We need to build a retaining wall as our plot is on a slope, and the house will be around 1.3 to 1.8 metres below the ground level to the north (there's a photo of the scale model here: http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=9114&page=1#Item_1).

The original plans (that came with the plot) stipulated steel piling driven in along the northern boundary then excavation, followed by the building of a stone wall, with the stone wall foundation being a massive reinforced concrete beam. I'm concerned that the piling will create a fair bit of nuisance, as I'd imagine that driving in around 35 metres length of piles isn't going to be quick or quiet.

The ground is reasonably OK, it's the lower part of a former orchard. The top soil layer is fairly thin, with chalk and then greensand underneath (no clay, AFAIK). There may well be springs that appear when we cut into the bank, I've been told, as there are several springs along the side of this valley that drain into the mill stream on the southern boundary.

The wall needs to be near-vertical, to give me room at the lower level, so a solution like the ABG Webwall one that Joiner linked to a day or so ago wouldn't work. I would prefer to minimise the amount of nuisance to the neighbours (who are generally OK about the build), plus access for big machinery isn't that easy, as the bridge over the stream has a weight and width limit.

Screw piles seem a possibility, as they can be placed using a JCB with a torque drive on the jib, but I've no experience of them and wonder about the long term reliability in wet ground.

Stone filled gabions might be another possibility, quite an appealing one as they would allowa water to drain through from the high ground to the north, but what do you do to shore up the excavation before they go in?

I think I'm resigned to having to have a fair bit of concrete in there somewhere, but would like to try and avoid it if possible.

Does anyone have any expertise or experience in retaining wall construction they could share, please?

JSH

Is this of interest?

http://www.acheson-glover.com/commercial/products/retaining-walls/

Posted By: JSHarris..................................... in that there's a need to put something in place to hold the ground behind in place whilst excavating.

Could try this but probably very expensive.
http://www.bdf.co.uk/ground_freezing.php

<blockquote><cite>Posted By: owlman</cite>Posted By: JSHarris..................................... in that there's a need to put something in place to hold the ground behind in place whilst excavating.

Could try this but probably very expensive.
<a rel="nofollow" href="http://www.bdf.co.uk/ground_freezing.php">http://www.bdf.co.uk/ground_freezing.php</a></blockquote>

That's a neat idea! As you say, probably a bit on the expensive side, though.



<blockquote><cite>Posted By: tony</cite>small sections will stand up on their own, then work across using boards to keep top of done ones clean (and hope) build like a brick wall racked back?</blockquote>

Thanks Tony, I hadn't though of that. The chances are that would work OK, as the slope isn't very steep at the moment and the bit where we suspect there might be water is at the 1.3 metre high end, rather than the 1.8 metre high end. I'm hopeful that we'll hit solid chalk a foot or two down, which will make life much easier, as a chalk "cliff" should present little risk of collapse, I'd have thought.

Worst case would be trying to do it now, after months of heavy rain and water flowing pretty much everywhere. In some respects the long delays I've hit with planning etc have done me a favour! Somehow I've got to allow for all the surface run off from the sloping land above this wall and direct it down to the stream, perhaps via a water feature in our garden. This is another reason that using gabions seems attractive, as they would allow presently unknown springs to flow through and down to be captured and diverted at the bottom. I suspect I'll still need a fairly substantial concrete foundation, not so much to support the gabions as to avoid water erosion at the base.

<blockquote><cite>Posted By: fostertom</cite>You can't get permission to encroach temporarily on next door? - excavate a bank shallow enough to be stable, build a single skin wall (or temporary shuttering) on the boundary and backfill behind with v weak conc full of lumps of old masonry - any old massive rough stuff with just enough cement to bind together. Or - put back the excavated soil with cement mixed in.</blockquote>

Yes and no. The land immediately above has a couple of small (but nice) trees on it, that are too close to allow me to excavate back. At the shallow end (to the west), the neighbour would quite like me to build up the height of his land, to get rid of the steep slope he has in that corner, so I can happily dig back there. The wall would then be built up to around the same height as at the deep end (to the east). The problem area is really from the centre to the eastern edge, as this is where the most material has to come out and where I can't dig back into the neighbours land.

I've also got to plan for water being around as soon as I dig this out. We already have a small intermittent spring right at the western end (where the land dips a bit) and suspect there may be more once we start to excavate. The ground rises steeply behind the plot (to the north east) with the ridge being around 60 m above the plot about 1/3rd mile to the north east. The slope to the NE is pretty steep, as the large area elevation cross section below shows (the plot is right at the bottom of this, to the left).

we are looking at this system of pile driving using a bobcat
http://m.youtube.com/#/watch?desktop_uri=%2Fwatch%3Fv%3DsLAW_YLumec&v=sLAW_YLumec&gl=FR

Thanks folks.

I like the look of the timber crib, my only concern would be long term safety. About half this wall will end up 1.5 m away from the rear wall of our house, making replacement in 20, 30 40, 50 years pretty difficult and endangering the house if it failed prematurely.

Screw piles are on my list of techniques to suggest to engineer, I like the way they can be driven in quickly and relatively quietly. I've already been in touch with a company who can do this.

I like the idea of the king post and sleepers solution. There aren't any adjacent buildings to worry about, the nearest house is a few tens of metres away. I don't really like the idea of a smooth stone wall, as currently proscribed, anyway, and would prefer something that looks a bit less regular, and over which we could grow climbers etc to give a more natural look.

I'll do some more digging around and then go and see the engineer armed with at least a bit more knowledge than I had before.

<blockquote><cite>Posted By: SteveZ</cite>Hi JSH. I have posted my experience with a retaining wall elsewhere on the forum, and I can see that you want a cast-iron guarantee that it won't fail, but around here (N Cornwall) we have Cornish Hedges (2-sides) and Banks (single side/retaining wall) well over the height of your requirements which don't seem to have moved at all over the years.

My retaining wall is around 6 feet high, and although it has only been up a couple of years, has shown no signs of moving. The water drains through it when necessary and it looks much more attractive than the concrete monstrosity designed by the civil engineer I consulted.

It will need a 'batter' or vertical concave curve when built to lock in the individual stones, so it won't be strictly vertical but it will be close to it. If the worst case happens and there is movement, it is not too difficult to repair a section. A real benefit in your case is that it can be a thin wall, maybe 15" thick or less. Mine is 'mortared' with quarry dust, not the more usual earth, which I think adds to the stability as the 'fines' in the dust bind together.

If you do consider this idea for such an important location, please employ a proper hedge builder.

Best wishes, Steve</blockquote>

That's a great idea! As it happens, I have a tame Cornish landscaper (Simon Harris Trees & Grounds Ltd, Polgear, Redruth) and he's got a waller/hedger I believe. Looks like a brotherly visit might be called for.................

with apologies for the diversion.....

Posted By: JSHarrishow do you dig away the ground and stop it sliding down before you put them in place?

I don't know, our 4.5m banks held up with luck alone until we back filled. I was asked the same question by an ex-miner on my way down the brick-lined lift shaft at the National Coal mining museum ( an interesting, free day out whatever the weather!) and I didn't get an answer. How did they do it? I'd love to know.

http://www.ncm.org.uk/visitors/underground-tour (second picture down)