Upper limit of Passive Lateral Soil pressure

[soils212]

Is there an upper limit generally accepted for the amount of passive pressure that can develop, either for resisting movement in a sheet pile wall or resisting movement in a large drilled pier??

 

[fattdad]

yes, but it depends on the soil strength.

f-d

¡papá gordo ain’t no madre flaca!

 

[ishvaaag]

The most usual value read for such limit, I think, it is 3 times the effective burden pressure, sometimes venturing over such value a bit more. Even so one still oversees calculations where such limits are olympically disregarded. Fortunately not all soil is bad.

 

[BigH]

fattdad is correct - and very small increases in the phi value past, say 40deg creates huge marginal increases in Kp. Most that I know use a maximum of 3 for Kp - as a practical and reasonable number (not getting caught up with the asymptotic increase due to tangent).

 

[PEinc]

I have very often (almost always) used Kp greater than 3. I have never had a problem. However, I almost never use a sheet pile or soldier beam embedment depth that is less than the exposed height of the wall. There are some "rules" that should be folowed despite what the "numbers" may say. The art of sheeting design is knowing the "rules." They keep you out of trouble over the long haul.

http://www.PeirceEngineering.com

 

[fattdad]

O.K. in response to my glib reply, when you throw in a non-plane-strain condition (i.e., acting on a drilled pier) a design value for passive pressure is affected by soil arching. Brinch-Hansen has a parameter called Cp that is essentially phi/10 that is used to increase the Rankine coefficient of passive earth pressure. So, for a friction angle of 30 degrees you'd calculate a Rankine Kp of 3 and then multiply that by another 3 - getting a design value of 9!!!!! Wow! How can that be? It's because the load from a horizontally-loaded drilled shaft attenuates in the X-Y plane whereas the load on a long retaining wall doesn't.

One item of note on passive pressure: Watch for strain compatibility. Just because the soil can offer an elevated amount of passive resistance, doesn't mean you want to realize that much movement for the resistance to develop.

Another item of note: DM-7 (I think it's 7.2, but it may be 7.1) has the log-spiral passive pressure charts and these are always much greater than the Rankine Kp value. There are cases where I could use more than 3, either when I'm not worried about strain compatability and I'm dealing with an open-graded aggregate (i.e., with a phi of 40 degrees or so. . .).

f-d

¡papá gordo ain’t no madre flaca!

 

[PEinc]

I have a clarification to "I almost never use a sheet pile or soldier beam embedment depth that is less than the exposed height of the wall." This is for a cantilevered sheeting system. For braced or tiedback sheets or soldier beams, the embedment is usually much less.

http://www.PeirceEngineering.com