Monday, 27 April 2009

The man from NHBC, he say 'OK'. Here are a few pictures of the finished foundation dig, the first one (as promised ages ago) standing on top of my garage:

One of the unexpected things we discovered, in a sand subsoil, was a strip of clay running diagonally across the site! When spades first started hitting hard clay instead of soft sand, alarm bells started ringing, because neither of the two trial pits found the underlying clay at a depth of 2m+, so to find it at 6-700mm down was a surprise to say the least, but we think this may be a deep service trench, possibly abandoned now, that was dug into the clay and backfilled with it, explaining why locally the clay is higher than you would expect. We solve this issue (clay takes much longer to settle than sand does, possibly leading to subsidence years down the line) by adding some steel mesh fabric to the bottom of the trench, like this:

Order a sheet of A393 mesh from our good friends at Senior Steel, and chop it up into 500mm wide strips:Chop a 2" thick concrete paving slab into little pieces:Support the strips of mesh on the bits of slab, making sure to overlap the mesh by 40D (40 x the diameter of the bars = 40 x 10mm = 400mm overlap):

Job done :-)

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