Immediate settlement of footing 1

[Samuee]

Hi guys I'm now designing for footing with 7m x 14m dimension

I have some questions on calculating immediate settlement of shallow foundation on granular soil.

Based on my knowledge, the immediate settlement can be calculated as
(S = q * B * (1-u2)/E)
S: settlement
q: unit stress on soil
B: lesser dimension of footing

On the other hand, by elastic theory

S = H x q/ E
H: soil depth

I notice first equation is linearly proportional to width B (I know there are some factors relating to dimension of footing and depth), second equation however, has no relationship with width. How should I consider while using this equation?

Thank you

 

[dik]

I would use a geotekkie if the answer was critical... They're the 'juju' boys when it comes to deflection calculations, and, their numbers are sometimes an educated guess.

Dik

 

[oldestguy]

dik is correct. Heck, your immediate settlement may be peanuts compared to what might come later.

 

[dik]

your immediate settlement may be peanuts compared to what might come later.

Just look at the Millenium Tower <G>.

Dik

 

[fattdad]

step 1: Find some way to obtain the soil modulus (moduli).
step 2: Evaluate the sustained load on the foundation and reduce it to applied bearing pressure for your foundation size.
step 3: Determine the attenuation of load with depth (i.e., Bousinesq or Westergard).
step 4: Make a plot of delta sigma V with depth and overlay that on the modulus profile.
step 5: Integrated delta sigma v with respect to moduli.

So, if you have a 5 ft layer below the footing that has an average stress change of 2,500 psf and the modulus value is 150 tsf, you'd get 0.5 in for that layer. Next layer down may be 10 ft thick and have an average increase of 1,800 psf and have a modulus of 200 tsf. That'd return another 0.54 inches of settlement. Keep doing that and add up the total.

All that will occur, "Immediately." For long term (i.e,. 30 years), we'd add some post-construction strain - like another 30 percent.

f-d

ípapß gordo ainÆt no madre flaca!

 

[oldestguy]

On the first of the steps in the fattdad post you need the geotech, so then the other steps may or may not be used.