Thread: Retaining walls, anyone?

I have had a retaining wall built around my land - about 150 m long, on three sides, with the fourth side being the road.

The land varied in depth from a metre or so below road level near the front (the road) sloping down to nearly three metres at the back, so the wall is between those heights intended to hold back the landfill, which was piled in the centre while the wall was being built. The landfill had been in place for about a year before the wall was built.

To cut a long story short the wall was badly designed and poorly built, using cheap materials and the construction company and I have parted ways, but I am now left with trying to make the best of a bad situation - knocking it down and starting again isn't an option.

The design of the wall looked good (at least to an amateur): posts every three metres going down 1.5m to 1msq footings, with a "stay" at 45 degrees from the top of every other stay going down to a 1msq footing level with the base of the wall, with "H" section posts into which 3m x 35cm pre-cast panels slotted, with a poured concrete beam top and bottom.

Unfortunately not only was the workmanship not great (no further comment necessary), but when the landfill was put back it was very clear only the next day after a couple of hours' heavy rain that there was no way that the wall as it stood could hold back the landfill - half a dozen of the 300+ panels had already "bowed" out and had a hairline crack in the middle. We immediately had the outside couple of metres of fill pulled away from the wall to limit any further damage.

The problem now is what to do to try to strengthen the wall so that we can fill it at least as high as it is practical, if necessary with a slope down around the perimeter.

My plan is to dig down to the base of the wall and install an extra set of panels, probably three panels high, against the posts so that I effectively have a double set of panels at the base going halfway up, with a space between the panels on the "inner" set so that water can drain out between the panels. The space between the two panels would be filled with cinder blocks and loose gravel, allowing water to drain out of the drain holes in the original panels; this wouldn't be as strong as concrete and re-bar, obviously, but it would still allow drainage and (hopefully) the "sandwich" of the two panels would be much stronger than the original single panel. The new panels would be held in place against the inside of the posts by the pressure of the earth against them, although initially I may tie the inner and outer panels together using the lifting loops built into the panels just to hold them in place while the earth fill was being put back. Where the outer panels had actually cracked (fortunately only 6 out of over 300) I would fill the space with concrete and re-bar instead, as the water could drain out elsewhere.

The drain holes aren't the problem with the panels - there are two drain holes in each panel, one metre in from each end, and all the cracks are in the middle of the panels not at the holes. The panels are simply not strong enough and under pressure they will eventually either crack completely or "bow" enough so that they pop out of their groove in the "H" posts.

Digging out to the base of the wall isn't as bad as it sounds (and I won't be doing the digging!) as there is a large hole at the end of the walls at the road end where we will put the first set of panels, then earth will be moved from the next set to fill the hole and hold those in place, then the next set of panels goes in place and earth is moved from the next set up and so on.

I know that the situation isn't ideal and it all depends on the friction of the loose fill, on the slope, etc, but I am just after advice or views on whether I am going to strengthen the wall by adding the extra "sandwich" of panels, or if adding the extra weight of the new panels may outweigh the advantages as it will put extra pressure on the posts and break them instead.

Any ideas??


(Sympathy and "you should have done x, y or z" accepted, but not needed!!)

3 metre retaining walls-- Sheet piles.

Go here for some possible ideas?

https://teakdoor.com/construction-in-...mees-wall.html (Boon Mee's Wall)

Originally Posted by Boon Mee

Go here for some possible ideas?

https://teakdoor.com/construction-in-...mees-wall.html (Boon Mee's Wall)

Yeah...that was a decent thread back when, Boons.

Looks as the OP needs to cut his losses and redo - learning from experiences [we've all been there] and acquiring a quality contractor using better quality material. This attentive really applies towards perimeter/retaining walls - one just can't scrimp in this manner.

It would help any of us if you had pics of the wall in the condition it's in now to get an idea of how to help you.

We are on a steep grade so have a solid concrete with mega footing retaining wall up hill of house.... no issues.
Down hill side of house have a panel type retaining wall for a garden area with pre-caste concrete posts in footings. It started to bow out since somchai did not tie the posts to the footings.
I dug down around posts lots or rubble and concrete....worked okay since only holding back a few cu metres of soil.....looks shite even though we cannot see it now for weeds.

I think perhaps the best solution is to bite the bullet and build a new solid reinforced concrete wall with buttresses Maybe in front of old one ...recover panels and back fill?...........Band Aid solutions, Ha'porth of tar and all that.....

A good few panel and Lego type walls collapsed locally.

^^^^^
In the shorter term perhaps planting some deep rooted native grasses, longer term similar tap root trees may well answer to inhibit erosion and a slippage?
A line of dense fast growing trees on your view side can hide many a sin of course. Perhaps bananas?....555

Chrysopogon zizanioides - Wikipedia, the free encyclopedia
this can help!

Originally Posted by crepitas

We are on a steep grade so have a solid concrete with mega footing retaining wall up hill of house.... no issues.
Down hill side of house have a panel type retaining wall for a garden area with pre-caste concrete posts in footings. It started to bow out since somchai did not tie the posts to the footings.
I dug down around posts lots or rubble and concrete....worked okay since only holding back a few cu metres of soil.....looks shite even though we cannot see it now for weeds.

I think perhaps the best solution is to bite the bullet and build a new solid reinforced concrete wall with buttresses Maybe in front of old one ...recover panels and back fill?...........Band Aid solutions, Ha'porth of tar and all that.....

A good few panel and Lego type walls collapsed locally.

Sounds as if my wall may be better made than yours, which is small comfort, as at least I know the posts and footings are tied together as they were all poured in situ, and strong enough!

I don't have the option of building another wall, unfortunately, as the present one is along the perimeter of the land already and any buttresses would be on the neighbours' land and would block their access to their fields.

Ho hummm ......

Your problem seems simple.
You don't want to start again and the existing 3m panels are not strong enough.
Now given those two truths you have few options.
A new panel wall will likely encounter the same problems as the existing one, it will crack and pass the strain to the old one, which will fail in turn.

Or you could try to strengthen the existing one.
Imagine an inverted U shape concrete form which fitted over the exiting wall at the mid point of the panels with the tail of the U anchored to a similar i meter anchor as the pillars. On each side you would cast a 10 or 20 cm reinforced column joined over the top bar.
The weak point would be where the U form goes over the existing fenceline, I'm not sure rebar concrete could handle the stress.
Ask an Engineer.

Okay so no pics:
Some assumptions:
Your property is raised, surrounded by a plank wall, the lower part of which is a retaining wall.
You have observed the cracks in planks from outside your property.
The substantial poles are intact and do not appear to have moved.
A suggestion purely based on the above:
Order some longer planks (a mite thicker with more rebar perhaps) and stack on each other against poles, holding them in place with temporary props or back fill as each one is set in place. For aesthetics, cement over cracks on your neighbor’s side.

Originally Posted by Necron99

A new panel wall will likely encounter the same problems as the existing one, it will crack and pass the strain to the old one, which will fail in turn.

Agreed - that's why I'm hoping my planned "sandwich", keeping the old wall and panels in place and putting an extra set of new panels along the bottom half where the pressure is greatest, fitted against the existing posts, with a filling of loose gravel between the old and new panels which would still allow water to get out but "share" the strain between the old and new panels could be the answer.

Originally Posted by JohnG

Originally Posted by Necron99

A new panel wall will likely encounter the same problems as the existing one, it will crack and pass the strain to the old one, which will fail in turn.

Agreed - that's why I'm hoping my planned "sandwich", keeping the old wall and panels in place and putting an extra set of new panels along the bottom half where the pressure is greatest, fitted against the existing posts, with a filling of loose gravel between the old and new panels which would still allow water to get out but "share" the strain between the old and new panels could be the answer.

Good idea ..Sharing the strain on existing already over stressed planks suggests that you are expecting new planks will be strained also.
Consider simply doubling up on the planks against the posts maybe or manufacturing more substantial ones on site? Stacking heavy preformed posts may also answer.
Think planks are primarily designed for domestic flooring loads.

Originally Posted by crepitas

Originally Posted by JohnG

Originally Posted by Necron99

A new panel wall will likely encounter the same problems as the existing one, it will crack and pass the strain to the old one, which will fail in turn.

Agreed - that's why I'm hoping my planned "sandwich", keeping the old wall and panels in place and putting an extra set of new panels along the bottom half where the pressure is greatest, fitted against the existing posts, with a filling of loose gravel between the old and new panels which would still allow water to get out but "share" the strain between the old and new panels could be the answer.

Good idea ..Sharing the strain on existing already over stressed planks suggests that you are expecting new planks will be strained also.
Consider simply doubling up on the planks against the posts maybe or manufacturing more substantial ones on site? Stacking heavy preformed posts may also answer.
Think planks are primarily designed for domestic flooring loads.

We're thinking along the same lines. I'll try to post some pics, but as I'm also moving house (only 100m down the road!) it may take a few days.

Thanks .....

Retaining wall being built near where I live. I assume a concrete lintel will be bridging the retaining part between pillars. The guy in the photo is applying a waterproof rendering prior to back-fill.

Originally Posted by Pragmatic

Retaining wall being built near where I live. I assume a concrete lintel will be bridging the retaining part between pillars. The guy in the photo is applying a waterproof rendering prior to back-fill.

Looks like the rebar will support the poles, if that is what they are,pretty well but perhaps a swift kick may demolish the cinder/cement block wall?

Your original wall is already compromised so it's retaining ability can't be considered doubled if you simply back it up with a wall of similar thinkness, id actually consider it useless from how you describe, with retaining walls it is all about thickness and density of materials used in the wall, these vertical posts every 3 meters do little to strengthen a retainer.
As demolition of the wall you've already build isn't an option you will need to build a new wall up against the compromised wall.
Somchai builder isnt all that safety conscious so don't let them dig long excavations for the footing or they will likely cause a collapse putting the workers in some considerable risk.
It'll be a tedious drawn out repair but I've done this a few times before, ex builder.

In sections of two metres dig and pour new concrete footings, when set build a block wall of appropriate thinkness relative to the hight of the retainer at that point, 225mm base width per 1000mm retaining wall hight, example: 3metres in hight = 3x225mm at base. The width of the wall is reduced in the same manner as the wall is built allowing for at least 100mm at top of wall.
At every 300mm build 8mm re-bar into the cement bed joints that extends past the section by at least 200mm, this will tie into the next section to be built and add considerable strength.
Without seeing it this is the best advice I can offer, have fun

Originally Posted by crepitas

Looks like the rebar will support the poles, if that is what they are,pretty well but perhaps a swift kick may demolish the cinder/cement block wall?

The re-bar will have form work put around them and concrete poured into it, which will overlap the block sections, thereby strengthening the wall further. Personally, I would have the horizontal-ish supports, which will be buried, attached to every post. But these people have been doing it this way for yonks so let them carry on. It ain't my wall.

Originally Posted by Pragmatic

But these people have been doing it this way for yonks so let them carry on.

That's what got him into this position in the first place.

Originally Posted by Pragmatic

Originally Posted by crepitas

Looks like the rebar will support the poles, if that is what they are,pretty well but perhaps a swift kick may demolish the cinder/cement block wall?

The re-bar will have form work put around them and concrete poured into it, which will overlap the block sections, thereby strengthening the wall further. Personally, I would have the horizontal-ish supports, which will be buried, attached to every post. But these people have been doing it this way for yonks so let them carry on. It ain't my wall.

Thanks for posting the pics - I'll try to do likewise with mine soon. To be honest, having seen that wall, mine is 1,000 % better so maybe I'm worrying too much! Those "ground anchors" look a bit iffy, but I'm guessing (praying, if I was his neighbour!) that the landfill will only just cover the bottom, thicker part of the wall and not go as high as it is in the photos since as Crepitas said there doesn't look to be any actual strength in the blocks forming the wall between the posts at all.

Originally Posted by JohnG

having seen that wall, mine is 1,000 % better

Well stop worrying then.

Originally Posted by JohnG

there doesn't look to be any actual strength in the blocks forming the wall between the posts at all.

There isn't really other than when the posts are formed the concrete overlaps the block-work. Thereby giving it some sort of strength.
This is the only way I've ever seen a retaining wall constructed here. But it's a monkey see, monkey do world and that doesn't make it right.

Tried to upload pics following KM's pic posting tutorial, but I am afraid my pictures are all too many megabites and re-sizing is beyond me. Sorry.