Large Overburden Behind a Retaining Wall
Large Overburden Behind a Retaining Wall
(OP)
I have read through previous posts on this and would like additional references.
Have a 12 ft tall retaining wall with 4,000 psf overburden starting at some, to be determined, distance behind it (probably 7 ft back). Using USS sheet pile equation, pressure equals = 2q/PI x [B - (SinB x Cos(2A))]. This gives me 4,000 psf horizontal soil pressure from the overburden if I have the overburden start at the wall.
However, using other equations for overburden the back pressure from overburden should be = Ka x 4,000 or conservatively half of what I am getting.
What am I missing? What have other engineers done?
Have a 12 ft tall retaining wall with 4,000 psf overburden starting at some, to be determined, distance behind it (probably 7 ft back). Using USS sheet pile equation, pressure equals = 2q/PI x [B - (SinB x Cos(2A))]. This gives me 4,000 psf horizontal soil pressure from the overburden if I have the overburden start at the wall.
However, using other equations for overburden the back pressure from overburden should be = Ka x 4,000 or conservatively half of what I am getting.
What am I missing? What have other engineers done?





RE: Large Overburden Behind a Retaining Wall
Is there no geotech reoport here to help you with the lateral load application here?
Mike McCann
MMC Engineering
RE: Large Overburden Behind a Retaining Wall
RE: Large Overburden Behind a Retaining Wall
To find the location & magnitude of the resultant, the diagram can be approximated as 2 triangles, one from the top of the wall to the point of maximum pressure and one from the point of maximum pressure to zero at a point where the wall pressure is suffiently small.
using Ka times the overburden pressure is accurate for a uniform load spread over a large area starting at the wall. Since this is not your case, I think you will find the results too consevative.
4,000 psf is a significant load and should be carefully acoounted in the design
RE: Large Overburden Behind a Retaining Wall
RE: Large Overburden Behind a Retaining Wall
RE: Large Overburden Behind a Retaining Wall
I have changed our approach from the above noted equation to one out of Bowles - "Foundation Analysis and Design." He corrects the mirror load mistake that puts an additional factor of 2 onto the surcharge load in the above equation.
We are now getting reasonable results that match with other accepted surcharge equations.
Thanks for your help.
As for settlement, it doesn't much matter. The surcharge loading is from steel slabs. The slabs will not have a problem adapting to any settlement.
RE: Large Overburden Behind a Retaining Wall
There is no guarantee that a line that extends up from the toe of the wall at an angle of 45+phi/2 (measured from the horizontal) will be accurate as the surcharge may affect this typical convention. This is what the Culman's construction will ascertain.
Is there anything critical about the surcharge load (i.e., is it the county courthouse)?
f-d
¡papá gordo ain't no madre flaca!
RE: Large Overburden Behind a Retaining Wall