Passive Earth Pressure: As Nonlinear Spring vs. As Applied Pressure?
Passive Earth Pressure: As Nonlinear Spring vs. As Applied Pressure?
(OP)
Hello--the concept of passive earth pressure is on my mind:
Seems like, in reality, passive earth pressure behaves like a spring with varying stiffness that is activated after, oh I don't know, a quarter inch of displacement or so...so how come people input passive pressure in computer programs such as Enercalc as an applied pressure, like 250 psf or something? This isn't really what happens, and your moments, shears, etc. in the foundation itself is thrown off?
Right? It shouldn't be an applied pressure, but a support modeled as a nonlinear spring with the stiffness according the soil's modulus? Thanks.
Seems like, in reality, passive earth pressure behaves like a spring with varying stiffness that is activated after, oh I don't know, a quarter inch of displacement or so...so how come people input passive pressure in computer programs such as Enercalc as an applied pressure, like 250 psf or something? This isn't really what happens, and your moments, shears, etc. in the foundation itself is thrown off?
Right? It shouldn't be an applied pressure, but a support modeled as a nonlinear spring with the stiffness according the soil's modulus? Thanks.





RE: Passive Earth Pressure: As Nonlinear Spring vs. As Applied Pressure?
RE: Passive Earth Pressure: As Nonlinear Spring vs. As Applied Pressure?
In my experinence this requires close work between the structural and geotechnical engineer, and may require several iterations to get to the final solution.
RE: Passive Earth Pressure: As Nonlinear Spring vs. As Applied Pressure?
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I am also aware of the following articles on this subject:
Mokwa, R.L. and Duncan, J.M. (2001) "Experimental Evaluation of Lateral-Load Resistance of Pile Caps" J. Geot. and Geoenv. Engr. ASCE, Vol. 127, No. 2
Duncan, J.M. and Mokwa, R.L. (2001) "Passive Earth Pressures: Theories and Tests" J. Geot. and Geoenv. Engr. ASCE, Vol. 127, No. 3
Rollins, K.M. and Sparkes, A. (2002) "Lateral Resistance of Full-Scale Pile Cap with Gravel Backfill" J. Geot. and Geoenv. Engr. ASCE, Vol. 128, No. 9
RE: Passive Earth Pressure: As Nonlinear Spring vs. As Applied Pressure?
For active pressures to get developed less than 0.5% strain is required. However, for passive pressures up to 2% strain is required to reach the max. passive resistance, and, 0.5% strain is reached at one-half the maximum passive resistance.
There are other references available, I have to dig through some of my stuff. They include field measurements on earth earth pressures versus wall movements.
Best Regards
Mohan