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Re: Active, At-Rest, Passive Soil Pressure

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--- Roger Turk <73527.1356(--nospam--at)> wrote:
> I also have a difficult time visualizing "at-rest"
> soils pressures.  For soil 
> to exert pressure against an object, it must be
> mobilized, i.e., unless 
> the soil particles move, there can be no pressure. 
When the propensity of a soil mass to attain its
natural angle of repose is prevented by a wall, the
soil has to exert a pressure on the wall (Imagine
someone losing consciousness and you are trying to
prevent him from falling down). The larger the wall
rigidity, the larger the pressure. When compared to a
free standing retaining wall, a basement wall is more
rigid. Thus it will see a pressure larger than the
active pressure, which is experienced by a free
standing retaining wall. Manual computation of earth
pressure behind a basement wall, including all the
boundary conditions is, in my opinion, is laborious,
if it is possible at all. Therefore, it is
conservative to design it for "at rest" earth
pressure. If the wall is long compared to its height
(L/H >3?) and the top end is free assuming active
condition would be reasonable, except near the edges.
However, at the edges, error in such assumption is of
no consequence because the perpendicular wall at the
edge is infinitely rigid and has more than adequate
capacity to support any larger earth pressures in that


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