Lateral Soil Bearing Pr, Unconstrained Soils and Foudations
Lateral Soil Bearing Pr, Unconstrained Soils and Foudations
(OP)
Has anyone tried to use Equation 18-1 out the IBC 2006 for unconstrained soils and foundations to determine lateral bearing strength?
I tried using it and found it to be very conversative. I have an 8' cantilever post with a concentrated load of 375 lbs at the end. And according to the equations, it concludes that a 1' diameter footing 3' deep will not restrain the lateral load (I believe it suggest a ~12' deep footing). Did I miss something here?
Please let me know if you have used this in a design along with any comments or concerns you have about it.
Thanks.
I tried using it and found it to be very conversative. I have an 8' cantilever post with a concentrated load of 375 lbs at the end. And according to the equations, it concludes that a 1' diameter footing 3' deep will not restrain the lateral load (I believe it suggest a ~12' deep footing). Did I miss something here?
Please let me know if you have used this in a design along with any comments or concerns you have about it.
Thanks.






RE: Lateral Soil Bearing Pr, Unconstrained Soils and Foudations
The 3 to 4 foot embedment with a 1 foot diameter footing seems reasonable to me. If you are getting a 12 foot embedment, I would look to your units to start. Otherwise, look to the lateral soil bearing you are using and the computation of the "S" value.
Mike McCann
MMC Engineering
RE: Lateral Soil Bearing Pr, Unconstrained Soils and Foudations
Enginerrred,
Three references you may find useful are:
Pole Building Design by Donald Patterson, 1957. and
Archon Engineering's WinPost ( about $40 )available at Sales at archonengineering.com
and Chart for embedment of Posts, Outdoor Advertising Association of America ( circa 1960 ) which has been reprinted in many structural engineering handbooks.
good luck
RE: Lateral Soil Bearing Pr, Unconstrained Soils and Foudations
Yep...thanks.
Mike McCann
MMC Engineering
RE: Lateral Soil Bearing Pr, Unconstrained Soils and Foudations
RE: Lateral Soil Bearing Pr, Unconstrained Soils and Foudations
LobstaEata,
Can you confirm that we are using the same variables? In my orginal calcs I used S1 = 100 psf (conservative due to non-testing), but in my calcs below I tried to match your results using S1 = 250 psf.
I have:
b = 1 ft
d = 3 ft (assumed)
h = 4 ft
P = 375 lbs
S1 = 250 psf
Resulting in:
A = 3.51 ft
d = 6.04 ft (required)
How did you get a 5 foot embedment? Can you let me know what we did differently?
RE: Lateral Soil Bearing Pr, Unconstrained Soils and Foudations
RE: Lateral Soil Bearing Pr, Unconstrained Soils and Foudations
One of the variables "h" was considered to be 8 ft per your original post, rather than 4 ft on the lastest post.
"I have an 8' cantilever post with a concentrated load of 375 lbs at the end."
Attached are output results for variables entered using our Enercalc module. It appears that if you are using 2 ft of inactive depth, which adds to the value taken from the Ruttledge Chart, then your embedment depth is pretty close. However, it seems that Enercalc may only consider 1 ft of inactive soil when considering engagement of passive pressure.
For the minimal additional cost, I'd use the 6 ft depth regardless and call it a day.
Hope this helps.
RE: Lateral Soil Bearing Pr, Unconstrained Soils and Foudations
The AASHTO method is identical to the method proposed in the Final Report for the Connecticut DOT "Foundation Design Methods for Poles and Towers" by Healy and Long, December 1973, School of Engineering, University of Connecticut.
RE: Lateral Soil Bearing Pr, Unconstrained Soils and Foudations