Mike Taylor wrote:

Look if you are offering advice make it totally unambiguous. You made a
comment on what the original poster stated to what the blockwork would be.
I think that was very dangerous as the original poster may follow your
advice. I and most of the others have started for a wall 10' high use a
structural engineer. I see no difficulty in following that advice. You may
have structural engineering capabilities, (but I personally doubt it) if so
how can you advise on what is required, in possibly, a very dangerous
situation, without knowing the full facts. Your advice about a good
foundation and good drainage behind the wall is fine but to say use "x"
block for the bottom third then use "Y" block for the rest is not good
advice in this situation.


A structuralk engineer is simly a DIYer who has access to more data than
the average, and has professional insurance to back it up.

When *I* said 'look at the way a dam is built', I did that from a sound
grounding in basic structural engineering. Water is teh worst of all
becuse it has no friction - its all weight and its all fluid. If a wall
will hold back water it will hold back soil.

The inverse parabolic arch with buttresses is a good design.

So is filling it with steel. Blockwork can take massive compressive
forces, but its lousy in tension.

The art of the design process is to make sure it never does.

The other technique is to use massive weight in the wall itself and
broaden its bsae so that the total vetor sum of the forces on any block
never falls outside the wall. Thats how they built the mediaeval
cathedrals and fortresses.

A 45 dgree trianguar corss sectuoj wall will never break, but it may
slide - thats fixed by keying it in underground.

You can protype a wall like this by using a few wood blocks and some
sand behind it and then hosing it. This will imediately illutstrate all
the failure modes and where the stresses come.

I agree that a badly built wall of these dimensions is an extreme hazard
- it will give way in wet weather and caase a slide. The solution is to
prootype it, to drain it - to seek professional advice if you want some
guarantee - but most f all to bbulid it extremely massive at teh base on
sunbstantial foundations and to build it sloping inwards and backards
into the soil wall. And arrange drainage and backfill with loose material.

I took a trip to Lolworth cove this summer: Its instructive to look at
the natural eroson there, and the angles of slopes of the softer
sandstomnes.

Sadly an arch I remember has now gone altogether. Thats sandstome for you