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Building a retaining wall: Will this work?
Hi again all,
I am about to dig out a section of sloping hillside to make a garage or carport. I will end up (on the highest side) with a sheer face of earth approx 10' high and 18' long which I will need to retain. I am not very good at laying bricks or blocks, but I was wondering if, after digging and pouring my foundations, I could do the following: I have seen concrete formwork blocks (don't know the correct name) which are effectively two square 'tubes' in one block. They are hollow. Looking from above, they look like this... ================= = = = = = = = = = ================= Now, I was wondering about laying these blocks with vertical steel inserted into the hollow sections, and pouring concrete into them as I build. Effectively, - ending up with a concrete wall, - containing steel reinforcement. Is this a reasonable proposition? Appreciate any advice. H. -- Howard Coakley e-mail... howarddot}coakleyatcoakleydot].codotuk ICQ:4502837. (Try ICQ at www.icq.com) |
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#2
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for that height and length you will need without fail to get a structual
engineer to design your wall. If you know nothing about it then do not even start. 10' high by 18' long is an enormous amount of weight. You will also have a problem constructing it due to possible slip unless it is designed properly. Back to your original question about hollow concrete blocks then yoes in principle what you have said is standard practise for smaller retaining walls. |
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#3
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On Wed, 1 Sep 2004 12:03:47 +0100, "Mike Taylor"
wrote: |for that height and length you will need without fail to get a structual |engineer to design your wall. If you know nothing about it then do not even |start. 10' high by 18' long is an enormous amount of weight. You will also |have a problem constructing it due to possible slip unless it is designed |properly. |Back to your original question about hollow concrete blocks then yoes in |principle what you have said is standard practise for smaller retaining |walls. | Thanks for the help. Really, I am viewing this as only a garden wall, - it's nowhere near the house at all and there is no structure behind it. Also, I was only putting a hard-standing on the lower side to use as a carport, (maybe convert to a garage later). So basically, I was hoping to avoid paying a structural engineer by asking here instead! I'm glad my thoughts on the hollow block with steel is a good starting point. Appreciate your help. H. -- Howard Coakley e-mail... howarddot}coakleyatcoakleydot].codotuk ICQ:4502837. (Try ICQ at www.icq.com) |
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#4
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"Howie" wrote in message
... Really, I am viewing this as only a garden wall, - it's nowhere near the house at all and there is no structure behind it. Also, I was only putting a hard-standing on the lower side to use as a carport, (maybe convert to a garage later). So basically, I was hoping to avoid paying a structural engineer by asking here instead! A ten foot high wall on a sloping hillside is holding back an awful lot of earth. Offset the cost of paying a structural engineer against how you will feel when one side of your car has been decorated using concrete and loose earth. At least give one a ring and ask them how much it will cost to specify your retaining wall. Al |
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#5
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ok lets start from the beginning
you have said it is 10' high. Is it holding back 10' of ground? What is this ground? is it clay sand, rock? all these will have different characteristics on what weight they have, how much slump they give with different amounts of water in them. Is the retaining wall on the boundary of your property? If so check with your local authority. In most areas boundary walls NOT onto a highway can only be at 2 metres (6') without permission. At that point almost certainly the local authority will want to see how the calculations were produced. Next problem and possibly the most difficult one if you are intending to do the work yourself is how do you hold up 10' high verticle face of ground for you to build a wall against it. In many ground conditions if you cut a trench 10 deep it will collapse, possibly not as you cut it but as you are down there trying to lay bricks. Note if the wall/ground you are holdin up is 10' high then the foundation will go deeper. Dangerous conditions. Of course there are many ways of dealing with this, Pilling, battering the slope back are two that come to mind. As I said if your dimensions are anywhere near correct then 10' is a serious problem unless you have it checked by a person on site. Ground conditions are the all important thing here and for that you cannot describe clearly enough on here |
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#6
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On Wed, 1 Sep 2004 16:48:42 +0100, "Mike Taylor"
wrote: snip Is the retaining wall on the boundary of your property? If so check with your local authority. In most areas boundary walls NOT onto a highway can only be at 2 metres (6') without permission. snip Actually *any* wall higher than 2 metres needs planning permission whether it's on the boundary or not, Cheers, John |
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#7
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Howie wrote:
On Wed, 1 Sep 2004 12:03:47 +0100, "Mike Taylor" wrote: |for that height and length you will need without fail to get a structual |engineer to design your wall. If you know nothing about it then do not even |start. 10' high by 18' long is an enormous amount of weight. You will also |have a problem constructing it due to possible slip unless it is designed |properly. |Back to your original question about hollow concrete blocks then yoes in |principle what you have said is standard practise for smaller retaining |walls. | Thanks for the help. Really, I am viewing this as only a garden wall, - it's nowhere near the house at all and there is no structure behind it. Also, I was only putting a hard-standing on the lower side to use as a carport, (maybe convert to a garage later). So basically, I was hoping to avoid paying a structural engineer by asking here instead! I'm glad my thoughts on the hollow block with steel is a good starting point. Appreciate your help. It is,. Retaining walls are an interesting thing. Natural slip angle of scree and we soil is about 40 degrees: And wall that is more 'vertical' than that needs to be designed to take a thrust force off the soil. Classic methods are using steel ties back to buried blocks that take the pressure, or a curved and slightly sloping wall like a dam has. The worst possible wall is tall thin and vertical and flat. Make it much wider at the base, and dig it into the soil to the foot doesn't slide. If you lay horizontal steel, you can have it convex, but best is to make it concave like an arch laid on its side. Buttresses are good things if you can't make it slope. What would I do? Make it parabolic in plan, and dig down a couple of feet below lowest ground level and lay a concrete base with reinforcing in it. Then build using blocks steel rods and plenty of ties to make at least double concrete block at top, going to 3-4 blocks wide at the base, and use a buttress every 10 ft or so of at least a block width. Tie it all together with ties at every point. Leave drainage in the wall base, or put a soakaway of gravel and a pipe there to prevent water build up. Back fill with loose rubble and gravel and use some polystyrene sheet of about 3" thick against the uphill side of the wall, to allow for some 'give'. Won't hold a landslide, but won't start one either... H. |
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#8
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"Howie" wrote in message ... Hi again all, I am about to dig out a section of sloping hillside to make a garage or carport. I will end up (on the highest side) with a sheer face of earth approx 10' high and 18' long which I will need to retain. I am not very good at laying bricks or blocks, but I was wondering if, after digging and pouring my foundations, I could do the following: I have seen concrete formwork blocks (don't know the correct name) which are effectively two square 'tubes' in one block. They are hollow. Looking from above, they look like this... ================= = = = = = = = = = ================= Now, I was wondering about laying these blocks with vertical steel inserted into the hollow sections, and pouring concrete into them as I build. Effectively, - ending up with a concrete wall, - containing steel reinforcement. Is this a reasonable proposition? Appreciate any advice. This is not a "garden wall" This project is capable of easily killing people both during construction and after. You must get an expert to advise you. You will probably need a professional to do the building (or some of it) too. mrcheerful |
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#9
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Howie wrote in message . ..
garage or carport. I will end up (on the highest side) with a sheer face of earth approx 10' high and 18' long which I will need to retain. I have seen concrete formwork blocks (don't know the correct name) which are effectively two square 'tubes' in one block. They Now, I was wondering about laying these blocks with vertical steel inserted into the hollow sections, and pouring concrete into them as I build. Effectively, - ending up with a concrete wall, - containing steel reinforcement. Is this a reasonable proposition? yep. Yuo'll need a pretty thick wall to retain 10' of earth though, with equally good foundations. NT |
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#10
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Howie wrote in message . ..
Hi again all, I am about to dig out a section of sloping hillside to make a garage or carport. I will end up (on the highest side) with a sheer face of earth approx 10' high and 18' long which I will need to retain. I am not very good at laying bricks or blocks, but I was wondering if, after digging and pouring my foundations, I could do the following: I have seen concrete formwork blocks (don't know the correct name) which are effectively two square 'tubes' in one block. They are hollow. Looking from above, they look like this... ================= = = = = = = = = = ================= Now, I was wondering about laying these blocks with vertical steel inserted into the hollow sections, and pouring concrete into them as I build. Effectively, - ending up with a concrete wall, - containing steel reinforcement. Is this a reasonable proposition? Appreciate any advice. H. I would not use those blocks nor that reinforcement. Use normal solid (7 or 4N) blocks 330 thickness for the bottom third, and then reduce to 225mm for the top two thirds. The most important thing is to ensure a good sound foundation. If you want to put some reinforcement in, then place it in the [horizontal] bed joints as this will resist the horizontal thrust better than vertical reinforcement would. Loose fill beind the wall will help drainage and allow some compression of the soil. A land drain behind the wall would be better than weep holes too. dg |
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#11
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your basis for stating what you have is? You have obviously checked out the
ground conditions and got the calculations on hand to confirm this type of build at 10' high plus foundation havnt you?. I have to say what you have suggested is seriously dangerous. You may be right but if the original poster is correct with his height then I think you are wrong to suggest anything except get a structural engineer in to specify. He may only park a car there but when a visitor arrives and the wall collapses on someone then you obviously will stand up and say "I told him what to do" Please note it is not only dangerous to have a structure like this but also to try to build it. A 10' high wall of ground could be seriously unstable in itself. |
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#12
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"Mike Taylor" wrote in message ...
your basis for stating what you have is? You have obviously checked out the ground conditions and got the calculations on hand to confirm this type of build at 10' high plus foundation havnt you?. I have to say what you have suggested is seriously dangerous. You may be right but if the original poster is correct with his height then I think you are wrong to suggest anything except get a structural engineer in to specify. Err, I only comment on what I know about, and yes I am qualified in this aspect of structural design, thank you. My comments are sufficiently lacking in detail to give the OP some food for thought as a basis for further research. He may only park a car there but when a visitor arrives and the wall collapses on someone then you obviously will stand up and say "I told him what to do" Please note it is not only dangerous to have a structure like this but also to try to build it. A 10' high wall of ground could be seriously unstable in itself. BTW, this is a newsgroup where comments and opinions are offered. What the OP does with those opinions is up to him. dg |
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#13
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Look if you are offering advice make it totally unambiguous. You made a
comment on what the original poster stated to what the blockwork would be. I think that was very dangerous as the original poster may follow your advice. I and most of the others have started for a wall 10' high use a structural engineer. I see no difficulty in following that advice. You may have structural engineering capabilities, (but I personally doubt it) if so how can you advise on what is required, in possibly, a very dangerous situation, without knowing the full facts. Your advice about a good foundation and good drainage behind the wall is fine but to say use "x" block for the bottom third then use "Y" block for the rest is not good advice in this situation. |
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#14
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Mike Taylor wrote:
Look if you are offering advice make it totally unambiguous. You made a comment on what the original poster stated to what the blockwork would be. I think that was very dangerous as the original poster may follow your advice. I and most of the others have started for a wall 10' high use a structural engineer. I see no difficulty in following that advice. You may have structural engineering capabilities, (but I personally doubt it) if so how can you advise on what is required, in possibly, a very dangerous situation, without knowing the full facts. Your advice about a good foundation and good drainage behind the wall is fine but to say use "x" block for the bottom third then use "Y" block for the rest is not good advice in this situation. A structuralk engineer is simly a DIYer who has access to more data than the average, and has professional insurance to back it up. When *I* said 'look at the way a dam is built', I did that from a sound grounding in basic structural engineering. Water is teh worst of all becuse it has no friction - its all weight and its all fluid. If a wall will hold back water it will hold back soil. The inverse parabolic arch with buttresses is a good design. So is filling it with steel. Blockwork can take massive compressive forces, but its lousy in tension. The art of the design process is to make sure it never does. The other technique is to use massive weight in the wall itself and broaden its bsae so that the total vetor sum of the forces on any block never falls outside the wall. Thats how they built the mediaeval cathedrals and fortresses. A 45 dgree trianguar corss sectuoj wall will never break, but it may slide - thats fixed by keying it in underground. You can protype a wall like this by using a few wood blocks and some sand behind it and then hosing it. This will imediately illutstrate all the failure modes and where the stresses come. I agree that a badly built wall of these dimensions is an extreme hazard - it will give way in wet weather and caase a slide. The solution is to prootype it, to drain it - to seek professional advice if you want some guarantee - but most f all to bbulid it extremely massive at teh base on sunbstantial foundations and to build it sloping inwards and backards into the soil wall. And arrange drainage and backfill with loose material. I took a trip to Lolworth cove this summer: Its instructive to look at the natural eroson there, and the angles of slopes of the softer sandstomnes. Sadly an arch I remember has now gone altogether. Thats sandstome for you  |
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#15
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"Mike Taylor" wrote in message ...
Look if you are offering advice make it totally unambiguous. You made a comment on what the original poster stated to what the blockwork would be. I think that was very dangerous as the original poster may follow your advice. I and most of the others have started for a wall 10' high use a structural engineer. I see no difficulty in following that advice. You may have structural engineering capabilities, (but I personally doubt it) if so how can you advise on what is required, in possibly, a very dangerous situation, without knowing the full facts. Your advice about a good foundation and good drainage behind the wall is fine but to say use "x" block for the bottom third then use "Y" block for the rest is not good advice in this situation. I am not sure that you have grasped the purpose of newsgroups. My understanding is that a question is posed, and then a number of opinions will be given, from which the OP will form his own opinion. If we followed your reasoning, then no answers or opinions will ever be given - except perhaps consult a qualified bricklayer/painter/electrician/engineer etc in every case. If you review past posts, then you will see many posts of a structural nature and replies which are given without full information and without the benefit of a visual inspection. How someone can answer a question about some structural work without a proper site survey appears to be impossible. Yet, contrary to your views, this appears to go on daily on much of Usenet. I find that odd. And then, in total contradiction to the basis of your argument of commenting without the full facts, you proceed to add your own little [doubtful] comment. I find that odd too. Your advice to consult a structural engineer is wrong too. We have a very good structural engineer in our office, and yet he knows little about soils except for basic soil loadings. Should he be consulted? |
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#16
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"Mike Taylor" wrote in message ...
Look if you are offering advice make it totally unambiguous. You made a comment on what the original poster stated to what the blockwork would be. I think that was very dangerous as the original poster may follow your advice. I and most of the others have started for a wall 10' high use a structural engineer. I see no difficulty in following that advice. You may have structural engineering capabilities, (but I personally doubt it) if so how can you advise on what is required, in possibly, a very dangerous situation, without knowing the full facts. Your advice about a good foundation and good drainage behind the wall is fine but to say use "x" block for the bottom third then use "Y" block for the rest is not good advice in this situation. Sorry, I posted before finishing my reply. So if you are going to give advice on who to consult, then please be accurate in the profession you advise to use. The OP should use a 'competant' or 'suitably qualified' person. That person may or may not be a structural engineer . Being pedantic? - well if the ill informed person asked the structural engineer from our office to design his wall, then he could be in just as much trouble as if he built the wall himself. dg |
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#18
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"Sam" wrote:
Sorry, dg, but you are wrong on this one. A 330mm blockwork wall will never be strong enough to retain 3m of soil, even with no surcharge on the retained side, no water etc. There's an awful lot of assertions in this thread. Outside my back door is an earth bank, sloping backwards at about 10 degrees to the vertical. There is an un-reinforced concrete footing which is 1.5ft high and about the same deep, followed by 3.5ft of dry stone walling, maybe 8" deep. The remaining 6ft of bank is not retained by any structure. In total, I am guessing that this is considerably less support than a 330mm blockwork wall, and it has all been in place for about 80 years. My point is that no-one can make absolute assertions about what is or isn't sufficient to retain an earth bank unless they investigate further. The best advice is to consult someone who knows what they are talking about, and is prepared to guarantee their conclusions. It doesn't help slagging off other people on here. Just my two cents, Al |
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#20
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Howie wrote:
I am about to dig out a section of sloping hillside to make a garage or carport. I will end up (on the highest side) with a sheer face of earth approx 10' high and 18' long which I will need to retain. This sounds like the sort of job that would be much simpler to pile before excavating the soil. i.e. you sink a series of adjacent piles to a depth of say 20' - effectively building a wall with its foundation in one process while still in the ground. Then you excavate the soil uncovering the top of the piles on the down hill side. You can then shutter them and pour concrete to face them neatly. Much less risky than attempting to retain the soil while digging foundations and building a wall from blockwork. As the others have suggested it will need calculations to decide on pile dimensions etc. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
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#21
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John Rumm wrote:
Howie wrote: I am about to dig out a section of sloping hillside to make a garage or carport. I will end up (on the highest side) with a sheer face of earth approx 10' high and 18' long which I will need to retain. This sounds like the sort of job that would be much simpler to pile before excavating the soil. i.e. you sink a series of adjacent piles to a depth of say 20' - effectively building a wall with its foundation in one process while still in the ground. Then you excavate the soil uncovering the top of the piles on the down hill side. You can then shutter them and pour concrete to face them neatly. Much less risky than attempting to retain the soil while digging foundations and building a wall from blockwork. As the others have suggested it will need calculations to decide on pile dimensions etc. I had a "professional" landscape gardener in to do very similar, three years ago, it has started leaning. I have just started proceedings through a solicitor to try get it sorted. I had several landscapers in to see if they could cure it, none would touch it. Similarly builders said the only way they would do it was with a Structural Engineer's plans. We were talking costs in excess of £20,000, maybe as much as £30,000, one builders guess. While I was prepared to pay a reasonable amount to get rid of the problem I cannot afford that. If I had the job done properly from the offset it would have been much cheaper, and a lot less hassle. -- Please do not reply by Email, as all emails to this address are automatically deleted. |
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#22
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Broadback wrote:
I had a "professional" landscape gardener in to do very similar, three years ago, it has started leaning. I have just started proceedings through a solicitor to try get it sorted. I had several landscapers in to see if they could cure it, none would touch it. Similarly builders said the only way they would do it was with a Structural Engineer's plans. We were talking costs in excess of £20,000, maybe as much as £30,000, one builders guess. While I was prepared to pay a reasonable amount to get rid of the problem I cannot afford that. If I had the job done properly from the offset it would have been much cheaper, and a lot less hassle. So is this an argument for or against using a professional? -- Chris Green |
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#23
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wrote in message ... Broadback wrote: I had a "professional" landscape gardener in to do very similar, three years ago, it has started leaning. I have just started proceedings through a solicitor to try get it sorted. I had several landscapers in to see if they could cure it, none would touch it. Similarly builders said the only way they would do it was with a Structural Engineer's plans. We were talking costs in excess of £20,000, maybe as much as £30,000, one builders guess. While I was prepared to pay a reasonable amount to get rid of the problem I cannot afford that. If I had the job done properly from the offset it would have been much cheaper, and a lot less hassle. So is this an argument for or against using a professional? Probably an entirely neutral argument. What is important whether you employ a professional or DIY is to ensure that they use the services of a Structural Engineer if the height warrants it, and it didn't sound like Broadback's guy did this. An interesting thing is that Cormaic - who tends to be a pretty authoritative source of best practise -says that professional design should be sought for any retaining structure 1m in height, so the OP's requirement for a 3m-ish wall is seriously over this limit. http://www.pavingexpert.com/featur03.htm#retain -- Richard Sampson mail me at richard at olifant d-ot co do-t uk |
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#24
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Hi again everyone,
Firstly, let me thank you all for your advice. I always highly value the information from this group. It does look like I will need to speak to a structural engineer doesn't it?! I have dug the first 4 feet and have a good idea what the ground is like. Luckily it is very solid, clay-based earth with numerous smallish rocks. it is very difficult to force anything to move, even with a mini-digger! However, I know that this is a much bigger risk as I move further down! I will probably attempt this in the spring as water tables lower. I am not digging a trench as such, I am levelling land on a hillside which will leave a 10' retaining wall on one side, and only a 6' one on the other. The lower side has little pressure as it continues down the hill anyway. I've put some pictures here, to show you the site itself: http://www.coakley.co.uk/temp/carport1.JPG http://www.coakley.co.uk/temp/carport2.JPG http://www.coakley.co.uk/temp/carport3.JPG I _would_ like to do this myself, as time is not as important as cost. However, following your advice, I will obtain help from a srtuctural engineer first. I'll report back with the advice. I will also take a few piccies and post the link in this thread so that you guys can see what I'm trying to do here (for those that are interested). Any other comments would be welcome. Thanks again. H. -- Howard Coakley e-mail... howarddot}coakleyatcoakleydot].codotuk ICQ:4502837. (Try ICQ at www.icq.com) |
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#25
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Howie wrote:
Hi again everyone, Firstly, let me thank you all for your advice. I always highly value the information from this group. It does look like I will need to speak to a structural engineer doesn't it?! I have dug the first 4 feet and have a good idea what the ground is like. Luckily it is very solid, clay-based earth with numerous smallish rocks. Clay is probably the most dangerous soil to work with. Make that 'unlucky' it is very difficult to force anything to move, even with a mini-digger! However, I know that this is a much bigger risk as I move further down! I will probably attempt this in the spring as water tables lower. I am not digging a trench as such, I am levelling land on a hillside which will leave a 10' retaining wall on one side, and only a 6' one on the other. The lower side has little pressure as it continues down the hill anyway. I've put some pictures here, to show you the site itself: http://www.coakley.co.uk/temp/carport1.JPG http://www.coakley.co.uk/temp/carport2.JPG http://www.coakley.co.uk/temp/carport3.JPG I _would_ like to do this myself, as time is not as important as cost. However, following your advice, I will obtain help from a srtuctural engineer first. I'll report back with the advice. I will also take a few piccies and post the link in this thread so that you guys can see what I'm trying to do here (for those that are interested). Any other comments would be welcome. I'll try and check the piccies out later. Structiral engineer who knows your soil is invaluable - shold only cost a couple of hundred. Wall will cost far more than that. Thanks again. H. |
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#26
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"Howie" wrote in message
... Hi again all, I am about to dig out a section of sloping hillside to make a garage or carport. I will end up (on the highest side) with a sheer face of earth approx 10' high and 18' long which I will need to retain. snip My advice, for what it's worth, would be to seek professional design for this structure before you start. This is going to be holding back a seriously large mass of earth and soil conditions might lead to special construction requirements. Falling walls can, and do, kill people, and if the worst did happen, then I'd certainly want to be able to demonstrate due diligence in the planning and execution of the project. -- Richard Sampson mail me at richard at olifant d-ot co do-t uk |
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