Retaining wall structure and strength

[David Chapman]

I am struggling with a project I've got and need some help.  I have quoted to level a garden by installing gabion cages as a retaining wall and filling the area with mixed hard core and finishing it to accept artificial grass, a competitor has suggested to him to use concrete slotted fence posts and concrete bases then back fill with soil.

 

It is my opinion that this is not structurally good enough, my worry is the soil will get water logged and slide against the concrete fence which is not adequate to hold it.

 

The area is 8.5m wide 8m long with a slope of 1m, if anybody has got technical knowledge or can sign post me to somewhere I can get the information that would be great, I will need to go back to my customer and show them the evidence if it's structurally sound or not.

 

Thanks in advance

[Mr Punter]

If it were me I would provide evidence of the gabions being satisfactory and suggest that your competitor does likewise for their proposal.  It is not for you to disprove someone else's scheme.  You could mention that you have not heard of similar being approved for such an application.

[David Chapman]

Thanks punter, I will look at that as an option.  

 

The customer is somebody I've worked for before so he wants me to do the work this time and now wants me to do it the way the landscape gardener has suggested but I'm not comfortable with it.  I know a 1m slope is not much but it's 20 ton of material plus water 

[PeterW]

So in a purely mechanical / geophysical view, the ground will not slide anywhere as it will be bearing straight down with the exception of the last metre that will be exerting "some" force at 45 degrees to the structure. Gabions can comfortably hold back 1m but would need to be stepped to acheive this although a 1m cube is not the most attractive of things unless you grow something out of it..?

 

I doubt I would go with the concrete boards as these I expect would crack pretty quickly  as they aren't designed to be structural - I would just suggest a pair of 500x500 gabions stacked to give you a step and then work from that.

[bissoejosh]

Might be something of use on here?

 

https://www.gabionbaskets.co.uk/gabion/gabion-wall-standard-design

 

[Mr Punter]

I have done a soldier pile wall using steel columns concreted into the ground with railway sleepers spanning.  This can look good in a garden.  What is to prevent falling from the edge?

[David Chapman]

Thank's all for the replies and advice, it's helped reinforce what I had thought in the first place, that the concrete slotted fence posts are not strong enough.

[daiking]

I’ve just had a double thickness solid block/brick wall to retain a main area approx 4.5m x 8m x 1m on 2 sides.

 

I wasn’t wholly convinced that would be enough until it was ‘anchored’ on the corner by a set of steps also on a large concrete foundation. The intention is to infill with crap and then a decent layer (200+mm) of type 1 to be able to lay a patio on top.

 

I would have liked to look at other solutions - gabions and self supporting stone had I wanted a more natural top finish. 

 

Went away from sleeper type arrangements early on when it was clear they were not cheap or long lasting for this application. Would not have entertained this concrete fence idea either.

[K78]

Gabions are crazy expensive. 

 

Precast concrete is a much cheaper solution. Even at 4m high. 

 

Gabions and timber crib were the most expensive option by far for me. 

 

A kingpost wall is probably the best solution for that. Not all concrete slotted fences are equal. 

Edited May 31, 2018 by K78

[mvincentd]

Any reason (like a nearby road imposing a heavy surcharge) why you cant just grade a metre of ground at 45 degrees....after all how is your client going to 'purpose' the high perimeter, which will probably end up half a metre thick anyway?

 

[Temp]

Great site for hard landscaping..Check out the site index for "retaining walls".

 

http://pavingexpert.com/featur04.htm

 

The concrete slotted fence posts used in this construction need to be sunk into the ground by at least 450mm and concreted in place. The base panels should be laid level across the top. See

Fences for further details of concreting in fence posts. This construction is only suitable to a maximum height of 2 panels (600mm).

 

Should also check with the manufacturer of the concrete panels.