Foundation Design For Retaining Wall

[kieran1]

I need to design a retaining wall which will retain 10.0m. I have a geotech report that states the N value of the soil at foundation level is 14. Can I assume a bearing capacity of roughly 10N + Overburden pressure. The soil is a Lateritic Clay and the water table is at 9.0m below ground level.

Kieran

 

[msquared48]

Don't assume anything here. Go back to the original Geotech and ask for an allowable soil bearing pressure.

If he is no longer available, engage a Geotech who is available and have him give you the value. To do otherwise is to assume too much unneeded liability and is too much of a risk of public safety.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[BigH]

Mike is right - you know the N value at the base - what kind of soil? Clay? Sand? What is the profile for the next 10 m or so under the foundation level? If clay, does it get "weaker" (i.e., the founding level might be in a desiccated crust) or stronger - or is there a change of materials? The allowable bearing pressure would be based on a review of both the capacity (shear) and serviceability (settlement - and most likely the governing factor) limits. Then, too, you must consider the overall global stability: 1. sliding, 2. overturning, 3. allowable bearing pressure, 4. global stability of the "system".

 

[kieran1]

Thanks I do intend to contact the geotech.This job is overseas and I'm just carrying out some prelim calcs to see what foundations are feasible and prepare a fee proposal.

The soil profile under the foundation soil is the same for about 6-7m then sandstone bedrock.
I need to get an opinon on my assumed bearing capacity of 300KN/m2 is correct. If appointed i will get the info from the geotech.

Kieran

 

[BigH]

I think that 300 kPa is too high - you never said if sand or clay . . . In sand you are probably talking about 150 kPa as allowable bearing pressure for 25 mm settlement - maybe 200 given that bedrock is relatively close; in clay, you are talking about 200 kPa (but need to check for settlement to see if this needs to be reduced - depends on size of footing, OCR, etc). you could probably go 300 kPa for short term transient loading.

 

[kieran1]

thanks BigH. I will assume a larger base for the wall

Kieran