2 site classes in one project 4

[pelelo]

Engineers,

Is it possible to report 2 site classes in one project?, or is just better to report the worst site class?

I am working on a project which we performed borings. The total area is about 1 Acre.

There is a portion of the project that is adjacent to a river. The borings close to the river provided different conditions than the ones farther away.

The ones by the river are class F, however, the ones farther away are class E.

I was wondering how to report this?, 2 site classes and specify the areas or just Class F for the whole site?

Please advise.

 

[EngMan40]

If you are dealing with one structure then one response and one class. If multiple separate structures then I would specify two separate classes to save on cost. Depending in size of the structure (s), few SCPT may be cost justified to perform if you believe you can up the E class to D class. My experience is SPT conservative for site class.

 

[GeoEnvGuy]

I assume your report will need to inform the client of both subsurface conditions encountered. You will also need to indicate that foundation recommendations vary depending on where they want to put there structure. It is only logical to reach out to inform your client on your broad recommendations for each area to ask if they want foundation recommendations for the better or worse or both subsurface conditions your investigation has identified.

 

[geotechguy1]

You could do more investigations to try and better delineate the areas.

Usually when this happens what I've seen done is give both classes, and use the worst class (for geotech) for the geotech calcs (eg liquefaction) and the worst class for structural for the structural calcs. Often it's different.

 

[Mccoy]

In my experience, engineers who design structures have no suitable means/software to work out a rigorous solution. They might try, with higher than average advanced software, to split the foundations into separate entities (slabs, usually) each with its own seismic stress. I should enquire if this is possible.
When this condition has happened to me, the engineers were not able to consider it in the design, so they usually adopted the worse site class.

I don't even know if the best structural design software available in my country is able to consider different seismic stresses. Maybe a very advanced FEM software is required.