Structural Engineering Question
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It doesn't need the slabs at the end, and they won't give it any strength whatsoever. Given a proper foundation, that wall will be fine just built of 100mm blocks (goodness, that sounds ugly, though!). If you are at all worried about its strength, (and you have no need to be), then leave some re-inforcing bars sticking out of your foundation behind the line of the blockwork, and cast a fillet of concrete behind your wall prior to backfilling.
Architect, not engineer, but the engineers (if we have any here) will tell you much the same.
Mike
Architect, not engineer, but the engineers (if we have any here) will tell you much the same.
Mike
[QUOTE 3064295, member: 9609"]the blockwork will be hidden by stone in a drystone dyke sort of appearance.
surprised you don't think anything at the ends would add strength, would have thought a dam shaped walls strength come from the ends. When you say a fillet of concrete behind the wall I'm presuming you mean on the opposite side to the load ?[/QUOTE]
No, the fillet would be on the same side as the load.
The normal rule of thumb for minor-works/ garden type retaining walls is that they should be 1/4 of their height in width, assuming there is no engineering involved. This assumes a straight wall. Your wall will be 2 blocks high, or 450mm. This gives a theoretical thickness of 112mm assuming it was a straight wall. The fact that you have curved it means that its structural depth is increased anyway, so already it is strong enough: it isn't going to get pushed over. Now you tell me there is a dry stone wall standing in front of it: well, this on it's own would retain the soil behind, but combined with the blocks, and the curve, mean that you have big margins built in already. Deal adequately with the movement of water behind, and that job is completely sorted.
The fillet of concrete I was suggesting is just additional thickness to the wall at the place where the strain is the greatest, and more than that, helps "stick" the wall to its foundation. But, as I've described above, you don't need it.
All of this, as I have said, assumes you put in a proper concrete foundation. If you don't, then disregard all of the above, and simply build a thicker drystone wall than you would have done otherwise. Indeed, this would be my preferred solution anyway, as not only are they brilliant retaining walls, aesthetically pleasing, but they also are great at letting groundwater out of places where you don't want groundwater.
surprised you don't think anything at the ends would add strength, would have thought a dam shaped walls strength come from the ends. When you say a fillet of concrete behind the wall I'm presuming you mean on the opposite side to the load ?[/QUOTE]
No, the fillet would be on the same side as the load.
The normal rule of thumb for minor-works/ garden type retaining walls is that they should be 1/4 of their height in width, assuming there is no engineering involved. This assumes a straight wall. Your wall will be 2 blocks high, or 450mm. This gives a theoretical thickness of 112mm assuming it was a straight wall. The fact that you have curved it means that its structural depth is increased anyway, so already it is strong enough: it isn't going to get pushed over. Now you tell me there is a dry stone wall standing in front of it: well, this on it's own would retain the soil behind, but combined with the blocks, and the curve, mean that you have big margins built in already. Deal adequately with the movement of water behind, and that job is completely sorted.
The fillet of concrete I was suggesting is just additional thickness to the wall at the place where the strain is the greatest, and more than that, helps "stick" the wall to its foundation. But, as I've described above, you don't need it.
All of this, as I have said, assumes you put in a proper concrete foundation. If you don't, then disregard all of the above, and simply build a thicker drystone wall than you would have done otherwise. Indeed, this would be my preferred solution anyway, as not only are they brilliant retaining walls, aesthetically pleasing, but they also are great at letting groundwater out of places where you don't want groundwater.
Mr Celine
Discordian
- Location
- Waxing my moustache
I built (and rebuilt) a similar height dry stane retaining wall. To avoid looking out of scale with the full height wall at the opposite end of the garden it was built with smaller stones and much smaller copes than normal. Due to the lack of weight of the copes it fell apart after about 8 years.
I rebuilt it with weak concrete instead of hearting behind the building stones and cemented the cope stones on. Looks the same as it did before, ie like a dry stane dyke, but it holds together fine and the stones don't get dislodged by cats / chickens / lawnmowers etc.
I rebuilt it with weak concrete instead of hearting behind the building stones and cemented the cope stones on. Looks the same as it did before, ie like a dry stane dyke, but it holds together fine and the stones don't get dislodged by cats / chickens / lawnmowers etc.
Archie_tect
De Skieven Architek... aka Penfold + Horace
- Location
- Northumberland
215 thick blocks infilled with a rubble/ cement mix will hold back more than 450mm but they will slide on the hardcore base without a foundation Reiver, especially if there's any sort of load on the ground behind them. You should build in a movement joint every 6 metres in blockwork for expansion/ contraction [ideally 2 in the 15m length would do it, one in the centre at a pinch...
Archie_tect
De Skieven Architek... aka Penfold + Horace
- Location
- Northumberland
Sorry Reviver.... I'd just have a go.... it's not the end of the world if you got a crack and had to rebuild a couple of blocks in a few years time anyway... forgot it'll all be masked by a dry stone facing so it'll all just settle in together.... would it matter that much if it settled a bit?
Don't worry too much about the movement joint/s, although Archie-tect is correct. You are hiding the wall anyway behind a dry-stone wall, so a crack or two is unimportant. However, not being on a foundation is important. You will have cement, you say, so why not do the job properly and cast up a concrete base?
Other than that, if you are determined to just use hardcore, then drive some reinforcing rods say 1200 long straight down through it, say every 3 feet (900mm), and leave them sticking up 150 or 200mm. These should stick into the holes in your blocks, and you MUST use concrete (not rubble) to fill the blocks. That way there should be not sliding on the base, at least for the 10 or 20 years it takes for the rods to rust through.
Other than that, if you are determined to just use hardcore, then drive some reinforcing rods say 1200 long straight down through it, say every 3 feet (900mm), and leave them sticking up 150 or 200mm. These should stick into the holes in your blocks, and you MUST use concrete (not rubble) to fill the blocks. That way there should be not sliding on the base, at least for the 10 or 20 years it takes for the rods to rust through.
