. A civil engineering graduate son of a friend said that it wasnt something they covered in his Uni course. But I have persevered and have now a design that meets the demands of BS8110 and I am confident it'll handle pretty much anything. It does come at a cost of £400-odd of extra steel but that was 1/2 the cost of the extra concrete needed in an alternate approach (not forgetting the need to dig the hole deeper as well).

It does make me wonder just how good a job the companies that estimated this work for me would have done. Yes they might have finished now, but the life-expectancy of the work would have been severely compromised. One wasnt using any steel at all ("not needed") and the other said "oh we'll throw some in if you want".

Here's a Sketchup of the steelwork... all 418kg of it!