Shallow Foundations

Using the Bousinesq Chart. I'm trying to get this straight!

When the problem is asking to find the stress increase 5 ft. beyond the edge of the footing and 10 ft. below (Strip footing with base 10 ft.) .

I'm getting the values X/B= 5+5/10= 1B and the vertical Z/B=10/10=1B so, I got the value of Influence factor (Iq) where the intersection of this coordinates in this case I got a value of Iq=0.27

In the problem they are obtaining a value of 0.18.....Which value is the correct?

Thanks in advance.

chess5329 said:

Using the Bousinesq Chart. I'm trying to get this straight!
When the problem is asking to find the stress increase 5 ft. beyond the edge of the footing and 10 ft. below (Strip footing with base 10 ft.) .

I'm getting the values X/B= 5+5/10= 1B and the vertical Z/B=10/10=1B so, I got the value of Influence factor (Iq) where the intersection of this coordinates in this case I got a value of Iq=0.27

In the problem they are obtaining a value of 0.18.....Which value is the correct?

Thanks in advance.

Click to expand...

You measure the horizontal and vertical distances from the center of the footing. Therefore, the 5 foot distance from the foundation edge is 10 feet from the foundation center, so you would use 10 feet horizontal and 10 feet vertical as your parameters for the Boussinesq equation and/or the Newmark chart to determine the influence factor.

chess5329 said:

Using the Bousinesq Chart. I'm trying to get this straight!
When the problem is asking to find the stress increase 5 ft. beyond the edge of the footing and 10 ft. below (Strip footing with base 10 ft.) .

I'm getting the values X/B= 5+5/10= 1B and the vertical Z/B=10/10=1B so, I got the value of Influence factor (Iq) where the intersection of this coordinates in this case I got a value of Iq=0.27

In the problem they are obtaining a value of 0.18.....Which value is the correct?

Thanks in advance.

Click to expand...

Hi,

From my chart for infinitely long foundation at depth=B and X=B I show it just outside the 0.2p line (somewhere between 0.15p & 0.2p), so 0.18 is proably right. My chart is only a half a page size, so it is hard to read.

At the edge of the footing where x=0.5B and depth z=B, it appears the vert stress is between 0.2-0.3p.

Badger said:

chess5329 said:

Using the Bousinesq Chart. I'm trying to get this straight!
When the problem is asking to find the stress increase 5 ft. beyond the edge of the footing and 10 ft. below (Strip footing with base 10 ft.) .

I'm getting the values X/B= 5+5/10= 1B and the vertical Z/B=10/10=1B so, I got the value of Influence factor (Iq) where the intersection of this coordinates in this case I got a value of Iq=0.27

In the problem they are obtaining a value of 0.18.....Which value is the correct?

Thanks in advance.

Click to expand...

Hi,

From my chart for infinitely long foundation at depth=B and X=B I show it just outside the 0.2p line (somewhere between 0.15p & 0.2p), so 0.18 is proably right. My chart is only a half a page size, so it is hard to read.

At the edge of the footing where x=0.5B and depth z=B, it appears the vert stress is between 0.2-0.3p.

Click to expand...

I think I have to find a better chart than the one I have, this still telling me X=B=1 is between 0.2 and 0.3.

Thanks guys for your fast response!

Chess5329

I found a better Boussinesq chart, see if this helps.

Geotech_Handouts_Boussinesq.pdf

Badger said:

Chess5329
I found a better Boussinesq chart, see if this helps.

Click to expand...

Thanks Badger of course this works better!!

Badger said:

Chess5329

I found a better Boussinesq chart, see if this helps.

Click to expand...

I finally figured it out with your chart.Thanks!