Soil Pressure on a Retaining Wall 2

[OKHawkeye]

I was hoping for some help in clearing up a bit of confusion on my part concerning the active pressure distribution of soil on the back face of a concrete or masonry retaining wall. If the top of the wall is considered "pinned" (i.e., not free to translate laterally in the direction of the active soil pressure), does the soil pressure against the back face of the wall vary linearly from zero at the level of the surface of the soil to ??? at the base of the wall, or is the soil pressure distribution uniform from top to bottom? My instincts tell me it varies linearly but I've actually seen some examples from engineering instructors and textbooks where it was drawn up as being uniform. Thank you for your help.

 

[msquared48]

The initial soil load distribution is triangular. Any additional surcharge, be it additional soil, traffic, seidmic, or buildings is uniform.

Mike McCann, PE, SE (WA)

 

[SteelPE]

As msquared referred to, the pressure distribution on the wall is triangular. In fact the pressure distributions on the wall will be distributed the same as if the wall was a cantilever and you were using the active pressure...... just higher as you would be using the at rest pressure coefficient Ko

 

[OKHawkeye]

Thanks very much to you both for taking the time to comment (I'm sort of a newbie at this website). It pretty much confirms my understanding of the matter and I appreciate your help.

 

[hokie66]

I pretty much agree with m^2 and SteelPE, but when you go deeper, as in the case of deep basements, the pressure distribution given by qualified geotechnical engineers (not me) is often trapezoidal between the different levels.

 

[GBS29X]

The active pressure coeffiecent "Ka" assumes the cantilever wall deflects horizontally slightly at top of wall manuals will tell you the magbitude of deflection ( based on wall height). If your wall is restrained from deflecting you need to use "Ko" which is larger than ka.

The uniform or rectangular distribution you are refering to is to be applied when you have a wall with two or more anchors or braces. I cant remeber exactly but i think AASHTO says use "Ko" with two or more anchor levels.. I would cerify tjis cant remember for sure, they have a diagram in the retaining wall chapter

Wheb upu have juat one anchor or brace a few feet down from top of wall use triangular diatribution with applicable soul pressure coefficient for your problem/site.

One thing to keep in mind is the installation sequence. When i have designed walls with two or more levels of anchors, i looked at cantilever comdition untill first anchor level is placed, then look at single anchor level condition until second anchor is installed, the. Finally the final condition. Also remeber to think througj the removal process.

Refer to AASHTO for more details

 

[OKHawkeye]

I think I remember seeing something about that very condition, but I'm not exactly sure where I saw it (I'll have to do a little digging in my library to 'rediscover' it). Thanks GBS29X...