SURCHARGE equations

[kkoloj]

Does anyone know if the lateral earth pressure equation for an infinite strip load breaks down if the loading is right next to the retaining wall? The equations for this condition generally show the load some distance 'b' away from the wall. I have not read about any limitations of 'b', but I am not sure if for example 'b'=0.5 ft is an issue? I guess this question would also apply to a finite strip load (e.g., like the one described in Soil Engineering (1982) by Spangler and Handy pp. 567-572).

The main reason for the question is that the lateral earth pressure equations for point loads and line loads depend on how far behind the wall the load occurs (i.e., with the 'm' value < 0.4 or > 0.4).

 

[VEGEO]

The short answer is that it depends of what equations you are using there isn't just one.

It is probably better to break the issue down into two parts:

1.What is the vertical stress, at various depths, under the strip footing? You can use Boussinesq for this analysis, but if the strip load is very near the wall face the distribution from the front half of the strip is limited by the physical geometry.

2.What is the approriate earth pressure coeficient to apply given the rigidity of the structure?

You can then superimpose the horizontal stresses from the soil rentention loads and the strip loads.

 

[DRC1]

For a unform infinate surcarge adjacent to the wall, the lateral load is the uniform vertical pressure multiplied by the lateral earth pressure coefficent, The pressure envelope is rectangular all the way down. Once you limit the area of the load, or move the wall away from the edge of the load,The geometry becomes important.Pearloff & Baron "Soil Mechanics" is very good for this topic. Other References are Fang & Winterhorn or Bowles.

 

[kkoloj]

VEGEO and DRC1:

It sounds like what you are essentially saying, which makes sense, is that if the strip load is right next to the retaining structure, then simply assume that the strip load is a UNIFORM surcharge behind the wall?

Thanks in advance, I appreciate the responses.

 

[DRC1]

I missed the part about the strip load. I was thinking of a large area. However if the srtip is sufficently wide, assuming a uniform load will be a little conservative, but not excessive. It also makes life a lot easier.