Essential Facility - Acceptable Settlement of Structure

[CBSE]

I'm in the beginning stages of designing a State Police Station. 60' x 120', one-story rectangle. We just completed the Geo-Tech study and the results were that the area is susceptible to liquefaction with a total anticipated settlement of 4". The 4" is if we just do a typical slab on grade foundation. We could do a waffle style slab a reduce the total differential settlement of the building, however, the overall settlement would be the 4". The other option is to do piles and get down to the good soil (piles would be about 30-35ft in length).

My question, what is an acceptable amount of overall settlement of soil? I'm really concerned about differential and total in this situation. They will have weapons, ammo, narcotics, money, files, etc. that are all sensitive material. In the event there is a major crisis and they need the weapons and ammo, if this building settles and the doors are jammed shut then this building is essentially useless (no pun intended!). Is there a code requirement for settlement? I'm surprised the Geo-Tech doesn't know.

Thanks.

 

[Bagman2524]

IBC-2012 section 1808.2 just states that differential settlement shall be minimized. Differential settlement is more of a concern that uniform settlement. If the whole structure settles uniformly, the problems of doors, windows, etc. not closing won't happen. My house has 4" of differential settlement from one corner to the other and everything works fine. Some of the doors require a door stop to keep them from swinging open however.

"Look for 3 things in a person intelligence, energy and integrity. If they don't have the last one, don't even bother with the first 2. W. Buffet

 

[steellion]

I'm not aware of any more stringent settlement requirements for a critical facility, but 4" of settlement sounds like a lot for ANY building. I typically design in an area of decent soil properties, but we design our foundations for 1" or less of settlement.