allowable bearing capacity+width of foundation

Can anyone tell me how I can relate allowable/safe bearing capacity to the width of a strip foundation or suggest a design chart that uses cone pnetrometer resistance as opposed to SPT 'N'?
Ta
Mike

 

[phuduhudu]

I found a reference in Tomlinson "Foundation design and construction" to a relationship between CPT test results and angle of shearing resistance of a soil. It refers to a study by Durgunoglu and Mitchell and gives a graph.

For getting the ultimate bearing capacity I would normally use the Brinch-Hansen equation which for the basic case of a vertical load on a cohesionless soil with no overburden pressure becomes

qn=1/2.g.B.Nq.dq

qn= ultimate bearing pressure
g = density of soil
B = width of footing
Nq = bearing capacity factor
dq = depth factor

Nq varies with phi, the angle of shearing resistance and you'll need to get hold of the graph. Any text book on soil mechanics has it. dq varies with the ratio of depth of foundation to width. A simplified value which holds for phi<25 degrees is dq=1 + 0.35D/B.

This is a very particular application of Brinch Hansen and I would recommend getting a text book or I understand the US army has some good technical papers on the web too.
Carl Bauer

http://www.bauerconsultbotswana.com

 

[ishvaaag]

I have a Mathcad 2000 Professional sheet that has built in this capacity. Ask someone that has Mathcad 2000 to download it from its Collaboratory site (it is free). The sheet can use the equivalence between SPT and cone penetrometer given in Bowles' text. I can send you the file as well, if you want so e-mail me

mom@arrakis.es.

 

[engcomp]

Joseph E. Bowles discusses bearing capacities at chapter 4, section 3 of his book &quot;Foundation Analysis and Design&quot; 5th edition.

A cue card for this chapter can be found at ...

http://www.engs-comp.com/mathserv/bowles4-3.html

Helmut
engcomp@pbq.com.au

 

[engcomp]

Of course, if the footing carries eccentric or inclined loads, you should refer to chapter 4, section 6 ...

http://www.engs-comp.com/mathserv/bowles4-6.html

Helmut
engcomp@pbq.com.au