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Basement retaining wall and interaction with existing house foundations


Moonshine

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I am trying to get my head around possible construction solutions to the situation below, one structural engineer is recommending piling, the other is going for a hit and miss retaining wall.

 

As below a proposed basement of the new house is under the party wall act of an existing house (mine), and the retaining wall needs to support the existing house (the blue dotted line is the proposed boundary line).

 

1047475009_retainingwall-existingfoundations.thumb.jpg.3e93daf3a0804fb149683b6f04819b6a.jpg

 

The thing is this is only an issue for 3-4 metres and other than this the other 14-16m of retaining walls are fairly 'simple'.

 

Obviously there needs to be a retaining structure, the questions is. what is the cheapest and easiest way to build it.

 

my gut says that piling is overkill for such a small section when everything else can be conventional, with excavations made behind the wall line 

 

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If you are not experienced it is high risk to design your own temporary works.  You will need some working room around the basement retaining wall.  I have used open augered concrete piles with a bit or rebar in this situation before and king pile steel with sleepers for the less crucial bits.

 

P1040656.thumb.JPG.e0646ce57ab369bfc203a9c875383ac8.JPG

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29 minutes ago, Russell griffiths said:

I don’t think things like this are in your remit to argue 

whos imdemnity insurance is it going on. 

 

Get it piled and sleep easy at night. 

 

Not saying it is, I have quotes from two structural engineers one with one potential solution, one with another.

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1 hour ago, Mr Punter said:

If you are not experienced it is high risk to design your own temporary works.

 

Oh I am not trying to design it, I just have two different potential solutions from two different engineers and I am trying to work out in my own head the construction phasing of each and the cost implications.

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15 hours ago, Mr Punter said:

If you are not experienced it is high risk to design your own temporary works.  You will need some working room around the basement retaining wall.  I have used open augered concrete piles with a bit or rebar in this situation before and king pile steel with sleepers for the less crucial bits.

 

P1040656.thumb.JPG.e0646ce57ab369bfc203a9c875383ac8.JPG

 

Thanks for this, as it helps me visualise what is needed, as i hadn't really know what would be needed in terms of temporary works

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Is it not dependant on the soil in the area?,has this been checked? picture above looks like fairly solid dry soil, if you tried that around here you would not only drown but have total collapse of the neighbours house.

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32 minutes ago, joe90 said:

Is it not dependant on the soil in the area?,has this been checked? 

 

The final solution will be, but one response that i have from an engineer was that, in the area i am in the ground conditions are good.

 

I am getting quotes for ground investigations and the results of these will go to the structural engineer for them to design to.

 

Edited by Moonshine
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as already said ,you have to go with what your SE advises ,as he will have the insurance if he is proved wrong later 

I would comment that when making a basement in dubious ground most Icf systems go for a wall at  twice as thick as the one standing on it above ground with drains etc and that will be with no extra load from another building very close 

your plan shows same dimensions as above ground ,which has no side loading on it at all .

I,m certainly no expert in any way -- but that just looks wrong 

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26 minutes ago, scottishjohn said:

as already said ,you have to go with what your SE advises ,as he will have the insurance if he is proved wrong later 

 

No where am i going against what any SE is advising (i haven't even appointed one yet ?), i have two different potential solutions from two different engineers who have quoted for the job.

 

The figure i have included is just an illustrative section of what the arrangement will be when built.

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