Retaining Walls: King Post Wall- Berlin Wall - Soldier Piles

[DIYalot]

Hi. I've just realised that the retaining wall that I have in mind to build in my garden (away from a public highway) is variously called a king post wall, or Berlin wall, or soldier pile wall. It consists of a series of posts set firmly in the ground with panels or boards fitted in between the posts.

Now, from the very little research I have done, it is perfectly acceptable to build a retaining wall by erecting a king post wall.

As to my particular situation: I have in mind to use regular concrete posts and regular concrete gravel board that you might buy to put up a fence. The wall will be about 1.5m high and 6 meters long. The regular gravel boards themselves are I think about 1 inch thick and about 6 feet long. One thing that seems clear though, is that if you significantly back-fill, these kind of gravel boards, held every 6 feet, would be susceptible to bowing. I think this is true. In my particular situation the higher land level is in fact very stable, inasmuch as it's been as it is for millennia, and there would be very little back filling. Therefore, I feel that I could use 6 foot long, 1 inch thick gravel boards and there would be no problem at all. There are however a row of conifer trees along the length of the raised bank.

There is an issue here about safety. Although building control say the retaining wall is exempt from building regulations I assume there is some responsibility on my part to erect a safe wall. The issue that concerns me, is what is the nature of that responsibility. Am I obliged to consult a structural engineer, or can I avoid consulting with a structural engineer? Thanks.

 

[r896neo]

You are grade A bonkers if you think concrete posts and gravel boards are suitable to retain 5 feet.

There is no legal or statutory requirement to use an engineer but unless you are experienced it would be foolish not to on a wall over 4 feet retaining. A wall that high could easily kill children should It fail suddenly and whilst that may seem alarmist it has happened before and is not a risk to be taken lightly.

 

[freddiemercurystwin]

Whilst it's not a legal requirement to employ a structural engineer that wall is a certain killer if it ever went over and sometimes they do go over and do kill so be a cheapskate if you like but frankly you're clueless if you think your madcap idea is anything like enough. Maybe change your username to DIYnever.

 

[DIYalot]

You are grade A bonkers if you think concrete posts and gravel boards are suitable to retain 5 feet.

There is no legal or statutory requirement to use an engineer but unless you are experienced it would be foolish not to on a wall over 4 feet retaining. A wall that high could easily kill children should It fail suddenly and whilst that may seem alarmist it has happened before and is not a risk to be taken lightly.

I went for a walk today and on it I noticed lots of drystone walls 4, 5, 6 foot high adjacent to public paths, some with houses about 12 feet from the "retaining wall". Probably no concrete foundations and certainly no king posts. There are thousands of such walls in the UK. The owners are not "grade A bonkers" by just leaving the arrangements as they are. And no-one is suggesting the walls are tested by a structural engineer. I suppose because there is an element of stability in the ground behind the wall which results in little pressure on the walls, because I imagine the walls would not resist much lateral pressure.

I think I have a similar situation at my boundary. The ground is stable and has been for thousands of years. It would probably be quite safe just putting up a drystone wall - it appears. However, that might be true without the trees. There are those line of conifers and that is a concern indeed and because of that it might well be justified to say I'd be "grade A bonkers" to put up concrete posts and gravel boards. If the trees were cut down, maybe concrete posts and gravel boards might do, because I don't think they would be inferior to a drystone wall arrangement, but I'm not totally certain about that.

Anyway, I do want to do right and ensure there is no retaining wall failure. And on that score certainly if the trees remain it is looking like (certain I think) I would need something better than regular concrete posts and regular 6 foot gravel boards. I am trying to avoid engaging a structural engineer. Is that possible though by informed choice of products for the wall?

I wonder how much a structural engineer would charge simply to okay a conservative design of mine.

 

[DIYalot]

Whilst it's not a legal requirement to employ a structural engineer that wall is a certain killer if it ever went over and sometimes they do go over and do kill so be a cheapskate if you like but frankly you're clueless if you think your madcap idea is anything like enough. Maybe change your username to DIYnever.

You know, I'm posting here to get people's input. I'm posting to ensure that the wall I put up is not a danger to anyone. Is that not obvious? So, why do you have to start on the road to being offensive?

 

[DIYalot]

In light of the ground conditions, and erring on the side of caution, if the trees were cut down, would the advice about avoiding concrete posts and concrete gravel boards be the same? Let's deal with that early on. I think the answer would be "yes" just checking.

Another point: I am assuming concrete posts would not do, because unlike steel "I" beams, they are much more susceptible to sudden shear fracture without warning. And I suppose they simply lack the shear strength and resistance to bending moments that might occur.

 

[bernardgreen]

I went for a walk today and on it I noticed lots of drystone walls 4, 5, 6 foot high adjacent to public paths

And were these all retaining walls ? You saw the front face and the top of the wall. How thick was the base of the wall. You can't tell that by just looking at a retaining wall.

As has been said a 1.5 metre retaining wall is not a simple structure. For a start you will be altering the drainage of the higher ground which could result in the retained soil being saturated by rain water if you do not include adequate means to remove that water. Saturated soil is not stable and can soften the ground below the wall rendering the foundations / "king posts" at risk of failing.

I wonder how much a structural engineer would charge simply to okay a conservative design of mine.

You would be unlikely to find one to put his or her signature to a conservative design as he or she would then be liable if ( when ) the wall collapsed.

Maybe it was wrong the way the advice was given but you are woefully ignorant of what is needed to build a safe and stable retaining wall.

 

[Newboy]

1) Concrete gravel boards are only designed to bear a small vertical load (from the fence panels above)
2) The slot in the concrete fence post is c. 35 mm deep - this is the only place where any lateral load is borne by the vertical post
3) Any significant lateral load on the panel will cause the panel to either bow or fracture
4) Any significant deflection of the panel will result in the panel pulling out of the post slot
5) The slot itself may fail

The materials you have suggested are not suitable for any form of retaining structure.

 

[DIYalot]

I see the wisdom of avoiding unacceptable risk. Understand that the first impression I have of the situation is that I'm hardly putting up a something that amounts to a restraining wall, when the ground behind it seems to be very stable and holding itself up without support. I'm just saying that this is the very first impression that comes to mind when I look at the situation. However, the fact that I'm here asking questions shows that I'm not so careless or indeed so potentially negligent as to just go ahead and put up a regular concrete post and gravel board arrangement without asking for advice.

From what is being said, the view must be that although the ground behind the wall might be stable and might be considered (by me) to be self-supporting (it isn't actually back-fill) one must avoid the temptation of assuming that (self supporting) is the case, or indeed that it is no great risk to proceed - on the ground that I don't need to put up a wall to actually act as a restraining wall. Folks are saying I imagine, don't ever be tempted to think like that. I've been tempted to think like that, but did not heed the temptation, inasmuch as I'm here asking for input from others.

 

[r896neo]

Honestly my grade a bonkers comment was just to reinforce how seriously you need to take large retaining walls and how inadequate the gravel boards idea is, as has been confirmed by others.

Regarding the stability of the earth bank etc, you are no more qualified or experienced to make a judgement on that than you are to design the wall and hence you must seek to over-engineer the design to be safe.

Drainage is absolutly key and must be a fundamental part of any design.

On a more helpful note your main choices for this are, gabions or crib walls which require a lot of material and take up a lot of room, Masonary wall of concrete blocks and faced with bricks or you could potentially use a dry stacking retaining wall like tobermore secura or acheson glover diamond (others available, as im in northern ireland these are the ones available to me and i have used both.

The benefit to buying a dry stacking retaining system are that its easy to diy and the mftrs often provide some assistance regarding the design. With walls under 6 feet they may include a specification which would be suitable and would have been engineered by them as deeming to satisfy in most situations. This may remove the need for you to engage and engineer.

If you did want to go masonary or reinforced concrete an engineer may be anwhere from £300- £???

 

[DIYalot]

I first was looking to erect a regular gravity wall, then I focused my attention on the king post wall because I'd read of their supposed economy.

But, what about practicality. I'm looking at some products by Naylor in Ossett, not far from where I live. In their brochure "Retaining wall solutions" there is some technical data. I see that infill panel K9 (100mm x 215mm) comes in at 52Kg per linear meter. Even if I could identify a 1 meter length infill panel, and could manage two people lifting 52Kg (which is perhaps doubtful) that would mean I'd need 7 king posts over the 6m span. 7 "I" beams probably. That seems to make for an expensive wall solution.

I don't know if anyone would agree with me, but it's looking like railway sleepers as infill panels (if suitable) might be the only way to achieve practicality and economy with a king post retaining wall. And even then maybe not the most economical solution. I'll have to check.