Concrete retaining wall


1 May 2009
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United Kingdom
I have a 33m long by 2m high reinforced concrete retaining wall to build along a riverbank which will then be stone faced. I have two solutions from the structural engineer 1) hire in shuttering and pour the concrete 2) build a 150mm cavity block wall and fill that with concrete both will have a steel reinforcing skeleton designed by him. anyone been through this scenario before and how did it work out

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Couple questions before making any comment.
How close to river is wall?
Approx depth of river in middle?
Foundation size on SE drawings?
No problem on dry land, along side river, will be a beast.
old un.
the river is really a stream and at this time of year only about 20cm deep about 3m wide but can flash flood. We have to build a coffer dam (just sandbags) to keep the footing dry, the foundations are to be excavated below stream level and the base 200 to 300mm deep about 1.5 m wide. I intend to do the wall in 3 sections each 11m long. In non flood conditions the base of the existing wall is above stream level up a short bank, in flood conditions or heavy rain the level will reach the wall bottom, the wall has to be removed to build the new reinforced retaining wall.
can it not be done with piled in oak sleepers or gabion baskets?
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Wouldn't have thought gabions would be waterproof enough to prevent flooding. Aren't they to stop erosion?
Gabions are used on the stream in places to stop erosion, they have been ruled out here, once the retaining wall is up foundations for a new hose will be built, the reinforced concrete is the solution agreed by 2 different structural engineers. My question is shuttering or build a block cavity and fill, farmers or ground blocks again have been ruled out as a solid concrete core is required. The existing wall is in poor nick but is not bulging showing the ground to be stable. We could use piles for the house and just tart up the wall but the concrete route seems the most complete to make a good job. Shuttering sounds easy but I sort of prefer the filled block wall for no other reason than that's what i'm used to...any thoughts
Read your last post, and reading between the lines, you appear to have a fair bit of knowledge about what you propose to do.
As you will appreciate the only scant information is what you have provided, so all I am going to do is ramble on a bit and hopefully some thing will be of use to you.
Couple of quick figures, materials stands, you in at £4500.00, conny, blocks sand and cement. No reinforcement allowed for as there are a couple of ways that SE could have gone about it, which should be shown on the comic.
Before going any further, do not know distance new house will be from stream, but would have given a lot of thought to piles well below bed of stream and ring beam for house or max 2.4m dig to below bot of stream and trench fill foundations and block and beam ground floor, with the beams running parallel to stream.
Possibly, you have thought about this, and for some reason unexplained you still want to go down the wall route. For all I know, you may have a ferry docking alongside once a week.
Would rule out the shuttering route and go blockwork. Reason, no where for raking shores to shutter unless you put some good heavy baulks in across stream. Shutter would all have to be tied back into bank, and even then I would be very suspect that it would hold together when poured and vibrated. That sounds sexy.
Go along with the 1.5m width founds and I would like to see 600mm dig below present water level with 400mm reinforced concrete across the width to stop er breaking er back
I know you have said that she is to be stone faced, but an over all thickness of 350mm by 2.0 metre high worries me. (Have I read the thickness correct?). Would have liked to have seen more meat down bottom, but then again do not know what or how SE has drawn up steel. Can only guess at what he has done.
Yer big problem is getting above the water table. We done one similar 5 years back and we caught a right cold getting up out of the water.
If yer still wish to go this route, and not trying to tell yer how to suck eggs, this is the way we would go.
Depending on present angle of repose, get 3 tonne 360, thats got a 3.0m dig, of set jib and 1.550 width. They are about with a 3.0m dig. Stand on top of bank and take out 1.7m on the flat 200mm above water height all along bank. Slew round 180 and deposit well clear. Go back to start, dig yer way down slope to bottom with enough width down bottom to turn er 90 degree. Start ripping out found trench and place spoil on top of bank. Could really do with 1 tonner on top pulling spoil back, if not watch banks very carefully, or you could get a slip that will take machine into stream. Try this first
Dpending on the excavated material, try tipping half dozen buckets in edge of stream tamp down with bucket to act as coffer dam. May work, may not. We have floated two or three scaffold boards fixed end on to one another and anchored down in stream with long length of visqueen 1.2m wide draped over boards and other edge placed in water by bank. place our excavated fill on this, tamped down and then from the middle pulled visqueen back over the top of temporary coffer. If you do this, then on completion, go back with ditching bucket, stand on top and clean out stream. If you do not think this will work then you will have to sand bag it. What ever way you go you will need decent pumps. Anywhere from 75mm centrifugal up to 150mm to deal with water coming through stream bed and into trench.
Dig yer 11metres, go on couple more metres and dig yer way out again. Use this route when you go back down again for next 11 metres.
One other thing if you dig your flat 200mm above water level and three to four hundred mm from stream edge you nay not need coffer, just pumps to deal with water coming from stream bed.
You will normally require expansion joints in block work 3.0m in and then every 6.0m, but depending on your skeleton and SE instruction they may not be required. Lets say they are required, so your bricklayer has got a 9metre lump to go at. He is only going to get 5 course, as over this they swim about like a newt, and they are to heavy to lift, well thats my excuse any way. Gives him 110 blocks for day. He is not going to get rich, but he has just about covered his days money.but not the the hoddies. Can not go any further as know nothing about your skeleton.
Hope there has been a few bits in here helpful to yer.
old un.
Thanks oldun for such a comprehensive reply, especially since you didn't have all the info. We have certain things forced on us by the Environment agency (coffer dam) but we also have some things going in our favour (hopefully). The drawing shows the section, the existing building is a large steel shed with minimal founds but the whole site appears stable and has been like this for many years (the building 20+yrs) also part of the stream shows outcrops of bedrock which we may or may not find. A lot of what you say is broadly in line with our plans and I'm glad you agree with the filled cavity option, we were going to run 4 courses let set for a couple of days then fill and tamp but not vibrate as this may break the wall apart. The SE feels the reinforced wall is mainly to protect from erosion in flood conditions rather than holding up the site. Once the wall is up the site should be able to be developed as a normal site although as you can see the front foundation wall will go right down onto the reinforced base and this will be layflat block upto ground. I am planning to go in with a smaller digger (at least for the first 11m) as it will be exploratory and we will see what we find. Also the operator already has done some digging on this site before and thinks it can be done by going down in a terrace much as you suggest.
Again thanks for the input, sometimes forums can be a chance for wringing of hands, you have restored my faith.

I would go with the pure RC wall.. it will last longer and wont need as much maintenance as the cavity filled option..

As oldun says movement joints will be required in the cavity filled wall about every 6m, and may well be required in the RC wall as well but should only require 1 joint..

ps. The weight of the building on the back of the wall will greatly help with the walls performance theoldun so dont worry about the thickness of the stem
Static. How will a pure RC wall last longer than a filled cavity. The pure RC was going to be 200mm thick compared to 150mm cavity but the cavity RC will be sandwiched between two 100mm block walls with lots of wall ties. The steel skeleton will be much the same whichever method. Also the idea of maintenance is a heart stopper! this is intended to be a whole life solution with the only exception being the stone facing which would be the case whichever method is used. It would be possible to fill the 650mm gap between the back of the RC wall and the layflat house foundation wall with concrete and even another skeleton but this is felt by the SE to be unnecessary and can be filled with loose stone/hard core keeping the costs down. What do you think??
Pure RC wall could have a design life of 120 may 150 years.. whereas the cavity wall tend by nature to have less cover to reinforcement thus can never achieve a 120 year lifespan, so may need replacing every 60 odd years.. most of this may seem like crazy talk and nothing to worry about but part of my job is to consider what your great grandkids are gonna have to do ;)..

Anyways the cavity wall will need more maintenance.. it will need repointing every 20 or so years, frost will cause bits of the blockwork to shear off as it is a weaker material subject to alot of water penetration..

The infill with conc is as the SE says not required.. better to put some drainage down there to keep water pressures down.. then backfill with loose stone..
Have seen the comic, as you say gives lot information I did not know about. Read Statics post. Am tied up couple days. ASAP will come back with another ramble for you to pick bones out of.
old un
Static, I believe the only stupid question is the one you don't ask so here goes.. are you sure you are looking at the sketch correctly? the only way to do maintenance to the block wall will be to excavate out the loose fill down to the base (~1.6m) thereby opening up a 650mm cavity on the house side, and on the stream side taking down an~300mm solid stone facing wall, doing a spot of pointing and then rebuilding everything!! and this every 20 years. The only frost damage should be to the outer stone wall which I agree will need pointing every 20 or so years. Everything else is buried as an integral part of the overall foundation. Also the longevity of the wall, maybe I should increase the cavity from 150mm to 200mm which will then match the pure RC spec, the blockwork then becomes simply a shuttering system and if it crumbles at all then so what, one side becomes part of the loose fill and the other just a bit of wall rubble. I'd be happy to do this little bit extra (~2.5 cu m of readymix) if it going to double the life of the wall. or am I missing something?
Sorry, but do not agree with Static regards maintenance. Have read CBA report with regard to life expectancy of concrete blocks being 60 years but it is not a proven point. Have also read CBA conflicting report stating that life expectancy of dense concrete block does not deteriorate with time, providing it is protected from aggressive chemical or abrasive situations. As your wall is completely encased on the inside and the outside is protected by an approx 150mm thick natural stone wall, I fail to see how any maintenance is, or will ever be required. There is one proven fact that I have read, the first recorded concrete block house built was on Staten Island USA in1837, and is still standing. That makes er 173 years old.
With regard to pointing of stone wall, stopped of on me way to London about 6 months ago to have a look at a large lump of York stone wall that I built with the old gentleman who taught me my trade back in 1953. There were half dozen odd bits of pointing missing down at ground level. Now that was done 57 years ago.
Okay Tul, Get back to post now. As said, sight of a comic is worth a 1000 words, but still very much to the imagination. At least puts me mind to rest about extra meat at bottom of wall. House founds lock all together.
Imagination, such as, what is length of present retaining wall, where does this fit into the equation of the new 33m wall? Why do you want a 33m wall for single unit.? Depth of house as shown about 4.7m. To pitch stairs from river front to first floor back wall and back corridor, with say 4 beds and bathroom, you are looking for about 14m in length. Once again what is rest of wall retaining?
Another point to bear in mind. At the top end of wall, flow end, consider splaying her back into bank at say 20 degrees to stop water going in back of wall when flash flood occurs. Will sweep water out into main channel and down wall.
Will come back to yer excavations and founds later, just want to pop this in.
Don’t know what your local stone is up there, or whether you buy it coursed, cropped, pitched, split ot random, but whatever you get, will have minimum of 150mm thickness, and if she is walled up right, yer can forget er for the next 50 years. The other reason I say block and fill, is that I started to throw a few figures at one another, and it soon came apparent that block and fill was going to come out cheaper and more easy. A good form work chippy would really struggle to rack that lot of shuttering up out of the stream. .
Will come back to excavations later. Consider, throwing your footings to house up to ground level first, and working yer way out to stream. Look at the section on the comic and you may see the reason why. See em. No. Okay, you will only have 450mm working room for house foundations if you work in towards house, no room for scaffold, and if you have a slip whilst blockwork is still green lads will be buried alive. This way they can jump into stream. You say block laid flat, this will only give you 215mm wall, yet you want a 300mm wall from splash course up, so lay 2 flat and one on edge in front to give yer 300mm wall. Bump yer flats up a bit to keep gauge. Reverse bond next course. You will get to ground level in two lifts. Over 900mm high conny blocks swim all over place. you might squeeze 1.050m high,, depending on weather.
Place some concrete blocks in stream as base plates, stand putlogs on them and run 5 board wide scaffold down and over stream. Issue brickies with frogman flippers and snorkels, they can lay back skin of wall overhand, lay front skin and scaffold is in place for stone work.
Am bored now, but there are still a few items to tell yer now that I have seen comic, so if you want will come back in couple days. Flag it up so know you read it.
old un.

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