Maximum safe cut angle for existing made ground

[jon-lee]

so a bit of a head scratcher for the geotechnics gurus!! I'm currently designing a MSE retaining wall, but in order to keep within the boundary i need the safe cut to be 60deg. going off the SI report no bore holes or trial pits are in the area required so they have exposed a small section of the embankment revealing a variety of materials including brick, rubble, colliery spoil/ash even a work boot. so you clever lot!! any advice is much appreciated. 

[eandg]

Our engineer advised a 45 degree angle of repose on made ground (so a 1:1 'batter'). We do though have bits that have been cut at probably 80 degrees in advance of landscaping and there's been no movement at all - I've found that spoil is fairly loose once disturbed but if it's compacted and dries then it's pretty stable. 

[Temp]

If you get stuck you can build a retaining wall using sheet piling before removing the soil, then clad with something better looking.

[jon-lee]

2 hours ago, eandg said:

Our engineer advised a 45 degree angle of repose on made ground (so a 1:1 'batter'). We do though have bits that have been cut at probably 80 degrees in advance of landscaping and there's been no movement at all - I've found that spoil is fairly loose once disturbed but if it's compacted and dries then it's pretty stable. 

For maximum safety yes 45° I would totally agree with you and I don't really like designing much steeper even when I know the soil cut will be stable at 80°+. Sorry I should have given more details. The made ground to be cut is an  embankment previously retained by a timber crib approximately 1m from a pedestrian footpath and road the retained height exceed 4m in some parts. I'm quite green re geotechnics (structural background) but my gut feeling is giving warning signs. I appreciate your advice, thank you 

[jon-lee]

3 hours ago, Temp said:

If you get stuck you can build a retaining wall using sheet piling before removing the soil, then clad with something better looking.

I'm a MSE retaining wall designer and made my concerns very clear to the client from the start. In fact my suggestion was actually metal sheet piled but wasn't to keen with the vibration close to the road that needed retaining or the additional cost for temporary works. Thanks for the advice, appreciated 

[Dave Jones]

gabions a section at a time ?

[ToughButterCup]

Our made ground 'batter' is 45 degrees at one end and 60 degrees at the other. Height - never less than 2 meters

[markc]

@jon-lee are you looking at the cut in order to build a retaining wall or the angle of back batter above a retaining wall?

[George]

You cannot give made ground any reliable mechanical properties so proceed with extreme caution.

 

I did not think MSE would be feasible without location specific ground information? 

 

[Temp]

11 hours ago, jon-lee said:

I'm a MSE retaining wall designer and made my concerns very clear to the client from the start. In fact my suggestion was actually metal sheet piled but wasn't to keen with the vibration close to the road that needed retaining or the additional cost for temporary works. Thanks for the advice, appreciated 

 

This isnt my field (I'm an electronics engineer) but if the main issue is vibration you can also drill a contiguous concrete pile retaining wall then excavate.

 

 

[Mr Punter]

12 hours ago, jon-lee said:

I'm a MSE retaining wall designer

 

Surely you have access to an engineer to design this type of work?

[jon-lee]

4 hours ago, George said:

You cannot give made ground any reliable mechanical properties so proceed with extreme caution.

 

I did not think MSE would be feasible without location specific ground information? 

 

Totally agree far too many unknown factors with made ground. Like I said in previous comments my gut feeling is warning me 

[Iceverge]

Have you considered soil nailing? 

 

https://www.designingbuildings.co.uk/wiki/Soil_nailing

 

 

[jon-lee]

Hi Chaps,

 

i have attached a section because its much easier than trying to explain parameters i need to work with.

[jon-lee]

On 21/07/2023 at 14:06, Mr Punter said:

 

Surely you have access to an engineer to design this type of work?

i do my own preliminary design calculations using GEO5 software however, i employ an external engineer to check and sign off my design (I'm only a technician under my PI so use a selection of external engineers depending on what I'm designing just so I'm covered).

my concerns have only come following me requesting that a section could be safely excavated to expose the made ground material.  

[dpmiller]

@jon-leewho are you designing this for? Is it for yourself or a (paying) client?

[jon-lee]

56 minutes ago, dpmiller said:

@jon-leewho are you designing this for? Is it for yourself or a (paying) client?

One of the top 5 house builders

[Marvin]

Hi @jon-lee

 

Bit complicated for several reasons.

 

Piles to support the ground before MSE:  Depending on ground conditions they may need to be anchored. Availability of steel? vibration and depth considerations including what they are being driven into for final support.

 

Blocks.  Before you start work you would need to know the slip angle of the concrete bed of the block wall.

 

Depth of made ground may be lower than the wall foundations. Composition of made ground: any asbestos content? 

 

If there is a foot path at the base of the wall it will be a no dig area!  Will there be any services? Gas water electricity communications, lighting cables, drainage, footpath kerb line to be put in or a road or future foundations?  This may need the design to be altered. 

 

Too many unknowns for such a tall wall in made ground.

 

You have no real choice in my humble opinion with either piling or a MSE wall:

 

Bore holes first, samples to lab, await lab results, results to geotechnical for design. Check design with site design.

 

Good luck

 

M

 

[George]

11 hours ago, jon-lee said:

Hi Chaps,

 

i have attached a section because its much easier than trying to explain parameters i need to work with.

That is too steep for made ground.

 

I'd be looking at sheet piling to form a safe working area. Now... If they need to sheet pile to enable a retaining wall then they may be better off installing permanent sheet piling as the retaining structure and face with brickwork.

 

You can only tell the contractor your best advice - ultimately temporary works is their responsibility but you don't want to show something that is potentially dangerous without making everyone very aware of the risks.

 

This is not an uncommon issue for house builders to try and squeeze in as many houses as possible and so end up with ridiculous retaining walls!

[Nickfromwales]

10 hours ago, jon-lee said:

One of the top 5 house builders

Top or biggest? 

To be called a top builder you have to be extremely skilled, conscientious, and provide a client with a good end product. 
The bigger companies seem to fail in many respects.

 

11 hours ago, dpmiller said:

@jon-leewho are you designing this for? Is it for yourself or a (paying) client?

Doesn’t matter, if this person has come here seeking advice then that’s what we can decide to do, or to not do. 
I’ve provided my clients with much better service (after gleaning advice and support here) since co-founding this forum a good few years ago.

It’s better for a professional to ask here than not bother asking at all, imho, as the end owner of this dwelling will benefit from something that's been done properly. 
 

@jon-lee  Any information gleaned here is utterly useless anyways, unless it’s professionally underwritten it cannot be surrendered to building control or a warranty provider, but many will help out wherever they can. You just can’t practically use the information that’s all.