Determine Existing Foundation 1

[Grouser]

A coworker brought up this problem and I thought it would make a worthy topic of discussion on the forum.

An existing warehouse is to be retro-fitted to house power generating equipment. The records of the existing foundation are scanty and contradicting, some say piles and some say spread footings.

How can the existing foundation type be determined with minimal disturbance? GPR comes to mind as does manual electro-magnetic mapping. Any other ideas/suggestions? Can siesmic data be used in this manner?

Thanks and

 

[JoeTank]

I have used impact echo methods to define the extent and details of the concrete. That's just the first step though. You also have to figure something about the rebar size and placement.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[Focht3]

Power generating equipment (turbines, transformers, etc.) generates a fair amount of dynamic loads; this isn't a simple retrofit. The new equipment needs to be isolated from the existing structure, and the existing foundation needs to be carefully evaluated for risk of damage from steady state - and variable - dynamic loading. (Don't forget about start-up and shut-down loadings.)

You will need a detailed geotechnical analysis, too - with cross-hole testing near the major equipment. This will probably run 3 to 5 times the cost of a typical geotechnical study for a "simple" warehouse.

This work will take at least twice as long - and likely cost more than twice as much - as designing a new building to contain the same equipment...



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.

 

[inaz]

Why not dig a test pit to observe the existing foundation?

 

[genomty]

Electrical resistivity could be helpful. Perhaps you will not obtain the dimensions of the elements but it could tell you if there is a spread footing or a pile below your columns. Nevertheless, Focht3 is right about the necessity of a widen geotechnical investigation.

 

[AlohaBob]

Considering the phenomenal underground duct requirements, interference issues, high area loads, dynamic harmonic compatability concerns, it would seem doubtful to save money retrofitting an existing foundation.

 

[dirtsqueezer]

Interesting quandry. You are probably trying to avoid digging around the base, in case it turns out to be ground-supported. If I were you I might just go ahead with a geotechnical investigation and see for yourself how they should have done it. Would you have built on spread footings or piles? What is the depth to bearing, would piling even be feasible? A geotechnical report around and inside the building I think would be of great help, though I agree with Focht3, if you are building to accomidate vibration, you may need to go w/ a more solid design anyway. Best of luck. Keep us posted.