surcharge loading on retaining wall
surcharge loading on retaining wall
(OP)
Hello,
Regarding surcharge loads on retaining wall, I've notice that, in some instances, a factor of,ie, Ka =1/3 was multiplied to surcharge loading, while others do not have any. I've checked some references ISTructE example do not have any "factor" while "Structural Foundation Designer's Manual(Curtins)" have one(wKa, pp 307). Any ideas why others doing it differently?
Regarding surcharge loads on retaining wall, I've notice that, in some instances, a factor of,ie, Ka =1/3 was multiplied to surcharge loading, while others do not have any. I've checked some references ISTructE example do not have any "factor" while "Structural Foundation Designer's Manual(Curtins)" have one(wKa, pp 307). Any ideas why others doing it differently?






RE: surcharge loading on retaining wall
RE: surcharge loading on retaining wall
"It is imperative Cunth doesn't get his hands on those codes."
RE: surcharge loading on retaining wall
www.PeirceEngineering.com
RE: surcharge loading on retaining wall
"It is imperative Cunth doesn't get his hands on those codes."
RE: surcharge loading on retaining wall
Thank you very much for all the replies.
Pls. see attached files, I have a huge surcharge loading of 75 kN/m2 as required. That's why,ie, multiplied it by a certain factor of 1/3 is of great help in terms of reducing rebar as explained by "PE..", it depends on certain cases. In the past, I normally design retaining walls with a surcharge of, between 10 & 20 kN/m2 and applied it directly to the retained structure. I have no problems understanding in applying a factor to soil pressure(ie, because it depends on the basic principles of "soil mechanics", angle of friction ..etc.). What it is "new" to me is applying a factor to surcharge loading, as in my previous query, others using a factor and some are not. The retaining wall I am designing is propped at the top and it is 2.4 m high.
Again, any additional explanation or reference to the code will be greatly appreciated.
RE: surcharge loading on retaining wall
If you have a low propped wall you shouldn't be using the active pressure for the backfill or the surcharge, but the same at rest pressure coefficient would be appropriate for both.
Is it possible to post an extract of the I StructE document saying you should apply the full surcharge load?
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: surcharge loading on retaining wall
RE: surcharge loading on retaining wall
It says:
For stress due to active pressure,
Siga(Z) = Ka (... + q - ...) + ...
where q is the surcharge pressure, so it is multiplied by Ka.
It seems a confusing way to show it, but their intention in the highlighted note seems to be to show why it is constant with depth.
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: surcharge loading on retaining wall
For a propped wall the horizontal pressure coefficient should be greater than Ka, but there is no reason why it should not be applied to the surcharge pressure.
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: surcharge loading on retaining wall
RE: surcharge loading on retaining wall
It would be much more clear for you to read reference books with correct examples than to read ET postings.
www.PeirceEngineering.com
RE: surcharge loading on retaining wall
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: surcharge loading on retaining wall
@PEinc
"You really should consult one or more different reference books on wall pressures and surcharge pressures. Q = q (lateral) x H, not q x Q. H = 3 and q = 10. Therefore, Q = 30"
-Can you cite a reference/documents regarding this(even just one..)? I'm only interested with the "surcharge" loading,which is actually "loads" on top of the soil. Previously, when I have a surcharge loading of 10 to 20 kN/m2,I've just directly applied it directly to the retained structure(without any factor). But when 50 & 75kN/m2 are required for a surcharge loading, others(engineers) suggested that a certain factor(similar to the factor applied to the soil pressure) can be multiplied to the surcharge loading. I've done some reading, and I found out, as in my previous comments, others are doing it and others are not.
I've shared the views of Mr. Jenkins, How come that a loads on top of the soil(surcharge), can be directly applied vertically to the retained structure,when in fact,there's a soil in between?That's why multiplying a factor(less than 1.0) makes sense to me.It is just like a boxer hitting you in the face but you partially deflect it with your hands.
RE: surcharge loading on retaining wall
You really should read books that discuss lateral earth pressures for wall design. This forum is not an easy place for us to explain earth pressure theory in detail.
www.PeirceEngineering.com
RE: surcharge loading on retaining wall
www.PeirceEngineering.com
RE: surcharge loading on retaining wall
-Principles of Foundation Engineering by Das
-Soil Mechanics for Foundations by Budhu
They both work their way up from basic principles to shorthand equations.
RE: surcharge loading on retaining wall
Replace the "+" with a "-" for the active coefficient, which would be 0.17 for phi=45 degrees.
RE: surcharge loading on retaining wall
tan^2(45 degrees) = 1.0. 45 - (0/2) = 45. tan^2(45) = 1.0. CarlB incorrectly said (45-0/2) = 22.5 degrees. Only phi gets divided by 2, not the 45 degrees.
www.PeirceEngineering.com
RE: surcharge loading on retaining wall
So I stand by my calcs.
I think you were thinking phi=0 degrees, so (45-phi/2)=45 degrees.
RE: surcharge loading on retaining wall
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: surcharge loading on retaining wall
Unknown
RE: surcharge loading on retaining wall
The point I was trying to make is that active lateral surcharge pressure cannot equal the vertical surcharge unless Ka = 1. That cannot happen unless both phi and c are 0. In my opinion, design examples showing the lateral and vertical pressures being the same are wrong or overly conservative.
Additionally, the only way that tan^2(45-phi/2) could equal 0.17, as CarlB indicated above, is if you incorrectly use Ka = tan^2((45-phi)/2) instead of tan^2(45-(phi/2)).
The Rankine formula is often used for cohesive soils in the drained condition where c is assumed to be 0 and a phi angle is used. Refer to various publications for graphs of phi angle vs. plasticity index.
www.PeirceEngineering.com
RE: surcharge loading on retaining wall
I agree with everything in your last post, except that the Ka of 0.17 for phi = 45 is wrong. Tan^2(45 - 45/2) is equal to 0.17.
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: surcharge loading on retaining wall
Tan^2((45+0)/2) = tan^2(22.5) = 0.17
www.PeirceEngineering.com
RE: surcharge loading on retaining wall
CarlB's numbers were for phi = 45, not phi = 0.
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: surcharge loading on retaining wall
www.PeirceEngineering.com
RE: surcharge loading on retaining wall
If you read my posts you'll see I weighed in only to try to clear up mis-information/errors/typos put forth by you.
Both me and IDS apparently felt it was worthwhile to point out inconsistenies for any future thread readers, so we both attempted- twice each. Thanks IDS for following through, we should now better spend our time elsewhere :)
RE: surcharge loading on retaining wall
www.PeirceEngineering.com