Helical or Strip Footing

[kxa]

In looking at the attached boring log for the east coast area where the water table is about 2.5’ below surface, I was considering helical piles and grade beams but the client is saying that the local engineers use strip and spread footings for the residential buildings. The loading would be about 2,500 plf of wall.

My concern is mostly settlement since the soil has very low blow counts. The house will be built on 10” concrete walls that would be 8’ above ground. The bottom of footing has to be 3’ below grade.

I was interested to see what others think. Also, wouldn’t we get more bearing capacity out of the soil since the weight of concrete foundation wall can consolidate the poor layers? Is there a way to estimate the capacity of the consolidated soil in this case? Any suggestions is greatly appreciated.

 

[dik]

Do you have frost issues? a basement? Is there a ready flow of groundwater? Can you effectively drain the excavation?

Best to have one of the geotekkies comment about settlement...

My experience is that with non-cohesive soils, this is not normally an issue, but it could just be the sands and gravels in these environs. I've not encountered blow counts this low for granular material... is your sand rounded and with little fine material for binding?

Dik

 

[kxa]

The original house has been demo'd. No basement due to high water table. Bottom of footing has to be 3'down due to frost.

 

[a2mfk]

Where is this project in the US?

In Florida, where we have lots of sandy soils (go figure), those would be considered very loose to loose soils down to 10ft.

You need to get a geotech involved, and those soils need improving or go with a deep foundation system.

 

[PEinc]

I'm with a2mfk on this one. The top 10' looks too loose to me. I would not put a strip footing on this unless the top layer were to be densified.

http://www.PeirceEngineering.com