Bearing Pressure analysis of a large fill 2

[mjredding]

I am looking for feedback as to the best approach and references that discuss the analysis of the soil bearing capacity for large engineered fills (both flat and on slopes). The example would be a 300 ft x 200 ft area with a maximum fill height of 15 ft.

 

[BigH]

I would approach it as slope stability to check on shear failure. If you are "worried" about bearing, you probably have weak clayey soils. The area is too large, in my view, for any thought to a traditional footing style approach. For stresses and settlements, see Polous and Davis (1974). You could always use stress path methods to see if you approach any first yielding.

 

[Focht3]

A slope stability approach is generally appropriate since the most likely area for instability is near an edge of the embankment.

But I do have one big caveat: Remember that the use of an "allowable bearing capacity" is really an effort to limit settlement; you need to look hard at the predicted settlements. It sounds like you need to look at consolidation settlement; but this depends on the site, soil conditions, and reason for placing a 15 foot high fill over a 200 ft by 300 ft area.

Give us more details - and we'll see if we can be of any additional help.

 

[mjredding]

Thanks for your inputs so far. More information about the site includes the following:

A neaby river is being dredged and the sediments are going to be placed in a landfill cell that is being constructed over a 2 acre site, that was a former burn dump/landfill. The preliminary design performed a cursory analysis of its slope stability and ignored a weak clay layer approximatley 25 feet below ground surface. The design seemed to focus predominatly on the soil bearing capacity and made the assumption that the landfill cell was the equivalent of a 400 foot footing and used the meyerhof equation to determine its value and settlement. Aside from the obvious issues from the oversight of the weak clay layer this project invoked a discussion on how to analyze the soil bearing capacity correctly for a large engineered fill.

 

[Focht3]

A footing analysis for that problem is simply wrong. A footing design approach assumes that the entire area will move in a planar fashion - not a valid assumption.

 

[BigH]

I agree with Focht3 that "footing" analysis is/was wrong. I've used it for 80 dual-sided reinforced earth walls of an approach embankment in conjunction with a slope stability analysis before. Analysis showed an interesting comparison of the "two".

I'd like some info on the 25ft of "soil" above the weak clay onto which the dredged material will be placed, properties of the weak clay (Su, thickness, does it extend "into" the river), how close to the river, etc. Unless the river plays a role in "steepening" the slope (embankment + river depth), a weak clay layer 25ft below ground onto which only a 15m dredged river sand/silt fill placed above does not sound all that ominous . Draw up the picture, look at the scale. If the very soft to soft (assumed as such as synonymous with "weak&quot clay had been within a few metres of the ground surface and was very soft, then, there might be more threat of a stability a problem. A quick GSlope analysis would give you a level of confidence.