Adjacent Footings

[BSVBD]

Pre-IBC we used to provide a 45 degree slope from adjacent footings to a new footing bearing surface.

The only reference to adjacent footings that i can find in 2009 IBC is in SECTION 1809 SHALLOW FOUNDATIONS. In 1809.6 Location of footings. Footings on granular soil shall be so located that the line drawn between the lower edges of adjoining footings shall not have a slope steeper than 30 degrees (0.52 rad) with the horizontal...

My supervisor tells me that since this is in the "SHALLOW FOUNDATIONS" section, it only applies to "SHALLOW FOUNDATIONS" such as grade beam foundations.

My thought is that it applies to adjoining or adjacent footings. And since i cannot find a reference to adjacent footings elsewhere in IBC, logically, if this would apply to the adjacent footing of a shallow foundation, this would apply to any adjacent footing.

Rather than the 30 degree, i thought there was a 2:1 slope in recent, past codes, but, i cannot find it. Consequently, there is only a 3.5 degree difference between 2:1 & 30 degrees.

Any thoughts?

Thank you!

 

[GeoPaveTraffic]

The 2:1 is a rough rule of thumb. The actual influence zone of any footing, (shallow, deep, or in between) depends on the soil type(s). If the footings are sensitive to settlement, I would suggest you talk with your geotechnical engineer about the potential impacts of having your footings close together.

Mike Lambert