Settlement Calculations - Concept

[kevin001]

Possibly an elementary question, but here goes.

I'm looking at calculating settlements in normally consolidated clays under a preload. I'm following Geotechnical Engineering by Cuduto, which uses a logarithmic formula which takes into account initial and final effective stresses within each soil layer. For final effective stresses, the loading from the preload is simply added to the initial effective stress, no matter what the depth is.

Why is it that Boussinesq's curves are not applied to reduce the load, from the preload, at deeper soil layers; thereby, reducing the final effective stress?

Thanks in advance!

 

[GeoPaveTraffic]

Typically, the size of the preload is large when compared to the depth of soil being considered for the settlement analysis. This results in the full wieght of the preload being applied. If this is not the case, then you need to set the depth at which you will be begin to reduce the effects of the preload, Boussinsq would be a fine way to do that.

The goal of most preloads is to remove the potential settlement from a site prior to building a settlement senitive structure, so you are just trying to load the soil to a depth that will be influenced by the new structure.

 

[fattdad]

What GPT said. Where Boussinesq calculations can be relavent is at the edge (and beyond). You can look at whether settlement of the compressive layer will extend beyond the limits of the preload (i.e., to the road) using stress attenuation from an areal load, for example.

These are interesting problems to solve!

f-d

¡papá gordo ain’t no madre flaca!

 

[tomsmith5532]

The distribution of pressure in the soil induced by preload or any load on the soil follows a pattern of bulbs of pressures. It diminishes as it goes deeper and eventually it becomes zero.

Settlement calculations would normally not be calculated for the entire layer of the soil down to the zero bulb but to a percentage of P (P being increase in pressure due to preload) and the result would have been acceptable.