Site Specific Soil Investigation, yes or no? 3

[jpw2913]

We get a fair amount of calls from people needing engineered foundation plans for a pre-engineered metal building.
In our proposals for these we typically always include to do a site specific soil investigation, but many times lose the job because of this.
Seemes like there is always somebody out there that will do a metal building foundation without a site specific soil investigation. I'm curious what everyone's thoughts on the subject are. These buildings could be anything from simple barns to autoshops, etc. I know (at least in my area in Texas) you can get some pretty good soil information from the NRCS (Natural Resources Conservation Service) website, but it's not "site specific"? I'd really like to hear more thoughts on doing site specific soil investigations for "simple" metal buildings. Thanks!

 

[CELinOttawa]

Unless the area is known to have problems, I put this in as a rider for the Owner to decide. Something like "While it is advisable to do a site-specific soils investigation in order to minimize the risk of settlement or other deleterious effects on the Owner's end-product, such investigations are only undertaken at the request of the Owner."

Ensure the contract puts the risk of not doing to soils report where it belongs - With the Owner who is saving money and incurring risk. Do not allow this to be a case of the Owner saving money and YOU incurring the risk.

At the start of every project, first meeting without fail, I outline the risks and benefits of the approach the Owner has chosen following our discussions. I ensure that it has been minuted just that way as well.

 

[ztengguy]

Some owners are cheap. Those are the best not to work for.

 

[steellion]

Getting a geotechnical report is always the best, but IBC has conservative allowable bearing pressures that can be used in absence of a report. Explain that spending a couple thousand on a geotech can save them money on foundation costs by avoid unnecessary conservatism.

 

[SteelPE]

On my metal building project I find that the outward thrust produced by the frames increases the size of the footing dramatically. In my area we typically deal with V=110mph and Pf=35-40psf so the outward kick tends to be substantial. I'm not sure how things are in the great state of TX but for me, sizing the footings for overturning stability tend to yield values much less than the conservative values listed in IBC.

 

[Ron]

CelinOttawa....while your approach is plausible on its surface and I agree with your intent, here's the downside....

The engineer is responsible for the design he provides. If he designs without sufficient information, then HE takes the risk for the design, not the owner.

The owner is often an "unsophicated party" with respect to the technical decision of whether to do a proper geotechnical investigation or not. The design engineer is not considered in the same light. We are expected to know more than the owner and to guide the owner accordingly. If the owner refuses to take our advice, we have three choices.....(1) walk away, (2) do the job with ultra-conservative design, or (3) do a design without sufficient information that leaves you exposed to risk. Only one of those choices prevents your liability.

 

[CELinOttawa]

Hi Ron,

I've actually had an owner pursue after we advised them as to their options and something went wrong. A measure of complaining, a meeting with lawyers, and they went away. My feeling of the situation was that once their lawyers saw the level of documentation in place and the clarity with which we advised of the possible consequences of trying to save money, they advised the Owner to drop the case. I agree that there is risk incurred, but I don't accept that it is insurmountable.

You are entirely right, however, that we are held to a much higher standard. The trick is that if you have openly and clearly advised your client, and then they fail to take your advice but direct you to continue, they are very unlikely to be able to successfully pursue you.

Limiting your liability to zero in this business is nearly impossible. Managing it through educating your client and documentation is the only way to stay in business. It is no longer a good profession to be involved in; No one wants to be responsible for anything, and everyone wants the product for dollar shop prices.

And I am *not* talking about anything in any way dangerous... But when you're talking about quality of the end result, Chevet versus Hummer, it is the Owner's money to spend (or save, while accepting the risk of doing so). The trick is to document that you warned them, and to do so VERY clearly.

 

[aaronPTeng]

CELinOttawa

I would have to disagree with your thought process on always getting a site specific investigation.
Yes we can put in conditions to try and avoid the legality etc......

However As a structural engineer the blame will always come back. Unless the law is very different over there, it is always brought back on what a competent structural engineer would do of average standard etc, and in this case I believe any competent engineer would insist on site specific investigation. Otherwise your just signing away on something the client wanted, which isnt the correct process,

"Structural Engineering is the Art of moulding materials we do not wholly understand into shapes we cannot precisely analyse, so as to withstand forces we cannot really assess, in such a way that the community at large has no reason to suspect the extent of our ignorance." Dr. Dykes, 1976

 

[CELinOttawa]

Gentlemen and Ladies (if we're lucky... They're still riding under 5% in our profession last I heard),

It is not the applicable law that matters, but the Geology. There are wise expanses of arees I have practiced where the competent load bearing capacity didn't waver more than thirty percent. That's not hard to work with, and does not necessitate always conducting site specific investigation for single storey pre-fab buildings.

If you are doing something that runs against the standard of practice in your area, you're doing it wrong. If you're loosing out to others on every second job, you'd better figure out why. It is likely that the standard of practice in your area is not what you're undertaking in the work in question.

This discussion started about a single storey pre-fab in an area where geotechnical information of reliable quality is available without site specific testing. Let's not forget the context of the conversation.

Oh, and as a good point of reference: In my years of doing this, I have never undertaken a project outside of the residential sphere in absence of site specific geotechnical investigation, and at that always by a qualified Geotechnical Engineer in Canada. New Zealand is very easy to handle in the aluvial planes, so I have done my own Geotech there, but again always on site specific info for anything other than residential.

My God, some days... The internet. *sigh* How many posts do we get to see which simply repeat a suggestion from above as if new? Everyone's an expert, and inevitably such expert comments are provided from the vacuum of their own thoughts...

 

[cvg]

I would not call NRCS soil surveys reliable enough for foundation design, only a general indication of what soils might be found in the area. especially for any site that may have been disturbed. I would always recommend site specific testing. if not done during design phase, than it can be done during excavation to verify any assumptions made during design.

and I do not see any reference to single story pre-fab in the original post.

 

[aaronPTeng]

Just because someone disagrees with what you have said doesn't warrant this type of reply.


jpw
I insist on site specific testing in all cases, each to there own.



"Structural Engineering is the Art of moulding materials we do not wholly understand into shapes we cannot precisely analyse, so as to withstand forces we cannot really assess, in such a way that the community at large has no reason to suspect the extent of our ignorance." Dr. Dykes, 1976

 

[CELinOttawa]

From the OP "engineered foundation plans for a pre-engineered metal building."

aaron: I believe most engineers would object to being called incompetent. I quote your post: "I believe any competent engineer would insist on site specific investigation"

This thread is no longer about the merit of the engineering, and it saddens me to say that it has lost the value it could have had.

 

[XR250]

I have to agree with CELinOttawa on this one. Ron has used this "unsophisticated party" argument in other posts. As long as it is not a safety issue and the owner is adequately notified, then it is his problem. I believe most attorneys would see it that way. I practice in an area where there is a bunch of plastic clay soils. I always put a note on my drawings recommending that a Geotech. provide guidance on the footing depth. The clients rarely take my advice. If I walked away from these jobs, I would be out of business.

 

[AELLC]

To answer the OP, it is a lot about local engineering practice.

For example, here in the Phoenix area, the soils are fairly good, and no extreme soil collapse or high expansion potential.

So generally, for small PFMB foundations, the Owner is unwilling to pay for Geotech. That is fine with me, because I don't believe a 40' by 40' 4" slab cast monolithically with a perimeter turndown 12" wide and 24" deep, 2-#4 cont top & bottom is going to go anywhere. The uplift on those frame columns results in much bigger footings than just for the gravity loads alone.

You should know in general how the soils are basically from past jobs ion the vicinity that did have Geotech reports.

Yes I know it is risk but you have to go out on a limb sometimes - that is your choice.

 

[ztengguy]

They dont do two story pre fab/pre eng buildings?