foundations for a light weight structure

[geo321]

Hello, i am designing a small structure where it is composed of 1 floor ( ground +roof). The loads are light ( spans between 4 and 5 meters).
Regarding the foundation i am hesitant between 2 scenarios:
1- found my columns at the ground floor level with removing the top 600 mm soil and compacting and flooding the bottom of the excavation.
2- found my columns on square foundations 1 meter below the ground floor level with marking that the contractor should ensure a minimum design pressure of 80kpa ( it is the pressure i am getting in scenario 2).
What do u think is the most appropriate method ?
Thanks in advance

 

[oldestguy]

Pass your information on to a geotech from the area. Here you say nothing about soil conditions, ground water, weather (cold or moderate), etc. We would be doing you a disservice without much more information to offer advice..

I add one point. Flooding is a very questionable procedure for any area for structure support. More commonly water is not our friend.

 

[geo321]

Oldestguy thank you. The problem that i dont have any information about the soil and no access to any geotech engineer. However the watertable is low (the only info u got it from the client) and the weather is moderate. I am trying to adopt a foundation system and based on it i will rectify the soil.
I am interested in ur flooding remark. I have been told that it is a sort of ground improvement.
Thank u

 

[oldestguy]

Flooding is done at places where structural supp0ort is not usually the aim, such as sections of some earth dams. Yes for real loose granular soil it does some degree of densifying, but not nearly as good as mechanical compaction. in some cases adding water causes significant problems for construction. I'd forget the idea.

If you can't get a local geotech, look for a very experienced contractor and see what he has to say. Apparently you have some idea of soil capabilities or lack thereof. In these cases sometimes just a wide footing is all that is done. Take a typical garage, the building sits on the slab over almost any ground.

 

[geomane]

I agree with oldestguy. Per Holtz and Kovacs, 1981, "Flooding is not a very good way to increase the overall density of a sand fill; the relative density of flooded fills will still be very low and thus not a very good foundation material."