Question about foundation 1

[GeoGab]

An engineer asked me a suggestion on the type of foundation to adopt for the enlargement of a building on a hilly slope. The foundation of the old part of the building is constituted by beams on silty clays. The ground of foundation of the new part shows a changement; in fact there are fessurates clays . Some buildings around there founded over this kind of clay have brought some small lesions. Is it possible to adopt another type of foundation (to es. piles) for the new part in comparison to the old part, considering that both of them will settled up to constitute an only one building?
Thanks for the collaboration.

 

[DaveAtkins]

I would get the recommendations of a Geotechnical Engineer, but if you are going to use two different types of foundation system, then a complete separation of the two structures would be required, in my opinion.

DaveAtkins

 

[Panars]

When adding to an existing building supported on spread footings in soil, you should keep in mind that the existing building may have already settled due to consolidation. If you place the new structure on the same type of foundation, it will probably settle and there will be relative displacement between the two structures.

However, if you can support the new structure on piles to rock so that there is very little settlement, then there will be little relative movement between the structures. This is common practice for widening bridges in my area.

 

[GeoGab]

The problem is that the bedrock in that area is very deep so it's impossible to do piles reaching the bedrock (there are only clays).
Thanks for yours answers!

 

[Mccoy]

Geogab,
in your area, that I know pretty well, you can still drill large diameter piles and have them work mainly by lateral friction.
It is not necessary to reach rock (it's about two thousand meters below!) , just a firmer layer beyond surface colluvium, at a suitable depth, since the loads you're dealing with are pretty small.
Panar's suggestions still hold. In my opinion that's your best choice, albeit, alas, not the cheapest.