foundation pad not deep enough 9

[Coalhouse]

​

Good Morning.
I am asking for a friend.
a builder who took the freedom to not do as per the structural engineer design.

The foundation pad should have been excavated with 1.25m depth. However, it seems like building control can only see on the photo 0.6m deep and brought this out to the builder attention (and mine)
Building control is saying (me) that according to structural engineer design, it should be 1.25m. however I can get another qualified structural engineer to sign off the 0.6m depth foundation. (note that the excavation has been now filled with concrete).

What are my options? if no structural engineer is willing to sign off the 0.6m depth foundation? I have read a bit and it seems like 1.25m is rather on the high side. is there a quick day to remedy to this. by digging a pile?

I am an engineer myself but from a different tribe (mechanical).
39

 

[phamENG]

There was probably a reason the engineer specified the foundation to be that deep. Have you asked him/her why? Are they willing to sign off on a shallower foundation depth? If not, why not?

If another engineer is willing to accept it, that's fine...as long as they're willing to accept responsibility for the entire design. If the footing doesn't perform as intended, the entire structure will be at risk.

Here's a bit about my opinion of the guys who swoop in and say all is well when the contractor screws up: thread507-491184

 

[MotorCity]

You should be asking this question to the structural engineer. He/she may have had good reason for the depth.

Mitigate frost heave? Resist uplift at the column?

I doubt you will find an engineer willing to take responsibility for the entire building design just so that your footing issue can be resolved. If you cannot contact the structural engineer, your only option maybe to have the contractor rebuild it correctly. Any other attempts to fix this situation other than what I described above should also be run by the structural engineer.

 

[JoelTXCive]

Is there a geotech report on the project?

The geotech might be the true person that is dictating the pad depth. There could be poor soils at the immediate surface; or settlement concerns; etc. etc.

 

[JStructsteel]

Why not require the builder to remedy. Either get an engineer to sign off, or they rebuild. By god if its the engineers fault, the builder does not try to remedy, they put it all back on the engineer.

 

[Coalhouse]

I have the calculations. some structural engineering jargons (don't understand). I have a document of the geological investigation (by structural engineer). Somehow i can not see where this depth excavation calcs has been derived. (feels to have been dropped on the drawing without calculations to show).

questions to all. it is a victorian house near London. Built in 1920.

 

[Klitor]

It could be that the plan was to make foundation on gravel layer (-1.40m).
Thats what I would probably do...put concrete foundations on -1.40 or do soil replacement to -1.40m.
Just my 2 cents

 

[kipfoot]

The footing was shown to be resting on the 'very dense angular gravel' and instead it's placed on bricks and debris in the upper layer.

It might be possible to install helical piles to carry the load to a deeper soil layer. Discuss it with the structural engineer and whichever builder you find to replace the current one.

 

[le99]

The first thing to look at is the local frost depth. For London, 0.6m (24") seems too shallow, though 1.25m (49") could be overkill.

 

[Coalhouse]

May I add that it is in my kitchen therefore in a heated space and when not heated well-insulated!! I think that 1.25m is too much. Why ? because if it not I am totally screwed.
but thank Le99. I will check the local frost depth. (where I can find this? I have just spent 10 min without luck). I have checked the name of the engineer (google search). graduated in 2017. I think he was not supervised and he may have put belt and braces.

 

[le99]

If it involves a single footing located in the middle of the building, then frost depth could not be a factor, I also doubt that you will need to place the interior footing that deep unless the soil is really a mess at the near-surface (your document is not legible, so I couldn't judge) such as the famous "London Clay". I think you do need a second opinion on this issue for your peace of mind, as well as safety.

 

[MotorCity]

You are asking for a friend about your kitchen??

Whether or not your kitchen is heated or insulated will have no bearing on the discussion (it is not related to the frost depth).

Your thought that 1.25m is too much just so you don't want to get screwed is also not a valid reason to not correct it.

Since you are the homeowner, I would hire a local structural engineer to look at it and advise you accordingly.
It may be ok, but I think you should have a qualified engineer take a look.

 

[countervail]

Talk to your enginner, its his / her design so shouldn't be altered without consulting. That said the depth is almost certainly to get down to the gravel (difference will be starting level TOC vs FGL), made ground is not generally (almost always) a suitable founding strata. Remedial options rip it out and re dig or talk through and price lots of different options then rip out and re dig.

 

[Coalhouse]

The engineer said that there was no SI study so he assumed 1.25m. What is an SI study. The more in investigate the more I think the work of that young engineer was not supervised.

that is his response " The depth of the strip footing can be reduced if we have soil at lower depth that can give us 100kpa bearing pressure
Do we know what the ground conditions are on site? As far as im aware no SI has been done for this project "

 

[Settingsun]

SI = site investigation. That borehole is from somewhere nearby, not from your property. The engineer doesn't have xray vision so estimated the required footing level and wanted the builder to dig until a suitable founding layer was reached. You'll have to check the drawing/specification/contract rather than the calculations to determine whether this was a contract requirement for the builder.

'Confirm on site' is fairly common. The cost of SI often isn't justified if you know approximately what the relevant ground conditions are.

 

[human909]

What is an SI study.

I'm guessing "soil investigation".

The more in investigate the more I think the work of that young engineer was not supervised.

Yep certainly sounds like it. In Australia that sort of thing certainly flys. Get the young guy who knows nothing to do the work. Who cares if he makes overly conservative assumptions.

that is his response " The depth of the strip footing can be reduced if we have soil at lower depth that can give us 100kpa bearing pressure

Which you don't know if nobody has looked at the soil. A experienced builder could quickly tell if the soil is "good enough". But to have an engineer sign off on it you normally want more evidence.

In some cases you can satisfactorily build your foundation 300mm down.. In others you might need to dig MUCH MUCH deeping. Local knowledge counts for alot, site specific knowledge is generally what you need to be sure.

I doubt you will find an engineer willing to take responsibility for the entire building design

That really depends on what locality you are working. If you shop around you can often get a signature for anything you want. But is it worth the paper it is written on?

(From my observations on this forum it seems that professional structural engineers in the US consider themselves much more liable and responsible than my observation from posts from other localities and my own observation of professionalism (or lack of) in my own locality in Australia. Not that I see the US as a pinnacle of structural engineering excellence. It is just that getting a engineering signature out them is harder.)

 

[Coalhouse]

ok. given the below. does that help
yveid

 

[Coalhouse]

Pls tell me what you get from the borehole survey and tell me if you think 1.25 m is rather much .

And also

While we are at it. Still asking for a friend. There are 2 steel beams now in the kitchen that need fire protection. What do you think of intumescent paint? (rather than plasterboard) the building control has agreed in principle provided one gets a certificate that the paint has been applied properly.

 

[phamENG]

yveid - if you have proof that an unlicensed engineer was not supervised by the engineer of record, then report them to the licensing authority. I have no personal experience with that in the UK, but I'd be surprised if it's significantly different from most US jurisdictions. If you don't have proof...then please stop throwing around unfounded accusations of unethical behavior. I doubt you want to be called a lying cheat behind your back, and neither does that engineer. Contact the engineer of record (in the US we have to affix our professional seal to the drawing, so even if my subordinate did all the work my name would still be on the drawing) and ask them about it if you're unsatisfied with what you're getting from the design engineer.

The engineer set the bearing depth to a suitable level based on the information he had. The only information he had was that there was fill in the area several feet deep, and you needed to get below that. If the contractor failed to get approval for a variation, it's his own fault even if it was justified.

This is a house. While I agree that it deserves due attention to ensure its safety and reliability...economics are economics. Usually the best way for a structural engineer to provide that and not lose their shirt is to be conservative. I'm much more conservative on houses than I am on commercial construction. For one thing, homeowners tend to sue more. For another, the contractors tend to be significantly less competent and more prone to ignoring the design and screwing things up. (Not all, mind you - I have a few residential clients who are absolutely top notch and I would gladly have them build my own house.)

This is not something that can be resolved by a bunch of anonymous strangers on the internet. Figure out what needs to be done for the EOR to approve it, or find somebody who will take over the roll of EOR who will approve it.

 

[human909]

Ok I am done and no doubt most other people here are too.

It seems you are a layman seeking free engineering advice. That is NOT what this forum is about.

Though tactful people can often get away with good responses, now you are just taking the piss. (to use the colloquial language)

Go get professional advice that isn't from a web forum. Pay for it.