Active vs Earth Pressure
Active vs Earth Pressure
(OP)
Can someone give a me an explanation of the differences and when to use each of the two earth pressures. I've read allot about it it seems kinda vauge about when to use each. If you know of any good references that would be great also. Thanks.





RE: Active vs Earth Pressure
The earthpressures that are used for design of retaining systems are selected based upon the expected movement of the retaining wall. The actual lateral earth pressures that are acting behind a retaining wall are highly nonlinear and can range as much as an order of magnitude. In order to make the design of retaining walls tractable, we commonly make one of three assumptions: 1) either the wall does not move under the action of the earth forces (At-rest condition); or 2) the wall moves away from the backfill sufficiently to fully mobilize the strength of the soil (Active Condition); or 3) the wall is pushed into the soil mass with sufficient force to fully mobilize the strength of the soil (Passive Condition).
The selection of the design case for a particular set of loadings should be referred to a geotechnical engineer.
In the case of tied-back retaining systems, the lateral earth pressures do not generally correspond with any of the above assumptions and the simplified calculation procedures are based upon measured earth pressures and are highly empirical.
RE: Active vs Earth Pressure
RE: Active vs Earth Pressure
Active earth pressures mean just that - wall moves until soil pressures change from "at rest" to "active." If the pressures build back up (although I don't see a mechanism for it), the wall moves again.
If the wall is somehow restrained, you can get an effect that looks like the "active" pressures are changing to "at rest"; but what is really happening is that the cohesion is decreasing over time as negative pore pressures dissipate.
RE: Active vs Earth Pressure
RE: Active vs Earth Pressure
Our earth pressure calculations really don't treat "locked-in" horizontal forces, do they?
So - best to use small compactors within, say, 1.5m of the wall.
RE: Active vs Earth Pressure
The soil cannot simply become "at rest" again. It has been densified and would need to be put back into an uncompacted state again to do so.