On Fri, 16 Apr 2010 22:40:59 +0100, ®óñ© © ²°¹°
wibbled:

On Fri, 16 Apr 2010 19:29:54 +0100, "rtreter"
wrote:

Hello -

I'm planning to have a retaining wall built to hold back a 1 metre
height difference between two gardens, It will be built from blocks
mortared togther. I guess the concrete footings will extend about 1
metre below the surface of the "low" garden. There are some trees within
30 cm of the planned location of the wall, their trunk diameters range
between about 5cm and 20cm. I don't want to kill or substantially harm
the trees.

The builder I'm getting a quote from says he will put lintels into the
wall and footings so that roots larger than about 1cm in diameter don't
have to be cut. Is this a sensible approach, for the trees and/or the
wall?


Sorry, I can make no sense of this at all.

I doubt that 1 metre of footings will be put in below the surface of the
bottom level.

And are you seriously saying that the wall footings will be within 12
inches of an unspecified number of trees and that the builder is going
to accommodate all of the tree roots larger than 1/3 of an inch, not cut
them and allow room for their future growth?

I am boggled. Are you using a builder or a conjuror?

He is suggesting building a wall within 12 inches of trees, some of
which have trunk diameters of 8 inches, without cutting or disturbing
their roots.

Why bother with such an impractical project. I would stick in a graded
slope and live with it.

If a wall is required, I would consider a curved wall - that's one that
leans over and into the earth mound - see a few ancient ones round here,
all of one brick thick and they've survived. However, won't work with
modern building methods (ie hard cement). If doing such a wall, I'd lay
the first course onto earth about 1 brick under the surface direct to
dirt and use clay or lime mortar for joining them. They work by the
physics of a graded slope but you can get away with a someone sharper
slope as the bricks reduce the tendency of the earth to wash down with
rain and the weight of the bricks works to balance the pressure of the
earth. Think dry stone wall on a sideways lean.

These sort of walls typically hold back 2-2.5 ft of earth bank quite
happily for decades - dunno if that is sufficient for the OP.

Then accept that as the trees grow, the wall moves and bits of it may
need adjusting and re-bedding.

The modern version of the same line of thought are these:

http://www.dme.co.za/sites/site1/ima...ation/RWBD.jpg

Got them at the local kiddy nursery - simple, effective and laid "dry".
Made of concrete and can be planted with ground cover plants like heather
and creepy things to make them look good. In the local case, I think
(without a tape measure to hand) they are holding back a bank about 3-4'
high at an angle of about 15 degrees off vertical. Work by interlocking
and dead weight (once filled with earth). Again, the trees may move them
and it won't matter too much. When/if it matters, disassemble and re bed
the damaged section to accommodate the tree. Building next to trees
requires the "earthquake" mentality - either stupidly strong (hoover dam
strong) otherwise the tree will prevail eventually - or make it flexible
and accept Nature.

Cheers

Tim
--
Tim Watts

Managers, politicians and environmentalists: Nature's carbon buffer.